Investigation of the Effects of Earthquake-Induced Deformations on Seepage at Trampas Canyon Dam

[9410895] Siddiqi这个研究项目是为了调查地震变形可能导致或促成土坝排水堵塞的假设，特别是坦帕斯峡谷大坝。这座大坝经历了几次大地震，包括1994年1月17日的北岭地震及其余震。近年来观察到，由于倾斜排水渠的作用不当，该大坝的地下水位（潜水面）明显上升，导致下游边坡发生渗流。坦帕斯峡谷大坝是一座土石坝，位于加利福尼亚州奥兰治县的圣胡安卡皮斯特拉诺。在过去三年中进行的一项完整的岩土工程调查表明，在现有升高的潜水面下，拟静力条件下的安全系数远远低于可接受的水平。几次钻孔显示，上游岩心材料严重堵塞了排水管。根据这项调查的结果，我们假设地核物质的存在是由于地震引起的变形破坏了排水管道和地核之间的现有联系。岩心和排液的相对位移，以及岩心材料的松动，被认为会导致细粒岩心材料侵入较粗且多孔的排液材料。到目前为止，还没有找到这一机制的确切证据。这次调查的目的是确定该大坝的潜水面变化是否是由地震引起的沉降引起的。这是通过监测由于强烈余震而导致的路堤内的水平和垂直运动来完成的。监测压力表读数和水池高度，以确定是否在潜水表面发生上升。＊＊＊

9410895 Siddiqi This research program is to investigate the hypothesis that seismic deformations can cause, or contribute to, drain clogging of earth dams, specifically, the Tampas Canyon Dam. This dam has been shaken by several significant earthquakes, including the January 17, 1994 Northridge earthquake and its after shocks. In recent years it has been observed that the water table (phreatic surface) has been rising significantly at this dam due to improper functioning of the inclined drains, resulting in seepage on the downstream slope. The Tampas Canyon Dam is an earth and rockfill dam, and is located in San Juan Capistrano, Orange County, California. A complete geotechnical investigation during the past three years has indicated that the factor of safety under pseudo-static conditions with the existing elevated phreatic surface is well below the acceptable level. Several borings have revealed significant clogging of the drains with upstream core material. Based on the results of this investigation, it is hypothesized that the presence of the core material has been caused by disruption of the existing bond between the drain and the core due to seismically induced deformations. Relative displacement of the core and drain, along with loosening of the core material, are thought to result in the intrusion of the fine-grained core material into the coarser and more porous drain material. No definitive proof of this mechanism has so far been found. The objective of this investigation is to determine if changes in the phreatic surface at this dam are caused by seismically- induced settlements. This is being accomplished by monitoring horizontal and vertical movements within the embankment due to significant aftershocks. Piezometer readings and pool elevations are monitored to determine if a rise in the phreatic surface occurs. ***