基于LVDT的小应变三轴仪研制及其软土试验应用

研制了基于LVDT（线性可变差动变压器）传感器的高精度小应变三轴仪，详细介绍了该三轴仪的结构、传感器特性及小应变测量的技术细节。三轴仪采用电控调压阀控制轴压和围压，同时可用电机驱动施加轴压，进行各种复杂应力路径的应变或应力控制三轴剪切试验。针对信号干扰等影响微小位移测量精度的问题，提出了恒温、接地、使用高精度直流电源等措施，并利用中值滤波的方法有效提高了LVDT局部位移计的测量精度。利用安装有LVDT位移传感器的三轴仪对上海软土进行K0固结不排水剪切试验，成功获得上海软土在0.001%～0.1%小应变范围内的割线模量变化情况；确认了LVDT位移传感器能够获得比霍尔效应局部位移计更小应变范围的软土割线模量，指出自主研制的设备比黑盒子产品更有利于实现测量精度的提高。

Development of small-strain triaxial apparatus using LVDT sensors and its application to soft clay test

In current study, a high accuracy small strain triaxial apparatus is developed using linear variable differential transformer (LVDT) sensors. The structure of the triaxial apparatus, the specification of the sensors, and the technical details of the small-strain measurement are introduced in detail. E/P regulators are used to control the axial load and cell pressure. Meanwhile, a motor driven actuator can be used to provide axial load. The apparatus can achieve complex stress path for triaxial tests with controlled stress or strain. Constant temperature, ground connection, and high accuracy DC power to reduce the electrical noise in the signals and to obtain a precise small strain measurement. Median filtering method is applied to increase the accuracy of measured LVDT displacement data. Undrained triaxial shear tests under K0 consolidation are conducted on Shanghai soft clay. The secant modulus of Shanghai soft clay in small strain level (0.001%-0.1%) is obtained. It is confirmed that the developed triaxial apparatus using LVDT displacement sensors can obtain secant modulus in smaller strain better than other existing products.