Appendix D Geotechnical and Pavement Reports.pdf

Appendix D

Geotechnical and Pavement Reports

Preliminary Geotech Report, Williamsburg Gateway (2020)

Project VA NP COLO 1A21, B42, C18, D51: Pavement and Subsurface Conditions Report for Segments A, D, E, and F (November 2021)

Pavement Depth Memo (2021)

D el iv er in g rig ht s ol ut io ns th ro ug h q ua lit y se rv ic es a nd e ng in ee rin g ex ce lle nc e”

Prepared for

Stantec April 1, 2020

Preliminary Geotechnical Report

Rehabilitation of the Colonial Parkway Williamsburg Gateway (30%) FHWA Task Order 11307-65748 Project NP-COLO 1C17, 1D49

Chantilly, VA Williamsburg, VA Washington, DC

Gaithersburg, MD

309 McLaws Cir, Suite F, Williamsburg, VA 23185 ● www.dmyec.com ● Phone: (757) 866-1086 ● Fax: (301) 768-4169

GEOTECHNICAL ● ENVIRONMENTAL ● DRILLING ● INSTRUMENTATION ● MATERIALS TESTING ● SPECIAL INSPECTIONS ● FACILITIES

April 1, 2020

Mr. Michael A Retton, PE Stantec 6110 Frost Place Laurel MD, 20707

Reference: Preliminary Geotechnical Report Rehabilitation of the Colonial Parkway Williamsburg Gateway (30%) Project NP-COLO 1C17, 1D49 Williamsburg, Virginia DMY Project No. 04.04106.01

Dear Mr. Retton:

DMY Engineering Consultants Inc. (DMY) is pleased to submit this Preliminary Geotechnical Engineering Report for the above-referenced project. This report presents our understanding of the project information provided to us, a discussion of the site and subsurface conditions encountered at the boring locations, our field exploration and laboratory testing programs, the field and laboratory test results, and our preliminary geotechnical recommendations related to the proposed construction. This report has been revised to address comments responses dated October 29, 2019 and our subsequent meetings.

We appreciate the opportunity to be of service to you on this project and would be happy to discuss our findings with you. We look forward to serving as your geotechnical engineer on the remainder of this project and on future projects.

Respectfully, DMY ENGINEERING CONSULTANTS INC.

Rabih Khouri, P.E. Peng “Paul” Zhang, P.E.

Principal Engineer Vice President

Sameer Ghany, P.E.

Project Engineer

Rehabilitation of the Colonial Parkway Williamsburg Gateway (30%)

DMY Project No. 04.04106.01

TABLE OF CONTENTS

1.0 PROJECT OVERVIEW

2.0 SITE GEOLOGY

3.0 FIELD EXPLORATION

4.0 SUBSURFACE CONDITIONS

4.1. SUBSURFACE CONDITIONS

4.2. GROUNDWATER

4.3. PAVEMENT CONDITION

4.4. INFILTRATION TESTING

5.0 LABORATORY TESTING AND RESULTS

6.0 HISTORY OF THE PARKWAY CONSTRUCTION

7.0 PRELIMINARY RECOMMENDATIONS

7.1. PAVEMENT

7.2. SUBGRADE PREPARATION

7.3. UNSUITABLE SOILS

7.4. PAVEMENT ALTERNATIVES

7.5. EXISTING ASPHALT RAMPS

7.6. PAVEMENT MATERIALS

7.7. SITE PREPARATION

7.8. DRAINAGE PIPES AND CULVERTS

7.9. RECOMMENDED ADDITIONAL GEOTECHNICAL INVESTIGATION

8.0 LIMITATIONS

APPENDIX A FIGURES

APPENDIX B FIELD OPERATIONS

APPENDIX C LABORATORY TESTING

APPENDIX D CALCULATIONS

1.0 PROJECT OVERVIEW

The Colonial Parkway (the Parkway) is an approximately 23-mile roadway that connects Jamestown, Williamsburg, and Yorktown in Virginia. The Parkway runs southwest from Jamestown to northeast past Williamsburg before heading generally eastward toward Yorktown. Although it does not have any lane demarcations, it is a three-lane road with a center passing lane. Numerous scenic pull-offs and parking areas are located along both sides of the Parkway. Most of the pavement consists of concrete although portions of the on- and off-ramps are paved with asphalt, as is the last mile at Jamestown. The Parkway was constructed in multiple phases beginning in 1931 and was completed in 1957. Currently, commercial vehicles are prohibited on the Parkway although bus traffic is still permitted.

Our current scope focuses on rehabilitation of the Williamsburg Gateway of the Parkway. This segment is approximately 2.61 miles and is located between mile posts 11.65 and 14.26. This segment generally starts southwest of the Merrimac Trail overpass, passes thru Williamsburg at the Williamsburg Circle, and terminates near the south city limits of Williamsburg, Virginia. A site location map showing the location of the project and project limits is included in Appendix A. The Parkway at this segment crosses below five bridges (noted from northeast to southwest): Parkway Drive, Page Street, a CSX Railroad line, Lafayette Street, and Newport Avenue. In this segment, the Parkway also passes thru the Williamsburg Historic Tunnel that crosses below East Nicholson Street, E Duke of Gloucester Street, and Francis Street.

Based on the 30% project scope, we understand that 100% of the existing concrete pavement on the main line will be removed and replaced as part of the proposed construction. No pavement rehabilitation is planned for the existing pull-offs and ramps other than tie-ins associated with the mainline pavement.

Also as part of this construction, we understand that stormwater management Best Management Practices (BMP’s) and culvert rehabilitations will be evaluated. Although the final type and configuration of the BMP’s are not known at this time, we understand that they will generally be shallow and likely consist of bio-retention or similar type structures. Several of the existing culverts identified by RK&K, the drainage consultant, will either be remediated or replaced as part of this construction. In addition, at this time, we understand that two new culverts for drainage will be required.

2.0 SITE GEOLOGY

The project site is located within the Coastal Plain Province of Virginia. Based on review of the Geology of the Williamsburg, Hog Island, and Bacons Castle Quadrangles, Virginia (Kenneth F. Bick and Nicholas K. Coch, Virginia Division of Mineral Resources, 1969), the coastal plain soils consist of terrace deposits of varying ages. The Sedley Formation is no longer recognized and the soils of this stratum are now considered part of the upper Yorktown Formation.

St Mary’s Formation (Ts): The deepest strata consist of soils belonging to the St Mary’s Formation (Ts) are believed to have been deposited during the early Miocene. In general, the description of the stratum closely mirrors that of the Yorktown Formation, and distinguishing between the two formations is sometimes difficult without an understanding of the fossil types. Within the project limits, the St Mary’s Formation is believed to have been encountered in the southern most edge of the site where the formation was exposed due to erosion from the nearby Paper Mill Creek. The soils in this formation are identified with M on the boring logs.

Yorktown Formation (Ty & Ts): Above the St Mary’s Formation, soils belonging to the Yorktown Formation (Ty) were encountered. These Miocene aged soils are generally subdivided into upper and lower aged soils and generally consist of green and gray silty sands and sandy silts with layers of highly plastic clays and silts. In general, the upper soils of this formation contain more fine-grained soils than the lower formation. The soils of Yorktown Formation usually contain significant shell and shell fragments with varying amounts of cementation. Due to the mineralogy and gradation of the soils, various studies and local experience demonstrate that the actual strengths of the soils in the Yorktown Formation are underestimated using conventional correlations with Standard Penetration Test (SPT) N-values. The soils in this formation are identified with Y on the boring logs.

Bacons Castle Formation (Qtbc): Above the Yorktown Formation in some of the borings, soils belonging to the Bacons Castle Formation (Qtbc) were encountered. In many locations, these soils were encountered near the surface and are some of the youngest formations. Gray, orange and reddish-brown sands and gravels with silt and highly plastic clay facies characterize this formation. The presence of hematite within the soils imparts some cementation to the coarser grained soils. Cobbles are sometimes present in this formation. The soils in this formation tend to exhibit higher strength due to both the gradation of the soils and the presence of cementation. The soils in this formation are identified with B on the boring logs.

Windsor Formation (Qw): The youngest formation encountered on the project is the Windsor Formation (Qw). This Pleistocene aged formation is widespread at the site and is generally encountered in most of the borings that extended into natural soils. The soils in this formation are characterized by tan, brown, and gray sandy lean clay and clayey sands. In some locations, where the soils are well above the water table, some of the clay soils have higher shear strength than anticipated due to desiccation. The desiccation also results in the clay soils behaving overly consolidated and therefore higher blow counts.

The soils in this formation are identified with W on the boring logs.

Alluvium (Qal): Near waterways, culverts, and streams, alluvial soils may be present. These soils tend to share similar behavior to the eroded surfaces from where they are generated; however, they may contain significantly more organic material. The soils can vary between sands, clays and silts, and generally have lower shear strengths and normally consolidated. The soils in this formation are identified with A on the boring logs.

Man placed fill soils were present above the natural soils throughout the project site. In general, the fill soils consist of sandy lean clays, fat clays, or clayey sands with varying amount of gravel, sometimes containing shell fragments and trace organics. Near the bottom of slopes and ravines, away from the roadway, the fill soils sometimes contain more significant decomposing organics and wood debris. A review of the historic information indicates that hydraulic fill methods were used for embankment construction. Hydraulic fill placement consists of moving soils from a borrow site to the embankment using water and a pump. Where coarse-grained soils are used as the borrow material, the fill generally settles relatively quickly, and settlement is less of a concern. However, when fine-grained soils are used, these fills tend to exhibit long-term settlement behavior. We understand that most of the borrow source for the hydraulic fills was likely obtained from York River.

3.0 FIELD EXPLORATION

The field exploration performed by DMY for the proposed project consisted of drilling Standard Penetration Test (SPT) borings, field infiltration testing, and obtaining bulk soil samples. The boring locations were selected by DMY and were surveyed in the field by Rice Associates. The boring locations are shown on the Boring Location Plans in Appendix A. The field exploration procedures are included in Appendix B. Following field operations, the soil samples were transported to our laboratory for further analysis and testing.

A total of 26 SPT borings were drilled for the current exploration. SPT borings were drilled using hollow-stem auger method with 2.25-inch or 3.25-inch I.D. augers. The borings where drilled using our in-house CME 55 and CME 45C drilling rigs with auto-hammers. The SPT-hammer efficiency were calculated as 87.4% for the CME 55 is and 89.2% for the CME 45C as calibrated by GRL Engineering, Inc. In addition to the SPT soil samples, seven (7) bulk soil samples were collected from the roadway soil borings for California Bearing Ratio (CBR) testing. Upon completion of the field exploration, all boreholes outside the pavement were backfilled with auger cuttings. Groundwater levels, where encountered, were measured at each boring location at the time of drilling. Borings located within the pavement area were backfilled with a bentonite grout to within 12-inches of the top of pavement. Borings drilled on concrete were patched with 12 inches of concrete mix. A layer of rounded aggregate was then pushed into the wet concrete and broomed to attempt to match the existing pavement. Borings located on asphalt were patched with cold-patch asphalt.

4.0 SUBSURFACE CONDITIONS

4.1. SUBSURFACE CONDITIONS

The subsurface conditions encountered at the locations explored are shown in the boring logs in Appendix B. The records represent our interpretation of the subsurface conditions based on visual observations and laboratory testing of the soil samples collected. The lines designating the interfaces between various strata on the boring logs are approximate, as the actual transitions between soil strata are often gradual. In the absence of foreign substances, it is difficult to distinguish between natural soils and clean soil fills.

A layer of topsoil approximately 3 to 6 inches thick was encountered in the majority of the borings drilled in the unpaved areas. Although the measured topsoil depths were found to be of minimal thickness in most borings during our exploration, the topsoil may be thicker in unexplored areas, particularly in vegetated undisturbed areas, such as most of the existing wooded median areas.

Below the topsoil or existing pavement, six basic strata were encountered at the borings within their termination depths. The soil strata observed in the current exploration at the site include man-made fill, alluvial soils (differentiated from Coastal Plain soils based on visual features and consistency), Windsor Formation, Bacons Castle Formation, Yorktown Formation, and St. Mary’s Formation. The following tables summarize the generalized soil descriptions from the available subsurface exploration. Refer to Section 2.0 Site Geology of this report for more descriptions of each of the soil strata.

Table 4-1: Summary of Subsurface Conditions

Geologic Strata Soil Description

Strata Elevations

(ft)

USCS

Classification SPT N-values

Primary Secondary Min Max

FILL

Generally composed of soils obtained from nearby natural soils. The soils from this stratum generally retain some of the properties of the parent soil, but may contain debris and organic material.

Ground Surface to EL -1.5

SC, SM

& CL

CH & SW-

SM, ML

Weight of

Hammer

(WOH)

Alluvium

Alluvium is defined as a deposit of clay, silt, sand and/or gravel left by flowing streams in a river valley or delta. The soils of these strata are loose, unconsolidated soil or sediments, which has been eroded, reshaped by water in some form, and redeposited in a non-marine setting. The soils of this stratum where only encountered in Boring BMP-

Ground Surface to EL 36.9

SC CH 6 8

Windsor

This Coastal Plain stratum is the youngest formation and developed from layers of flat sediment deposited during the late Tertiary and early Quaternary Geologic Age.

EL 70.6

to EL 26.0

CL

SM, ML, &

CH WOH 6

Bacons Castle

The soil of Coastal Plain developed on loose, unconsolidated, generally flat layers of sediment, which were deposited during Tertiary age.

Cobbles, gravels, and cemented hematite are common in this formation.

Ground Surface to EL 24.0

SC & CL

CH &SM 4 16

Yorktown

Soils of this formation consist of weathered and Upper Yorktown formation.

Soils of this formation were deposited during the Miocene age. This formation contains significant shell fragments particularly in the upper soils.

Ground Surface to EL 17.8

SC, SM,

& CL MH & GM 3 19

St. Mary’s

The oldest formation encountered in this project.

Soils of this formation were deposited during the early Miocene age. This formation contains significant shell fragments particularly in the upper soils.

EL 36.7

to EL -1 SM -- 7 18

4.2. GROUNDWATER

Groundwater was measured at the time of drilling in each boring, and if feasible, it was measured at least 24 hours after drilling completion; however, most of the borings drilled along the roadway had to be backfilled and patched upon completion. Where encountered, groundwater was recorded between depths of 6 and 18 feet below site grade, which corresponds to between EL 57.6 and 5.5 feet. Where 24-hour readings were obtained, the groundwater was measured at depths of 4.2 to 10.8 feet below current site grades, which corresponds to between EL 33.6 and 39.3 feet. It should be noted that groundwater levels fluctuate with seasonal and climatic variations and may be different at other times and locations than those stated in this report.

4.3. PAVEMENT CONDITION

A total of seven (7) pavement cores were obtained along the mainline of the Parkway and Williamsburg Circle. The pavement data are summarized in the table below. The as-built plans indicate that an aggregate base underlies the concrete pavement, but no aggregate base was encountered below any of the concrete pavement cored for this investigation. We suspect that the definition of aggregate used at the time the pavement was originally constructed consisted of sandy soils with some gravel.

Table 4-2: Summary of Pavement

Pavement Core

Number Station Offset Type of Pavement

Thickness of Pavement (inches)

RW-01 107+22.2 R 2.1 Concrete 6.6

RW-02 109+06.6 R 2.4 Concrete 8.0

RW-03 151+06.4 R 140.9 Concrete 6.9

RW-04 152+34.2 R 138.9 Concrete 6.5

RW-05 163+54.4 L 2.1 Asphalt / Aggregate 10.5 / 4.5

RW-06 203+95.4 L 4.5 Concrete 6.9

RW-07 154+04.9 L 76.4 Concrete 7.5

4.4. INFILTRATION TESTING

Infiltration testing was conducted using the Aardvark automated constant head permeameter device. The Aardvark Permeameter estimates soil hydraulic conductivity using the amount of supplied water measured at equal time intervals. Soil-water infiltration rate is the amount of percolated water over time which is equivalent to the reservoir flow rate. The measurement ends when the reservoir flow rate does not change over several consecutive readings and a steady state flow is observed. The soil hydraulic conductivity (Ksat) is then calculated using the steady flow rate. The testing were performed following the Earth Manual of the US Bureau of Reclamation (USBR 7300-89). The details of the infiltrating rates are summarized in the following table:

Table 4-3: Summary of Infiltration Testing

BMP Boring Number

Test Depth (feet)

Saturated Hydraulic

Conductivity, Ksat (in. /hr.)

Groundwater Depth

BMP-03 4.7 0.08 Not Encountered

BMP-10 6.0 0.0 12.0

BMP-11 4.2 0.05 5.5

BMP-16 5.0 12.38 Not Encountered

BMP-17 4.2 0.07 Not Encountered

The high infiltration rates observed in BMP-16 are likely associated with a sandy layer at the infiltration depths noted.

5.0 LABORATORY TESTING AND RESULTS

Representative soil samples were selected and tested to verify field classifications and to determine pertinent engineering properties. The tests were performed in accordance with applicable ASTM and AASHTO standards. The table below is a summary of the laboratory testing program. The laboratory testing results are included in Appendix C.

Table 5-1: Summary of Laboratory Tests

Lab Test Test Method Number of Tests

Natural Moisture Content AASHTO T-265 125 Atterberg Limits AASHTO T-89 & T-90 20 Grain Size Analyses AASHTO T-88 20

Proctor AASHTO T-99 7 California Bearing Ratio AASHTO T-193 7

6.0 HISTORY OF THE PARKWAY CONSTRUCTION

As noted above, the Colonial Parkway was constructed in multiple phases. The focus of this section is to highlight both construction and geotechnical issues related to the proposed construction. The first phase of construction of the Parkway was between the Yorktown Cliffs and Hubbard lane. The construction of Williamsburg Gateway, the second phase of the Parkway, began in 1935 with clearing of the existing trees beginning from Hubbard Lane to Capital Landing. Typical fill embankment construction at this time consisted of hydraulic fill from borrow sources along the York River. In the late 1930s, many of the pavement constructed in the initial phase experienced distresses caused by settlement of the hydraulic fill. We understand that the typical solution used at the time was mud jacking using a soil, cement and water slurry through holes drilled within the pavement.

It is noted that a “bleeding” method was used for the hydraulic fill placement for most of the phases of construction. This method uses discharged dredged material from a borrow source thru pipes placed at the centerline of the embankment. Dredged material is allowed to run out and settle without any compaction. It is likely that no additional effort to induce settlement of the hydraulic fill was performed at the time of construction. Timber bulkheads were used to protect creeks at the location of bridges, but otherwise, very little additional effort was used to construct the roadway embankments.

The tunnel construction, which marked the third major phase of the Parkway, began in 1936, although the excavation for the tunnel itself appears to have started closer to 1940. Some of the construction records indicate that cave-ins were common along the side slopes during construction. Historic documents also note that the tunnel was built on hard marl without the use of piles with much of the excavated material spread on the grubbed right-of-way between Williamsburg and Halfway Creek.

Numerous underground springs were also encountered during construction of the tunnel. Much of the work on the Parkway itself slowed due to both funding and World War II. In 1952, temporary pavement was placed from the tunnel to Tazewell Hall Avenue. The temporary pavement consisted of asphalt and the Parkway from Williamsburg to Yorktown was opened to the public.

By 1955, additional funding was secured and construction resumed with additional fill placement used for both the roadway and bridges up College and Mill Creeks. Where additional fill placement was required, the use of hydraulic fill placement persisted. Additional discussion on the hydraulic fill as it relates to Segment G is included below.

Most of the bridges within Segment G were completed by 1956. Evaluation of the bridge conditions is outside the scope of this study. However, as it relates to the Parkway pavement, edge drains were constructed along the outside edges of the concrete pavement at most of the bridges. Information on the existing culverts within Segment G were obtained from the historic plans as well as RK&K’s report for this project. Most of the culverts consist of reinforced concrete or concrete arches. The culvert headwalls, however, are clad in hand-made “Virginia Style” bricks. The following tables are the current culverts within Segment G:

Table 6-1: Existing Culverts within Segment G

Culvert Designation Diameter/Size Material

3-1 4'x3' Arch Concrete

3-2 18" RCP

6-3 24" RCP

6-4 18" RCP

7-4 24" RCP

8-6 4'x3' Arch Concrete

15-1 36" RCP

16-1 24" RCP

Within Segment G, the final pavement construction was completed in three major phases under numerous contracts. The initial phase began in 1937 and spans between Hubbard Lane to approximately location of the Williamsburg Circle. This section of roadway consists of tapered reinforced concrete pavement underlain by 6-inches of gravel. The concrete sections are generally thinner at the middle of each section measuring about 6-inch and 8-inch of concrete at the edges. The concrete was lightly reinforced with a combination of No. 00 and No. 5 gauge steel. Wooden dowels fitted with metal sleeves were placed 3.5” below the surface at the transverse joints. The formwork within this section was 10 feet by 40 feet. The aggregate used in this section consisted of 75 percent large stone and 25 percent small stones from local borrow areas. The concrete was first brushed stiff with wire brushes and brooms. A mixture of water and 10 percent muriatic acid was used to clean the cement from the exposed aggregate.

It is noted that this was considered labor intensive and some concerns of the effect of the muriatic acid on the long-term strength of the concrete were also noted. Access roads were constructed of 2.5-inches of asphalt underlain by 6-inches of gravel base.

The second phase consisted of grading, drainage construction, and a temporary paving with hot asphalt through the tunnel up to Tazewell Hall Avenue in 1952. The current concrete pavement in this section was constructed in 1956. The structure of the concrete pavement changed to a uniform 7-inch concrete underlain by 12-inches of aggregate base. The concrete was placed in 10 feet by 60 feet long sections with 2-foot of steel dowels every 1 foot along the length of the longitudinal joints and three 40-inch tie rods for transverse joints. The concrete in this section was reinforced with No. 6 wire and No. 2 steel bars. These joints did not sit flush with one another but were instead fitted to be “tongue-and-grooved”.

As noted in the above section, the surface was broomed to expose the surface aggregate and then acid washed to remove concrete staining. Substantial settlement occurred in areas of fill at this location particularly at the Williamsburg Circle and areas north the tunnel. Mud jacking was also used to repair damaged pavement although by 1973 and later the damaged pavements were removed and replaced with asphalt patches.

The third phase of construction consisted of a series of minor roadway changes and numerous repairs and rehabilitations to extend the useful life of the pavement. These include additional drainage structures along the sides of the roadway. The most recent major rehabilitation within the project limits occurred between 1989 and 1994. It is at this time that a unique identification of each slabs was implemented.

This phase also included additional drop inlets and other erosion control devices such as concrete curb and gutter at the bridges. Numerous damaged slabs were repaired at this time. These repairs are divided into partial depths and full depths repairs. Partial depth replacement consisted of a vertical saw cut into the slab parallel to the joints to a depth of 1.5 to 4 inches. The damaged pavement was removed, and the exposed concrete area was then sandblasted to remove all loose particles. The slabs were then patched with epoxy, a bonding grout and then cement was placed to match the adjoining pavement. Full depth repairs were performed in a similar manner except that the saw cut extended the full depth of the concrete slab. Most of the joints noted with a “tongue-and-groove” were replaced at this time.

7.0 PRELIMINARY RECOMMENDATIONS

7.1. PAVEMENT

Assumed traffic data was provided to us for use in our design by Eastern Federal Lands as a traffic study has yet to be completed. Two different traffic patterns will be considered for this project. One will be for traffic near the Williamsburg Circle which will have higher bus traffic than locations outside of the Williamsburg Circle. Traffic data is summarized in Table 1 below. We have assumed end of construction year for the replacement as 2022. The design was performed using AASHTO Design for Pavement Structures and the 1998 supplement.

Per our discussions, we have assumed that the internal pavement reinforcing steel will be designed as if the pavement is continuously reinforced. Joint reinforcing design was performed assuming AASHTO’s design methodology for Jointed Reinforced Concrete pavement. The internal reinforcing design assumes crack spacing no greater than 8 feet on center and no less than 2.5 feet for punchout and spalling.

Although more narrow transverse cracking is feasible, there is a higher risk of spalling and given the proposed aggregate size a wider minimum spacing is desired. Per our discussions, we have also designed the pavement reinforcing for a maximum crack opening width of 0.02 inches to prevent migration of fines and water. Parameters from the FHWA Project Development and Design Manual (PDDM) were used when appropriate. We have assumed that the design vehicle as a Class 4 Bus (Single Wheel load of 16kips). The pavement was designed for 50-year life for all the alternatives below.

The final report should refine these assumptions once updated traffic data is obtained, additional subsurface investigation is completed, and a better understanding of the construction dates is available.

The design traffic data are summarized in the following table:

Table 7-1: Design Traffic Data

Colonial Parkway Inside Williamsburg Circle

Colonial Parkway Outside Williamsburg Circle

Initial Design Year (assumed) 2022 2022

Two-way AADT (Initial) 8,000 8,000

Annual Growth Rate 2.03% 2.03%

Directional Ratio 50% 50%

Percent Cars/Passenger Vehicles 97.9% 98.9%

Percent Bus 2.0% 1.0%

Percent Tractor Trailer Trucks 0.1% 0.1%

From a review of the available historic data, it appears that most of the damaged pavement sections are related to settlement of the embankment fill or loss of fines between joints. The most recent pavement evaluation for the project was performed in 2013. It notes that the majority of concrete slab failure consists of edge and transverse cracking. Detailed pavement design including the traffic load information and calculations are attached to this report in Appendix D.

Existing concrete pavement where cored varied between 6.5 and 8 inches thick. During the final exploration, where existing pavement are to remain in place such as at the ramps or the pull-offs, the existing concrete should be cored and the thickness measured. Where the difference between existing and new concrete is greater than 0.5 inches, a specific tie-in slab will be required.

7.2. SUBGRADE PREPARATION

Following the site preparation and any required excavation, an authorized representative of the Geotechnical Engineer of Record should evaluate the newly exposed roadway subgrade. During this evaluation, we recommend that all subgrade areas be proof-rolled using a fully loaded tandem axle dump truck (10-ton minimum) or similar rubber-tired vehicle. The proofrolling should be performed in such a pattern that the entire subgrade areas are loaded with at least one pass. Areas that are not accessible to proofrolling may be evaluated using other suitable methods such as probing with a steel probe rod.

If the subgrade exhibits excessive deflections or pumping when proof-rolled or soft subgrade is detected by probing, the Geotechnical Engineer of Record would recommend an appropriate remedial measure at that time. Potential problem subgrade areas as identified by this soil investigation and the recommended remedial measures are detailed in the following paragraphs. The stabilized subgrade areas should be again evaluated and approved by the Geotechnical Engineer of Record prior to fill placement or pavement installation.

7.3. UNSUITABLE SOILS

We anticipate that the construction will require that the entire existing concrete and asphalt pavement be removed within the project limits. As noted in the historical discussions above, the existing concrete slab in numerous areas are underlain by hydraulic fill soils.

Unsuitable soils generally include soils that have excessive moisture, high plasticity Index (PI>15), soils with low SPT N-values (less than 5 bpf), low CBR value (CBR < 6), high swell (swell >5%), and soils containing excessive debris and organics. None of the CBR results indicated high swell soils present.

Soils that are considered unsuitable will require treatment. The pavement subgrade soils at the test boring locations are summarized in Table 7-2 Below. The definition of unsuitable soils are explained in the subsequent sections.

Table 7-2: Pavement Subgrade Summary

Boring Subgrade Condition

RW-01 High Moisture

RW-02 High Moisture, High Plasticity

RW-03 High Moisture, High Plasticity, Low CBR, and SPT < 5 bpf to EL 92

RW-04 High Moisture, High Plasticity

RW-05 High Moisture, Low CBR, and SPT < 5 bpf to EL 97

RW-06 High Moisture, High Plasticity

RW-07 High Moisture

High Moisture Subgrade Soils:

This condition has the potential to cause pumping problems during subgrade and base construction and is typically caused by construction activities. Upon completion of any necessary excavation and construction activities, it is likely that these areas will be identified as unstable by proofrolling.

Highly Plastic Index (PI>15) Subgrade Soils:

Highly plasticity index soils were encountered in Borings RW-02, RW-03, RW-04 and RW-06. The PDDM defines the sub-excavations for highly plastic soils in Table 7-3 below.

Table 7-3: Depth of Undercut for Highly Plastic Soils

Plasticity Index (PI) Liquid Limit (LL) Depth of Sub-excavation

15-25 <50 2 feet

25-35 50-60 3 feet

>35 >60 5 feet

Low CBR Subgrade Soils:

CBR samples collected from the seven roadway borings (RW-01 to RW-07) varied between 3.5 and 17.0.

A design CBR value of 6.0 was used for preliminary evaluation of the new pavement sections. Low CBR (<6) soils were encountered in Borings RW-03 and RW-05.

Soft or Very Loose Subgrade Soils:

Soft and loose (SPT N-values less than 5 bpf) soils were encountered in Borings RW-03 and RW-05.

Paul Zhang Missing

Potential Settlement Concerns

Presently, it appears that poor subgrade soils are located at Williamsburg Circle and north of the Tunnel.

These areas also experience the highest bus traffic and historically have seen the most distressed and patched pavement. The embankment fills at these locations appear to have experienced long-term settlement and we understand that this area still requires intermittent patching. The final report should evaluate the locations where on-going settlement is a concern. We understand that sub-excavations are not feasible in all the pavement alternatives due to the historic nature of the site. Where sub-excavations are feasible and an area of potential on-going settlement is identified, the sub-excavation should be backfilled a light weight fill material in lieu of regular backfill. In cases where sub-excavations are not feasible or practical, surcharging the subgrade with at least 2 feet of backfill is a viable alternative. The final report should identify areas where on-going settlement may be occurring, delineate the areas, and provide additional recommendations. Lightweight fill material typically have unit weights of between 70 and 105 pcf and should also meet Section 703 for base or sub-base.

7.4. PAVEMENT ALTERNATIVES

Based on discussions with the project team, we have considered multiple alternatives to address both pavement sections and the unsuitable soils above. The following section provides details on each alternative. Although many iterations of alternatives were reviewed, we believe the following are the most economical for the project. Additional alternatives can be reviewed during the final design.

Alternative 1

Design Life 50 Years Slab Length 30 Feet

Base 6" Aggregate Base Subgrade Untreated CBR 6 with undercuts Drainage None, assumed poor drainage with 5-25% saturation

Pavement Section Inside Circle Outside Circle

Concrete Thickness 10.5 9.5 Inches Transverse & Tie Bars #5 #5 Bar Size

Transverse & Tie Bar Spacing 43 47 Inches Longitudinal Bars #8 #8 Bar Size

Longitudinal Spacing 9 11 Inches Longitudinal Dowel Diameter 1.3125 1.1875 Inches Longitudinal Dowel Length 18 18 Inches Longitudinal Dowel Spacing 12 12 Inches

Alternative 1 is the baseline case for this project. All other options will be compared to this one.

Alternative 1 Subgrade:

We have assumed that the subgrade treatment due to unsuitable soils will consist of sub-excavations for Alternative 1. Table 7-4 summarizes the anticipated sub-excavation depths at each location.

Table 7-4 Summary of Undercut Depth

Boring Sub-Excavation Depth (inches)

RW-01 12

RW-02 24

RW-03 36

RW-04 24

RW-05 36

RW-06 36

RW-07 12

The final report should further define the excavation depths noted here. Sub-excavation greater than 12 inches will require the use of geotextile fabric as noted below. Sub-excavations are to be backfilled with CBR 6 or greater granular material.

Alternative 2

Base None Subgrade 12” Lime treated Drainage None, assumed poor drainage with 5-25% saturation

Pavement Section Inside Circle Outside Circle

Concrete Thickness 10.0 9.0 Inches Transverse & Tie Bars #5 #5 Bar Size

Transverse & Tie Bar Spacing 37 41 Inches Longitudinal Bars #7 #7 Bar Size

Longitudinal Spacing 9 11 Inches Longitudinal Dowel Diameter 1.25 1.125 Inches Longitudinal Dowel Length 18 18 Inches Longitudinal Dowel Spacing 12 12 Inches

Alternative 2 considers the use of lime treatment of the subgrade for strength. Additional recommendations for lime treatment of the subgrade are included in below. We have assumed a treatment depth of 12 inches with an elastic modulus of 40,000 psi (based on VDOT’s parameters for lime treatment). In general, it is assumed that the soils will be improved to a liquid limit of no more than 27 and a plasticity index of 4.

Based on our local experience, an estimated 6% to 8% lime by weight will be required to improve the strength characteristics of the soil. Where highly plastic clays are present, lime treatment on the order of 10% to 15% may be required to reduce the plasticity and liquid limits to acceptable values. Lime treated subgrade are also more resilient to the effects of high moistures and seasonal variation. No sub-excavations are required.

Alternative 3

Base 6" of Cement Treated Aggregate Subgrade Untreated CBR 6 with undercuts Drainage None, assumed poor drainage <1% saturation

Pavement Section Inside Circle Outside Circle

Concrete Thickness 8.0 8.0 Inches Transverse & Tie Bars #5 #5 Bar Size

Transverse & Tie Bar Spacing 47 47 Inches Longitudinal Bars #6 #6 Bar Size

Longitudinal Spacing 9 9 Inches Longitudinal Dowel Diameter 1.00 1.00 Inches

Alternative 3 considers the use of cement treated aggregate in lieu of conventional aggregate base. The advantage of a cement treated base is the protection against moisture in the underlying subgrade. We have used VDOT’s recommended elastic modulus of 80,000 psi for the Cement Treated Aggregate. We have considered that the pavement subgrade will be in accordance with Alternative 1 above and Table 7-4 above.

Alternative 4

Base 6" of Full Depth Reclamation (FDR) Subgrade Treated Full Depth Reclamation (nothing below FDR) Drainage None, assumed poor drainage <1% saturation

Pavement Section Inside Circle Outside Circle

Concrete Thickness 9.0 8.0 Inches Transverse & Tie Bars #5 #5 Bar Size

Transverse & Tie Bar Spacing 41 47 Inches Longitudinal Bars #6 #6 Bar Size

Longitudinal Spacing 8 10 Inches Longitudinal Dowel Diameter 1.125 1.00 Inches

Alternative 4 considers that the existing pavement will be demolished and the reinforcing steel removed.

The rubble concrete and underlying subgrade will then be mixed 12 inches or more. Two alternatives can then be considered, either a portion of the mixed subgrade will be removed to eliminate a change in existing grade or the subgrade will remain after mixing and the final grade of the pavement is increased from current grades. At this time, we have assumed the top of grade will be maintained and that the remaining 6 inches of mixed aggregate will be treated as Full Depth Reclamation (FDR). FDR should be constructed in accordance with 304 of the standard specifications. Locally FDR is being used on I-64 Segment 2 and Segment 3, and is treated with cement (in lieu of asphalt). We have used VDOT’s recommended elastic modulus of 80,000 psi for FDR. No other treatment of the subgrade will be required.

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Alternative 5

Base 6" of Cement Treated Aggregate Subgrade None Drainage None, assumed poor drainage <1% saturation

Pavement Section Inside Circle Outside Circle

Concrete Thickness 9.0 8.0 Inches Transverse & Tie Bars #5 #5 Bar Size

Transverse & Tie Bar Spacing 41 47 Inches Longitudinal Bars #8 #7 Bar Size

Longitudinal Spacing 12 11 Inches Longitudinal Dowel Diameter 1.125 1.00 Inches

Alternative 5 assumes that work will only be performed within 13 inches of the subgrade. This will increase the grade by 2 inches overall. With this alternative, we have designed the pavement for the lowest encountered CBR of 3.5. It should be noted that this alternative does not fully address unsuitable soils encountered in Table 7-2 above but attempts to mitigate the risks. We have included the following discussions to address these risks here:

Where high moisture soils are observed at the subgrade at the time of construction, the contractor should allocate additional time to allow the moisture to evaporate prior to final compaction. The subgrade should be compacted within the top 12 inches in accordance with Section 204.11 of FP-14. Where highly plastic soils and soils with high swell are encountered, there exist risks that the pavement life will be reduced due to swell forces acting on the pavement section. The following measures will not eliminate these risks, but can mitigate them to some extent:

• A relatively impermeable layer will help mitigate the chance for water to enter the subgrade. The CTA layer will act as the impermeable layer.

• Compacting the subgrade wet of optimum moisture content.

• Constructing an impermeable layer (such as CTA, 12-inches of lime, etc.) outside the pavement section to prevent water from entering the subgrade. This layer will need to extend 3 feet laterally beyond the edge of pavement.

• Installing edge drainage to prevent ponded water entering the subgrade if feasible.

Please note that the subgrade will still require a satisfactory proofroll and some sub-excavation will still be required where excessive pumping and rutting is observed. The extent of undercuts will depend on the severity observed and will need to be evaluated on a case by case basis, but Table 7-4 above can provide a general guideline for depths.

7.5. EXISTING ASPHALT RAMPS

From the as-built plans, the exit and entrance ramps to the parkway consist of at least 2-inches of asphalt underlain by 7-inches of cement concrete base course (Project 1A4-B12-D11-E4 plan sheet 3). The existing asphalt on the ramps currently appear to be in good condition and we understand that it has been replaced in sections within the last 5 years. The project will require that existing asphalt on the ramps be milled 2-inches and replaced with 2-inches of new asphalt pavement. We have assumed a design life of 20 years for the asphalt pavement at the ramps using the same traffic data as the mainline pavement. A design traffic of 441,905 Equivalent Single Axle-Load (ESAL) was used to evaluate the asphalt pavement. No pavement cores of the existing asphalt pavement were obtained as part of the current field investigation, but additional pavement cores will be required. Pavement cores where the ramps tie into the streets should also be obtained and the pavement section should be determined based on the additional cores and traffic data on the ramps to ensure that the pavement thickness is sufficient.

Additional information on the type of asphalt is included below.

7.6. PAVEMENT MATERIALS

We understand that the decorative elements of the existing parkway pavement will apply to the new pavement. The concrete used for the pavement will contain exposed aggregate that is larger than normal concrete (up to 2 inches.) The selected mix should be carefully tested for both abrasion, tensile strength, and compression strength. For the purpose of this study we have assumed that the concrete will have a minimum compressive strength of 4,000 psi and we have assumed a modulus of rupture of 645 psi. The exposed aggregate surface and finishing of the mainline must be installed in accordance with the enabling legislations for the parkway and will need to be maintained during construction.

Reinforcement should consist of No. 5 welded wire mesh. Longitudinal reinforcement should consist of dowels 18 inches long spaced 12 inches on center. All steel is assumed to have a yield strength of 60 ksi. We do not recommend that new pavement be “tongue-and-grooved” due to both the added difficulty in construction and the likelihood of failure of the joints except where the pavement connects to existing slabs. The final pavement section should evaluate the connection in further detail. However, the joints should be sealed with an approved joint material meeting the requirements of Section 712 of the Federal Highway Standard Specifications. Transverse joints should be saw cut shortly after removal of the forms to prevent cracking. Longitudinal joints should not be located within typical wheel paths. We have considered a typical joint width of 10 feet to generally match the existing joint width for the travel lanes.

The joint spacing will need to be adjusted at transitions and curves to maintain the 10 feet width.

Standard Detail 501 may be used for additional detailing on pavement joints and reinforcement.

Where aggregate base is recommended, the aggregate material should meet the requirements of Standard Specification 703 Type B or C (except as noted). The cement treated aggregate should meet the criteria of Section 311 of the Standards and Specifications.

Asphalt pavement will be required for ramps onto the parkway. If the asphalt for the project is specified using FP-14 Sections 401/402, given the anticipated traffic volume and location, the asphalt should consist of ½-inch NMSA >0.3 to <3 Mil Type 1-A or Type IV with PG64V-22 Binder. At this time, we understand that the total tonnage of new asphalt will be less than 1,000 tons and that the asphalt may be specified using Sections 403/404 using a locally supplied pavement. We anticipate that a VDOT approved mix consisting of SM-12.5 with grade D binder (PG64H-22) will meet the project requirements.

The geotextile fabric should meet requirements for Class 2 Woven type with hydraulic properties A or B (based on Section 714 of the Standard Specifications for Construction of Roads and Bridges on Federal Highway Projects) of the spec, AASHTO M 288 and be non-woven needle punch with an apparent opening less than the 10% of soil particles finer (D10) of the lightweight aggregate material. The geotextile should fully wrap all the aggregate and the sidewall of the sub-excavation but should not be placed between the aggregate and concrete.

The use of lime for stabilization and strength should be in accordance with section 213 Subgrade Stabilization. This will require a mix design to be performed along multiple sections of the parkway.

Cement may be used in lieu of lime if the treated material is shown to be improved to the required liquid limit and plasticity index noted above.

7.7. SITE PREPARATION

Site preparation should consist of any proposed demolition, removing existing underground utilities, existing pavement from the proposed construction areas. Utilities such as pipes should be removed entirely or abandoned by filling the pipe with grout to prevent future migration of soils into the pipe.

Disposal of demolition debris should be performed in accordance with local, state and federal regulations.

Additional requirements included in Section 200 of the Standard Specifications for Construction of Road and Bridges on Federal Highway Projects should be followed.

7.8. DRAINAGE PIPES AND CULVERTS

New drainage pipes are planned to replace existing drainage pipes for the preliminary proposed construction. The following table provides a summary of the drainage pipes with a size of 24 inches or greater. For additional information on culvert locations and information, please see the Drainage Report.

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Table 7-5: Summary of Drainage Pipes and Culverts

Structure

ID

Approximate Structure Location

New or Replacement

New Structure Size

Length (Feet)

Invert Elevation

(Feet)

3-1 120+20 Replacement 88x54-inch Box 121 38.78 to 35.00

3-2 122+75 Replacement 24-inch RCP 91 50.58 to 48.00

6-1 to 6-2 142+50 Replacement 24-inch RCP 101 55.00 to 53.25

7-2 to 7-3 249+00 New 24-inch RCP 87 41.30 to 38.50

7-3 to 8-1 249+00 Replacement 24-inch RCP 106 38.4 to 37.15

8-1A to 8-1 350+90 New 24-inch RCP 43 37.9 to 37.15

8-1 to 8-2 251+10 Replacement 24-inch RCP 85 37.05 to 36.60

8-4 to 8-5 351+05 New 24-inch RCP 52 38.40 to 38.00

8-5 to 8-5A 351+00 New 24-inch RCP 63 37.90 to 37.50

8-5A to 8-2 250+90 New 24-inch RCP 36 37.40 to 36.60

8-2 to 8-3 251+00 New 24-inch RCP 100 36.50 to 35.10 8-3 to 8-6

Outlet 251+90 New 24-inch RCP 74 35.00 to 32.00

8-6 252+00 Replacement 8 by 6 feet Box 298 32.00 to 27.50

8-16 to 8-17 352+05 New 24-inch RCP 64 38.10 to 37.25 8-18 to 8-6

Outlet 252+90 New 24-inch RCP 182 36.40 to 32.00

8-17 to 8-18 253+00 New 24-inch RCP 84 37.15 to 36.50

8-14 to 8-18 253+10 New 24-inch RCP 84 37.40 to 36.50

8-13 to 8-14 253+90 New 24-inch RCP 95 38.37 to 38.00

8-12 to 8-14 254+00 Replacement 24-inch RCP 49 37.90 to 37.50

8-11 to 8-12 254+90 New 24-inch RCP 50 38.37 to 38.00

8-10 to 8-12 255+00 Replacement 24-inch RCP 114 39.50 to 38.00

8-8 to 8-10 255+50 New 24-inch RCP 51 39.35 to 39.10

8-9 to 8-10 255+60 Replacement 24-inch RCP 41 38.86 to 38.60

8-21 to 8-22 NA Replacement 24-inch RCP 36 40.98 to 40.89

9-1 to 9-2 162+80 New 24-inch RCP 46 52.50 to 52.00

9-2 to 9-3 162+50 New 24-inch RCP 58 51.90 to 50.00

10-6 to 9-2 163+50 Replacement 24-inch RCP 147 53.90 to 53.00

10-5 to 10-6 164+10 New 24-inch RCP 34 55.00 to 54.00

10-4 to 10-6 165+00 Replacement 24-inch RCP 187 54.90 to 54.00

10-3 to 10-4 166+00 New 24-inch RCP 30 55.40 to 54.00

12-1 to 12-3 179+00 Replacement 24-inch RCP 20 49.20 to 49.10

12-3 to 12-5 179+50 New 24-inch RCP 50 49.00 to 48.8

12-5 to 12-7 180+00 New 24-inch RCP 53 48.70 to 48.50

12-7 to 12-9 180+60 New 24-inch RCP 48 48.40 to 48.00 12-9 to 12-

10 181+00 Replacement 36-inch RCP 104 48.00 to 46.90

12-11 to 12- 10 181+50 Replacement 24-inch RCP 48 50.00 to 48.00

12-10 to 12- 12 181+80 Replacement 42-inch RCP 110 46.98 to 44.89

12-12 to 13- 1 185+00 Replacement 42-inch RCP 352 44.89 to 38.79

13-1 to 13-2 186+50 Replacement 42-inch RCP 175 38.79 to 36.50 13-E2 to

13-2 187+80 Replacement 30-inch RCP 41 41.34 to 40.22

13-2 to 13- E3 188+50 Replacement 42-inch RCP 190 36.40 to 32.80

13-E3 to 14-E1 192+00 Replacement 42-inch Jacked 272 32.72 to 28.54

14-E1 to 14-2 194+00 Replacement 42-inch RCP 340 28.54 to 25.00

The proposed drainage pipes and culverts should be constructed in accordance with Section 602 – Culverts and Drains of the Standard Specifications. Highlighted pipe runs and structures in the table above indicate that no boring data was available at this time. Additional borings will be required during the subsequent field investigation at the above locations. The following table indicates pipes and culverts runs where some geotechnical data was available as well as the anticipated soils at the pipe invert elevation.

Why are you highlighting some of the numbers?

Table 7-6: Summary of Available Subsurface…