考虑裂隙的膨胀土非饱和渗透特性及边坡降雨入渗数值模拟

Intensive rainfall is one of the most important factors which induce the failure of expansive soil slope. At Present, the infiltration analysis is usually based on continuum theory, and it does not consider the effect of fracture induced by water loss on unsaturated permeability and REV volume of expensive soil. Furthermore, existing methods are incapable of considering the effect of pore gas and runoff simultaneously. So, deeper research is necessary. This proposal would make an attempt to establish a new feasible method for infiltration analysis for expansive soil slope numerical experiments and the integrated model for water-air two-phase flow and runoff. Based on the unsaturated permeability of intact expansive soil, the fracture distribution, and water and gas unsaturated permeability of single fracture, numerical experiments on SWCC, water and gas unsaturated permeability and REV of expansive soil would be done. Furthermore, the integrated model from the kinematic wave approximations of the Saint Venant equations and water-air two-phase flow equations would be established, and a finite element program for numercal simulation corresponding to the above model would be coded. Finally, introducing the unsaturated permeability of expansive soil and verified by the infiltration experiments, the program is used to simulate numerically infiltration process of expansive soil slope cosidering gas flow and runoff would be established. The achievements are of interest in understanding the failure mechanism and reinforcement design of slopes.

强降雨是诱发膨胀土边坡失稳的重要因素之一。目前降雨入渗分析中，在借助连续介质理论分析膨胀土裂隙充分发育层的渗流问题时，未考虑裂隙对非饱和渗透特性及表征单元体体积的影响，且现有分析方法无法同时考虑气相和坡面径流对入渗的影响。本课题拟开展膨胀土非饱和渗透特性数值试验研究，建立边坡水气两相流与坡面径流联合求解模型，寻求一种切实可行的膨胀土边坡降雨入渗分析方法。基于完整膨胀土非饱和渗透特性、膨胀土失水开裂裂隙分布、单裂隙非饱和渗透特性，开展数值试验，建立考虑裂隙影响的膨胀土SWCC、水和气体相对渗透函数模型并确定表征单元体体积；基于水气两相流和运动波方程，结合有限元法，将运动波方程融入两相流方程坡面入渗边界，消去入渗率，建立边坡水气两相流与坡面径流联合求解模型,实现膨胀土边坡降雨入渗数值模拟，用膨胀土入渗强度试验加以验证。研究成果对于理解边坡失稳机制和边坡加固工程具有重要的理论和实际意义。

强降雨是诱发膨胀土边坡失稳的重要因素之一。而目前降雨入渗分析中，在借助连续介质理论分析膨胀土裂隙充分发育层的渗流问题时，未考虑裂隙对非饱和渗透特性及表征单元体体积的影响；且现有分析方法无法全面考虑降雨时坡面产汇流对边坡入渗的影响，也无法同时考虑气相和坡面径流对入渗的影响。针对上述问题，本课题开展了如下三个方面的研究。.1、.进一步完善了降雨入渗与坡面径流联合求解有限元模型，实现了径流对边坡入渗的流量补给的模拟。模拟结果表明，径流水深对入渗量影响不大；但当边坡渗透性上段小而下段大时，上段边坡的径流对下段边坡的渗流有流量补给，而现有数值模拟方法往往忽略了这一作用，导致大大低估了边坡入渗量，从而高估边坡稳定性。.2、.基于水气两相流和运动波方程，结合有限元法，将运动波方程融入两相流方程坡面入渗边界，消去入渗率，从而建立了边坡水气两相流与坡面径流联合求解有限元模型，实现了边坡水、气运移和降雨时坡面产汇流的同步计算；更加真实准确的再现边坡水分运动的运动过程。实现的方法为。发现当气体封闭在边坡内时，将大大减小水分入渗，对边坡稳定性有利；但气体未被封闭时，则影响不大，与不考虑气相的Richards方程结果基本相同。.3、.基于完整膨胀土非饱和渗透特性、膨胀土失水开裂裂隙分布、单裂隙非饱和渗透特性，开展数值试验，发现干密度为1.5-1.6 g/cm3的膨胀土表征单元体尺寸(REV)为6-8cm；确定建立考虑裂隙影响的膨胀土SWCC、水和气体相对渗透函数模型，发现考虑裂隙影响的渗透系数比不考虑大1-2个数量级，基质吸力则降低1-2个数量级。表明裂隙对膨胀土非饱和渗透特性有重要影响。