分级加载与波浪荷载耦合作用下软黏土动力响应特性

Dynamic Response Characteristics of Soft Clay Under the Coupling Action of Graded Loading and Wave Loading

摘要:

以长江口长兴岛潜堤后方滩涂圈围工程为研究背景，采集堤坝地基土样，根据实际工况应力路径设计不同围压和动静应力组合，对淤泥质软黏土进行动三轴试验，探究地基土在分级施工加载与波浪荷载耦合作用下软黏土应变、孔压特性以及强度弱化特性。研究结果表明：耦合应力加载后土样的应力-应变曲线呈现应变软化和强度弱化特性，分级加载效应可使应变及孔压增量减少，且应变增量、孔压增量与循环振后静强度折减度，均和固结围压、静偏应力比、动偏应力比等因素相关。当动偏应力比相同时，深度较浅土层围压较小，静偏应力比反而较大，其应变与孔压增量越大，静强度衰减越明显。随着动偏应力比增大，土单元的应变增量与孔压增量、强度折减度有不同程度的增大，并且不同深度的差异性较大。在此基础上，分别对强度折减度β、广义综合剪应变γgs及广义综合孔压增量比Δu/σ3进行了量化，并对（γgs-β）及（Δu/σ3-β）相关性进行了探讨。研究结果对于指导具体工程实践具有一定的参考价值。

Abstract:

Taking the mudflat enclosure project， located behind the Changxing submerged breakwater in the Yangtze Estuary， as the research object， indoor dynamic triaxial tests of the silty soft clay were conducted at different confining pressures and different combinations of dynamic and static stress based on the soil samples of the dam foundation and the actual load stress path. Besides， the strain and pore pressure properties and strength weakening characteristics were explored under the coupling effect of wave force and vertical hierarchical construction action. The research results show that the stress-strain curves in the coupling stress path appear to have the properties of strain softening and strength weakening. Moreover， the strain increment and pore pressure increment decrease on account of the graded loading effect. The strain increment， the pore pressure increment， and the strength weakening after cyclic loading are related to the confining pressure， the static deviatoric stress ratio， and the dynamic deviatoric stress ratio. Corresponding to the same deviatoric stress ratio， when the soil layer is shallow， the confining pressure is smaller， on the contrary the static deviatoric stress ratio is larger， hence the greater the strain increment and pore pressure increment will be， along with the more obvious static strength attenuation. With the increase of dynamic deviatoric stress ratio， the strain increment， the pore pressure increment， and the degradation of strength after cyclic loading increase， with a more obvious deviation of different depths. Based on the results，the degradation of strength β， the generalized shear strain γgs and the generalized composite pore pressure increment ratio Δu/σ3 were quantified respectively. Furthermore the relation between (β-γgs) and (β-Δu/σ3) were explored. The research results have certain reference value for guiding specific engineering practice.