一类三维土压力盒的设计及试验验证

为测试土体内部一点的三维应力状态，基于常规应力状态与主应力之间的关系，给出了一类三维土压力盒的设计原理和制作方法。与普通土压力盒相比，该类三维土压力盒能测试空间一点完整的应力状态，即3个正应力和3个剪应力。该类装置均由1个特定基座和6个镶嵌于基座上的微型土压力盒组成。基座的形式可以多种多样，但根据6个土压力盒法线的方向余弦得到的转换矩阵必需是满秩的。考虑工程应用方面的要求，分别阐述3种三维土压力盒的制作方法和数据处理方法，并进行了误差和适用性分析。在一个模型槽内对某重塑土进行了压缩试验，分别用给出的3种三维土压力盒测试土中不同深度处的三维应力状态。研究结果表明：土体在一维侧限压力作用下，2个水平方向的正应力均小于竖向应力且与之具有线性关系；随着土体固结度的增加，外荷载引起的土体应力状态变化偏于平缓；采用分层密实方法制备的模型土体仍具备明显的各向异性，外荷载作用下土中的各向应力增量仍存在一定差异；侧限形式和外荷载大小是引起土体应力状态不同的主要因素，分层密实导致的土体初始各向异性在加载-卸载作用后趋于缓和；测得的竖向应力随深度增加逐渐减小，反映出随深度增加附加应力的扩散效应，从而初步证实该类测试装置是科学和可靠的。

Design and Experimental Verification of a Kind of Three-dimensional Earth Pressure Cells

In order to test the three-dimensional stress state in soil, the design principle and manufacturing method of three-dimensional earth pressure cells were given based on the relationship between the normal stress state and the principal stress. Compared with the common earth pressure cells, this kind of three-dimensional earth pressure cells could test the three-dimensional stress state of the space, that is, three normal stresses and three shear stresses. The device was composed of a polyhedron base and 6 micro earth pressure cells, embedded on the base. The form of the base can be varied, but the transition matrix obtained from the directional cosine of the 6 earth pressure cells' normal line must be non-singular. Considering the requirements of engineering application, the production methods and data processing methods on three kinds of three-dimensional earth pressure cells were described, whilst the error and applicability analysis were carried out. A compression test was carried out by the remolded soil in a rigid model box, and the three-dimensional stress state at different depths were tested by the three three-dimensional earth pressure cells. The results show that, the two horizontal normal stresses, less than the vertical stress, keep linear relationship with vertical stress under the one-dimensional lateral confining pressure. With the increase of soil consolidation degree, the stress state of soil caused by external load tends to be slow. The model soil prepared by the layered compaction method presents obvious anisotropy, whilst there is still an obvious difference in the increment of stress in the soil under the external load. The lateral confining form and the external load level are the main factors that cause the different stress state of soil, and the initial anisotropy caused by layered compaction method tends to be isotropic after the loading-unloading process. The measured vertical stress gradually decreases with the increase of depth, which reflects the diffusion effect of additional stress with depth. It is proved that this kind of test device is scientific and reliable.