REP49917 - Laserfiche WebLink

Home Browse Search

1 1 1~ above the presumed boundary at elevation 4879.25, thus material above this boundary is affected by a sloping piezometric surface. To allow for slight. piezometric level adjustments a piezometric head of 5-feet (pore pressure of 312.00 PSF) was applied to the stability model within the pile (below elevation 4879.25) and a piezometric head of 9-feet (pore pressure of 561.60) was applied to the foundation material. The material above the presumed boundary at elevation 4879.25 was modelled with a sloping piezometric level line which reflects the highest piezometric surface measured to date above that boundary. SECTION C-C: Section C-C represents piezometric conditions measured in the 100 and 300 series piezometers. Piezometric level plots for the 100 and 300 series piezometers are presented as Plates 33 and 34 respectively of the Appendix. In general the piezometric levels measured in the 100 series piezometers have remained constant during the 18-day monitoring period. However, piezometric surfaces measured in the 300 series piezometers have varied dramatically in the relatively short observation period (18-days). Initial conditions in piezometers 302, 303, 304 and 305 indicated that discrete piezometric levels were being measured. With the next observation measurement (5-days later) these four piezometers appeared to measure the same piezometric surface at elevation 4886.00 +/-. As was previously discussed this data suggests that a large reservoir or dome of pore pressure exists above an impervious or less pervious boundary at elevation 4855.15 (piezometer 405's impervious boundary). The presence of a well established pore pressure dome is consistent with persistent surface seepage reports and the historic record of piezometer P-1 measurements which show the same or nearly same piezometric surface since the time of its installation 10-years ago. The possibility that a connection between piezometers 302, 303, 304 and 305 within or near the drill hole created by drilling and piezometer installation was also considered. The presence of drill hole connections became Less likely when considering section C-C as a whole and as additional measurement data was gathered. When evaluating piezometer series 100 and 300 data together the perceived boundary affecting the 300 series piezometers appears to conform to the level of the piezometric surface and boundary indicated from measurements of piezometers 101 and 102. By graphically connecting boundary elevations (from PZ 102 and PZ 305) a surface, which gently slopes toward the face of the pile, appears. This boundary surface is consistent with surface seepage indications and pile placement techniques as we understand them. Further evidence of a boundary condition can be seen when considering the measurements of piezometers 302, 303, 304, 305, 306 and 307 made between April 13, 1994 and April 20, 1994. During this time period the piezometric surface measured in piezometer 306 rapidly increased to near the level apparent in piezometers 302, 303; 304 and 305. The piezometric level measured in piezometer 306 remained at this elevated level for 5-days, then rapidly decreased 21