596-333 Geotechnical Report.pdf

REPORT COVER PAGE

Geotechnical Engineering Report

VAMC Continuing Care Facilities – Phase 2

Lexington, Fayette County, KY

December 16, 2020

Terracon Project No. N3195011

Prepared for:

RDC/John Poe Architects

Miamisburg, Ohio

Prepared by:

Terracon Consultants, Inc.

Lexington, Kentucky

Terracon Consultants, Inc. 2460 Palumbo Dr ive Lexington, Kentucky 40509

P (859) 303 9000 F (859) 303 9001 terracon.com

REPORT COVER LETTER TO SIGN

RDC/John Poe Architects

3131 Newmark Drive, Suite 200

Miamisburg, Ohio 45342

Attn: Mr. Mike Duke – Project Manager

P: (937) 461 3290

E: mduke@johnpoe.com

Re: Geotechnical Engineering Report

VAMC Continuing Care Facilities – Phase 2

2250 Leestown Road

Lexington, Fayette County, KY

Terracon Project No. N3195011

Dear Mr. Duke:

We have completed the Geotechnical Engineering services for the above referenced project. This study was performed in general accordance with Terracon Proposal No. PN3195011 dated

November 10, 2020. This report presents the findings of the subsurface exploration and provides geotechnical recommendations concerning earthwork and the design and construction of foundations, floor slabs, and pavements for the proposed project.

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

Sincerely, Terracon Consultants, Inc.

Samuel G. Guy, P.E. Jeffrey D. Dunlap, P.E.

Office Manager Senior Engineer

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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

PAVEMENTS

GENERAL COMMENTS

FIGURES

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

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

http://client.terracon.com/

VAMC Continuing Care Facilities – Phase 2 ■ Lexington, Fayette County, KY

December 16, 2020 ■ Terracon Project No. N3195011

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REPORT SUMMARY

Topic Overview Statement

Project Description

One 1-story residential building (Bldg 204) and one 2-story (with walkout basement

– Bldg. 205) residential building with pedestrian connector Max. Column loads: 90 kips, Max. Wall loads: 2.6 kips per lineal foot Up to 17 feet of fill and up to about 7 feet of cut to achieve final grade Up to 7 feet of excavation around the north and east sides of the north building (Bldg 205)for the walkout basement

Geotechnical Characterization

Some areas of existing fill varying from about 3 to 6.5 feet deep Lean clays, silts, and fat clays depths varying from about 1.5 to about 20.5 feet Slightly weathered limestone bedrock below these depths Groundwater not encountered

Earthwork Existing controlled fill may be left in place, if it passes proofroll inspection Existing low-volume-change soils can be used for engineered fill Clays are sensitive to moisture variation

Shallow Foundations

Shallow foundations will be sufficient bearing on stiff or better native soils or existing controlled fill. See discussion regarding where foundations transition from bearing on bedrock to native soils Allowable bearing pressure = 3,000 psf Expected settlements: < 1-inch total Detect and remove zones of unsuitable soils as noted in Earthwork.

Below-Grade Structures

Basements: below-grade foundation walls are proposed at this site

Pavements

With subgrade prepared as noted in Earthwork.

Concrete:

■ 5 inches Portland Cement Concrete (PCC) over 4 inches of granular base in Light-Duty areas

■ 8 inches PCC over 4 inches of granular base for Dumpster Pad or drive aprons

Asphalt:

■ 4 inches Asphaltic Concrete (AC) over 6 inches granular base in Light-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 for design purposes.

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INTRODUC TION

Geotechnical Engineering Report

VAMC Continuing Care Facilities – Phase 2

2250 Leestown Road

Lexington, Fayette County, KY Terracon Project No. N3195011

INTRODUCTION

This report presents the results of our subsurface exploration and geotechnical engineering services performed for the proposed VAMC Continuing Care Facilities – Phase 2 project to be located at 2250 Leestown Road in Lexington, Fayette County, KY. 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 ■ Floor slab design and construction

■ Karst Evaluation ■ Seismic site classification per IBC

■ Site preparation and earthwork ■ Lateral earth pressures

■ Excavation considerations ■ Pavement design and construction

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

(10) test borings to depths ranging from approximately 1.5 to 40.5 feet below existing site grades.

The scope of services also included geophysical survey of the proposed building areas using

Electrical Resistivity Imaging (ERI) methods to investigate possible evidence of karst within the proposed building areas.

Maps showing the site and 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 and/or as separate graphs in the Exploration Results section.

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 2250 Leestown Road in Lexington, Fayette County, KY.

Coordinates: 38.070011/-84.540599 (approximate) See Site Location

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Item Description

Existing

Improvements

Newly completed earthwork and ongoing construction activity associated with a new VA development located to the southeast of and within the immediate vicinity of the proposed development. The site was recently seeded and strawed.

Current Ground

Cover Grass, seed, and straw

Existing Topography

Review of provided grading plans indicates the site is gently to moderately sloping downward from east to west, with slopes varying from as steep as

3H:1V to less than 10H:1V in the proposed building, parking, and detention pond areas.

Geology

A review of geologic literature indicates that the site is located within an area consisting of unconsolidated sediments of the Quaternary Age underlain by the Ordovician Period’s Lower Part of the Lexington Limestone Formation as well as the Brannon Member.

The Lexington Limestone consists of fossiliferous limestone with minor amounts of shale. The Cane Run Bed is light gray to light brownish-gray and part silty, with dense limestone nodules and boulders in convolute beds, locally. The Grier Limestone member is medium to dark-gray, weathers to lighter shades of gray and brown and includes very thin shale layers in the upper few feet.

The Brannon Member consists of limestone, light-gray to light-brownish-gray, microgranular, and argillaceous. The limestone is in part silty with thin beds of medium-dark-gray shale and interbeds of clastic limestone locally present.

Chert occurs as thin beds and as nodules.

Based on available information from the Kentucky Geological Survey (KGS)

Interactive Mapping Service’s Karst Potential Map, the underlying bedrock is reported to have a “low” karst potential within the Brannon Member and “high” karst potential within the Lower Part of the Lexington Limestone. The majority of the site lies within the Lower Part of the Lexington Limestone. No sinkholes are mapped within the project area.

Karst Susceptible Rock

Review of the Kentucky Geological Survey’s Karst Potential map indicates a signifcant potential for karst development within the Lower Part of the Lexington Limestone’s carbonate rocks. Karst features, including clay seams, caverns, sinkholes, and highly irregular rock surfaces, are common features within carbonate rocks like those encountered in this exploration. While the initial limited desktop study performed for this report found that the site is within formations with

“low” to “high” karst potential, no sinkholes were mapped within the vicinity of this site and no

Responsive ■ Resourceful ■ Reliable 3 sinkholes were observed within the proposed building areas during our site reconnaissance or during our field exploration.

Karst is a distinctive landscape that commonly occurs where carbonate bedrock strata (i.e.

limestone) are subjected to dissolution weathering by even slightly acidic surface and groundwater. Rainwater picks up carbon dioxide from the atmosphere as it infiltrates down through the soil profile. The weathering is typified by a chemical solutioning process that progresses along joints, fractures, and bedding planes in the bedrock. This process often results in a highly-irregular rock profile that contains deep weathering slots filled with soft soils. Voids are created as the bedrock dissolves and over time widened fractures, solution cavities, and caves form. This may progress to ground subsidence and/or sinkholes as soil overburden ravels into or is eroded by groundwater into the subsurface voids.

Prediction of future subsidence or collapse is very difficult and even an extensive subsurface exploration cannot rule out the possibility of future ground subsidence. As with any site underlain by a carbonate bedrock formation, karst activity is on-going and there is always the risk of future impact to ground-supported structures.

Findings of our geophysical study for karst activity at this site are provided in the Geophysical

Exploration section of this report.

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 conditions is as follows:

Item Description

Information Provided

Plans for Phase 1 (which included preliminary plans for Phase 2) of the project provided in email by Mr. Mike Duke, dated March 19, 2019.

Proposed revisions for Phase 2 of the project were stated in email by Ms.

Pamela Rigling, dated April 1, 2019. The revised (65%-complete) plan set was provided by Mr. Duke on September 29, 2020 for our review. 95% drawings were provided on December 15, 2020.

Project Description

Proposed development of one 1-story residential building (south building - Building 204) and one 2-story (including walkout basement) residential building (north building – Building 205) with a pedestrian connector located between the two buildings. The project will also include parking and drive areas in addition to utilities. An expansion of the existing stormwater detention basin is also proposed.

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Building Construction

Past experience with similar projects indicates the proposed buildings will be wood-framed with brick veneer exterior walls. Concrete foundation walls will be used for below-grade portions of the building. It is expected that utility pads will also be constructed for the required utilities to service the facilities.

Finished Floor Elevation First Floor FFE = 918.50 feet, MSL

Lower Level FFE = 904.83 feet, MSL

Maximum Loads

■ One Story Columns: 5 to 40 kips (with maximum of 60 kips)*

■ Two Story Columns: 5 to 60 kips (with maximum of 90 kips)*

■ Walls: 2.6 kips per linear foot (klf)

*Provided information indicates that column loads in exterior walls are under half the typical loads provided above, with approximately half the loads acting as dead loads and half the loads acting as live loads.

Slabs: 150 pounds per square foot (psf)

Grading/Slopes

West Fill Slope and Grading: Review of provided grading plans indicates up to about 17 feet of fill and minimal cut will be required to achieve final grades. The west fill slope appears to vary from between about 2¾H:1V to 3½H:1V in the vicinity of the residential buildings, with maximum slope heights varying from about 10 feet to 23 feet.

North Building’s North/East Walls Cut/Fill Grading and Slopes: Up to about 7 feet of cut and 2 feet of fill will be required on the northeast corner of the north residential building to reach design grade. The northeast cut slope will vary from about 2¾H:1V to 4½H:1V, with a maximum slope height of about 5 feet.

Detention Pond Grading and Slopes: Up to about 7 feet of fill to achieve design grade. Review of provided information indicates the west fill slope is about 3H:1V and will be modified slightly from its existing configuration.

The revised slope is proposed to have a maximum height of about 10 feet.

The slope located on the east side of the detention pond and west side of the pavement area will vary from about 3¼H:1V to 5H:1V and will have maximum slope heights of about 10 to 11 feet. Up to about 5 feet of fill will be needed to achieve design grade in this area.

Below-Grade Structures

Review of provided grading plans indicate that below-grade foundation (including basement) walls are proposed along portions of the north, east and west sides of Building 205. An east-west oriented foundation/basement wall will be required in the southern portion of Building 205.

Free-Standing Retaining Walls

A small retaining wall structure with a maximum height of about 3 feet is proposed on the north side of the north building.

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Pavements

Anticipated pavement traffic information has not been provided. We have anticipated Portland Cement Concrete (PCC) trash container pads with Asphalt Cement Concrete (ACC) drive lanes and employee/visitor parking lot(s) and driveways will be utilized for this project.

Based on available information, light-duty pavement section thicknesses have been provided for light-duty areas and heavy-duty pavement section thicknesses have been provided for the dumpster pad area, only. If information is available and provided to Terracon for heavy-duty traffic areas outside the dumpster pad area, heavy-duty section design recommendations can be provided, upon request.

GEOTECHNICAL CHARACTERIZATION

Geophysical Survey

Terracon performed geophysical exploration services consisting of Electrical Resistivity Imaging

(ERI) on October 26, 2020. The primary goal of this survey was to map the bedrock topography and explore for potential karst features beneath the planned building site. Terracon used an

Electrical Resistivity Imaging (ERI) system consisting of an Advanced Geosciences Inc. (AGI)

SuperSting R8 control unit.

The method uses an array of potential and current electrodes, driven into the ground, that function independently of one another to measure the potential field. A transmitting current dipole is followed by a series of potential dipoles which measure the resulting voltage gradient at each station. As the transmitting dipole is advanced along the electrodes, the resulting gradient measurements were collected as a 2D section below the survey array. After field collection, the resistivity data was processed using Earth Imager 2D (engineered by AGI), an inversion and modeling software package. Changes in the earth resistivity can indicate changes in lithology, saturation, and amount of fracturing.

Six ERI survey lines were conducted within the project area (see Site Location and Exploration

Plans). Site access was limited due to on-going construction and construction fencing. The lines were placed in the accessible areas but did not cover the entire building site. The lines are oriented west to east and used electrode spacing of 10 feet.

The cross-sectional images generated from the ERI testing are displayed in Exploration Results.

The images are representations of the electrical resistivity of the subsurface. The findings include the following:

■ High resistivity values (red, orange, and yellow) are indicative of quality bedrock with minimal fractures and voids.

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■ Lower resistivity values (green, blue, and purple) are indicative of soil overburden or weak, saturated, or fractured bedrock.

■ Very low resistivity zones (less than 50 ohm-m) at or below the interpreted bedrock surface, may indicate clay or water filled cavities in the bedrock. Very low resistivity zones can also be caused by utility interference.

■ Potential karst anomalies are highlighted on the cross-sections (displayed in the

Exploration Results section of this report) and plan view (displayed in the Site Location and Exploration Plans section of this report)

■ The approximate top of bedrock is indicated by a dashed line on the cross-section exhibits.

In general, competent bedrock appears to be within the range of approximately 5 to 20 feet of the existing grade. Interpreted top of bedrock is an estimate and actual depth can vary due to differences in resistivity values between weathered and competent bedrock.

■ Boring K-1 was drilled to assess the geophysical anomaly and indicated deeper bedrock, with overlying silt material, and weathered bedrock at the top of bedrock interface. K-1 and the ERI data appear to indicate an area of increased groundwater infiltration but the bedrock appears to be competent.

All geophysical testing methods rely on instrument signals to indicate physical conditions in the field. Signal information can be affected by on-site conditions beyond the control of the operator, such as, but not limited to, cultural features, standing water, high subsurface moisture content, and other buried objects. Interpretation of those signals is based on a combination of known factors combined with the experience of the operator and geophysical scientist evaluating the results.

This report has been prepared for the application discussed and in accordance with generally accepted geophysical practices. No warranties, expressed or implied, are intended or made. The findings presented in this report are based upon the data obtained from the geophysical surveys and from other information discussed in this report. This report does not reflect variations that may occur in areas not tested or inaccessible to the geophysical equipment, across the site, or due to the modifying effects of construction or weather.

Geotechnical Exploration

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 can be found in the

Exploration Results section and the GeoModel can be found in the Figures 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.

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Model Layer Layer Name General Description

Existing Fill Lean clay and silt with chert and trace amounts of organics and rock fragments

Cohesive Soils Lean Clay, Silt, Fat Clay, and Elastic Silt, brown to reddish brown, stiff to very stiff

3 Bedrock Limestone, gray, slightly weathered, weak to strong

The boreholes were observed while drilling and after completion for the presence and level of groundwater. No groundwater was encountered while drilling or observed after drilling operations were completed in the borings.

The absence of observed water in the borings does not necessarily mean that the borings terminated above groundwater. In cohesive soils, long-term observations in piezometers or observation wells sealed from the influence of surface water are often required to define groundwater levels.

Groundwater level fluctuations should be expected to occur due to seasonal variations in rainfall, runoff and other factors not evident at the time the test borings were performed. Therefore, groundwater levels during construction or at other times in the life of the structure may be higher or lower than the levels indicated on the attached test boring logs. The possibility of groundwater level fluctuations should be considered when developing the design and construction plans for the project.

GEOTECHNICAL OVERVIEW

The near surface, stiff to very stiff, medium-plasticity cohesive soils encountered at this site could become unstable with typical earthwork and construction traffic, especially after precipitation events. The effective drainage should be completed early in the construction sequence and maintained after construction to avoid potential issues. If possible, the grading should be performed during the warmer and drier times of the year. If grading is performed during the winter months, an increased risk for possible undercutting and replacement of unstable subgrade will persist. Additional site preparation recommendations, including subgrade improvement and fill placement, are provided in the Earthwork section.

Based on conversation with the client and encountered conditions onsite, it is our understanding that earthwork activity was recently completed for a development adjacent to and east of the project site. Existing fill soils encountered in our boring program appear to have been part of this recent earthwork activity, indicating the recent earthwork lies within at least a portion of our project site. Conversation with the client also indicates that proper placement and compaction of the newly-placed fill was most likely documented for the adjacent project. However, Terracon has

Responsive ■ Resourceful ■ Reliable 8 not been provided with this documentation for our review to confirm the newly-placed fill is indeed controlled. Encountered conditions do indicate the fill appears to have been consistently placed with at an acceptable degree of compactive effort. Regardless, placement and compaction documentation would need to be provided for our review to confirm this.

From review of the grading plans, while it appears most of the residential complex will not be bearing directly on nor within the recently placed fill, we expect that a portion of the south residential building will bear on, within, or just above the existing fill. The remaining portion of the building will be supported on new structural fill extending to the recently placed fill. Based on this information, it is recommended the controlled nature of this fill be reviewed to confirm the soils placed are suitable for support of new structural fill (as discuss in the Earthwork section of this report) and direct support of the new building foundations in areas where this is applicable prior to construction commencing.

Provided grading plans indicate that new structural fill depths will vary from less than about 2 feet on the northeast end of the proposed development to up to about 17 feet in the western portion of the development near the crest of the west fill slope. Proposed fill placement within the building footprint is also expected to vary from less than about 2 feet to up to about 17 feet. Care should be taken to ensure the rate of settlement from placement of new structural fill dissipates to acceptable levels prior to commencement of construction of the new building and associated pavements and utilities.

Review of the grading plans and discussion with the client also indicates that the north building will include a walk-out basement and below-grade foundation walls at this portion of the development. It is anticipated that at least a portion of the north building’s floor slab and foundations will be bearing directly on bedrock.

The Shallow Foundations section addresses support of the building bearing on stiff native soils, engineered fill extending to at least stiff native soils, or bedrock. The Floor Slabs section addresses slab-on-grade support of the buildings.

Flexible and rigid pavement systems are considered suitable for this site. The Pavements section addresses the design of pavement systems.

Relatively shallow limestone bedrock was encountered at this site in some of our test borings.

The rock varied in depth from about 1.5 feet to 20.5 feet below existing grades. Slight bedrock weathering was encountered, with strength varying from weak to (at least) strong, based on visual classification and lab testing. Based on provided information, it is possible that excavation into bedrock will be necessary for below-grade structures, floor slabs, foundations, and/or installation of utilities. If excavation into bedrock is required, shallow, completely to highly weathered bedrock

(where encountered) can be mechanically ripped; heavy excavation equipment is generally required for deeper excavation. Slightly weathered to unweathered rock may require drilling and blasting.

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Hoe-rams and/or rock-trenchers may be needed in excavations where working space will be limited.

Final elevations should be chosen to minimize the amount of potential bedrock excavation required.

Expansive soils (including fat clays and elastic silts at greater depths) are present on this site in some areas. Review of provided grading plans indicates these soils could potentially have an impact on the proposed building structure (foundations and floor slab) across a portion of the site;

particularly on the northern side of the property where proposed fill depths are minimal and where some minor cutting is proposed. These soils may also directly impact proposed utilities in some areas and planned pavements on the southern side of the project site. This report provides recommendations to help mitigate the effects of soil shrinkage and expansion, where exposed.

However, even if these procedures are followed, some movement and (at least minor) cracking in the pavements should be anticipated. The severity of cracking will probably increase if modification of the site results in excessive wetting or drying of the expansive soils. Eliminating the risk of movement and distress may not be feasible, but it may be possible to further reduce the risk of movement if significantly more expensive measures are used during construction.

Some of these options are discussed in this report such as complete replacement of expansive soils.

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

EARTHWORK

Earthwork is anticipated to include clearing and grubbing, excavations, and fill placement. The following sections provide recommendations for use in the preparation of specifications for the work. Recommendations include critical quality criteria, as necessary, to render the site in the state considered in our geotechnical engineering evaluation for foundations, floor slabs, and pavements.

Proposed Grading

Existing surface grades surrounding the proposed buildings range from elevations of about 901 feet to 916 feet within the footprint of the proposed residential complex (sloping downward in a east-to-west direction). Based on the available site plan and proposed first floor FFE of 918.50 feet (with an assumed building subgrade elevation of about 918 feet) and lower level FFE of 904.83 feet

(with assumed building subgrade of about 904 feet), we anticipate as much as approximately 17 feet of fill will be placed in the building area at this site to achieve desired grades and elevations.

Cutting will also occur along the northeast portion of the north residential building and is not expected to exceed about 7 feet.

For purposes of this report, we will assume a floor slab subgrade elevation of 918 feet for the south building. Review of the grading plan indicates a walkout basement will be utilized for the

Responsive ■ Resourceful ■ Reliable 10 north building. For purposes of this report, we will assume the proposed subgrade elevation for the north building will be approximately 904 feet.

On the following table, we have tabulated the anticipated cuts and fills at the seven building borings and one karst boring (located within the immediate vicinity of the residential building complex) locations.

Site Preparation

The following presents general recommendations for site preparation, excavation, and fill placement. Special considerations will be needed where site grading may expose unstable soils.

Our recommendations presented for design and construction of earth supported elements (i.e.

Boring

No.

Location

Existing

Ground

Surface

Elev.

(feet)1

Proposed

Subgrade

Elevation

(feet)2

Cut (-)/ Fill (+)

(feet)3

Material

Anticipated at

Subgrade

B-1 North Building - SE Corner 911 904 -7 Native Soils 5

B-2 North Building - NE Corner 911

-7 Native

Soils/Bedrock 5, 6

B-3 North Building - NW Corner 901 904 +3 Engineered Fill

B-4 See Note 4 911 918 +5 Engineered Fill

B-5 South Building - NW Corner 902 918 +16 Engineered Fill

B-6 South Building - SW Corner 906 918 +12 Engineered Fill

B-7 South Building - SE Corner 916 918 +2 Engineered Fill

K-1 North Building - South Wall 911 918 +5 Engineered Fill

1. Approximate and based on provided existing grading plan

2. Estimated subgrade elevation based on existing grading plan, provided FFE of Elevation

918.50 feet, and estimated finished walkout basement subgrade elevation of 904 feet for the north building, only.

3. All cut and fill values are approximate

4. Located at the North Building’s SW Corner and the South Building’s NE Building Corner at the

Pedestrian Connector

5. Native soils are comprised mostly of stiff to very stiff lean clays, silts, fat clays, and elastic silts.

High-plasticity fat clays were encountered near the surface within Boring B-2.

6. Encountered bedrock varied from weak to strong, with slight weathering. Bedrock should be anticipated in the area of boring B-2

Responsive ■ Resourceful ■ Reliable 11 foundations, slabs, etc.) are contingent upon following the recommendations outlined in this section. All earthwork activities on the project should be observed and evaluated by a representative of the geotechnical engineer.

Removal and/or relocation of any “to be abandoned” utilities should be performed prior to rough site grading activities. Any abandoned underground pipes left in place should be fully grouted.

Excavations created due to utility relocations should be backfilled with granular structural fill material, placed and compacted in accordance with the recommendations provided in the following paragraphs, or with lean concrete or flowable fill. If lean concrete is used as backfill, the contractor should refer to the new-build Mechanical-Electrical-Plumbing (MEP) and foundation drawings to confirm that the concrete backfill materials will not conflict with any new item installations or construction.

Prior to placing fill, existing vegetation and root mat should be removed. Complete stripping of the topsoil should be performed in the proposed building and parking/driveway areas. Topsoil thickness listed in the boring logs are for specific locations tested. The thickness of the topsoil may vary across the site; thus, we recommend that a contingency for topsoil volume removal be considered to account for this variability. Additionally, we recommend that geotechnical personnel be on site to observe topsoil removal.

To minimize risk to foundations and floor slabs from potentially expansive soils, where fat clays or elastic silts are exposed at subgrade elevation, a 18-inch layer of properly compacted structural fill meeting low volume change (LVC) requirements in the Fill Material Types section of this report should exist below floor slab subgrade elevation. We also recommend 18 inches of LVC structural fill lie below pavement subgrade elevation to address risks associated with potentially expansive soils.

For the floor slab, pavement, and any areas to receive structural fill, once any required stripping/undercutting of existing fill or topsoil is complete and prior to placement of structural fill, the exposed subgrade soils should be carefully proof rolled under close observation by geotechnical personnel. This proof rolling program is very important with respect to evaluating structural fill, floor slab, and pavement support areas. Proof rolling should be accomplished using a pneumatic-tired, fully-loaded (minimum gross weight of 20 tons) tandem-axle dump truck. Soft or yielding areas should be undercut or stabilized as necessary to achieve suitable, stable subgrade conditions. Stabilization can include scarification and recompaction to 98 percent of the material’s maximum Standard Proctor dry density, placement and compaction of coarse, angular stone into the subgrade, utilization of geogrid, and/or partial undercutting and replacing the unstable materials with more stable granular material. The proof rolling program should consist of a minimum of 3 passes by the proof rolling equipment. Excessively wet or dry material should either be removed or moisture conditioned and recompacted. If groundwater is encountered during the undercutting process, measures should be implemented to control it during and after construction.

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Based on available information, it is estimated that up to 17 feet of new structural fill will occur in the building area to bring the site to finished grade. The settlement of any new fill over 5 feet of depth should be monitored to ascertain that the majority of the settlement associated with the fill placement is completed prior to commencing construction of the building and pavements supported on the fill. Typically, the construction of the foundations, slabs, and pavements on the fill may commence once the rate of settlement drops below 1/8 of an inch per week for at least 2 consecutive weeks. Terracon can assist with providing a settlement monitoring program, upon request.

Existing Fill

As noted in Geotechnical Characterization, Borings B-1, B-4, B-6, B-7, and K-1 encountered existing fill to depths ranging from about 3 feet to 6.5 feet below existing grade. Based on discussion with the client and review of available information, the fill appears to have been placed in a controlled manner, but we have no records to indicate the degree of control. Support of footings, floor slabs, and pavements, on or above existing fill soils, is discussed in this report.

However, even with the recommended construction procedures, there is 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.

If the owner elects to place new engineered fill and construct foundations, floor slabs and pavements on the existing fill or above the existing fill (in areas where this is applicable), the following protocol should be followed. All areas of existing fill should be thoroughly proof rolled with a pneumatic-tired, fully-loaded (minimum gross weight of 20 tons) tandem-axle dump truck.

Any weak areas indicated by the proof rolling should be undercut and replaced with new structural fill, prior to placing new structural fill to achieve design subgrade elevation. For footing excavations, visual observation and appropriate testing by qualified personnel should be performed to determine the bearing soils’ suitability for foundation support. For new structural fill, floor slabs, and pavements, once the planned subgrade elevation has been reached the entire slab and/or pavement area should be proofrolled. Areas of soft or otherwise unsuitable material should be undercut and replaced with either new structural fill or suitable, existing on-site materials.

After proof-rolling and prior to the placement of structural fill in areas below design grade, the subgrade should be scarified, moisture conditioned and re-compacted to the density recommended in the Fill Compaction Requirements section below. This process will further help to delineate soft or disturbed areas. Unstable areas identified during scarification and re-compaction should be undercut to expose stable material.

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Fill Slopes

Fill slopes for the project are proposed to range from between about 2¾H:1V to about 5H:1V; with a 3½H:1V fill slope with a maximum proposed height of 23 feet on the west side of the proposed building complex and a 2¾:1V fill slope with a maximum proposed height of 17 feet on the southwest side of the building complex.

Our scope of work did not include recommendations related to embankment design. We can provide these services, upon request. Additional analyses may be required to provide these services.

When constructing embankments on side slopes, as is expected here, care must be given to make sure that adequate interlock occurs between the proposed embankment and sloping foundation to minimize the risk of developing slip planes. Based on available data, the existing site has terrain with natural slopes ranging from less than 10H:1V to slopes of about 3H:1V. For natural slopes less than 5H:1V, existing ground can be scarified and re-compacted according to specifications listed in this report. Benching is recommended for slopes equal to or greater (or steeper) than 5H:1V. Weak existing fill and/or native soils encountered during earthwork activities in areas to receive embankment fill should be completely removed and the new fill benched into competent existing fill (with at least a stiff consistency) or stiff native residual soils.

Fill operations should commence at the lowest portion of the fill slope and the finished grades should be established with quality controlled structural fill. Special base preparation measures may need to be implemented prior to placement of any structural fill if any weak existing soils are encountered. Any yielding areas should be stabilized with crushed stone or durable rock materials until a stable base to receive structural fill is achieved.

For areas that require benching, each horizontal cut for the bench must begin in competent material after removal of poor-quality foundation materials, including topsoil and any existing weak soils or rock with the potential for creep. The structural fill should be placed in horizontal lifts and should be adequately benched into the slope. The benches should be wide enough for placement and compaction equipment and operations and should have a minimum rise of 12 inches. This construction measure is recommended to allow all structural fill to be keyed into the sloping ground surface. Any keyways, which bear the overall thrust of the slope, should extend a minimum of 2 feet into intact foundation materials.

Furthermore, we recommend that fill slopes be overfilled and then cut back to develop an adequately compacted slope face. The fill slopes should be overfilled an additional 5 feet beyond the desired slope configuration to achieve the desired compaction at the edge of the finished slope. Once final grades are reached, the excess perimeter fill can be sloped to the desired appearance.

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5' min.

Temporary Overfill, Cut back to desired

Slope Contour

Overburden

Engineered Fill

Note: Slope angles shown in figure above are for illustration purposes only; proposed fill slope angles are mostly anticipated to vary from 2H:1V to less than 5H:1V

Proper drainage should be provided for any seeps or springs that are encountered during embankment construction. Adequate provisions should also be made to drain/divert surface runoff water so that its flow on the proposed fill slopes is prevented/minimized.

Typically, it is recommended that buildings and other structures maintain enough distance from the crest of any slopes to prevent crown loading of the slope due to area loads associated with the structures, which could lead to slope instability. The zone of influence from foundation stresses should not overlap with proposed slopes. One method of estimating the zone of influence is by assuming foundation stresses generated from building loads spread outwardly at an angle of 2 (vertical) to 1 (horizontal) from the edges of the loaded areas (or shallow foundations). If grading plans or loading conditions change from those currently proposed, this information should be provided to Terracon for our review so we may modify our recommendations, where appropriate.

For pavement areas, care should be taken to avoid placing pavements within 5 feet of the top (or crest) of proposed fill slopes.

Fill Material Types

Fill required to achieve design grade should be classified as structural fill and general fill.

Structural fill is material used below, or within 10 feet of structures, pavements or constructed slopes. General fill is material used to achieve grade outside of these areas. Earthen materials used for structural and general fill should meet the following material property requirements:

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Soil Type USCS Classification Acceptable Location for Placement

Low Plasticity

Cohesive (Low

Volume Change

Material)

CL, CL-ML

(LL<40, PI<25)

All locations and elevations

High Plasticity

Cohesive

CH, MH and CL

(LL≥40, PI≥25)

Greater than 18 inches below building grade

Greater than 18 inches below pavement grade

Granular (Low Volume

Change Material) SW, GW All locations and elevations

On-Site Soils CL, CH, ML, MH

Some on-site soils generally appear suitable for reuse as engineered fill, pending further testing.

Deleterious materials (e.g., wood, organic matter, construction debris, etc.) should be removed and not used as engineered fill. Moderately to highly-plastic soils (with a LL>40) should be placed a minimum of

36 inches below floor slab subgrade elevation.

Moisture conditioning of the on-site native soils may be required to achieve optimum moisture conditions for placement as engineered fill.

1. Structural and general fill should consist of approved materials 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 the Geotechnical Engineer for evaluation prior to use on this site.

2. CH or MH soils should not be used within 18 inches of finished grade in building and pavement areas

Fill Compaction Requirements

Structural and general fill should meet the following compaction requirements.

Item Structural Fill General 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-guided equipment (i.e. jumping jack or plate compactor) is used

Same as Structural fill

Minimum Compaction

Requirements 1, 2, 3

98% of max. below foundations and within 1 foot of finished pavement subgrade

98% of max. above foundations, below floor slabs, and more than 1 foot below finished pavement subgrade

92% of max.

Water Content

Range

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

High plasticity cohesive: 0 to +4% of optimum

Granular: -3% to +3% of optimum

As required to achieve min.

compaction requirements

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Item Structural Fill General Fill

1. Maximum density and optimum water content as determined by the standard Proctor test (ASTM D 698).

2. High plasticity cohesive fill should not be compacted to more than 100% of standard Proctor maximum dry density.

3. 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).

Utility Trench Backfill

For low permeability subgrades, utility trenches are a common source of water infiltration and migration. Utility trenches penetrating beneath the building should be effectively sealed to restrict water intrusion and flow through the trenches, which could migrate below the building. The trench should provide an effective trench plug that extends at least 5 feet from the face of the building exterior. The plug material should consist of cementitious flowable fill or low permeability clay.

The trench plug material should be placed to surround the utility line. If used, the clay trench plug material should be placed and compacted to comply with the water content and compaction recommendations for structural fill stated previously in this report.

Grading and Drainage

All grades must provide effective drainage away from the building during and after construction and should be maintained throughout the life of the structure. Water retained next to the building can result in soil movements greater than those discussed in this report. Greater movements can result in unacceptable differential floor slab and/or foundation movements, cracked slabs and walls, and roof leaks. The roof should have gutters/drains with downspouts that discharge into approved below grade storm collection systems or onto splash blocks at a distance of at least 10 feet from the building.

Exposed ground should be sloped and maintained at a minimum 5% away from the building for at least 10 feet beyond the perimeter of the building. Locally, flatter grades may be necessary to transition ADA access requirements for flatwork. After building construction and landscaping have been completed, final grades should be verified to document effective drainage has been achieved. Grades around the structure should also be periodically inspected and adjusted, as necessary, as part of the structure’s maintenance program. Where paving or flatwork abuts the structure, a maintenance program should be established to effectively seal and maintain joints and prevent surface water infiltration.

Earthwork Construction Considerations

Shallow excavations for the proposed structure are anticipated to be accomplished with conventional construction equipment. Upon completion of filling and grading, care should be taken to maintain the subgrade water content prior to construction of floor slabs. Construction traffic over the completed subgrades should be avoided. The site should also be graded to prevent

Responsive ■ Resourceful ■ Reliable 17 ponding of surface water on the prepared subgrades or in excavations. Water collecting over or adjacent to construction areas should be removed. If the subgrade freezes, desiccates, saturates, or is disturbed, the affected material should be removed, or the materials should be scarified, moisture conditioned, and recompacted prior to floor slab construction.

Depth to bedrock varied from about 1.5 feet to 20.5 feet below existing grade. Generally, stiff to very stiff clay was encountered beneath existing grades and eventually transitioned to weak to strong limestone bedrock with increasing depth. Cutting of existing rock may be required in some areas to reach foundation or floor slab design bearing elevation or for utility purposes. A portion of the limestone bedrock near these elevations may be rippable using a large dozer or track-type excavator equipped with either a single tine or multiple rippers to excavate into the rock. However, contactors should be prepared to use rock chisels and hammers to remove harder bedrock, if encountered.

As a minimum, excavations should be performed in accordance with OSHA 29 CFR, Part 1926, Subpart P, “Excavations” and its appendices, and in accordance with any applicable local, and/or state regulations.

Construction site safety is the sole responsibility of the contractor who controls the means, methods, and sequencing of construction operations. Under no circumstances shall the information provided herein be interpreted to mean Terracon is assuming responsibility for construction site safety, or the contractor's activities; such responsibility shall neither be implied nor inferred.

Construction Observation and Testing

The earthwork efforts should be monitored under the direction of the Geotechnical Engineer.

Monitoring should include documentation of adequate removal of vegetation and topsoil, proofrolling, and mitigation of areas delineated by the proofroll to require mitigation.

Each lift of compacted fill should be tested, evaluated, and reworked, as necessary, until approved by the Geotechnical Engineer prior to placement of additional lifts. Each lift of fill should be tested for density and water content at a frequency of at least one test for every 2,500 square feet of compacted fill in the building areas and 5,000 square feet in pavement areas. One density and water content test should be performed for every 50 linear feet of compacted utility trench backfill.

In areas of foundation excavations, the bearing subgrade should be evaluated under the direction of the Geotechnical Engineer. If unanticipated conditions are encountered, the Geotechnical

Engineer should prescribe mitigation options.

In addition to the documentation of the essential parameters necessary for construction, the continuation of the Geotechnical Engineer into the construction phase of the project provides the continuity to maintain the Geotechnical Engineer’s evaluation of subsurface conditions, including assessing variations and…