Abstract

The magnitude of the pore water pressure developed by a soft fine-grained soil subjected to shear stresses is what determines the occurrence of sudden failure. As part of an extensive testing programme, besides identification and classification tests, 20 monotonic simple shear tests and 139 cyclic simple shear tests with different levels of static stresses (τ_o) before the cyclic phase were performed. In this research, reference is made to pore water pressure (u) developed by a soft fine-grained soil subjected to combined monotonic (τ_o) and cyclic shear (τ_c) stresses. Laboratory tests were carried out on undisturbed samples from the Port of Barcelona, Spain. The samples were obtained at depths between 29 m and 52 m, that correspond to an effective vertical stress of (σ’_ov) between 277 kPa and 413 kPa, respectively. In general, the results indicate that: (a) the combination of τ_o and τ_c controls the generation of pore water pressure (u); (b) it is not always true that, as a consequence of increased pore water pressure when τ_o/σ’_ov + τ_c/σ’_ov ≈ S_u/σ’_ov, the soil reaches the failure cyclically (with S_u being the undrained shear strength); (c) in the monotonic case, it is possible to establish empirical functions between u/σ’_ov and the monotonic shear strain (γ_m); and (d) in the combined monotonic and cyclic case, it is possible to establish empirical functions among u/σ’_ov, the cyclic shear strain (γ_c) and the number of cycles (N), for different (τ_o/σ’_ov) ratios. In addition, an application was made to study the seabed stability based on the knowledge of the material under cyclic load.

摘要

软质细粒土在剪切应力作用下产生的孔隙水压力的大小决定了突然破坏的发生。作为广泛测试计划的一部分，除了识别和分类测试外，还进行了 20 次单调简单剪切测试和 139 次循环简单剪切测试，在循环阶段之前具有不同水平的静应力 ( _τo ) 。在这项研究中，参考了软细粒土在单调 ( τo ) 和循环剪切 ( _τc )作用下产生的孔隙水压力₍ u )) 强调。对来自西班牙巴塞罗那港的未受干扰样品进行了实验室测试。样品是在 29 m 和 52 m 之间的深度获得的，这对应于 ( σ' _ov )的有效垂直应力分别在 277 kPa 和 413 kPa 之间。总的来说，结果表明：_{_ _} (b) 当τ _o /σ' _ov + τ _c /σ' _ov ≈ S _u /σ' _ov时，由于孔隙水压力增加，土壤周期性地达到破坏并不总是正确的（与S _u为不排水抗剪强度）；(c) 在单调情况下，可以在u/σ' _ov和单调剪应变 ( γ _m ) 之间建立经验函数；(d) 在单调和循环组合的情况下，可以在u/σ' _ov、循环剪切应变 ( γ _c ) 和循环次数 ( N ) 之间建立经验函数，对于不同的 ( τ _o /σ ' _ov ) 比率。此外，还应用了基于材料在循环载荷下的知识来研究海床稳定性。