动、静荷载下孔压对饱和高温冻土力学性质影响机理

When subjected to an external load, the pore water pressure develops in the saturated warm frozen soil. Accordingly the pore water pressure variation influences the effective stress of the soil in the meantime which results in the change of the mechanical property. Then, a series of engineering problems are prompted to appear. In addition, the change laws of the pore water pressure as well as the mechanical response of warm frozen soil are significantly affected by the load types. In order to research the influence of the pore water pressure on the mechanical behavior of warm frozen soil under different kinds of loadings, the pore water pressure tests with saturated warm frozen soil will be carried out in this paper, under the static and dynamic loadings, using the Qingzang silty clay as the research object. The pore water pressure curves in the different temperature conditions and different drainage conditions will be compared. Then, the relationship between the pore water pressure dissipation and the deformation under static loading will be discussed to clear whether the consolidation exists. The variation of pore water pressure and the development of the effective stress under long-term dynamic loading will be analyzed to interpret the role of the pore water pressure plays in the soften process of the mechanical behavior. On the basis, a numerical model for predicting the pore water pressure variation and the settlement tendency of warm permafrost beneath the embankment under multiple loadings will be established finally.

饱和高温冻土在受到外荷载作用时会产生一定的孔隙水压力，相应地会改变土体中的有效应力进而促使其力学性质发生变化，随之又会带来一系列的工程问题。不同类型的荷载会引起不同的孔隙水压力变化规律，从而使得高温冻土力学响应有所差别。为了研究不同荷载类型下孔压变化对高温冻土力学性质的影响，本项目选择青藏粉质黏土作为研究对象，拟在静荷载和动荷载两种类型下开展饱和高温冻土的孔隙水压力试验，在试验中改变土样温度状态以及排水条件对孔隙水压力变化曲线进行对比分析。通过静荷载下高温冻土孔压消散与变形之间的关系明确在其变形过程中是否存在固结作用。分析孔隙水压力在长期动荷载作用下的变化趋势以及相应的有效应力的发展过程，进而探讨孔压对高温冻土力学性质软化效应的影响机制。在此基础上建立数值模型模拟预测路基下部高温冻土在复合荷载作用下孔压变化及沉降变形趋势。

在外荷载的作用下，高温冻土可能会产生超孔隙水压力并对力学性质产生一定的影响，从而引起一系列的工程问题。为了认识在不同类型荷载下高温冻土中的孔压变化规律，进而探究在此条件下高温冻土的变形机制，本项目开展了恒定荷载、循环荷载条件下的高温冻土孔隙水压力试验，分析了孔压变化与骨架变形相互作用关系，探讨了高温冻土变形机理过程。研究结果表明，冻土中的未冻水在受压时会被挤压排出土体外，且此过程对冻土体积变形影响较大。在排水条件下外荷载作用会促使高温冻土内的超孔隙水压力逐渐增大直到达到峰值，而后孔压缓慢消散。孔压变化特征会随着温度、含冰量以及土质不同而呈现较大差异。孔压变化是孔隙未冻水与骨架变形相互作用结果，是在受挤压增大与渗透消散这两个对立过程的综合作用下发展变化的。这一过程证明了在高温冻土变形中存在固结作用，即冻土体积变形是由固结和蠕变共同作用导致的。在循环荷载下孔压变化与恒定荷载下较为类似，但加载频率对孔压变化特征影响较大。另外，本项目验证了冻土的孔隙连通性以及测量了在不同温度条件下冻土的渗透系数。最后，基于试验结果建立了高温冻土固结变形数值模型，并针对多年冻土区原位静载试验进行了模拟，结果能较好地模拟地温及沉降曲线，并能够反映出孔压变化过程以及渗流作用对应力、变形的影响。