21-124_Geotech Report_Signed.pdf

REPORT C OVER PAGE

Geotechnical Engineering Report

21-124 VAMC (John Cochran) St. Louis – EHRM Upgrades

St. Louis, Missouri

March 17, 2022

Terracon Project No. 15215343

Prepared for:

Apogee Consulting Group, P.A.

Cary, NC

Prepared by:

Terracon Consultants, Inc.

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REPORT TOPICS

INTRODUCTION

SITE CONDITIONS

PROJECT DESCRIPTION

GEOTECHNICAL CHARACTERIZATION

GEOTECHNICAL OVERVIEW

DEEP FOUNDATIONS

SEISMIC CONSIDERATIONS

GENERAL COMMENTS

ATTACHMENTS

15185268 VAMC – SLJC Project Book Geotech Report

15185268 VAMC – SLJC Project Book_Site-Specific Ground Response Report – Revision 1

INTRODUCTION

Geotechnical Engineering Report

21-124 VAMC (John Cochran) St. Louis – EHRM Upgrades

915 N Grand Blvd

St. Louis, Missouri Terracon Project No. 15215343

March 17, 2022

INTRODUCTION

This report presents our foundation recommendations for the proposed EHRM tower addition to be located at 915 N Grand Blvd in St. Louis, Missouri. Our recommendations are based on geotechnical data previously collected by Terracon for other projects at the VAMC, and our experience near the project site. The purpose of these services is to provide information and geotechnical engineering recommendations relative to:

■ Subsurface soil (and rock) conditions ■ Foundation design and construction

■ Groundwater conditions ■ Seismic site classification per IBC

Terracon reviewed borings drilled in 2019 for the SLJC Project Book project. The locations of the borings and results of the laboratory testing performed on soil samples obtained from the site during the field exploration are included on the boring logs within the attached 2019 SLJC Project

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

SITE CONDITIONS

The following description of site conditions is derived from our site visit and our review of publicly available geologic and topographic maps.

Item Description

Parcel Information The project is located at 915 N Grand Blvd in St. Louis, Missouri.

Latitude: 38.6422ºN, Longitude: 90.2307ºW (See Exhibit D)

Existing

Improvements

The proposed tower addition will be located between the existing buildings, and the end of an alleyway.

Current Ground

Cover The existing surface in the area of the proposed tower addition is concrete.

Existing Topography The area between the buildings is level.

21-124 VAMC (John Cochran) St. Louis – EHRM Upgrades ■ St. Louis, Missouri

March 17, 2022 ■ Terracon Project No. 15215343

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Item Description

Geology

Based on the Geological Map provided by the United States Geologic Survey

(USGS), the subject site is located over the Meramecian Series. The

Meramecian Series consists of the St. Louis Limestone, Salem Formation, and

Warsaw Formation. These units are characterized by massive, argillaceous, and fossiliferous limestone.

A sinkhole area is mapped approximately 1,500 feet to the west of the site, but no sinkholes are mapped on the site itself. A seismic fault is mapped approximately 3,500 feet east of the site.

PROJECT DESCRIPTION

Our initial understanding of the project was provided in our proposal and was discussed during project planning. A period of collaboration has transpired since the project was initiated, and our final understanding of the project is as follows:

Item Description

Information Provided

Our understanding of the project is from conversations and email correspondence with the Client and provided 95% CD Plan Sheets numbered 01-G1000, 01-G1001, 01-SF101, 01-SF102, 01-SF300, 01-SF500 and 01-SF501 C101 and S101 provided by the Client dated

February 24, 2022.

Project Description The project will include the construction of a new nine-story tower addition with a basement. Each level of the structure has a footprint of 11 ft. x 19.25 ft.

Proposed Structure

We understand the addition will include structural steel framing supported by reinforced concrete basement walls, which are in turn supported by either helical piles or micropiles designed for a service load of 50 kips each.

Finished Floor

Elevation (FFE)

According to the provided plans, the basement level FFE will be 18.5 ft.

below the main level, at-grade FFE.

Grading/Slopes

We have considered about 19 feet of excavation and associated wall backfill will be required to construct the basement level. Besides the basement, general site grading is expected to be limited to approximately 2 feet of cut and/or fill and no permanent slopes are anticipated.

Free-Standing

Retaining Walls None anticipated

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GEOTECHNICAL CHARACTERIZATION

Subsurface Profile

Due to site constraints, Terracon was unable to perform a boring near the proposed tower addition location, instead we are utilizing existing data to develop our recommendations. Some contingency for variation of top of bedrock elevation should be included in the overall design specifications. Based on our nearby geotechnical data and publicly available resources we have developed the following estimate of subsurface conditions.

Approximate

Depth (feet) Material General Description

1 Concrete Estimated to be approximately 6 to 12 inches thick

2 Base Rock Estimated to be approximately 6 to 12 inches thick

5 to 20 Existing Fill

Lean clay and fat clay with variable amounts of sand, gravel, and brick, estimated to be approximately 5 to 20 feet thick, with greater depths immediately adjacent to the existing basement walls.

25 to 40 Lean to Fat

Clay

Lean to fat clay, transitioning to more fat clay with depth, variable amounts of sand and gravel, estimated to be approximately 5 to

30 feet thick (depending upon existing fill depth)

Below 25 to 40 Bedrock Limestone bedrock, a thin layer of weathered limestone bedrock is likely present above the intact bedrock

Groundwater Conditions

The previously completed boreholes were observed while drilling for the presence and level of groundwater, prior to introducing water into the holes at a depth of 20 feet when wash boring methods were implemented. Groundwater was only observed in Boring B-6 at a depth of about 16 feet below the ground surface. Groundwater was not observed in the remaining borings prior to utilizing mud rotary drilling.

The overburden soils are generally clayey and of low permeability. Therefore, a relatively long period of time may be 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 are often required to define groundwater levels in materials of this type.

Groundwater level fluctuations occur due to seasonal variations in the amount of rainfall, runoff, and other factors not evident at the time the borings were performed. In addition, perched water can develop over low permeability soil and rock strata, particularly in the existing fill. Therefore, groundwater levels during construction or at other times in the life of the structures may be different from the levels indicated on the boring logs. The possibility of groundwater level

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GEOTECHNICAL OVERVIEW

Existing Fill

In the City of St. Louis, it is common for multiple generations of structures to have existed and been demolished. If the previous structures contained basements, then rubble fill can be encountered to depths of 10 to 12 feet where the previous demolition consisted of collapsing the previous structure into the basement and capping it with 2 or more feet of soil. In areas where the previous structures did not have basements, the fill depths are typically on the order of 2 to 4 feet, with a thin layer of soil cover.

Foundations for the tower addition should not bear on or above the undocumented fill materials and should extend through any concrete/brick rubble that may appear to be bedrock upon first encounter.

Bedrock

The depth to intact bedrock is the biggest unknown variable due to being unable to drill a boring at the tower addition location. Based on our previous borings and experience at and near the project site, it is anticipated the top of bedrock will be between 25 and 40 feet in depth, with an increased chance of it being encountered close to 25 feet. Any existing as-built information could help with estimating the approximate depth. Otherwise, we recommend assuming a certain rock depth/elevation and requesting add/deduct rates as part of the project bidding process that would apply to actual bedrock-depth variations.

Construction Adjacent to Existing Building

Care should be taken to not disturb the bearing soils beneath the existing building foundations and slabs. It is our understanding the existing structures in each direction of the planned tower addition have basement levels; therefore, we do not anticipate undermining should be an issue.

However, if excavations do extend below the existing foundations or floor slabs, it is recommended, where possible, that excavations below these elements not extend below an imaginary plane extending out and down from the outside edge of existing footings, grade beams, and/or floor slabs at a slope of approximately 2H:1V. Even with these criteria, excavations that extend below the level of existing structures should be backfilled the same day they are excavated. Where this is impractical, shoring or underpinning of existing foundations may be required to resist undermining or movement of the existing structures.

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Underpinning of the structural elements is also recommended, even when utilizing micropiles or helical anchors to further secure the existing foundations and preventing potential movement caused by installation operations. Connections between the new and existing structures should be designed to allow for the anticipated differential movement. Differential settlement between new and existing structures may approach the estimated total settlement, unless the foundations are structurally tied together.

DEEP FOUNDATIONS

Micropile or Helical Piles Design Parameters

Soil design parameters are provided below in the Design Summary. The values presented for allowable side friction, end bearing and passive pressure include a factor of safety.

Design Summary 1

Approximate Depth (feet)

Allowable Skin

Friction

(psf) 2

Allowable End

Bearing Pressure

(psf)

Effective Unit

Weight

(pcf) 3

Allowable Passive Pressure

(psf)

Cohesion (psf)

Internal Angle of Friction

(Degrees)

Strain

50 4

Lateral Subgrade Modulus

(pci) 4

0 to 3 -- -- -- -- -- -- -- --

3 to 6 -- -- 120 500 500 -- 0.017 70

6 to 20 150 -- 125 750 750 -- 0.015 100

20 to top of rock

150 -- 60 750 750 -- 0.015 100

Competent Limestone

6,000 80,000 150 10,000 10,000 -- 0.0001 3,000

1. Design capacities can be increased by 33 percent for highly transient loads unless those loads have been factored to account for transient conditions.

2. Foundation observation is recommended to adjust overall length if variable top of bedrock is encountered.

Applicable for compressive loading only. Reduce to 2/3 of values shown for uplift loading.

3. Effective unit weight values should be used below groundwater.

4. Lateral subgrade modulus and ε50 values provided above are to be used with LPILEplus software.

The above-indicated cohesion and lateral subgrade modulus values are ultimate values without factors of safety. The end bearing is an allowable parameter with a factor of safety of 3. The skin friction and passive resistance are allowable parameters with factors of safety of 2. The values given in the above table are based on our borings and past experience with similar soil types.

Lateral resistance and friction in the upper 3 feet should be ignored due to the potential effects of frost action, desiccation, and drilling disturbance.

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Long-term settlement of a foundation designed and constructed in accordance with the recommendations presented in this report, should be about ½ inch or less.

Micropile or Helical Piles Construction Considerations

Micropiles or helical piles can be used to support the tower addition. These elements are regularly used to underpin existing foundations, to raise and support shallow foundations that have experienced excessive settlement, and have been used successfully in new construction applications. Unlike typical deep foundations or ground improvement techniques, these foundation elements can usually be installed in areas with limited horizontal and overhead clearance due to the relatively small construction equipment. A specialty contractor can design and install the elements to meet the specified structural capacity and settlement tolerances. Upon request, Terracon can provide contact information for specialty contractors experienced in these methods.

LATERAL EARTH PRESSURES

Lateral Earth Pressure Design Parameters

Rigid below-grade structures with unbalanced backfill levels on opposite sides, such as reinforced concrete walls, 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 and is commonly used for basement walls, loading dock walls, or other walls restrained at the top. The recommended design lateral earth pressures do not include a factor of safety and do not provide for possible hydrostatic pressure on the walls.

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Lateral Earth Pressure Design Parameters

Earth Pressure

Condition 1

Coefficient for Backfill Type

Minimum Φ Angle

(degrees)

Equivalent Fluid Density

(pcf)

Surcharge Pressure, p1

(psf)

Earth Pressure, p2 (psf)

Active (Ka) Granular - 0.33

Lean Clay - 0.39

(0.33)S

(0.39)S

(40)H

(50)H

At-Rest (Ko) Granular - 0.50

Lean Clay - 0.56

(0.50)S

(0.56)S

(60)H

(70)H

Passive (Kp) Granular - 3.0

Lean Clay - 2.5

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Applicable conditions to the above include:

■ For active earth pressure, wall must rotate about base, with top lateral movements as indicated in the above tables

■ For passive earth pressure to develop, wall must move horizontally to mobilize resistance as indicated in the above tables

■ Uniform surcharge, where S is surcharge pressure

■ Horizontal backfill, compacted at 95 to 98 percent of its standard Proctor maximum dry density

■ Loading from heavy compaction equipment not included

■ No hydrostatic pressures acting on wall

■ No dynamic loading

■ No safety factor included in soil parameters

■ Ignore passive pressure in frost zone

Backfill placed against structures should consist of granular soils or low plasticity cohesive soils

(i.e., fat clay is not acceptable backfill material). 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, 45 and 60 degrees from vertical for the active, at-rest and passive cases, respectively. To calculate the resistance to sliding, a value of 0.30 should be used as the ultimate coefficient of friction between the footing and the underlying soil.

A perforated rigid plastic or metal drain line installed behind the base of walls that extend below adjacent grade is recommended to limit hydrostatic loading on the walls. The invert of a drain line around a below-grade wall should be placed near foundation bearing level. The drain line should be sloped to provide positive gravity drainage or to a sump pit and pump. The drain line should be surrounded by clean, free-draining granular material having less than 5 percent (by weight) passing the U.S. No. 200 sieve. The free-draining aggregate should be encapsulated in a filter fabric. The granular fill should extend to within 2 feet of final grade, where it should be capped with compacted cohesive fill to reduce infiltration of surface water into the drain system.

SEISMIC CONSIDERATIONS

The seismic design information is provided in the SLJC Project Book, which is attached to this report.

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GENERAL COMMENTS

Our services are conducted with the understanding of the project as described in the proposal, and incorporate collaboration with the design team as we complete our services. The design team should collaborate with Terracon to confirm these assumptions and to prepare the final design plans and specifications. Any information conveyed prior to the final report is for informational purposes only and should not be considered or used for decision-making purposes.

Our analysis and opinions are based upon our understanding of the project, the geotechnical conditions in the area, and the data obtained from the referenced site exploration. Natural variations may occur between exploration point locations or due to the modifying effects of construction or weather. The nature and extent of such variations may not become evident until during or after construction. Terracon should be retained as the Geotechnical Engineer, where noted in the final report, to provide observation and testing services during construction. If variations appear, we can provide further evaluation and supplemental recommendations. If variations are noted in the absence of our observation and testing services on-site, we should be immediately notified so that we can provide evaluation and supplemental recommendations.

Our scope of services does not include either specifically or by implication any environmental or biological (e.g., mold, fungi, bacteria) assessment of the site or identification or prevention of pollutants, hazardous materials or conditions. If the owner is concerned about the potential for such contamination or pollution, other studies should be undertaken.

Our services and any correspondence or collaboration through this system are intended for the sole benefit and exclusive use of our client for specific application to the project discussed and are accomplished in accordance with generally accepted geotechnical engineering practices with no third party beneficiaries intended. Any third party access to services or correspondence is solely for information purposes to support the services provided by Terracon to our client. Reliance upon the services and any work product is limited to our client, and is not intended for third parties.

Any use or reliance of the provided information by third parties is done solely at their own risk. No warranties, either express or implied, are intended or made.

Site characteristics as provided are for design purposes and not to estimate excavation costs.

Any use of our report in that regard is done at the sole risk of the excavating cost estimator as there may be variations on the site that are not apparent in the data that could significantly impact excavation costs. Any parties charged with estimating excavation costs should seek their own site characterization for specific purposes to obtain the specific level of detail necessary for costing. Site safety, cost estimating, excavation support, and dewatering requirements/design are the responsibility of others. If changes in the nature, design, or location of the project are planned, our conclusions and recommendations shall not be considered valid unless we review the changes and either verify or modify our conclusions in writing.

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ATTACHMENTS

REPORT C OVER PAGE

VAMC - SLJC Project Book

September 9, 2019

Terracon Project No. 15185268

Prepared for:

Anderson Engineering of Minnesota, LLC

Plymouth, Minnesota

Prepared by:

Terracon Consultants, Inc.

REPORT TOPICS

INTRODUCTION

SITE CONDITIONS

PROJECT DESCRIPTION

GEOTECHNICAL CHARACTERIZATION

GEOTECHNICAL OVERVIEW

EARTHWORK

SHALLOW FOUNDATIONS

DEEP FOUNDATIONS

SEISMIC CONSIDERATIONS

FLOOR SLABS

PAVEMENTS

GENERAL COMMENTS

ATTACHMENTS

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 PLAN

SD-001 PREFERRED ALT A

SD-002 PREFERRED ALT B

GEOLOGIC MAP

EXPLORATION PLAN

REFRACTION MICROTREMOR DIAGRAM

EXPLORATION RESULTS

REFRACTION MICROTREMOR RESULTS

CHEMICAL LABORATORY TEST REPORT

SUPPORTING INFORMATION

Note: Refer to each individual Attachment for a listing of contents.

http://client.terracon.com/

VAMC - SLJC Project Book ■ St. Louis, Missouri

September 9, 2019 ■ Terracon Project No. 15185268

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REPORT SUMMARY

Topic Overview Statement

Project Description

The improvements to the Veterans Administration John Cochran facility at 915 North Grand Boulevard will include nine new structures. There are currently two options for the layout of the new structures. The new structures for Alternate A include:

■ A new bed tower with a footprint of 75,304 square feet. This structure will be nine stories.

■ Three new parking structures, with footprints of 55,000 square feet (138 spaces) per floor, 30,400 square feet (76 spaces) per floor, and 30,250 square feet (75 spaces) per floor. The parking garages are anticipated to be five to six floors each.

■ A two-story, utility plant with a footprint of 25,000 square feet, and rooftop equipment.

■ A single-story, SATP clinic with a footprint of 5,040 square feet.

■ A two-story, FES/OIT building with a footprint of 6,200 square feet.

■ A new substation, the size of which is unknown at this time.

■ A new water storage structure.

The new structures for Alternate B include:

■ A new bed tower with a footprint of 60,480 square feet. This structure will be

13 stories.

■ Three new parking structures, with footprints of 40,800 square feet (110 spaces) per floor, 71,600 square feet (179 spaces) per floor, and 30,250 square feet (75 spaces) per floor. The parking garages are anticipated to be four floors each.

■ A two-story, utility plant with a footprint of 28,000 square feet, and rooftop equipment.

■ A single-story, SATP clinic with a footprint of 4,680 square feet.

■ A one- to two-story, OIT building with a footprint of 1,500 square feet.

■ A new substation, the size of which is unknown at this time.

■ A new water storage structure.

Geotechnical Characterization

■ Borings generally encountered asphalt pavement over base rock underlain by existing fill to depths of 3 to 8 feet. The fill generally consisted of lean and fat clay with variable amounts of sand, gravel, and brick.

■ Beneath the fill, lean (CL), lean to fat (CL/CH), and fat clay (CH) soils were encountered to the top of rock. The overburden soils were typically medium stiff, although soft zones were noted.

■ Limestone bedrock was encountered at depths of 25 to 37 feet.

■ Mud rotary drilling was used below a depth of 20 feet in all of the borings.

Groundwater was only encountered in one boring (B-6 at a depth of 16 feet) prior to introducing water for the mud rotary drilling.

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Topic Overview Statement

Earthwork

■ The existing fill is variable. There is a risk of excessive settlements if foundations, floor slabs, or pavements are founded in or above the existing fill.

■ Due to the lean to fat (CL/CH) and fat clay (CH) soils, at least the upper 24 and

12 inches of soil below the bottom of the on-grade slabs and pavement base rock, respectively, should consist of low plasticity (LP) material

■ Clays are sensitive to moisture variation and could become unstable under construction traffic.

Shallow Foundations

Lightly-loaded structures may be supported on shallow foundations.

■ Allowable bearing pressure = 1,500 psf

■ Expected settlements: less than 1-inch total, less than ¾-inch differential

Moderately-loaded structures may be supported on shallow foundations if ground improvement is utilized.

■ Anticipated allowable bearing pressure = 5,000 psf (actual to be provided by ground improvement contractor)

■ Expected settlements: less than 1-inch total, less than ¾-inch differential

Detect and remove zones of soft soils as noted in Earthwork.

Deep Foundations

Deep foundations may be used to support heavily-loaded structures.

Seismic Considerations

IBC site class C

Concrete Slabs Floor slabs will likely be slab-on-grade; on at least 24 inches of low plasticity (LP) material. The existing fill will need to be removed and recompacted after any deleterious materials have been removed.

Pavements

With subgrade prepared as noted in Earthwork

Concrete:

■ 5 inches PCC over 4 inches in light-duty areas

■ 6 inches PCC over 4 inches in medium-duty areas

Asphalt:

■ 3 inches ACC over 8 inches granular base in light-duty areas

■ 5 inches ACC over 8 inches granular base in medium-duty areas

General Comments

This section contains important information about the limitations of this geotechnical engineering report.

1. If the reader is reviewing this report as a pdf, the topics above can be used to access the appropriate section of the report by simply clicking on the topic itself.

2. This summary is for convenience only. It should be used in conjunction with the entire report.

Geotechnical Engineering Report

VAMC - SLJC Project Book

915 North Grand Boulevard

St. Louis, Missouri Terracon Project No. 15185268

September 9, 2019

This report presents the results of our subsurface exploration and geotechnical engineering services performed for the proposed improvements to the Veterans Administration John Cochran facility at 915 North Grand Boulevard in St. Louis, Missouri. The purpose of these services is to provide information and geotechnical engineering recommendations relative to:

■ Subsurface soil conditions ■ Foundation design and construction

■ Groundwater conditions ■ Floor slab design and construction

■ Site preparation and earthwork ■ Seismic site classification per IBC

■ Excavation considerations ■ Pavement design and construction

The geotechnical engineering Scope of Services for this project included the advancement of six

(6) test borings to depths ranging from approximately 35 to 47 feet below existing site grades. At least 10 feet of rock coring was performed in each boring. The site has been heavily developed, so boring locations were selected to provide general aerial coverage of the site at locations accessible to our drill rig.

Maps showing the site, the two development options, and our boring locations are shown in the

Site Location and Exploration Plan sections, respectively. The results of the laboratory testing performed on soil samples obtained from the site during the field exploration are included on the boring logs in the Exploration Results section.

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

SITE CONDITIONS

The following description of site conditions is derived from our site visit in association with the field exploration and our review of publicly available geologic and topographic maps.

Item Description

Parcel Information The project is located at 915 North Grand Boulevard in St. Louis, Missouri.

Latitude: 38.6426ºN, Longitude: 90.2318ºW

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Existing

Improvements Numerous single- and multi-story buildings and parking lots.

Current Ground Cover Asphalt pavement where buildings are not present

Existing Topography

Based on Google Earth, the site slopes down from the east towards the west with approximately 35 feet of relief across the site (elevation 545 to elevation

510).

Geology

Based on the Geologic Map provided by the United States Geologic Survey

(USGS), the subject site is located over the Meramecian Series. The

Meramecian Series consists of the St. Louis Limestone, Salem Formation, and Warsaw Formation. These units are characterized by massive, argillaceous, and fossiliferous limestone.

A sinkhole area is mapped approximately 1,500 feet to the west of the site, but no sinkholes are mapped on the site itself. A seismic fault is mapped approximately 3,500 feet east of the site.

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PROJECT DESCRIPTION

Item Description

Project Description

The improvements to the Veterans Administration John Cochran facility at

915 North Grand Boulevard will include nine new structures. There are currently two options for the layout of the new structures. The new structures for Alternate A include:

■ A new bed tower with a footprint of 75,304 square feet. This structure will be nine stories.

■ Three new parking structures, with footprints of 55,000 square feet (138 spaces) per floor, 30,400 square feet (76 spaces) per floor, and 30,250 square feet (75 spaces) per floor. The parking garages are anticipated to be five to six floors each.

■ A two-story, utility plant with a footprint of 25,000 square feet, and rooftop equipment.

■ A single-story, SATP clinic with a footprint of 5,040 square feet.

■ A two-story, FES/OIT building with a footprint of 6,200 square feet.

■ A new substation, the size of which is unknown at this time.

■ A new water storage structure.

The new structures for Alternate B include:

■ A new bed tower with a footprint of 60,480 square feet. This structure will be 13 stories.

■ Three new parking structures, with footprints of 40,800 square feet (110 spaces) per floor, 71,600 square feet (179 spaces) per floor, and 30,250 square feet (75 spaces) per floor. The parking garages are anticipated to be four floors each.

■ A two-story, utility plant with a footprint of 28,000 square feet, and rooftop equipment.

■ A single-story, SATP clinic with a footprint of 4,680 square feet.

■ A one- to two-story, OIT building with a footprint of 1,500 square feet.

■ A new substation, the size of which is unknown at this time.

■ A new water storage structure.

Finished Floor

Elevation

Multiple structures are planned, but the various finished floor elevations are unknown at this time.

Maximum Loads

(estimated by Terracon)

Single-story building:

■ Columns: 75 kips

■ Walls: 3 kips per linear foot (klf)

■ Slabs: 150 pounds per square foot (psf)

9- to 13-story building:

■ Columns: 2,500 kips

■ Walls: 10 kips per linear foot (klf)

■ Slabs: 150 pounds per square foot (psf)

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Grading/Slopes Minimal grading is anticipated. Any slopes are anticipated to be no steeper than 3H:1V (Horizontal: Vertical) or taller than 3 feet.

Below-Grade

Structures The water storage may be provided by an underground structure.

Pavements

We assume both rigid (concrete) and flexible (asphalt) pavement sections should be considered.

Anticipated traffic is as follows:

■ Autos/light trucks: 2,000 vehicles per day

■ Light delivery and trash collection vehicles: 45 vehicles per day

■ Tractor-trailer trucks: one vehicle per day

The pavement design period is 20 years.

GEOTECHNICAL CHARACTERIZATION

We have developed a general characterization of the subsurface conditions based upon our review of the subsurface exploration, laboratory data, geologic setting and our understanding of the project. This characterization, termed GeoModel, forms the basis of our geotechnical calculations and evaluation of site preparation and foundation options. Conditions encountered at each exploration point are indicated on the individual logs. The individual logs and the GeoModel can be found in the Exploration Results section of this report.

As part of our analyses, we identified the following model layers within the subsurface profile. For a more detailed view of the model layer depths at each boring location, refer to the GeoModel.

Model Layer Layer Name General Description

1 PAVEMENT

Asphalt pavement (4 to 6 inches) over crushed limestone base rock (6 to 10 inches).

2 EXISTING FILL

Lean clay and fat clay, with variable amounts of sand, gravel, and brick.

3 LEAN CLAY

Lean clay (CL), with variable amounts of sand and silt, very soft to stiff.

LEAN TO FAT

CLAY

Lean to fat clay (CL/CH), with variable amounts of sand and silt, soft to stiff.

5 FAT CLAY

Fat clay (CH), with variable amounts of sand and gravel, soft to hard.

LIMESTONE

BEDROCK

Unweathered to slightly weathered, medium strong to very strong rock, RQD fair to excellent. Highly weathered with very poor RQD above competent rock in B-3 and B-4.

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Atterberg limits tests were performed on selected samples and had the following measured liquid limits, plastic limits, and plasticity indices:

Sample Location Depth (feet) Liquid Limit Plastic Limit Plasticity Index

Boring B-1 3 - 5 41 19 22

Boring B-2 6 - 7½ 45 20 25

Boring B-3 3½ - 5 40 18 22

Boring B-4 8½ - 10 47 22 25

Boring B-5 23½ - 25 52 18 34

Boring B-6 8½ - 10 49 21 28

Geology

Based on the 2003 Geologic Map of Missouri, Missouri Department of Natural Resources, bedrock at this site consists primarily of the Mississippian aged Meramecian Series (Mm). The

Meramecian Series consists of the St. Louis Limestone, Salem Formation, and Warsaw

Formation. These units are characterized by massive, argillaceous, and fossiliferous limestone.

A Geologic Map is provided in the Attachments.

A sinkhole area is mapped approximately 1,500 feet to the west of the site, but no sinkholes are mapped on the site itself. A seismic fault is mapped approximately 3,500 feet east of the site.

Groundwater Conditions

The boreholes were observed while drilling for the presence and level of groundwater, prior to introducing water into the holes at a depth of 20 feet when wash boring methods were implemented. Groundwater was only observed in Boring B-6 at a depth of about 16 feet below the ground surface. Groundwater was not observed in the remaining borings prior to utilizing mud rotary drilling.

The overburden soils are generally clayey and of low permeability. Therefore, a relatively long period of time may be 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 are often required to define groundwater levels in materials of this type.

Groundwater level fluctuations occur due to seasonal variations in the amount of rainfall, runoff, and other factors not evident at the time the borings were performed. In addition, perched water can develop over low permeability soil and rock strata, particularly in the existing fill. Therefore, groundwater levels during construction or at other times in the life of the structures may be different from the levels indicated on the boring logs. The possibility of groundwater level

Responsive ■ Resourceful ■ Reliable 6 fluctuations should be considered when developing the design and construction plans for the project.

GEOTECHNICAL OVERVIEW

Existing Fill

In the City of St. Louis, it is common for multiple generations of structures to have existed and been demolished. If the previous structures contained basements, then rubble fill can be encountered to depths of 10 to 12 feet where the previous demolition consisted of collapsing the previous structure into the basement and capping it with 2 or more feet of soil. In areas where the previous structures did not have basements, the fill depths are typically on the order of 2 to 4 feet, with a thin layer of soil cover.

Existing fill was encountered to depths of about 3 to 8 feet below existing grades in all of the borings. The fill could extend deeper in areas not explored. No documentation or records regarding the placement of this fill were provided for our review. If records are available, Terracon should be supplied with these documents to better assess the suitability of the existing fill. Further exploration and testing (e.g., borings, test pits, geophysical testing) of the existing fills could be performed, if requested.

Foundations for the new buildings should not bear on or above the undocumented fill materials.

The existing fill could be removed and replaced so that the foundations for the new buildings bear on suitable native soils or on properly placed and compacted engineered fill extending to suitable native soils. If the fill is completely removed and replaced, it should be removed within the proposed building footprint and extend at least 5 feet outside the building perimeter.

If the owner is willing to accept the risks associated with supporting floor slabs and pavements over the existing fill materials in exchange for reduced construction costs, portions of the existing undocumented fill could be left in place for support of floor slabs and pavements. If this alternative is chosen, at least 24 and 12 inches of new engineered fill should be placed directly below the floor slab and the pavement base rock, respectively, and the building foundations should be extended through the fill to bear on suitable native soils. If the owner is not willing to accept the risks of supporting floor slabs and pavements over existing undocumented fill materials, the existing fill should be completely removed and replaced.

To reduce the risk of adverse performance from higher settlement and provide more consistent support for floor slabs, the exposed existing fill materials should be observed and tested during construction. Where unsuitable conditions are observed, the materials should be improved by scarification and compaction or be removed and replaced with engineered fill. Unsuitable fill materials observed during construction may warrant further exploration at that time.

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Support of floor slabs and pavements on or above existing fill materials is discussed in this report within the Floor Slabs and Pavements sections. 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 following the recommended reworking of the material.

We understand a section of distressed pavement was recently replaced, and that when the existing pavement was removed, rubble fill was observed. While Terracon was not involved with the repair of the pavement, we understand that the existing fill was removed prior to repaving, and that the nature of the existing fill was thought to have been the major contributing factor to the distress to the pavement. In consideration of this experience, it may be more cost effective over the design period of the pavements and floor slabs to completely remove and replace/recompact the existing fill rather than leaving any of it in place.

Expansive Soils

Some of the lean to fat clay (CL/CH) and fat clay (CH) soils encountered in the borings are moderate to high in plasticity (LL≥45, PI≥25) and prone to volume change with variations in moisture content. For this reason, we recommend that at least the upper 24 and 12 inches below the bottom of the floor slab level in the building footprints and the pavement base rock, respectively, consist of low plasticity (LP) material as defined in the Earthwork section.

This LP layer should also be confirmed or placed below other flatwork abutting the structure. The procedures recommended in this report may not eliminate all future subgrade volume change and resultant floor slab movements. However, the procedures outlined should reduce the potential for subgrade volume change. Additional reductions in floor slab movements could be achieved by using a thicker LP zone.

Imported LP fill may be required to satisfy this recommendation. Alternatively, it may be cost effective to create the recommended LP zones by chemically modifying the on-site soils with lime

(Code L) to reduce their volume change susceptibility.

This report provides recommendations to help mitigate the effects of soil shrinkage and expansion. However, even if these procedures are followed, some movement and at least minor cracking in the structure could still occur. The severity of cracking and other cosmetic damage such as uneven floor slabs on grade will likely increase if any modification of the site results in excessive wetting or drying of the expansive soils. Eliminating the risk of movement and cosmetic distress may not be feasible, but it may be possible to further reduce the risk of movement if more

Responsive ■ Resourceful ■ Reliable 8 extensive measures are used during construction. We would be pleased to discuss other construction alternatives with you upon request.

Pavements may be somewhat more tolerant of shrink and swell characteristics of high plasticity soil subgrade conditions. Even so, we recommend that at least the upper 12 inches of pavement subgrade be constructed of engineered LP material, or the soils be chemically modified to reduce their volume change susceptibility.

Demolition

Demolition of any existing structures to be removed should include removal of all above- and below-grade elements including floor slabs, foundation walls, footings, and pavements. Attention should be given to removing all loose or poorly compacted existing fill materials that are often located adjacent to existing and former foundation walls. All existing utilities should also be properly abandoned and/or relocated. This should include removal of all poorly compacted trench backfill extending into the proposed building area. In addition, care should be taken by contractors to protect all existing improvements to remain, such as pavements and utilities. Excavations created by demolition and removal of existing features should be backfilled with engineered fill that is placed and compacted as recommended in this report.

Soft Subgrade

The near surface soils could become unstable with typical earthwork and construction traffic, particularly after precipitation events. Effective drainage should be implemented early in the construction sequence and maintained after construction to reduce potential issues. If possible, the grading should be performed during the warmer and drier times of the year. If grading is performed during the wetter months, an increased risk for possible undercutting and replacement of unstable subgrade will exist. Additional site preparation recommendations including subgrade improvement and fill placement are provided in the Site Preparation section.

EARTHWORK

Earthwork is anticipated to include clearing and grubbing, excavations, and fill placement.

Site Preparation

Prior to placing fill, any existing vegetation and root mat should be removed. Complete stripping of the topsoil should be performed in the proposed building and parking/driveway areas. At this time, the existing fill should be removed and replaced or recompacted after any deleterious materials have been removed. If any of the existing fill is to be left in place, it should be evaluated at this time.

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We recommend that the exposed subgrade be thoroughly evaluated by the Geotechnical

Engineer prior to placement of new fill. The soils on the site are sensitive to disturbance from construction equipment traffic, particularly during wet periods. Excessively wet or dry material should either be removed, or moisture conditioned and recompacted. The exposed subgrade should be proofrolled where possible to aid in locating loose or soft areas. Proofrolling can be performed with a loaded, tandem-axle dump truck. If unsuitable areas are observed during construction, subgrade improvement will then be necessary to establish a suitable subgrade support condition. Potential subgrade stabilization techniques are discussed below.

■ Scarification and Recompaction – It may be feasible to scarify, dry, and recompact the exposed soils. The success of this procedure would depend primarily upon favorable weather and sufficient time to dry the soils. Stable subgrades likely would not be achievable if the thickness of the unstable soil is greater than about 1 foot, if the unstable soil is at or near groundwater levels, or if construction is performed during a period of wet or cool weather when drying is difficult.

■ Crushed Stone – The use of crushed stone or gravel is the most common procedure to improve subgrade stability. Typical undercut depths would be expected to range from about 6 to 30 inches below finished subgrade elevation with this procedure. The use of high modulus geotextiles could also be considered to reduce the aggregate thickness. It is difficult to predict rock thicknesses that will be needed until the conditions are observed during construction. A test section could be used to observe the effectiveness of the chosen section.

Prior to placing the fabric or geogrid, we recommend that all below-grade construction, such as utility line installation, be completed to avoid damaging the fabric or geogrid.

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 should meet the manufacturer’s guidelines and generally should not exceed 1½ inches.

■ Chemical Stabilization – Improvement of subgrades with Portland cement, lime kiln dust, Code L, or Class C fly ash could be considered for improving unstable soils. Chemical modification should be performed by a prequalified contractor having experience with successfully stabilizing subgrades in the project area on similar sized projects with similar soil conditions. Results of chemical analysis of the additive materials should be provided to the geotechnical engineer prior to use. The hazards of chemicals blowing across the site or onto adjacent property should also be considered. Additional testing would be needed to develop specific recommendations to improve subgrade stability by blending chemicals with the site soils. Additional testing could include, but not be limited to, evaluating various stabilizing agents, the optimum amounts required, the presence of

Responsive ■ Resourceful ■ Reliable 10 sulfates in the soil, and freeze-thaw durability of the subgrade. For estimating purposes, the incorporation rates for chemical treatment (on a dry soil unit rate basis) are typically:

o 2 to 4 percent for hydrated lime, by weight;

o 5 to 7 percent for Code L, by weight; or o 5 to 7 percent for Portland cement, by weight.

Further evaluation of the need and recommendations for subgrade stabilization can be provided during construction as the geotechnical conditions are exposed.

Fill Material Types

Compacted structural fill should meet the following material property requirements:

Fill Type 1 USCS Classification Acceptable Location for Placement

High Plasticity Material CH (LL≥70 or PI≥40)

Below upper 3 feet of slabs and other lightly-loaded structures; 2 feet of shallow foundations;

and 1 foot below pavement

Moderate to High

Plasticity Material 2

CH or CL, with

70>LL≥45 or 40>PI≥25

Below upper 2 feet of slabs and any other lightly-loaded structures; and 1 foot below base rock

Granular Material 3 GM, GC, SM, or SC

All locations and elevations Low Plasticity Material 4

CL (LL<45 & PI<25)

or Granular Material 3

1. Compacted structural fill should consist of approved materials that are free of organic matter and debris.

Frozen material should not be used, and fill should not be placed on a frozen subgrade. A sample of each material type should be submitted to Terracon for evaluation. On-site soils generally appear suitable for use as fill outside of the LP zone.

2. Delineation of moderate to high plasticity clays should be performed in the field by a qualified geotechnical engineer or their representative and could require additional laboratory testing.

3. Crushed limestone aggregate, limestone screenings or granular material such as sand, gravel or crushed stone containing at least 15 percent low plasticity fines.

4. Low plasticity cohesive soil or granular soil having low plasticity fines. Material should be approved by the geotechnical engineer.

Fill Compaction Requirements

Fill Lift Thickness

9 inches or less in loose thickness for heavy compaction equipment

4 to 6 inches or less in loose thickness for light, hand-operated compaction equipment

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Compaction

Requirements 1 At least 95 percent of the material’s maximum standard Proctor dry density

Moisture Content –

Cohesive Soil

-1 to +3 percent of the optimum moisture content value as determined by the standard Proctor test

Moisture Content –

Granular Material Workable moisture levels 2

1. We recommend that engineered fill be tested for moisture content and compaction during placement.

Should the results of the in-place density tests indicate the specified moisture or compaction limits have not been met, the area represented by the test should be reworked and retested as required until the specified moisture and compaction requirements are achieved.

2. Specifically, moisture levels should be maintained low enough to allow for satisfactory compaction to be achieved without the cohesionless fill material pumping when proofrolled.

Utility Trench Backfill

All trench excavations should be made with sufficient working space to permit construction including backfill placement and compaction. If utility trenches are backfilled with relatively clean granular material, they should be capped with at least 18 inches of cohesive fill in non-pavement areas to reduce the infiltration and conveyance of surface water through the trench backfill.

Utility trenches are a common source of water infiltration and migration. All utility trenches that penetrate beneath buildings should be effectively sealed to restrict water intrusion and flow through the trenches that could migrate below the structure.