非饱和黄土地基降雨入渗离心模型试验及多物理量联合监测

Centrifuge modelling of rainfall infiltration in an unsaturated loess and joint monitoring of multi-physical parameters

对非饱和土降雨入渗过程及其致灾机制的深入认识有赖于室内外试验及多物理量联合监测。基于离心机超重力环境下土体响应监测技术,开展了非饱和黄土地基降雨入渗离心模型试验,测试研究了超重力环境对新研制的微型TDR探针及张力计测量的影响规律,并利用TDR、张力计及弯曲元对降雨入渗过程中土体响应进行多物理量联合监测。研究结果表明:在不同离心加速度下微型TDR探针与给定含水率土体实测原始波形重合,说明超重力环境对TDR测试没有影响,含水率的测试误差在2%以内。在离心机加速过程中,张力计所测吸力下降约2.0~2.9 kPa,当离心加速度稳定在40g时,所测吸力在10min内上升并接近常重力下土体初始吸力。在降雨入渗过程中,埋设在同一深度的TDR探针、张力计和弯曲元对湿润锋响应的时间点基本一致,降雨入渗导致土体含水率增加,基质吸力降低,剪切波速降低。这些多物理量监测数据有助于建立非饱和土含水率-吸力-剪切模量之间的关系。

Understanding rainfall infiltration process and rain-induced failure mechanism in unsaturated soils depends on experimental study with joint monitoring of multi-physical parameters. Based on the monitoring technology of soil response under a high-gravity environment, centrifuge modelling of rainfall infiltration in a unsaturated loess is carried out. Effects of high-gravity on micro-probe of time domain reflectometers(TDR) and tensiometer were evaluated. TDR probes, tensiometers, bender elements were jointly used to monitor the multi-physical response in the soil model. The experimental results showed that consistent waveforms were measured by the TDR probes for a given soil subjected to at different g levels. It indicated that the measurement by TDR was not influence by the high gravity, and the measurement error of gravimetric moisture content was within 2%. The value of matric suction measured by the tensiometer appeared to decline during centrifugal acceleration process. After the acceleration reached the stable value of 40 g, the recorded suction was recovered to the initial suction measured under normal gravity within 10 minutes. During the process of rainfall infiltration, the TDR, tensiometer and bender element, which were buried at same depth, showed a concurrent response to the arrival of wetting front. Rainfall infiltration resulted in an increase in moisture content, a decline in matric suction, and a decrease in shear-wave velocity. The joint monitoring of muti-physical parameters will provide useful data for establishing the relationships among moisture content, matric suction and shear modulus.