Study on Hydraulic Fracturing of Filltype Dams During Earthquake

采用压实岩心材料进行水力压裂（渗流破坏）试验，研究岩心破坏i_f时有效竖向应力sigma_V′与水力梯度的关系。结果表明：(1)sigma_V′与i_f的关系非常密切，可以作为解释水力压裂现象的最有效参数；(2)抗水力压裂的阻力取决于压实土的初始饱和程度。在研究桥台基础形态与路堤内部变形关系的离心模型试验中，发现(1)最大剪切应变gamma_<max>的分布很大程度上取决于桥台形态，在基础边坡拐点附近出现较大的gamma_<max>值；(2)简单的重力开启有限元计算可作为定性评价这些力学方面的有用工具。另一堆石坝模型离心变形试验结果表明：(1)在堆芯上部和堆芯槽附近，与堆芯宽度无关，均出现较大的伽玛<max>值；(2)抗高温安全系数较低的区域集中在堆芯槽附近。在堆石坝中心堆芯的离心hf模型试验中，在20G和30G下加载27cm高的模型堆芯，采用相应的传感器测量堆芯内的沉降和应力分布。试验得出的结论如下：(1)由于水库的第一次填充导致岩心的不同沉降和应力重新分布，导致岩心围压降低；(2)这直接导致了与实际大坝类似的堤防内部侵蚀和相关渗流破坏。

Hydraulic fracturing (Seepage failure) tests were conducted on compacted actual core materials to investigate the relationship between the effective vertical stress sigma_V' and the hydraulic gradient at failure i_f. Results are summarized as follows : (1) sigma_V' has a very close relation to i_f and can be the most effective parameter to explain the phenomenon of Hydraulic Fracturing (H.F.), and (2) the resistance against H.F.depends on the initial degree of saturation of compacted soil.In the centrifuge model tests of investigating the relationship between configuration of abutment foundation and internal deformation of embankment, it is recognized that (1) distribution of the maximum shear strain gamma_<max> depends much on the abutment configuration and large value of gamma_<max> appears in the vicinity of the turning point of foundation slope, and (2) a simple gravity turn-on FEM calculation can be a useful tool to evaluate such mechanical aspects qualitatively.In another centrifuge deformation tests on model rockfill dams, results presented that (1) large value of gamma_<max> appears irrespective of the core width in the upper part of the core and in the vicinity of core trench, and (2) area of low factor of safety against H.F.then concentrates near the core trench.In the centrifuge H.F.model tests on a rockfill dam with a centrally located core, a 27cm high model fill was loaded in 20G and 30G,and settlement and stress distributions in the core were measured by using appropriate transducers. Concluding remarks drawn in the test are as follows : (1) differential settlement and stress redistribution in the core due to the first filling of the reservoir causes reduction in confining pressure in the core, and (2) this directly leads to an internal erosion and associated seepage failure in embankments in a similar manner as observed in actual dams.