土工模型试验和现场试验中常采用膜式土压力盒作为压力测试元件,即通过测量膜的变形(挠曲)量获取压力值。膜式土压力盒作为埋入介质内部的测试元件,由于土压力盒与岩土介质的刚度差,测试中受到由差异变形导致的岩土介质土拱效应的影响,特别是模型试验的应力历史也会产生不同程度的土拱效应影响。针对桩承式路堤多陷阱门模型试验中的加卸载条件,采用相同的试验用砂在相同的相对密度条件下进行了1组加载标定和4组不同填料高度下的卸荷标定试验。结果显示,加载曲线线性较好,而卸载曲线可采用指数曲线来进行拟合。将获取的标定系数应用于桩承式路堤多陷阱门模型试验当中,发现填料填筑过程中采用砂标系数处理得到的平均土压力值与路堤自重应力较为吻合。在陷阱门下沉模拟桩间土下沉过程中,分别采用砂标加载系数和卸荷系数处理土压力数据,与实际情况能够较好的吻合。
Diaphragm-type pressure cells are often used in geotechnical model tests and in-situ tests. The soil pressures are obtained through the measurement of the diaphragm deflection. With a gauge inserted into the soil or sand, the stiffnesses of the cells and the geo-medium are different. The soil arching in the soil or sand above the cells caused by the differential deformation will reduce the pressure on the diaphragm. In addition, different stress histories in the model tests result in different levels of influence. In the piled embankment multiple trapdoors model tests, the cells on the pile(fixed beams) experience a loading process, while the cells in the soil(movable beams) experience an unloading process. One loading calibration test and four unloading calibration tests are carried out on the same sand under the same relative density as in the model tests. The calibration results show that the stress-strain loading curves are almost linear and the unloading curves are quite similar to exponential ones. The calibration coefficients are obtained and then used to deal with the measurements. During the sand filling procedure, the average pressures obtained using the calibration coefficients coincide well with the self-weight of the embankments. During the settling(trapdoor movement) procedure, the pressures of the cells on the pile and in the soil are calculated using loading coefficients and unloading coefficients respectively. The results show that the soil pressure curves coincide well with those in the real model tests.