Study on Hydraulic Fracturing of Filltype Dams During Earthquake

对压实的实际岩心材料进行了水力压裂(渗透破坏)试验，研究了有效垂直应力Sigma_V‘与破坏时水力坡度I_f的关系。结果表明：(1)Sigma_V’与I_f关系非常密切，可以作为解释水力劈裂现象的最有效参数；(2)抗水力劈裂能力取决于压实土的初始饱和程度。在研究桥台基础形状与路堤内部变形关系的离心机模型试验中，认识到(1)最大剪切应变的分布；在另一次模型堆石坝的离心机变形试验中，结果表明：(1)在土石坝模型的离心机变形试验中，(1)在土石坝模型的离心机变形试验中，高值的伽马；在中心心墙堆石坝的离心机高频模型试验中，分别在20g和30g加载了27 cm高的模型填料，并采用合适的换能器测量了心墙内的沉降和应力分布。试验的结论如下：(1)水库首次蓄水后，心墙不均匀沉降和应力重分布导致心墙围压降低；(2)这直接导致堤防的内部冲刷和渗流破坏，与实际大坝中观察到的情况类似。

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.