应力幅值比对土-结构接触面非共轴特性影响研究

运用80 t大型三维多功能土工试验机（3DMAS），进行了不同应力幅值比下粗粒土与结构接触面大型三维循环直剪试验，深入分析了应力控制往返椭圆剪切路径下接触面切向位移、非共轴角和剪切柔度等三维力学特性以及应力幅值比的影响规律。应力控制往返椭圆剪切路径下，接触面产生了明显的x向和y向位移、非共轴角和剪切柔度。x向和y向位移幅值、剪切柔度峰值均随循环剪切的进行逐渐减小而后趋于稳定，表现出演化特性。非共轴角受切向应力幅值及切向应力增量方向共同影响，其最值、稳定值随循环周次基本保持不变；正向剪切时非共轴角最大值（最小值）与反向剪切时最小值（最大值）基本出现在同一位置。接触面剪切柔度与非共轴角随旋转角度的变化趋势相反，剪切柔度的增加会抑制非共轴角的发展，反之亦然，两者对立统一。应力幅值比对接触面切向位移间椭圆关系及其时程变化形式、切向应力位移类椭圆关系等影响较小，主要影响切向位移幅值及其偏移程度、切向位移间椭圆关系的长短轴大小及方向、切向应力位移类椭圆关系的长短轴大小、非共轴角的数值及其随旋转角度的变化形式和最值出现位置、剪切柔度随旋转角度的变化形式和峰值及其产生位置等。应力幅值比越大，切向位移幅值越大、向负向偏移越大，剪切柔度峰值越大，随循环剪切的进行减小的速率越慢。应力幅值比ξ_τ=1和ξ_τ≠1时接触面非共轴角和剪切柔度随旋转角度的发展变化形式差别很大。

Role of stress amplitude ratio in the non-coaxial behavior of the interface between gravel and structure

A series of 3D cyclic large-scale direct-shear tests of a gravel-structure interface was conducted at different stress amplitude ratios using 80 t 3D multifunction apparatus for soil-structure interface (3DMAS). The 3D cyclic interface behavior, including tangential deformation, non-coaxial angle and shear flexibility, was addressed in stress-controlled two-way elliptical shear path and the influence of stress amplitude ratio was discussed in detail. Distinct tangential displacements in the x and y directions, non-coaxial angle, shear flexibility are observed subjected to two-way elliptical cycling of shear stress. The tangential displacement amplitudes in the x and y directions and the shear flexibility of the interface gradually decrease with cyclic shearing and then tends to be stabilized, indicating noticeable evolution characteristics. The non-coaxial angle is significantly dependent on the shear stress amplitude and the shear stress increment direction, and the maximum, minimum and stabilized non-coaxial angles almost remain invariable throughout cyclic shearing. The development of the shear flexibility against rotation angle is contrary to that of the non-coaxial angle, and the rapid growth of the peak shear flexibility will impede the development of the non-coaxial angle of the interface. The stress amplitude ratio slightly influences the relationship patterns of the tangential displacements in the x and y directions and their relationship patterns against shear cycle, and the shear stress-displacement relationship patterns, but significantly affects the tangential displacement amplitudes and their migration extent, the length of the major and minor axis of the elliptical curves of the tangential displacements in the x and y directions and of the shear stress-displacement response, as well as the magnitude and development trend of the non-coaxial angle and shear flexibility. Increased stress amplitude ratio leads to magnified tangential displacement amplitudes and enlarged migration towards the negative direction, increased peak shear flexibility and slowed evolution with cyclic shearing. In addition, the non-coaxial angle and the shear flexibility present different performances when the stress amplitude ratio equals and does not equal 1.0.