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

9410895 Siddiqi这项研究计划是为了调查地震变形可能导致或促成土坝，特别是坦帕斯峡谷大坝的排水堵塞的假设。这座大坝已经被几次重大地震所震动，包括1994年1月17日的北岭地震及其余震。近年来，据观察，由于倾斜排水沟的不正常运行，导致下游边坡渗漏，该大坝的地下水位(潜水面)一直在大幅上升。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。过去三年的一项全面岩土勘察表明，现有高位潜水面在拟静态条件下的安全系数远低于可接受的水平。几次钻探显示，上游岩芯材料严重堵塞了排水沟。根据这次调查的结果，假设岩芯材料的存在是由于地震引起的变形破坏了排水沟和岩心之间的现有结合造成的。岩芯和排水管的相对位移，以及岩芯材料的松动，被认为导致细粒岩心材料侵入较粗和更多孔的排水管材料。到目前为止，还没有找到这种机制的确凿证据。这项调查的目的是确定该大坝潜水面的变化是否是由地震引起的沉降引起的。这是通过监测由于重大余震引起的堤坝内的水平和垂直移动来实现的。监测压力计读数和水池高度，以确定潜水表面是否出现上升。***

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. ***