Abstract

Although the undrained shear strength has been widely studied for evaluating the factor of safety in slope, the effects of the initial shear stress induced by slope inclination are not fully understood. Some studies begin considering the conditions where the secondary shear direction along the direction of slope inclination, namely unidirectional shears. In the submarine environment, however, two directions are required to properly evaluate the true multidirectional shear strength because of the random direction of the wave and seismic load. This paper reports the bi-directional shear behavior of the Leighton Buzzard sand (Fraction B) from a specifically designed experimental program. The stress-strain relation, pore water pressure development, and flow liquefaction line are discussed. The test results show that the stress ratio at the peak of the stress-strain curve, called the gradient of flow liquefaction line, is unique for given vertical consolidation stress regardless of the direction and amount of initial shear stress. Though the sand behavior varies between different shear methods (bi-directional and unidirectional shear), the stress ratio at the initiation of instability is almost identical. Therefore, the total shear strength for submarine slopes under bi-directional shear conditions can be predicted through the constant gradient value of flow liquefaction line.

摘要

尽管不排水抗剪强度已被广泛研究用于评估边坡的安全系数，但边坡倾斜引起的初始剪应力的影响尚未完全了解。一些研究开始考虑次剪力方向沿坡倾方向的情况，即单向剪力。然而，在海底环境中，由于波浪和地震载荷的随机方向，需要两个方向才能正确评估真正的多向剪切强度。本文报告了 Leighton Buzzard 砂（B 级分）在专门设计的实验程序中的双向剪切行为。讨论了应力-应变关系、孔隙水压力发展和流动液化线。试验结果表明，无论初始剪应力的方向和大小如何，应力-应变曲线峰值处的应力比，称为流动液化线的梯度，对于给定的垂直固结应力是唯一的。尽管不同剪切方法（双向和单向剪切）的沙子行为不同，但不稳定开始时的应力比几乎相同。因此，双向剪切条件下海底边坡的总抗剪强度可以通过流动液化线的恒定梯度值进行预测。尽管不同剪切方法（双向和单向剪切）的沙子行为不同，但不稳定开始时的应力比几乎相同。因此，双向剪切条件下海底边坡的总抗剪强度可以通过流动液化线的恒定梯度值进行预测。尽管不同剪切方法（双向和单向剪切）的沙子行为不同，但不稳定开始时的应力比几乎相同。因此，双向剪切条件下海底边坡的总抗剪强度可以通过流动液化线的恒定梯度值进行预测。