Geotechnical Report
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GEOTECHNICAL REPORT EQUIPMENT DIVISION REPAIR FACILITY PARKING LOT RENO, NEVADA MARCH 2010 MATERIALS DIVISION STATE OF NEVADA DEPARTMENT OF TRANSPORTATION MATERIALS DIVISION GEOTECHNICAL SECTION GEOTECHNICAL REPORT EQUIPMENT DIVISION REPAIR FACILITY PARKING LOT RENO, NEVADA MARCH 2010 WASHOE COUNTY, NEVADA Prepared by: ______________________________ Ashley Ablahani, E.I. Geotechnical Engineering Section Reviewed by: ______________________________ Jeffrey A. Palmer, Ph.D., P.E. Principal Geotechnical Engineer Approved by: ______________________________ Reid Kaiser, P.E. Chief Materials Engineer TABLE OF CONTENTS INTRODUCTION .……………..…………..…………………………………………. 1 General …………………………………………………………………………. 1 Scope ………………………………………………………………………........ 1 FIELD INVESTIGATION ....…...…………….…………………………………. …… 1 Standard Penetration Testing……………………………………………………. 2 LABORATORY ANALYSES ………….………………………………………...…… 2 DISCUSSION ...……………………………...…………………………………… …… 3 RECOMMENDATIONS ..…………………………….…………………………. …… 5 REFERENCES .…..……………………………………………………………….…… 7 APPENDICES: APPENDIX A Boring Location Map Photographs of Cuttings Photographs of SPT Samples APPENDIX B Key to Boring Logs Boring Logs APPENDIX C Summary of Results Tables Particle Size Distribution Reports APPENDIX D Structural Design and Material Information APPENDIX E Geotextile Specifications INTRODUCTION General This report has been prepared to address pavement distress concerns at the NDOT Equipment Division Repair Facility parking lot in Reno. According to the Equipment Division Repair Facility staff, the pavement condition has been progressively deteriorating over the last few years. NDOT Maintenance and Operations Division requested that the NDOT Materials Division investigate the area to determine an appropriate structural section and to make recommendations for repaving the parking lot. The parking lot will need to support heavy equipment loads. Scope The scope of this report consists primarily of geotechnical investigation, soil testing and recommendations for construction. The geotechnical investigation included gathering data and plans from previous construction projects at the site (no previous subsurface investigation information could be found), soil sampling, and analysis of field and laboratory testing data. The purpose of the geotechnical investigation was to characterize the general subsurface soil conditions at the site and to provide geotechnical construction recommendations. FIELD INVESTIGATION A geotechnical field investigation was conducted on November 5, 2009. The subsurface soil conditions were explored by drilling six boreholes, identified as RES2 through RES7. Borehole RES2 was explored to a depth of 15 feet. Boreholes RES 3 through RES7 were explored to a depth of 5 feet. Please note that location RES1 was not drilled because of possible underground utility conflicts. Borehole locations and ground surface elevations were surveyed by NDOT Materials Division Field Crew staff. The approximate locations of the borings are shown on the Borehole Location Map in Appendix A. All boreholes were backfilled soon after drilling was completed. The Key to Boring Logs and Boring Logs presenting the findings of the investigation are included in Appendix B. 1 Logs of the subsurface conditions, as encountered during the field investigation, were recorded by NDOT geotechnical engineering staff. All soil samples were examined and identified in the field in accordance with ASTM D2488. Additional soil classification was subsequently performed on soil samples using the Unified Soil Classification System (USCS) in accordance with ASTM D2487 upon completion of laboratory testing. Where soil tests are not listed in the appropriate column of the boring log, the USCS symbols and terminology are based solely on manual identification (ASTM D2488) rather than laboratory classification. Drilling was performed using an NDOT Diedrich D-120 drill rig (Drill Rig Unit #1082) equipped with an automatic hammer. Hollow Stem Continuous Flight Augering (HSA) methods were used to explore all borings. Representative bulk soil samples were obtained from cuttings from a depth of 1 foot to a depth of 5 feet in every borehole. Drive samples were obtained using a Standard Penetration Testing (SPT, ASTM D1586) sampler at locations noted on the boring logs. Existing asphalt pavement thickness was measured to the nearest quarter inch in every borehole and is recorded on the boring logs. Asphalt thickness ranged from 3 inches to 3 ¾ inches. Existing asphalt pavement was placed directly on subgrade; no base layer was apparent in any of the boreholes. Groundwater was not observed in any boreholes. Standard Penetration Testing The SPT sampler was advanced using a 140-pound hammer with a drop of 30 inches. The energy transfer from the automatic hammer into the drill string is 87.5% (SPT energy calibration by Gregg Drilling and Testing, Inc., June 11, 2009) with an approximate energy correction factor of 1.45. Sampler driving resistance (N-value), expressed as blows per one foot of penetration, is presented on the boring logs at the respective depth. The N-value is an indication of the apparent density of coarse-grained soils and the consistency of fine-grained soils. The blow counts presented on the boring logs have not been corrected for hammer efficiency, overburden pressure, rod length, etc. LABORATORY ANALYSES Soil particle size gradations through No. 200 sieve (Nevada T206), Atterberg limits (AASHTO T89 & T90), Resistance Value (R-value, Nevada T115) and natural moisture content (AASHTO 2 T265) tests were completed to determine sample classification and evaluation. Soils were classified using the Unified Soil Classification System (USCS) in accordance with ASTM D2487. Individual laboratory test results can be found in Appendix C of this report. In addition, select laboratory test results are presented on boring logs. Representative bulk soil samples were tested to determine the R-value of the subgrade. R-value is a measure of subgrade strength and expansion potential, and is used in design of flexible pavements. This test is used to determine the ability of a soil to resist lateral deformations under a vertical load and the data is used to determine the thickness of overburden necessary to prevent expansion. DISCUSSION Based on the conditions encountered in the exploratory borings, the soil profile generally consists of brown, medium dense to dense, moist, medium plasticity clayey sand with varying amounts of cobbles to low plasticity silty sand with varying amounts of cobbles. Laboratory testing determined that the soil samples tested contain an average of about 25% fines, material passing the No. 200 sieve. R-value results for the subgrade from a depth of 1 to 5 feet ranged from 19 to 54, with an average of 31. An R-value of 25, with consideration of heavy equipment loading, was used to determine the recommended structural section for the parking lot. Soil with an R-value in the 25 to 30 range can be considered a weak soil. An R-value of 45 or greater is desirable for the subgrade in a roadway. The Equipment Division Repair Facility parking lot stores vehicles ranging from pickup trucks to heavy equipment. Many of these vehicles enter and exit the parking lot on a daily basis. There are two gates on the west side of the parking lot in which vehicles can enter and exit the parking lot. The heavy equipment typically uses the northwest entrance and not the southwest entrance. The area with the worst observed pavement distress runs in line with the northwest entrance along the north side of the main equipment shop. This area of the parking lot gets the most heavy equipment traffic according to the Equipment Division Repair Facility staff. A 3 photo of this area is shown on the cover of the report. Photos 1 and 2 show close up views within this area. Inadequate drainage contributes to the pavement deterioration. The paved v-ditch that runs along the north side of the main equipment shop, as seen in the Photos 1 and 2, shows extreme pavement distress. Water settles in the bottom of the v-ditch between the intermittent slotted drains causing progressive deterioration. Photo 1. Pavement distress along the swale and slotted drains north of the main equipment shop. 4 Photo 2. Pavement distress north of the main equipment shop. RECOMMENDATIONS The parking lot structural section recommended by the Materials Division Roadbed Design Section based on the findings of the subsurface investigation can be found in Appendix D. It is highly recommended to place a nonwoven geotextile fabric between the subgrade and the flexible pavement structural section. The geotextile will increase stability and improve performance of flexible pavement constructed on subgrade with high fines content. The geotextile will provide separation, filtration and reinforcement functions providing a method of mechanical stabilization for weak subgrade soils. Separation improves construction by minimizing subgrade disturbance and preventing loss of aggregate. The geotextile acts as a filter and separator by preventing the migration of fines from the subgrade into the base/sub-base, maintaining the support and drainage characteristics of the base/sub-base over the life of the pavement system. Recommended geotextile material and placement specifications for this application are included in Appendix E. System performance will also be improved through reinforcement by geotextile placed on subgrade or within the base/sub-base layer. 5 Many underground utilities