02_Geotech Report 05215016R01 final.pdf

REPORT C OVER PAGE

Geotechnical Engineering Report

Omaha National Cemetery Expansion

Papillion, Nebraska

November 19, 2021

Terracon Project No. 05215016

Prepared for:

Anderson Engineering of Minnesota, LLC

Plymouth, Minnesota

Prepared by:

Terracon Consultants, Inc.

Omaha, Nebraska

Terracon Consultants , Inc. 15080 A Circle Omaha, Nebraska 68144

P (402) 330 2202 F (402) 330 7606 terracon.com

REPORT C OVER LETTER TO SIGN

November 19, 2021

Anderson Engineering of Minnesota, LLC

13605 1st Ave N, Suite 100

Plymouth, Minnesota 55441

Attn: Mr. Derek Siefert

P: (763) 412-4033

E: DSeifert@ae-mn.com

Re: Geotechnical Engineering Report

Omaha National Cemetery Expansion

14250 Schram Road

Papillion, Nebraska

Terracon Project No. 05215016

Dear Mr. Siefert:

We have completed the Geotechnical Engineering services for the above referenced project. This study was performed in general accordance with Terracon Proposal No. P05215016 dated April

18, 2021. This report presents the findings of the subsurface exploration and provides geotechnical recommendations concerning earthwork and the design and construction of foundations and floor slabs for the proposed Omaha National Cemetery Expansion project.

We appreciate the opportunity to work with you on this project. Please contact us if you have any questions concerning this report or if we may be of further service.

Sincerely, Terracon Consultants, Inc.

Amelia C. Ganze, P.E. Michael D. Ringler, P.E.

Senior Staff Engineer Senior Engineer

Distribution: Addressee (pdf)

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REPORT TOPICS

INTRODUCTION

SITE CONDITIONS

PROJECT DESCRIPTION

GEOTECHNICAL CHARACTERIZATION

GEOTECHNICAL OVERVIEW

EARTHWORK

SHALLOW FOUNDATIONS

SEISMIC CONSIDERATIONS

FLOOR SLABS

LATERAL EARTH PRESSURES AND DRAINAGE

PAVEMENTS

FROST CONSIDERATIONS

GENERAL COMMENTS

Note: This report was originally delivered in a web-based format. Orange Bold text in the report indicates a referenced section heading. The PDF version also includes hyperlinks which direct the reader to that section and clicking on the

GeoReport logo will bring you back to this page. For more interactive features, please view your project online at client.terracon.com.

ATTACHMENTS

EXPLORATION AND TESTING PROCEDURES

SITE LOCATION AND EXPLORATION PLANS

EXPLORATION RESULTS

SUPPORTING INFORMATION

http://client.terracon.com/

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INTRODUCTION

Geotechnical Engineering Report

Omaha National Cemetery Expansion

14250 Schram Road

Papillion, Nebraska Terracon Project No. 05215016

November 19, 2021

INTRODUCTION

This report presents the results of our subsurface exploration and geotechnical engineering services performed for the proposed expansion to the Omaha National Cemetery, located at

14250 Schram Road in Papillion, Nebraska.

The field exploration included four soil borings to depths ranging from approximately 15 to 20 feet below existing grades. Maps showing the site and boring locations are shown on Site Location and Exploration Plan, respectively. The results of the laboratory testing performed on soil samples obtained during the field exploration are included on the boring logs in Exploration

Results.

We understand three site concepts are under consideration for the layout and grading of the proposed expansion. We are providing recommendations for Concept A, and will revise the report if a different site concept is chosen.

The purposes of this exploration and report are to provide information and geotechnical engineering recommendations relative to:

■ Soil conditions ■ Seismic site classification per IBC

■ Groundwater conditions ■ Lateral earth pressures

■ Site preparation and earthwork ■ Pavement design and construction

■ Foundation design and construction ■ Frost considerations

■ Floor slab design and construction

SITE CONDITIONS

Item Description

Parcel

Information

The project is located at 14250 Schram Road in Papillion, Nebraska.

Latitude: 41° 8.17' N, Longitude: 96° 8.02' W. See Site Location.

Existing

Improvements Existing cemetery facilities.

Current Ground

Cover Based on our site visit, the planned expansion areas are grass covered.

Omaha National Cemetery Expansion ■ Papillion, Nebraska

November 19, 2021 ■ Terracon Project No. 05215016

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Item Description

Existing

Topography

Existing grades vary across the site and expansion locations. In general, the site slopes downward from the southeast towards the northwest.

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PROJECT DESCRIPTION

Item Description

Information Provided

Grading Plan, provided by AEM

Expansion Boundary Map, provided by AEM

Urn Crypt Details, provided by AEM

Casket Crypt Details, provided by AEM

Columbarium Details, provided by AEM

Project Description

The expansion will include a new casket crypt section (B-4), urn crypt section (B-1), and one new columbarium (B-2) for the existing Omaha

National Cemetery. A second columbarium (B-3) was initially planned, but has since been removed from the planned expansion to the cemetery.

Finished Floor Elevation Unknown

Maximum Loads

■ Walls: 2-3 kips per linear foot (klf)

■ Slabs: 150 pounds per square foot (psf)

Grading/Slopes

Urn Crypt: 9 feet of cut to 19 feet of grade-raise fill

North Columbarium: 5 feet of cut to 3 feet of fill

Casket Crypt: Less than 1 foot of cut or fill

Below Grade Structures The urn crypts will extend about 4¼ feet below final adjacent grades, and the casket crypts will extend about 6¼feet below final adjacent grades.

Free-Standing Retaining

Walls None

Pavements

A new drive lane will be constructed south of the new urn crypt plot.

Traffic information is not available. We assume low volumes of automobile traffic and weekly garbage trucks.

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GEOTECHNICAL CHARACTERIZATION

Subsurface Profile

We have developed a general characterization of the soil and groundwater conditions based upon our review of the boring information, the geologic setting, and our understanding of the project.

This characterization, termed GeoModel, forms the basis for our geotechnical evaluations and recommendations for site preparation and earthwork, foundations, pavements, and below-grade retaining walls. Conditions encountered at each boring location are indicated on the individual boring logs. The GeoModel and individual logs are provided in Exploration Results.

The GeoModel is based upon our boring information. Variations can occur between boring locations and across the site. Previous construction and grading may have created additional variations.

Groundwater Conditions

Groundwater was not observed in the borings while drilling or for the short duration the borings could remain open. However, this does not necessarily mean the borings terminated above groundwater.

A relatively long period is often necessary for a groundwater level to develop and stabilize in a borehole. Long term observations in piezometers or observation wells sealed from the influence of surface water would be necessary to define groundwater levels.

GEOTECHNICAL OVERVIEW

Borings B-2 and B-3 encountered fill soils to depths of about 3 to 5 feet, underlain by native loess soils consisting of lean clay and fat clay. Borings B-1 and B-4 encountered native loess soils to their completed depths.

The fill soils were reportedly placed under controlled conditions, and the samples from our borings generally appear to be moderately-well compacted. Based on this information, the existing fill may generally remain in place with a low risk of settlement. We recommend observation and testing of existing fill exposed at floor slab and pavement subgrade levels, as well as footing bearing level in foundation excavations as discussed in Earthwork and Shallow Foundations.

Grade raise of up to 19 feet is planned at the urn crypt. This amount of grade raise fill will result in settlements that could damage structures and pavements. . Therefore, we recommend these areas be brought to final grades and surcharge loaded prior to construction of structures and pavements.

Additional recommendations can be found in the Earthwork section.

High-moisture, low strength soils were encountered in all borings. Care will need to be taken during earthwork and in excavations for the casket crypts to avoid disturbing these soils. Consideration should be given to completing excavations in soft soils with remote equipment, such as a backhoe

Responsive ■ Resourceful ■ Reliable 5 with a smooth-mouth bucket. In addition, soil stabilization with a granular layer may be required to accommodate construction traffic. Additional recommendations may be found in the Earthwork section.

We understand a granular drainage layer with trench drains is planned below the urn crypts. With the expected high moisture soils, we recommend a similar drainage system be placed below the casket crypt.

The on-site soils generally appear suitable for support of a shallow foundation system, but the soft soils will limit allowable bearing pressures. The Shallow Foundations section addresses support of the building bearing on native clay soils and engineered fill.

We recommend floor slabs and pavements be underlain by a minimum of 8 inches of reworked and recompacted soils. The Floor Slabs section addresses slab-on-grade support of the structures.

The Pavements section addresses the design of pavement systems.

Support of floor slabs, foundations, and pavements on or above existing fill materials is discussed in this report. However, even with the recommended construction procedures, there is an inherent risk for the owner that compressible fill or unsuitable material within or buried by the fill will not be discovered. This risk of unforeseen conditions cannot be eliminated without completely removing the existing fill, but can be reduced by following the recommendations contained in this report. To take advantage of the cost benefit of not removing the entire amount of undocumented fill, the owner must be willing to accept the risk associated with building over the undocumented fills.

Should this be the case, structures can be supported on a shallow foundation system.

The General Comments section provides an understanding of the report limitations.

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EARTHWORK

Site Preparation

Stripping of all existing vegetation, organic topsoil, and any other materials unsuitable for re-use as engineered fill should be performed within all cut, fill, structure, and pavement areas. A stripping depth of about 6 to 9 inches is expected to be adequate in grassy areas; however, areas requiring deeper stripping may be encountered. We recommend that site stripping and subgrade preparation procedures extend at least 5 feet beyond the columbarium slab and urn and casket crypts, and 2 feet beyond new pavements, where feasible. A Terracon geotechnical representative should help evaluate actual stripping depths at the time of construction.

Grade raise fill is planned at the urn crypt site. This area is on an existing slope. Slippage can occur if fill is placed on slopes steeper than about 5 horizontal to 1 vertical (5H:1V). Therefore, we recommend that slopes steeper than about 5H:1V be flattened or benched prior to placing fill. We recommend this process consist of removing vegetation and sod, and then forming benches or horizontal steps wide enough to accommodate construction equipment and separated by vertical risers less than 3 feet high.

Clay soils with high moisture contents will be encountered across the site, in particular these soils are expected in the casket crypt excavations. These soils will be easily disturbed by construction traffic, and scarification and recompaction may not be sufficient to provide a stable subgrade in wet areas. Therefore, we recommend unstable subgrade soils be undercut and replaced with crushed stone. If the depth of instability extends more than 2 feet below grade, placement of geogrid reinforcement would help limit the undercut depth. Geotextile or geogrid should ideally be installed after underground work, such as utility construction, is completed. Equipment should not be operated above the fabric or geogrid until one full lift of crushed stone fill is placed above

it. The maximum particle size of granular material placed over geotextile fabric or geogrid generally should not exceed 1½ inches. Gradation requirements for granular material provided by the geosynthetic product manufacturer should be verified prior to material purchase and delivery to the site. As the casket crypts will be below grade, we recommend trench drains be included below the granular stabilizing layer. A sump pit and pump may also be required, to remove water that will accumulate in the granular layer, unless the trench drains are connected to a storm drain system or can outlet to a nearby slope.

We recommend a layer of compacted cohesive fill be installed below the columbarium floor slab and aggregate base, and also below exterior pavements. We recommend this layer be formed by cutting to approximate subgrade, and then scarifying the exposed soil to a depth of about 8 inches, moisture-conditioning as needed, then recompacting as recommended in Fill

Compaction Requirements below. Scarified soil which cannot be recompacted to the recommended compaction level should undercut and replaced with stable fill.

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Prior to placing fill in areas to receive fill, the subgrade should be proofrolled in the presence of a

Terracon geotechnical representative. Proofrolling aids in providing a firm base for compaction of fill and delineating soft, or disturbed areas that may exist below subgrade level. Unsuitable areas observed at this time should be improved by scarification and recompaction or by undercutting and replacement with structural fill. Proofrolling may be accomplished with a fully loaded, tandem-axle, dump truck with a minimum gross weight of 25 tons or other equipment providing an equivalent subgrade loading. Please note, proofrolling should not be completed within the urn and casket crypts, due to the presence of high moisture, low strength soils.

Terracon should be retained to monitor stripping, subgrade stability, existing fill and structure removal, utility abandonment, site excavation, removal of unsuitable materials, and proofrolling.

Terracon can assist in identifying existing fill soils or low-strength native soils that should be undercut and removed, as well as identifying additional corrective measures for conditions that may become apparent during construction.

Fill Material Types

Structural fill should meet the following material property requirements:

Fill Type USCS Classification Acceptable Location for Placement

Low-plasticity, cohesive soil

CL

(LL ≤ 45 and 10 ≤ PI ≤ 20) 2 All locations and elevations.

Granular 3 SP, SW, GW Below interior slabs-on-grade.

Drainage Fill 4 SP, SW, GW Free-draining granular fill.

“Working Platform”

As a working layer across excavations exposing high-moisture soils.

On-site soil

6 CL

Some of the on-site soils are suitable for use as low-plasticity cohesive fill.

1. Structural fill should consist of approved materials that are free of organic matter or debris. Frozen material should not be used, and fill should not be placed on a frozen subgrade. Each proposed fill material should be sampled and evaluated by the geotechnical engineer prior to its delivery and/or use.

2. LL = Liquid Limit, PI = Plasticity Index. Moderate to high plasticity clay soils (LL>45 and PI>25) that do not meet the criteria presented above were encountered in the boring; however, these soils are expected to be buried by the planned grade raise fill and are not expected to be exposed during floor slab and foundation construction.

3. A well graded granular material, with 100 percent passing the 1-inch sieve, less than 6 percent passing the No. 200 sieve. Terracon can review proposed materials. Using a material similar to NDOT

Crushed Rock for Base Course, with 6% or less fines (material passing the #200 sieve) for this layer will improve subgrade stability during compaction and slab construction.

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Fill Type USCS Classification Acceptable Location for Placement

4. Well-graded, free-draining granular material. A general gradation should be 100% passing the 1½-inch sieve, about 40 percent passing the No. 10 sieve, and less than 6 percent fines. Terracon can review proposed materials. NDOT 47B Fine Aggregate for Concrete or approved alternative.

5. Well-graded crushed stone or crushed concrete with a maximum particle size of about 2 inches and less than about 10 percent fines. Terracon can review proposed materials.

6. Sorting of topsoil and on-site soils containing debris, organics, etc., will be necessary. Delineation of unsuitable on-site soils should be performed in the field by a Terracon representative. Moisture conditioning of the on-site soils will be necessary to facilitate compaction.

Terracon should be retained to evaluate proposed fill materials, including sampling and performing laboratory tests on proposed fill to evaluate compliance with the project specifications. We can also review data for proposed materials which are generated by the contractor or suppliers.

Fill Compaction Requirements

Structural fill should meet the following compaction requirements.

Item Structural Fill

Maximum Lift

Thickness

8 inches or less in loose thickness when heavy, self-propelled compaction equipment is used

4 to 6 inches in loose thickness when hand-operated equipment (i.e.

jumping jack or plate compactor) is used

9 to 12 inches for a granular stabilization layer on soft or wet clay subgrade

Minimum Compaction

Requirements 1, 2, 3, 4

98% of maximum within upper 8 inches of finished pavement subgrade

95% of maximum all other locations

Water Content Range

Low plasticity cohesive: -2% to +3% of optimum

Granular: Workable moisture levels

1. Maximum density and optimum water content as determined by the standard Proctor test (ASTM D

698).

2. If the granular material is a coarse sand or gravel, or of a uniform size, or has a low fines content, compaction comparison to relative density may be more appropriate. In this case, granular materials should be compacted to at least 70% relative density (ASTM D 4253 and D 4254).

3. Crushed stone / crushed concrete placed over a subgrade composed of wet or soft clay should not be overcompacted; overcompaction can cause subgrade disturbance and loss of strength of the underlying subgrade. In these areas, we recommend that the granular layer be drifted into place in advance of compaction equipment. Compaction be accomplished with 2 or 3 mutually perpendicular passes of each thin lift with light-weight vibratory compaction equipment. Instead of a strict compaction requirement, consideration should be given to using visual evaluation of material stability using factors such as surface stability and aggregate interlock when evaluating compaction and performance of the granular material.

4. Consideration can be given to compacting all fill below pavements to 95% during mass grading.

Immediately prior to paving, we recommend that the subgrade below exterior pavements be rough-graded as needed, and then scarified and recompacted. We recommend this process include

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Item Structural Fill scarifying the subgrade to a depth of about 8 inches, moisture conditioning the scarified soil to within

-2 to +3 percent of the material’s optimum, and compacting the scarified soil to at least 98%. Scarified soils which cannot be recompacted to this degree should be undercut and replaced with stable material.

5. Specifically, moisture levels should be maintained low enough to allow for satisfactory compaction to be achieved without the cohesionless fill material pumping when proofrolled or containing excess water (ponding).

We recommend the following frequencies of testing for structural fill:

Each lift of compacted fill should be tested, evaluated, and reworked as necessary until approved by Terracon personnel prior to placement of additional lifts. We recommend the following frequencies of testing for structural fill:

◼ one test for every 2,500 square feet of compacted fill in the building areas

◼ one test for every 5,000 square feet in pavement areas

◼ one test for every 50 linear feet of compacted utility trench or foundation wall backfill.

Settlement

Discussion

The expected grade raises will cause stress increases extending into the loess soils. The soils will respond by consolidating and causing settlement. We estimate the proposed grade raise will cause settlements of up to 2 to 4 inches within the area of the greatest amount of grade raise. Therefore, we recommend these structures be preloaded and surcharge loaded where more than 4 feet of grade raise is planned prior to construction of the urn crypt and south columbarium , as discussed in the following sections. It should be noted that significant grade raise fill placed adjacent to existing structures or pavements could result in cracking of pavements and differential settlement of the existing structures.

Preload Fill and Surcharge Fill Placement

Although in lean clay soils, about ¼ to ½ of the consolidation settlement commonly occurs during fill placement, consolidation settlement requires additional time to occur and therefore affects the project schedule. We recommend the preload and surcharge fill be placed as early in the grading process as possible. We also recommend settlement monitoring be performed, as discussed below, to measure actual settlement magnitude and time frame.

We recommend the preloading and surcharge loading process be initiated by placing permanent fill up to final grade or floor slab subgrade level, whichever is greater, within the urn crypt footprint; and for a distance of 20 feet beyond the structures’ perimeter. Permanent fill should be placed and compacted according to the recommendations presented in Fill Compaction Requirements. We

Responsive ■ Resourceful ■ Reliable 10 then recommend placing preload fill and surcharge fill to a vertical distance of at least 5 feet above exterior final grade. The preload fill and top of surcharge fill should extend at least 15 feet laterally beyond the exterior of the structure perimeters. In areas within a structure footprint where there is a transition from surcharge fill to no surcharge fill, the side slopes should be about 4H:1V. The side slopes can be about 1H:1V around the exterior of the building.

We will review the preload/surcharge plans to confirm that our recommendations have been interpreted as intended. The as-built configuration of the preload/surcharge fill should be verified by an as-built survey.

The preload fill and surcharge fill can be tracked into place with loaded scrapers or dump trucks, in lifts of 12 inches or less in loose thickness. A minimum compaction criterion is not required, but the as placed material should have a minimum in situ wet unit weight of 100 pcf. It would be possible to use fill soils which would later be used to raise site grades outside the building area for the preload/ surcharge fill. Topsoil strippings / unsuitable material could also be used for preload/ surcharge material.

Settlement Monitoring

After placing the permanent fill, and prior to placing preload or surcharge fill, survey monuments should be installed for settlement monitoring. We recommend a minimum of three settlement plates in for the Urn Crypt. The monuments should consist of 2-foot square steel plates firmly embedded on the permanent fill, with metal riser pipe coupled to the top of the settlement plate and extending above the surcharge fill. Plastic pipe should be installed around the steel riser pipes. Care should be taken not to disturb the monuments during surcharge fill placement. A monument which is damaged or disturbed should be repaired or replaced immediately.

We recommend surveying the elevations of the settlement monuments to the nearest 100th of a foot, and the elevation of the top of the adjacent fill to the nearest 10 th of a foot, according to the following schedule:

Time Period Monitoring Schedule

At Time of Monument Seating Initial Readings

During Surcharge Fill Placement Daily

For Two Weeks Following Surcharge Fill Placement Three times per week

More than Two Weeks Following Surcharge Fill Placement Two times per week

The monitoring data should be submitted to Terracon for analysis and evaluation of when construction may proceed. A settlement period of 4 to 8 weeks is estimated. This is only an estimate based on our experience with projects of this type and the soil conditions encountered.

Other factors affecting the effective drainage path and permeability of the soils may reduce the time for the settlement to occur. We anticipate at least 2 to 3 weeks of settlement data will be

Responsive ■ Resourceful ■ Reliable 11 required before we can begin evaluation of eventual total settlements and refinement of our time frame estimates.

Utility Trench Bedding and Backfill

All trench excavations should be made with sufficient working space to permit construction, including backfill placement and compaction. Utility trenches are a common source of water infiltration and migration. If utility trenches are backfilled with relatively clean granular material, they should be capped with either paving or at least 18 inches of cohesive fill to reduce the infiltration and conveyance of surface water through the trench backfill.

We also recommend constructing an effective clay “trench plug” that extends at least 5 feet out from the face of the building exterior. The plug material should consist of either cementitious flowable fill or low permeability clay. The trench plug should be placed to completely surround the utility line.

Construction Considerations

Any areas of standing surface water should be drained as far in advance of construction as possible.

Any saturated soils should be removed prior to placing fill or proceeding with construction.

The clays encountered in the borings will be sensitive to disturbance from construction activity and water seepage. If precipitation occurs immediately prior to or during construction, the near-surface clay soils could increase in moisture content and become more susceptible to disturbance.

Construction activity should be monitored, and should be curtailed if the construction activity is causing subgrade disturbance. A Terracon representative can help with monitoring and developing recommendations to avoid subgrade disturbance.

Surface water should not be allowed to pond and soak into the soil during construction. Construction staging should provide drainage of surface water and precipitation away from the columbarium and pavement areas. Any water that collects over or adjacent to construction areas should be promptly removed, along with any softened or disturbed soils. Surface water control in the form of sloping surfaces, drainage ditches and trenches, and sump pits and pumps will be important to avoid ponding and associated delays due to precipitation and seepage.

Upon completion of filling and grading, care should be taken to maintain the subgrade moisture content prior to construction of slabs and pavements. Construction traffic over the completed subgrade should be avoided. The site should also be graded to prevent ponding of surface water on the prepared subgrades or in excavations. If the subgrade should become frozen, desiccated, saturated, or disturbed, the affected material should be removed or these materials should be scarified, moisture conditioned, and recompacted prior to slab and pavement construction.

As a minimum, all temporary excavations should be sloped or braced as required by Occupational

Safety and Health Administration (OSHA) regulations to provide stability and safe working conditions. Construction site safety is the sole responsibility of the contractor who controls the

Responsive ■ Resourceful ■ Reliable 12 means, methods, and sequencing of construction operations. All excavations should comply with applicable local, state and federal safety regulations, including the current OSHA Excavation and

Trench Safety Standards.

Exterior Grading

Poor site drainage and ponding of surface water can increase the potential for frost heave or settlement. Excessive moisture can reduce bearing capacity and contribute to slab and pavement settlement and cracking.

Finished grading slopes should promote drainage away from the new structures and pavements.

We recommend final grades for seeded and landscaped areas be sloped at least 5 percent within

10 feet around the structures. We recommend cohesive backfill be placed in utility trenches and adjacent to building foundations and curbs, and this fill be compacted to at least 95 percent of standard Proctor maximum dry density to help prevent surface water infiltration. Roof drains should be extended to discharge on pavements or in lawn areas more than 5 feet from the buildings.

Pavements or sidewalks installed adjacent to the building should slope away from the building at a grade of 2% or more.

Overwatering of grass or landscaping vegetation is a significant source of water, and should be avoided near the columbarium and pavements. Sprinkler heads should be adjusted to miss the exterior building walls and pavements. Automated watering systems should be programmed to not run after natural rain events, and to not overwater. Any utility leaks should be promptly repaired.

Lining the bottom of irrigated planter areas along the buildings with an impermeable moisture barrier, and installing tile lines leading to gravity outlets or sump pits and pumps, would also help to control surface water that infiltrates into these features.

SHALLOW FOUNDATIONS

Design Parameters – Compressive Loads

In our opinion, the proposed structures can be supported by a shallow, spread footing foundation system bearing on tested and approved soil. Design recommendations for shallow foundations are presented in the following table.

Design Recommendations – Spread Footing Foundations

Description Column Wall

Net allowable soil bearing pressure 1 1,500 psf 1,500 psf

Minimum dimensions 30 inches 18 inches

Minimum embedment 42 inches 42 inches

Estimated total settlement 3 < 1 inch < 1 inch

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Design Recommendations – Spread Footing Foundations

Description Column Wall

Estimated differential settlement 3 2/3-inch between columns 2/3-inch over 30 feet

1. The recommended net allowable bearing pressure is the pressure in excess of the minimum surrounding overburden pressure at the footing base elevation. Assumes disturbed or soft soils, will be undercut and replaced with engineered fill.

2. For perimeter footings and footings in unheated areas. For frost protection and to reduce the effects of seasonal moisture variations in the subgrade soils. If construction extends into freezing weather, we recommend that either all footings extend to frost depth (as measured from adjacent grade at the time of construction) or that the foundations be protected from the elements by straw, frost blankets, or similar means.

3. The foundation settlement will depend upon the variations within the soil profile, the structural loading conditions, the embedment depth of the footings, the thickness of compacted fill, and the quality of the earthwork operations. The above settlement estimates assume the maximum footing size is 5 feet for column footings, 2 feet for continuous footings, and relatively uniform loading.

Design Parameters - Uplift Loads

Uplift resistance of spread footings can be developed from the effective weight of the footing and the overlying soils. As illustrated on the subsequent figure, the effective weight of the soil prism defined by diagonal planes extending up from the top of the perimeter of the foundation to the ground surface at an angle, , of 20 degrees from the vertical can be included in uplift resistance. The maximum allowable uplift capacity should be taken as a sum of the effective weight of soil plus the dead weight of the foundation, divided by an appropriate factor of safety. A maximum total unit weight of 100 pcf should be used for the backfill. This unit weight should be reduced to 40 pcf for portions of the backfill or natural soils below the groundwater elevation.

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Foundation Construction Considerations

Terracon should be retained to observe and test the bearing materials exposed in all foundation excavations. If disturbed or otherwise unsuitable bearing materials are encountered in a footing excavation, the excavation should be extended deeper, as necessary, to suitable materials. The footing could bear directly on the suitable materials at the lower level or on lean concrete backfill placed back up to design bearing level. The footings could also bear on approved, properly compacted backfill extending down to the suitable materials. Overexcavation for compacted backfill placement below footings should extend laterally at least 8 inches beyond the edges of the footings for each foot of depth below footing base elevation. The overexcavation should then be backfilled up to the footing base elevation with approved fill placed and compacted as recommended in Earthwork. The adjacent figures depict these options.

The clay soils on this site are susceptible to disturbance from construction activities, particularly if the soils have high natural moisture contents or become wetted by surface water or seepage.

Care should be taken during excavation and construction of footings to avoid disturbing the bearing soils. The base of all foundation excavations should be free of water and loose material prior to placement of concrete. Concrete should be placed within a few hours after excavating to reduce disturbance of the bearing materials. If the materials at bearing level become excessively dry, disturbed or saturated, the affected material should be removed prior to placing concrete.

SEISMIC CONSIDERATIONS

Based upon the results of the borings, we estimate the project site as “Site Class D” according to the 2012 International Building Code (IBC), which references Chapter 20 of ASCE-7. This site class assumes that soils similar to the native soils encountered at the bottom of the borings continue to a depth of 100 feet. A more detailed and accurate Site Class evaluation can be achieved by retaining Terracon to perform a deeper soil boring or to use the SeisOpt®ReMi™ method to develop the full depth shear wave profile.

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FLOOR SLABS

Design Recommendations

Item Description

Floor slab support 1

Aggregate base (see below) underlain by low-plasticity cohesive fill or a granular stabilizing layer prepared according to Earthwork.

Modulus of subgrade reaction 2 100 pounds per square inch per inch (psi/in) for point loading conditions.

Aggregate base course/capillary break 3 4 inches of free draining granular material

1. Floor slabs should be structurally independent of any building footings or walls to reduce the possibility of floor slab cracking caused by differential movements between the slab and foundation.

2. Modulus of subgrade reaction is an estimated value based upon our experience with the subgrade condition, the requirements noted in Earthwork, and the floor slab support as noted in this table. It is provided for point loads. For large area loads the modulus of subgrade reaction will be lower.

3. The floor slab design should include a capillary break, comprised of compacted, granular material, as described in Earthwork.

Slabs-on-grade should be isolated from structures and utilities to allow independent movement.

Joints should be constructed at regular intervals as recommended by the American Concrete

Institute (ACI) to help control the location of any cracking. Keyed and doweled joints should be considered. The owner should be made aware that differential movement between the slabs and foundations could occur.

The use of a vapor retarder should be considered beneath concrete slabs on grade that will be covered with wood, tile, carpet or other moisture sensitive or impervious coverings, or when the slab will support equipment sensitive to moisture. When conditions warrant the use of a vapor retarder, the slab designer should refer to ACI 302 and/or ACI 360 for procedures and cautions regarding the use and placement of a vapor retarder.

Construction Considerations

On most project sites, the floor slab subgrades are developed early in the construction phase.

However as construction proceeds, the subgrade may be disturbed due to utility excavations, construction traffic, desiccation, rainfall, etc. As a result, the floor slab subgrade may not be suitable for placement of base rock and concrete and corrective action will be required.

We recommend the floor slab subgrade be rough graded and then proofrolled with a loaded tandem axle dump truck prior to fine grading and placement of base rock. Particular attention should be paid to high traffic areas that were rutted and disturbed earlier and to areas where backfilled trenches are located. Areas where unsuitable conditions are located should be repaired by removing and replacing the affected material with compacted fill. All floor slab subgrades should

Responsive ■ Resourceful ■ Reliable 16 be moisture conditioned and properly compacted to the recommendations in this report immediately prior to placement of the aggregate base course and concrete.

LATERAL EARTH PRESSURES AND DRAINAGE

Design Parameters

The lateral earth pressure recommendations given in this section are applicable to the design of rigid retaining walls subject to slight rotation, such as cantilever, or gravity type concrete walls.

These recommendations are not applicable to the design of modular-block retaining walls (also termed segmental retaining walls).

Reinforced concrete walls with unbalanced backfill levels on opposite sides should be designed for earth pressures at least equal to those indicated in the following table. Earth pressures will be influenced by structural design of the walls, conditions of wall restraint, methods of construction and/or compaction and the strength of the materials being restrained. Two wall restraint conditions are shown. Active earth pressure is commonly used for design of free-standing cantilever retaining walls and assumes wall movement. The "at-rest" condition assumes no wall movement. The recommended design lateral earth pressures do not include a factor of safety and do not provide for hydrostatic pressure on the walls.

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Earth Pressure Coefficients

Earth Pressure

Conditions

Coefficient for

Backfill Type

Equivalent Fluid

Density (pcf)

Surcharge

Pressure, p1 (psf)

Earth Pressure, p2 (psf)

Active (Ka) Granular - 0.33

Lean Clay - 0.42

(0.33)S

(0.42)S

(40)H

(50)H

At-Rest (Ko) Granular - 0.46

Lean Clay - 0.50

(0.46)S

(0.50)S

(55)H

(60)H

Passive (Kp) Granular - 3.0

Lean Clay - 2.4

Applicable conditions to the above include:

■ For active earth pressure, wall must rotate about base, with top lateral movements of about

0.002 H to 0.004 H, where H is wall height

■ For passive earth pressure to develop, wall must move horizontally to mobilize resistance.

■ Uniform surcharge, where S is surcharge pressure

■ In-situ soil backfill weight a maximum of 120 pcf

■ Horizontal backfill, compacted between 95 and 98 percent of standard Proctor maximum dry density

■ No hydrostatic pressure acting on wall

■ No loading from compaction equipment

■ No loading from nearby footings or slabs

■ No dynamic loading

■ No safety factor included in soil parameters

■ Ignore passive pressure in frost zone

Backfill placed against structures should consist of granular drainage fill or low plasticity cohesive soils. For the granular values to be valid, the granular backfill must extend out from the base of the wall at an angle of at least 45 and 60 degrees from vertical for the active and passive cases, respectively. To calculate the resistance to sliding, a value of 0.45 should be used as the ultimate coefficient of friction between the footing and the underlying soil.

To control the water level behind the retaining wall, we recommend a perimeter drain be installed behind the wall as described in Drainage of Cantilever Retaining Walls. If this is not possible, then combined hydrostatic and lateral earth pressures should be calculated using the values shown in the following table.

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Undrained Lateral Earth Pressure Parameters

Backfill Type Active Condition 1, 2 At-Rest Condition 1, 2

Clay Backfill 85 pcf 96 pcf

Granular Backfill 83 pcf 91 pcf

1. These pressures do not include the influence of surcharge, equipment, or floor loading, which should be added.

2. Calculated using a saturated soil unit weight of 125 pcf.

These pressures do not include the influence of surcharge, equipment or floor loading, which should be added. Footings and other loads located adjacent to walls may have a significant effect on lateral pressures. Placement of footings in wall backfill should be avoided unless structural analyses are performed to evaluate the resulting loads and effects on the wall. To avoid excessive lateral wall loads, heavy compaction equipment should not be operated within a distance out from new or existing walls equal to the height above the base of the wall.

Drainage of Cantilever Retaining Walls

A perforated rigid plastic or metal drain line should be installed behind the walls to prevent hydrostatic loading on the walls. The invert of a drain line around the walls should be at least 6 inches below the adjacent slabs. The drain line should be sloped to provide positive gravity drainage to a sump or other suitable outlet. The drain line should be surrounded by free-draining granular material graded to prevent the intrusion of soil fines into the granular material or the intrusion of the granular material into the drain pipe perforations. Alternatively, a coarse, clean, free-draining granular material could be used to surround the pipe if this material is encapsulated with suitable filter fabric.

At least a 2-foot wide section of free-draining granular fill is recommended for backfill above the drain line and adjacent to the wall and should extend up to the slab;

if the drain pipe is around the exterior of the building, then a cohesive fill cap should be installed as shown in the schematic.

A prefabricated drainage structure may be used above a drain line and the surrounding filter, in lieu of free-draining granular fill. A prefabricated drainage structure is a plastic drainage core or mesh which is covered with filter fabric to prevent soil intrusion, and is fastened to the wall prior to placing backfill.

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PAVEMENTS

General Pavement Comments

The pavements should be underlain by a layer of compacted fill prepared in accordance with the recommendations presented in Earthwork. Typical construction in this area is not to place a granular base below pavements for this type of project. Rather, the pavements are supported directly on the cohesive subgrade soils. Installing finger drains along low points of pavements and around intakes should be considered. If the project design results in a granular base being installed below pavements, Terracon should be retained to provide additional recommendations. For example, subdrains are recommended in conjunction with a granular base to prevent water from ponding in the granular base.

Design Recommendations

We recommend the design and thicknesses for new pavements be consistent with the existing pavements at the site.

Terracon has observed dishing in some parking lots surfaced with ACC. Dishing is usually observed in frequently-used parking stalls (such as near the front of the building), and occurs under the wheel footprint in these stalls. The use of higher grade asphaltic cement such as PG70-34, or surfacing these areas with PCC, is recommended. The dishing is exacerbated by factors such as irrigated islands or planter areas, sheet surface drainage to the front of the building, and placing the ACC directly on a compacted clay subgrade. The use of lower grade asphalt cement, such as PG64-34 is relatively common in this area and may be considered, but would provide lower reliability against rutting and creeping during warm weather.

Proper joint spacing will also be required to prevent excessive slab curling and shrinkage cracking. Joints should be sealed to prevent entry of foreign material and dowelled where necessary for load transfer. The contractor should submit a joint layout plan for approval by the engineer prior to placement of concrete. The plan should identify the location of all joints in the pavement which should be designed to avoid acute angles in accordance with the guidance in

ACI 330R-33 sections 3.7, 3.11 and Figure C.1 Typical Joint Layout for Parking Area.

Where practical, we recommend early-entry cutting of crack-control joints in PCC pavements.

Cutting of the concrete in its “green” state typically reduces the potential for micro-cracking of the pavements prior to the crack control joints being formed, compared to cutting the joints after the concrete has fully set. Micro-cracking of pavements may lead to crack formation in locations other than the sawed joints, and/or reduction of fatigue life of the pavement.

We recommend joints be sealed to help prevent moisture infiltration, including a sprayed concrete sealer and a hot-pour joint sealer. The use of backer rods is not recommended.

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In addition to the joint sealing recommendations above, modifying the concrete mix can also be considered to improve the durability of the concrete. To reduce Alkali Silica Reactivity (ASR) and help reduce the concrete permeability, consideration should be given to using Type IP or IPF

(Duracem F) cement. Other pozzolans such as slag can also be considered to decrease permeability. We also recommend a water-reducing admixture be utilized to facilitate a water-cement ratio or not more than 0.42, preferably closer to 0.40. A ready-mixed concrete producer, local to the project, should be consulted regarding mix performance and material availability. In addition, a mix design prepared in accordance with ACI 211.5R should be submitted for review by the design team prior to construction.

Periodic maintenance will extend the service life of the pavements and should include patching and repair of deteriorated areas, crack sealing, and surface sealing.

Construction Considerations

Construction scheduling often involves grading and paving by separate contractors and can involve a time lapse between the end of grading operations and the commencement of paving.

Disturbance, desiccation or wetting of the subgrade soils between grading and paving can result in deterioration of the previously completed subgrade. A non-uniform subgrade can result in poor pavement performance and local failures relatively soon after pavements are constructed. We recommend the moisture content and density of the subgrade be evaluated within two days prior to commencement of actual paving operations. A proof roll using heavy equipment similar to that required for pavement construction is recommended to verify subgrade stability for pavement construction. Scarification and recompaction may be required.

Areas not in compliance with the required ranges of moisture or density should be moisture conditioned and recompacted. If significant precipitation occurs after the evaluation or if the surface becomes disturbed, the subgrade condition should be reviewed by Terracon personnel immediately prior to paving.

Drainage Considerations

Preventing subgrade saturation is an important factor in maintaining the subgrade strength. Water allowed to pond on or next to pavements could saturate the subgrade and cause premature pavement deterioration. Positive surface drainage should be provided away from the edges of paved areas, and all pavements should be sloped to provide rapid surface drainage. Pavements should drain toward the edges rather than the center, and perimeter subsurface drains should be installed next to irrigated planters or other areas where surface water could pond.

FROST CONSIDERATIONS

The clayey soils on this site are considered frost susceptible. Grade-supported exterior slabs are expected to heave. The amount of heave may be reduced by providing surface drainage away

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Consideration should be made to installing drain-tile around the perimeter of exterior slabs that connect directly to the storm drainage system to help further reduce the potential for frost heave.

GENERAL COMMENTS

Terracon should be retained to review the final design plans and specifications so comments can be made regarding interpretation and implementation of our geotechnical recommendations in the design and specifications. In the event that changes in the nature, design, or location of the project as outlined in this report are planned, the conclusions and recommendations contained in this report shall not be considered valid unless Terracon reviews the changes and either verifies or modifies the conclusions of this report in writing. Terracon also should be retained to provide observation and testing services during grading, excavation, construction, paving and other earth-related construction phases of the project. Site safety, excavation support, and dewatering requirements are the responsibility of others.

The analysis and recommendations presented in this report are based upon our understanding of the project, the data obtained from the borings performed at the indicated locations, and from other information discussed in this report. This report does not reflect variations that may occur between borings, across the site, or due to the modifying effects of construction or weather.