B1619 Geotechnical Evaluation Report - 11 Oct 21.pdf

Prepared for:

Wood-ZAPATA JV

1105 Lakewood Parkway, Suite 300, Alpharetta, GA 30009 10/11/2021

Geotechnical Evaluation Report Naval Air Station (NAS) Fort Worth Joint Reserve Base Building # B1619 (Revision 1) Fort Worth, Texas Project # 7Z7D210002

Wood Project: 7Z7D210002

10/11/2021

Mr. Matthew Silvi, AIA Wood-ZAPATA JV Project Manager 1105 Lakewood Parkway, Suite 300 Alpharetta, GA 30009

Re: Geotechnical Evaluation Report Naval Air Station (NAS) Fort Worth Joint Reserve Base, Building # B1619 (Revision 1) Fort Worth, Texas Project Number: 7Z7D210002

Mr. Silvi:

Wood Environment & Infrastructure Solutions, Inc., (Wood), has performed a geotechnical exploration in support of the remodeling of Building #B1619 located within Naval Air Station (NAS) Fort Worth Joint Reserve Base in Fort Worth, TX. This updated revision of the report addresses the elevator shaft foundation bearing capacity requirement.

Wood appreciates the opportunity to have provided these services and we look forward to serving as your geotechnical consultant throughout the project execution. Please contact us if you have any questions regarding the information presented.

Sincerely, Wood Environment & Infrastructure Solutions, Inc.

Texas Registered Engineering Firm F-0012 Texas Registered Geosciences Firm 50184

Sanjay K. Dhakal, PE

Athar Khawaja, PE, PEng

Geotechnical Engineer Sr. Associate Geotechnical Engineer

Wood Project: 7Z7D210002

Geotechnical Evaluation Report Naval Air Station (NAS) Fort Worth Joint Reserve Base Building # B1619 (Revision 1) Fort Worth, TX Project # 7Z7D210002

Prepared for:

Wood-ZAPATA JV 1105 Lakewood Parkway, Suite 300 Alpharetta, GA 30009

Prepared by:

Wood Environment & Infrastructure Solutions, Inc.

17325 Park Row Houston, TX 77084, USA T: 832-809-2635

10/11/2021

Copyright and non-disclosure notice

The contents and layout of this report are subject to copyright owned by Wood (© Wood Environment & Infrastructure Solutions, Inc.). save to the extent that copyright has been legally assigned by us to another party or is used by Wood under license. To the extent that we own the copyright in this report, it may not be copied or used without our prior written agreement for any purpose other than the purpose indicated in this report. The methodology (if any) contained in this report is provided to you in confidence and must not be disclosed or copied to third parties without the prior written agreement of Wood. Disclosure of that information may constitute an actionable breach of confidence or may otherwise prejudice our commercial interests. Any third party who obtains access to this report by any means will, in any event, be subject to the Third-Party Disclaimer set out below.

Third-party disclaimer Any disclosure of this report to a third party is subject to this disclaimer. The report was prepared by Wood at the instruction of, and for use by, our client named on the front of the report. It does not in any way constitute advice to any third party who is able to access it by any means. Wood excludes to the fullest extent lawfully permitted all liability whatsoever for any loss or damage howsoever arising from reliance on the contents of this report. We do not however exclude our liability (if any) for personal injury or death resulting from our negligence, for fraud or any other matter in relation to which we cannot legally exclude liability.

Naval Air Station (NAS) Fort Worth Joint Reserve Base, Building #1619 (Rev 1)

Fort Worth, TX

Project # 7Z7D210002 | 10/11/2021 Page i

Purpose of This Report The purpose of this exploration was to obtain subsurface data, review available geologic information pertinent to the area, and develop foundation and site preparation recommendations for use in project design.

Project # 7Z7D210002 | 10/11/2021 Page ii

Table of contents

1.0 Background and Scope

2.0 Field Exploration

2.1 Geotechnical Soil Borings

2.2 Laboratory Testing

3.0 Site conditions

3.1 Site geology

3.2 Subsurface conditions

3.3 Groundwater

3.4 Seismic site classification

4.0 Project Considerations

4.1 Existing Fill Soils

4.2 Potential for Expansive Soils

4.3 Settlement Considerations

4.4 Proximity to Existing Foundation

5.0 Foundation Recommendations

5.1 Shallow Foundations

5.2 Utility Duct Bank

6.0 Earthwork and Site Preparation Recommendations

6.1 Site Preparation

6.2 Site Grading and Drainage (for exterior structures)

6.3 Groundwater

6.4 Excavation

7.0 General Site Preparation Recommendations

8.0 Basis for recommendations

Fort Worth, TX

Project # 7Z7D210002 | 10/11/2021 Page iii

Figures

Figure 1: Site Vicinity Map Figure 2: Boring Plan Figure 3: As Built Plan (1990)

Tables

Table 2.1 – Soil Boring Summary Table 2.2 – Summary of Swell Tests Table 3.1 – Generalized Soil Stratification (Exterior Borings) Table 3.2 – Generalized Soil Stratification (Interior Borings) Table 3.3 – Groundwater Level Measurements Table 3.4 - Recommended Seismic Design Parameters (ASCE 7-16) Table 5.1 - Recommended Shallow Foundation Parameters

Appendices Appendix A - Limitations

Appendix B - Descriptive Key, Boring Logs

Appendix C - Laboratory Test Results

Project # 7Z7D210002 | 10/11/2021 Page 1 of 10

1.0 Background and Scope

Wood Environment & Infrastructure Solutions (E&IS) has completed a subsurface exploration and evaluated the results of the subsurface exploration to provide foundation and site preparation recommendations for the above referenced project.

The proposed site is located approximately 5½ miles west of Fort Worth Metropolitan as shown on Figure

1. The subject building is located at north side of intersection of D Street with Carswell Avenue in Fort Worth, Texas.

Based on the provided information, the proposed project will include construction of approximately 7-feet deep utility duct and interior improvement of the building 1619. The existing building is a two-story building and building improvement will include changes to the floor plan by removing some of the partition walls and installing new partition walls. The scope will also include the relocation of the existing elevator shaft as well as external metal staircase on the north end of the building.

Wood’s scope of work included drilling a total of six (6) soil borings (4 exterior borings and 2 interior borings), conducting laboratory testing on recovered samples, analyzing field and laboratory data, and preparing geotechnical recommendations for the proposed construction.

Please note that the recommendations presented in this report are based on the information provided to us at the time of this report and the subsurface encountered during our field investigation.

2.0 Field Exploration

2.1 Geotechnical Soil Borings

A total of six (6) soil borings were drilled to depth ranging from 10 to 40 feet below ground surface (bgs) as presented in Figure 2 and as summarized in Table 2.1. Borings B-01 through B-04 were drilled with a truck-mounted drilling rig utilizing a solid flight augers and wet rotary techniques. However, borings B-05 and B-06 were drilled by a hydraulically pushed portable drilling rig.

Table 2.1 – Soil Boring Summary

Boring Number

Termination Depth

(feet)

Latitude*

(degrees)

Longitude*

(degrees)

Approximate Elevation**

(feet)

Associated Structure

Mapped Geology***

B-01 (Ext. Boring) 40 32.777990 -97.429091 602

Elevator Shaft

Terrace Deposits

B-02 (Ext. Boring) 20 32.777929 -97.428987 602

B-03 (Ext. Boring) 20 32.778192 -97.428791 602 External

Stair B-04

(Ext. Boring) 10 32.778304 -97.428948 605 Utility Duct

B-05 (Int. Boring) 12 -- -- 603

Interior Remodeling B-06

(Int. Boring) 12 -- -- 603

Project # 7Z7D210002 | 10/11/2021 Page 2 of 10

Notes:

*Latitude and Longitude were approximated from google earth.

** Elevations were approximated from as built plan dated 30 October, 1990.

***Based on the Geologic Atlas of Texas, Austin Sheet1

The borings were located in the field by Wood’s field engineer using handheld GPS and standard measuring techniques utilizing on site landmarks as references

The exploration was supervised by a field engineer who directed the drill rig and visually examined and logged soil samples. Borings were advanced using solid-stem augers and mud rotary methods to termination depths and sampled in general accordance with the requirements of American Society for Testing and Materials ASTM D 1586 (Penetration Test and Split-Barrel Sampling of Soils) and ASTM D 1587 (Standard Practice for Thin-Walled Tube Sampling of Fine-Grained Soils) to assess the overburden soil engineering characteristics. Upon completion, the exterior soil borings were backfilled with cement-bentonite grout and interior borings were backfilled with bentonite grout and patched with concrete on top. Soil samples were transported to Wood’s laboratory for further testing.

2.2 Laboratory Testing

Laboratory testing consisting of moisture contents (ASTM D2216), grain size analyses (D422), and Atterberg limits (ASTM D4318) was performed on selected samples. Strength testing, consisting of unconfined compressive strength (ASTM D2166) completed. Swell Tests (ASTM D4546 Method B) were also completed on surficial soils and the results are presented in Table 2.2.

Table 2.2 – Summary of Swell Tests

Boring Number Sample Depth

(feet) Swelling %

B-01 2-4 1 B-01 8-10 0.8 B-02 4-6 0.8 B-05 4-6 0.3 B-06 1-3 0.5

Our interpretations of the soil samples along with laboratory test results are included on the graphic logs presented in Appendix B, and the laboratory test results are also included in Appendix C.

3.0 Site conditions

At the time of our field exploration, the site was developed with existing building and associated paved parking (asphalt/concrete) lots and drive lanes. The ground surface across the exterior borings is relatively flat.

1 Proctor, C.C., Jr., Brown, T.E., McGowen, J.H., and Waecter, N.B., (1974) Geologic Atlas of Texas, Austin Sheet, The University of Texas at Austin, Bureau of Economic Geology, Geologic Atlas, Scale 1:250,000.

Project # 7Z7D210002 | 10/11/2021 Page 3 of 10

3.1 Site geology

A review of the Geologic Map of the Geologic Atlas of Texas, Austin Sheet, published by the Bureau of Economic Geology, 1974, indicates the site is located in Terrace Deposits of Pleistocene and Holocene age.

The Terrace Deposits outcrop adjacent to outside of the immediate channels of the Trinity River and its tributaries and primiraly consists of various proportion of sand, silt, clay, and gravel. Based on soil borings, the soil stratigraphy is generally matching the geology for the site.

3.2 Subsurface conditions

Based on the field and laboratory test results, a generalized subsurface stratigraphy was created and is presented in Tables 3.1 and 3.2. Please note that the generalized profile highlights the major subsurface stratification and the boring logs included in Appendix B should be reviewed for specific information in individual borings. Boring logs with detailed descriptions of the subsurface conditions encountered are provided in Appendix B. These logs represent our interpretation of subsurface conditions based on field observations and laboratory testing of representative samples.

Table 3.1 – Generalized Soil Stratification (Exterior Borings)

Stratum USCS Classification

Top of Layer bgs (feet)

Bottom of Layer bgs (feet)

LL(1)

Range

PI(2)

Range passing sieves

N(3) Range

Su(4) Range (tsf)

1 Fill–Sandy Lean Clay 0 8 26‒33 15‒22 71 - 0.4‒1.5

2 Clayey Sand

(SC) 8 20 ‒ ‒ ‒ 13 TO

50/0.5” 1.2‒1.3

3 Limestone 20 40 ‒ ‒ ‒ 50/3.25” to 50/0.75”

Notes:

1 Liquid Limit (%) 2 Plasticity Index (%) 3 Standard Penetration Test blow count (blows/12-inch penetration) 4 Undrained shear strength based on Hand Penetrometer, unconfined or unconsolidated undrained compressive strength tests. Please note that the hand penetrometer reading presented in logs are undrained shear strength.

Project # 7Z7D210002 | 10/11/2021 Page 4 of 10

Table 3.2 – Generalized Soil Stratification (Interior Borings)

Stratum USCS Classification

Top of Layer bgs (feet)

Bottom of Layer bgs (feet)

LL(1)

Range

PI(2)

Range passing sieves

N(3) Range

Su(4) Range (tsf)

Fill–Sandy Lean

Clay/Clayey Sand

0 8 20‒22 11 ‒ ‒ 0.7‒1.2

2 Sandy Lean Clay (CL) 8 12 ‒ ‒ ‒ ‒ 0.8‒1

Notes:

1 Liquid Limit (%) 2 Plasticity Index (%) 3 Standard Penetration Test blow count (blows/12-inch penetration) 4 Undrained shear strengths based on Hand Penetrometer, unconfined or unconsolidated undrained compressive strength tests.

3.3 Groundwater

Groundwater was encountered at a depth of 12 ft in exterior borings and at a depth of 6 ft in the interior borings during the field exploration. The groundwater in the interior boring could be perched water trapped on top of less permeable lean clays at boring B-6. It is likely that shallow, perched water may be present at various locations across the site, based on the characteristics of the encountered soils. The approximate depths and corresponding elevations of the groundwater are presented in Table 3.3.

Table 3.3 – Groundwater Level Measurements

Boring Approximate Surface Elevation

(feet)

Depth to Water1 (feet)

Water Elevation (feet)

B-01 602 12 592 B-02 602 12 592 B-03 602 12 592 B-04 605 -- -- B-05 603 -- -- B-06 603 62 597

Notes:

1. Water encountered with augers and measurement taken during drilling.

2. Potential perched water table at 6 ft.

3.4 Seismic site classification

The 2018 edition of the International Building Code (IBC) was reviewed to determine the seismic site classification. The IBC requires soil and rock conditions be evaluated to a minimum depth of 100 feet below the foundation-bearing elevation to determine the proper site class definition for seismic design. We have performed a seismic site classification analysis using the soil conditions encountered in the borings. These

Project # 7Z7D210002 | 10/11/2021 Page 5 of 10 borings were terminated at depths of 40 feet bgs. The results of our Seismic Site Classification evaluation indicate the site is a Site Class “D”. The web-based application program developed by Applied Technology Council (ATC)2 was used to compute the recommended seismic parameters, which are summarized in the Table 3.4.

Table 3.4 - Recommended Seismic Design Parameters (ASCE 7-16)

Parameter Recommended Calculated Value

Ss – Mapped Spectral Response Acceleration for Short Period (0.2-second)

0.093

S1 – Mapped Spectral Response 1-second period

0.051

Fa – Site Amplification Factor at 0.2 seconds 1.3 Fv – Site Amplification Factor at 1.0 seconds 1.5

4.0 Project Considerations

Based on provided information, we understand the existing two-story timber framed building is supported on spread footing along the perimeter and the interior walls sits on a pedestal wall footing.

Based on our discussion with ZAPATA, we understand that the proposed elevator shaft is planned to be constructed along south end of the building and will be supported on shallow foundation. The footings for the interior walls will be supported on existing subgrade soil underneath the slab. The slab along the proposed wall alignment will be sawcut to facilitate the footing installation. Additionally, for the external staircase, the existing concrete slab will be demolished to facilitate the proposed construction. The external stair will be structurally connected to the existing building to provide lateral support only. No additional loads are anticipated from stair to the existing foundation.

Based on the review of as built drawing dated October 3, 1990 as well as google earth photographs, the proposed site consists of a metal building in the west side, a culvert pipe near northwest corner, and the Building 1617 on the north side of the building 1619. All appeared to have been demolished at the time of our field explorations. The west side building and the culvert appeared to have been demolished during the proposed upgrades in 1990 and the northside building was demolished around 2004. Information on the type of demolished foundations was not available at the time of preparation of this report. The provided as built plan is presented in Figure 3.

Based on the subsurface conditions encountered in our borings and our experience, we believe the site is suitable for the proposed construction. However, there were some site and subsoil conditions that pose concerns from a geotechnical standpoint. These concerns are described in section 4.1.

4.1 Existing Fill Soils

Exterior Borings: The soil borings and laboratory testing indicate that the site has approximately 8‒10 feet of fill soils that were encountered at the soil borings. These fills may be the remainings from the demolition of the existing structures during the upgrades in 1990. The placement as well as degree of compaction of these fill soils is not available at this time. As such the possibility exists that the fill may contain soft

2 Applied Technology Council (ATC), Hazards by Location, https://hazards.atcouncil.org/#/seismic https://hazards.atcouncil.org/#/seismic

Fort Worth, TX

Project # 7Z7D210002 | 10/11/2021 Page 6 of 10 compressible zones that are not disclosed by our soil borings. The foundation supported on such fill can have excessive or uneven settlement under service loads and there are certain risks associated with structures supported on the fill materials. The risk can be mitigated by proper site preparation that may include removal and replacement of existing fill soil or removal and recompaction of the fill soil in place.

Interior Borings: Fill soils were also encountered in the interior borings. The fill soil consists of sandy clays/clayey sands with low plasticity. These fills are assumed to be placed at time of construction of building 1619. Based on the observation of the existing building, the subgrade/foundation soil has been performing satisfactorily and it is our opinion that the fill soil must have been compacted properly during the time of construction and is assumed to perform satisfactiorly for the proposed interior remodeling.

4.2 Potential for Expansive Soils

Based on field and laboratory test results, the existing on-site soil consists of low to medium plastic sandy clays/clayey sands. These soils have low to moderate potential to shrink and swell movements induced by changes in moisture contents. The depth in a soil where moisture changes can occur seasonally is typically referred to as the active zone. Based on the recovered soil samples, results of laboratory testing and the observed groundwater depths at the time of drilling, the zone of seasonal moisture change at this site is anticipated to extend to 12 to 15 feet below the ground surface. However, for the purposes of design, soils are not likely to become fully saturated in the entire zone of seasonal moisture change, and considerations were made to evaluate the design active zone for this project.

Shallow foundations are more susceptible to volume changes in expansive soils due to the contact area exposed. Recommendations for shallow foundations consider impacts of moisture changes down to a depth of about 10 feet bgs. The amount of movement due to shrink and swell can be estimated using the Potential Vertical Rise (PVR).

The Potential Vertical Rise (PVR) of the encountered soils near the proposed elevator shaft, external stair area, as well as for the interior remodeling were evaluated using the Texas Department of Transportation (TxDOT) method Tex-124-E3. Based on the laboratory test results a PVR value of approximately 1 inch was estimated for this site, if foundation loads are neglected.

4.3 Settlement Considerations

Exterior Borings: As discussed earlier, the area for the elevator shaft as well as for the stair area consists of 8-10 feet of fill soils. These soils may settle unevenly if not removed and replaced or properly compacted in place. In order to avoid the settlement, we recommend that the existing fill be replaced with structural fill or CLSM below the proposed foundations. The required replacement depth is discussed in Section 5.0. The subgrade preparation recommendations for the foundation area are presented in Section 6 of this report.

Interior Borings: The interior borings also indicate approximately 6-8 feet of fill soils at soil borings. These fill soils appeared to be performing well under prevailing conditions and are assumed to have been consolidated under the building loads between the time of construction and the time of our soil borings.

Therefore, the settlement of a new foundation is assumed to be negligible provided that the subgrade soil for the footing is compacted properly before placing the new footing.

4.4 Proximity of Elevator to Existing Foundation

Based on provided information, the proposed construction will be in the vicinity of the existing building and the proposed foundation may be structurally connected to the existing foundations. Care must be taken for

3 (2017) Potential Vertical Rise of Natural Subgrade Soils, Tex-124-E, Texas Department of Transportation.

ftp://ftp.dot.state.tx.us/pub/txdot-info/cst/TMS/100-E_series/pdfs/soi124.pdf

Fort Worth, TX

Project # 7Z7D210002 | 10/11/2021 Page 7 of 10 any foundations that are planned to be supported in the proximity of the existing foundations. The existing foundation may also settle resulting in the differential settlement between the existing foundations.

Therefore, it is advised to design the footing as a stand-alone footing.

5.0 Foundation Recommendations

The following recommendations are provided assuming the site has been prepared as recommended in this report.

5.1 Shallow Foundations

For Exterior Structures: Based on the soil conditions encountered, lightly loaded exterior structures may be supported on structural slab-on-grade for this project. We understand that elevator shaft will be at the same elevation as existing slab and bearing pressure of about 2,200 psf is anticipated. It is assumed that the proposed slab would be minimum 12-inch thick and top to be level with existing slab. Refer to section 6.5 for excavation recommendation near the existing foundations.

As discussed on section 4.1, to mitigate the risk of supporting the foundations on top of fill soils, we recommend at least 4 feet of existing fill soil below the bottom of the elevator slab foundation be removed and replaced with Controlled Low Strength Materials (CLSM). For the foundations of the external metal staircase, it is recommended that 2 feet of existing fill below the foundations should be replaced with structural fill or CLSM. The requirement for the fill (CLSM) is presented in the subsequent section.

For interior walls footings: Based on the soil conditions encountered, proposed walls can be supported on shallow wall footings. The spread/strip footings can be supported at 2 ft below the bottom of the existing slab.

After excavating to desired depth, for both exterior and interior footings, the exposed clay soils should be proof rolled or manually compacted to detect any soft or yielding soils. If soft soils are encountered these soils should be further excavated until firm subgrade is exposed and replaced with structural fills or CLSM.

Structural fills should be placed in uniform, horizontal lifts. The thickness of the loose lift (prior to compaction) should not exceed 12 inches where large equipment can be used. In areas where manual compactors are required, the loose lift should not exceed 6 inches. Structural fill soils should be compacted to minimum 95 percent of the maximum dry density determined according to ASTM D-698 specifications (standard proctor) for cohesive materials. These soils should be compacted at moisture contents within 2% of the optimum moisture content (+/- 2%).

All load bearing structures should bear on properly placed and compacted and accepted structural fill materials or CLSM. Acceptable structure fill materials include soils designated according to the United Soil Classification System (ASTM D-2487-85) as CL and CL-ML. Pit run material, approved by the geotechnical engineer, may also be considered acceptable, or crushed limestone base material meeting the requirements presented in the Texas Department of Transportation (TxDOT) Standard Specification for Construction of Roadways and Bridges, Item 247, Type A, Grade 3. In addition, structural fill should have a plasticity index of less than 20 percent and the liquid limit shall be less than 40 percent. Onsite soils that are free of organics and construction debris can be tested in bulk to check their suitability for use as structural fill soils. Proposed borrow material should be submitted for testing by the geotechnical engineer prior to placement. Coarse grained soils such as sands and clean gravels are not recommended as structural fill. CLSM with a minimum unconfined compressive strength of 100 psi is an acceptable alternative for structural fill.

Shallow foundations should be adequately reinforced and proportioned to resist uplift/swell forces associated with near surface clay soils. The following parameters are recommended for design of shallow foundations. A maximum bearing pressure of 2,300 psf is recommended for exterior footings when

Fort Worth, TX

Project # 7Z7D210002 | 10/11/2021 Page 8 of 10 supported on 4 feet of CLSM, and a maximum bearing pressure of 2,500 psf at an embedment depth of 2 ft is recommended for the interior wall structures.

Table 5.1 - Recommended Shallow Foundation Parameters Soil Design Parameter Preliminary Design Value for

Shallow Foundations

Moist Unit Weight, pcf 125 Modulus of Subgrade Reaction (kip/ft2/ft) 216

Net Allowable Bearing Pressure (psf) for exterior spread footings (4 feet replacement below footing) 2,300(1)

Net Allowable Bearing Pressure (psf) for exterior spread footings (2 feet replacement below footing) 1,700

Net Allowable Bearing Pressure (psf) for interior wall foundations 2,500

1Based on the assumption that the exterior foundations supported on 4 feet of CLSM.

Recommendations concerning site drainage and moisture protection are considered critical for the satisfactory performance of foundation at this site and are provided in Section 6.0.

5.2 Utility Duct Bank

A Utility duct bank is planned to be constructed near the northwest end of building 1619. The depth of excavation will be approximately 7 feet below the existing grade. The excavation should be in accordance with Occupational Safety and Health Administration (OSHA) guidelines. We recommend that these regulations should be strictly enforced, if not followed the owner and the contractor could be liable for substantial penalties.

After completion of excavation, depending upon use of the duct bank, the bottom of the excavation should be manually compacted to locate any soft spots. Areas of loose/soft soil encountered should be undercut and replaced with compacted structural fill. The detailed information about various components within the duct bank was not available at the time of preparation of this report. However, we anticipate that the trench will be eventually backfilled and paved on the top. If the area on top of the duct bank is planned to be paved, we recommend the subgrade should be properly compacted to at least 95% of standard proctor density before construction of any pavement.

6.0 Earthwork and Site Preparation Recommendations

We have assumed that existing grade is anticipated to remain within +/- 2 feet of the existing grades for the proposed facilities. The following recommendations are provided to prepare the site for construction

6.1 Site Preparation

Areas to be cut should be stripped to remove organic materials or other deleterious materials to expose competent soils. These soils are not suitable for use as compacted fill. The required depth of stripping will vary based on the location and amount of existing vegetation. Areas of loose or wet soil encountered should be undercut and replaced with compacted structural fill. After excavation to desired depth, the exposed subgrade should be proof rolled or manually compacted to identify any soft spots. The soft soils should be removed and replaced with structural fill soils.

The onsite fill soils can be tested in bulk to check their suitability for use as structural fill soils. These results should be evaluated by the geotechnical engineer.

Project # 7Z7D210002 | 10/11/2021 Page 9 of 10

6.2 Site Grading and Drainage (for exterior structures)

Controlling site drainage during and after construction is one of the most critical items for foundation performace in areas with expansive soils. The site should be maintained in a well-drained condition during and after construction, to inhibit water from ponding on exposed soil subgrades and foundation or utility excavations. Ponding water could lead to soil subgrade deterioration.

Exposed ground should be sloped away from structures for at least 5 feet beyond the perimeter of the structures. Minimum landscape gradients of 2 percent are recommended to reduce the risk of run-off ponding in localized areas. A minimum grade of 1 percent is recommended for paved surfaces. Positive drainage away from grade-supported sidewalks and shallow foundations is critical to the long-term performance of these structures.

Drainage should be directed away from any foundations or structure to prevent moisture changes in the subgrade. Downspouts should be positively directed away from the structures, or if regulations permit, directed toward the storm drain system. Care should be taken to ensure that ponding does not occur at the pile locations. The ground surface should be sloped to promote positive drainage away from the piles.

Utility trenches are a common source of water infiltration and migration. All utility trenches that penetrate beneath structures should be effectively sealed to restrict water intrusion and flow through the trenches, which could migrate below the strutures. Trenches should be backfilled with compacted clay at a water content at or slightly above the optimum water content.

6.3 Groundwater

Groundwater was generally encountered at a depth of 12 feet during drilling operations. It is not uncommon for elevated perched water to be encountered during wet periods. We do not anticipate groundwater to encroach on shallow excavations for the majority of the work to be completed onsite. The geotechnical engineer should be contacted if heavy seepage occurs, or there is evidence of soil particle migration such as silting of the sump.

6.4 General Excavation

Soil excavation for grade beams, slabs, and buried structures may be made by open cutting. We recommend that temporary construction slopes comply with OSHA requirements for Type B soils and be no steeper than 1H:1V (horizontal: vertical). If sloping is not practical due to buried utilities or other site constraints, trench boxes or shoring may be appropriate. We recommend that temporary shoring should be designed by a structural engineer registered in the State of Texas, if required.

6.5 Excavation near existing footings

We understand that the existing footing is about 2 feet below the existing grade and the proposed elevator footings are recommended at a depth of 5 feet below the existing grade at the site. This would imply that excavation would need to extend below the existing foundation level by about 3 feet.

In order to eliminate the lateral movement of the existing foundation due to the excavation, we recommend the existing foundation to be underpinned properly to provide enough support during excavation.

Underpinning is required wherever the foundations of the existing wall footing exist above the depth of proposed excavation. An underpinning system comprising of Helical Piles or similar should be utilized. For existing soil undrained shear strength of 800 psf can be utilized for design of helical piles. The underpinning should extend beyond the planned depth of excavation (5 ft below existing grade) and should be designed by a structural engineer registered in the State of Texas. All temporary support/underpinning elements

Project # 7Z7D210002 | 10/11/2021 Page 10 of 10 should be kept in place and functioning until new foundations are installed and open/excavated area are backfilled with properly compacted structural fill soil or flowable fill/CLSM.

7.0 General Site Preparation Recommendations

The following recommendations are provided to prepare the site for construction:

• Establish site drainage as part of site clearing and grubbing operations.

• Remove any buried structures and utilities encountered during excavation.

• Strip all organic material and debris from the construction area. Remove these materials from the site or use as topsoil in landscape areas.

• Proof-roll or manually compact the exposed subgrade to detect unstable conditions, remove any weak, compressible or other unsuitable materials; such material should be replaced with compacted select fill or clean stabilized soils. Measures should be adopted to reduce the potential for moisture change in the subsurface soils under the proposed structure in order to mitigate potential for shrink and swell.

• Excavation limits should extend a minimum of 2 feet (or as recommended previously) beyond the limits of the proposed structure footprint.

• Compact the exposed subgrade prior to placement of structural fill, and construction of foundations.

• Undercut loose, soft, organic, or highly plastic soil, or old unstable fill encountered during proof-rolling and replace with properly compacted fill.

• Scarify and re-compact the existing subgrade soils to a depth of at least 6 inches prior to foundation construction.

• Retain the geotechnical engineer to observe the proof-rolling operations and make recommendations for unstable or unsuitable conditions encountered.

Select fill should consist of uniform, non-active inorganic lean clays with a PI between 10 and 20 percent and not more than 50 percent passing a No. 200 sieve. Select fill should be compacted to at least 95 percent of standard maximum dry density.

8.0 Basis for recommendations

Recommendations are based in part on project information provided to Wood, and only apply to the specific project and site discussed in this report. You should, if this report contains incorrect project information or if additional information is available, convey the correct or additional information to us and retain us to review our recommendations. We can then modify the recommendations if they are inappropriate for the proposed project.

This report does not address the chronology of previous land use, determination of the presence of any toxic or hazardous substances, or any related environmentally-sensitive issues. This report does not address regulatory issues associated with storm water runoff, identification and modification of regulated wetlands, or groundwater recharge areas. Our professional services, findings obtained, and recommendations have been prepared in accordance with generally-accepted engineering principles and practices. No other warranty, either express or implied, is made.

There is always a possibility, regardless of the geotechnical exploration’s thoroughness, that conditions between borings will be different from those at specific boring locations and that conditions will not be as

Project # 7Z7D210002 | 10/11/2021 Page 11 of 10 anticipated by the designers or contractors. The construction process may itself alter soil conditions.

Therefore, experienced geotechnical personnel should observe and document the construction procedures used and conditions encountered. Unanticipated conditions and inadequate procedures should be reported to the design team along with timely recommendations to solve the problems created. We recommend the owner retain Wood to provide this service based on our familiarity with the project, the subsurface conditions, and the recommendations’ intent.

We recommend this complete report be provided to the various design team members, the contractors, and the project owner. Potential contractors should be informed of this report in the "instructions to bidders" section of the bid documents. The report should not be included or referenced in the actual contract documents.