3. FIELD INVESTIGATION PROGRAM

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4 Department of Public Works U.S. Army Corps of Engineers Phase 1B Geotechnical Investigation Geotechnical Data Report 3.3 FIELD METHODS AND PROCEDURES 3. FIELD INVESTIGATION PROGRAM The borings were advanced with hollow stem auger or rotary wash methods through overburden soils and by diamond coring in bedrock Soil Drilling Testing and Sampling Soils in the vertical borings were tested using the Standard Penetration Test (SPT) according to ASTM D1586 to the top of rock. Testing was continuous in the Phase 1A borings. In the Phase 1B borings, SPT testing was conducted every 2.5 feet to a depth of 10 feet and below 10 feet samples were collected at 5-foot intervals. Results from the SPT testing for the borings are included in Appendix A. The drill rigs were equipped with automatic hammers to conduct the SPT testing. The number of blows was counted while split spoon samplers were driven a full 18 inches with blows counted for each 6-inch interval or until refusal was encountered. Refusal was defined as 50 blows to the SPT without advancing the split spoon 6 inches. Recovered samples from the SPT split spoon testing were placed in glass jars for shipment to the soil testing laboratory if sampling was determined to be necessary by the field geologist. Thin-walled tube samples were taken in thick strata of cohesive soil according to ASTM D1587. The 3-inch diameter thin-walled tubes were pushed two feet by hydraulic pressure from the drill head. Of the three attempted thin-walled tube samples at 2-foot depths, one met refusal after nine inches in boring B-22. The soil portions of the holes were monitored for volatile organic contamination with a photo-ionization detector (PID). In addition, during Phase 1B the headspace above the boreholes was monitored for hazardous and explosive gases during drilling and piezometer installation. No hazardous or explosive gases were detected Core Drilling Bedrock was cored according to ASTM D2113 using diamond bits and double tube, swivel type, M design barrels with split inner barrel and water as a drilling fluid. The inner barrel was retrieved and split open to expose the core for logging after each run. The core was placed in wooden boxes with hooked lids according to ASTM 3-4

5 Department of Public Works U.S. Army Corps of Engineers Phase 1B Geotechnical Investigation Geotechnical Data Report 3. FIELD INVESTIGATION PROGRAM D5079. Core samples were collected from the rock for testing and double wrapped in polyethylene and then aluminum foil. Most of the core samples were collected near the proposed tunnel depth; however, other rock units were tested to determine their characteristics for shaft construction. Any drilling core loss or samples pulled from the boxes were replaced by Styrofoam strips of equal length marked with the depths. The core was logged while still in one-half of the split inner core barrel and the rock quality designation was determined according to ASTM D6032. The core was photographed in the boxes as each box was filled. The core logs are presented in Appendix A, and the core photos are included in Appendix B Water Pressure Testing Constant head injection permeability testing was performed in the bedrock portions of the borings at approximately 10 to 20-foot intervals using pneumatic straddle packers. The testing conformed to United States Bureau of Reclamation (USBR) procedure 7310 (USBR, 1990) with the exception that the Phase 1B investigation interval test pressures were measured directly with a down-hole transducer. The down-hole transducer was used because it eliminates the need to account for friction losses in the piping and packer, which yields more accurate results. The interval tests were conducted in five steps at three ascending and then two descending pressures, except when no flow occurred at the highest pressure, the descending steps were not performed. The pressure and flow rate were allowed to stabilize at each step before timing and recording the flow and pressure over three one-minute intervals. The resulting data was used to calculate permeabilities in Lugeons (Houlsby, 1976) and centimeters per second (cm/sec) according to formulas contained in Zanger (1953). Where the stage permeabilities varied significantly within a test interval, the representative permeability was selected according to guidelines in Houlsby (1976). 3-5

6 Department of Public Works U.S. Army Corps of Engineers Phase 1B Geotechnical Investigation Geotechnical Data Report 3. FIELD INVESTIGATION PROGRAM Down-Hole Imaging Six Phase 1B borings were down-hole imaged by acoustic televiewer in the bedrock portion. A tabulation of the discontinuity dips, dip directions and descriptive ranking were developed from the imaging Piezometer Installation, Slug Testing and Water Levels Piezometers were installed in the vertical borings except boring B-20B drilled during Phase 1A to a depth of 39 feet. B-20B was originally named B-20 until it was later renamed B-20B when a second boring was drilled during Phase 1B. The Phase 1B boring is named B-20A and has an installed piezometer. The piezometers were installed in accordance with ASTM D5092. Four piezometers were installed to monitor ground water in the overburden (Borings B-1B, B-10B, B-21 and B-22). All other piezometers were installed to monitor bedrock groundwater. The piezometer casings and screens consisted of flush-coupled PVC pipe: inch nominal diameter, Schedule 80 in the Phase 1A borings; and 2-inch nominal diameter, Schedule 40 in B-21 in Phase 1B; and 1-inch nominal diameter, Schedule 40 in all the other Phase 1B borings. All materials (grout, sand and bentonite pellets) in the annular space around and below the PVC casings and screens were placed by tremie methods. Flush mount covers were imbedded in concrete pads at the ground surface. Table 3-3 lists the monitored zone for each piezometer and the bedrock unit monitored. Appendix C contains the piezometer installation logs. Depth to groundwater has been measured regularly in the installed piezometers. Piezometers were measured weekly on Phase 1A borings for the first 90 days following installation beginning on June 30, 2006 and bi-weekly thereafter. Phase 1B piezometers were measured bi-weekly beginning July 12, 2007 or upon completion. Water level measurements are ongoing. During Phase 1A, Hvorslev slug tests (time lag tests) were performed by injecting water into the Phase 1A piezometers. 3-6

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