2025.5.2 Supplement1 Geotech Report_Utilities.pdf

551 League City Parkway, Suite F

League City, Texas 77573

P (281) 557-2900

Terracon.com

Facilities | Environmental | Geotechnical | Materials

Report Cover Letter to Sign

May 2, 2025

RS&H Architects-Engineers-Planners, Inc.

10748 Deerwood Park Boulevard South

Jacksonville, Florida 33256

Attn: Scott Coleman, AIA, DBIA – Associate Vice President

P: 904-256-2135

E: scott.coleman@rsandh.com

Re: Additional Geotechnical Engineering Recommendations

NASA Engineering Consolidation Phase 1A

2101 NASA Road 1

Houston, Texas

Terracon Project No. 91235100.Supplement1

Dear Mr. Coleman:

As requested, we are providing additional geotechnical recommendations for the proposed underground utility planned to be constructed at the above-referenced project site.

We understand that the route for the underground utilities (stream and chilled water lines, power line and compressed air pipes) planned for the above-referenced project has been changed. We also understand the proposed underground utilities will tie into the existing underground utility tunnel which is approximately 15 feet below grade.

Two borings (designated C-01 and C-02) were drilled for this scope. Boring C-01 was drilled on Avenue D pavement and boring C-02 was drilled adjacent to the underground tunnel. Drawing showing the boring locations is presented in the attachments. The results of the laboratory testing performed on soil samples obtained from the site during our field exploration are included on the boring logs in the attachments.

As requested, this report includes information pertaining to soil and groundwater conditions, borings logs, and utility construction consideration recommendations.

Additional Geotechnical Engineering Recommendations

NASA Engineering Consolidation Phase 1A | Houston, Texas

May 2, 2025 | Terracon Project No. 91235100.Supplement1

Subsurface Conditions

Subsurface Profile

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. Conditions observed at each exploration point are indicated on the individual logs attached to this report.

As part of our analyses, we identified the following soil layers within the subsurface profile.

Layer Layer Name General Description

1 Pavement about 5 inches of asphaltic concrete overlying about 3 inches of crushed stone

2 Fill- Fat Clay tan and gray, with ferrous and calcareous nodules, and sand seams

Fat Clay, Sandy

Fat Clay, and

Sandy Lean Clay tan and light gray, stiff to hard, with ferrous and calcareous nodules, and sand pockets and seams

Clayey Sand and

Silty Sand tan, medium dense

5 Fat Clay tan and gray, very stiff, with ferrous nodules

Groundwater Conditions

Borings C-01 and C-02 were advanced using dry drilling techniques to their termination depths (approximately 15 and 30 feet). Groundwater was not observed at boring C-01 during or upon completion of drilling. Groundwater was initially observed at boring C-02 at a depth of about 13 feet during dry drilling. After a 15-minute monitoring period, groundwater was observed at boring C-02 at a depth of about 10.5 feet.

Groundwater level fluctuations occur due to seasonal variations in the amount of rainfall, runoff and other factors not evident at the time the borings were performed. 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 boring logs. The possibility of groundwater level fluctuations should be considered when developing the design and construction plans for the project and should be evaluated prior to construction.

Utility Construction Considerations

Temporary Groundwater Control

Based on the soil and groundwater information obtained during our field activities, we anticipate that excavations that extend into the near-surface clay soils to a depth of

10 feet may occur without advance dewatering. Seepage from the near-surface clay soils is expected to be minor and can be managed by pumping water collected within sumps positioned at the bottom of the trench.

However, excavations that extend below 10 feet into or through the sand layer, such as observed at boring C-02, will likely require some form of advance dewatering, depending on the groundwater conditions at the time of construction. Groundwater within silty/sandy soils is typically controlled by the installation of vacuum well-points. However, vacuum well-points are generally less effective below a depth of about 15 feet beneath the top of the well-point. In addition, dewatering with well-points may not be effective in zones containing significant amounts of fine-grained soils. Deeper dewatering requires eductors or deep wells with submersible pumps or multiple-stage well-points.

The suggested methods given above serve as a guideline for groundwater control. Other appropriate means may be required for groundwater control during construction. Control of groundwater should be accomplished in a manner that will preserve the strength of the soils, will not cause instability of the excavation, and will not result in damage to existing structures, if any. If necessary, the water should be lowered in advance of excavation by well-points, deep wells, eductors, or similar methods. Open pumping should not be permitted if it results in boils, loss of fines, softening of the subgrade, or excavation instability. Well-points, deep wells and eductors should be installed with suitable screen and filter so that pumping of fines does not occur.

The well system should be in operation for at least several days prior to excavating to the design depth. We recommend that the groundwater head be lowered at least 3 feet below the bottom of the excavation to provide a working area with increased stability. The dewatering should continue until the construction has been completed, and the dewatering system should be turned off in stages to allow groundwater to recover to its original level gradually, over a period of about 3 to 5 days.

Dewatering of loose to medium dense sands might cause subsidence or compression of adjacent soils and adjacent structures, in spite of safeguards and methodology selected and used. For this reason, the dewatering operations must be performed and provided with great care to ensure caution and control of the potential subsidence resulting from the dewatering operations.

To further evaluate the groundwater at the time of construction, piezometers may be set just prior to construction. As an alternative, test pits may be excavated to the planned utility depth. Based on the results, the contractor should determine effective methods of groundwater management prior to starting excavation operations.

Excavation Considerations

For this project, either excavated side slopes or vertical cut excavations are feasible. For vertical cut excavations greater than 5 feet in depth, excavations will require the use of a trench box or shoring and bracing to prevent sloughing and caving of the soil into the excavation. The contractor should use a trench box or shoring and bracing as necessary to maintain a safe and clean excavation which meets Occupational Safety and Health

Administration (OSHA) requirements.

In lieu of shoring, bracing, or trench boxes for excavations greater than 5 feet, OSHA standards provide recommendations for the design of temporary sloped excavations with a depth less than 20 feet. The OSHA standards provide maximum allowable slopes contingent on three designated soil types: Type A, Type B, or Type C. According to OSHA standards, temporary sloped excavations should be no steeper than 0.75-horizontal on

1-vertical (0.75H:1V) for Type A soils, 1H:1V for Type B soils, and 1.5H:1V for Type C soils. The surface slopes should be protected from deterioration and weathering if they are left open for significant periods of time.

Excavations must be performed and evaluated under the supervision of the contractor’s designated Competent Person. The Competent Person, (as defined by the OSHA Standard, 29 CFR Part 1926.650 to .652, Subpart P - Excavations), must evaluate the excavations at the time of construction activity to safeguard workers.

We recommend that no equipment be operated within a horizontal distance equal to the excavation depth from the edge of the excavation and no materials should be stockpiled within this distance. Excavations should not approach closer than a horizontal distance equivalent to the excavation depth from existing structures or buried utilities without some form of protection for the facilities. The maximum height of the stockpiled material should not be greater than 4 feet.

Excavations should be performed with equipment capable of providing a relatively clean bearing area. Excavating equipment should not disturb the soil beneath the design excavation bottom and should not leave loose soil in the excavation.

The bearing surface should be protected against disturbance and deterioration by completing the waterline installation and backfilling operations as quickly as possible. The excavation bottom should be properly sloped to allow water infiltrating into the excavation to be collected at a convenient location along the edge of the excavation. Proper berming or ditching should be done to divert any surface runoff away from the excavations. Water should not be allowed to stand within the bearing area.

Uplift Pressures

Uplift forces on below-grade structures will be generated by a difference in water level in the soil adjacent to the structure and inside the structure. If the backfill around any buried structure is a sand or silt material, the backfill will approach saturation during periods of heavy rainfall and the effective static water level will be at the surface. The uplift pressures will be resisted by adhesion or skin friction of the soil to the wall and by the dead weight of the structure. An allowable skin friction for an engineered clay fill compacted to a minimum of 95 percent of the maximum Standard Effort (ASTM D698) maximum dry density may be considered to be 300 psf. The upper 4 feet of skin friction should be neglected for a clay backfill due to potential for soil shrinkage away from the structure.

Sand backfill, compacted to at least 70 percent of the maximum relative density (ASTM

D4253 and D4254), may be considered to have an allowable skin friction of zero at the surface varying linearly to 105 psf at a depth of 15 feet below grade.

An alternate design method would be to place a heel extending out from the utility foundation into the backfill and rely on the weight of the soil above the heel on a 4-vertical to 1-horizontal slope to resist the uplift forces. The unit weight of soil above and below the water table for a properly compacted backfill will be 120 pcf and 60 pcf, respectively.

If the buried structures are installed by excavating from the inside and allowing the structure to sink under its own weight, the soil contact with structure walls may be very low immediately after construction due to the annulus created during construction. In this case, the uplift pressure must be resisted by structural dead weight alone or by restoring the contact between the soil and the structure. If the annulus is open, grouting would be one way to restore skin frictional resistance. If the annulus is properly grouted, an allowable skin frictional resistance of 100 psf may be used.

Lateral Earth Pressures

Backfill around an embedded structure will impose active to at-rest earth pressures against the embedded walls. Design lateral earth pressures imposed by compacted fill may be computed using an equivalent fluid weighing 90 pcf for clean sand backfill and 110 pcf for clayey backfill soils. These pressures include hydrostatic pressures but do not include surcharge forces imposed by construction or vehicular loading. The lateral pressure produced by surcharge may be computed as 50 percent of the vertical surcharge pressure applied as a constant pressure over the full depth of the buried structure. If sand backfill is used, a 2-foot thick compacted clay seal should be placed at the top of the sand backfill to reduce the amount of infiltration of surface water.

Utility Bedding

The subgrade and bedding for the proposed utilities should conform to City of Houston, Harris County, or other appropriate standards on pipeline bedding details. The soils observed in the upper 10 feet of the borings, above groundwater level, consisted of clay soils. Standard bedding details for pipes placed in “Dry Stable Trench” conditions should be followed. For excavations extending below groundwater, if observed, or where wet sand conditions are encountered, bedding details for “Wet Stable Trench” conditions should be used.

Since groundwater levels and subsurface conditions can vary, the decision regarding whether a wet sand condition applies should be made in the field based on actual conditions at the time of construction and the response of the soil and water to open trenching and to dewatering.

The excavations should be monitored to detect any variation in soil conditions from those found in the borings drilled for this report. Any changes noted in the soil stratigraphy should be brought to the attention of Terracon so that the conditions may be assessed and changes to the required bedding details and/or recommendations made, as necessary.

Utility Backfill

The type fill placed above the utility bedding will depend on whether the surface above the utilities are paved or unpaved ground. If the surface is outside of the pavement areas, then the backfill may consist of the excavated, native soils provided they are free of debris and organics. The in-situ soils used as backfill should be placed in thin lifts not exceeding

8 inches loose measure, moisture conditioned to within 2 percent of the optimum moisture content, and compacted to at least 95 percent of the Standard Effort (ASTM D698) maximum dry density.

Within pavement areas or within 3 horizontal feet of pavement, the backfill should consist of cement stabilized sand to within 12 inches of the top of the subgrade compacted to at least 95 percent of the Standard Effort (ASTM D558) maximum dry density. On-site clean soils compacted to at least 95 percent of the Standard Effort (ASTM D698) maximum dry density should be placed above the cement stabilized sand. The subgrade soils immediately below the pavement will require chemical treatment as part of the pavement design.

Prior to any filling operations, samples of the proposed borrow materials should be obtained for laboratory moisture-density testing. The tests will provide a basis for evaluation of fill compaction by in-place density testing. A qualified soil technician should perform sufficient in-place density tests during the filling operations to verify that proper levels of compaction are being attained.

Conclusion

We trust that the information contained herein meets your project needs at this time.

Please note that any items not specifically discussed above should be addressed in our original geotechnical engineering report (Terracon Project No. 91135100 dated March 29, 2024). If you have any questions concerning this report or if we may be of further service, please contact us.

Sincerely, Terracon Consultants, Inc.

(Texas Firm Registration No. F-3272)

Daniel B. Mabirizi, E.I.T. Joshua C. Miles, P.E.

Project Manager Senior Engineer

Attachments

Contents:

Exploration Plan

Boring Logs (C-01 and C-02)

Additional Geotechnical Engineering Recommendations Report

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Exploration Plan

DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS NOT INTENDED FOR CONSTRUCTION PURPOSES MAP PROVIDED BY MICROSOFT BING MAPS

PAVEMENT, about 5 inches of asphaltic concrete overlying about 3 inches of crushed stone FILL - FAT CLAY (CH), tan, with ferrous and calcareous nodules, and sand seams

- tan and gray 2 to 4 feet

FAT CLAY (CH), tan and light gray, stiff to very stiff, with ferrous and calcareous nodules, and sand pockets

SANDY FAT CLAY (CH), tan, soft to medium stiff, with sand seams

Boring Terminated at 15 Feet

Boring Log No. C-01

W at er L ev el

O bs er va tio ns

D ep th

Ft

Facilities | Environmental | Geotechnical | Materials

G ra p h ic

L o g

M o d el

L ay er

23.9

20.0

21.1

9.3

11.5

8.3

0.72

2.64

0.48

UC

UC

UC

57-14-43

50-17-33

0.7

4.0

10.0

15.0

1.5 (HP)

4.0 (HP)

3.5 (HP)

2.0 (HP)

2.5 (HP)

2-3-5 N=8

2101 Nasa Road 1 | Houston, TX

Terracon Project No. 91235100 League City, TX

551 W League City Pkwy Ste F

Drill Rig

ATV

Hammer Type Automatic

Driller M.Tobey

Logged by T.Roth

Boring Started 04-04-2025

Boring Completed 04-04-2025

Abandonment Method Boring backfilled with soil cuttings upon completion.

Advancement Method Dry augered to the depth of about 15 feet.

Notes

Water Level Observations Groundwater not encountered

See Exploration and Testing Procedures for a description of field and laboratory procedures used and additional data (If any).

See Supporting Information for explanation of symbols and abbreviations.

NASA Engineering Consolidation Phase 1A

S am pl e

T yp e

Pe rc en t

Fi n es

W at er C o n te n t

D ry

U n it

W ei g h t

(p cf

S tr ai n

C o m p re ss iv e S tr en g th

(t sf

T es t T yp e

Atterberg Limits

LL-PL-PI

See Exploration PlanLocation:

Latitude: 29.5550° Longitude: -95.0920°

Depth (Ft.)

Strength Test

Fi el d T es t

R e su lt s

FILL - FAT CLAY (CH), gray, with ferrous nodules and sand seams

- with scattered roots 0 to 2 feet

SANDY LEAN CLAY (CH), tan and light gray, very stiff to hard, with ferrous and calcareous nodules, and sand pockets

- with sand seams 8 to 10 feet

CLAYEY SAND (SC), tan, medium dense

SILTY SAND (SM), tan, medium dense

FAT CLAY (CH), tan, very stiff, with ferrous nodules

- gray 28 to 30 feet

Boring Terminated at 30 Feet

Boring Log No. C-02

W at er L ev el

O bs er va tio ns

D ep th

Ft

Facilities | Environmental | Geotechnical | Materials

G ra p h ic

L o g

M o d el

L ay er

4.5+ (HP)

4.5+ (HP)

4.5+ (HP)

4.5+ (HP)

13-19-20 N=39

10-13-15 N=28

8-10-10 N=20

5-6-4 N=10

6-7-10 N=17

7-8-9 N=17

17.8

12.5

11.1

7.1

3.14

6.17

UC

UC

27-11-16

44-12-32

29-19-10

70-18-52

4.0

10.0

13.0

23.0

30.0

2101 Nasa Road 1 | Houston, TX

Terracon Project No. 91235100 League City, TX

551 W League City Pkwy Ste F

Drill Rig

ATV

Hammer Type Automatic

Driller M.Tobey

Logged by T.Roth

Boring Started 04-04-2025

Boring Completed 04-04-2025

Abandonment Method Boring backfilled with soil cuttings upon completion.

Advancement Method Dry augered to the depth of about 30 feet.

Notes

Water Level Observations

After 15 minutes

After 5 minutes

While drilling

See Exploration and Testing Procedures for a description of field and laboratory procedures used and additional data (If any).

See Supporting Information for explanation of symbols and abbreviations.

NASA Engineering Consolidation Phase 1A

S am pl e

T yp e

Pe rc en t

Fi n es

Fi el d T es t

R e su lt s

W at er C o n te n t

D ry

U n it

W ei g h t

(p cf

S tr ai n

C o m p re ss iv e S tr en g th

(t sf

T es t T yp e

Atterberg Limits

LL-PL-PI

See Exploration PlanLocation:

Latitude: 29.5562° Longitude: -95.0917°

Depth (Ft.)

Strength Test

Auger Cuttings

Shelby Tube

Standard Penetration Test

Facilities | Environmental | Geotechnical | Materials

> 4.00

2.00 to 4.00

1.00 to 2.00

0.50 to 1.00

0.25 to 0.50 less than 0.25

Unconfined Compressive Strength Qu (tsf)

NASA Engineering Consolidation Phase 1A

2101 Nasa Road 1 | Houston, TX

Terracon Project No. 91235100 551 W League City Pkwy Ste F

League City, TX

N

(HP)

(T)

(DCP)

UC

(PID)

(OVA)

Standard Penetration Test Resistance (Blows/Ft.)

Hand Penetrometer

Torvane

Dynamic Cone Penetrometer

Unconfined Compressive Strength

Photo-Ionization Detector

Organic Vapor Analyzer

Water Level After a Specified Period of Time

Water Level After a Specified Period of Time

Cave In Encountered

Water Level Field Tests

Water Initially Encountered

Sampling

Water levels indicated on the soil boring logs are the levels measured in the borehole at the times indicated.

Groundwater level variations will occur over time. In low permeability soils, accurate determination of groundwater levels is not possible with short term water level observations.

General Notes

Location And Elevation Notes

Exploration point locations as shown on the Exploration Plan and as noted on the soil boring logs in the form of Latitude and Longitude are approximate. See Exploration and Testing Procedures in the report for the methods used to locate the exploration points for this project. Surface elevation data annotated with +/- indicates that no actual topographical survey was conducted to confirm the surface elevation. Instead, the surface elevation was approximately determined from topographic maps of the area.

Soil classification as noted on the soil boring logs is based Unified Soil Classification System. Where sufficient laboratory data exist to classify the soils consistent with ASTM D2487 "Classification of Soils for Engineering Purposes" this procedure is used. ASTM D2488 "Description and Identification of

Soils (Visual-Manual Procedure)" is also used to classify the soils, particularly where insufficient laboratory data exist to classify the soils in accordance with ASTM D2487. In addition to USCS classification, coarse grained soils are classified on the basis of their in-place relative density, and fine-grained soils are classified on the basis of their consistency. See "Strength Terms" table below for details. The ASTM standards noted above are for reference to methodology in general. In some cases, variations to methods are applied as a result of local practice or professional judgment.

Exploration/field results and/or laboratory test data contained within this document are intended for application to the project as described in this document. Use of such exploration/field results and/or laboratory test data should not be used independently of this document.

Relevance of Exploration and Laboratory Test Results

Descriptive Soil Classification

> 30

15 - 30

8 - 15

4 - 8

2 - 4

Hard

> 50 Very Stiff

Stiff

Medium Stiff

Soft

Very Soft

30 - 50

10 - 29

4 - 9

0 - 3Very Loose

Loose

Medium Dense

Dense

Very Dense

Relative Density of Coarse-Grained Soils

(More than 50% retained on No. 200 sieve.)

Density determined by Standard Penetration Resistance

Consistency of Fine-Grained Soils

(50% or more passing the No. 200 sieve.)

Consistency determined by laboratory shear strength testing, field visual-manual procedures or standard penetration resistance

0 - 1

Relative Density Consistency Standard Penetration or

N-Value (Blows/Ft.)

Standard Penetration or N-Value

(Blows/Ft.)

Strength Terms

Additional Geotechnical Engineering Recommendations Report

Unified Soil Classification System

Criteria for Assigning Group Symbols and Group Names Using

Laboratory Tests A

Soil Classification

Group Symbol Group Name

B

Coarse-Grained Soils:

More than 50% retained on No. 200 sieve

Gravels:

More than 50% of coarse fraction retained on No. 4 sieve

Clean Gravels:

Less than 5% fines C

Cu≥4 and 1≤Cc≤3 E GW Well-graded gravel F

Cu<4 and/or [Cc<1 or Cc>3.0] E GP Poorly graded gravel F

Gravels with Fines:

More than 12% fines C

Fines classify as ML or MH GM Silty gravel F, G, H

Fines classify as CL or CH GC Clayey gravel F, G, H

Sands:

50% or more of coarse fraction passes No. 4 sieve

Clean Sands:

Less than 5% fines D

Cu≥6 and 1≤Cc≤3 E SW Well-graded sand I

Cu<6 and/or [Cc<1 or Cc>3.0] E SP Poorly graded sand I

Sands with Fines:

More than 12% fines D

Fines classify as ML or MH SM Silty sand G, H, I

Fines classify as CL or CH SC Clayey sand G, H, I

Fine-Grained Soils:

50% or more passes the

No. 200 sieve

Silts and Clays:

Liquid limit less than

Inorganic:

PI > 7 and plots above “A” line J CL Lean clay K, L, M

PI < 4 or plots below “A” line J ML Silt K, L, M

Organic:

𝐿𝐿 𝑜𝑣𝑒𝑛 𝑑𝑟𝑖𝑒𝑑

𝐿𝐿 𝑛𝑜𝑡 𝑑𝑟𝑖𝑒𝑑

< 0.75 OL

Organic clay K, L, M, N

Organic silt K, L, M, O

Silts and Clays:

Liquid limit 50 or more

Inorganic:

PI plots on or above “A” line CH Fat clay K, L, M

PI plots below “A” line MH Elastic silt K, L, M

Organic:

𝐿𝐿 𝑜𝑣𝑒𝑛 𝑑𝑟𝑖𝑒𝑑

𝐿𝐿 𝑛𝑜𝑡 𝑑𝑟𝑖𝑒𝑑

< 0.75 OH

Organic clay K, L, M, P

Organic silt K, L, M, Q

Highly organic soils: Primarily organic matter, dark in color, and organic odor PT Peat

A Based on the material passing the 3-inch (75-mm) sieve.

B If field sample contained cobbles or boulders, or both, add “with cobbles or boulders, or both” to group name.

C Gravels with 5 to 12% fines require dual symbols: GW-GM well-graded gravel with silt, GW-GC well-graded gravel with clay, GP-GM poorly graded gravel with silt, GP-GC poorly graded gravel with clay.

D Sands with 5 to 12% fines require dual symbols: SW-SM well-graded sand with silt, SW-SC well-graded sand with clay, SP-SM poorly graded sand with silt, SP-SC poorly graded sand with clay.

E Cu = D60/D10 Cc =

F If soil contains ≥ 15% sand, add “with sand” to group name.

G If fines classify as CL-ML, use dual symbol GC-GM, or SC-SM.

H If fines are organic, add “with organic fines” to group name.

I If soil contains ≥ 15% gravel, add “with gravel” to group name.

J If Atterberg limits plot in shaded area, soil is a CL-ML, silty clay.

K If soil contains 15 to 29% plus No. 200, add “with sand” or

“with gravel,” whichever is predominant.

L If soil contains ≥ 30% plus No. 200 predominantly sand, add

“sandy” to group name.

M If soil contains ≥ 30% plus No. 200, predominantly gravel, add

“gravelly” to group name.

N PI ≥ 4 and plots on or above “A” line.

O PI < 4 or plots below “A” line.

P PI plots on or above “A” line.

Q PI plots below “A” line.

DxD

)(D