Treece and Lambert, LLC - Portland.gov

October 29, 2014 HGSI Project No. 14-1762 Marty Treece Treece and Lambert, LLC 2905 SW 1st Avenue Portland, Oregon 97201 [email protected] 503-221-0584 Copies: Barry Smith / Travis Sowerby, Barry A. Smith Architecture Darron Hayden, Hayden Consulting Engineers Via e-mail with hard copies mailed on request Subject: GEOTECHNICAL ENGINEERING REPORT

GLISAN STREET APARTMENTS 2238 AND 2248 NE GLISAN STREET PORTLAND, OREGON

Hardman Geotechnical Services Inc. (HGSI) performed a geotechnical engineering study for the proposed new apartment building at 2238 and 2248 NE Glisan Street in the City of Portland, Oregon (see Vicinity Map, Figure 1). The general site layout and locations of subsurface explorations are shown on the attached Site Plan and Exploration Locations, Figure 2. The purpose of the geotechnical study was to explore and evaluate the surface and subsurface conditions at the site, and to provide geotechnical recommendations for foundation design and construction of the currently proposed development.

PROJECT DESCRIPTION

The site is approximately 0.22 acres in size and is located on the south side of NE Glisan Street between NE 22nd and NE 24th Avenues. The site is currently occupied by two existing residential structures with detached garages. Both homes have basements. Vegetation at the site consists of landscape vegetation surrounding the structure. Topography at the site is relatively flat to gently sloping. Preliminary site plans provided by the architect indicate the proposed development will consist of an apartment structure 4 to 5 stories high, stormwater disposal facilities, and associated underground utilities. The proposed ground floor plan is shown on Figure 3. We anticipate maximum cuts and fills will be on the order of a few feet or less. The deepest excavations will be needed for installation of underground utilities and a planned dry well. The dry well is to be located near the southern property boundary, about 5 feet from the new apartment building. At present, specific wall and column locations, and structural loading, are being determined. HGSI should review the structural configurations and loads during the design process, and update the recommendations of this report as necessary based on specific design details.

24560 SW Middleton Road Tel (503) 822-5347 Sherwood, Oregon 97140 Mobile (503) 575-5634

mailto:[email protected]

October 29, 2014 HGSI Project No. 14-1762

SCOPE OF WORK AND AUTHORIZATION

The scope of work for this geotechnical study was presented in Proposal No. 14-995, dated August 21, 2014. Our field exploration program consisted of site reconnaissance, exploratory drilling, geotechnical analyses, and preparation of this report. This scope of services and our General Conditions for Geotechnical Services were authorized by the client prior to the work being performed.

REGIONAL GEOLOGY AND SEISMIC SETTING

The subject site lies within the Portland Basin, a broad structural depression situated between the Coast Range on the west and the Cascade Range on the east. The Portland Basin is a northwest-southwest trending structural basin produced by broad regional downwarping of the area. The Portland Basin is approximately 20 miles wide and 45 miles long and is filled with consolidated and unconsolidated sedimentary rocks of late Miocene, Pliocene and Pleistocene age. The subject site is underlain by the Quaternary age (last 1.6 million years) Willamette Formation, a catastrophic flood deposit associated with repeated glacial outburst flooding of the Willamette Valley, the last of which occurred about 10,000 years ago (Madin, 1990). Underlying the project site, these deposits consist of horizontally layered, micaceous, silt to coarse sand forming distinct beds less than 3 feet thick. Willamette Formation in the vicinity of the subject site is estimated to be approximately 30 feet thick (Madin, 1990). At least three major fault zones capable of generating damaging earthquakes are known to exist in the region. These include the Portland Hills Fault Zone, Gales Creek-Newberg-Mt. Angel Structural Zone, and the Cascadia Subduction Zone. These potential earthquake source zones are included in the determination of seismic design values for structures, as presented in the Seismic Design section.

FIELD EXPLORATION

Subsurface conditions were explored on October 18, 2014 by drilling three exploratory borings (designated B-1 through B-3). Boring depth ranged from 15 to 21.5 feet below ground surface (bgs). Infiltration testing was performed in one of the borings, B-2.

EXPLORATORY BORINGS

Dan Fisher Excavating of Banks, Oregon, performed the borings under subcontract to HGSI. The exploration locations are shown on the attached Site Plan, Figure 2. Boring locations were limited by the presence of existing structures, landscaping and other existing improvements. The explorations were located in the field by pacing or taping distances from property corners and other site features. As such, the locations of the explorations should be considered approximate. At each boring location, SPT (Standard Penetration Test) sampling was performed in general accordance with ASTM D1586 using a 2-inch outside diameter split-spoon sampler and a 140-pound hammer equipped with a mechanically driven air clutch control cathead mechanism. During the test, a sample is obtained by driving the sampler 18 inches into the soil with the hammer free-falling 30 inches. The number of blows for each 6 inches of penetration is recorded. The Standard Penetration Resistance (“N-value”) of the soil is calculated as the number of blows required for the final 12 inches of penetration. If 50 or more blows are recorded within a single 6-inch interval, the test is terminated, and the blow count is recorded as 50 blows for the number of inches driven. This resistance, or N-value, provides a measure of the relative density of granular soils and the relative consistency of cohesive soils.

14-1762 - Glisan Apartments-GR 2 HARDMAN GEOTECHNICAL SERVICES INC.


Explorations were conducted under the full-time observation of HGSI personnel. Soil samples obtained from the borings were classified in the field and representative portions were placed in relatively air-tight plastic bags. These soil samples were then returned to the laboratory for further examination. Pertinent information including soil sample depths, stratigraphy, soil engineering characteristics, and groundwater occurrence was recorded. Soils were classified in general accordance with the Unified Soil Classification System. Summary borehole logs are attached to this report. The stratigraphic contacts shown on the individual borehole logs represent the approximate boundaries between soil types. The actual transitions may be more gradual. The soil and groundwater conditions depicted are only for the specific dates and locations reported, and therefore, are not necessarily representative of other locations and times.

INFILTRATION TESTING

On October 18, 2014, HGSI performed one open-hole falling head infiltration test in boring B-2 (see Figure 2). The infiltration test was conducted in 3-inch diameter holes excavated into the native soil at an approximate depth of 15 feet bgs. The soil encountered at the depth of the infiltration tests consisted of Silty Sand (SM). The test hole was pre-saturated prior to performing the test. During the test, water levels were measured over intervals with approximate head pressures ranging between 20 to 40 inches until three successive measurements showing a consistent infiltration rate was achieved. Table 1 presents a summary of our infiltration test measurement results.

Table 1. Results of Infiltration Testing

Location Depth (feet)

Infiltration Rate (inches/hour) Soil Description

B-2 15 17 Silty SAND (SM)

SUBSURFACE CONDITIONS

The following discussion is a summary of subsurface conditions encountered in our explorations. For more detailed information regarding subsurface conditions at specific exploration locations, refer to the attached boring logs. Also, please note that subsurface conditions can vary between exploration locations, as discussed in the Uncertainty and Limitations section below.

SOIL

Results of the exploration program indicate that the site is underlain by fill and silt and sand belonging to the Willamette Formation. The observed conditions and soil properties are summarized below.

Fill: Borings B-1 and B-3 encountered driveway pavement sections consisting of 3 to 4 inches of concrete over 2 to 6 inches of crushed rock. Other areas of undocumented fill and/or deeper fill deposits may exist on site in areas beyond the explorations. In particular, we anticipate undocumented fill in the backfill zone adjacent to existing structural basements. Willamette Formation: Underlying the fill material in borings B-1and B-3, and beneath a thin topsoil zone in B-2, the explorations generally encountered silt, sandy silt, and silty fine sand belonging to the Willamette Formation. The sand content of the Willamette Formation soils generally increased with depth. In the upper 12 to 13 feet of the profile, soils consisted generally of



medium stiff to stiff silt. Below depths of about 12 to 13 feet, soils consisted generally of medium dense silty fine sand. All three borings were terminated in the Willamette Formation materials, at depths ranging from 15 to 21.5 feet bgs.

GROUNDWATER

At the time of our explorations, groundwater was not encountered beneath the site. Regional geologic mapping (Snyder, 2008) indicates that static groundwater is present at a depth of 100 to 120 feet below the existing ground surface at the site. In our experience, it is not uncommon to encounter thin perched groundwater zones within the Willamette Formation in this area, particularly during the wet season. Typically, such zones are less than 1 foot thick and found directly above or within a silt deposit. The groundwater conditions reported above are for the specific date and locations indicated, and therefore may not necessarily be indicative of other times and/or locations. Furthermore, it is anticipated that groundwater conditions will vary depending on the season, local subsurface conditions, changes in land use and other factors.

CONCLUSIONS AND RECOMMENDATIONS

Results of this study indicate that the proposed development is geotechnically feasible, provided that the recommendations of this report are incorporated into the design and construction phases of the project. Spread foundations are feasible for support of the proposed building. Additional discussion and recommendations are presented below regarding site preparation and basement backfill, old drywell backfill, engineered fill, wet weather construction, spread footing foundations, concrete slabs-on-grade, perimeter footing drains, below-grade walls, seismic design, storm water infiltration systems, temporary excavations, utility trench backfill, and erosion control.

SITE PREPARATION AND BASEMENT BACKFILL

All proposed structure and driveway areas to receive fill should first be cleared of vegetation, pavement, loose debris, and undocumented fill, and all debris from clearing should be removed from the site. The basement portions of the existing structures on site should be backfilled using engineered fill material. Removal of basement walls and the floor slab should be performed in a manner that will not damage the existing structures on the adjacent properties. Basement backfill should consist of crushed rock, recycled concrete or other granular material reviewed by HGSI prior to its use. Excavations for the new structure should be made in a manner that will limit disturbance of the soils. Exposed subgrade soils should be evaluated by HGSI. If soils are disturbed or softened by saturation, it may be necessary to process the upper 12 inches, moisture condition the soils, and compact them in-place prior to placement of the crushed aggregate working surface. Soft/loose soils identified during subgrade preparation should be compacted to a firm and unyielding condition or over-excavated and replaced with engineered fill, as described below. The depth of overexcavation, if required, should be evaluated by HGSI at the time of construction.

OLD DRYWELL BACKFILL

Based on the age of the existing structures on site, it is possible that one or more old dry wells may be present. In the event that old drywell(s) are encountered during site development, the following recommendations are made. Deeper portions of dry wells should be backfilled with controlled density fill (CDF), which is essentially a lean mix concrete consisting of water, sand and cement. We recommend use of “excavatable” CDF so that future excavations can be made through the dry well backfill if any new utilities or other excavations are needed in the affected areas. Above a depth of about 8 feet, at the contractor’s



option, backfill may consist of granular soils such as “reject rock,” recycled concrete or similar material approved by HGSI. The granular backfill should be placed in lifts no thicker than about 18 inches and compacted with a “hoe-pac” excavator attachment to a minimum of 90 percent of Modified Proctor (ASTM D-1557). This backfill specification should also be used for any basements or other depressions that require fill during the demolition process.

ENGINEERED FILL

On-site soils are considered suitable for use as engineered fill in dry weather conditions, provided they are relatively free of organics and are properly moisture conditioned for compaction. Imported fill material must be approved by the geotechnical engineer prior to being imported to the site. Oversize material greater than 6 inches in size should not be used within 3 feet of foundation footings, and material greater than 12 inches in diameter should not be used in engineered fill. Engineered fill should be compacted in horizontal lifts not exceeding 8 inches using standard compaction equipment. We recommend that engineered fill be compacted to at least 90 percent of the maximum dry density determined by ASTM D1557 (Modified Proctor) or equivalent. On-site soils may be wet of optimum; therefore, we anticipate that aeration of native soil will be necessary for compaction operations performed during late spring to early summer. Proper test frequency and earthwork documentation usually requires daily observation and testing during stripping, rough grading, and placement of engineered fill. Field density testing should conform to ASTM D2922 and D3017, or D1556. Engineered fill should be periodically observed and tested by the project geotechnical engineer or his representative. Typically, one density test is performed for at least every 2 vertical feet of fill placed or every 500 yd3, whichever requires more testing. Because testing is performed on an on-call basis, we recommend that the earthwork contractor be held contractually responsible for test scheduling and frequency.

WET WEATHER EARTHWORK

The on-site soils are moisture sensitive and may be difficult to handle or traverse with construction equipment during periods of wet weather. Earthwork is typically most economical when performed under dry weather conditions. Earthwork performed during the wet-weather season will probably require expensive measures such as cement treatment or imported granular material to compact fill to the recommended engineering specifications. If earthwork is to be performed or fill is to be placed in wet weather or under wet conditions when soil moisture content is difficult to control, HGSI should be contacted for additional recommendations. Under wet weather, the construction area will unavoidably become wet and the condition of fill or native soils exposed will degrade. To limit the impacts of wet weather on the finished building pad surface, consideration may be given to placement of a crushed aggregate pad. Where used, we recommend the working pad be constructed using 1½”–0 crushed aggregate, and should have minimum thickness of at least 12 inches. This thickness is considered adequate to support light construction traffic, but will not be sufficient to support heavy traffic such as loaded dump trucks or other heavy rubber-tired equipment.

SPREAD FOOTING FOUNDATIONS

Based on our understanding of the proposed project and the results of our exploration program, it is our opinion that the new structure may be supported on spread footings. We recommend a maximum allowable bearing pressure of 3,000 pounds per square foot (psf) for designing spread footings bearing on undisturbed native soils or engineered fill. The recommended maximum



allowable bearing pressure may be increased by a factor of 1.33 for short term transient conditions such as wind and seismic loading. Assuming construction is accomplished as recommended herein, and for the foundation loads anticipated, we estimate total settlement of spread foundations of less than about 1 inch and differential settlement between two adjacent load-bearing components supported on competent soil of less than about ½ inch. We anticipate that the majority of the estimated settlement will occur during construction, as loads are applied. Wind, earthquakes, and unbalanced earth loads will subject the proposed structure to lateral forces. Lateral forces on a structure will be resisted by a combination of sliding resistance of its base or footing on the underlying soil and passive earth pressure against the buried portions of the structure. For use in design, a coefficient of friction of 0.45 may be assumed along the interface between the base of the footing and subgrade soils. Passive earth pressure for buried portions of structures may be calculated using an equivalent fluid weight of 390 pounds per cubic foot (pcf), assuming footings are cast against dense, natural soils or engineered fill. The recommended coefficient of friction and passive earth pressure values do not include a safety factor. The upper 12 inches of soil should be neglected in passive pressure computations unless it is protected by pavement or slabs on grade. Footing excavations should be trimmed neat and the bottom of the excavation should be carefully prepared. Loose, wet or otherwise softened soil should be removed from the footing excavation prior to placing reinforcing steel bars. HGSI should observe foundation excavations prior to placing crushed rock, to verify that adequate bearing soils have been reached. HGSI should monitor crushed rock placement beneath foundations and perform density tests to verify compliance with the engineered fill density specification.

CONCRETE SLABS-ON-GRADE

Preparation of areas beneath concrete slab-on-grade floors should be performed as recommended in the Site Preparation section. Care should be taken during excavation for foundations and floor slabs, to avoid disturbing subgrade soils. If subgrade soils have been adversely impacted by wet weather or otherwise disturbed, the surficial soils should be scarified to a minimum depth of 8 inches, moisture conditioned to within about 3 percent of optimum moisture content, and compacted to engineered fill specifications. Alternatively, disturbed soils may be removed and the removal zone backfilled with additional crushed rock. For evaluation of the concrete slab-on-grade floors using the beam on elastic foundation method, a modulus of subgrade reaction of 200 kcf (115 pci) should be assumed for the soils anticipated at subgrade depth. This value assumes the concrete slab system is designed and constructed as recommended herein, with a minimum thickness of crushed rock of 8 inches beneath the slab. Interior slab-on-grade floors should be provided with an adequate moisture break. The capillary break material should consist of ODOT open graded aggregate per ODOT Standard Specifications 02630-2. The minimum recommended thickness of capillary break materials on re-compacted soil subgrade is 8 inches. The total thickness of crushed aggregate will be dependent on the subgrade conditions at the time of construction, and should be verified visually by proof-rolling. Under-slab aggregate should be compacted to at least 90% of its maximum dry density as determined by ASTM D1557 or equivalent. In areas where moisture will be detrimental to floor coverings or equipment inside the proposed structure, appropriate vapor barrier and damp-proofing measures should be implemented. A commonly applied vapor barrier system consists of a 10-mil polyethylene vapor barrier placed directly over the capillary break material. With this type of system, an approximately 2-inch thick layer of sand is often placed over the vapor barrier to protect it from damage, to aid in curing of the concrete, and also to help prevent cement from bleeding down into the underlying capillary break materials. Other damp/vapor barrier systems may also be



feasible. Appropriate design professionals should be consulted regarding vapor barrier and damp proofing systems, ventilation, building material selection and mold prevention issues, which are outside HGSI’s area of expertise.

PERIMETER FOOTING DRAINS

Due to the potential for perched surface water above fine grained deposits and engineered fill such as those encountered at the site, we recommend the outside edge of perimeter footings be provided with a drainage system consisting of 4-inch minimum diameter perforated PVC pipe embedded in a minimum of 1 ft3 per lineal foot of clean, free-draining sand and gravel or 1”- ¼” drain rock. The drain pipe and surrounding drain rock should be wrapped in non-woven geotextile (Mirafi 140N, or approved equivalent) to minimize the potential for clogging and/or ground loss due to piping. Water collected from the footing drains should be directed into the local storm drain system or other suitable outlet. A minimum 0.5 percent fall should be maintained throughout the drain and non-perforated pipe outlet. The footing drains should include clean-outs to allow periodic maintenance and inspection. Down spouts and roof drains should collect roof water in a system separate from the footing drains in order to reduce the potential for clogging. Roof drain water should be directed to an appropriate discharge point well away from structural foundations. Grades should be sloped downward and away from buildings to reduce the potential for ponded water near structures.

PERMANENT BELOW-GRADE WALLS

Lateral earth pressures against below-grade retaining walls will depend upon the inclination of any adjacent slopes, type of backfill, degree of wall restraint, method of backfill placement, degree of backfill compaction, drainage provisions, and magnitude and location of any adjacent surcharge loads. At-rest soil pressure is exerted on a retaining wall when it is restrained against rotation. In contrast, active soil pressure will be exerted on a wall if its top is allowed to rotate or yield a distance of roughly 0.001 times its height or greater. If the subject retaining walls will be free to rotate at the top, they should be designed for an active earth pressure equivalent to that generated by a fluid weighing 35 pcf for level backfill against the wall. For restrained wall, an at-reset equivalent fluid pressure of 55 pcf should be used in design, again assuming level backfill against the wall. These values assume that the recommended drainage provisions are incorporated, and hydrostatic pressures are not allowed to develop against the wall. During a seismic event, lateral earth pressures acting on below-grade structural walls will increase by an incremental amount that corresponds to the earthquake loading. Based on the Mononobe-Okabe equation and peak horizontal accelerations appropriate for the site location, seismic loading should be modeled using the active or at-rest earth pressures recommended above, plus an incremental rectangular-shaped seismic load of magnitude 5.5H, where H is the total height of the wall. We assume relatively level ground surface below the base of the walls. As such, we recommend passive earth pressure of 390 pcf for use in design, assuming wall footings are cast against competent native soils or engineered fill. If the ground surface slopes down and away from the base of any of the walls, a lower passive earth pressure should be used and HGSI should be contacted for additional recommendations. A coefficient of friction of 0.5 may be assumed along the interface between the base of the wall footing and subgrade soils. The recommended coefficient of friction and passive earth pressure values do not include a safety factor, and an appropriate safety factor should be included in design. The upper 12 inches of soil should be neglected in passive pressure computations unless it is protected by pavement or slabs on grade.



The above recommendations for lateral earth pressures assume that the backfill behind the subsurface walls will consist of properly compacted structural fill, and no adjacent surcharge loading. If the walls will be subjected to the influence of surcharge loading within a horizontal distance equal to or less than the height of the wall, the walls should be designed for the additional horizontal pressure. For uniform surcharge pressures, a uniformly distributed lateral pressure of 0.3 times the surcharge pressure should be added. Traffic surcharges may be estimated using an additional vertical load of 250 psf (2 feet of additional fill), in accordance with local practice. The recommended equivalent fluid densities assume a free-draining condition behind the walls so that hydrostatic pressures do not build-up. This can be accomplished by placing a minimum 12-inch wide zone of sand and gravel containing less than 5 percent fines against the walls. A 3-inch minimum diameter perforated, plastic drain pipe should be installed at the base of the walls and connected to a suitable discharge point to remove water in this zone of sand and gravel. The drain pipe should be wrapped in filter fabric (Mirafi 140N or other as approved by the geotechnical engineer) to minimize clogging. HGSI should be contacted during construction to verify subgrade strength in wall keyway excavations, to verify that backslope soils are in accordance with our assumptions, and to take density tests on the wall backfill materials.

SEISMIC DESIGN

Structures should be designed to resist earthquake loading in accordance with the methodology described in the 2012 International Building Code (IBC) with applicable 2014 Oregon Structural Specialty Code (OSSC) revisions. We recommend Site Class D be used for design per the OSSC, Table 1613.5.2. Design values determined for the site using the USGS (United States Geological Survey) Earthquake Ground Motion Parameters utility are summarized on Table 3, on the following page.

Table 3. Recommended Earthquake Ground Motion Parameters (2012 IBC / 2014 OSSC)

Parameter Value

Location (Lat, Long), degrees 45.5263, -122.6425 Mapped Spectral Acceleration Values

(MCE, Site Class B): Short Period, Ss 0.974 g 1.0 Sec Period, S1 0.415 g

Soil Factors for Site Class D: Fa 1.110 Fv 1.585 SDs = 2/3 x Fa x Ss 0.721 g SD1 = 2/3 x Fv x S1 0.439 g

Potential seismic impacts also include secondary effects such as soil liquefaction, fault rupture potential, and other hazards as discussed below:

• Soil Liquefaction Potential – Soil liquefaction is a phenomenon wherein saturated soil deposits temporarily lose strength and behave as a liquid in response to earthquake shaking. Soil liquefaction is generally limited to loose, granular soils located below the water table. On-site soils consist of generally medium stiff to stiff silt and dense silty sand. Permanent ground water table lies below the depth of exploration, and, therefore, soils under the project site are not



considered susceptible to liquefaction. It is our opinion that special design or construction measures are not required to mitigate the effects of liquefaction.

• Fault Rupture Potential – Based on our review of available geologic literature, we are not aware of any mapped active (demonstrating movement in the last 10,000 years) faults on the site. During our field investigation, we did not observe any evidence of surface rupture or recent faulting. Therefore, we conclude that the potential for fault rupture on site is low.

• Seismic Induced Landslide – Topography in the vicinity of the subject site is generally flat to gently sloping. The potential for slope instability and seismic induced landslide on site is considered low to very low.

• Effects of Local Geology and Topography – In our opinion, no additional seismic hazard will occur due to local geology or topography. The site is expected to have no greater seismic hazard than surrounding properties and the Portland area in general.

STORMWATER INFILTRATION SYSTEMS

In-situ infiltration tests were conducted to assess the infiltration capacity of the near surface soils on site. Design of stormwater infiltration facilities will be performed by other. The approximate locations of the tests are shown on Figure 2, and the test methodology is discussed above in the Infiltration Testing section, above. Table 1 summarizes results of the infiltration testing. Infiltration test results and observed soil conditions indicate site soils below a depth of about 13 feet exhibit moderate infiltration characteristics. For dry wells extending at least 15 feet below ground surface, we recommend a design infiltration rate of 17 inches/hour (Table 1). The infiltration rate presented herein does not incorporate a factor of safety. For the design infiltration rate, the system designer should incorporate an appropriate factor of safety against slowing of the rate over time due to biological and sediment clogging. We understand one or more dry wells will be located near the building’s southern exterior wall. The manholes should be designed and constructed in a manner which will limit disturbance of surrounding soils, and prevent the loss of soil from the surrounding area into the manhole. We recommend use of geotextile fabric between the manhole and any surrounding drain rock, and the native soils. Any annular space between the manhole and surrounding soil should be backfilled tightly with compacted crushed rock or drain rock. Dry wells should be located at least 3 feet from any structural foundations. The potential for soil saturation has been accounted for in development of the allowable soil bearing pressures used in design. Therefore, soil saturation from dry well operation is not anticipated to cause significant adverse impacts on foundation support. Infiltration test methods and procedures attempt to simulate the as-built conditions of the planned disposal system. However, due to natural variations in soil properties, actual infiltration rates may vary from the measured and/or recommended design rates. All systems should be constructed such that potential overflow is discharged in a controlled manner away from structures, and all systems should include an adequate factor of safety. Infiltration rates presented in this report should not be applied to inappropriate or complex hydrological models such as a closed basin without extensive further studies. This report presents infiltration test results only, and should not be construed as an approval of a system design. Evaluation of environmental implications of storm water disposal at this site is beyond the scope of this study.

TEMPORARY EXCAVATIONS

We anticipate that on-site soils can be excavated using conventional heavy equipment such as trackhoes. Maintenance of safe working conditions, including temporary excavation stability, is the responsibility of the



contractor. Actual slope inclinations at the time of construction should be determined based on safety requirements and actual soil and groundwater conditions. All temporary cuts in excess of 4 feet in height should be sloped in accordance with U.S. Occupational Safety and Heath Administration (OSHA) regulations (29 CFR Part 1926), or be shored. The existing native soils classify as Type B Soil and temporary excavation side slope inclinations as steep as 1H:1V may be assumed for planning purposes. This cut slope inclination is applicable to excavations above the water table only. Flatter temporary excavation slopes will be needed if groundwater is present, or if significant thicknesses of sandy soils are present in excavation sidewalls. Vibrations created by traffic and construction equipment may cause some caving and raveling of excavation walls. In such an event, lateral support for the excavation walls should be provided by the contractor to prevent loss of ground support and possible distress to existing or previously constructed structural improvements.

UTILITY TRENCH BACKFILL

Utility trench backfill should consist of ¾”-0 crushed rock, compacted to at least 90% of the maximum dry density obtained by Modified Proctor (ASTM D1557) or equivalent. Initial backfill lift thick nesses for a ¾”-0 crushed aggregate base may need to be as great as 4 feet to reduce the risk of flattening underlying flexible pipe. Subsequent lift thickness should not exceed 1 foot. If imported granular fill material is used, then the lifts for large vibrating plate-compaction equipment (e.g. hoe compactor attachments) may be up to 2 feet, provided that proper compaction is being achieved and each lift is tested. Use of large vibrating compaction equipment should be carefully monitored near existing structures and improvements due to the potential for vibration-induced damage. Adequate density testing should be performed during construction to verify that the recommended relative compaction is achieved. Typically, one density test is taken for every 4 vertical feet of backfill on each 200-lineal-foot section of trench.

EROSION CONTROL CONSIDERATIONS

During our field exploration program, we did not observe soil types that would be considered highly susceptible to erosion. Erosion at the site during construction can be minimized by implementing the project erosion control plan, which should include judicious use of bio-bags, silt fences, or other appropriate technology. Straw bales are not allowed in the City of Portland for temporary erosion control. Where used, erosion control devices should be in place and remain in place throughout site preparation and construction. Areas of exposed soil requiring immediate and/or temporary protection against exposure should be covered with either mulch or erosion control netting/blankets.

UNCERTAINTIES AND LIMITATIONS

We have prepared this report for the owner and his/her consultants for use in design of this project only. This report should be provided in its entirety to prospective contractors for bidding and estimating purposes; however, the conclusions and interpretations presented in this report should not be construed as a warranty of the subsurface conditions. Experience has shown that soil and groundwater conditions can vary significantly over small distances. Inconsistent conditions can occur between explorations that may not be detected by a geotechnical study. If, during future site operations, subsurface conditions are encountered which vary appreciably from those described herein, HGSI should be notified for review of the recommendations of this report, and revision of such if necessary. Sufficient geotechnical monitoring, testing and consultation should be provided during construction to confirm that the conditions encountered are consistent with those indicated by explorations.


October 29,2014

HGSI Project No. 14-17 62

Recommendations for design changes will be provided should conditions revealed during construction differfrom those anticipated, and to verify that the geotechnical aspects of construction comply with the contractplans and specifications.

Within the limitations of scope, schedule and budget, HGSI executed these services in accordance withgenerally accepted professional principles and practices in the freld of geotechnical engineering at the timethe report was prepared. No warranty, expressed or implied, is made. The scope of our work did not includeenvironmental assessments or evaluations regarding the presence or absence of wetlands or hazardous ortoxic substances in the soil, surface water. or sroundwater at this site.

OoO

We appreciate this opportunity to be of service.

Sincerely,

IIInonraN GnorncrrucAr, SERVICES INc.

EXPIRES: 06-30-20

Scott L. Hardman, P.E., G.E.Principal Geotechnical Engineer

Attachments: ReferencesFigure 1-VicinityMapFigure 2 - Site and Exploration PlanFigure 3 - Proposed Ground Floor PlanLogs of Borings B-1, B-2 and B-3

* {. t {. * * * * {. .i. * * *.t .f. * * r * * * r t * ... ....i. * t {. {. * * t t * t .i..i. .i. t * * * * * .1. €.

REFERENCES

Beeson, M.H., Tolan,T.L., and Madin, LP., 1991, Geologic map of the Portland Quadrangle, Multnomah, andWashington Counties, Oregon: Oregon Department of Geology and Mineral Industries Geological MapSeries GMS-75, scale l:24,000.

Madin, I.P., 1990, Earthquake hazard geology maps of the Portland metropolitan area, Oregon: OregonDepartment of Geology and Mineral Industries Open-File Report 0-90-2, scale 1:24,000,22p.

Snyder, D.T., 2008, Estimated Depth to Ground Water and Configuration of the Water Table in the Portland,Oregon Area: U.S. Geological Survey Scientific Investigations Report 2008-5059, 4l p.,3 plates.

11| 4 -I7 62 - Glisan Aoartrnents-GR HARDMAN GEOTECHNICAL SERVICES INC.

Base Map: USGS Portland, Oregon Quad, from US Topo, 2014

VICINITY MAP

Project No. 14-1762Glisan Street ApartmentsPortland, Oregon FIGURE 1Project:

Legend Approx. Scale: 1 inch = 2000 feet

Approximate Site Location

SITE ANDEXPLORATION PLAN


LegendBoring Designation and Approximate Location

B-3

B-3

PROPOSED GROUNDFLOOR PLAN


LegendBoring Designation and Approximate Location

B-1

B-2

B-3

B-3

Material Description

Dep

th(ft

)

Sam

ple

Inte

rval

In-S

ituD

ryD

ensi

ty(lb

/ft3 )

Moi

stur

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nt(%

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Gro

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BORING LOG

Boring No. B-

LEGEND

Water Level atTime of Drilling

5

10

Project No. 14-1762Glisan Street ApartmentsPortland, Oregon

Date Excavated: 10/18/14

Logged By: SLH

Surface Elevation:

Project:

SP

TN

-Val

ue(B

low

s/fo

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SPT DriveSample

24560 SW Middleton Road, Sherwood, OR 97140(503) 822-5347

3-inch Diam.Split Barrel

Sample

Shelby TubePush Sample

15

20

25

30

35

Minor seepage at 10 feet

Boring terminated at 21.5 feetNo groundwater or seepage encountered

4-inch thick concrete slab over 6 inches of crushed rock

Medium stiff, brown mottled with red brown, SILT with clay (MH), moist.

Medium stiff, light brown, SILT with fine sand (ML), slightly micaceous, moist.

5

8

7

9

14

18

Gradational contact

Medium dense, brown to light brown, silty fine SAND (SM), slightly micaceous,moist.

1


Dep

th(ft

)

Sam

ple

Inte

rval

In-S

ituD

ryD

ensi

ty(lb

/ft3 )

Moi

stur

eC

onte

nt(%

)

Gro

undw

ater

BORING LOG

Boring No. B-

LEGEND


5

10



Logged By: SLH

Surface Elevation:

Project:

SP

TN

-Val

ue(B

low

s/fo

ot)

SPT DriveSample



Sample


15

20

25

30

35

3.0

1.0

2

Medium stiff, brown organic Silt (OL), some roots, slightly moist (Topsoil)

Infiltration test performed at 15 feet

Boring terminated at 15 feetNo groundwater or seepage encountered

Stiff, brown mottled with red brown, SILT with clay (MH), dry to slightly moist.


12

13

9

9

Gradational contactMedium dense, brown to light brown, silty fine SAND (SM), slightly micaceous,moist.


Dep

th(ft

)

Sam

ple

Inte

rval

In-S

ituD

ryD

ensi

ty(lb

/ft3 )

Moi

stur

eC

onte

nt(%

)

Gro

undw

ater

BORING LOG

Boring No. B-

LEGEND


5

10



Logged By: SLH

Surface Elevation:

Project:

SP

TN

-Val

ue(B

low

s/fo

ot)

SPT DriveSample



Sample


15

20

25

30

35

>4.5

3

Boring terminated at 21.5 feetNo groundwater or seepage encountered

3-inch thick concrete slab over 2 inches of crushed rock

Medium stiff, brown mottled with red brown, SILT with clay (MH), moist.


7

7

6

7

10

10

Gradational contact

Medium dense, brown to light brown, silty fine SAND (SM), slightly micaceous,moist.

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Treece and Lambert, LLC - Portland.gov