Geotechnical Summary Report_Sept 30 2014pdf

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GEOTECHNICAL SUMMARY REPORT

Prepared for:

A l i t C t D t t f E i t l S i Di i i f


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Crystal City Streetcar Project

Geotechnical Summary Report

Table of Contents

1. Overview............................................................................................................................ 11.1 PROJECT CORRIDOR AND STUDYAREA ............................................................................................ 1

2. Geologic Setting ............................................................................................................... 42.1 LOCAL GEOLOGY ............................................................................................................................. 4

3. Surface Conditions ........................................................................................................... 6

4. Subsurface Conditions ..................................................................................................... 75. Geotechnical Considerations and Recommendations for Future Investigation .........13

6. References .......................................................................................................................14

APPENDICES

1 Three Metropolitan Geotechnical Report

2 Crystal Drive, Route 1 and South Glebe Road Extended Geotechnical Report

3 Potomac Yard Transitway Stations B and C Geotechnical Report


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1. Overview

This report summarizes the collection and review of readily available geologic and geotechnicaldata, as well as a field site reconnaissance along the proposed Crystal City Streetcar Project.

The review performed for this task focused solely on the geologic and geotechnical aspects and

their potential impacts on the proposed streetcar design and construction. Recommendations

for continued review, additional literature review and field investigations are presented based on a

review of the literature and previous experience with design and construction on previous

projects.

1.1 PROJECT CORRIDOR AND STUDY AREA

The project corridor extends from the Potomac Avenue crossing of Four Mile Run north

approximately 2 miles to the Pentagon City Metro Station. Although alternative streetcar

alignments are still under consideration in the corridor, the streetcar will generally occupy existing

right-of-way. Construction excavation is anticipated to be relatively shallow for the track

elements, station stops and electrical improvements. The streetcar corridor will approximately

parallel U.S. Route 1 and Crystal Drive through the northern portion of Potomac Yard, Crystal

City, and Pentagon City in Arlington County, Virginia.

At the time of this report the proposed streetcar corridor and potential alignments were located

within a study area within Arlington County. The study area and base alignment are illustrated in


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Figure 1: Crystal City Streetcar Alignment


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Table 1: Crystal City Streetcar Alignment Description

Segment Name Description of Segment

Arlington Potomac Yard Potomac Avenue at the Alexandria/Arlington border, turning west on SouthGlebe Road. North on Jefferson Davis Highway merging with Crystal Drive.

Arlington Crystal City Begins at 26th Street South and runs northbound along Crystal Drive to18th StreetSouth. The southbound track runs along 18 thStreet South andthen along Crystal Drive from 18

thStreet South to 26

thStreet South, joining

the Arlington Potomac Yard segment.

Arlington Pentagon City The Arlington Pentagon City segment begins at the intersection of CrystalDrive and 18

thStreet South. It travels north on Crystal Drive before turning

west on 12th Street South, terminating at South Eads Street. The

southbound track runs along 12thStreet South from South Eads Street to

South Clark Street, turning south parallel to U.S. 1 to join the Arlington

Crystal City segment at 18thStreet South.


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2. Geologic Setting

The Crystal City Streetcar Project is geologically located completely within the Atlantic CoastPlain Physiographic Province. The project study area is located east of the boundary zone

between the Piedmont Plateau and the Coastal Plain physiographic provinces, also commonly

known as the Fall Line, or Fall Zone (Reed and Obermeier, 1982). The Fall Zone lies west of the

project study area and generally runs along Route 66 in Arlington from Rosslyn to Four Mile Run

and within Alexandria the Fall Line tends to parallel Interstate 95. The Fall Line separates the

Piedmont Plateau Province on the northwest from the Coastal Plain on the southeast.

The Piedmont Plateau Province is characterized by rolling upland topography consisting of

igneous and metamorphic rocks. The Atlantic Coastal Plain is located to the south and east of

the Fall Line and consists of a wedge of unconsolidated sentiments of gravel, sand, silt and clay.

The Piedmont bedrock began as Precambrian sediments that formed a stack of four units that

lithified into rock consisting primarily of gneiss and schist. The bedrock has been folded and

faulted and in the western portion of the Piedmont Plateau the rock has been intruded by granite

and quartz. Paleozoic metamorphic bedrock does not outcrop within the study area and can only

be seen in the far western portion of the City of Alexandria.

Two of the underlying metamorphic rock units are mapped in the Arlington-Alexandria area; the

MatherGeorge and Sykesville formations and the Annandale Group and Indian Run formation.

The Annandale-Indian Run formation consists of poorly to well foliated sedimentary mlange

consisting of medium grained quartz-plagioclase-muscovite-biotite chlorite granite matrix The


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soils are all fluvial in origin and that all of the sedimentary facies indicate that the deposits are not

deltaic, estuarine or marine in origin. The beds at the base of the layer resemble the underlying

sedimentary rock in that they contain feldspathic sand, smectitic clay and clasts of crystalline

rocks (Fleming et.al., 1994). The Potomac Group in the study area includes an upper silty and

sandy claydominated facies and a lower sand and graveldominated facies (Flemming et al.,

1994.

The Potomac formation is overlain by poorly to well bedded, lowland terrace deposits of sand, silt,

gravel and clay. Most of the preliminary streetcar alignment is located along an area mapped as

middle Pleistocene Terrace Deposits of gravel, sand, silt and clay and Holocene Alluvial deposits

and Artificial Fill. The terrace deposits are gray-brown to medium orange in color and range up to35 feet thick west of the Potomac River. The alluvium is generally poorly sorted and poorly

bedded and where streams drained is derived from weathered Saprolite and older alluvial

deposits consisting of well-rounded pebbles and cobbles as well as sand, silt and clay.

Artificial Fill is mapped along Route 1 from the Alexandria border north to near 33rd Street in

Arlington. Other areas to the north in Arlington are mapped as having Terrace deposits although

Artificial Fills can be in other areas of modern development.


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3. Surface Conditions

Surface conditions along the preliminary alignment consist primarily of 4 and 6 lane existingpaved right of way and bridge crossings. The roadways are mainly asphaltic concrete with some

new roadway being planned at Potomac Yard. Most of the streetcar corridor traverses populated

residential and commercial properties. The roadways have curb and gutter with drainage inlets

and adjacent sidewalks with grass lawn and tree landscaping in some areas.

Most of the proposed right of way will be using existing asphalt and concrete pavements and will

require removing a portion of the pavement, stabilizing and preparing the underlying fill materials

and construction of the new support section for the streetcar. The subsurface soils that are

anticipated to be encountered are described below.


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4. Subsurface Conditions

Readily available geotechnical reports were provided by The City of Alexandria and by theCounty of Arlington. These reports were reviewed to provide preliminary geotechnical data

regarding the near surface soils along the proposed alignment. No appreciable change in the

elevation of the pavement is anticipated, and no additional fill placement and subsequent

consolidation settlement are expected. Therefore, the literature review concentrated on the

characteristics of the near-surface subgrade soils. As previously mentioned, most of the

alignment is mapped as being in artificial man-made fill. The classification, thickness and the

consistency of the fill material varies along the alignment are described in the reports below:

Report of Subsurface Exploration and Geotechnical Engineering Analysis, ThreeMetropolitan Park, Arlington County, Virginia, prepared by ECS Mid-Atlantic LLC,dated September 15, 2008.

According to the boring logs, the near-surface fill soils consist primarily of a lean clay with

sand, sandy clay, silt and clay and sand. The fill contained gravel and brick fragments.

The consistency of the fill materials varied from soft to stiff and the granular fill was loose

to dense. The clayey materials generally were classified as being moist and the granular

fills were moist to wet. Groundwater level was measured to be from 25 to 35 feet in

depth.

Figure 2 on the next page shows the boring locations. Appendix 1 contains the Three


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Arlington County, Virginia Soil Survey - the most recent Arlington county Soil survey

maps the alignment as an urban land Udorthents complex, with 2 to 15 percent slopeswith more than 85 percent of the surface covered by buildings, asphalt, concrete or otherimprovements. The Udorthents consist mainly of material that has been graded, disturbedand urbanized and the materials are loamy and generally reflect the soils in the adjacentarea.

http://gis.arlingtonva.us/Maps/Standard_Maps/Environmental_Maps/Soils_Map.pdf

Arlington County Bus Rapid Transit (BRT) System, Crystal Drive, Route 1 andSouth Glebe Road Extended, Arlington, Virginia, prepared by GeoConceptsEngineering, Inc., dated April 7, 2003.

According to the boring logs, the near-surface fill soils consist primarily of a clayey sand

and lean clay, with about 17 to 76 percent fines passing the U.S. Standard No. 200 sieve.

Liquid limits and plasticity indices ranged from 27 to 37 and 9 to 16, respectively. The

natural moisture contents ranged from 7.9 to 21.0 percent. The fill soils are believed to be

grading fill associated with the sites previous use as a railroad yard. The soils beneaththe near-surface soils are lean clay believed to be river terrace deposits associated with

the nearby Potomac and its tributaries. Terrace deposits represent ancient flood plain

sediments deposited when the Potomac River and its tributaries were at a higher

elevation than they are today. Groundwater was observed at depths of about 6 to 20 feet

below the existing ground surface.
http://gis.arlingtonva.us/Maps/Standard_Maps/Environmental_Maps/Soils_Map.pdfhttp://gis.arlingtonva.us/Maps/Standard_Maps/Environmental_Maps/Soils_Map.pdfhttp://gis.arlingtonva.us/Maps/Standard_Maps/Environmental_Maps/Soils_Map.pdf


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Report of Subsurface Exploration and Geotechnical Engineering Analysis, PotomacYard Transitway Stations B and C, Arlington, Virginia, prepared by ECS Mid-AtlanticLLC, dated January 17, 2008.

According to the boring logs, the near-surface fill soils consist of a combination of sandy

clay, clay, clayey silt, sand, and silty sand with varying amounts of gravel, asphalt, brick

fragments and organics. The soils beneath the fill soils consisted of medium stiff to stiff

clay and organic silt and clay, as well as medium dense to dense sand and medium stiff to

very stiff clay and sandy clay. Groundwater level was measured to be from 23 to 34 feet in

depth.

Figure 4 on the next page shows the boring locations.Appendix 3contains the PotomacYard Transitway Stations B and C geotechnical report, which includes the boring locationsand logs.


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5. Geotechnical Considerations andRecommendations for Future Investigation

Based on a review of the literature and the readily available subsurface information

located in the general vicinity of the proposed alignment, the preliminary geotechnical

considerations for the design and construction of the streetcar and appurtenances are: 1)

the heterogeneous nature of the near-surface fill soils, 2) and the relatively high plasticity

and moisture content of the more clayey fill soils.

The near-surface fills soils underlying the existing pavement sections are heterogeneous

in nature and potentially compressible. These soils are non-uniform and will probably

require reworking and or stabilization. It must be noted however, that the boring

information reviewed for this preliminary study were taken in areas away from the

proposed alignment pavements. It may be that the fill materials were previously stabilized

during pavement construction along the majority of the proposed alignment. Therefore, it

is recommended that a series of borings be performed along the proposed alignment to

further investigate the surface and subsurface conditions.

Some of the clayey fill soils have a moderate to high plasticity. Where these soils are

encountered below the proposed support section for the streetcar, these soils will require

undercutting and replacement with soils having a higher CBR value. The granular fill soils

th t ti t t t ill d t b d i d t d t d t t


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6. References

Arlington County, Virginia Soil Survey, (2010), - Mapped by Louis Heidel and Fred

Garst from 1996-1997, USDA Natural Resource Conservation Service Woodstock, VA

Service Center, Soils surveyed at a scale of 1:7200.

Bromberg, Francine W. (2010). The History of Potomac Yard: A Transportation Corridor

Through Time.Appendix III of North Potomac Yard Small Area Plan. City of Alexandria.

Cohen, Robert (2003). History of the Long Railroad Bridge Crossing Across thePotomac River. National Railway Historical Society, Washington D.C. Chapter.

Fleming et. al., (1994) - Geologic map of the Washington West Quandrangle, District of

Columbia, Montgomery and Prince Georges counties, Maryland, and Arlington and

Fairfax Counties, Virginia. U.S. Geological Survey Geologic Quadrangle Map GQ-1748,

scale 1:24,000.

National Railway Historical Society, Washington, D.C. Chapter. Timeline of

Washington, D.C. Railroad History. Accessed 2012-11-14 (http://www.dcnrhs.org).

Reed and Obermeier, (1982) The geology beneath Washington, D.C.; the foundations

of a nations capital, In Legget, R.F. ed. Geology under Cities; Reviews in Engineering


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a Superfund site. In 1995 the Environmental Protection Agency (EPA) approved RF&P's study

and cleanup plan, and cleanup was declared completed by 1998.

The geotechnical data search and recommendations cannot confirm or deny the validity of theEPA 1998 declaration regarding Potomac Yard. It is assumed to be a safe site for the purposes

of construction of streetcar track elements and station stops. Additional geotechnical

investigation and soil testing is recommended along the selected alignment alternative during the

preliminary engineering phase of project development.
http://en.wikipedia.org/wiki/Superfundhttp://en.wikipedia.org/wiki/United_States_Environmental_Protection_Agencyhttp://en.wikipedia.org/wiki/United_States_Environmental_Protection_Agencyhttp://en.wikipedia.org/wiki/Superfund


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Appendix 1

Three Metropolitan Geotechnical Report


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Appendix 2


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Crystal Drive, Route 1, and South Glebe RoadExtended Geotechnical Report


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Appendix 3

Potomac Yard Transitway Stations B and C


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Geotechnical Report


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January 17, 2008

Mr. Ross VoorheesGreenhorne & OMara6110 Frost PlaceLaurel, Maryland 20707

ECS Job No. 14081

Reference: Report of Subsurface Exploration and Geotechnical Engineering Analysis,Potomac Yard Transitway Stations B and C, Arlington, Virginia

Dear Mr. Voorhees:

As authorized by your acceptance of ECS Mid-Atlantic, LLC (ECS) Proposal No. 28346-GPR, dated October 24, 2007, and revised November 27, 2007, we have completed thegeotechnical engineering analysis for the above-referenced project in Arlington, Virginia.O h i l i i l i i b d d illi f il b i Thi

Greenehorne & OMara

ECS Project No. 14081

January 17, 2008Page 2


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Purposes and Scope of Exploration

The purposes of this exploration were to explore the soil and groundwater conditions at thesite and to develop geotechnical engineering recommendations to guide general feasibilityplanning of the project. We accomplished these purposes by:

1. drilling borings in undeveloped areas to explore the subsurface soil andgroundwater conditions,

2.

performing laboratory tests on selected representative soil samples from theborings to evaluate pertinent preliminary engineering properties,

3. analyzing the field and laboratory data from this and earlier studies to developappropriate engineering recommendations, and

4. preparing this preliminary report.

The conclusions and recommendations contained in this report are based on four soil boringsperformed by ECS in December 2007. The boring locations for our exploration wereestablished in the field by representatives of ECS utilizing Global Positioning System (GPS)

Greenehorne & OMaraECS Project No. 14081


A field log of the soils encountered in the ECS borings was maintained by the drill crew.After recovery, each sample was removed from the sampler and visually classified.


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Representative portions of each sample were then sealed and brought to our laboratory inChantilly, Virginia for further visual examination and laboratory testing.

Laboratory Testing Program

Representative soil samples from the ECS borings were selected and tested in our laboratoryto check field classifications and to determine pertinent engineering properties. Thelaboratory testing program included visual classifications, moisture content, grain size

analysis, and Atterberg Limits tests. All data obtained from the laboratory tests are includedon the attached, respective boring logs or on separate sheets.

Each ECS soil sample was visually classified on the basis of texture and plasticity inaccordance with the Unified Soil Classification System (USCS). The group symbols for eachsoil type are indicated in parentheses following the soil descriptions on the boring logs. Abrief explanation of the USCS is included with this report. The soil engineer grouped thevarious soil types into the major zones noted on the boring logs. The stratification lines

designating the interfaces between earth materials on the boring logs and profiles areapproximate; in situ, the transitions may be gradual, rather than distinct.



similar to natural alluvial soil deposits. Further, as the fill soils age, they may obtain thevisual characteristics of natural soils. Hence, it is difficult at times to distinguish between


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natural alluvial soils and man-made fill materials.

Subsurface Conditions

The subsurface conditions encountered within the four soil test borings were consistent with theregional geology and the findings of our geotechnical reports prepared for nearby sites. Theconditions for Borings B-1 and B-2, when compared to B-3 and B-4 varied due to the differentlocations of the proposed transit stations. Beneath a gravel layer approximately 4 to 18 inches

thick, two major soil strata were encountered within our boring termination depths. These strataare described in the subsequent text. For detailed information at specific locations, please refer tothe Boring Logs attached to this report.

Stratum I Old Fill Soils

Old fill and possible fill soils were encountered in all of the borings to depths ranging

from 8 feet to 29 feet below the existing ground surface. Deeper fill was encountered atStation C. The old fill soils consisted of a combination of Sandy CLAY and CLAY(CL), Clayey SILT (ML), SAND and SILTY SAND (SP, SM) with varying amounts

l h l b i k f d i Th ld fill id ifi d b d



Furthermore, visual observation of the moisture content of soil samples retrieved during theauger drilling exploration can often be used in evaluating the groundwater conditions.


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Observations for groundwater were made during sampling and upon completion of drillingoperations at each boring location. Groundwater seepage was observed during drillingoperations in each of the four borings, at depths ranging between 23 and 34 feet below theexisting ground surface. These groundwater depths correspond to elevations ranging fromapproximately EL. -10 feet to EL. 1 foot. Furthermore, visual observation of the moisturecontent of soil samples retrieved during the auger drilling exploration can often be used inevaluating the groundwater conditions.

The highest groundwater observations are normally encountered in the late winter and earlyspring. Generally, variations in the location of the long-term water table may occur as aresult of changes in precipitation, evaporation, surface water runoff, and other factors notimmediately apparent at the time of this exploration. The project site may also be subject toshallower perched water conditions where surface water becomes trapped within the variablecomposition of the existing fill or within granular deposits underlain by more cohesive soils.Where perched groundwater is encountered, surficial groundwater control, such as trenchingor French Drains, may be required. For excavations which terminate above the groundwater

table, dewatering can generally be performed by sump pit and pumping operations.

G t h i l R d ti



to depths of 12 to 25 feet below the existing ground surface and typically consist of 30-inchdiameter drilled excavations, which are backfilled in 1-foot lifts utilizing compactive effortand granular aggregate. The aggregate piers are compacted with different methods,


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g gg g gg g p p ,depending on the propriety means of the contractor/vendor. The soil reinforcement occurs asa result of the excavation of the existing soils and replacement by dense granular aggregate.In addition, some limited densification of the surrounding soils is reported to occur. Theengineering characteristics of the reinforced soil are significantly improved to allow theplacement of spread footing foundations.

The aggregate piers can be utilized under the canopy footings. Aggregate piers are normallydesigned by a design build contractor and the proposed soil improvement plan is reviewed by

the Geotechnical Engineer of Record.

To reduce and largely eliminate the risk of long term unacceptable settlement. Footingssupported by the aggregate piers could be designed for pressures of 3,000 to 5,000 psf, asdetermined by the design/build contractor of these systems. Design settlement should belimited to 1 inch of total settlement and inch of differential settlement.

Option II: Shallow Foundations with Limited Undercutting

The proposed structure may be supported on a shallow spread and/or continuous foundation



For footings that are to bear on approved lightweight engineered fill, consistent with thesketch titled Foundation Subgrade Undercutting, a maximum allowable bearing pressure of2,000 pounds per square foot (psf) may be utilized for the design of the structure.


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, p p q (p ) y g

The allowable soil bearing pressure refers to that pressure which may be transmitted to thefoundation bearing soils. During construction, verification of the foundation subgradesshould be documented in the field by an experienced geotechnical engineer to ensure that therecommendations contained herein are followed.

Settlement of a structure is a function of the compressibility of the underlying soils, thedesign bearing pressure, column loads, fill depths, and the elevation of the footing with

respect to the original ground surface. Because of the underlying fill soils and potentiallycompressible clay (CL) and organic clay and silt (OH/OL) layers, long-term foundationsettlement values could be more than one inch utilizing the shallow foundation systemoption.

In order to reduce the possibility of foundation bearing failure and excessive settlement dueto local shear or "punching" action, we recommend that continuous footings have a minimumwidth of 2.0 feet and that isolated column footings have a minimum lateral dimension of 3

feet. In areas where individual footings are stepped down and founded at differentelevations, it is important to ensure a minimum slope of 1H:1V exists between the bottomedge of each foundation at their closest point.


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Geotechnical Summary Report_Sept 30 2014pdf

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