Piedmont Geotechnical, Inc. 286 High Rail Terrace, SE • Leesburg, Virginia 20175 540-882-9350 • [email protected] June 15, 2018 Toole Design Group Attn: Ms. Melany Alliston-Brick, P.E. 8484 Georgia Avenue #800 Silver Spring, Maryland 20910 Re: Task Order No. 3 - Oak Lee Drive Water Main Break Repairs Marketplace at Potomac Town Center Ranson, West Virginia PGI No. 2255WV Dear Ms. Alliston: In accordance with your direction, Piedmont Geotechnical, Inc., has conducted geophysical surveys and pavement coring at the referenced site. The purposes of the study were to evaluate the extent of damage to Oak Lee Drive and portions of West Virginia Way that resulted from a water line break, and to recommend appropriate repairs and/or replacement of affected roadways. Introduction Oak Lee Drive serves as the entrance road to the Marketplace at Potomac Town Center. It begins at West Virginia Route 9, and extends approximately 1,200 feet northward to a multi-lane roundabout at the rear entrance to the shopping center. The roadway is currently seven to eight lanes wide near Route 9, and narrows to four lanes wide at the traffic circle. Sidewalks are limited to the area between West Virginia Way and the roundabout, and do not extend all the way to Route 9. On December 22, 2017, Decisive, Inc., a contractor installing a communications cable, broke a 16-inch water main owned and maintained by Jefferson Utilities, while attempting to bore under Oak Lee Drive to install a cable. The break released a large volume of water from an adjacent water storage tank, resulting in substantial damage to Oak Lee Drive from a point just north of West Virginia Way to the intersection with Route 9. The break also damaged the private road section behind Panera Bread. Geotechnical and Geo-Environmental Consulting _______________________________________________ Virginia, Maryland, District of Columbia, West Virginia, New Jersey North Carolina, Pennsylvania, Delaware, US Virgin Islands An initial field inspection found that water from the water main break raised the roadway pavement along Oak Lee Drive and the private road to the south, and water was observed surging from cracks and joints in the pavement as far away as the edge of Route 9. Following the event, it is our understanding that loaded trucks were used to proofroll the affected pavements which had been raised, and that the pavement sections, to a large extent, responded by lowering to a position close to original. Over the next several weeks following the event, there was a degree of deterioration of the relocated pavements. The deterioration included localized depressions, rutting, upheaval, and alligator cracking. Subsequently, weeks of variable temperatures accompanied additional buckling, heaving, and some breakage of the affected pavement surfaces. The local Karst terrain is prone to solution activity, and latent sinkholes and subsurface voids that may not be expressed at the ground surface were subject to the release of massive volumes of water during and immediately following the water line break. Based on descriptions by City staff who visited the site shortly after the initial break, it was concluded that much of the water that was released from the storage tank traveled under the pavement surface all the way to the edge of concrete near the Route 9 intersection. Scope of Study Toole Design Group, in conjunction with Piedmont Geotechnical, Inc., developed a work plan wherein the nature and extent of pavement system damage would be explored so that repair or replacement recommendations could be generated. The following elements were included in the work plan: • Geophysical Survey - Electrical Resistivity Survey • Geophysical Survey - Ground penetrating Radar • Pavement Coring to visually assess the extent of the damage • Limited soil laboratory testing • Periodic site visits for observation Summary of Geophysical Survey Findings On March 27, 2018, Electrical Resistivity (ER) and Ground Penetrating Radar (GPR) studies were made at affected sections of Oak Lee Drive and West Virginia Way. The Geophysical Report is appended to this report for reference. 2 Two ER lines were imaged, including Oak Lee Drive (ER Line 1) and West Virginia Way (ER Line 2). A deep solution channel was identified below Oak Lee Drive. Substantial weathering of the bedrock with residual “float” rock was identified below West Virginia Way. These two interrelated conditions were pre-existing and are evidence of a high degree of karst activity. The GPR survey included Oak Lee Drive and West Virginia Way, and identified shallow conditions including the presence of utilities and voids. By its nature the penetration depth of the GPR image is limited to the uppermost few feet in fine-grained, wet soils with a 250 MHz antenna; however, the data collected are consistent with the ER results within the depths imaged. In order to maintain the flow of traffic the GPR scanning was limited to the two outer lanes on Oak Lee Drive. The images were consistent and it is our opinion the conditions also reflect those under the inner lanes. Summary of Pavement Coring Findings On April 27, 2018, six (6) asphalt cores were taken on Oak Lee Drive from Route 9 to West Virginia Way. The asphalt cores were taken to the laboratory where they were observed, measured, and photographed. While on site, the crushed stone pavement base was observed and samples were retrieved to evaluate the moisture content and gradation. Six-inch diameter cores were taken and a hand auger was used to sample the stone base at each location. The core dimensions are identified more fully in the attached Daily Field Inspection Report. In general, it was found that the asphalt cores were intact with no significant gap between the bottom of the asphalt and top of the stone base. The stone base was saturated, and laboratory testing was conducted to measure the moisture content. It was determined that the base moisture content was 95.4 percent at location number 2. Evaluation of Testing Results The ER survey identified deep discontinuities below the pavement system. The discontinuities are consistent with the karst nature of the bedrock and were not created by the results of the water line breakage; however, the large influx of water from the line breakage may have aggravated the extent of the solution activity. Experience shows that the introduction of large quantities of water into pre-existing karst features can be destructive; however, without the benefit of information on the original geometry of the karst features the extent of additional damage caused cannot be quantified. The shallower materials imaged in the ER survey are 3 consistent with a wet soil profile. The GPR results are also consistent with the presence of wet soils at a shallow depth. In the coring operation it was observed that the stone roadway base was saturated, and the limited laboratory test result confirms this observation. Some of the base saturation may have been due to the introduction of water from the coring operation itself. Conclusion and Recommendation On the basis of our findings, it is our opinion that the layered pavement system in the survey area was compromised from the massive introduction of water resulting from the water line break. The water which was introduced into the system saturated the underlying stone base and soil subgrade, and these conditions persist. Sub- freezing weather conditions along with freeze-thaw cycles were detrimental to the integrity of the pavements. The pavement distress is visible on the asphalt concrete sections of the roadways. Although the concrete apron at the intersection of Oak Lee Drive and Route 9 is generally intact, subgrade distress is inferred below this area as well. The water line breakage event also physically dislocated the asphalt concrete system. The pavements were raised before being lowered by the addition of heavy wheel loads after the water subsided. Given the extent of latent damage to the pavement system and the persistence of saturated conditions, it is recommended that the pavements in affected areas be removed and replaced with a new section. The pavement system reconstruction should include removal of saturated layer components, proper preparation of the exposed subgrade, and full replacement with a new layered system. The pavement system reconstruction should include the removal of asphalt concrete surface and base, and the stone base. The exposed subgrade should be exposed and proofrolled. Where excessive pumping or rutting is observed, or where the subgrade remains saturated, the weakened soils should be undercut until firm conditions occur, but not in excess of 18 inches without the approval of the inspector. Undercut areas may be treated with surge stone (2 inch to 3 inch diameter clean stone) to reestablish the original subgrade elevation. The original pavement system profile, including 15 inches of stone base, 3.5 inches of asphalt base, and 1.5 inches of asphalt surface should be satisfactory. For a properly prepared and firm soil subgrade the addition of a geotextile is not expected to be required; however, there may be locations where the use of a geotextile will expedite reconstruction. 4 ATTACHMENTS 1. Geophysical Survey of March 27, 2018 2. Asphalt Coring and Hand Augering Report April 27, 2018 3. Laboratory Test Report of May 2, 2018 Geophysical Survey Route 9 and Oak Leaf Drive Ranson, West Virginia Geophysical Survey Route 9 and Oak Lee Drive Ranson, West Virginia Prepared For: Piedmont Geotechnical, Inc. 286 High