700 Miscellaneous Civil

AbstractSection 700 covers: site clearing and grading requirements; excavation and backfill for foundations, trenches, roads, and other earthwork; pavement selection and design (asphalt and concrete); selection and specification of chain link fencing; and required clearances around railroad tracks in Company facilities.

This section includes a variety of civil engineering tasks commonly encountered throughout the Company. Some of these tasks require the approval of a registered specialist. In these cases, the intent of this section is to provide Company personnel with sufficient information to: (a) develop preliminary designs and (b) communi-cate effectively with contractors.

This section is written for entry-level engineers or experienced engineers working outside their discipline or area of expertise.

Contents Page

710 Soils and Earthwork Principles 700-3711 Soils Report

712 Hazardous Materials

713 Soils Background Information

714 Soil Compaction Principles

715 Fill Materials720 Grading Design and Layout 700-9721 Rough Grading Plan

722 Finished Grading, Paving and Drainage Plans

723 Recommended Slopes

724 Recommended Road Grades

725 Balance of Cut and Fill726 Slope StabilizationChevron Corporation 700-1 December 1993

730 Earthwork Equipment and Construction Methods 700-12731 Equipment

700 Miscellaneous Civil Civil and Structural Manual732 Clearing, Dewatering and Surcharging

733 Soil Placement and Compaction

734 Excavation and Backfill (Foundations and Trenches)735 Mudwaves740 Roads and Paving 700-20741 General Considerations and Layout of Pavements

742 Paving Selection

743 Asphalt Paving

744 Concrete Paving

745 Paving Repairs746 Alternative Surface Treatments for Foot or Vehicle Traffic Areas747 Alternative Surface Treatments for Non-Traffic Areas

750 Chain Link Fencing 700-48751 Fencing Components752 Materials753 Fencing Installation760 Railroad Clearances 700-53770 Model Specifications, Standard Drawings, and Engineering Forms 700-57771 Model Specifications

773 Engineering Forms

753 Fencing Installation780 References 700-58December 1993 700-2 Chevron Corporation

Civil and Structural Manual 700 Miscellaneous Civil710 Soils and Earthwork PrinciplesThis section provides an overview of grading and earthwork fundamentals, termi-nology, references, and guidelines for design and layouts.

711 Soils ReportA soils report is a fundamental component of many civil projects. Many of the early design decisions will be shaped by the information in this report. Issues addressed in a soils report include:

Site topography

Classification of on-site soils

Identification of surface or subsurface rock or other materials difficult to excavate

Identification of weak soils that must be either excavated and removed, or improved to stabilize or strengthen

Water table level

Identified sources of borrow material for engineered backfill

Specific site recommendations for:

Cut and fill procedures Compaction procedures Soil stabilization programs Road and paving Subgrade Base/subbase Paving thicknesses

Section 200 explains how to obtain a soils report.

712 Hazardous MaterialsIt is becoming increasingly important to determine if the soils at a site have become contaminated with hazardous wastes. This potential problem must be investigated whenever the site was previously occupied by, or in close proximity to industrial facilities. It will be necessary to work closely with the Companys environmental specialists to determine the hazard, reporting requirements, handling, and disposal procedures. Verification that hazardous materials are present will almost certainly result in a significant impact on project costs, schedule, and permits. Protective clothing and equipment may be required to handle the material.Chevron Corporation 700-3 December 1993

700 Miscellaneous Civil Civil and Structural Manual713 Soils Background InformationThis section defines some of the standard terminology used in soils engineering, and discusses soil classification and compaction.

Soils TerminologyThe primary soils terminology used when discussing earth moving activities includes:

Consolidation: Increasing the density of soil. Consolidation of soils occurs as the loading pressure is increased with the addition of overlying materials or the applica-tion of external loads. The voids in the soil decrease and the soil particles are forced closer together. In a saturated soil, discharge of water must occur to have consolida-tion.

Density: Density is the weight of a given soil quantity divided by the measured volume, expressed in lb/ft3.

Dry Density: Same as density excluding the weight of any water or moisture in the soil (lb/ft3).Moisture Content: Expressed as Percent Moisture Content.

Permeability: The ability of soil to discharge water vertically or laterally. This property depends on soil density, particle size, and degree of saturation. Coarse-grained soils have high permeability. Silts and clays have low permeability.

Plasticity: The ability of soils to deform without cracking or crumbling. Plastic soils can be rolled between the fingers to form a long thin, flexible thread.

Porosity: Porosity is the ratio of voids to the total volume of the soil aggregate. Frequently expressed as a percentage, and referred to as percentage of voids.

Soils Classification: The common classification is made by size of individual soil particles. Major divisions are, by decreasing grain size: gravels, sand, silts and clays.

Grain-size DistributionTo classify soils, a mechanical analysis (Particle-Size Analysis of Soils, ASTM D 422) is made using sieves to determine the size of the grains which make up the soil and the percentage of the total weight represented by the various grain sizes. This distribution is normally represented on a semi-logarithmic plot as shown in Figure 700-1 below. The finest mesh sieve used is 0.07 mm (200 sieve) so that anal-ysis is normally limited to grain sizes larger than this size. Other techniques are used to further classify the silt and clay particles which pass through the 200 sieve.

Percent Moisture Content =weight of wet soil weight of dry soil

weight of dry soil------------------------------------------------------------------------------------------- 100December 1993 700-4 Chevron Corporation

Civil and Structural Manual 700 Miscellaneous CivilSoil ClassificationThe significant properties associated with the major classifications are:Gravel and Sand. Gravel and sand have essentially the same engineering proper-ties, differing mainly in degree. These soils are easy to compact, little affected by moisture, not subject to frost action, and are highly permeable. Stability of these materials will depend on how uniformly they are graded in size. If all grains tend to be approximately the same size (a near vertical line on the grain size plot) the soil will be more permeable, and less stable when not confined. Such soils are referred to as being poorly graded. Soils that have a less vertical line on the grain-size plot are called well-graded and are less permeable and more stable.

Silt. Silt is inherently unstable, particularly when the moisture content increases. Silty soils are difficult to compact, susceptible to frost heave, have low perme-ability, and erode readily. Silts exhibit little or no plasticity.

Clay. Clay is frequently identified as having a grain size less than 0.005 mm. It may possess considerable strength when air-dried, and can be made plastic by increasing water content. It exhibits shrinking and cracking when it dries and expansion when moisture is restored. The bearing capacity is extremely variable depending on the moisture content. Clay has low permeability which can make it difficult to compact, and consolidation under loads may take months or years.

Natural soil deposits can be a mixture of the major classifications. For more details on soil classification refer to a soils text book.

Fig. 700-1 Grain-size DistributionChevron Corporation 700-5 December 1993

700 Miscellaneous Civil Civil and Structural Manual714 Soil Compaction PrinciplesTo achieve a high degree of soil compaction, it is necessary to understand the mois-ture and density relationship for the soils under review. This is particularly true for cohesive soils, rather than sands or gravel.

A series of density-moisture tests are conducted on the soil(s) encountered at a construction site: both the natural on-site soils and any planned imported fill. The testing procedure the Company generally specifies is the Modified Proctor Test (ASTM D 1557, AASHTO T-180), as it is considered appropriate for the earthwork equipment in modern use. This testing is done under controlled laboratory condi-tions and results cannot be duplicated in the field.

A typical plot of the laboratory test results is given in Figure 700-2. The compac-tion curve will normally exhibit an increase in dry density as the water content increases up to a peak, after which density decreases with additional water content. Optimum moisture may run from 8% to 15% for sandy clays, 15% to 25% for silty clays, and 20% to 30% for clays.

Most specifications are written to require a field compaction from 90 to 95% of the maximum dry density. For areas designed to support future loads, it is desirable to specify the higher density. In areas where some settlement can be accepted, a lesser compaction requirement may reduce the cost of construction.

Moisture ControlFor soils with moderate to very cohesive properties, the success of a compaction program is totally dependent on control of the moisture content. Such a program requires a combination of activities to achieve the desired moisture, including spreading and reworking the soil if too moist and spraying with water if too dry. Ordinarily, specify that compaction be done with a moisture content within 2 to 3% of the optimum content, to achieve a high degree of compaction without extraordi-nary or costly effort.

Fig. 700-2 Moisture/Density CurveDecember 1993 700-6 Chevron Corporation

Civil and Structural Manual 700 Miscellaneous CivilCohesionless soils may not require strict moisture control to achieve design compaction. These soils are not frequently encountered.

A program of field measurements for moisture content and density must be main-tained during earth moving activities. There are standard ASTM and AASHTO procedures that cover field measurements. The use of a third-party inspection orga-nization is recommended.

Field Soil Density TestsFour test methods listed below can determine the in-place density of soils.

The last three methods are time consuming, and are being phased out in favor of the nuclear density moisture gage. These older methods all follow the same basic proce-dure:

1. Remove a soil sample.

2. Determine a nearly exact volume of the hole (the inplace volume of the sample).

3. Weigh the soil sample.

4. Calculate the soil density.

The nuclear density moisture gage operates by emitting either neutrons or gamma rays into the soil. The number of gamma rays absorbed by soil particles is indi-rectly proportional to the soil density. The number of neutrons reflected back to the detector is directly proportional to soil moisture content. With this gage, a trained operator can take many readings in a relatively short time. Calibration of the nuclear density moisture gage is done by comparing measurements using one of the other methods. For a detailed discussion of nuclear density test methods, refer to ASTM D2922 and D3017.

+ Caution For soils with large-size gravel or rock, the nuclear density moisture gage may yield erroneous results.

715 Fill MaterialsSpecifications for backfill material usually aim at getting well-graded materials. This means there is a smooth gradation of grain sizes from coarse to fine, but with a limitation on the percent of material passing the No. 200 sieve from about 5% to 12%. Such material is considered relatively stable, can be readily compacted to a high density, and can develop high shear resistance and bearing capacity.

Nuclear density moisture gage ASTM D2922 and D3017 Sand cone method ASTM D1556 Balloon method ASTM D2167 Drive cylinder method ASTM D2937Chevron Corporation 700-7 December 1993

700 Miscellaneous Civil Civil and Structural ManualOne measure of whether a soil has acceptable gradation is called the Uniformity Coefficient. This coefficient is frequently included in specifications for fill mate-rials, and is derived from a plot of the mechanical analysis for the material as shown in Figure 700-3.

Grain Size (mm)

(Eq. 700-1)where:

D60= Grain size that is coarser than 60% of the soil.

D10= Grain size that is coarser than 10% of the soil.

For the example shown in Figure 700-3,

Fig. 700-3 Uniformity Coefficient

Uniformity Coefficient D60D10----------=

D60D10----------

1 mm0.14 mm--------------------- 7.1= =December 1993 700-8 Chevron Corporation

Civil and Structural Manual 700 Miscellaneous CivilTypical coefficient values for various materials are given below. Soils with a unifor-mity coefficient over 6 and with little or no plasticity can generally be satisfactorily placed and compacted.

720 Grading Design and LayoutThe development of grading plans requires the following information:

Topographic map to show existing site contours and drawings

General plot plan to show the proposed location for facilities and roads

Completion of sufficient field soil investigation to determine the presence of either very hard (rock) or exceedingly soft materials

Conceptual plans for treating and disposal of storm water runoff

As the work progresses on the layout of the rough grading plan, maintain good communication with those responsible for plot plan development. This will enable you to exchange current information on changes, and to identify problem areas that could impact other designs.

General design considerations given in Section 521, Drainage, also apply here.

721 Rough Grading PlanRough grading and finished grading plans may be combined, but are usually devel-oped as separate plans to accommodate different contracts, and for the sake of clarity. Elevations shown for rough grading are usually to the closest 1/10 foot.

Items included on the rough grading plans are:

Limits of site clearing

GradingGeneral area grading, sub-grades for roads, and rough grading of tank field including impounding basins and berms. May include earthen tank foundation pads

DrainageGeneral grading to develop ditches and canals. Requirements for culverts. At the conclusion of rough grading all areas where there will be subse-quent work activity should be relatively well-drained.

ObstructionsUnderground obstructions which the contractor must avoid, such as conduit banks and underground lines. Overhead lines or other above ground obstructions to contractors work must also be noted.

Poorly-graded materials 1 to 2Well-graded materials 5 to 10Silty sand and gravel 15 to 300Chevron Corporation 700-9 December 1993

700 Miscellaneous Civil Civil and Structural Manual722 Finished Grading, Paving and Drainage PlansFinished grading drawings include the following information. Elevations for finished grading, paving and drainage are frequently shown on drawings to the closest 1/100 foot.

Scope of work to dress up the rough grading work and other areas torn up by other construction activities

Invert elevations for ditches and final design elevations for other areas. Require-ments for embankments, ditch slopes and tank berms. Required surface treat-ment for slope protection

Plans and details for underground drainage and sanitary systems

Plans for concrete and asphaltic concrete for paved areas with high points of paving and slope requirements. Crushed rock or other specified material for unpaved areas

723 Recommended SlopesThe maximum acceptable slope for cut sections or embankments will vary with the type of soil materials, ground loading above the slope, climatic conditions, mois-ture, and intended slope stabilization, if proposed. For noncohesive soils, slope stability depends on factors other than the height of the slope, whereas for cohesive soils the greater the height of the slope, the smaller the slope angle must be. For any major embankments, or locations where stability is critical, a slope stability study should be made. Steeper slopes will be subject to a greater amount of erosion because of water runoff.

Because of the variety of conditions affecting the design, no hard-and-fast rules can be laid down for acceptable slopes. Figure 700-4, based on railroad and highway practices, gives some general guidelines.

The range of slopes, listed in Figure 700-4, is considered acceptable for embank-ments in cohesionless soils up to 20 feet, and for cohesive soils up to 15 feet. For higher slopes, unusual ground water or soil conditions, and for critical slopes, a detailed slope stability analysis is recommended.

Fig. 700-4 Stable Cut and Fill Slopes

Soil Cut Fill

Sand 1-1/2:1 to 2:1 1-1/2:1 to 4:1

Gravel 1-1/2:1 1-1/2:1

Cohesive soils, damp, plastic (up to 15 ft. high)

1-1/2:1 to 3:1 2:1 to 4:1

Sand and/or gravel with cohesive binder

1-1/3:1 1-1/2:1December 1993 700-10 Chevron Corporation

Civil and Structural Manual 700 Miscellaneous CivilObservations of nearby slopes in similar soils, natural slopes in the vicinity, or trial cut excavations can be valuable guides for slope design.

724 Recommended Road GradesThe following grades are recommended for heavily traveled roads that are intended for unrestricted use by all vehicle types:

3% Preferred maximum 5 - 6% Maximum desirable 5% Maximum grade for areas with ice and snow

Steeper grades may be used for roads with limited traffic requirements (number and vehicle size).In the layout of road grades, special attention must be paid to road clearances at vertical sag and summit curves. The critical vehicle dimensions that govern design are:

Distance between axles Vehicle clearances Projections beyond front and rear axles.Special purpose vehicles, such as fire protection equipment, may govern the minimum radii for vertical curves.

725 Balance of Cut and FillIn the development of a grading plan, it is desirable to minimize the quantity of earthwork. Where only on-site materials are proposed for use in grading, it is neces-sary to calculate cut and fill volumes and try to achieve a reasonable balance. The two methods commonly used for volume calculation are: vertical cross sections and contour maps.

Vertical Cross-sectionsEarthwork volumes are calculated from plotted cross-sections using average end areas between successive cross-sections.

Contour MapsBy this method, volumes are calculated by measuring the area of upper and lower horizontal surfaces that bound increments of cut or fill. Horizontal projected areas are determined using contour lines and a planimeter. The volume of cut or fill between any two successive areas is calculated by multiplying the average of the two areas by the depth between them.

Errors in determining volumes using these two methods depend on the accuracy and frequency of cross sections, on the scale of the drawing, the contour interval, and the precision with which contours are drawn and areas measured.

In the calculation of cut and fill volumes, it is necessary to account for the shrinkage factor. This factor is the ratio of compacted cubic yards to excavated cubic yards. Since soils are frequently compacted to a density greater than their Chevron Corporation 700-11 December 1993

700 Miscellaneous Civil Civil and Structural Manualoriginal state, a greater volume of material must be excavated than the measured volume of fill.

Exceptions to Balanced Cut and FillFrequently there are conditions that preclude a balanced earthwork program, such as undesirable material on the site that cannot be used and must be replaced by imported fill; or for consideration of drainage or elevation with respect to adjacent facilities, the desired nominal grade must be higher (or lower) than balanced earth-work dictates. This will necessitate hauling of material to or away from the site.

726 Slope StabilizationStabilization of cut or fill slopes is frequently required. The forces and factors that contribute to slope failures are:

Weight of earth in the slope Weight of surcharge, structures, or traffic above the slope Vibrations from earthquakes and traffic Weight of water within the slope Hydrostatic water pressure Erosion undercutting the toe of the slope Slope surface erosion

Actions that can be taken to alleviate these problems include:

Flattening the slopes Improving slope drainage by installing internal drains Diverting surface water flows Stabilizing the face of slope with shotcrete, asphalt, coarser materials or vegeta-

tion (See Section 747) Stabilizing with geotextile materials (See Section 742) Providing benches in the slope

730 Earthwork Equipment and Construction Methods

731 EquipmentThe type of equipment required for a particular job depends on such factors as: Nature of material Quantity of material Length of haul Size and terrain of work sites

The type of equipment typically used for various earthmoving operations are discussed below.December 1993 700-12 Chevron Corporation

Civil and Structural Manual 700 Miscellaneous CivilExcavation Crawler or rubber tired tractors with bulldozer bladesUsed for ripping,

scraping and stockpiling

Wheel Tractor-ScrapersGenerally self-propelled but may be towed scrapers. Most efficient piece of earthmoving equipment, as individual unit can exca-vate, transport and spread fill. Capacities range from approximately 20 CY to over 50 CY.

LoadersTractor or rubber-tired

Power shovelsUsed for excavations from embankments

Draglines/ClamshellsUsed for areas too soft for access with other equip-ment. Clamshells may be used for deep excavations; for example, ones that require sheet pile shoring.

BackhoeWidely used for foundations, trenching, and ditch construction. Highly mobile, can work in confined areas. Reasonably good control over dimensions of excavation.

Trenching There are two basic types of trenchers: wheel type and ladder trencher. The

wheel trencher has digging buckets on the circumference of a rotating wheel. It is used mainly for shallow trenching. The ladder-type trencher has buckets attached to a rotating chain mechanism, and can be used for deeper trenching than the wheel type. Trenchers are best suited for soil that can be easily exca-vated. The required width of trench excavated by a trencher is generally signifi-cantly less than when excavation is performed with other equipment.

Earthmoving Wheel Tractor-Scrapersmost economical when earthmoving is confined to a

single site. Not allowed to operate on public roads

Off-Highway Truck or Dump Truckrequired for longer haul distances

On-Highway Trucksused for import or export of material using public roads

Spreading Wheel Tractor-ScrapersRubber tires provide some initial compaction Tractors with dozer blades

Compaction Sheepsfoot rollerHigh-speed production for cohesive material, from moder-

ately cohesive to clay

Grid or mesh rollersUsed to break down oversized particles of non-sticky material

VibratoryUsed for granular materialsChevron Corporation 700-13 December 1993

700 Miscellaneous Civil Civil and Structural Manual Multi-tired pneumaticUsed for a range of soils from granular to moderately cohesive

Tamping compactorCan be used for a range of soils from coarse grained to fine grained. The large units, towed or self-propelled, usually have low produc-tion rates. Hand operated units are extensively used for compacting backfill around foundations.

Final Grading Motor graders with 12- to 14-foot blade

Moisture and Dust Control Water truck with sprayer attachment

Earthmoving Production RatesProduction rates for earthmoving are subject to many variables: Type of equipment Length of haul Type of material, firmness, particle size Unfavorable grades Rolling resistance (type of ground surface) Traction Percent of swell for the soil Provision for push loading Job efficiency Size of jobA good source of information on earthmoving production rates may be found in References 2 and 3. Rule-of-thumb quantities are given for various sizes of equip-ment, types of soil, and other site variables. Current unit prices for various opera-tions are also available.

Order-of-magnitude earthmoving production rates for various operations are given below. In each case the rates are based on average undisturbed soil. Adjustments would have to be made for hard and difficult soils or unusual conditions.

Dozer ExcavationMass excavation and pushing soil 150 feet to stockpile.

Scraper ExcavationMass excavation and transport of soil.

25 CY self-propelled scraper

D-6 dozer 50 CY/hrD-9 dozer 200 CY/hr

1000-foot haul 9 cycles/hr 225 CY/hr4000-foot haul 4.5 cycles/hr 113 CY/hrDecember 1993 700-14 Chevron Corporation

Civil and Structural Manual 700 Miscellaneous CivilBackhoe Excavation

Grading with Motor Grader

Caution should be used in using any published rates. A total spread must be consid-ered to determine impact on production rates for any one piece of equipment.

732 Clearing, Dewatering and Surcharging

ClearingProposed construction sites often are occupied by other, previously built industrial facilities. Assuming that all above-ground equipment has been removed, site clearing will probably consist of removing old foundations and below grade piping and conduit banks. If foundations were pile-supported it may be necessary to exca-vate down about 5 feet and cut off existing piles to avoid interference with proposed new construction.

Try to locate all existing lines and electrical conduit prior to starting field work. You must verify that lines and conduit are out-of-service before dismantling. Piles that are cut off should be surveyed to aid in new pile location and installation.

For a grass roots site development, a program to first clear all organic materials must be undertaken. Small stumps, roots, and other vegetation should be removed to a depth of 6 to 12 inches below the natural grade. Larger stumps should be removed entirely. The presence of organic matter in soils is not desirable from an engineering standpoint because organic matter usually has low bearing capacity, can draw moisture, can reduce soil stability and, if it decays, will create voids.

The common approach for clearing and grubbing a site is to use a tractor with a bulldozer blade to scrape away the undesirable material. Old vegetation may be hauled to an acceptable offsite dump, or, where local regulations permit, it is pushed into piles, allowed to dry, and burned on-site.

DewateringThere are three situations where dewatering (lowering the water table) may be required or desirable:

To keep construction excavation dry To improve soil strength To reduce lateral pressure

Keep Construction Excavation Dry. Dewatering is required for foundation or other construction excavations where the bottom of the excavation is at or below the water table. For typical foundation work, a hole dug in one corner of the excavation will generally be adequate to permit water removal. For other situations a tempo-

1-1/2 CY Backhoe 77 CY/hr

Rough Grading 0.7 acre/hrFine Grading 0.4 acre/hrChevron Corporation 700-15 December 1993

700 Miscellaneous Civil Civil and Structural Manualrary lowering of the water table 2 to 5 feet below the excavation may be required. This can generally be accomplished with well points and pumps. The techniques used for a particular installation will be influenced by many factors but will prima-rily depend on the soils being dewatered. Since water table draw down may occur over a fairly large area, care must be taken to avoid damage to adjacent existing structures.

The choice of pumps used for dewatering will depend on the height of lift and flow volumes. Types of pumps used for this service are:

Vacuum Centrifugal Submersible Jet-eductor

Figure 700-5 provides a schematic of the dewatering procedure.

Improve Soil Strength. Dewatering can be used to increase the strength and reduce future settlement of subsurface soils, particularly for highly compressible silts or clay-type materials. To achieve these conditions, a permanent lowering of the water table is required. This involves diversion of surface water by ditching, and drainage of subsurface soils to provide gravity flow of ground water away from the area. For every foot the water table is lowered, the soils below are subjected to an increased effective pressure equivalent to the weight of that foot of water. Lowering the water table can sometimes significantly improve the soil conditions at a site with consoli-dation of the subsurface soils.

Reduce Lateral Pressure. Dewatering may also be used to reduce lateral soil and hydrostatic pressure against sheet piling, as might be encountered on a deep excava-tion.

Fig. 700-5 Dewatering an ExcavationDecember 1993 700-16 Chevron Corporation

Civil and Structural Manual 700 Miscellaneous CivilSurcharging (Preloading)Preloading involves the placement of a surface load prior to construction to precom-press subsurface soils, such as unconsolidated clay or silts. For consolidation of soils to occur, pore water must be drained from the soils. For soils with low perme-ability this consolidation process will take place over a long period of time. The time rate of consolidation can be greatly accelerated if the distance the water must travel in the soil is reduced. This is frequently accomplished by the installation of sand drains as shown in Figure 700-6.

By installing sand drains, on, say 10-foot centers, water needs to migrate only a maximum of 5 feet to reach the permeable sand drain. Desired consolidation can be reached in a matter of months instead of years. Holes for the drains may be augured and backfilled with sand, or driven with a pile, the soil extracted, backfilled with sand, and the pile removed.

An alternative to sand drains is the use of geotextile drainage wicks. The prin-ciple is identical to sand drains but instead of drilling the required holes, the approx-imate 5-inch wide drainage wicks are pushed into the ground to the desired depth with a mandrel. When the drainage wicks are in place, water can easily work its way to the surface by capillary action.

After removal of the preload (usually excess fill material) the bearing capacity of subsoils will have increased, and predicted settlements that will result from construction of new facilities will be decreased. Since preloading may take months to complete, it may have a significant impact on the construction schedule.

733 Soil Placement and CompactionDepending on the soil properties, different compaction procedures and equipment are used. Regardless of the equipment, effectiveness falls off rapidly as the depth increases from the surface. Therefore, compaction programs limit the depth for each layer of fill. This depth varies from 4 inches to 12 inches depending on the soil and compaction method.

Fig. 700-6 Surcharging With Sand DrainsChevron Corporation 700-17 December 1993

700 Miscellaneous Civil Civil and Structural ManualCohesionless SoilsSand and gravel-type materials are best compacted with vibratory equipment. Multiple passes with 5- to 15-ton rollers equipped with vibrators are made over the filled area to achieve desired compaction. Granular soils are compacted most effec-tively in lifts of 6 to 12 inches; however, even greater lifts have been compacted with very large compactors.

Soils with Moderate CohesionThe compacting effect of vibration decreases with increasing cohesion. For such soils, compaction by rollers is more successful. Of the two most commonly used rollers, sheepsfoot rollers perform better on plastic soils, while pneumatic-tired rollers have proven successful for soils with low plasticity. Compaction is generally done in lifts of 4 to 8 inches for pneumatic rollers, and 6 to 12 inches for sheepsfoot rollers.

ClaysHighly cohesive soils can be difficult to compact and to control moisture. Under some conditions the use of sheepsfoot rollers can be effective. However, if the water content is much above the plastic limit of the soil, the clay will adhere to the roller or the equipment will settle in the ground. Fill layers are generally limited to 6 to 12 inches.

734 Excavation and Backfill (Foundations and Trenches)Excavation work must be undertaken with attention paid to the risks involved to personnel, equipment, and existing facilities. The following items should be consid-ered before excavation work proceeds:

Existing underground obstructions should be clearly identified on drawings and marked in the field. Hand excavation may be required to identify buried obstructions.

Equipment operators must be fully informed of the excavation program and potential interferences.

Careful consideration should be given to shoring and bracing requirements, or alternative methods to maintain slope stability.

Excavations near existing facilities must be undertaken in a manner that will not affect vertical or lateral support.

For unusual loading or soil conditions, or where the factor of safety may be marginal, a detailed stability analysis is recommended.

Backfill should be compacted in 6-inch lifts to 95% of the soils maximum density where the excavation is close to or under other structures or equipment. Excavation in open areas that will not be built upon should be compacted to 90 or 95% of the soils maximum density. The lower compaction limit could be used for naturally dense soils (dry density > 110 lb/ft3) and the higher compaction limit for naturally lighter soils.December 1993 700-18 Chevron Corporation

Civil and Structural Manual 700 Miscellaneous CivilShoring for ExcavationsThe Companys Safety in Designs Manual covers general protection requirements for personnel in excavations, maximum slopes for unshored excavations, and shoring member sizes and details for excavations up to 20 feet deep. Please refer to this manual.

735 MudwavesWhen placing fill over highly saturated organic silty or clay soils, a displacement condition called mudwaves may occur. The result is lateral displacement of the soft material and settlement of the fill. The displaced material will often be pushed up as a wave exceeding the original grade level. This can occur during the fill opera-tions or shortly thereafter. See Figure 700-7.

If there is reason to believe this situation could develop, remedial action is called for. Remedial actions might include:

Complete removal of the weak soils if not too thick, and replacing with stronger material

Controlled gradual displacement of the soft material with the fill. This involves continuous pushing of the wave ahead of the edge of new fill.

Placing a layer of granular material extending outward beyond the edge of the new fill. The weight and dimensions of this material are calculated so it serves as a counterweight, resisting failure of the soils supporting the new fill.

Limiting fill procedures to very shallow incremental lifts over an extended period of time to permit underlying soils to consolidate and gain strength

Limiting the size of equipment used, to reduce loading on the soils

Fig. 700-7 MudwaveChevron Corporation 700-19 December 1993

700 Miscellaneous Civil Civil and Structural Manual740 Roads and PavingThis section provides the civil engineer, or other engineers working outside their disciplines, with an overview of paving fundamentals, terminology, references, and broad guidelines to assist in selecting and specifying appropriate materials for road and area paving and surfacing. In addition to asphalt and portland cement concrete, a variety of alternative surfacing materials is also discussed.

741 General Considerations and Layout of PavementsThe purpose of paving includes the following:

Provide an all-weather surface with good non-skid qualities for vehicles

Improve storm water runoff

Provide a surface that channels liquid spills into collection systems and prevents infiltration into the sub-grade

Provide a cleaner working surface by controlling dust problems and promoting good housekeeping

Prevent soil erosion problems

Minimize damage from frost

Typical sections for two types of paving are shown in Figure 700-8.

Fig. 700-8 Paving SectionsDecember 1993 700-20 Chevron Corporation

Civil and Structural Manual 700 Miscellaneous CivilLayers of Roads

Subgrade. The foundation soil placed and compacted during the rough grading work is called the subgrade. Usually it consists of the natural soils found on the site, unless they have inadequate strength and are replaced with imported soils.

Subbase. The subbase is a compacted layer of well-graded fill. It is sometimes, but not always required under the base course. It is used over fine grained subgrade soils to improve drainage, resist frost heave, provide structural support by distrib-uting loads, and to prevent pumping of finer grained soils into the base material at paving joints and edges.Base Course. The base course is the layer of well-graded granular material that supports the paving. It distributes wheel loads over a greater area of the subgrade.

Paved Surface. Paved surfaces are of reinforced concrete or asphaltic concrete that distributes the load to base and subbase, seals against penetration of surface water (or liquids), resists abrasion and provides traction. Sections 743, 744 and 745 will help you select and design the thickness of paved surfaces.

Layout

Road Widths. Lane and shoulder dimensions are given in Figure 700-9 as guide-lines for typical road requirements. These are not mandatory dimensions, and judg-ment should be used to conform to local need or standards.

Minimum Radii. The minimum radii at road intersections and curves should be based on vehicles expected to use the road regularly. Figure 700-10 illustrates the critical dimensions for determining minimum radii, and Figure 700-11 gives dimen-sional turning data for other types of vehicles.

Sets of turning radii curves are oftentimes available at Company facilities for the vehicles in use there. If curves are not available, it may be necessary to develop a new curve for a particular vehicle. To do this, field measurements are made to check out turning dimensions with the actual vehicle. Additional information for turning radii is available in Reference 9.

Fig. 700-9 Standard Lane and Shoulder Dimensions for Typical Roads

Width (feet)

Road Type & Traffic Single Lane Shoulder

For high-quality, heavy-duty road with up to 500 or more heavy vehicles daily. Used for heavily truck-traveled roads and main thoroughfares.

20 4

For not over 2000 cars and 50 heavy trucks or other heavy vehicles daily. Used for heavily-traveled access roads.

10 4

For less than 300 cars and 20 heavy trucks or other vehicles daily. It is recommended for lightly-traveled access roads.

8 4

For less than 50 cars and 5 heavy vehicles daily. Suitable for lower-quality access roads.

8 2-1/2Chevron Corporation 700-21 December 1993

700 Miscellaneous Civil Civil and Structural ManualPaving Layouts for Plants

Perimeter Roads. The location of the inside edge of perimeter roads must comply with Process Plant and Equipment Spacing Guide for Fire Protection Consider-ations (previously called Design Practice A-233), in the Fire Protection Manual.Center line elevation should be 6 inches higher than corresponding plant high point to prevent major plant spills from running off to adjacent areas.Setback Area. The setback area should be surfaced with asphaltic concrete or 4 inches of compacted crushed rock.

Process Plant Paving. Paving for a process plant (Figure 700-12) should extend 4 feet outside the equipment setback lines. Design of paving should be AASHTO Designation H-20 loading, or proposed crane loads if greater.

Paving Material. Concrete paving should be used where hydrocarbon spills or drips may occur during operation or cleanup of equipment, around all machinery to a width of not less than 4 feet, and where required because of heavy wheel load-ings. Where general areal settlement occurs, such as at Richmond, asphaltic concrete may be required to handle differential settlement problems. See Section 744 for a discussion of concrete paving.

Fig. 700-10 Turning Radius for Passenger CarDecember 1993 700-22 Chevron Corporation

Civil and Structural Manual 700 Miscellaneous CivilFig. 700-11 Vehicle Dimensions for Turning Radii

Fig. 700-12 Process Plant Paving LayoutChevron Corporation 700-23 December 1993

700 Miscellaneous Civil Civil and Structural ManualAsphaltic concrete may be used for all other plant paving, except in areas subject to hazardous waste leaks or spills that could damage paving. Acid bricks or corrosion-resistant protective coatings should be used in such areas. Standard Drawing GF-S-99943 provides typical details for drainage surfaces in sulfuric acid and sodium hydroxide service. See Section 743 for a discussion of asphalt paving.

Parking Layout. Layout of parking must be based on intended traffic flow (one-way or two-way), and frequency of in-and-out movement. For space planning, Figure 700-13 provides general dimensional requirements for 45-degree and 90-degree angle parking. The 9-foot stall width is suitable for standard-sized cars.

For additional information on layout of parking lots refer to Reference 9.

Guard PostsIn the layout of paved areas it is frequently necessary to install guard posts. These can be stationary posts to restrict traffic and protect certain areas, or removable posts to control access to specific vehicles. Refer to Standard Drawing GE-S-99975 for details.

Fig. 700-13 Parking Layout AlternativesDecember 1993 700-24 Chevron Corporation

Civil and Structural Manual 700 Miscellaneous Civil742 Paving SelectionTwo types of paving can be selected, rigid or flexible. Rigid paving such as port-land cement concrete has low flexibility and is capable of distributing wheel loading over a wide area of subgrade. Flexible paving such as asphaltic concrete, relies on a relatively thin paving (2 to 4 inches thick) in combination with layers of base and subbase material to distribute vehicle loads.

The relative costs of Portland cement and asphaltic concrete paving vary consider-ably between geographic locations. Generally, the initial cost of Portland cement concrete paving is higher (as much as 30 to 50% in some cases) than asphaltic concrete paving. However, studies of state and federal highway records by the Port-land Cement Association have shown that portland cement concrete paving has a lower life-cycle cost than asphaltic concrete paving. Life-cycle cost data for pave-ments in Company facilities are not readily available.

Concrete PavingAdvantages:

Hard wearing surface Excellent for areas subject to hydrocarbon leaks or spills Low maintenance when used in areas with stable subgrade

Disadvantages:

Does not perform well on unstable subgrades

Is subject to severe cracking if areal settlement occurs Is difficult and expensive to repair

Requires special joints to control the location of cracks, relief from expansion, and for construction

Requires installation of and periodic testing of gas test wells to avoid collec-tion of volatile gases under the slab

Asphaltic Concrete PavingAdvantages:

Easier to shape surface to desired slopes

The greater flexibility of asphaltic concrete paving permits it to adjust to subgrade changes

Easier to repair

Makes access to subsurface lines easier

Disadvantages:

May be damaged by hydrocarbons Surface is more easily damaged by heavy concentrated wheel loadsChevron Corporation 700-25 December 1993

700 Miscellaneous Civil Civil and Structural ManualGeneral Applications of PavingConcrete paving can be used in:

Main process operating areas

Walking areas

Areas subject to heavy vehicle traffic within plant areas Areas around machinery, or where hydrocarbon spills may occur during plant

operation or cleanup of equipment during maintenance

Asphaltic concrete paving can be used in:

Main process operating areas Walking areas Plant setback areas Roads Parking lots

Traffic Analysis for Pavement DesignAn important consideration in the selection and design of paving is the size of vehi-cles using the paving and frequency of use. For highway designs, both rigid and flexible, design aids are based on Equivalent Single-axle (18-kip) Loads (EAL or ESAL). By this approach, varying axle loads are converted to one design loading, and traffic volume is measured as the number of repetitions of this design axle load. For Company designs, a detailed traffic analysis and development of EALs is not warranted. However, it is important to understand the concept of equivalent loading. Tabulated in Figure 700-14 are EALs developed for typical vehicles.

This tabulation demonstrates the significant effect of axle loading on pavements. A single trip by a 40 ST truck theoretically does as much damage to the paving, base, and subbase as 7800 autos. A large crane, which may be double the truck weight, contributes 10 times the equivalent loading of the truck.

Paved areas that will see frequent use of large vehicles obviously must be designed more carefully and will require greater thicknesses.

Fig. 700-14 Equivalent Single-axle Loads for Typical Vehicle

VehicleTotal Equivalent 18,000-lb Axle Load

Passenger 0.00036

Pickup Truck 0.00227

Vacuum Truck, Flatbed, Tanker (40 ST) 2.79

75 Ton Crane 26.6December 1993 700-26 Chevron Corporation

Civil and Structural Manual 700 Miscellaneous CivilDrainage of PavementsGood drainage for all the materials supporting pavements is of great importance to the performance of the paving. The presence of water within the pavement structure can badly affect an otherwise properly designed project. Excess water will cause the following problems:

Saturation of the subgrade, base, and subbase reduces the effective load-bearing capacity of these layers.

In areas with freezing climates, thawing occurs from the top downward, trap-ping water between the pavement and frozen ground below.

The presence of water can cause pumping of fines from the subgrade into the subbase layer and displacement of the subbase aggregate into the subgrade.

Proper design and maintenance of paved area cross-sections promotes good drainage. This is accomplished by:

Providing adequate area drainage so that the water table is maintained at an elevation lower than the upper part of the subgrade

Shaping the subgrade to provide a slight crown effect, which will give a slope to the subbase and base of about 1/4 inch per foot towards the shoulder

Extending base and/or subbase materials beyond the edge of paving with adequate slope to provide drainage away from under the pavement

Maintaining paving surfaces to minimize the penetration of surface water through cracks and joints into the materials below

A recommended slope for road shoulders is 1 inch per foot, with a maximum slope of 1-1/2 inches to 1 inch per foot for subgrade or subbase materials.

Paving Over Low-Strength SoilsIn the past whenever low-strength soils were encountered the available choices were to excavate the undesirable soils and replace with better material, or to overlay with thicker subbase materials to reduce unit loading to the subgrade. However, with the development of a line of geogrid and geotextile products, other alternatives are available for working with problem soils.

Geogrids. Manufactured of high tensile strength polymer, these grids are designed with transverse and longitudinal ribs. When laid directly on the subgrade, the grid geometry provides a mechanism for interlocking aggregate base or subbase mate-rial placed on the geogrid. The interlocking serves to prevent lateral movement of the aggregate and improves load distribution to the subgrade. Grid materials are inert to chemical and biological conditions normally encountered in soils and are not expected to degrade.

Information on geogrids may be obtained from The Tensar Corporation, Morrow, Georgia.Chevron Corporation 700-27 December 1993

700 Miscellaneous Civil Civil and Structural ManualGeotextile. Manufactured of polyester, geotextile comes in rolls up to 16 feet wide and 300 to 1000 feet long. When laid over subgrade materials directly below an aggregate subbase, the geotextile is designed to perform four functions:

The geotextile material maintains separation of the subbase from the subgrade. Coarse aggregate cannot move downward, and fine soil particles in the subgrade cannot be pumped upward into the subbase.

The geotextile material is permeable, allowing pore water to pass vertically through the fabric.

The tensile strength of the fabric provides tensile reinforcement for the subbase.

The geotextile material allows lateral water flow within the plane of the fabric. This serves to dissipate excess pore water pressure.

Geotextiles are designed to be resistant to freeze-thaw and soil chemicals. Informa-tion on the use of geotextiles may be obtained from:

Other products whose function is similar to the ones described above may be avail-able. The decision to use such products to solve soil problems should be based on economics. An investigation of some actual installations where these products have been used is recommended until the Company has some in-house experience.

743 Asphalt PavingThe purpose of this section is to provide guidelines for engineers involved in design and specifications for asphalt and paving. Normally, Company engineers would not be expected to design actual asphalt mixes; however, they may participate in deter-minations that will influence final design, or be responsible for paving specifica-tions and construction. The objectives of this section are: Provide working knowledge of the terminology used for asphalt paving Provide an understanding of the concepts that control designs Discuss basic materials and installation methods Provide guidance on typical paving requirements

The Asphalt Institute as a ResourceThe Asphalt Institute has published a large number of excellent manuals covering every aspect of asphalt use. Copies of these manuals may be obtained through the Institute by writing to or calling: The Asphalt Institute, Lexington, Kentucky 40512-

Product Name SourceTrevira Hoechst Fibers Industries

Spartanburg, South CarolinaSupac Phillips Fibers Corporation

Greenville, South CarolinaTypar Reemay Inc.

Old Hickory, TennesseeDecember 1993 700-28 Chevron Corporation

Civil and Structural Manual 700 Miscellaneous Civil4052, (606) 288-4960. Both Chevron U.S.A. Inc. and Chevron Canada Limited are members of the Institute, so discounts on purchase of Institute manuals may be available. An annotated list of references on materials, design, installation, mainte-nance and repair of asphalt paving is included in Section 780.

Asphalt TerminologyFigure 700-8 illustrates a typical cross section through an asphalt pavement struc-ture.

The following terminology is taken from literature published by The Asphalt Insti-tute:

Asphalt Concrete. High-quality, thoroughly-controlled hot mixture of asphalt cement and well-graded, high-quality aggregate, thoroughly compacted into a uniform dense mass.

Asphalt Pavement Structure. A structure that is a combination of asphalt courses and asphalt-aggregate or untreated aggregate courses, placed above the subgrade.

Full-Depth Asphalt Pavement. A pavement in which asphalt mixtures are employed for all courses above the subgrade.

Asphalt Prime Coat. A spray application of low-viscosity asphalt emulsion to an untreated base. Its purpose is to bind the granular material to the asphalt layer.

Asphalt Tack Coat. A spray application of asphaltic material to existing pavement (Portland cement or old asphalt) to insure bond between the superimposed material and the existing surface.

Asphalt Seal Coat. A thin asphalt surface treatment used to waterproof and improve the durability of an existing surface.

Emulsified Asphalt. Consists of fine droplets of asphalt suspended in water. Drop-lets are held in suspension for a long time because of emulsifying agents. The mate-rial can be handled with little or no heat. Comes as rapid setting (RS), medium setting (MS), and slow setting (SS). Is used for road construction, sealing and surface treatments and patching mixes.

Liquid Asphalt (Cutback Asphalt). Liquid asphalt, once commonly used, incorpo-rates solvents to thin the asphalt to enable handling at lower temperature. Solvents include naphtha-type, kerosene-type, or light oil to produce rapid, medium, or slow curing asphalt materials.

Because of environmental concerns, liquid asphalts have been largely supplanted by emulsified asphalts. EPA and state regulations either severely restrict or prohibit the use of liquid asphalts.

Asphalt Cold Mix. A mixture of unheated mineral aggregate and emulsified asphalt. Mixes may be produced in stationary plants with close control of the production process, or mixed in place. Spreading and compaction is done with conventional equipment.Chevron Corporation 700-29 December 1993

700 Miscellaneous Civil Civil and Structural ManualWearing Course (Surface Course). The part of the paving that directly supports the traffic. It consists of fine aggregate or coarse sand held by an asphalt binder designed to resist wear from traffic.

Binder Course. In a multi-layered paving system this layer, directly below the wearing course, is composed of intermediate-sized aggregate with a somewhat lesser amount of asphalt.

Basic Design Concepts of Asphalt PavingCompany-wide standard design criteria cannot be used for asphalt paving for the following reasons:

There are major environmental characteristics that impact the strength and performance of subgrade materials. AASHTO, for example, has subdivided the continental U.S.A. into six climatic regions for various combinations of such characteristics as freeze/thaw cycling, wet, dry, hard freeze, and no freezing.

Materials of construction vary widely. In some locations the highest quality aggregate is readily available, whereas it may be prohibitively expensive in others. For example, at Pascagoula sand and shell materials are used exten-sively for base materials because of their availability in comparison to other materials.

Asphaltic concrete mixes should be based on local and state highway depart-ment specifications. These are the mixes that local asphalt mixing plants are prepared to furnish, and it is expected they are properly designed to meet local requirements.

If paving work is required in an area where the Company has not had previous expe-rience, considerable knowledge of local paving practices can be developed from the following sources:

District office for the state department of highways County or city offices responsible for public roads Local geotechnical engineers Asphalt plant operators and paving contractors Personal observation of local roads under equivalent service

Information from these sources should provide a sound basis for making a judg-ment about materials, design criteria, and installation procedures for achieving a quality paving at reasonable cost.

Subgrade Strength EvaluationThickness requirements for asphalt pavements depend largely on the strength of the finished subgrade. For a project with significant paving requirements, with heavy vehicle loading, and no directly relatable paving experience at the site, subgrade evaluation should be included as part of other geotechnical studies. Since stability of the subgrade is closely related to its density and moisture content, soil testing should be done as near as possible to anticipated in-service conditions.December 1993 700-30 Chevron Corporation

Civil and Structural Manual 700 Miscellaneous CivilFrequently, however, because of the nature and intended use of the proposed paving and the available local knowledge and experience with the subgrade materials, an engineer can proceed with confidence to design a paving without a site specific subgrade evaluation.

If testing is to be made to evaluate the strength of the subgrade, there are a number of widely used methods employed for asphalt pavement design. These same tests can be used for testing in-place base and subbase strengths. These tests include:

Plate Bearing Test California Bearing Ratio (CBR) Method Resistance Value Method (R-Value) Resilient Modulus (Mr) MethodResults from any of these four evaluation methods cannot be converted from one value to an equivalent value in another method; however, References 4 and 5 provide information on approximate relationships. Following is a brief description of these test procedures.

Plate Bearing Test (ASTM D1195). This test can be used for subgrade evaluations but also strength measurements for subbase, base, or finished pavement. The proce-dure involves loading a test plate (from 6 to 30 inches in diameter) on the surface of the materials. Deflection and rebound measurements are made at the plate and at distances up to 1.5 times the diameter from the edge of the plate.

California Bearing Ratio (ASTM D1883 or AASHTO T193). The CBR test consists of measuring the load required to cause a plunger of standard size to pene-trate a soil specimen at a specified rate. The CBR rating is the resultant of the above test expressed as a percentage of the load for the same test performed on a standard sample of crushed rock.

Resistance Value Method (R-Value) (ASTM D2844 or AASHTO T190). This evaluation follows a two-step procedure:

The resistance value determines the thickness of a pavement structure required to prevent plastic deformation of the soil under imposed wheel loads.

The expansion pressure test determines the thickness or weight of cover required to maintain the compaction of the soil.

The design R-Value is determined from the moisture content and density at which these two thicknesses are equal.

Resilient Modulus (Mr) Method (Asphalt Institute Manual MS-10). This test determines the resilient modulus of untreated fine-grained subgrade soils for condi-tions that are representative of stresses in pavements subjected to moving wheel loads. It involves testing of soils in a triaxial chamber, subjected to repeated loads of fixed magnitude, frequency, and load duration. It is expressed in pounds per square inch (psi).Chevron Corporation 700-31 December 1993

700 Miscellaneous Civil Civil and Structural ManualThickness GuidelinesFigure 700-15 provides some guidelines for estimating paving and base/subbase thicknesses for three types of subgrade materials and five types of service/traffic requirements for the roads.

The guideline thicknesses are based on a relatively dry and non-freezing location. Figure 700-16 provides a relative comparison of roadbed soils to show the impact that various climates have on design requirements.

Thickness Guidelines for Untreated Aggregate BasesFigure 700-16 shows that relatively poor subgrade soils can be treated in about the same manner regardless of the climatic conditions at a particular site. For subgrade soils judged to be fair, additional base/subbase thickness is probably required for the more severe climates. For soils rated good, climate becomes a more important consideration. Subgrade soils rated good in locations subject to hard freezes could be expected to perform no better than fair soils in areas without freezing. For example, good subgrade materials in Wyoming should prob-ably be downgraded to fair when using Figure 700-15. Subbase and base thick-nesses should be adjusted accordingly.

(1) In considering the total pavement structure it should be understood that there is no single unique design solution. Instead there are many combinations of paving, base and subbase that will provide satisfactory results. The combination selected should be the one most attractive for reasons of cost and construction/maintenance considerations.

(2) Paving thicknesses are based on asphaltic concrete (hot-mix). Alternative paving materials (cold-mix) may require additional thickness or additional base/subbase.

(3) A minimum of 6-inches of higher quality base materials should be placed over lower quality subbase materials.

Fig. 700-15 Thickness Guidelines for Untreated Aggregate Bases

Subgrade Soils Approximate Thickness (in.)(1)

Relative Quality

Typical Evaluation Values Traffic VolumeTrucks & Cars

CBR Resist. Mod. (Mr)>500

Unlimited

Civil and Structural Manual 700 Miscellaneous CivilBase and Subbase Construction

Compaction. Base courses should be compacted in layers not exceeding 4 inches. Subbase should be compacted in layers not exceeding 6 inches.

Base course, subbase, and top 6 inches of subgrade should be compacted to a dry density not less than 95% of the maximum dry density (Modified Proctor).

MaterialsFor a subbase with a minimum CBR of 20 (R-Value 55) the following materials are acceptable:

Coarse sand Poorly graded gravel Sandy loam Decomposed granite with fines Gravel containing fines Sand/shell mixtures

Not over 20% by weight of this material should pass a 200 mesh sieve. A very fine sand or a silty sand is unacceptable as a base or subbase material. Maximum size of stone should be not greater than one-third the thickness of the base course or the subbase course.

For a base with a minimum CBR of 70 (R-Value 80) the following materials are acceptable:

Crushed rock Pit run gravel (well-graded)

Fig. 700-16 Impact of Climate on Various Roadbed Soils

ClimateDescription Examples

Relative Subgrade QualitySoil Resilient Modulus (psi)

Good Fair Poor

Dry, no freeze So CalifSo Texas

12,000 5,500 3,000

Wet, no freeze W OregonNo CalifGulf States

9,500 5,000 2,800

Wet, freeze/thawcycling

Midwest andEast Central States

7,300 4,500 2,700

Wet, hard-freezespring thaw

Great Lakes to New England

5,700 4,000 2,700

Dry, freeze/thawcycling

E WashingtonNo Texas

8,200 5,000 3,000

Dry, hard freeze,spring thaw

WyomingMontana

5,700 4,100 2,800Chevron Corporation 700-33 December 1993

700 Miscellaneous Civil Civil and Structural Manual Well-graded sand (asphalt stabilized) Coarse decomposed granite (well-graded)Not over 7% by weight of this material should pass a 200 mesh sieve. Maximum size of stone should be not greater than one-third the thickness of the base course.

If the depth of frost penetration exceeds the total thickness of subbase, base and pavement, the subbase thickness shall be increased until this total equals the frost depth or a maximum of 18 inches.

In areas subject to frost damage, base and subbase materials should contain not more than 8% by weight of particles finer than 200 mesh. This requirement is to maintain good drainage through the materials and reduce frost heave potential.

Where low-quality subgrade soils are present, consideration should be given to the use of geotextiles, as discussed in Section 742. It may be that the cost of using geotextile fabric over the weak subgrade can be offset by reduction in base/subbase costs.

Types of Asphalt PavingThe two types of asphalt paving most frequently used for new construction are plant mix (hot mix or cold mix) and road mix (mixed-in-place).Plant Mix (Hot Mix). Asphalt paving mixtures prepared in a central mixing plant are known as plant mixes. Asphalt concrete is considered the highest-quality plant mix. It consists of well-graded, high-quality aggregate and asphalt cement. The asphalt and aggregate are heated separately from 250 to 325F, carefully measured and proportioned, then mixed until the aggregate particles are coated with asphalt. The hot mixture, kept hot during transit, is hauled to the construction site, where it is spread on the roadway by an asphalt paving machine at temperatures above 240F. The uniform layer of asphalt mix is spread by a paver, motor grader, or by hand followed by compaction with rollers to proper density before the asphalt cools. Spreading of asphalt can be done in lifts from 2 to 4 inches compacted thick-ness.

Advantages

Produces a high-quality paving surface suitable for heavy traffic

Good quality control can be achieved at the mix plant

Ambient temperatures are not as critical, and since the aggregate is heated the moisture can be controlled

Limitations

Requires carefully monitoring the work to make sure that compaction proce-dures and equipment are adequate to meet specified compaction before the mixture has cooledDecember 1993 700-34 Chevron Corporation

Civil and Structural Manual 700 Miscellaneous Civil Requires a hot-mix plant within a suitable distance of the work site. If the plant is too far from the site, mix temperature considerations and economics may preclude use of hot mix.

Hot-mix plants in cold regions usually shut down during winter months.

Plant Mix (Cold Mix). Cold-mix paving is a mixture of unheated mineral aggre-gate and emulsified asphalt that can also be produced at a central mixing plant. Like a hot mix, the production can be closely controlled, but cold mix has the advantage of being spread and compacted at normal ambient temperatures. Cold mix can be placed in lifts of 2 to 3 inches compacted thickness. The disadvantage of cold mixes is that they do not provide the high-quality, long-wearing paving that is attainable with hot mixes.

Road Mix (Mixed-in-Place). Road mix paving is emulsified asphalt sprayed onto and mixed into aggregate at moderate-to-warm ambient temperatures. Mixed-in-place construction can be used for surface, base, or subbase courses. As a surface or wearing course, it usually is satisfactory for light and medium traffic rather than heavy traffic. However, mixed-in-place layers covered by a high-quality asphalt plant-mix surface course produce a pavement suitable for heavy traffic. The advan-tages and limitations of mixed-in-place asphalt are:

Advantages

Utilization of aggregate already on the roadbed or available from nearby sources and usable without extensive processing

Elimination of the need for a central mixing plant. Construction can be accom-plished with a variety of machinery often readily available, such as motor graders, rotary mixer with revolving tines, and traveling mixing plants.

Limitations

Should not be done when atmospheric temperatures are under 50F. If the temperature is too cold, proper mixing of asphalt and aggregate is difficult.

Control of surface moisture for the aggregate is important. Excessive moisture causes problems in mixing, curing and compacting. Generally surface moisture must not exceed about 3%.

Cold mix used for a surface course is suitable only for medium and light traffic.

The quality of mixed-in-place paving is more difficult to control than plant mixes.

Asphalt Application

Prime Coat. For most untreated granular bases an asphalt prime coat should be used. When the base course for paving has been properly compacted and loose material removed, it is ready to be primed with asphalt. A pressure distributor is used to spray approximately 0.2 to 0.5 gal/yd2 of low-viscosity asphalt on the prepared surface of the base. The asphalt should be fully absorbed by the base and allowed to set and cure before placing the surfacing.Chevron Corporation 700-35 December 1993

700 Miscellaneous Civil Civil and Structural ManualTack Coat. Any time asphalt surfacing is to be applied over a surface of existing asphalt, such as a surface (wearing) course over a binder course, a tack coat should be applied to achieve proper bonding. The tack coat must be very thin and must uniformly cover the area to be paved. Asphalt is sprayed on at a rate of approxi-mately 0.05 to 0.15 gal/yd2.

Asphalt Consultation ServiceChevron, through its Asphalt Technical Service (510) 242-2736, provides a consul-tation service for customers on asphalt-related problems. This group does not provide design services, but its broad background and reference sources provide an excellent in-house resource to respond to specific questions or problems.

744 Concrete PavingThis section discusses the principles for design of Portland cement concrete paving for roads and plant areas.

SubgradeThe most important consideration for a concrete subgrade is its ability to provide uniform support. Concentrated wheel loads are distributed over a large supporting area of the subgrade because of the rigidity of the concrete slab. The effectiveness of slabs on grade to distribute loads is demonstrated by tests conducted by the PCA and others. Wheel loads up to 15,000 pounds applied to 6-inch and 8-inch thick slabs resulted in subgrade pressures of 5 psi or less. If the subgrade is non-uniform, with abrupt changes from hard to soft, cracking may occur where the slab bridges over soft spots or rides on hard spots.

Most references for thickness design of Portland cement concrete paving evaluate subgrade support on the basis of modulus of subgrade reaction (Westergaards k). The modulus is determined by the loading pressure to make a rigid 30-inch diameter bearing plate deflect 0.05 inches into the subgrade material (ASTM D-1196). This factor is intended to measure the temporary (elastic) properties of the subgrade, rather than long term soil bearing properties.

The value of k is as follows (pounds/cubic inch):

(Eq. 700-2)where:Deflection = actual measured deflection (approximately 0.05 inch)

Typical values for subgrade materials are shown in Figure 700-17.

SubbaseA subbase is not mandatory for concrete paving slabs, but should be considered where the following conditions exist:

k load (psi)deflection (inches)--------------------------------------------=December 1993 700-36 Chevron Corporation

Civil and Structural Manual 700 Miscellaneous Civil When the subgrade lacks uniformity because of minor soil variations. A subbase layer will not correct major subgrade defects, which should be corrected by excavating poor material.

For paving where a significant number of vehicles with axle loads exceeding H-20 are expected to routinely use it

To provide a stable working surface during paving construction

Where subgrade materials are known to be problem soilsdifferential shrinkage and expansion or excessive frost heave.

If a subbase is provided, it is recommended that the thickness be limited to 4 inches. Tests by the Portland Cement Association show minor increases in subgrade support with thicker subbase. A thicker subbase should only be used for large wheel loads on poor material.

For subbase construction, dense-graded material meeting the following limits is recommended:

Sizemaximum aggregate size not to exceed 1/3 subbase thickness Passing 200 sieve15% maximum Plasticity Index6% maximum

Paving Design For light traffic areas, walkways, and areas restricted to automobiles or pick-up trucks, a 4-inch slab is considered adequate. For any areas expected to carry heavier vehicles, up to an equivalent H-20 loading, a minimum 6-inch slab should be used. For areas expected to carry heavier loads, such as work areas for large mobile cranes, a more detailed paving design may be appropriate. Refer to References 5, 6, and 7 for design procedures and thickness design charts. Refer to Figure 700-18 for recommended thickness guidelines for various subgrade strengths and anticipated loading.

Wire-Mesh Reinforcement. Wire-mesh reinforcement serves mainly to keep shrinkage-temperature cracks that may occur in the slab from opening up. If cracks are kept closed, shear will continue to be transferred by aggregate interlock. Rein-forcement does not appreciably increase the load carrying capacity of the slab, nor does it prevent cracking. The recommended wire-mesh reinforcement for slabs is

Fig. 700-17 Typical k Values for Subgrade Material

Relative Quality K Value (pci) Examples of Subgrade Soils

Very Good >550 Crushed Rock

Good 400-550 Well-graded gravel

Fair 250-350 Sand/Clay Mixture, Well-graded

Poor 150-250 Gravel/Clay, Poorly Graded

Very Poor

700 Miscellaneous Civil Civil and Structural Manual6 x 6W1.4 x W1.4. It should be placed at mid-depth or slightly higher in the slab, as flexural stresses can be expected at both the top and bottom of the slab.

Paving Details. Refer to CIV-EF-738 for standard paving details. The following comments relate to details that appear on this form.

Thickened Edges. At places where there is a loss of continuity for the slab, it is necessary to provide additional slab strength. All free edges for 4-inch slabs should be thickened to 6 inches at the edge, and 6-inch slabs thickened to 8 inches. Thick-ened edges should taper to the nominal slab thickness about 2 feet from the slab edge.

JointsJoints are placed in concrete paving to control the location of cracks and avoid uncontrolled random cracking. The basic joint types, as illustrated in Figure 700-19, are:

Expansion (or Isolation) Joints Control (or Contraction) Joints Construction Joints

Expansion Joints. Expansion joints provide horizontal and vertical relief to the slab for expansion caused by temperature and moisture changes. They also allow differential movement between the slab and other fixed structures or foundations. There is no load transfer across the joint. Typical locations for expansion joints include:

At high points within a concrete paved area Where foundations penetrate the paving slab Where it is desirable to avoid transfer of vibrations from equipment to the slab Where there are pile-supported structures or foundations Where slabs abut buildings

Fig. 700-18 Thickness Guides for Concrete Paving

Subgrade Description and (K) Value

Design Vehicle Loading

Silts & Clay (Highly Compressible)< 100 pci

Sandy Silts & Clays Poorly-graded Sands or Gravel 100-250 pci

Sand/Clay Mixtures Well-graded Sand & gravel >250 pci

Pickup Slab (in.) 4-1/2 4 4

Subbase (in.) 4 4 with or without

H-15 Slab (in.) 6 5-1/2 5

Subbase (in.) 4 4 4

H-20 Slab (in.) 7 6-1/2 6

Subbase (in.) 6 4 4December 1993 700-38 Chevron Corporation

Civil and Structural Manual 700 Miscellaneous CivilControl Joints. The objective of control joints is to purposely induce a plane of weakness in the slab so that shrinkage cracks will occur along that line and nowhere else. It is recommended that the depth of the control joint be no less than 1/4 the depth of the slab. Common methods for making the joints include adding molded inserts at pour time or sawing the concrete while it is still green. Control joints should be spaced no more than 20 feet apart unless expansion or construction joints are present to control cracking. Control joints should form a square pattern if possible.

Construction Joints. Construction joints should be made where interruptions occur in the concreting operation or at the end of each days pour. The location of construction joints can be shown on drawings or preplanned when construction begins. At other times the requirements must be determined in the field when inter-ruptions to pouring operations occur. Weather is a common factor in determining if a construction joint is required. A 30-minute delay on a hot, dry windy day might

Fig. 700-19 Concrete Slab JointsChevron Corporation 700-39 December 1993

700 Miscellaneous Civil Civil and Structural Manualbe the maximum acceptable delay between concrete pours. Under less severe condi-tions a longer delay might be acceptable. The objective is to avoid formation of seams or planes of weakness that can occur if fresh concrete is deposited against concrete which has partially set, instead of still being plastic. Reinforcement is carried continuously across construction joints, to assure load transfer between slab sections. Load transfer-capability can be increased with the use of dowels or keyed construction joints.Location of Joints. The location of joints is an important consideration. Figure 700-20 illustrates some recommended practices regarding joint location.

Paving FinishIt is recommended that paving for walks or area paving first be given a float-finish followed by drawing a broom or burlap belt across the surface. This practice gives a coarse scored texture that provides traction.

Concrete MaterialsMinimum 28-day concrete strength for paving should be 3000 psi. Prohibit all vehicle loads on concrete slabs until 75% of design strength is reached. Limit loading on slabs to lighter weight vehicles only, until full design compressive strength is reached. For areas subject to freezing, air-entrained concrete should be used. See Section 200 of this manual for a discussion of soils, foundations, and concrete.

Fig. 700-20 Typical Joint LayoutDecember 1993 700-40 Chevron Corporation

Civil and Structural Manual 700 Miscellaneous CivilGas Test WellsA potential explosion hazard is created if gas pockets form beneath concrete paving. This may occur if there is damage to drain lines. Hydrocarbon spills that migrate under the slab may also collect at drain line locations if backfill materials are more permeable than the surrounding soils. Gas test wells per CIV-EF-738 should be provided at maximum 20-foot spacing over all drain lines that underlay concrete paving.

Gas test wells serve a dual purpose. First, they allow inspection for settlement and gas pockets by probing and testing with a combustible gas indicator. Second, they allow injection of grout under the concrete pavement to fill the voids. The grout is injected under pressure through the well after removal of the plug. A special grout consisting of fine sand, soil, cement, and sometimes other ingredients is used. This procedure has also been used to raise slabs in areas where considerable settle-ment occurred. Where general areal settlement is predicted, gas test wells should be installed on a 20-foot center-to-center grid in both directions to permit grout pumping.

Joint SealantsSealants prevent the intrusion of liquids through the slab and keep the joint free of undesirable material. Expansion joint material should have the following properties: Resist hydrocarbons Be impermeable Deform to accommodate movement at the joint Recover original properties and shape after cyclical deformations Remain bonded to the joint face Not harden or become brittle through aging or weathering

An excellent summary of sealant products currently on the market can be found in ACI 504R, Guide to Joint Sealants for Concrete Structures (Reference 8).

Pile-Supported SlabsAt sites where equipment foundations are pile-supported because of poor soil condi-tions, some consolidation of the subgrade soil between foundations is often expected. Asphalt paving for such areas can usually accommodate this type of movement or can be resurfaced as required to correct this condition. Reinforced concrete slabs cannot respond easily to such differential settlement conditions, and the result is unwanted cracking and tilting of slabs.

Pile support designs have been used to prevent settlement of slabs for sites with poor soil conditions. To minimize piling requirements, the most common practice is to support slabs from planned foundation structures to the greatest possible extent. Where additional support is required, pile-supported grade beams can be used. Refer to Section 200 for design of piles and to Specification CIV-MS-4841 (Section 2000).Chevron Corporation 700-41 December 1993

700 Miscellaneous Civil Civil and Structural Manual745 Paving Repairs

Flexible PavingAsphalt paving is subject to a variety of failures, whose causes and methods of repair vary. The Asphalt Institute has an outstanding reference on this subject enti-tled Asphalt in Pavement Maintenance (MS-16). This publication has excellent photos illustrating the major problems for purposes of identification. Recom-mended repair procedures are given for each type of problem. Subjects include but are not limited to:

Excessive deflection Alligator cracks Shrinkage cracks Slippage cracks Distortions Corrugations Raveling (progressive separation of aggregate) Potholes

Rigid PavingMaintenance consists mainly of filling in cracks and expansion joints to prevent entry of water to the subgrade, and to minimize further deterioration of the concrete along the edges of the crack or joint. Cracks should be cleaned out as thoroughly as possible and sealed. Deteriorated jointing materials should be cleaned out and replaced with rubber asphalt compounds. Such sealing materials for cracks and joints have less tendency to become brittle in cold weather, and to soften and track under traffic in hot weather Joint crack sealants are covered by ASTM Specification D 1190 and AASHTO M 173.

In extreme cases where a concrete slab has settled, it may be desirable to pump a grout mixture to the underside of the slab to restore it back to the original elevation. Sometimes differences in slab elevations can be corrected with asphalt concrete patching, or by completely overlaying the slab with asphalt concrete.

The Asphalt Institute Manual (MS-6) provides recommended repair procedures for Portland cement concrete paving, such as cracks, scaling, and spalling.

Subgrade ProblemsPaving problems often are traced to inadequate subgrade support. This may be due to poor drainage, improperly compacted subgrade, low-strength subgrade materials, or inadequate backfill and compaction over trenched lines or culverts. In such cases it may be necessary to remove the damaged portion of paving to expose the subgrade. Subgrade replacement, recompaction or use of geotextile materials are possible remedies. For information on geotextile materials refer to Sub-section 742.December 1993 700-42 Chevron Corporation

Civil and Structural Manual 700 Miscellaneous Civil746 Alternative Surface Treatments for Foot or Vehicle Traffic AreasPaving with asphalt or portland cement concrete is generally limited in scope to areas where, because of traffic loads or other considerations, the cost of paving is justified. There are, however, other surface treatments that have application for loca-tions with foot or limited vehicle traffic. These include:

Crushed rock Gravel Stabilized soil

Walking on these surfaces is difficult unless the suggested gradations are used and the materials are compacted to 90 to 95% of their maximum density.

Compacted Crushed Rock. Depending on the subgrade, the use of approximately 4 inches in depth of crushed rock will provide adequate support for occasional vehicle loads.

Crushed rock surfacing is commonly used where an all-weather, well-drained surface is desired, where neat appearance is important, and where heavy vehicle traffic is not a factor.

For the best wearing surface, a well-graded crushed rock material is desired. The following gradation is suggested for a well-compacted surface:

To limit the growth of vegetation through the rock surface, an application of an approved weed killer is recommended prior to spreading the crushed rock.

Gravel. Gravel as used herein refers to the wide variety of soil mixtures that have a significant portion of gravel (grain size 2 mm to about 3 inches) and/or coarse sand.

Gravel may be found naturally on the site, or may be imported to the location from a borrow pit. It can be well-graded (relatively uniform distribution of grain-size particles) to poorly graded (with excessive percentages of certain grain sizes and absence of others). Some gravel will exhibit some plasticity, whereas others will be non-plastic.

The well-graded gravels provide better and longer-lasting surfaces, and they tend to perform better if they have a small percentage of clay which acts as a binder. Poorly-graded gravel materials have a tendency to become soft during wet weather and loose and dusty in dry weather. The wearing properties for gravel surfaces can be improved by the application of emulsified asphalt to further cement the gravel.

Sieve Size Amount Passing Sieve, %1 inch 1003/4 inch 90-1001/2 inch 25-603/8 inch 10-15No. 4 0-3Chevron Corporation 700-43 December 1993

700 Miscellaneous Civil Civil and Structural ManualWell-graded gravel usually has grading (grain-size distribution) that falls within the following limits.

Stabilized Soil. Besides normal compaction techniques for strengthening soils, there are chemical additives that will enhance soil properties. These include:

Portland cement Asphalt Lime Calcium chloride

These treatments can be used to accomplish the following:

Upgrade the strength of very poor subgrade materials under roads Decrease the permeability of soils Act as a palliative to control dust problems To surface areas not subject to heavy vehicle loadsThe quantity of additive required and the anticipated stabilization gain will depend on the properties of the natural soil and the depth of soil to be stabilized. Labora-tory testing may be required to assess the value of using chemical additives. The common procedure followed for stabilizing soils includes:

Scarifying the existing surface Spreading chemical additives Mixing with motor grader using windrow mixing or alternative procedure Spreading Compacting as required

747 Alternative Surface Treatments for Non-Traffic AreasThis section discusses surface treatments for non-traffic areas where, for reasons of erosion and dust control or esthetics, a treatment other than paving is desired.

Treatments discussed are:

Shotcrete (gunite) Vegetation Spray-on-asphalt

Designated Sieve Amount Passing Sieve, %No. 10 20-100No. 40 10-70No. 200 3-25December 1993 700-44 Chevron Corporation

Civil and Structural Manual 700 Miscellaneous CivilShotcreteShotcrete is the generic name for the process of pneumatically projecting mortar or concrete at high velocity onto a surface. The name Gunite, often used inter-changeably with shotcrete, is one of a number of names for this application.

As an alternative to paving, shotcrete has been used extensively for:

Embankment stabilization

Improvement of hydraulics and side stabilization for ditches and channels

Surfacing under grade-level pipeways for improved drainage and appearance. It is effective for getting between lines and into areas which are difficult of access. See Section 600 for more details on this subject.

In general shotcrete is a structurally sound and durable material. It exhibits good bonding characteristics if properly applied. The strength of shotcrete is considered comparable to conventional concrete having the same composition. Shotcrete has a greater potential for shrinkage cracking because of a high-cement factor.

There are two types of shotcreting processes: dry mix and wet mix.

Dry-mix process. This process starts with a mixture of aggregate and cement. This material is carried by hose to a distribution nozzle using compre