B08_Attachment_13_BIBE_259631-317515_Final_CD_Reports_6_18_2025.pdf

BIG BEND NATIONAL PARK

TEXAS

REPLACE THE CHISOS MOUNTAINS LODGE

AND

REHABILITATE THE CHISOS BASIN WATER SYSTEM

BIBE

PMIS 259631-317515

PROJECT REPORTS

VOLUME 4

100% COMPLETE CONSTRUCTION DOCUMENTS

LODGE AND WATER COMPONENTS

November 4, 2024

NATIONAL PARK SERVICE (NPS)

DENVER SERVICE CENTER (DSC)

GEOTECHNICAL REPORTS – LODGE AND WATER COMPONENTS

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20182012.003A/DFW21R120916 Page i of iv March 11, 2021 © 2021 Kleinfelder www.kleinfelder.com

KLEINFELDER 7805 Mesquite Bend Drive, Suite 100, Irving, TX. 75063 p | 972.868.5900 f | 972.409.0008

GEOTECHNICAL STUDY

CHISOS BASIN LODGE RESTAURANT

BIG BEND NATIONAL PARK, TEXAS

KLEINFELDER PROJECT # 20182012.003A

MARCH 11, 2021

Copyright 2021 Kleinfelder All Rights Reserved

ONLY THE CLIENT OR ITS DESIGNATED REPRESENTATIVES MAY USE THIS DOCUMENT AND ONLY FOR THE SPECIFIC

PROJECT FOR WHICH THIS REPORT WAS PREPARED.

http://www.kleinfelder.com/

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March 11, 2021 Kleinfelder Project No.: 20182012.003A

Architectural Resources Group, Inc.

9 Pier, Ste 107 San Francisco, California 94111

Attention: Ms. Debbie Cooper Mr. Gary Koll

Subject: Geotechnical Study Chisos Basin Lodge Restaurant Big Bend National Park, Texas

Dear Ms. Cooper and Mr. Koll:

This report presents the findings of our geotechnical study for the Chisos Basin Lodge Restaurant, located at Big Bend National Park, Texas. The purpose of this report is to evaluate the subsurface conditions for the potential future movement in the subgrade soil and to discuss options for repair, dependent upon the results of our study. This report has been prepared and submitted in general accordance with our proposal. We appreciate the opportunity to assist you in your evaluation of this structure.

If you have any questions regarding our report or wish to discuss any additional services, please call us at 972.868.5900.

Best Regards, KLEINFELDER, INC.

Texas Registered Engineering Firm F-16438

Christian Martinez, PE Richard J. Hammerberg, PE Project Engineer Senior Project Manager

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A Report Prepared for:

Architectural Resources Group, Inc.

9 Pier, Ste 107 San Francisco, California 94111

Prepared by:

Christian Martinez, PE Project Engineer

Richard J. Hammerberg, PE Senior Project Manager

Reviewed by:

Sri Dinakaran, PE, DGE, DBIA Senior Program Manager

KLEINFELDER, INC.

Texas Registered Engineering Firm F-16438

7805 Mesquite Bend Drive, Suite 100 Irving, Texas 75063 Phone: 972.868.5900 Fax: 972.409.0008

March 11, 2021 Kleinfelder Project No.: 20182012.003A

3/11/2021

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TABLE OF CONTENTS

SECTION PAGE

1 INTRODUCTION

PROJECT DESCRIPTION

PURPOSE AND SCOPE

2 FIELD EXPLORATION AND LABORATORY TESTING

FIELD EXPLORATION

LABORATORY TESTS

3 SUBSURFACE CONDITIONS

GEOLOGY

STRATIGRAPHY

GROUNDWATER OBSERVATIONS

4 ANALYSIS

EXPANSIVE SOIL CHARACTERISTICS

FINDINGS

5 RECOMMENDATIONS

REHABILITATION OF THE EXISTING STRUCTURE

5.1.1 Floor Slab Treatment

5.1.2 Underpinning

5.1.3 Drilled Shaft Construction

5.1.4 LPILE Parameters (Version 2018) for Soil

REPLACING THE EXISTING STRUCTURE

5.2.1 Grade Beams

5.2.2 Suspended Floor Slab System

SHALLOW FOUNDATIONS

5.3.1 Subgrade Modifications

5.3.2 Structural Load Support

5.3.3 Interior Floor Slab

5.3.4 Construction Considerations

LATERAL EARTH PRESSURES

SEISMIC CONSIDERATIONS

6 LIMITATIONS

ATTACHMENTS:

APPENDIX A

Important Information about This Geotechnical-Engineering Report

APPENDIX B

Exploration Location Plan and Vicinity Map ...................................................................... Figure 1 Floor Level Elevation........................................................................................................ Figure 2 Graphics Key ................................................................................................................... Figure 3 Soil Description Key ......................................................................................................... Figure 4 Boring Logs ............................................................................... B-01 to B-09 and TP-01 to TP-02 One Dimensional Expansion or Compression of Cohesive Soils Test Results ...... Figures 5 to 12

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1 INTRODUCTION

PROJECT DESCRIPTION

The building is located at 1 Basin Rural Station within the Big Bend National Park, Texas. We understand the building was constructed in 1964 and the structure is comprised of structural steel and wood framing with non-load bearing concrete masonry unit (CMU) walls and a concrete slab-on-grade. The structure is supported by a shallow foundation system. Modifications to the structure have been made since original construction. Over the years, park and restaurant staff have observed cracks in the CMU and loading dock walls, and differential movement of the floor slab. Kleinfelder performed a preliminary geotechnical evaluation for this structure in 2018 and presented our findings and recommendations in a report dated October 12, 2018 (Kleinfelder

Project No. 20182012.002A). We understand the National Park Service (NPS) is now considering three options: structural and architectural rehabilitation of the existing structure, replace the existing structure in the same general footprint, or rehabilitate the existing structure and design an expansion to the structure to include a Visitor Center and Retail Store. Additional geotechnical work was required for each of these scenarios.

PURPOSE AND SCOPE

The purpose of this study was to provide the design team with geotechnical information of the near surface fill soils directly under the existing slab on grade as well as the native soils on the west side of the building to supplement the information provided in our previous report (Kleinfelder

Project No. 20182012.002A). The study is intended to assist the project team in designing structural repairs and/or designing a new foundation system for new structures. To accomplish the intended purpose, the study has been conducted based on the following scope:

• Drilled and sampled six borings (2 exterior and 4 interior) and two test pits to assess general subsurface conditions and to obtain samples for testing.

• Performed laboratory tests on representative samples to assess pertinent engineering properties of the subsurface materials.

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• Performed engineering analyses, using the field and laboratory data to offer an opinion as to the cause of distress from a geotechnical point of view and to estimate future movement potential which can be used by the design team to develop an appropriate repair plan.

The recommendations contained herein are based on a combination of the borings and laboratory data (performed by Kleinfelder), data supplied by Architechtural Resources Group, Inc., and our stated assumptions within this report. Our recommendations are also based on the provisions outlined in the Limitations section of this report. We recommend that all individuals read the report limitations along with the document from the Geoprofessional Business Association provided in

Appendix A.

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2 FIELD EXPLORATION AND LABORATORY TESTING

FIELD EXPLORATION

Drilling operations were conducted on December 03, 2020 using an ATV (CME-55) drill rig, and a portable drilling rig. Subsurface materials at the project site were explored by drilling two exterior borings designated as B-04 and B-05, to depths ranging from 20 to 35 feet; and four interior borings designated as B-06 to B-09 to depths ranging from 2 to 9.5 feet. Additionally, two test pits designated as TP-01and TP-02 were excavated at the site.

The two exterior borings were drilled at the northwest side of the building. B-04 was drilled near the patio and B-05 was drilled at the other extreme of the building behind the loading dock. The interior borings B-06, B-07, B-08, and B-09 were drilled at the break room, the kitchen hallway, dry food storage room, and the loading dock.

GPS coordinates of the boring locations were recorded using a portable handheld GPS receiver with a horizontal accuracy of approximately 15 feet. For the interior borings the coordinates were estimated using Google Earth. GPS coordinates are shown in the top left side of the boring logs just above the lithologic description. The approximate locations are shown on Exploration

Location Plan and Vicinity Map, Figure 1, in Appendix B.

Auger drilling and sampling drilling techniques were used without drilling fluids for the exterior borings and continuous push tube sampling for the interior borings. At the completion of drilling, each boring was backfilled with auger cuttings. Concrete surfaces (Borings B-06 to B-09) were backfilled with bentonite chips and patched with Portland cement concrete grout.

A log of each boring is presented in Appendix B, along with a key to the symbols and terms used on the logs. The logs indicate the material types, depths, and other details encountered for each boring. Soil descriptions presented upon the boring logs resulted from a combination of field and laboratory test data. Stratigraphy lines correspond to the approximate boundary between strata.

However, the in-situ subsurface transition can be, and is often gradual.

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The exterior borings (B-04 and B-05) were continuously sampled in the upper 10 feet using intermittent sampling with seamless steel tubes or split-spoon samplers. Following the continuous sampling, the exterior borings were completed using auger drilling procedures with intermittent sampling. Relatively undisturbed samples of cohesive soils were collected by using the drilling rig to push a seamless, steel tube sampler into the soil. The depths at which these samples were collected are indicated on the boring logs. After a tube was recovered, the sample was extruded in the field, examined, and logged. The sample was then sealed in a plastic bag to reduce moisture loss and protect the sample.

At select locations, samples were collected by driving a split-spoon sampler in conjunction with the Standard Penetration Test (SPT). This technique involves driving the spoon sampler a distance into the soil using a free-falling hammer. During the test the logger records the number of blows required to drive the spoon sampler over three successive 6-inch increments. The first

6 inches is the “seating drive,” while the number of blows required to drive the sample the last two

6-inch increments is the “penetration” in blows per foot. The results of the penetration test are reported on the boring logs at the corresponding depth. Materials recovered from the split-spoon sampler are then placed in a plastic bag to reduce moisture loss and protect the sample.

The interior borings (B-06 to B-09) were completed by coring through the concrete floor slab followed by continuous sampling with seamless steel tubes. These tubes were hydraulically advanced into the subsurface materials. The seamless tube samples were extruded in the field.

During logging, an estimate of the sample consistency was obtained using a pocket penetrometer.

This test provides relative strength data that is used as an approximate indicator of shear strength.

The result of the penetrometer reading is recorded at a corresponding depth on the boring logs.

Note that a reported value of “4.5+” indicates that the capacity of the penetrometer device was exceeded.

LABORATORY TESTS

Laboratory testing was performed on select samples collected from the borings during drilling.

These samples were selected as being generally representative of that stratum and/or boring(s).

Testing was performed to allow for material classification according to the Unified Soil

Classification System (ASTM D2487), and to evaluate the engineering properties of the materials.

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These tests included:

• Moisture content;

• Atterberg limits (liquid and plastic limits);

• Percent passing No. 200 sieve;

• Unit dry weight;

• Unconfined Compression; and

• One-dimensional swell.

The results of these tests are presented at the corresponding depth on each individual boring log and on Figures 5 through 12 in Appendix B.

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3 SUBSURFACE CONDITIONS

GEOLOGY

Based on the Emory Peak - Presidio Sheet of the Geologic Atlas of Texas, and the contents of our borings, in our opinion, the project is underlain by Young Quaternary Deposits, consisting of alluvial fan deposits from the erosion of the mountains surrounding the site underlain by the

Chisos Formation. Quaternary deposits are generally comprised of fine to medium grained sand, silt, clay, gravel, and weakly to strongly cemented caliche. The Chisos Formation typically consists of clay, mudstone, and sandstone.

STRATIGRAPHY

The subsurface conditions observed under the floor slab consisted of fill material. Borings

B-06, B-07, and B-08 encountered refusal at depths ranging from 2 to 3 feet. Therefore, the extent of the fill material is not known at these locations. Boring B-09 which was drilled near the loading dock, consisted of 4 feet of fill material underlain by fat clay. The fill material consisted of moderately expansive sandy lean clay and lean-to fat clay soils.

The subsurface conditions observed in Borings B-04 and B-05, consisted of approximately 2 to

3 feet of undocumented fill underlain by fat clay and lean clay soils, with varying amounts of sand.

The undocumented fill consisted of clayey sand material. The clay soils encountered just below the fill to depths of 10 to 13 feet below the existing grade appear to be disturbed. It is difficult to confirm that these soils are fill, so a “PROBABLE FILL” descriptor has been added to this stratum.

Detailed descriptions of the stratigraphy are included in the boring logs presented in Appendix B.

One test pit was excavated with a small backhoe excavator at the northwest side of the building.

Based on this test pit, we estimate that the east to west footing is about 5.5 feet below the cantilever deck, with approximately 4.5 feet of fill above the footing. The fill material consisted of a mixture of lean and fat clay with large concrete boulders at the surface. Samples of the soil materials below the footing were obtained for laboratory testing.

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Another test pit was hand excavated inside the building near the loading dock. The footing in this area was encountered at a depth of approximately 4.5 feet. The fill above the footing consisted of a sandy fat clay with various amounts of gravel. Samples of the soil materials below the footing were obtained for laboratory testing.

GROUNDWATER OBSERVATIONS

The borings were advanced using techniques that allow for direct and indirect observations of seepage and groundwater during drilling operations. At the time of our field exploration, groundwater was not encountered in the borings. However, it is not unusual to encounter shallow groundwater within these formations, especially during and after periods of rainfall. Water tends to percolate down through the surficial soils until encountering a relatively impervious layer, and then either flow down gradient or become trapped. Water also tends to flow through vertical and horizontal fractured planes in the clay mass and through sand seams.

It should be noted that these observations are indicative only of conditions at the time and place indicated. The occurrence of and variations in groundwater levels can vary due to many factors, including seasonal changes, topography, surface runoff, the layering/permeability of subsurface strata, irrigation from adjacent tracts, and other factors not evident at the time of this study. The possibility of groundwater and its fluctuation should be considered when developing this project.

The water observations conducted for this study were short-term and should not be interpreted as a groundwater study.

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4 ANALYSIS

The building is located at 1 Basin Rural Station within the Big Bend National Park, Texas. We understand the building was constructed in 1964 and the structure is comprised of structural steel and wood framing with non-load bearing concrete masonry unit (CMU) walls and a concrete slab-on-grade. The structure is supported by a shallow foundation system. Modifications to the structure have been made since original construction. Over the years, park and restaurant staff have observed cracks in the CMU and loading dock walls, and differential movement of the of floor slab. Our conclusions and remediation options for use in developing the appropriate repair plan have been provided in the following sections.

EXPANSIVE SOIL CHARACTERISTICS

Based on the laboratory test results, the underlying fill material can be classified as moderately to highly plastic clay soils. The expansive clay soil will exhibit shrink and swell behavior, the amount of which will depend upon moisture fluctuations that occur over the design life of the structure. The total magnitude of the shrink/swell behavior is also dependent upon the thickness of the expansive soil and the depth of the active moisture zone. Moisture fluctuations occur due to seasonal cycles, but can also be influenced to varying degrees by drainage conditions; site grades/sloping ground, landscaping, irrigation practices, the presence of vegetation, groundwater, and the presence of flatwork or other impervious barriers. This large number of variables complicates the evaluation of the magnitude of shrink/swell movements that could occur.

Typically, building pads for structures, such as this, are designed for a potential of 1 inch of post-construction movement. An estimate of the potential expansive soil movement was made by using swell test results, engineering judgment, and our experience. Based on these procedures, the Potential Vertical Movement (PVM) for this site, based on existing moisture conditions, is estimated to be on the order of 5 to 5-½ inches. This estimate includes fill and native soils in the top 10 feet.

These are not exact values but are only an indication of the potential movements due to expansive soil for seasonal moisture fluctuations. Actual movements may be significantly larger than estimated due to inadequate site grading, poor drainage, ponding surface water, and/or leaks in utility lines. Significant changes to existing site grading can also alter actual vertical movements

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FINDINGS

As previously mentioned, we calculated potential vertical movement ranging from 5 to 5-½ inches at this site. In our opinion, the clay soils below the floor slab have a moisture content low enough such that risk of further significant floor slab movement due to increased moisture content of the near surface clay soils is high. Therefore, significant floor slab movement can be expected.

Based on the field exploration and laboratory testing, in our opinion, the fill material was not moisture conditioned and compacted in a manner that would mitigate the expansion potential of the clay material. Typical moisture requirement for this material is +2 to +6% of optimum moisture content.

The test pits indicate that the footings exposed are being supported on stiff to hard fat clay. Typical bearing capacities for these soils range between 2,000 to 3,000psf assuming a factor of safety of about 3. Laboratory testing indicates a current swell pressure for the clays below the footings to be on the order of 5,000 psf. Consequently, the presumptive downward pressure exerted on the footings will not be high enough to prevent the clay soils from swelling. Thus, continued movement of the footings should be anticipated.

A survey of the top of the floor slab was performed by Kleinfelder. Based on this survey, the floor slab has experienced a differential movement of approximately 11-½ inches across the building.

The clays present at this site do not exhibit the potential to cause upwards of 16 inches of vertical movement; therefore, it is our opinion that the structure has been subjected to heave as well as settlement. The cause of settlement would have most likely come from low relative compaction of the clay fill during construction.

The lowest point of the floor slab is located on the southwest corner of the building in the office room and the highest point is located on the northeast corner of the building in the pantry.

According to the damage map provided to us, it appears that much of the damage in the building is concentrated on the northeast portion of the building which appears to correlate with the portion of the building that has the highest floor slab elevation.

Remediation options for use in developing the appropriate repair plan are discussed in the following section.

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5 RECOMMENDATIONS

We understand the National Park Service (NPS) is now considering three options: structural and architectural rehabilitation of the existing structure, replacement of existing structure in the same general footprint, or rehabilitate the existing structure and design an expansion to the structure to include a Visitor Center and Retail Store.

REHABILITATION OF THE EXISTING STRUCTURE

5.1.1 Floor Slab Treatment

A PVM of about 1 inch is generally considered acceptable for the interior floor slab. Based on our calculations, this site presents a future movement potential of up to 5-½ inches. Therefore, we recommend staged removal and replacement of the existing slab on grade. Expansive clay soils should be removed to the footing elevation and replaced with a relatively non-expansive select fill and the subgrade regraded as appropriate to re-establish the finish floor slab elevation. The over excavation would reduce the PVM to about 2-1/2 inches. Prior to placing any fill, the top 12 inches of the exposed soil should be scarified, moisture conditioned, and recompacted to a minimum density of 95 percent of the maximum dry density determined by ASTM D698 at moisture contents ranging between +2 to +6 percent of the optimum moisture content. Select fill should be compacted to a minimum of 98 percent of Standard Proctor Density at moisture contents ranging between -1 and +3 percent of optimum moisture content.

A vapor retarder recommended where floor coverings or painted floor surfaces will be applied with products which are sensitive to moisture or if products stored on the building floors are sensitive to moisture.

Subgrade conditions may vary underneath the building slab and Kleinfelder should be allowed to observe and test the subgrade soils under the existing building slab and revise our recommendations, as necessary.

As an alternative to removal of the expansive clay soil, a structurally supported floor slab may be considered. The floor slab should be designed by a structural engineer and have a minimum void space of 12 inches. This alternative should only be considered after the existing foundation has been stabilized.

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5.1.2 Underpinning

Underpinning the structure with straight drilled shafts can be considered to stabilize the existing footings. Helical anchors can also be considered to underpin the structure. The feasibility of underpinning this foundation will need to be verified by the structural engineer. These shafts should be designed to allow for some future upward movement of the foundation if any continued soil expansion occurs below the ground-supported foundation. Some cosmetic distress should be expected if the structure is leveled.

Subject to review by the structural engineer, underpinning and stabilizing the structural foundation with drilled shafts (piers) can be considered. There is potential for future soil expansion below the ground supported foundation system, therefore there is some potential for future movement of the foundation and floor slab if it remains in contact with the underlying clay. If the foundation is leveled, cosmetic repairs should not be undertaken for a period of at least 12 months to allow for some stabilization of the re-leveled foundation to occur and to monitor the effectiveness of the underpinning to reduce future movement. The underpinning system, consisting of drilled shafts, should be capable of resisting upward movement due to soil expansion. The following recommendations are provided for design and construction of reinforced concrete straight drilled shafts required to underpin and re-level the foundation.

TABLE 5.1: DRILLED SHAFT DESIGN VALUES

Design Item Design Value

Shaft type Auger-excavated and straight-sided

Bearing Stratum Description Dark Brown, Reddish Brown, and Yellowish Brown Fat and Lean Clay

Minimum Penetration (1) 28 feet bottom of footing assuming footing depth of 6 feet below top of slab

Maximum Allowable Bearing Pressure (2) 8,000 pounds per square foot (psf)

Maximum Allowable Side Shear (2) 700 psf after penetration

Minimum Shaft Diameter 18 inches (3)

Note: (1) Penetration is based on calculated uplift only, the actual penetrations will need to be determined by the project structural engineer during structural design.

(2) A factor of safety of at least 3 was used to evaluate allowable bearing pressure and for side shear.

(3) For constructability purposes. Actual shaft diameter is the responsibility of the Structural Engineer.

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Some reduction for group effects should be considered where shafts will be installed in a group condition or where any shafts will be installed close together. In order to develop full load carrying capacity in side resistance, adjacent straight drilled shafts should have a minimum center to center spacing of 2.5 times the diameter of the larger shaft. Closer spacing will require some reductions in side resistance and/or changes in installation sequences. The design side shear for axial or uplift loads may be considered to vary linearly from the full value at a spacing of 2.5 times the diameter of the larger shaft to 50 percent of the design value at a spacing of 1 times the diameter of the larger shaft.

The recommended bearing capacity and the side resistance values include a minimum factor of safety of three. Differential shaft settlement is estimated to be less than one half inch. The settlements of shafts will be primarily elastic with some of the settlement occurring during loading.

Due to the presence of expansive clay soils at the site, we recommend that drilled shafts be designed for a potential average uplift pressure of 2,300 psf acting on the drilled shafts to a depth of 5 feet below top of pier. Uplift resistance may be provided by structure dead load and side resistance in the clay soils below 10 feet from the top of slab.

5.1.3 Drilled Shaft Construction

Excavations for the shafts should be maintained in the dry. Groundwater was not encountered in the borings, however if groundwater is encountered during construction, temporary steel casing will be required to assist in the reduction of the inflow of groundwater or to reduce the possibility of caving or sloughing of the pier excavations. In some cases, rapid placement of steel and concrete will permit shaft installation to proceed; however, the seepage rates could be sufficient to require the use of temporary casing for proper installation of some of the shafts. The casing should be seated in the bearing stratum with all water and most loose material removed prior to beginning the design penetration. Care must be taken that a sufficient head of plastic concrete is maintained within the casing during extraction. Another option would be to use slurry method to keep the excavation open and this needs to be designed by a specialty contractor.

The concrete should have a slump in the range of 4 and 6 inches for uncased shafts and in the range of 5 and 7 inches for cased shafts and must be placed in a manner to avoid striking the reinforcing steel during placement. Higher slump ranges are recommended if the concrete will be placed by pumping. Complete installation of individual shafts should be accomplished within an

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8-hour period in dry excavations and preferably as rapidly as possible in order to minimize deterioration of bearing surfaces.

Allowable bearing capacity recommendations provided in this report are based on proper construction procedures, including maintaining a dry shaft excavation and proper cleaning of bearing surfaces prior to placing reinforcing steel and concrete. All drilled shaft installations should be carefully observed by the geotechnical engineer to help verify the bearing stratum, the design penetration, and perform related duties.

Drilled shaft installations should follow the guide specifications from The Association of Drilled

Shaft Contractors Inc. “Standards and Specifications for the Drilled Shaft Industry” or other recognized specifications for proper installation of drilled shaft foundation systems.

Repairs conducted without addressing the in-situ moisture will likely be subject to additional movement.

Helical piles may also be considered for foundation support as these foundation elements could more easily and quickly be installed. A qualified, experienced helical pile designer and installer should design the actual helical geometry and verify design values through load testing at the site. The recommended preliminary allowable bearing capacity of the lean-to fat clay is 8,000 psf with a factor of safety of 3. This allowable bearing capacity may be used for preliminary design of the helical piles; however, the actual capacities must be confirmed through load testing of the selected helical piles since the installation process impacts the actual bearing capacity.

5.1.4 LPILE Parameters (Version 2018) for Soil

Tables 5.2 provide the LPILE parameters for soil. The top 3 feet of the subsurface profile in contact with the drilled shaft is neglected. The Stiff Clay w/o free water p-y curve model was used for the

CL and CH soils encountered in the borings. The strain factor (ε50) can be determined by the

LPILE program and are not provided in Table 5.2 below.

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TABLE 5.2: LPILE PARAMETERS FOR SOIL

Lpile p-y Curve Model

Cohesion, psf

Friction

Angle, degrees

Unit Wt., pcf(1) Modulus k, pci

Neglect upper 0 – 3 feet --- --- --- ---

Stiff Clay w/o free water

(3 – 6 feet) 1,500 --- 110 ---

Stiff Clay w/o free water

(6 - 25 feet) 2,500 --- 124 ---

(1) Represents total unit weight. In conditions where soils are below the water table, submerged unit weights should be used. Submerged unit weight is obtained by subtracting the unit weight of water (62.4 pcf) from the total unit weight.

REPLACING THE EXISTING STRUCTURE

As mentioned before, the soils encountered in this area are considered moderately to highly expansive and significant soil induced shrinks/swell movements can be expected. Due to the type of structure and the soils encountered during our field explorations, we recommend drilled shaft foundations with a structurally supported floor slab for the support of the building. The shafts should be straight-sided, steel reinforced concrete and designed based on the geotechnical recommendations provided in sections 5.1.2 and 5.1.3, with the exception that the minimum pier length shall be 35 feet.

5.2.1 Grade Beams

All grade beams should be structurally supported by the drilled shafts and be suspended above the final subgrade soils using properly placed and protected void carton forms. A minimum 12-inch void space should be provided between grade beams and the subsoil. Void boxes that become weak due to moisture should be replaced prior to placing concrete. Concrete should be placed in a manner which mitigates overload and collapse of void boxes. The sides of the voids should be protected with soil retainers so that the soil will not slough beneath the grade beams and thus fill the void after the cartons are gone. The side of the grade beams should be formed rather than being cast directly against the soil. Additionally, we do not recommend the use of a fully wax impregnated void box. Fully wax impregnated means all sides of the carton forms, inside and out. Using these types of void boxes can cause issues with the eventual break-down of the void boxes. The void box should be installed in such a manner that the void box softens and deteriorates over time and does not transmit upward movements to the floor slab.

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5.2.2 Suspended Floor Slab System

A structurally suspended floor system is recommended to support the floor system above the on-site soils to reduce floor movement due to expansive/compressive soils. A minimum space of

12 inches should be provided between the final bottom of the floor system and the underlying subgrade. When void space is formed using cardboard carton forms, the forms must be protected so that they are not crushed or allowed to become wet prior to or during concrete placement. We do not recommend the use of a fully wax impregnated carton forms. The condition of the carton forms should be evaluated just before concrete placement and corrected if necessary. The ground surface beneath the floor system should be graded such that any water which infiltrates into the void space will flow to a common collection area and be readily removed from underneath the proposed structure. Water should not be allowed to collect or pond below or around the perimeter of the structure. Where the building crawl space is below the exterior grades, this condition increases the possibility that water can infiltrate below the floor system and become trapped in the crawl space.

A passive ventilation system is recommended where floor coverings or painted floor surfaces will be applied with products which are sensitive to moisture or if products stored on the building floors are sensitive to moisture.

SHALLOW FOUNDATIONS

Shallow foundations may also be considered for new construction, although, it should be recognized that using drilled piers and a suspended floor slab system has a better chance of reducing potential damage to the structure. The owner must carefully consider the intended use and expectations of the structure versus the costs associated with different options.

5.3.1 Subgrade Modifications

As mentioned in Section 4.1, the estimated soil movement or PVM is on the order of 5 to

5-½ inches. To reduce the PVM to 1 inch or less, obtain reasonable bearing pressure values, and reduce distress due to settlement of undocumented fill material, we recommend the following:

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Over excavate the building pad to a depth of 8 feet below bottom of slab elevation and replace with relatively, “non-expansive” select fill material. If undocumented fill is encountered in the bottom of the excavation, continue excavating until all existing fill is removed.

Select fill material should be a clean, low-expansive sandy soil, free of organic matter, wood or other foreign material. The plasticity index of the select fill should be in the range of 8 to 15, its liquid limit should not exceed 35 percent. The select fill should classify as clayey sand (SC) or sandy clay (CL) by the Unified Soil Classification System. Select fill should be compacted to a minimum of 98 percent of Standard Proctor Density at moisture contents ranging between -1 and

+3 percent of optimum moisture content.

Prior to placing any fill, the top 12 inches of the exposed soil should be scarified, moisture conditioned, and recompacted to a minimum density of 95 percent of the maximum dry density determined by ASTM D698 at moisture contents ranging between +2 to +6 percent of the optimum moisture content.

5.3.2 Structural Load Support

Shallow foundations may consist of isolated spread or strip footings founded on a properly compacted pad of select fill (as described in Section 5.3.1). Individual footings should be founded on similar materials (i.e. wholly on select fill) so as not to create differential settlement across the footing. Footings may be designed based on an allowable bearing capacity of 3,000 psf when bearing on a minimum of 2 feet of select fill material. The select fill should extend at least two feet beyond the perimeter of the footing. We recommend that all footings have a minimum width of

24 inches and extend a minimum of 24 inches below final grade. Structural loading-related settlement of about one inch or less should be expected. Differential settlements of footings are usually in the range of 50 to 75 percent of the total settlement and occur due to differences in subsurface conditions and foundation loading. A modulus of subgrade reaction (k) of 150 pci may be used for select fill.

For frictional resistance, an ultimate coefficient of friction of 0.35 for select fill may be used. The frictional force may be calculated by using the dead weight of the footing and the soils that is above the footing. A minimum factor of safety of 1.5 is recommended for the sliding analysis.

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5.3.3 Interior Floor Slab

The interior floor slab may be formed at grade, supported on properly compacted select fill material, as discussed in Section 5.3.1.

The subgrade modification option is intended to assist in reducing the swell potential to tolerable limits (about 1 inch of vertical movement), allowing the use of a ground-supported floor system.

However, ground-supported floor systems are passive systems, unlike a structurally suspended floor system, and ground supported slabs placed on expansive soils will experience some movement over the life of the structure.

The Owner must be aware that the use of a ground-supported floor slab will result in some movement, possibly resulting in cracking of the dry wall and façade of the structure. The use of a ground-supported floor slab represents a compromise between construction costs and an acceptable risk of potential structural and cosmetic distress. The owner, along with the design team must decide if the increased risk is acceptable.

A properly designed moisture retarder is recommended below on-grade building floor slabs where floor coverings or painted floor surfaces will be applied with products which are sensitive to moisture or if products stored on the building floors are sensitive to moisture. The use of polyethylene sheeting placed directly below the slab will serve as a moisture retarder but may increase the possibility of cracking of the slab during curing. Procedures for installation of vapor retarders are recommended in ACI 302, Section 3.2.3.

5.3.4 Construction Considerations

Excavations into the site overburden soils should be readily accomplished using conventional construction methods and procedures including the use of large backhoes, bulldozers, track or wheel loaders and scrapers. Foundation excavations should be observed by the geotechnical engineer or his representative to evaluate if the slab will bear on satisfactory materials. Loose material should be removed from the bottoms of all foundation excavations. Soil exposed in the bottoms of all satisfactory foundation excavations should be protected against detrimental changes in conditions, such as disturbance, rain or excessive drying. Surface runoff should be drained away from excavations and not allowed to pond in structural excavations. Concrete for foundations should be placed as soon after completion of the excavations as possible.

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It is recommended that all vegetation be stripped from the building pad areas. Where subgrade modification is performed, the soils should be undercut the required depth. The subgrade soils should then be scarified to a depth of 12 inches and be moisture conditioned and re-compacted as recommended in Section 5.3.1. Select fill should then be placed to the grade required for support of the foundation. The select fill should be placed and compacted as recommended in

Section 5.3.1. Soft surface areas identified during compaction will need to be undercut and re-compacted as recommended.

LATERAL EARTH PRESSURES

We understand that some short retaining walls may be required to establish required grades. The lateral earth pressure on the retaining walls will depend on the restraint conditions of the walls, type of backfill, surcharge pressure, and hydrostatic pressure potential. Depending on the wall type, the design condition could be active or at-rest. If the walls are constructed to be restrained at the top, thus the at-rest (Ko) earth pressure coefficient will be developed. Active pressures will apply for walls that are allowed to rotate. Equivalent fluid pressures are provided in Table 5.3 and may be used for horizontal backfill.

TABLE 5.3: EARTH PRESSURE CRITERIA

Material Earth Pressure Condition

Equivalent Fluid Pressure, pcf

Drained Condition Undrained Condition

Granular/Select Fill Φ=28°, ɣt=120 pcf

At-rest, ko = 0.53 64 93

Active, ka = 0.36 43 83

Passive, kp = 2.77 332 222

Lean Concrete Φ=34°, ɣt=125 pcf

At-rest, ko = 0.441 55 90

Active, ka = 0.283 35 80

Passive, kp = 3.537 442 284

The above values do not include the effect of hydrostatic pressures or lateral pressures induced by surface loads, which must be taken into account by the structural engineer. Subsurface drain systems must be included in the design to prevent hydrostatic build-up behind the walls. These values also assume that the soil behind the walls is excavated at an angle of 1.0 horizontal to 1.0

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Appropriate factors of safety must be used.

SEISMIC CONSIDERATIONS

For structural designs based upon the 2015 IBC and ASCE/SEI 7-10, the following Criteria will apply. The Site Class is D. The Mapped Spectral Response Acceleration at short periods (SS) is about 0.249g, and the Mapped Spectral Response Acceleration at a 1 second period (S1) is about

0.071g. Site Coefficients Fa and FV are 1.6 and 2.4 respectively. Hazards associated with slope stability, soil liquefaction, surface rupture, and lateral spreading are not considered to be a significant constraint with this site, due to the study area being in a seismically inactive area.

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6 LIMITATIONS

This work was performed in a manner consistent with that level of care and skill ordinarily exercised by other members of Kleinfelder’s profession practicing in the same locality, under similar conditions and at the date the services are provided. Our conclusions, opinions, and recommendations are based on a limited number of observations and data. It is possible that conditions could vary between or beyond the data evaluated. Kleinfelder makes no other representation, guarantee, or warranty, express or implied, regarding the services, communication (oral or written), report, opinion, or instrument of service provided.

This report may be used only by the Client and the registered design professional in responsible charge and only for the purposes stated for this specific engagement within a reasonable time from its issuance, but in no event later than two (2) years from the date of the report.

The work performed was based on project information provided by the National Park Service and

Architectural Resources Group. If there are any changes in the field to the plans and specifications, Client must obtain written approval from Kleinfelder’s engineer that such changes do not affect our recommendations. Failure to do so will vitiate Kleinfelder’s recommendations and design.

A ppendix A

Geotechnical-Engineering Report Important Information about This

Subsurface problems are a principal cause of construction delays, cost overruns, claims, and disputes.

While you cannot eliminate all such risks, you can manage them. The following information is provided to help.

The Geoprofessional Business Association (GBA) has prepared this advisory to help you – assumedly a client representative – interpret and apply this geotechnical-engineering report as effectively as possible. In that way, you can benefit from a lowered exposure to problems associated with subsurface conditions at project sites and development of them that, for decades, have been a principal cause of construction delays, cost overruns, claims, and disputes. If you have questions or want more information about any of the issues discussed herein, contact your GBA-member geotechnical engineer.

Active engagement in GBA exposes geotechnical engineers to a wide array of risk-confrontation techniques that can be of genuine benefit for everyone involved with a construction project.

Understand the Geotechnical-Engineering Services Provided for this Report Geotechnical-engineering services typically include the planning, collection, interpretation, and analysis of exploratory data from widely spaced borings and/or test pits. Field data are combined with results from laboratory tests of soil and rock samples obtained from field exploration (if applicable), observations made during site reconnaissance, and historical information to form one or more models of the expected subsurface conditions beneath the site. Local geology and alterations of the site surface and subsurface by previous and proposed construction are also important considerations. Geotechnical engineers apply their engineering training, experience, and judgment to adapt the requirements of the prospective project to the subsurface model(s). Estimates are made of the subsurface conditions that will likely be exposed during construction as well as the expected performance of foundations and other structures being planned and/or affected by construction activities.

The culmination of these geotechnical-engineering services is typically a geotechnical-engineering report providing the data obtained, a discussion of the subsurface model(s), the engineering and geologic engineering assessments and analyses made, and the recommendations developed to satisfy the given requirements of the project. These reports may be titled investigations, explorations, studies, assessments, or evaluations.

Regardless of the title used, the geotechnical-engineering report is an engineering interpretation of the subsurface conditions within the context of the project and does not represent a close examination, systematic inquiry, or thorough investigation of all site and subsurface conditions.

Geotechnical-Engineering Services are Performed for Specific Purposes, Persons, and Projects, and At Specific Times Geotechnical engineers structure their services to meet the specific needs, goals, and risk management preferences of their clients. A geotechnical-engineering study conducted for a given civil engineer will not likely meet the needs of a civil-works constructor or even a different civil engineer. Because each geotechnical-engineering study is unique, each geotechnical-engineering report is unique, prepared solely for the client.

Likewise, geotechnical-engineering services are performed for a specific project and purpose. For example, it is unlikely that a geotechnical-engineering study for a refrigerated warehouse will be the same as one prepared for a parking garage; and a few borings drilled during a preliminary study to evaluate site feasibility…