Final_Geotechnical_Report_Mod_2__NCRO_201409B.pdf

National Park Service

U.S. Department of the Interior

DENVER SERVICE CENTER

in collaboration with

NATIONAL CAPITAL REGION

DIVISION OF LANDS PLANNING AND DESIGN

WASHINGTON, DC

Eliminate Flooding Risk at Hains Point Facilities

Water Distribution System Improvements to NCR

& USPP Headquarters

Geotechnical Engineering Report for Modification #2

National Park Service National Capital Region

Washington, DC

July 2014

Prepared by:

Protection Engineering Group Chantilly, VA

Contract No. P09PC60802

Task Order No. 25

PMIS No. 201409

Geotechnical Engineering Report

Modification No. 2 Eliminate Flooding Risk at

Hains Point Facilities Water Distribution System Improvements to NCR & USPP Headquarters Maine Avenue to Ohio Drive, SW

Washington, DC

July 18, 2014

19955 Highland Vista Drive, Suite 170 Ashburn, VA 20147 Phone 703 726 8030 ● www.geoconcepts-eng.com

19955 Highland Vista Dr., Suite 170 Ashburn, Virginia 20147

(703) 726-8030 www.geoconcepts-eng.com

July 18, 2014

Mr. Matthew J. Batbouta, PE The Protection Engineering Group, Inc.

14585 Avion Parkway, Suite 150 Chantilly, VA 20151

Subject: Geotechnical Engineering Report, Modification No. 2, Eliminate Flooding Risk at Hains Point Facilities Water Distribution System Improvements to NCR & USPP Headquarters, Maine Avenue to Ohio Drive, SW, Washington, DC (GeoConcepts Project No. 14067)

Dear Mr. Batbouta:

GeoConcepts Engineering, Inc. (GeoConcepts) is pleased to present the following geotechnical engineering report prepared for the Hains Point Facilities Water Distribution System Improvements and improvements to the USPP Headquarters located at 1100 Ohio Drive, SW, Washington, DC.

We appreciate the opportunity to serve as your geotechnical consultant on this project. Please do not hesitate to contact me if you have any questions or want to meet to discuss the findings and recommendations contained in the report.

Sincerely, GEOCONCEPTS ENGINEERING, INC.

Rebecca L. Smith-Zakowicz, PG Associate rsmith@geoconcepts-eng.com

Table of Contents

1.0 Scope of Services

2.0 Site Description and Proposed Construction

3.0 Subsurface Conditions

3.1 Geology

3.2 Stratification

3.3 Groundwater

3.4 Soil Laboratory Test Results

3.5 Seismic Site Classification

3.6 Metal Corrosion/Concrete Attack Test Results

4.0 Engineering Analysis

4.1 Foundations

4.2 Lower Floor Slab

4.3 Lateral Earth Pressures and Subdrainage – Elevator Pit

4.4 Earthwork

4.5 Waterline Recommendations

4.6 Infiltration Analysis

4.6.1 Infiltration Test Results

4.6.2 Classification Test Results

4.6.3 Recommended Design Infiltration Rate

5.0 General Limitations

Figure 1: Design Earth Pressures for Elevator Pit Walls Figure 2: Elevator Pit Subdrainage Design Recommendations

Appendix A: Subsurface Investigation Appendix B: Soil Laboratory Test Results

July 18, 2014 14067 Page 1

1.0 Scope of Services

This geotechnical engineering report presents the results of the field investigation, soil laboratory testing, and engineering analysis of the geotechnical data. This report specifically addresses the following:

An evaluation of subsurface conditions within the area of the proposed site development, including a seismic site classification and site-specific spectral response acceleration parameters per the International Building Code, and metal corrosion and concrete attack potential of on-site soils.

Foundation recommendations for support of the proposed new building and the elevator addition to the existing building. Both shallow and deep foundations were evaluated.

Lateral earth pressures and subdrainage for use in design of the proposed elevator pit at the existing building.

Earthwork recommendations for construction of loadbearing fills, including an assessment of on-site soils to be excavated for re-use as fill.

Recommendations regarding the proposed utility installation including soil design parameters, horizontal directional drilling (HDD) techniques, excavation support, and temporary dewatering during construction for entrance trenches.

Estimated infiltration rates of the proposed stormwater management facilities based on in-situ testing and laboratory test results.

Services not specifically identified in the contract for this project are not included in the scope of services.

2.0 Site Description and Proposed Construction

It is our understanding that a new building (USPP D-1) will be constructed at the site. The exact footprint and number of stories have not been determined at this writing. For our purposes, we assumed the proposed building will be 2 stories with no below grade levels and constructed within the approximate footprint of the existing Annex buildings.

Additionally, an elevator will be added to the existing headquarters building. The exact location of the elevator has not been determined, as a result we evaluated subsurface conditions at each of two proposed locations. Additionally, we evaluated the site for the feasibility of stormwater management through infiltration, and the proposed waterline that will be extended from Buckeye Drive to the USPP D-1 building.

3.0 Subsurface Conditions

Subsurface conditions were investigated by drilling 21 test borings ranging in depths from 15 feet each in the proposed stormwater management facility, 20 feet each in the extended proposed waterline alignment, and about 65 to 90 feet each outside the existing headquarters building and in the new building area. The stormwater management borings were offset and drilled to a maximum depth of 10 feet each for in-situ infiltration testing. Test boring logs and a boring location plan are presented in Appendix A of this report.

3.1 Geology

The site is located within the Fall Line of the District of Columbia, which is the dividing line between the Coastal Plain and the Piedmont. The Coastal Plain consists of a seaward thickening wedge of unconsolidated to semi-consolidated sedimentary deposits from the Cretaceous Geologic Period to the Holocene Geologic Epoch. These deposits represent marginal-marine to marine sediments consisting of interbedded sands and clays. The Coastal Plain is bordered to the east by the Atlantic Ocean and to the west by the Piedmont Physiographic Province.

July 18, 2014 14067 Page 2

The Piedmont is bordered to the east by the Coastal Plain Physiographic Province and to the west by the Blue Ridge Physiographic Province and contains several fault bordered basins. Bedrock in the Piedmont typically consists of highly weathered metamorphic and igneous bedrock. Surface topography in the Piedmont is the result of millions of years of erosion. Alluvium associated with the nearby Potomac and Anacostia Rivers cap the Piedmont strata.

During original development of this area, fill (Stratum A) was placed to reclaim what was a tidal marsh.

Beneath the existing fill is natural alluvium (Stratum B) associated with the nearby Potomac River and its tributaries, and then the Pleistocene age terrace deposits (Stratum C), and the Potomac Group sediments (Stratum D). At the base of the Stratum C or Stratum D soils is a gneiss bedrock from the Lower Cambrian geologic period.

3.2 Stratification

The subsurface materials encountered have been stratified for purposes of our discussions herein. These stratum designations do not imply that the materials encountered are continuous across the site. Stratum designations have been established to characterize similar subsurface conditions based on material gradations and parent geology. The subsurface materials encountered in the test borings completed at the site have been assigned to the following strata:

Stratum A (Existing Fill) generally firm, sandy lean clay, clayey sand, silty sand, FILL, moist, brown, gray, orange, orange-brown, black

Stratum B (Alluvium) soft to medium stiff, ORGANIC SILT (OH), ELASTIC SILT (MH), LEAN CLAY (CL), with various amounts of sand; and generally loose to firm, clayey SAND (SC), silty SAND (SM), POORLY GRADED SAND (SP-SM) with silt, moist to wet, brown, gray, tan, brown, orange-brown

Stratum C (Terrace) firm to compact, clayey SAND (SC), silty SAND (SM), POORLY GRADED SAND (SP-SM) with silt, clayey GRAVEL (GC) with sand, moist to wet, brown, gray, tan, brown, orange-brown

Stratum D (Potomac Group) firm to compact, clayey SAND (SC), POORLY GRADED SAND (SP-SC) with clay, moist, brown, gray, and greenish-gray

The two letter designations included in the strata descriptions presented above and on the test boring logs represent the Unified Soil Classification System (USCS) group symbol and group name for the samples based on laboratory testing per ASTM D-2487 and visual classifications per ASTM D-2488. It should be noted that visual classifications per ASTM D-2488 may not match classifications determined by laboratory testing per ASTM D-2487.

3.3 Groundwater

Groundwater level observations were made in the field during drilling and after the completion of the test borings. Groundwater was encountered at depths of about 8 to 25 feet below the existing ground surface, or at about elevation (EL) -13.0 to EL +5.5. Accordingly, groundwater is expected to generally be above proposed waterline invert depths, but below proposed proposed building slabs. A summary of the water level readings rounded off to the nearest 0.5 feet elevation is presented in the table below.

Test Boring No. Depth to Groundwater (feet) Groundwater Elevation (feet)

D-1 23.0 -12.0

D-2 25.0 -13.0

D-3 13.0 -1.0

July 18, 2014 14067 Page 3

Test Boring No. Depth to Groundwater (feet) Groundwater Elevation (feet)

D-4 8.5 4.5

D-5 8.5 5.5

SWM-1 8.0 4.0

SWM-2 Dry Dry

SWM-3 Dry Dry

SWM-4 9.0 2.0

SWM-5 Dry Dry

SWM-6 Dry Dry

SWM-7 14.0 -3.0

SWM-8 Dry Dry

SWM-9 Dry Dry

SWM-10 Dry Dry

SWM-11 13.5 -2.5

B-9 Dry Dry

B-10 Dry Dry

B-11 Dry Dry

B-12 Dry Dry

The groundwater observations presented herein are considered to be an indication of the groundwater levels at the dates and times indicated. Where more impervious Strata A and B clay soils are encountered, the amount of water seepage into the borings is limited, and it is generally not possible to establish the location of the groundwater table through short term water level observations. Accordingly, the groundwater information presented herein should be used with caution. Also, fluctuations in groundwater levels should be expected with seasons of the year, construction activity, changes to surface grades, precipitation, or other similar factors.

3.4 Soil Laboratory Test Results

Selected soil samples obtained from the field investigation were tested for grain size distribution, textural analysis, Atterberg limits, consolidation, and natural moisture contents. A summary of soil laboratory test results is presented below, and the results of natural moisture content tests are presented on the test boring logs in Appendix A.

Test Boring

No.

Depth (feet)

Sample Type Stratum Description of

Soil Specimen

Sieve Results

Atterberg Limits Natural

Moisture Content

Percent Retained #4 Sieve

Percent Passing #200 Sieve

LL PL PI

B-9 8.5-10 Jar B ELASTIC SILT (MH) 0.0 91.1 53 29 24 42.8

B-13 8.5-10 Jar B ELASTIC SILT (MH) 0.0 99.6 61 33 28 47.5

D-1 63.5-65 Jar C clayey GRAVEL (SC) with sand 52.8 15.2 37 22 15 20.7

July 18, 2014 14067 Page 4

Boring

No.

Depth (feet)

Sample Type Stratum Description of

Soil Specimen

Sieve Results

Atterberg Limits Natural

Moisture Content

Percent Retained #4 Sieve

Percent Passing #200 Sieve

LL PL PI

D-3 8.5-10 Jar B silty SAND (SM) 0.0 30.8 NP NP NP 31.3

D-3 23.5-25 Jar B silty SAND (SM) 0.0 35.9 24 NP NP 29.0

D-4 8.5-10 Jar B silty SAND (SM) 0.9 46.4 20 NP NP 24.3

D-4 49-50.5 Jar B FAT CLAY (CH) with sand 0.0 72.2 55 29 26 50.7

D-4 78.5-80 Jar D

POORLY GRADED

SAND (SP-SC) with clay

4.1 10.4 35 23 12 14.8

D-4 47-49 Tube B ORGANIC CLAY (OH) with sand 0.0 79.3 85 38 47 45.8

D-5 20-22 Tube B sandy LEAN CLAY

(CL) 0.0 50.1 46 26 20 38.8

Notes:

1. Soil tests are in accordance with applicable ASTM standards

2. Soil classification symbols are in accordance with Unified Soil Classification System

3. Visual identification of samples is in accordance with ASTM D-2488

4. Key to abbreviations: LL = liquid limit; PL = plastic limit; PI = plasticity index; NP = nonplastic; N/T = not tested

Results of consolidation tests performed on the Stratum B soils are presented below. These consolidation test results indicate that the Stratum B soils are slightly over-consolidated, and have moderate to high secondary compressibility.

Test

Boring No.

Sample

Depth (feet)

USCS

Classification eO Pc (ksf) Cc Cr C

D-4 47-49 OH 1.214 2.08 0.46 0.06 0.011

D-5 20-22 CL 1.112 1.90 0.35 0.03 0.007

eO = initial void ratio; Pc = preconsolidation pressure; Cc = compression index; Cr = recompression index; C= coefficient of secondary compressibility.

3.5 Seismic Site Classification

Based on the results of the subsurface investigation and our knowledge of local geologic conditions, the site soils have been assigned to a site class E per the International Building Code (IBC). It may be possible to improve the site classification from an “E” to a “D” with in-situ shear wave testing at the site. We can provide this additional service upon request.

The site coefficients and adjusted Maximum Considered Earthquake (MCE) spectral response acceleration parameters were obtained from the USGS computer program and are presented in the table below.

Mapped Spectral Accelerations for Site Class B and 5% Damping (Step 1)

Site Coefficients to Modify Accelerations Based on Site Classification E (Step 2)

Ss = 0.118(g) Fa = 2.5

S1 = 0.051(g) Fv = 3.5 MCE Spectral Response Accelerations

(Step 3) Design Spectral Response Accelerations

(Step 4) SMS = 0.296 (g) (=Ss*Fa) SDS = 0.197(g) (=2/3*SMS)

SM1 = 0.178(g) (=S1*Fv) SD1 = 0.119(g) (=2/3*SM1)

July 18, 2014 14067 Page 5

3.6 Metal Corrosion/Concrete Attack Test Results

In addition to standard geotechnical soil laboratory testing, two samples were submitted to an analytical laboratory for metal corrosion and concrete attack testing. Corrosion testing consisted of analysis for moisture content (ASTM D-2216), pH (EPA 9045), resistivity (ASTM G57), sulfides (EPA 9030), and reduction-oxidation potential (ASTM D-1498 mod.). The results of these tests are presented below:

Boring

No.

Sample Depth (feet)

Moisture Content pH Resistivity

(ohm – cm) Sulfides (ppm)

Red-ox Potential

(mV)

Point Total

B-5 4-12 41 6.6 4000 <1.2 -138 11

B-11 8.5-15 45 6.6 1500 <1.2 +122 14

For each test presented above, points are assigned based on the range of the test results. If the total points from the five tests completed for a particular sample are 10 or more, the soil is considered to be corrosive. The methods described herein are based on information from the American Water Works Association (AWWA). Using the methods described by AWWA, the point total for the samples tested averaged 12.5. Accordingly, the site soils are considered corrosive.

Sulfate (CA Test 417) tests were performed on selected soil samples to determine the severity of sulfate attack on concrete structures. The results of sulfate testing are presented in the table below.

Test Boring No. Sample Depth (feet) Sulfate Concentration (ppm)

B-5 4-12 76

B-11 8.5-15 18

Based on correlations between sulfate concentrations and severity of sulfate attack as presented in American Concrete Institute (ACI) 318, the above sulfate concentrations are considered to pose a negligible threat of sulfate attack on concrete.

4.0 Engineering Analysis

Recommendations regarding foundation and floor slab support, lateral earth pressures, subdrainage, waterline installation, and stormwater management by infiltration are presented herein.

4.1 Foundations

Shallow foundations and deep foundations were evaluated for support of the proposed building and elevator pit addition. Due to the relatively high secondary compressibility of the organic clay soils of Stratum B, we do not recommend the use of shallow foundations to support structures. It is known that the underlying alluvial soils in this area of Washington, DC (Jefferson Memorial, FDR Memorial, East Potomac Park, etc.)

continue to settle over time, and we estimate that this site will continue to settle on the average of about

0.05 to 0.10 inches per year. Accordingly, we recommend that the proposed building and elevator pit addition should be supported on deep foundations. Historic building documents show that existing buildings on the NPS Headquarters campus are founded on 12-inch square concrete piles embedded down to EL -55 with a 40 ton working load capacity.

We recommend that driven 12-inch square precast concrete piles or 14-inch diameter auger cast piles, designed for 65 tons allowable capacity, be used for support of the proposed building and elevator addition.

The table below presents pile tip bearing elevations at the test borings. Pile tip elevations between test boring locations may be estimated by linear interpolation. However, some variations in depths to suitable bearing material should be expected when using linear interpolation.

July 18, 2014 14067 Page 6

Test Boring No. Estimated Tip Elevation for Pile Foundations

D-1 EL -60

D-2 EL -55

D-3 EL -55

D-4 EL -65

D-5 EL -55

The tip elevations presented herein are intended for use in design and construction planning. Actual pile tip elevations should be based on criteria established during pile load testing as discussed below. Piles should be placed at least 3.0 times the pile diameter, center to center from the nearest pile, to prevent capacity reduction due to pile group action.

For driven piles, some pre-drilling and/or spudding may be necessary to penetrate dense portions of the existing fill, rubble material, and other obstructions that may be encountered during construction. Since the need for pre-drilling and/or spudding will not be determined until the start of pile installations, the contractor should be prepared to mobilize pre-drilling equipment to the site, and should provide unit fees for pre-drilling in their contract. Greater than normal pile breakage and problems during installation of piles should be anticipated. Point protection of piles may also be considered to reduce pile damage.

For auger cast piles, piles are installed by drilling with a hollow stem auger with a plug at the tip of the auger. After the bearing level is reached, a sand-cement grout is placed under pressure through the hollow stem as the augers are withdrawn. The upper portion of the pile is cast to subgrade level and cut off about 6 inches above the bottom of the pile cap. A reinforcing bar should be installed in the upper portion of each pile as determined by the structural engineer. This reinforcement will provide added structural capacity and provide some assurance that the pile will not be damaged during excavation for the pile caps.

For auger cast piles, the center opening should be at least 3-½ inches to limit head loss of grout. A fluidifier should be used to inhibit early setup and to increase fluidity. The grout pump used for pile construction should be a high pressure, positive displacement pump equipped with a stroke counter to allow measurements of grout volume. The pump should be calibrated within 6 months of use on this project.

The contractor should establish an accurate method of determining the auger depth at all times, and pressure gauges should be in place for determining grouting pressure. Careful observations and monitoring of the grout pressures and volumes should be provided by the contractor and should be documented by a GeoConcepts field representative. Insufficient grout pressures may result in necking of the piles.

During pumping of grout, the auger withdrawal should be a smooth operation. The auger withdrawal rate should be slower than the rate of grout pumping such that the grout will form a relatively uniform shaft to the surface. Records should be maintained of the grout pumped into the pile at 3 feet to 5 feet intervals.

Should the grout take at any interval be less than 125 percent of the theoretical volume, that pile interval should be re-drilled and re-grouted prior to continuing grout installation. In this case, no consideration of the previously placed grout should occur. The contractor should be prepared to install greater than normal grout volumes due to the soft Stratum B soils. Piles should not be installed within five pile diameters of an adjacent pile (center to center dimension) for a period of at least 24 hours after casting the adjacent pile.

Quality control of auger cast piles should include documentation of augering depths and monitoring of grout pressures, volumes, and consistency. Flow cone tests should be performed periodically to verify minimum and maximum efflux times of not less than 16 seconds or more than 25 seconds. In addition, prior to the start of production piles, a 55-gallon drum should be filled with grout under observation of the geotechnical engineer to establish grout volumes per pump stroke.

July 18, 2014 14067 Page 7

The installation of precast concrete or auger cast piles for this project should be restricted to contractors with demonstrated ability and experience. Contractors should have at least five years of experience in the installation of these types of piles.

The recommended allowable pile capacity presented herein is based on our experience, load test data from similar installations, and the subsurface data obtained for this project. Based on the results of the load test program, GeoConcepts will prepare driving criteria to be followed by the pile driving contractor. The actual tip elevations of production piles should be determined in the field based on the driving criteria and observations during installation.

Axial load tests should be performed on piles installed to the recommended tip elevations presented herein.

Precast concrete test piles should be dynamically load tested during initial driving and at least 72 hours after driving, in accordance with ASTM D-4945. Auger cast piles should be statically load tested in accordance with ASTM D-1143. Additional tests may be required depending upon the results of the initial load test program. Installation of production piles should not begin until the data from the load tests have been evaluated by the geotechnical engineer. Adjustments to the pile hammer, pile lengths, etc. may result from this load test program. In addition, for precast concrete piles, the contractor should submit their proposed pile hammer information to the geotechnical engineer, supported by a Wave Equation Analysis, to confirm that the pile hammer has the ability to drive the piles to the required bearing elevations without overstressing the piles.

4.2 Lower Floor Slab

The lower floor slab should be framed on the deep foundations due to the potential long term settlement of the existing soils. The use of structural slabs will provide a complete assurance against long-term ground subsidence or differential settlement due to compression of the existing fill.

All debris and soft soils near the final floor slab subgrade as a result of construction operations should be stripped and removed prior to placement of underfloor stone. A 4-inch minimum thickness of washed gravel or crushed stone meeting the requirement of AASHTO No. 57 should be placed below floor slabs on grade to serve as a capillary break. An impermeable plastic membrane should be placed on top of the crushed stone layer to assist as a moisture barrier. Special attention should be given to the surface curing of the slab in order to minimize uneven drying of the slab and associated cracking.

We recommend that mesh (fiber or welded wire fabric) reinforcement be included in the design of the floor slab to minimize the development of any shrinkage cracks near the surface of the slab. If welded wire fabric is used, the mesh should be located in the top half of the slab.

4.3 Lateral Earth Pressures and Subdrainage – Elevator Pit

Elevator pit walls should be designed to withstand lateral earth pressures. An equivalent fluid pressure of 60H (psf) should be used for design of elevator pit walls, where H refers to the height of the wall. The design should account for any surcharge loads within a 45 degree slope from the base of the wall. A coefficient of friction of 0.35 may be used for sliding resistance at the soil/concrete interface. A recommended lateral earth pressure diagram for use in the design of elevator pit walls is presented as Figure 1 at the end of this report.

Hydrostatic pressures are not included in the lateral earth pressure diagrams assuming the use of relatively granular or free draining backfill, and perimeter subdrainage at the base of pit walls below grade.

Recommended subdrainage for elevator pit walls are presented as Figure 2 at the end of this report. Any building elements extending below the subdrainage system should be designed for hydrostatic and uplift pressures, and be waterproofed. Details regarding waterproofing should be provided by a waterproofing specialist and are beyond the scope of this report.

July 18, 2014 14067 Page 8

4.4 Earthwork

Fill will be required for site grading in building and pavement areas, and as backfill against walls below grade. Unsuitable existing fill, soft or loose natural soils, organic material, and rubble should be stripped to approved subgrades as determined by the geotechnical engineer. Topsoil depths presented on the boring logs should not be considered as stripping depths, as topsoil depths may vary widely across the site, particularly in wooded or previously cultivated areas. Stripping depths will probably extend to greater depths than the topsoil depths indicated herein due to the presence of minor amounts of organics, roots, and other surficial materials that will require removal as a part of the stripping operations. In addition, seasonal soil moisture variations can affect stripping depths. In general, less stripping may occur during summer months when drier weather conditions can be expected. The depth of required stripping should be determined prior to construction by the excavation contractor using test pits, probes, or other means that the contractor wishes to employ, and this determination should be the responsibility of the excavation contractor. All subgrades should be proofrolled with a minimum 20 ton, loaded dump truck or suitable rubber tire construction equipment approved by the geotechnical engineer, prior to the placement of new fill.

Fill material should be placed in lifts not exceeding 8 inches loose thickness, with fill materials compacted by hand operated tampers or light compaction equipment placed in maximum 4-inch thick loose lifts. Fill should be compacted at +/- 2% of the optimum moisture content to at least 95 percent of the maximum dry density per ASTM D-698.

Materials used for compacted fill for support of floor slabs should consist of soils classifying SC, SM, SP, SW, GC, GM, GP, or GW per ASTM D-2487, with a liquid limit and plasticity index less than 40 and 15, respectively. It is expected that portions of soils excavated at the site will be suitable for re-use as fill based on classification. However, the Stratum A existing fill may not be suitable for re-use as new compacted fill due to deleterious man-made materials in the fill. In addition, drying of excavated soils by spreading and aerating may be necessary to obtain proper compaction. This may not be practical during the wet period of the year. Accordingly, earthwork operations should be planned for early Spring through late Fall, when drier weather conditions can be expected. Individual borrow areas, both from on-site and off-site sources, should be sampled and tested to verify classification of materials prior to their use as fill.

Fill materials should not be placed on frozen or frost-heaved soils, and/or soils that have been recently subjected to precipitation. All frozen or frost-heaved soils should be removed prior to continuation of fill operations. Borrow fill materials should not contain frozen materials at the time of placement.

Compaction equipment that is compatible with the soil type used for fill should be selected. Theoretically, any equipment type can be used as long as the required density is achieved; however, sheepsfoot roller equipment are best suited for fine-grained soils and vibratory smooth drum rollers are best suited for granular soils. Ideally, a smooth drum roller should be used for sealing the surface soils at the end of the day or prior to upcoming rain events. In addition, compaction equipment used adjacent to walls below grade should be selected so as to not impose undesirable surcharge on walls. All areas receiving fill should be graded to facilitate positive drainage of any water associated with precipitation and surface run-off.

For utility excavation backfill, we recommend that open graded stone be used to backfill the pipe trench to the spring line of the pipe. Backfill should be compacted in lifts not exceeding 6 inches loose thickness, to at least 95 percent of the maximum dry density per ASTM D-698. Hand operated compaction equipment should be used until the backfill has reached a level 1 foot above the top of the pipe to prevent damaging the pipe. Also, backfill material within 2 feet of the top of the pipe should not contain rock fragments or gravel greater than 1-inch in diameter.

After completion of compacted fill operations in building areas, construction of building elements should begin immediately, or the finished subgrade should be protected from exposure to inclement weather conditions. Exposure to precipitation and freeze/thaw cycles will cause the finished subgrade to soften and become excessively disturbed. If development plans require that finished subgrades remain exposed to

July 18, 2014 14067 Page 9 weather conditions after completion of fill operations, additional fill should be placed above finished grades to protect the newly placed fill. Alternatively, a budget should be established for reworking of the upper 1 to 2 feet of previously placed compacted fill.

4.5 Waterline Recommendations

We understanding that the proposed waterline will be installed using a technique known as Horizontal Directional Drilling (HDD), which is a steerable trenchless method of installing underground utilities by using a surface-launched drilling rig with minimal impact on the surrounding ground surface area. It is suitable for a variety of soil conditions with the exception of soils with cobbles or voids or highly variable rock layers.

The soils encountered at the site during our subsurface investigation were generally consistent in composition with very little gravel. As a result, we believe that this technique of utility installation is feasible.

The proposed HDD process typically requires entrance pits/trenches. A temporary vertical excavation support system such as steel trench boxes may be used to construct the entrance pits. The excavations may also be constructed by laying back the earth with temporary slopes. Based on the on-site soils, an OSHA type C soil classification should be used for design of earth slopes. A type C classification requires a maximum allowable slope of 1.5H:1V for excavations less than 12 feet in depth. Any benching of excavations should be performed in accordance with OSHA requirements.

Temporary excavations will likely extend below groundwater levels. Groundwater will decrease the stability of open cuts. Accordingly, construction dewatering will be necessary to excavate and maintain temporary excavations. We recommend that the dewatering consist of both an aggressive system of individual sumps and pumps during excavation. To help maintain bottom stability of excavations, groundwater levels should be drawn-down a minimum of 3 feet below the lowest portion of the excavation.

Backfill may be required in the entrance pits/trenches after installation of the utility. Soft or loose soils should be stripped to approved subgrades as determined by the geotechnical engineer. We believe it is feasible to leave the soft soils in place and stabilize them by tracking crushed stone into the soft subgrade, until the subgrade is firm. Backfill should be compacted in lifts not exceeding 6 inches loose thickness, to at least 95 percent of the maximum dry density per ASTM D-698.

We recommend that the following soil design parameters be used for the design of the HDD and the entrance pits, as needed:

Depth (feet)

Total Unit

Weight (pcf)

Angle of Internal Friction

(degrees)

Lateral Earth Pressure Coefficients Coefficient of Sliding Friction Active

(Ka)

At- Rest (Ko)

Passive (Kp)

0 to 5 125 30 0.33 0.50 3.0 0.35

Below 5 115* 25 0.41 0.58 2.5 0.30

* Use 53 pcf buoyant weight below 8 feet depth

4.6 Infiltration Analysis

Two methods were used to estimate infiltration capabilities on the subject site: in-situ infiltration testing and published correlations with soil classifications. Details regarding the in-situ infiltration and classification test techniques, the estimated infiltration rates from the individual methods, and the recommended design infiltration rate for the site soils are presented herein.

4.6.1 Infiltration Test Results

In-situ infiltration tests are performed in the field to observe the rate at which water will permeate the soil under saturated conditions. Eleven test borings were drilled in the area of planned infiltration. Test borings

July 18, 2014 14067 Page 10 were initially drilled to depths of at least 4 feet below the planned infiltration invert elevations, and allowed to remain open for a period of approximately 24 hours to allow any groundwater levels within the boreholes to stabilize. After 24 hours, offset infiltration test holes were drilled at the boring locations to planned infiltration invert elevations. Four-inch diameter PVC casing was set to the bottom of the test holes. The purpose of the casing is to prevent caving of test hole sidewalls. After setting the PVC casing, the borehole was filled with water to saturate the bottom subsoils. The following day, the test hole was refilled with water and the water level in each test hole was recorded every hour for a 4-hour period. Using this procedure, the average change in the water level over the 4-hour period is considered the infiltration rate.

Based on the results of the in-situ infiltration tests, estimated infiltration rates have been assigned for the site soils, as presented in the table below:

Test Boring No. Approximate Test Depth (feet) Estimated Infiltration Rate (inches/hour)

SWM-1 5.0 0.3

SWM-2 6.0 5.1

SWM-3 6.0 3.6

SWM-4 8.0 0.0

SWM-5 4.0 10.2

SWM-6 10.0 0.0

SWM-7 6.0 3.0

SWM-8 8.0 0.0

SWM-9 7.5 5.4

SWM-10 7.5 3.3

SWM-11 10.0 2.4

4.6.2 Classification Test Results

The classification test method is performed with grain-size sieve analyses including hydrometer testing on samples obtained from corresponding proposed infiltration depths, to determine the USDA soil texture classifications. Published correlations between USDA classifications and infiltration rates were used to provide estimated hydraulic conductivity values. Since hydraulic conductivity and infiltration values are essentially equal at no head conditions, using the hydraulic conductivity values to estimate the infiltration rates provides a conservative estimate of infiltration for use in design. Estimated infiltration rates using the USDA soil texture classifications are presented below.

Test Boring No.

Approximate Test Depth (feet)

USDA Soil Texture Classification

Estimated Infiltration Rate (inches/hour)

SWM-1 5.0 Loam 0.52

SWM-2 6.0 Loam 0.52

SWM-3 6.0 Loam 0.52

SWM-4 8.0 Clay Loam 0.09

July 18, 2014 14067 Page 11

Test Boring No.

Approximate Test Depth (feet)

USDA Soil Texture Classification

Estimated Infiltration Rate (inches/hour)

SWM-5 4.0 Clay Loam 0.09

SWM-6 10.0 Clay Loam 0.09

SWM-7 6.0 Clay Loam 0.09

SWM-8 8.0 Clay Loam 0.09

SWM-9 7.5 Clay Loam 0.09

SWM-10 7.5 Silty Clay 0.04

SWM-11 10.0 Sandy Loam 1.02

4.6.3 Recommended Design Infiltration Rate

Based on the results of the in-situ infiltration tests and soil laboratory classification tests, we recommend that a design infiltration rate of 0.52 inches/hour be used for design of infiltration structures located in the loam and sandy loam materials of Stratum B that is at least 2 feet above the groundwater table. Based on the in-situ and classification test results, it should be feasible to provide stormwater management through infiltration at the following locations: SWM-2, SWM-3, and SWM-11.

It should be noted that the recommended design infiltration rate presented herein is intended for use in design. However, during construction, observations of the subgrade conditions should be made to confirm that the subgrade soils are consistent with the soils analyzed in this report.

5.0 General Limitations

Recommendations contained in this report are based upon the data obtained from the relatively limited number of test borings. This report does not reflect conditions that may occur between the points investigated, or between sampling intervals in test borings. The nature and extent of variations between test borings and sampling intervals may not become evident until the course of construction. Therefore, it is essential that on-site observations of subgrade conditions be performed during the construction period to determine if re-evaluation of the recommendations in this report must be made. It is critical to the successful completion of this project that GeoConcepts be retained during construction to observe the implementation of the recommendations provided herein.

This report has been prepared to aid in the evaluation of the site and to assist your office and the design professionals in the design of this project. It is intended for use with regard to the specific project as described herein. Changes in proposed construction, grading plans, etc. should be brought to our attention so that we may determine any effect on the recommendations presented herein.

An allowance should be established for additional costs that may be required for foundation and earthwork construction as recommended in this report. Additional costs may be incurred for various reasons including wet fill materials, soft subgrade conditions, unexpected groundwater problems, etc.

This report should be made available to bidders prior to submitting their proposals to supply them with facts relative to the subsurface conditions revealed by our investigation and the results of analyses and studies that have been performed for this project. In addition, this report should be given to the successful contractor and subcontractors for their information only.

July 18, 2014 14067 Page 12

We recommend the project specifications contain the following statement: “A geotechnical engineering report has been prepared for this project by GeoConcepts Engineering, Inc. This report is for informational purposes only and should not be considered part of the contract documents. The opinions expressed in this report are those of the geotechnical engineer and represent their interpretation of the subsoil conditions, tests and results of analyses that they performed. Should the data contained in this report not be adequate for the contractor’s purposes, the contractor may make their own investigations, tests and analyses prior to bidding.”

This report was prepared in accordance with generally accepted geotechnical engineering practices. No warranties, expressed or implied, are made as to the professional services included in this report.

We appreciate the opportunity to be of service for this project. Please contact the undersigned if you require clarification of any aspect of this report.

Sincerely, GEOCONCEPTS ENGINEERING, INC.

Rebecca L. Smith-Zakowicz, PG Associate

Paul E. Burkart, PE Principal

RSZ/PEB/shm N:\PROJECTS\Active 14 Projects\14067, NCRO Waterline\Final\NPS HQ Report\Geotechnical Report, Mod. 2.docx

Appendix A Subsurface Investigation Subsurface Investigation Procedures (1 page)

Identification of Soil (1 page)

Test boring Notes (1 page)

Test Boring Logs (21 pages)

Boring Location Plan, Figure 3 (1 page)

Subsurface Investigation Procedures

1. Test Borings – Hollow Stem Augers The borings are advanced by turning an auger with a center opening of 2-¼ or 3-¼ inches. A plug device blocks off the center opening while augers are advanced. Cuttings are brought to the surface by the auger flights. Sampling is performed through the center opening in the hollow stem auger, by standard methods, after removal of the plug. Usually, no water is introduced into the boring using this procedure.

2. Standard Penetration Tests Standard penetration tests are performed by driving a 2 inch O.D., 1-⅜ inch I.D. sampling spoon with a 140-pound hammer falling 30 inches, according to ASTM D-1586. After an initial 6 inches penetration to assure the sampling spoon is in undisturbed material, the number of blows required to drive the sampler an additional 12 inches is generally taken as the N value. In the event 30 or more blows are required to drive the sampling spoon the initial 6 inch interval, the sampling spoon is driven to a total penetration resistance of 100 blows or 18 inches, whichever occurs first. The sampling operation is terminated after a total of 100 hammer blows and the depth of penetration is recorded.

3. Undisturbed Tube Samples Undisturbed tube sampling is accomplished by inserting 3 inch I.D. thin walled steel tubes into the soil through the hollow stem of the augers with hydraulically actuated rams.

4. Test Boring Stakeout The test boring stakeout was provided by GeoConcepts personnel using available site plans. Ground surface elevations were estimated from topographic information contained on the site plan provided to us and should be considered approximate. If the risk related to using approximate boring locations and elevations is unacceptable, we recommend an as-drilled survey of boring locations and elevations be completed by a licensed surveyor.

Identification of Soil I. DEFINITION OF SOIL GROUP NAMES ASTM D-2487 Symbol Group Name

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

GW WELL GRADED GRAVEL

GP POORLY GRADED GRAVEL

Gravels with Fines More than 12% fines

GM silty GRAVEL GC clayey GRAVEL

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

Clean Sands Less than 5% fines

SW WELL GRADED SAND

SP POORLY GRADED SAND

Sands with fines More than 12% fines

SM silty SAND SC clayey SAND

Fine-Grained Soils 50% or more passes the No. 200 sieve

Silts and Clays Liquid Limit less than

Inorganic CL LEAN CLAY

ML SILT

Organic OL ORGANIC CLAY

ORGANIC SILT

Silts and Clays Liquid Limit 50 or more

Inorganic CH FAT CLAY

MH ELASTIC SILT

Organic OH ORGANIC CLAY

ORGANIC SILT

Highly Organic Soils Primarily organic matter, dark in color, and organic odor PT PEAT

II. DEFINITION OF MINOR COMPONENT PROPORTIONS

Minor Component Approximate Percentage of Fraction by Weight Gravelly, Sandy (adjective) 30% or more coarse grained Sand, Gravel (with) 15% to 29% coarse grained Silt, Clay (with) 5% to 12% fine grained

III. GLOSSARY OF MISCELLANEOUS TERMS

SYMBOLS Unified Soil Classification Symbols are shown above as group symbols. Use “A” Line Chart for laboratory identification. Dual symbols are used for borderline classification.

BOULDERS & COBBLES Boulders are considered pieces of rock larger than 12 inches, while cobbles range from 3 to 12 inches.

DISINTEGRATED ROCK Residual rock material with a standard penetration test (SPT) resistance between 60 blows per foot and refusal.

ROCK Rock material with a standard penetration test (SPT) resistance of 100 blows for 2 inches or 50 blows for 0 inches, or less penetration DECOMPOSED ROCK Residual rock material exhibiting rock-like properties that can be excavated by backhoe equipment.

Similar to Disintegrated Rock, but cannot be classified as such because SPT N-Values were not obtained.

ROCK FRAGMENTS Angular pieces of rock, distinguished from rounded transported gravel, which have separated from original vein or strata and are present in a soil matrix.

QUARTZ A hard silicate mineral often found in residual soils. Only used when describing residual soils.

CEMENTED SAND Usually localized rock-like deposits within a soil stratum composed of sand grains cemented by calcium carbonate, iron oxide, or other minerals. Commonly encountered in Coastal Plain sediments, primarily in the Potomac Group sands (Kps).

MICA A plate-like phyllosilicate mineral found in many rocks, and in residual or transported soil derived there from.

ORGANIC MATERIALS

(Excluding Peat)

Topsoil - Surface soils that support plant life and contain organic matter.

Lignite - Hard, brittle decomposed organic matter with low fixed carbon content (a low grade of coal).

FILL Man made deposit containing soil, rock, and other foreign matter.

PROBABLE FILL Soils which contain no visually detected foreign matter but which are suspect with regard to origin.

LAYERS ½ to 12 inch seam of minor soil component.

COLOR Two most predominant colors present should be described.

MOISTURE CONDITIONS Wet, moist, or dry to indicate visual appearance of specimen.

Test Boring Notes

1. Classification of soil is by visual inspection and is in accordance with the Unified Soil Classification

System.

2. Estimated groundwater levels are indicated on the logs. These are only estimates from available data and may vary with precipitation, porosity of soil, site topography, etc.

3. Sampling data presents standard penetrations for 6-inch intervals or as indicated with graphic representations adjacent to the sampling data. Where undisturbed tube samples are taken, they are designated “Shelby Tube” on the test boring log.

4. The logs and related information depict subsurface conditions at the specific locations and at the particular time when drilled. Soil conditions at other locations may differ from conditions occurring at the test locations. Also, the passage of time may result in a change in the subsurface conditions at the test locations.

5. The stratification lines represent the approximate boundary between soil types as determined in the sampling operation. Some variation may be expected vertically between samples taken. The soil profile, groundwater level observations and penetration resistances presented on the logs have been made with reasonable care and accuracy and must be considered only an approximate representation of subsurface conditions to be encountered at the particular location.

6. Auger refusal is taken as the depth at which further penetration of the auger is not possible without risking significant damage to the drilling equipment.

10.8

8.5

-9.0

A

B

Topsoil = 2 inches sandy lean clay FILL, moist, brown and orange

ELASTIC SILT (MH), moist, dark gray with sand below 18.5 ft.

Bottom of Boring at 20.0 ft

1+4+4

2+1+1

0+2+1

0+0+0

0+0+0

0+0+0

42.8

PROJECT NUMBER:

DATE STARTED:OWNER/CLIENT:

GROUND SURFACE ELEVATION (ft): DRILLING METHOD:

6/3/14

6/3/142.25" I.D. HSA

DRILLER:

DATE COMPLETED:

Protection Engineering Group

14067

D. Williams

11.0 ±

SHEET 1 OF 1

ENCOUNTERED:

UPON COMPLETION:

LOCATION:

LOGGED BY:PROJECT:

GROUND WATER LEVELS:

REMARKS:

B-9

None

Dry

THE STRATIFICATION LINES REPRESENT APPROXIMATE BOUNDARIES. THE TRANSITION MAY BE GRADUAL.

SAMPLE TYPES:

MATERIAL DESCRIPTION

Split Spoon

DRILLING CONTRACTOR:

BORING NUMBER:

NCRO USPP D-1 & Water Distribution Improvements

1100 Ohio Drive, SW, Washington, DC Connelly and Associates, Inc.

K. Fordney

703-726-8030 703-726-8032 fax

19955 Highland Vista Dr. #170 Ashburn, VA 20147

B O

R E

H O

LE

/T

E S

T P

IT

L

O G

S

H Q

.G P

J G

E O

C O

N C

E P

T S

.G D

T

7/

/1

ELEV. 7.0

ELEV.

(ft)

20 40 60 80

STANDARD

PENETRATION

TEST RESISTANCE

(BLOWS/FOOT)

S T

R A

T U

M

DEPTH

(ft) ftCAVED: 4.0

S P

T B

LO

W

C O

U N

T S

R E

C O

V E

R Y

(in

S A

M P

LE

T

Y P

E

M C

12.8

4.5

-0.5

-7.0

A

B

Topsoil = 2 inches silty sand FILL with gravel, moist, gray and brown without gravel below 2.5 ft.

clayey SAND (SC), moist, brown

ELASTIC SILT (MH), moist, gray

Bottom of Boring at 20.0 ft

2+3+3

14+9+10

11+15+10

0+0+0

0+1+2

0+2+1

PROJECT NUMBER:

DATE STARTED:OWNER/CLIENT:

GROUND SURFACE ELEVATION (ft): DRILLING METHOD:

6/3/14

6/3/142.25" I.D. HSA

DRILLER:

DATE COMPLETED:

Protection Engineering Group

14067

D. Williams

13.0 ±

SHEET 1 OF 1

ENCOUNTERED:

UPON COMPLETION:

LOCATION:

LOGGED BY:PROJECT:

GROUND WATER LEVELS:

REMARKS:

B-10

None

Dry

THE STRATIFICATION LINES REPRESENT APPROXIMATE BOUNDARIES. THE TRANSITION MAY BE GRADUAL.

SAMPLE TYPES:

MATERIAL DESCRIPTION

Split Spoon

DRILLING CONTRACTOR:

BORING NUMBER:

NCRO USPP D-1 & Water Distribution Improvements

1100 Ohio Drive, SW, Washington, DC Connelly and Associates, Inc.

K. Fordney

703-726-8030 703-726-8032 fax

19955 Highland Vista Dr. #170 Ashburn, VA 20147

B O

R E

H O

LE

/T

E S

T P

IT

L

O G

S

H Q

.G P

J G

E O

C O

N C

E P

T S

.G

/1

ELEV. 10.0

ELEV.

(ft)

20 40 60 80

STANDARD

PENETRATION

TEST RESISTANCE

(BLOWS/FOOT)

S T

R A

T U

M

DEPTH

(ft) ftCAVED: 3.0

S P

T B

LO

W

C O

U N

T S

R E

C O

V E

R Y

(in

S A

M P

LE

T

Y P

E

M C

11.8

7.0

3.5

-8.0

A

B

Topsoil = 2 inches sandy silt FILL, moist, brown with organics below 2.5 ft.

sandy lean clay FILL, moist, brown

ELASTIC SILT (MH), moist, gray

Bottom of Boring at 20.0 ft

3+4+9

11+9+4

5+4+2

0+0+2

0+0+0

0+0+0

PROJECT NUMBER:

DATE STARTED:OWNER/CLIENT:

GROUND SURFACE ELEVATION (ft): DRILLING METHOD:

6/2/14

6/2/142.25" I.D. HSA

DRILLER:

DATE COMPLETED:

Protection Engineering Group

14067

D. Williams

12.0 ±

SHEET 1 OF 1

ENCOUNTERED:

UPON COMPLETION:

LOCATION:

LOGGED BY:PROJECT:

GROUND WATER LEVELS:

REMARKS:

B-11

None

Dry

THE STRATIFICATION LINES REPRESENT APPROXIMATE BOUNDARIES. THE TRANSITION MAY BE GRADUAL.

SAMPLE TYPES:

MATERIAL DESCRIPTION

Split Spoon

DRILLING CONTRACTOR:

BORING NUMBER:

NCRO USPP D-1 & Water Distribution Improvements

1100 Ohio Drive, SW, Washington, DC Connelly and Associates, Inc.

K. Fordney

703-726-8030 703-726-8032 fax

19955 Highland Vista Dr. #170 Ashburn, VA 20147

B O

R E

H O

LE

/T

E S

T P

IT

L

O G

S

H Q

.G P

J G

E O

C O

N C

E P

T S

.G

/1

ELEV. 9.0

ELEV.

(ft)

20 40 60 80

STANDARD

PENETRATION

TEST RESISTANCE

(BLOWS/FOOT)

S T

R A

T U

M

DEPTH

(ft) ftCAVED: 3.0

S P

T B

LO

W

C O

U N

T S

R E

C O

V E

R Y

(in

S A

M P

LE

T

Y P

E

M C

3.5

-1.5

-8.0

A

B

Topsoil = 2 inches silty sand FILL with gravel, moist, brown sandy LEAN CLAY (CL), moist, gray and tan

ELASTIC SILT (MH), moist, gray

Bottom of Boring at 20.0 ft

4+8+8

8+4+4

17+7+6

2+2+2

1+1+2

1+1+1

PROJECT NUMBER:

DATE STARTED:OWNER/CLIENT:

GROUND SURFACE ELEVATION (ft): DRILLING METHOD:

6/2/14

6/2/142.25" I.D. HSA

DRILLER:

DATE COMPLETED:

Protection…