基于三维应力状态的静止侧压力系数研究

Study on Static Lateral Pressure Coefficient Based on Three-dimensional Stress State

为研究土体静止侧压力系数K_(0),基于土的压缩变形特性,设计制作了一种能够测算K_(0)的圆筒模型试验装置,对天津地区浅层砂土进行了一维加卸载压缩试验。采用三维土压力盒测试了各方向土压力,得到了深度分别为20、70、120 cm处土体的三维应力状态。基于比值形式的K_(0)计算公式,揭示了K_(0)在不同深度处的变化规律,进行了同一深度水平方向x和y上K_(0)大小的对比分析。结果表明:经过加载、卸载和稳定3个阶段,不同深度的正应力σ_(x)、σ_(y)和σ_(z)均随测试时间先增大再减小后平稳,其中竖向应力值沿深度增加明显减小;不同深度的K_(0)变化趋势基本一致,加载前期K_(0)突变是合理的,且120 cm处的稳定值满足设计规范要求;加卸载条件下K_(0)值随深度增加而增大,同一深度处K_(0x)和K_(0y)稳定值的差值在0.04~0.07之间,这与轴对称受力条件和土的各向异性相吻合;通过传统经验方法得到的K_(0)值为0.416,处于试验测算得到的K_(0)稳定值范围内;该试验装置结构具有稳定性和系统性,操作简单方便,测试结果准确可靠,研究结果可为各种土的K_(0)研究提供参考。

To study the static lateral pressure coefficient K_(0) of soil,based on the compression deformation characteristics of soil,a cylinder model test device which can measure K_(0) was designed and made,and one-dimensional loading and unloading compression test was carried out on shallow sand in Tianjin area.The earth pressures in all directions were measured by using a three-dimensional earth pressure box,and the three-dimensional stress states of the soil at the depths of 20,70,120 cm were obtained.Based on the K_(0) calculation formula in the form of ratio,the variation law of K_(0) at different depths was revealed,and the values of K_(0) in the horizontal direction x and y at the same depth were compared and analyzed.The results show that after three stages of loading,unloading and stabilization,the normal stresses σ_(x),σ_(y) and σ_(z) of different depths firstly increase and then decrease and finally stabilize with the test time,and the vertical stress decreases obviously along the depth.The change trend of K_(0) in different depth is basically the same,the sudden change of K_(0) in the early stage of loading is reasonable,and its stable value at 120 cm meets the requirements of the design code.Under the condition of loading and unloading,the value of K_(0) increases with the increase of depth,and the difference between stable values of K_(0x) and K_(0y) at the same depth is between 0.04 and 0.07,which is consistent with the axisymmetric stress condition and the anisotropy of soil.The K_(0) value obtained by the traditional empirical method is 0.416,which is within the range of the stable K_(0) value calculated by the experiment.The structure of the test device is stable and systematic,the operation is simple and convenient,the test results are accurate and reliable,and the research findings can provide a reference for the K_(0) study of all kinds of soil.