基于小型平板载荷试验的粉质黏土变形演化状态特征分析

Analysis of the deformation characteristics of silt clay in a small-sized plate loading test

为掌握中低压缩性粉质黏土长期变形特征,开展了单元结构填土模型的小型平板载荷蠕变试验,测试了在最佳含水率下压实系数分别为0.90、0.95和1.00的3种填土模型在不同荷载水平作用时的竖向沉降时程曲线和回弹变形量;根据土力学流变原理中蠕变界限、长期强度和相对瞬时强度的基本概念,将土体在不同荷载水平下的变形演化状态划为快速稳定、缓慢稳定、缓慢破坏和快速破坏共4种类别;基于土体蠕变速率随时间呈现负幂函数形式的衰减规律,论证了收敛型衰减蠕变过程中塑性变形具有分形特性,建立了定量区分土体变形演化状态的"幂次判别准则",据此通过小型平板载荷蠕变试验确定了相应的3个荷载阈值;结合模型填土回弹变形量随荷载水平呈近似线性增长的特征,推求了粉质黏土4类变形演化状态对应的3个回弹应变阈值,所得成果为控制和评价地基变形演化状态提供了理论和试验依据。

To determine the deformation characteristics of silt clay under long-term static loadings, small-sized plate loading creeping tests are performed using the element model with filling soil at compaction efforts of 0.90, 0.95 and 1.00m, respectively, through which the vertical settlement-time curves and rebound deformations under designed load levels are obtained. According to the concept of creep limit, long-term strength and relative instantaneous strength in the soil rheology, four categories including fast stability, long-term stability, long-term damage and rapidly damage are identified. Based on the attenuation characteristics that the soil creep rate shows a negative power function with the time, the fractal characteristic during convergence-type decay creep is revealed. To discriminate the category of deformation characteristics, a ＂power criterion＂ is proposed for quantitatively distinguishing soil deformation evolution state, based upon which three loading thresholds are determined by the small-sized plate loading creep tests. Combined with the feature that rebound deformation amount grows approximately linearly as load increases, three rebound strain thresholds for the four deformation evolution states are obtained. These results provide theoretical and experimental bases for determining the deformation evolution state of geotechnical structures.