真空预压负压分布规律模型试验研究

Model tests on negative pressure distribution in vacuum preloading

负压分布规律是真空预压机理研究的重要课题。通过讨论真空预压负压空间分布特点及负压相关概念,广义地定义了负压,分析了负压的测量方法及影响因素。设计高15.0 m的竖向大比尺室内模型,开展真空预压负压分布规律试验研究。试验结果表明,饱和黏土土中真空度测量存在滞后效应,本次试验真空度存在的极限深度为8.9 m;膜下真空度稳定后,零压面之上孔压及板中真空度沿深度呈对称线性分布,斜率均近似为静水压力梯度;负压沿深度为分段线性分布,在地下水位之上的非饱和段因提水做功而衰减,稳定期负压平均衰减值为21.4 k Pa,在水位之下排水板埋深范围内基本均匀分布而无衰减,稳定期平均负压为-67.0 k Pa。结合试验规律及等效排水管中气液两相流的流型分布,给出了真空预压稳定期竖向排水板中的分段线性负压边界。

The rule of negative pressure distribution is an important subject in the studies on vacuum preloading mechanism. By discussing the spatial distribution characteristics of vacuum preloading and the associated concepts, the negative pressure is defined in a broad sense, and the methods and influencing factors for the negative pressure measurement are analyzed. The tests are carried out, with a well-designed large scale indoor model 15 m in vertical height, to study the negative pressure distribution in vacuum preloading. The test results show that there is hysteresis effect in vacuum measurement in saturated clay soil, and the limit depth where vacuum exists is 8.9 m. The pore water pressure and vacuum degree in drain board exhibit a symmetrical linear distribution above zero pressure plane at the vacuum stable stage, and the slope is similar to hydrostatic pressure gradient. The negative pressure distribution along the depth is of piecewise linear type, due to the energy consumption in water lifting, attenuation is found in the unsaturated soil above the underground water level, and the average attenuation value is 21.4 k Pa in the stable period. The negative pressure is uniform with no attenuation under the average water level, and the corresponding average negative pressure is-67.0 k Pa within the depth scope of drainage board in the stable period. Based on the experimental results and the flow pattern distribution of gas-liquid two-phase flow in the equivalent drainage tube, the piecewise linear negative pressure boundary of the vertical drainage board in the stable period of vacuum preloading is put forward.