Lot 51 Aldasoro Ranch

GEOTECHNICAL ENGINEERING STUDY

FOR THE

LOT 51 ALDASORO RANCH RESIDENTIAL STRUCTURE

Telluride, Colorado

November 24, 2017

Prepared For: Mr. Jesse DiFiore

Project Number: 54975GE

PN: 54975GE November 24, 2017

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1.0 REPORT INTRODUCTION ................................................................................................... 2 1.1 Scope of Project ................................................................................................................... 3

2.0 GEOTECHNICAL ENGINEERING STUDY ........................................................................ 4 2.1 Geotechnical Engineering Study Scope of Service ............................................................. 4

3.0 FIELD STUDY ........................................................................................................................ 6 3.1 Project location .................................................................................................................... 6 3.2 Site Description and Geomorphology .................................................................................. 6 3.3 Subsurface Soil and Water Conditions ................................................................................ 7

4.0 LABORATORY STUDY ...................................................................................................... 10 5.0 BASIC/FEASIBILITY LEVEL SLOPE STABILITY ANALYSES .................................... 11 6.0 FOUNDATION RECOMMENDATIONS ............................................................................ 20

6.1 Drilled Micro-Pile Foundation System .............................................................................. 21 6.2 Drilled Piers ....................................................................................................................... 22 6.3 Grade Beams and Void Form ............................................................................................ 23

7.0 RETAINING STRUCTURES ............................................................................................... 24 8.0 SUBSURFACE DRAIN SYSTEM ........................................................................................ 26 9.0 CONCRETE FLATWORK .................................................................................................... 28

9.1 Interior Concrete Slab-on-Grade Floors ............................................................................. 28 9.2 Exterior Concrete Flatwork Considerations ........................................................................ 30 9.3 General Concrete Flatwork Comments .............................................................................. 31

10.0 CONSTRUCTION CONSIDERATIONS ............................................................................ 32 10.1 Fill Placement Recommendations..................................................................................... 32

10.1.1 Embankment Fill on Slopes ....................................................................................... 32 10.1.2 Natural Soil Fill......................................................................................................... 34 10.1.3 Granular Compacted Structural Fill ........................................................................... 34

10.2 Excavation Considerations................................................................................................ 35 10.2.1 Excavation Cut Slopes ............................................................................................... 36

10.3 Utility Considerations ....................................................................................................... 36 10.4 Exterior Grading and Drainage Comments....................................................................... 36 10.5 Landscaping Considerations ............................................................................................. 37 10.6 Soil Sulfate Content, Corrosion Issues ............................................................................. 39 10.7 Radon Issues ..................................................................................................................... 39

11.0 CONSTRUCTION MONITORING AND TESTING......................................................... 39 12.0 CONCLUSIONS AND CONSIDERATIONS .................................................................... 40 Appendix A: Logs of Test Borings Appendix B: Laboratory Test Results


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1.0 REPORT INTRODUCTION This report presents our geotechnical engineering recommendations for the proposed Lot 51 Aldasoro Ranch Residential Structure Project. This report provides design level foundation recommendations, and a basic level slope stability study. The project layout had not been determined at the time of issue of this report. This report was requested by Mr. Jesse DiFiore. The field study was completed on October 26, 2017. The laboratory study was completed on November 20, 2017. Geotechnical engineering is a discipline which provides insight into natural conditions and site characteristics such as; subsurface soil and water conditions, soil strength, swell (expansion) potential, consolidation (settlement) potential, and often slope stability considerations. Typically, the information provided by the geotechnical engineer is utilized by many people including the project owner, architect or designer, structural engineer, civil engineer, the project builder and others. The information is used to help develop a design and subsequently implement construction strategies that are appropriate for the subsurface soil and water conditions, and slope stability considerations. It is important that the geotechnical engineer be consulted throughout the design and construction process to verify the implementation of the geotechnical engineering recommendations provided in this report. Generally, the recommendations and technical aspects of this report are intended for design and construction personnel who are familiar with construction concepts and techniques, and understand the terminology presented below. The geotechnical engineering report is the beginning of a process involving the geotechnical engineering consultant on any project. It is common for unforeseen, or otherwise variable subsurface soil and water conditions to be encountered during construction. As discussed in our proposal for our services, it is imperative that we be contacted during the foundation excavation stage of the project to verify that the conditions encountered in our field exploration were representative of those encountered during construction. Compaction testing of fill material and testing of foundation concrete are equally important tasks that should be performed by the geotechnical engineering consultant during construction. We should be contacted during the construction phase of the project and/or if any questions or comments arise as a result of the information presented below. The following outline provides a synopsis of the various portions of this report;

� Sections 1.0 and 2.0 provide an introduction and an establishment of our scope of service.

� Sections 3.0 and 4.0 of this report present our geotechnical engineering field and laboratory studies

� Sections 5.0 through 9.0 presents our geotechnical engineering design parameters and recommendations which are based on our engineering analysis of the data obtained.


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� Section 10.0 provides a brief discussion of construction sequencing and strategies which may influence the geotechnical engineering characteristics of the site.

The discussion and construction recommendations presented in Section 10.0 are intended to help develop site soil conditions that are consistent with the geotechnical engineering recommendations presented previously in the report. Ancillary information such as some background information regarding soil corrosion and radon considerations is presented as general reference. The construction considerations section is not intended to address all of the construction planning and needs for the project site, but is intended to provide an overview to aid the owner, design team, and contractor in understanding some construction concepts that may influence some of the geotechnical engineering aspects of the site and proposed development.

The data used to generate our recommendations are presented throughout this report and in the attached figures. 1.1 Scope of Project

We understand that the project will consist of designing and constructing a single family residential structure that is supported by a steel reinforced concrete foundation system. The structure will likely be designed with multiple retaining walls due to the topography of the lot. We anticipate that exterior retaining structures will also be utilized to establish the structure access driveway and parking areas. This report provides basic level slope stability analyses based on hypothetical excavation cut slope geometries. Additional design level slope stability modeling, both for temporary and permanent excavations and fill slopes (retained or unrestrained), will need to occur as the project design progresses. The basic level slope stability modeling provided in this report should be considered as feasibility level modeling. The development of the project may require specialty shoring design and construction, including the use of soil nail and reinforced shotcrete and/or micropile shoring features. We do not provide design for these types of specialty shoring/slope revetment structures. A specialty shoring design engineer will be needed for the design of these types of structures. The selected shoring design engineer will need to provide engineering design documents for these types of structures. The design documents will need to be stamped by a professional engineer that is registered in the State of Colorado.


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2.0 GEOTECHNICAL ENGINEERING STUDY Our services include a geotechnical engineering study of the subsurface soil and water conditions for development of this site for single family residential use. 2.1 Geotechnical Engineering Study Scope of Service The scope of our study which was delineated in our proposal for services, and the order of presentation of the information within this report, is outlined below. Field Study

• We advanced four (4) continuous flight auger test borings (Test Borings One through Four) at the project within the areas we understand are planned for construction of the proposed structure, and two (2) shallow test borings (Test Borings Five and Six) along the potential access driveway alignment.

• Select driven sleeve and bulk soil samples were obtained from the test borings and returned to our laboratory for testing.

Laboratory Study

• The laboratory testing and analysis of the samples obtained included;

� Moisture content and dry density, � Estimates of soil strength parameters, including direct shear strength tests, to help

establish a basis for development of soil bearing capacity and lateral earth pressure values,

� Swell/consolidation tests to help assess the expansion and consolidation potential of the site soils,

� Plastic and liquid limit tests to determine the Plasticity Index of the soil, and, � Sieve analysis tests.

Geotechnical Engineering Recommendations

• This report addresses the geotechnical engineering aspects of the site and provides recommendations including;

Geotechnical Engineering Section(s)

� Subsurface soil and water conditions that may influence the project design

and construction considerations


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� Basic/Feasibility level slope stability analyses, � Geotechnical engineering design parameters including; 9 Viable foundation system concepts including soil bearing capacity

values, 9 settlement considerations for the foundation system concepts that are

viable for this project, and, 9 Lateral Earth Pressure values for design of retaining structures

� Soil support considerations for interior and exterior concrete flatwork.

Construction Consideration Section

� Fill placement considerations including cursory comments regarding site preparation and grubbing operations,

� Comments for placement and compaction of fill on sloped areas, � Considerations for excavation cut slopes, � Natural soil preparation considerations for use as backfill on the site, � Compaction recommendations for various types of backfill proposed at the

site, � Utility trench comments, and, � Cursory exterior grading considerations

• This report provides design parameters, but does not provide foundation design or

design of structure components. The project architect, designer, structural engineer or builder may be contacted to provide a design based on the information presented in this report.

• Our subsurface exploration, laboratory study and engineering analysis do not address

environmental or geologic hazard issues


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3.0 FIELD STUDY 3.1 Project location The project site is designated as Lot 51 Aldasoro Ranch, located about two (2) miles north-northwest of Telluride, Colorado. The project site is located with San Miguel County Limits. The project site is accessed via Aguirre Road, just prior to and adjacent to the north side of the cul-de-sac at the end of Aguirre Road. The approximate location of the project site is shown on Figure 3.1 below. The imagery used for Figure 3.1 was obtained from Google Earth (imagery date: 10/12/2015). Figure 3.3 provided later in this report may be referenced for a closer view of the project location. Figure 3.1: Approximate Project Location: 3.2 Site Description and Geomorphology The driveway that will access the proposed structure area will be constructed off the north side of Aguirre Road and will be aligned to the north for a distance of approximate 400 lineal feet to the proposed structure area. The ground surface on and adjacent to the driveway alignment general slopes down to the south-southwest with slope inclinations of about ten to one (10;1,

Approximate Project Location


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horizontal to vertical) or flatter. The west and east sides of the lot are bounded by small creeks which appear to flow water year-round. A small irrigation ditch bisects through the lot from the northwest corner of the property to the central area of the east property line. The irrigation ditch contours the toe of the steeper sloped features which are located in the northern area of the lot. A small amount of flowing water was observed in the irrigation ditch at the time of our October 26, 2017 field study. The proposed structure site is located at the toe of relatively steep south facing slopes of a ridge feature. The slope surfaces on the subject lot and within the proposed structure area slope down to the south-southwest with inclinations in the range of about three to one (3:1, h:v) to two to one (2:1, h:v). The slope surfaces above and to the north of the lot and proposed structure area are steeper with slope inclinations down to the southwest in the range of about two to one (2:1,h:v) to one and one-half to one (1½:1, h:v). The total vertical relief of the slope features on and above the project site is in the range of about 225 to 250 vertical feet. The subsurface soil and rock materials encountered in the Aldasoro Ranch area can vary dramatically over relatively short distances. Relatively dense and granular soil deposits associated with historic glacial and general colluvial deposition to highly expansive clay soils associated with the Mancos Shale formation may be encountered. In general, the Mancos Shale formation underlies a large part of the Aldasoro Ranch area, however intrusive rocks through the Mancos Shale formation in the form of sills and dike features are encountered in some areas of Aldasoro Ranch development. 3.3 Subsurface Soil and Water Conditions We advanced four (4) test borings in the vicinity of the proposed structure location (Test Borings One through Four), and two (2) test borings along the proposed roadway alignment (Test Borings Five through Six). The approximate locations of our test borings are shown on Figure 3.3 below. The imagery used for Figure 3.3 was obtained from Google Earth (imagery date: 10/12/2015). The logs of the soils encountered in our test borings are presented in Appendix A.


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Figure 3.3: Approximate Test Boring Locations The approximate test boring locations shown on the figure above were prepared using notes taken during the field work and are intended to show the approximate test boring locations for reference purposes only. Test Borings One through Three were advanced on the slope surfaces above the irrigation ditch. Test Boring One was advanced the furthest north up the hillside. In Test Boring One we encountered a mixture of clay and silt soil with sand and organic matter from the ground surface to a depth of about one (1) foot below the ground surface elevation where we encountered sandy clay soils with scattered gravel to a depth of about five (5) feet below the ground surface elevation. We encountered the Mancos Shale formation at a depth of about five (5) feet below the ground surface elevation. The formational material encountered consisted of hard to very hard shale material. Test Boring One was advanced to a depth of about thirty-two (32) feet below the ground surface elevation. We subsequently measured free water in Test Boring One at a depth of about twenty-two (22) feet below the ground surface elevation about two (2) weeks after the initial advancement of the boring. In Test Borings Two and Three we encountered similar soil materials in the upper portions of the test borings as those encountered in Test Boring One, however the clay soil materials were

TB-1

TB-2

TB-3

TB-4

TB-5

TB-6


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encountered to depths ranging from about fourteen (14) to eighteen (18) feet below the ground surface elevation where we encountered the Mancos Shale Formation. Stiff and jumbled shale material with clay soil and periodic gravels was encountered above the in-place formational shale materials. We encountered subsurface free water at a depth of about nine (9) feet below the ground surface elevation in Test Boring Two at the time of our field study. We anticipate that the subsurface free water encountered in Test Boring Two is related to water flow in the creek and/or irrigation ditch system located in the area of the project site. Test Boring Four was advanced just to the south (below) the irrigation ditch at the base of the slope surfaces. In Test Boring Four we encountered a mixture of clay and cobbles with sand and gravel from the ground surface a depth of about two (2) feet below the ground surface elevation where we encountered stiff and moist to very moist sandy clay soil with scattered gravel and cobbles to the bottom of the test boring. Test Boring Four was advanced to a depth of about ten (10) feet below the ground surface elevation. We expected to encounter subsurface free water in Test Boring Four at a relatively shallow depth, as the position of Test Boring Four was about four (4) or five (5) feet from the irrigation ditch which was flowing water at the time of our field study. Oddly, subsurface free water was not encountered in this test boring and was not subsequently measured in the boring after a period of about two (2) weeks. Test Borings Five and Six were advanced along the proposed access driveway alignment. We encountered a mixture of sandy clay soil with varying quantities of gravel and cobbles in these test borings. The test borings were advanced to depths ranging from about seven (7) to nine (9) feet below the ground surface elevation. Subsurface free water was located at a depth of about six (6) feet below the ground surface elevation in Test Boring Five after a time period of about two (2) weeks. Several of the test borings were left open and covered with large cobbles after our initial field study to measure the subsurface free water elevation at a later date. The test borings have since been backfilled. We suspect that the subsurface water elevation and soil moisture conditions will be primarily influenced by water located in the irrigation ditch and stream channels that surround the project site. In addition, we suspect that the subsurface water and moisture conditions will be influenced by snow melt and/or precipitation. The sandy clay soil materials and formational shale materials that were encountered and tested exhibit a very high swell potential when wetted. As discussed in Section 5.0 below, we recommend that a deep foundation system be used to support the structure due to the highly expansive soils on this project site. The logs of the subsurface soil conditions encountered in our test borings are presented in Appendix A. The logs present our interpretation of the subsurface conditions encountered exposed in the test borings at the time of our field work. Subsurface soil and water conditions are often variable across relatively short distances. It is likely that variable subsurface soil and


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water conditions will be encountered during construction. Laboratory soil classifications of samples obtained may differ from field classifications. 4.0 LABORATORY STUDY The laboratory study included tests to estimate the strength, swell and consolidation potential of the soils tested. We performed the following tests on select samples obtained from the test borings. Moisture content and dry density; the moisture content and in-situ dry density of some of the soil samples were assessed in general accordance with ASTM D2216. Atterberg Limits; the plastic limit, liquid limit and plasticity index of some of the soil samples was determined in general accordance with ASTM D4318. Sieve Analysis Tests; We performed sieve analysis tests on select samples of soil in general accordance with ASTM D422 and/or ASTM C136, depending upon the nature of the materials sampled and tested. The primary use of the sieve analysis test, in conjunction with the Atterberg Limits is for classification and characterization of the materials tested. The results of the sieve analysis and Atterberg Limits tests are provided on Figure 4.1 of Appendix B. The soils tested and obtained from Test Boring Two from the ground surface to a depth of about seven (7) feet below the ground surface elevation consist classify as USCS type “SC” clayey sand. We anticipate that in other areas of the project, the soil materials that overlie the formational shale material classify as USCS type “CL” sandy clay material. Swell-Consolidation Tests; the one dimensional swell-consolidation potential of some of the soil samples obtained was determined in general accordance with constant volume methodology. The soil sample tested is exposed to varying loads and usually the addition of water. The one-dimensional swell-consolidation response of the soil sample to the loads and/or water is represented graphically on Figures 4.2 through 4.4. Both the formational shale materials and overlying clay soil materials exhibit a very high swell potential and related swell pressure when wetted. A summary of some of the pertinent information obtained from the swell portion of swell-consolidation tests are tabulated below.


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Sample Designation

Moisture Content (percent)

Dry Density (PCF)

Measured Swell

Pressure* (PSF)

Load Back Swell

Pressure (PSF)

Swell Potential

(% under 100 psf load)

TB-1 @ 12 feet 6.6 129.6 2,140

3,300 5.6

TB-3 @ 8 feet 9.9 129.7 Not obtained 7,000 6.1

TB-4 @ 3 feet 8.8 120.8 4,020

4,500 12.6

*NOTE: The measured swell pressure may be different from that obtained from the load back obtained swell pressure. Direct Shear Strength tests; Direct shear strength tests were performed on select soil samples to estimate the soil strength characteristics in general accordance with ASTM D3080. The results of the direct shear strength tests are provided on Figure 4.5 of Appendix B. We used an angle of internal friction (phi) of 28 degrees and a cohesion of about 150 pounds per square foot in our analyses. 5.0 BASIC/FEASIBILITY LEVEL SLOPE STABILITY ANALYSES This section of the report provides a basic/feasibility level slope stability study for the project. We have provided slope stability analyses for “hypothetical” excavation cut scenarios, as the structure layout plans had not been developed at the time of issue of this report. The analyses presented below are intended to provide the project owner and members of the project design team with general information regarding the slope stability aspects of the lot. Additional and more detailed slope stability analyses will be required as the project design progresses. The slope surface cross sections analyzed are based on the available topographic data that has been provided to us. The cross sections shown on Figure 5.1 below were used as a basis for the slope surface geometry used in our analyses.


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Figure 5.1: Location of Cross Sections Used for Stability Analyses (Lot 51 Topographic Survey)

Cross Section A


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There are numerous methods and techniques available for slope stability analysis. Most methods include an evaluation of;

• the strength of the soil materials and/or formational materials within the slope, • anisotropies within the slope materials, such as formational material bedding planes, and

anomalous soil contacts, • the subsurface water and soil moisture conditions, and, • the pre-construction and post-construction geometry of the slope areas where

development and construction is proposed. The data developed during the analysis is condensed and used to estimate the forces within a soil mass that tend to drive movement and the forces that tend to resist movement. The ratio of resisting forces to driving forces is often referred to as the “theoretical slope factor of safety” (FOS) which is a somewhat misleading term to describe this ratio. The ratio is not a true factor of safety, but is a useful mathematical characterization of the forces within a soil mass and the associated stability condition of the slope being analyzed. A ratio of less than one (1) indicates that the driving forces within a soil mass are greater than the resisting forces, therefore movement of the slope is occurring. A ratio of one (1) indicates that the driving forces are equal to the resisting forces, which indicates that movement within the soil can be triggered by only slight increases in the driving forces or slight reductions in the resisting forces. A ratio of greater than one (1) is an indication that the driving forces are less than the resisting forces and the slope is not moving. Since there are numerous variables and incongruities within most soil masses, a slope is generally not considered as stable unless the ratio is about 1.5 or greater. Generally, slopes or slope/structure combinations with a theoretical factor of safety that is greater than 1.5 are considered appropriate for sites where structures are planned. Temporary excavation cut slopes that exhibit a factor of safety of about 1.3 are often considered as being stable for temporary applications, and for some roadway applications. We used SLIDE 7.0 slope stability software to evaluate the stability of computer modeled slope cross sections of select portions of this site. We primarily used the Modified Bishop’s Method of slices to analyze the computer modeled slopes. The Modified Bishop’s Method of Slices evaluates the resisting and driving forces within slices of the sloped soil mass along a theoretical semi-circular failure plane. The semicircular failure plane with the lowest theoretical factor of safety is labeled the critical circle. We have used multiple soil regions/types for the analyses presented below. The soil region shown in the color grey represents the formational shale material that was encountered in our test borings. We used an undrained shear strength of 10,000 pounds per square foot, and a unit weight of 135 pounds per cubic foot for the competent formational shale materials. The region shown in the color orange represents the weathered formational shale materials. We used an undrained shear strength of about 800 pounds per square foot and a unit weight of 130 pounds


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per cubic foot for the weathered formational shale materials that we encountered in our test borings. The undrained shear strength parameters that we used are partially based on unconsolidated-undrained compressive strength tests that we performed on “in-situ” liner samples obtained from the formational shale materials encountered in our test borings. The region shown in the color yellow represents the sand and clay soils that were encountered in the upper portions of our test borings, overlying the formational shale materials. We used an angle of internal friction of twenty-eight (28) degrees and cohesion of 150 pounds per square foot for these materials. A unit weight of 125 pounds per cubic foot was used for the sand and clay soils. We encountered subsurface water in Test Boring Three at a depth of about nine (9) feet below the ground surface. Subsurface free water was measured at a depth of about twenty-two (22) feet below the ground surface elevation in Test Boring One during subsequent water measurements after the time of our original field study. We anticipate that subsurface water will be encountered within the project excavation extents. The subsurface water must be adequately drained to ensure that excess hydrostatic pressures do not develop within the retained soil mass. We suspect that the subsurface drain systems associated with the project will flow water in some locations throughout the majority of the year. Water must not be allowed to pool on the ground surface of the lot, particularly above retaining structures or unrestrained cut or fill slopes. Exterior backfill must be well compacted to ensure that surface water does not readily access the subsurface slope mass. Collected water, such as water obtained from roof gutters or concrete flatwork such as driveways must be directed to areas away from the structure retaining features. Accumulation of subsurface free water in the slopes of the project lot will greatly reduce the long-term stability conditions of the project lot, project structure, and slope surfaces above the project lot (slope surfaces on adjacent lots above and to the north of the project lot). The cross-sectional geometries of the various soil and formational shale material regions are based on estimates, especially in areas above and below our test boring locations. The analysis shown on Figure 5.2 below indicates the theoretical factor of safety for the existing (preconstruction) global slope conditions on the project lot, and for the slope surfaces above the project lot. We obtained a theoretical factor of safety in the range of about 1.38.


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Figure 5.2: Theoretical Factor Safety for the Global Slope Conditions, F.O.S.=1.38

The analysis shown on Figure 5.3 below is intended to indicate the influence that a “hypothetical” excavation cut slope associated with the proposed structure has on the global slope stability conditions. The excavation cut shown exhibits a tiered excavation. The upper tier of the excavation in our model is about ten (10) feet in height, while the lower tier of the excavation is about twenty (20) feet in height. We obtained a similar theoretical factor of safety as that for the existing global slope conditions of about 1.38. This indicates that the “hypothetical” excavations do not have a negative impact on the overall “global” slope stability conditions.


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Figure 5.3: Theoretical Factor Safety for the Global Slope Conditions with Hypothetical Excavation Cut Slopes, F.O.S.=1.38

The analysis presented on Figure 5.4 below indicates the “local” stability of the “hypothetical” excavation cut slopes. We obtained a theoretical factor of safety of about 1.0 for the hypothetical unrestrained excavation cut slopes modeled which should be considered as being unstable. It should be noted that the excavation cut slope heights modeled consist of an upper approximate ten (10) foot vertical excavation and a lower approximate fifteen (15) foot vertical excavation the excavations are separated by a bench with a width of about twenty (20) feet. Note that we modeled the phreatic water conditions that were encountered in Test Borings One and Three in this model. The portion of the phreatic water surface geometry above and below our test boring locations was estimated.


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Figure 5.4: Theoretical Factor Safety for the Local Slope Conditions with Hypothetical Excavation Cut Slopes, F.O.S.=1.00

Figure 5.5 presented below indicates the theoretical factor of safety for these excavation cut slopes that are unrestrained and laid back to an inclination of about one to one (1:1, h:v). We obtained a theoretical factor of safety of about 1.55 which may be considered as being stable.


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Figure 5.5: Theoretical Factor Safety for the Local Slope Conditions with Hypothetical Excavation Cut Slopes Laid Back to 1:1, H:V, F.O.S.=1.55

The analysis presented below indicates the theoretical factor of safety for the vertical excavation cut slopes (10 foot high upper excavation and 15 foot high lower excavation) when the at-rest lateral earth pressures are applied against these excavations. We used the at-rest lateral earth pressures for an imported granular fill material in our analysis (see Section 7.0 below for the lateral earth pressure values for imported granular fill materials). We obtained a theoretical factor of safety of about 1.6 which may be considered as being stable.


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Figure 5.6: Theoretical Factor Safety for the Local Slope Conditions with Hypothetical Excavation Cut Slopes Restrained with At-Rest Lateral Earth Pressures, F.O.S.=1.61

We did not model soil nail components in the slope stability analyses presented above as theoretical factor of safeties greater than 1.5 were obtained in our basic/preliminary models. However, we anticipate that specialized shoring will be needed to stabilize some of the project short-term and long-term excavations. We recommend that the project owner have an allowance in the construction budget for specialized shoring such as the use of soil nail and shotcrete structures. The degree of needed specialized shoring will be highly dependent on the structure geometry, finished floor elevations, and magnitudes of excavations or retained fill placements. We anticipate that the project topography and other constraints such as the location of the building envelope and irrigation ditch will greatly influence the project layout and subsequent need for specialized shoring structures.


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We do not provide design for specialized shoring structures such as soil nail and shotcrete and/or micropile curtain walls. These types of structures will need to be designed by a professional engineer that specializes in the design of these types of structures. The selected shoring design engineer will need to perform their own slope stability analyses based on their shoring design. In general, the need for specialized types of shoring structures can be reduced or minimized by designing the structure in order to limit the vertical extent of excavation cut slopes/retaining features. Retaining structures may be terraced to help limit the overall height of singular retaining structures. The structure may be strategically placed to help minimize the extent of retaining features. In general, we feel that placement of the structure within the existing designated building envelope for the lot will help minimize the need for specialized shoring features. This is due to the fact that slightly flatter topography exists within the designated building envelope. 6.0 FOUNDATION RECOMMENDATIONS The soil materials and the formational shale materials encountered in our test borings exhibit a very high swell potential when wetted. Based on the fact that highly expansive soil materials exist on the project site we recommend that a deep foundation system be used to support the structure to help decrease the potential for movement to occur in the structure foundation system. Of the available deep foundation systems, we feel that a drilled micro-pile foundation system or drilled pier foundation system is most applicable for the project. We have provided recommendations for drilled micro-piles in Section 6.1 below, and for drilled piers in Section 6.2 below. Recommendations for void form below the foundation system grade beams are provided in Section 6.3 below. The integrity and long-term performance of any type of foundation system is influenced by the quality of workmanship which is implemented during construction. It is imperative that all excavation and fill placement operations be conducted by qualified personnel using appropriate equipment and techniques to provide suitable support conditions for the foundation system. Deep foundation systems require the use of specialized construction and equipment. The foundation systems discussed below must be installed by a contractor who specializes in the installation of these types of foundation systems. The elevation of the existing ground surface at our test boring locations at the time the borings were advanced should be established as part of the design process for deep foundation systems for this project. It is critical that the depths to various strata delineated in our test borings logs can be correlated to final project elevations.


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6.1 Drilled Micro-Pile Foundation System Micro-pile foundation systems are specialized foundation support elements, requiring specialized installation equipment and experience. An experienced micro-pile/soil nail anchor contractor should be used for the installation of the micro-pile components. The development will include retaining structures that will require lateral restraint. We do not recommend accounting for any shear or moment capacity for uncased micro-piles. Lateral loads or moments should be resolved with battered micro-pile components or steel cased micro-pile components. We are available to provide L-PILE computer analysis parameters to analyze lateral deflections of heavy section steel cased micro-pile elements. The following general specifications should be followed for the micro-pile design:

• The micro-piles should consist of minimum four (4) to six (6) inch diameter elements. We recommend that the micro-piles be constructed with open-hole techniques with grout injected via a grout tube from the bottom of the boring to the top of the element at the base of the grade beam.

• As discussed below, we recommend that several test piles be installed to verify the preliminary grout bond capacities provided below.

• We recommend that the grout take/volume be monitored during the installation process to help ensure that the boring diameter volume is adequately grouted throughout the length of the micro-pile element.

• The project structural engineer should specify the minimum bar and bar yield strength criteria for the project depending on the structural loads that will be applied to the micro-pile elements.

• Centralizers must be used for open hole micro-pile installations to ensure that the reinforcement bar is centralized with the boring.

• We recommend that the grout used for the micro-piles develop a minimum compressive strength of at least 4,000 pounds per square inch within 7 days of placement.

• The micro-piles should extend a minimum depth of at least eighteen (18) feet below the bottom of the supported grade beam. A maximum micro-pile depth of about thirty (30) feet should be considered for load carrying capacity calculations.

We recommend that a preliminary ultimate grout to soil bond capacity of about 2,000 pounds per square foot of grouted circumference area be assumed for initial project design calculations, therefore an allowable grout to soil bond capacity of about 1,000 pounds per square foot of grouted circumference area (factor of safety of 2.0) may be used for the initial project design. The grout to soil bond capacity may be considered valid for both tensional and compressive capacity. We recommend that the upper three (3) feet of grout bond capacity be deducted from the micro-pile capacity calculations. We recommend that several test micro-piles be installed prior to the completion of the project design to ensure that accurate grout pond capacities are


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used. For micro-pile groups, no reduction in the allowable capacity for the individual piles will be necessary for individual piles spaced greater than six (6) pile diameters center-to-center. A reduction factor of 0.65 for each individual pile should be assumed for piles spaced as close as two and one-half (2.5) pile diameters center-to-center. The reduction factor for piles spaced between six (6) and two and one-half (2.5) pile diameters center-to center may be interpolated between the reduction factors provided above. The micro-piles should not be spaced closer than two and one-half (2.5) pile diameters center-to-center. We should be contacted to log the micro-pile borings to ensure that the minimum embedment depth of the elements is obtained, and ensure that the elements are properly constructed. We recommend that a minimum of about ten (10) percent or minimum of five (5) of the production micro-piles be proof tested to at least 150% of the design capacity, and at least two (2) sacrificial test piles be tested to 200% of the needed design capacity. We are available to provide updated allowable capacities for micro-pile components based on the actual load test data. We are available to install initial project design test micro-piles to help assess the grout to soil bond capacities for the project. We are also available to perform load testing of the sacrificial and production piles at your request. 6.2 Drilled Piers Drilled piers which are designed as end bearing and supported by the clean competent unweathered formational material underlying the site are a viable foundation system option. The drilled pier borings should be advanced a minimum of two (2) pier diameters into the formational material, or to a minimum depth of at least fifteen (15) feet, whichever is deeper. Drilled piers supported by the clean, competent formational material may be designed using a bearing capacity of 25,000 pounds per square foot. The portion of the pier in the unweathered formational material may be designed using a side friction of 1,000 pounds per square foot. The drilled piers should be designed to resist uplift associated with swelling of the support soils. The top of the piers should not be flared, which can allow the soils to “grab” the pier and cause uplift. The piers should be installed using drilling equipment which is good working order and intended for advancing large diameter borings. Proper performance of the drilled piers requires appropriate drilling and installation techniques. All drilled piers must be installed by a contractor who is familiar with pier construction. The piers should be cased, as required by the site soil conditions so that no flares or “mushrooms” exist at the tops of the piers. Flares allow for increased uplift forces to develop in the piers and subsequent movement which may cause damage to the structure. Proper performance of the drilled pier is partially influenced by the character and quality of the concrete used to construct the pier. The pier concrete should not be too stiff, which may prevent


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proper consolidation of the concrete, or too fluid, which may adversely affect the strength of the concrete. Generally, the concrete should have a slump between about three (3) to six (6) inches. It may be necessary to use mid- or high-range water reducing concrete admixtures to obtain concrete with both a suitable slump and acceptable concrete compressive strength characteristics. Use of a tremmie and/or pumping equipment should be used to place concrete in drilled pier borings deeper than about ten (10) feet. Concrete should not be allowed to drop more than about five (5) feet during the installation process. We encountered free subsurface water in our test borings at the time of our field work. It has been our experience that subsurface water is often encountered along fractures, fissures and joints within the formational material. Occasionally the drilling operations will increase the pore pressures within the adjacent material to produce a small amount of water access to the drilled pier excavation. If water and/or caving soils are encountered during the pier installation operation it may be necessary to dewater the pier excavations and remove any caved soils. Pier concrete should not be conventionally placed if more than a few inches of water exists in the bottom of the pier boring. If more than a few inches of water exists in the bottom of the boring the concrete should be placed using a tremmie, or pump, so that the concrete displaces any water during the pier foundation construction operation. The support elevation of the pier must be thoroughly cleaned prior to placement of the pier concrete. Loose material in the bottom of the pier borings will cause settlement of the pier. The pier support elevation may be cleaned using clean-out tools attached to the drill rig, hand equipment, excavation suction equipment, or a combination of these. Under no circumstances should the pier foundation concrete be placed when loose material exists in the bottom of the borings. The interface between the weathered formational and the underlying competent formational material was relatively obscure in some of our test borings and was a transitional contact in other borings. We should be contacted during construction to aid in determining the appropriate pier support elevation. We should be contacted to measure the depth of the piers, verify the competency of the support materials, and check the plumbness of the piers. We are available provide an as-built record of the installed drilled pier foundation system. Please contact us if this service is desired. 6.3 Grade Beams and Void Form Grade beams are utilized in a pier and grade beam foundation system to distribute the structure loads to each of the piers. The grade beam reinforcement and associated span distance is developed by the project structural engineer. The structural considerations of the grade beam in association with an assessment of the structure being supported by the project structural engineer will, in part determine the spacing between each of the deep foundation components. It is


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imperative that an appropriate void be developed below the grade beam so that swelling soils do not create uplift of the supported structure. Voids are most commonly developed with commercially available cardboard “void forms” that are placed at the bottom of the concrete forms prior to placement of reinforcement steel and the grade beam concrete. If the soils below the grade beam become moistened and expand, the cardboard void form will collapse without the soils having the ability to impose uplift forces on the bottom of the grade beam. The height of the void is often related to the expansion potential of the site soils and anticipated depth of wetting that will develop within the soils below the grade beam. We recommend that a minimum of five (5) inch void be established below the foundation grade beam components. We are available to provide additional information in regard to void forms and associated conditions if additional information is needed. 7.0 RETAINING STRUCTURES We understand that laterally loaded walls will be constructed as part of this site development. Lateral loads will be imposed on the retaining structures by the adjacent soils and, in some cases, surcharge loads on the retained soils. The loads imposed by the soil are commonly referred to as lateral earth pressures. The magnitude of the lateral earth pressure forces is partially dependent on the soil strength characteristics, the geometry of the ground surface adjacent to the retaining structure, the subsurface water conditions and on surcharge loads. As discussed in Section 6.0 above, a deep foundation system that is supported over void should be used to support the structure. The lateral earth pressures that act on the structure retaining walls will either need to be resolved with battered micropiles or soil nail anchors (essentially near horizontal micropile components) or steel cased micropiles that exhibit sufficient rigidity to resolve the lateral pressures that will be transferred to the foundation system. A drilled pier foundation system (Section 6.2) may exhibit sufficient rigidity within the drilled pier components to resolve the lateral forces that will act on the foundation system. As discussed in Section 6.0 above, we are available to provide LPILE design parameters to analyze laterally loaded foundation components. Due to the expansive nature of the site soils we do not recommend that the natural clay soils be used for retaining wall backfill. The retaining walls may be designed using the lateral earth pressure values for imported granular soil that are tabulated below.


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Type of Lateral Earth Pressure Level Granular Soil Backfill (pounds per cubic foot/foot)

Active 35 At-rest 55 Passive 460

Allowable Coefficient of Friction 0.45 The granular soil that is used for the retaining wall backfill may be permeable and may allow water migration to the foundation support soils. We recommend that an impervious geotextile layer and shallow drain system may be installed in the upper portions of the backfill soil materials. We have provided a general concept for this type of drain system in Section 10.5, Landscaping Considerations, below. The values tabulated above are for well drained backfill soils. The values provided above do not include any forces due to adjacent surcharge loads or sloped soils. If the backfill soils become saturated the imposed lateral earth pressures will be significantly higher than those tabulated above. The granular imported soil backfill values tabulated above are appropriate for material with an angle of internal friction of thirty-five (35) degrees, or greater. The granular backfill must be placed within the retaining structure zone of influence as shown below in order for the lateral earth pressure values tabulated above for the granular material to be appropriate.

55 Degrees

Retaining wall zone of influence

Retaining Structure

Retaining Structure Zone of Influence Concept, No Scale

Impervious soil backfill for upper 2 feet


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If a granular backfill is chosen it should not extend to the ground surface. Some granular soils allow ready water migration which may result in increased water access to the foundation soils. The upper few feet of the backfill should be constructed using an impervious soil such as silty-clay and clay soils from the project site, if these soils are available. Backfill should not be placed and compacted behind the retaining structure unless approved by the project structural engineer. Backfill placed prior to construction of all appropriate structural members such as floors, or prior to appropriate curing of the retaining wall concrete (if used) may result in severe damage and/or failure of the retaining structure.

8.0 SUBSURFACE DRAIN SYSTEM We encountered subsurface water at a depth of about eight and one-half (8½) feet below the ground surface in Test Boring Three, and at a depth of about twenty-two (22) feet below the ground surface elevation in Test Boring One. We anticipate that subsurface water will be encountered within the structure extents. The drain system concepts discussed below are intended to address the geotechnical engineering related issue of relieving hydrostatic pressures from the retained soils. The recommendations provided below may help alleviate the potential for subsurface water to access interior portions of the structure, however likely will not completely mitigate the potential for water to access the structure living areas. The drain system and waterproofing strategy must be carefully designed to ensure that water does not access interior portions of the structure. The project architect and/or builder may be contacted to provide recommendations for adequately waterproofing the structure to mitigate the potential for water to access interior portions of the structure. A subsurface drain system and/or weep holes should be included in the retaining structure design. Exterior retaining structures may be constructed with weep holes to allow subsurface water migration through the retaining structures. A drain system constructed with a free draining aggregate material and a perforated pipe should be constructed adjacent to retaining structures or adjacent to foundation walls on sites with expansive soil conditions. We suggest that the system consist of a fabric-wrapped aggregate, or a sand material (some sands may not need fabric, we are available to discuss this with you) which surrounds a rigid perforated pipe. We typically do not recommend use of flexible corrugated perforated pipe since it is not readily possible to establish a uniform gradient of the flexible pipe throughout the drain system alignment. Corrugated drain tile is perforated throughout the entire circumference of the pipe and therefore water can escape from the perforations at undesirable locations after being collected. The nature of the perforations of the corrugated material further decreases its effectiveness as a subsurface drain conduit. The drain system pipe should be graded to surface outlets or a sump vault. Typically, a minimum gradient of about two (2) percent is preferred for subsurface drain systems, but site


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geometry and topography may influence the actual installed pipe gradient. Water must not be allowed to pool along any portion of the subsurface drain system. An improperly constructed subsurface drain system may actually promote water access to undesirable locations. The drain system pipe should be surrounded by about two (2) to four (4) cubic feet per lineal foot of free draining aggregate or sand. If a sump vault and pump are incorporated into the subsurface drain system, care should be taken so that the water pumped from the vault does not recirculate through pervious soils and obtain access to the basement or crawl space areas. A generalized subsurface drain system concept is shown below.

There are often aspects of each site and structure which require some tailoring of the subsurface drain system to meet the needs of individual projects. We are available to provide consultation for the subsurface drain system for this project, if desired. We do not provide detailed drainage plans. The project civil engineer may be contacted to assist with the preparation of drainage plans for the project.

Perforated pipe surrounded by fabric wrapped free-draining material. Note: The elevation of the pipe will depend on the location in the system at which the cross section is considered. We recommend that the drain pipe be located below the grade beam void form.

Impervious backfill for upper 2 feet

Compacted backfill that meets lateral earth pressure design criteria.

Retaining or foundation wall

Water proof membrane or similar placed on the foundation wall and extending below outer face of footing and below drain pipe*

Pervious drain board or fabric (optional)

Grade Beam Void Form

Subsurface Drain System Concept No Scale

Geotextile filter fabric, if appropriate

*From a geotechnical engineering perspective, the waterproof membrane or other means of waterproofing such as spray on products is not needed to relive hydrostatic pressures from the retained soils. The project architect and/or builder should provide recommendations for the best method of sealing the retaining wall system to mitigate the potential for water to access interior portions of the structure.


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If the utility trenches extend from areas above the site, the trench(s) may be a source for subsurface water within the proposed basements. We suggest that the utility trench backfill be thoroughly compacted to help reduce the amount of water migration. The subsurface drain system should be designed to collect subsurface water from the utility trench and fractures within the formational material and direct it to surface discharge points. 9.0 CONCRETE FLATWORK We understand that both interior and exterior concrete flatwork will be included in the project design. Concrete flatwork is typically lightly loaded and has a limited capability to resist shear forces associated with uplift from swelling soils and/or frost heave. The design and construction of concrete flatwork on this project must be able to accommodate some movement associated with swelling soil conditions. 9.1 Interior Concrete Slab-on-Grade Floors Due to the highly expansive nature of the soils tested we do not recommend that interior floor slabs be considered unless the owner thoroughly understands the implications of movement of these structural components. Development of sites with walk-out style basements typically utilize the basement floor concrete slab-on-grade to help resolve lateral loads imposed on the basement walls. There are techniques, such as placement of grade beams below a structurally supported floor system to help resolve these loads to allow for construction of a crawl space below the lower level floor. The structural engineer should be contacted to provide these recommendations, if they are feasible for the development of this site. If a floor slab is chosen for the lower level floor it is imperative that interior walls are isolated from the lower level floor slab so that movement of the slab associated with swelling soils does not cause uplift of the interior walls and subsequently upper potions of the structure. A primary goal in the design and construction of interior concrete slab-on-grade floors is to reduce the amount of post construction uplift associated with swelling soils, or downward movement due to consolidation of soft soils. A parallel goal is to reduce the potential for damage to the structure associated with any movement of the slab-on-grade which may occur. There are limited options available to help mitigate the influence of volume changes in the support soil for concrete slab-on-grade floors, these include; • Preconstruction scarification, moisture conditioning and re-compaction of the natural

soils in areas proposed for support of concrete flatwork, and/or, • Placement and compaction of granular compacted structural fill material.


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Damage associated with movement of interior concrete slab-on-grade floor can be reduced by designing the floors as “floating” slabs. The concrete slabs should not be structurally tied to the foundations or the overlying structure. Interior walls or columns should not be supported on the interior floor slabs. Movement of interior walls or columns due to uplift of the floor slab can cause severe damage throughout the structure. Interior walls may be structurally supported from framing above the floor, or interior walls and support columns may be supported on interior portions of the foundation system. Partition walls should be designed and constructed with voids above, and/or below, to allow independent movement of the floor slab. This concept is shown below.

The sketch above provides a concept. If the plans include isolation of the partition walls from the floor slab, the project architect or structural engineer should be contacted to provide specific details and design of the desired system. The only means to completely mitigate the influence of volume changes on the performance of interior floors is to structurally support the floors. Floors that are suspended by the foundation system will not be influenced by volume changes in the site soils. The suggestions and recommendations presented below are intended to help reduce the influence of swelling soils on the performance of the concrete slab-on-grade floors.

Partition Wall

Corner molding or Trim, not fastened to wall

Wall bottom plate

Sill, or floor plate Floor

Spike or bolt isolated from bottom plate through drilled hole Wallboard, not

fastened to floor plate

PARTITION WALL CONCEPT No Scale


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Interior concrete flatwork, or concrete slab-on-grade floors, should be underlain by a minimum one (1) foot layer of compacted structural fill that is placed and compacted as discussed in the Construction Considerations, “Fill Placement Recommendations” section of this report, below. Capillary and vapor moisture rise through the slab support soil may provide a source for moisture in the concrete slab-on-grade floor. This moisture may promote development of mold or mildew in poorly ventilated areas and may influence the performance of floor coverings and mastic placed directly on the floor slabs. The type of floor covering, adhesives used, and other considerations that are not related to the geotechnical engineering practice will influence the design. The architect, builder and particularly the floor covering/adhesive manufacturer should be contacted regarding the appropriate level of protection required for their products. The project structural engineer should be contacted to provide steel reinforcement design considerations for the proposed floor slabs. Any steel reinforcement placed in the slab should be placed at the appropriate elevations to allow for proper interaction of the reinforcement with tensile stresses in the slab. Reinforcement steel that is allowed to cure at the bottom of the slab will not provide adequate reinforcement. 9.2 Exterior Concrete Flatwork Considerations Exterior concrete flatwork includes concrete driveway slabs, aprons, patios, and walkways. The desired performance of exterior flatwork typically varies depending on the proposed use of the site and each owner’s individual expectations. As with interior flatwork, exterior flatwork is particularly prone to movement and potential damage due to movement of the support soils. This movement and associated damage may be reduced by following the recommendations discussed under interior flatwork, above. Unlike interior flatwork, exterior flatwork may be exposed to frost heave, particularly on sites with high silt-content soils. It may be prudent to remove silt soils from exterior flatwork support areas where movement of exterior flatwork will adversely affect the project, such as near the interface between the driveway and the interior garage floor slab. If silt soils are encountered, they should be removed to the maximum depth of frost penetration for the area where movement of exterior flatwork is undesirable. If some movement of exterior flatwork is acceptable, we suggest that the support areas be prepared by scarification, moisture conditioning and re-compaction of about four (4) inches of the natural soils followed by placement of about four (4) to six (6) inches of compacted granular fill material. The scarified material and granular fill materials should be placed as discussed under the Construction Considerations, “Fill Placement Recommendations” section of this report, below. It is important that exterior flatwork be separated from exterior column supports, masonry veneer, finishes and siding. No support columns, for the structure or exterior decks, should be placed on exterior concrete unless movement of the columns will not adversely affect the


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supported structural components. Movement of exterior flatwork may cause damage if it is in contact with portions of the structure exterior. Exterior flatwork should not be placed on soils prepared for support of landscaping vegetation. Cultivated soils will not provide suitable support for concrete flatwork. 9.3 General Concrete Flatwork Comments It is relatively common that both interior and exterior concrete flatwork is supported by areas of fill adjacent to either shallow foundation walls or basement retaining walls. A typical sketch of this condition is shown below.

Settlement of the backfill shown above will create a void and lack of soil support for the portions of the slab over the backfill. Settlement of the fill supporting the concrete flatwork is likely to cause damage to the slab-on-grade. Settlement and associated damage to the concrete flatwork may occur when the backfill is relatively deep, even if the backfill is compacted. If this condition is likely to exist on this site it may be prudent to design the slab to be structurally supported on the retaining or foundation wall and designed to span to areas away from the backfill area as designed by the project structural engineer. We are available to discuss this with you.

Limit of construction excavation

Foundation or retaining wall

Concrete Slab-on-grade

Wall backfill area

Wall Backfill and Slab Support Sketch

No Scale


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10.0 CONSTRUCTION CONSIDERATIONS This section of the report provides comments, considerations and recommendations for aspects of the site construction which may influence, or be influenced by the geotechnical engineering considerations discussed above. The information presented below is not intended to discuss all aspects of the site construction conditions and considerations that may be encountered as the project progresses. If any questions arise as a result of our recommendations presented above, or if unexpected subsurface conditions are encountered during construction we should be contacted immediately. 10.1 Fill Placement Recommendations There are several references throughout this report regarding both natural soil and compacted structural fill recommendations. The recommendations presented below are appropriate for the fill placement considerations discussed throughout the report above. All areas to receive fill, structural components, or other site improvements should be properly prepared and grubbed at the initiation of the project construction. The grubbing operations should include scarification and removal of organic material and soil. No fill material or concrete should be placed in areas where existing vegetation or fill material exist. 10.1.1 Embankment Fill on Slopes Embankment fill placed on slopes must be placed in areas that have been properly prepared prior to placement of the fill material. The fill should be placed in a toe key and benches constructed into the slope. The concept is shown below.


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The width of the toe key should be at least one-fourth (1/4) of the height of the fill. The elevation difference between each bench, width, and geometry of each bench is not critical, but generally, the elevation difference between each lift should not exceed about three (3) to four (4) feet. The benches should be of sufficient width to allow for placement of horizontal lifts of fill material, therefore the size of the compaction equipment used will influence the bench widths. Embankment fill material thicker than five (5) feet should be analyzed on a site specific basis. The fill mass may impose significant loads on, and influence the stability of the underlying slope. We suggest that no fill slopes steeper than two and one-half to one (2½:1, horizontal to vertical) be constructed unless a slope stability analysis of the site is conducted. The toe key and bench drains shown above should be placed to reduce the potential for water accumulation in the embankment fill and in the soils adjacent to the embankment fill. The placement of these drains is more critical on larger fill areas, areas where subsurface water exists and in areas where the slopes are marginally stable. The toe key and bench drains may consist of a perforated pipe which is surrounded by a free draining material which is wrapped by a geotextile filter fabric. The pipe should be surrounded by four (4) to six (6) cubic feet of free draining material per lineal foot of drain pipe.

New Embankment Fill

Bench Drain

Toe Key Drain

Benches Toe Key

Pre-construction ground surface

Toe Key and Bench Concept No Scale


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10.1.2 Natural Soil Fill Any natural soil used for any fill purpose should be free of all deleterious material, such as organic material and construction debris. Natural soil fill includes excavated and replaced material or in-place scarified material. Due to the expansive characteristics of the natural soil we do not recommend that it be used as fill material for direct support of structural components. The natural soils may be used to establish general site elevation. The natural soils should be moisture conditioned, either by addition of water to dry soils, or by processing to allow drying of wet soils. The proposed fill materials should be moisture conditioned to between about optimum and about two (2) percent above optimum soil moisture content. This moisture content can be estimated in the field by squeezing a sample of the soil in the palm of the hand. If the material easily makes a cast of soil which remains in-tact, and a minor amount of surface moisture develops on the cast, the material is close to the desired moisture content. Material testing during construction is the best means to assess the soil moisture content. Moisture conditioning of clay or silt soils may require many hours of processing. If possible, water should be added and thoroughly mixed into fine grained soil such as clay or silt the day prior to use of the material. This technique will allow for development of a more uniform moisture content and will allow for better compaction of the moisture conditioned materials. The moisture conditioned soil should be placed in lifts that do not exceed the capabilities of the compaction equipment used and compacted to at least ninety (90) percent of maximum dry density as defined by ASTM D1557, modified Proctor test. We typically recommend a maximum fill lift thickness of six (6) inches for hand operated equipment and eight (8) to ten (10) inches for larger equipment. Care should be exercised in placement of utility trench backfill so that the compaction operations do not damage the underlying utilities. Typically, the maximum lift thickness is about six (6) to eight (8) inches, therefore the maximum allowable rock size for natural soil fill is about six (6) inches. If smaller compaction equipment is being used, such as walk behind compactors in trenches, the maximum rock size should be less than about three (3) inches. 10.1.3 Granular Compacted Structural Fill Granular compacted structural fill is referenced in numerous locations throughout the text of this report. Granular compacted structural fill should be constructed using an imported commercially produced rock product such as aggregate road base. Many products other than road base, such as clean aggregate or select crusher fines may be suitable, depending on the


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intended use. If a specification is needed by the design professional for development of project specifications, a material conforming to the Colorado Department of Transportation (CDOT) “Class 6” aggregate road base material can be specified. This specification can include an option for testing and approval in the event the contractor’s desired material does not conform to the Class 6 aggregate specifications. We have provided the CDOT Specifications for Class 6 material below

Grading of CDOT Class 6 Aggregate Base-Course Material Sieve Size Percent Passing Each Sieve ¾ inch 100

#4 30 – 65 #8 25 – 55

#200 3 – 12 Liquid Limit less than 30 All compacted structural fill should be moisture conditioned and compacted to at least ninety (90) percent of maximum dry density as defined by ASTM D1557, modified Proctor test. Areas where the structural fill will support traffic loads under concrete slabs or asphalt concrete should be compacted to at least ninety-five (95) percent of maximum dry density as defined by ASTM D1557, modified Proctor test. 10.2 Excavation Considerations Unless a specific classification is performed, the site soils should be considered as an Occupational Safety and Health Administration (OSHA) Type C soil and should be sloped and/or benched according to the current OSHA regulations. Excavations should be sloped and benched to prevent wall collapse. Any soil can release suddenly and cave unexpectedly from excavation walls, particularly if the soils is very moist, or if fractures within the soil are present. Daily observations of the excavations should be conducted by OSHA competent site personnel to assess safety considerations. We encountered subsurface water in our test borings. We suspect that it may be necessary to dewater excavations to provide for suitable working conditions. We encountered formational material in our test borings. We suspect that it will be possible to excavate the formational shale materials using conventional excavation techniques. If for some reason blasting becomes necessary we must be contacted. If blasting is planned it must be conducted strategically to reduce the effect of the blasting on the support characteristics of the site materials and the stability of adjacent slopes. We typically recommend that where possible blasting be avoided, however blasting is often needed to aid in the excavation of the site to develop the desired footing support elevations. It is typical to have about two (2) to three (3) feet of loose angular clasts of rock, commonly called “shot-rock” below the desired bottom of


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excavation elevations. This material is not suitable for support of structural components and should be removed and replaced with compacted structural fill in areas proposed for support of structural components. If possible, excavations should be constructed to allow for water flow from the excavation the event of precipitation during construction. If this is not possible it may be necessary to remove water from snowmelt or precipitation from the foundation excavations to help reduce the influence of this water on the soil support conditions and the site construction characteristics. 10.2.1 Excavation Cut Slopes We anticipate that some permanent excavation cut slopes may be included in the site development. Temporary cut slopes should not exceed five (5) feet in height and should not be steeper than about one to one (1:1, horizontal to vertical) for most soils. Permanent cut slopes of greater than five (5) feet or steeper than two and one-half to one (2½:1, h:v) must be analyzed on a site specific basis. We did not observe evidence of existing unstable slope areas influencing the site, but due to the steepness and extent of the slopes in the area we suggest that the magnitude of the proposed excavation slopes be minimized and/or supported by retaining structures. 10.3 Utility Considerations Subsurface utility trenches will be constructed as part of the site development. Utility line backfill often becomes a conduit for post construction water migration. If utility line trenches approach the proposed project site from above, water migrating along the utility line and/or backfill may have direct access to the portions of the proposed structure where the utility line penetrations are made through the foundation system. The foundation soils in the vicinity of the utility line penetration may be influenced by the additional subsurface water. There are a few options to help mitigate water migration along utility line backfill. Backfill bulkheads constructed with high clay content soils and/or placement of subsurface drains to promote utility line water discharge through the foundation drain system. Some movement of all structural components is normal and expected. The amount of movement may be greater on sites with problematic soil conditions. Utility line penetrations through any walls or floor slabs should be sleeved so that movement of the walls or slabs does not induce movement or stress in the utility line. Utility connections should be flexible to allow for some movement of the floor slab. 10.4 Exterior Grading and Drainage Comments The ground surface adjacent to the structure should be sloped to promote water flow away from


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the foundation system and flatwork. Snow storage areas should not be located in areas which will allow for snowmelt water access to support soils for the foundation system or flatwork. Water flow from the roof of the structure should be captured and directed away from the structure. If the roof water is collected in an eave gutter system, or similar, the discharge points of the system must be located away from areas where the water will have access to the foundation backfill or any structure support soils. If downspouts are used, provisions should be made to either collect or direct the water away from the structure. The project civil engineering consultant or builder should develop a drainage scheme for the site. We typically suggest a minimum fall of about eight (8) to ten (10) percent away from the structure, in the absence of design criteria from others. Care should be taken to not direct water onto adjacent property or to areas that would negatively influence existing structures or improvements. 10.5 Landscaping Considerations We recommend against construction of landscaping which requires excessive irrigation. Generally landscaping which uses abundant water requires that the landscaping contractor install topsoil which will retain moisture. The topsoil is often placed in flattened areas near the structure to further trap water and reduce water migration from away from the landscaped areas. Unfortunately, almost all aspects of landscape construction and development of lush vegetation are contrary to the establishment of a relatively dry area adjacent to the foundation walls. Excess water from landscaped areas near the structure can migrate to the foundation system or flatwork support soils, which can result in volume changes in these soils. A relatively common concept used to collect and subsequently reduce the amount of excess irrigation water is to glue or attach an impermeable geotextile fabric or heavy mill plastic to the foundation wall and extend it below the topsoil which is used to establish the landscape vegetation. A thin layer of sand can be placed on top of the geotextile material to both protect the geotextile from punctures and to serve as a medium to promote water migration to the collection trench and perforated pipe. The landscape architect or contractor should be contacted for additional information regarding specific construction considerations for this concept which is shown in the sketch below.


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Shallow Landscaping Drain Concept No Scale

Foundation Wall

Approximate limit foundation excavation backfill

Impermeable geotextile material, lapped and glued to the foundation wall above grade

Perforated pipe surrounded by free-draining material

Filter Fabric


39

A free draining aggregate or sand may be placed in the collection trench around the perforated pipe. The perforated pipe should be graded to allow for positive flow of excess irrigation water away from the structure or other area where additional subsurface water is undesired. Preferably the geotextile material should extend at least ten (10) or more feet from the foundation system. Care should be taken to not place exterior flatwork such as sidewalks or driveways on soils that have been tilled and prepared for landscaping. Tilled soils will settle which can cause damage to the overlying flatwork. Tilled soils placed on sloped areas often “creep” down-slope. Any structure or structural component placed on this material will move down-slope with the tilled soil and may become damaged. 10.6 Soil Sulfate Content, Corrosion Issues The requested scope of our services did not include assessment of the chemical constituents of corrosion potential of the site soils. Most soils in southwest Colorado are not typically corrosive to concrete. There has not been a history of damage to concrete due to sulfate corrosion in the area. We are available to perform soluble sulfate content tests to assess the corrosion potential of the soils on concrete if desired. 10.7 Radon Issues The requested scope of service of this report did not include assessment of the site soils for radon production. Many soils and formational materials in western Colorado produce Radon gas. The structure should be appropriately ventilated to reduce the accumulation of Radon gas in the structure. Several Federal Government agencies including the Environmental Protection Agency (EPA) have information and guidelines available for Radon considerations and home construction. If a radon survey of the site soils is desired, please contact us. 11.0 CONSTRUCTION MONITORING AND TESTING Construction monitoring including engineering observations and materials testing during construction is a critical aspect of the geotechnical engineering contribution to any project. Unexpected subsurface conditions are often encountered during construction. The site foundation excavation should be observed by the geotechnical engineer or a representative during the early stages of the site construction to verify that the actual subsurface soil and water conditions were properly characterized as part of field exploration, laboratory testing and engineering analysis. If the subsurface conditions encountered during construction are different than those that were the basis of the geotechnical engineering report then modifications to the design may be implemented prior to placement of fill materials or foundation concrete.


40

Compaction testing of fill material should be performed throughout the project construction so that the engineer and contractor may monitor the quality of the fill placement techniques being used at the site. Generally, we recommend that compaction testing be performed for any fill material that is placed as part of the site development. Compaction tests should be performed on each lift of material placed in areas proposed for support of structural components. In addition to compaction testing we recommend that the grain size distribution, clay content and swell potential be evaluated for any imported materials that are planned for use on the site. Concrete tests should be performed on foundation concrete and flatwork. If asphaltic concrete is placed for driveways or aprons near the structure we are available to provide testing of these materials during placement. We are available to develop a testing program for soil, aggregate materials, concrete and asphaltic concrete for this project. 12.0 CONCLUSIONS AND CONSIDERATIONS We feel that it is feasible to develop this site for the proposed residential use. The information presented in this report is based on our understanding of the proposed construction that was provided to us and on the data obtained from our field and laboratory studies. We recommend that we be contacted during the design and construction phase of this project to aid in the implementation of our recommendations. Please contact us immediately if you have any questions, or if any of the information presented above is not appropriate for the proposed site construction. The recommendations presented above are intended to be used only for this project site and the proposed construction which was provided to us. The recommendations presented above are not suitable for adjacent project sites, or for proposed construction that is different than that outlined for this study. Our recommendations are based on limited field and laboratory sampling and testing. Unexpected subsurface conditions encountered during construction may alter our recommendations. We should be contacted during construction to observe the exposed subsurface soil conditions to provide comments and verification of our recommendations. We are available to review and tailor our recommendations as the project progresses and additional information which may influence our recommendations becomes available.


41

Please contact us if you have any questions, or if we may be of additional service.

Respectfully submitted, TRAUTNER GEOTECH

Jonathan P. Butler, P.E. Staff Geotechnical Engineer

APPENDIX A

Logs of Test Borings

Field Engineer : Jon ButlerHole Diameter : 4" SolidDrilling Method : Continuous Flight AugerSampling Method : Mod. California SamplerDate Drilled : 10/26/17Total Depth (approx.) : 32 feetLocation : See FIgure

LOG OF BORING TB-1

PN:54975GE

Mr. Jesse DiFioreTelluride, Colorado

Lot 51 Aldasaro Ranch Residential Structure

Depthin

feet

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

DESCRIPTION

Sample TypeShelby Tube

Bag Sample

Standard Split Spoon

Water LevelWater Level During Drilling

Water Level on 11/6/17

CLAY, SILT, sandy, organics, medium stiff, slightly moist, light brownCLAY, sandy, few gravels, stiff, moist, brown

FORMATIONAL MATERIAL at five (5) feet, Shale, hard to very hard, fractured, moist, gray, Mancos Shale Formation

Increasing moisture with depth

Bottom of test boring at thirty-two (32) feet

USC

S

CL-ML

CL

FX

GR

APH

IC

Sam

ples

Blow

Cou

nt

6/615/6

50/6

50/5

50/4

Wat

er L

evel Well: TB-1

Bentonite Seal

Gravel Pack

Cap

Screen

CapBottom of Well @21.6'Water level at 22.4 feet on 11/6/17

LOG OF BORING TB-2




Depthin

feet

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

DESCRIPTION

Sample TypeMod. California Sampler

Bag Sample



Water Level After Drilling

CLAY, SILT, sandy, organics, stiff, slightly moist, dark brown

CLAY, sandy, few gravels, stiff, moist, brown

CLAY, sandy, few gravels, few cobbles, very stiff, moist to very moist, brown

FORMATIONAL MATERIAL at eighteen (18) feet, Shale, hard, fractured, moist, dark gray, Mancos Shale Formation

Bottom of test boring at twenty-two (22) feet

USC

S

CL-ML

CL

CL

FX

GR

APH

IC

Sam

ples

Blow

Cou

nt9/6

11/6

8/68/68/6

Wat

er L

evel

REMARKS

Field Engineer : R. BarrettHole Diameter : 4 inch SolidDrilling Method : Continuous Flight AugerSampling Method : Mod. California SamplerDate Drilled : 10/26/2017Total Depth (approx.) : 22 feetLocation : See Figure

Field Engineer : Jon ButlerHole Diameter : 4" SolidDrilling Method : Continuous Flight AugerSampling Method : Mod. California SamplerDate Drilled : 10/26/17Total Depth (approx.) : 23 feetLocation : See FIgure

LOG OF BORING TB-3

PN:54975GE



Depthin

feet

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

DESCRIPTION

Sample TypeShelby Tube

Bag Sample




USC

S

GR

APH

IC

Sam

ples

Blow

Cou

nt17/628/6

9/610/650/6

Wat

er L

evel Well: TB-3

Bentonite Seal

Gravel Pack

Cap

Screen

CapBottom of Well @18.5'

Water level at 8.7 feet

Water level duringdrilling

on 11/6/17

CLAY, SILT, sandy, stiff, slightly moist, light brown

CLAY, sandy, few gravels, stiff, moist, brown

DISTURBED SHALE with sandy clay soil, stiff to very stiff, moist, gray-brown

Wet layer from seven (7) to nine (9) feet

FORMATIONAL MATERIAL at fourteen (14) feet, Shale, very hard, wet to moist, brown-gray, Mancos Shale Formation

Bottom of test boring at twenty-three (23) feet

CL-ML

CL

CL

FX

LOG OF BORING TB-4




Depthin

feet

0

1

2

3

4

5

6

7

8

9

10

11

DESCRIPTION


Bag Sample



Water Level After Drilling

CLAY, SILT, sandy, organics, medium stiff, moist, dark brownCOBBLES, CLAY, sandy, gravels, dense, moist, brown

CLAY, sandy, few gravels, few cobbles, stiff, moist to very moist, brown

Bottom of test boring at nine and one-half (9.5) feet

USC

S

CL-ML

GC

CL

GR

APH

IC

Sam

ples

Blow

Cou

nt

17/6

21/6

7/6

6/6

6/6

Wat

er L

evel

REMARKS

Field Engineer : R. BarrettHole Diameter : 4 inch SolidDrilling Method : Continuous Flight AugerSampling Method : Mod. California SamplerDate Drilled : 10/26/2017Total Depth (approx.) : 9.5 feetLocation : See Figure

Field Engineer : R. BarrettHole Diameter : 4 inch SolidDrilling Method : Continuous Flight AugerSampling Method : Mod. California SamplerDate Drilled : 10/26/2017Total Depth (approx.) : 6.5 feetLocation : See Figure

LOG OF BORING TB-5




Depthin

feet

0

1

2

3

4

5

6

7

8

DESCRIPTION


Bag Sample




CLAY, sandy, gravels, slightly silty, few cobbles, stiff, moist, dark brown

Bottom of test boring at six and one-half (6.5) feet

USC

S

CL

GR

APH

IC

Sam

ples

Blow

Cou

nt

4/6

8/6

Wat

er L

evel

REMARKS

One foot of organics

Water level at 6.2 feet on 11/6/17

Field Engineer : R. BarrettHole Diameter : 4 inch SolidDrilling Method : Continuous Flight AugerSampling Method : Bag SampleDate Drilled : 10/26/2017Total Depth (approx.) : 8.5 feetLocation : See Figure

LOG OF BORING TB-6




Depthin

feet

0

1

2

3

4

5

6

7

8

9

10

DESCRIPTION


Bag Sample



Water Level on After Drilling

COBBLES, GRAVEL, clayey, sandy, dense, moist, dark brown and tan

Bottom of test boring eight and one-half (8.5) feet

USC

S

GC

GR

APH

IC

Sam

ples

Blow

Cou

nt

Wat

er L

evel

REMARKS

Six inches of organics

APPENDIX B

Laboratory Test Result

Tested By: Checked By:

(no specification provided)*

PL= LL= PI=

USCS (D 2487)= AASHTO (M 145)=

D90= D85= D60=D50= D30= D15=D10= Cu= Cc=

Remarks

SC-Clayey Sand

1/2"3/8"#4#8

#10#16#30#40#50#100#200

10098938583777067635649

19 31 12

SC A-6(3)

3.5466 2.2882 0.22080.0807

10-27-17 11-1-17D. Hughes

R. BarrettEngineer Tech.

10-27-17

Jesse DiFioreLot 51 Aldasoro Ranch, Telluride

54975GE

Material Description

Atterberg Limits (ASTM D 4318)

Classification

Coefficients

Date Received: Date Tested:Tested By:

Checked By:Title:

Date Sampled:Location: Test Boring 2Sample Number: C10109-I Depth: 0-7'

Client:Project:

Project No: Figure: 4.1

TEST RESULTSOpening Percent Spec.* Pass?

Size Finer (Percent) (X=Fail)

PE

RC

EN

T FI

NE

R

0

10

20

30

40

50

60

70

80

90

100

GRAIN SIZE - mm.

0.0010.010.1110100

% +3" % Gravel Coarse% Sand

Fine Silt% Fines

Clay0 17 16 18 49

6 in

.

3 in

.

2 in

.

1½ in

.

1 in

.

¾ in

.

½ in

.

3/8

in.

#4 #10

#20

#30

#40

#60

#100

#140

#200

Particle Size Distribution Report

Initial Final6.6 14.1

129.6 129.21.000 0.9861.94 1.94

4.2

3,300

54975GE10/27/2017Date:

Figure:

Project Number:

SWELL - CONSOLIDATION TEST

2,140Measured Swell Pressure (P.S.F):Load Back Swell Pressure (P.S.F):

Moisture Content (%):Dry Density (P.C.F):

Height (in.):Diameter (in.):

SUMMARY OF TEST RESULTS

Soil Description:Sample Source: TB-1@12'

Shale

-2

-1

0

1

2

3

4

5

610 100 1000 10000 100000

Con

solid

atio

n %

Sw

ell

Pressure (Pounds per Square Foot)

Swell/Consolidation due to wetting under constant load

Water added tosample


129.7 129.91.000 0.9931.94 1.94

4.

7,000

54975GE10/27/2017Date:

Figure:

Project Number:


Measured Swell Pressure (P.S.F):Load Back Swell Pressure (P.S.F):





Shale

-2

-1

0

1

2

3

4

5

6

710 100 1000 10000 100000

Con

solid

atio

n %

Sw

ell





120.8 120.11.000 0.9521.94 1.94





Sandy Clay


4,020Measured Swell Pressure (P.S.F):Load Back Swell Pressure (P.S.F):

4.4

4,500

54975GE10/26/2017Date:

Figure:

Project Number:

-6-4-202468

101214

10 100 1000 10000 100000

Con

solid

atio

n %

Sw

ell




Direct Shear Test Results ASTM D3080-90

Project: Lot 51 Aldasoro Ranch Visual Soil Description: Clayey sandProject Number: 54975GE Type of Specimen: RemoldedLaboratory Number: C10109-I Diameter 1.946 in.Date: 10/27/2017 Thickness 2.0 inProject Technician: RB Sample Source: TB-2, 0'-7'

FIGURE 4.5

Summary of Sample Data:Initial Moisture Content (%) 11.9Intial Dry Density (P.C.F) 119Final Moisture Content (%) 15.5Final Dry Density (P.C.F) 118.7

Residual Direct Shear Test Results:Normal Stress (P.S.I) 2.08 4.17 8.34Max. Shear Stress (P.S.I) 2.43 4.56 5.46

ESTIMATED STRENGTH PARAMETERSAngle of Internal Friction, phi 30Cohesion, P.S.F. 200

Figure 4.5

0

2

4

6

8

0 5 10

Shea

r Str

ess,

P.S

.I.

Normal Stress, P.S.I.

0

2

4

6

8

10

12

0.00 0.05 0.10 0.15 0.20

Shea

r Ste

ss, P

.S.I.

Horizontal Deformation, inches

Documents

Lot 51 Aldasoro Ranch