膨胀土边坡浅层坍滑破坏机理及稳定分析

Under the wetting-drying cycles, shallow failure of expansive soil slopes often occurs during or after the rain, which is one of the worst geological disasters frequently happening during the road construction in expansive soil regions. It can result in serious engineering damage, huge economic losses and serious environmental damage. However, how to reasonably explain the causes of this phenomenon, to clarify the considerable decay law of strength and its mechanism, and to present the slope stability analysis method in line with the actual shallow failure are still the research hotspots for expansive soil engineering and urgent problems to be solved..Therefore, the residual expansive soils in Guangxi region are mainly investigated in this project. With consideration of the actual environment and boundary conditions of the soil for slope shallow failure, existing triaxial strength test equipment and method are improved to study the strength significant decay law, the relationship between stress and strain and seepage characteristics in the wetting-drying cycles significantly affected zone, to research the effects of wetting-drying cycles and low stress on shallow failure of expansive soil slope; The environmental scanning electron microscope are utilized to perform microscopic mechanism research; Combined with the laboratory testing and field monitoring results, the expansive soil slope shallow failure is analyzed by numerical theory analysis method with the consideration of the moisture expansion effect and with the application of nonlinear strength parameters. It can be expected to explain the reasons for expansive soil slope shallow failure, and to provide a theoretical basis for its effective treatment design.

经干湿循环作用的膨胀土边坡，降雨期或雨后发生浅层坍滑破坏是膨胀土地区公路建设中常见的一种频繁且严重的地质灾害，往往带来严重的工程、经济损失和生态环境破坏。如何合理解释该现象产生的原因、弄清边坡坍滑时土体强度显著衰变规律及机理并提出与破坏实际吻合的稳定性分析方法，仍是当今膨胀土工程问题研究的热点和亟待解决的难题。.为此，本项目拟以我国广西地区的残积型膨胀土为研究对象，根据边坡浅层坍滑时土体的实际环境和边界条件，改进现有室内三轴强度试验设备和方法，研究干湿循环显著影响区膨胀土应力应变、强度衰变及渗透特性，弄清干湿循环效应与低应力条件的作用和影响，并采用环境扫描电子显微镜分析微观作用机理；结合室内试验及现场监测结果，通过数值理论分析手段，考虑吸湿膨胀作用，采用非线性抗剪强度参数，开展膨胀土边坡浅层坍滑破坏分析，可望真正合理解释膨胀土边坡浅层坍滑原因，为开展有效的工程处治设计提供理论依据。

本项目主要以百色膨胀土为对象，设计并开展了经干湿循环作用含低围压条件的重塑土饱和三轴固结排水试验，分析了橡皮膜约束对围压的影响并做出校正，进行了校正前后的实测抗剪强度参数对比分析，探究了不同干湿循环次数及试验围压下的强度及应力应变关系；通过开展干湿循环及低应力等因素对膨胀土抗剪强度的影响，研究了干湿循环条件下膨胀土的抗剪强度衰减规律，开展了干湿循环作用下膨胀土边坡的浅层坍滑分析；采用有限元软件开展了系列瞬态渗流和极限平衡分析，研究了不同降雨强度与历时对膨胀土边坡渗流场的影响，研究了降雨强度及历时、不同坡比和坡高等因素对边坡稳定性的影响；以广西酸雨重灾区百色原状膨胀土为对象，模拟酸雨（pH=3、5、7）干湿循环（n=1、2、3、4）共同作用的环境，开展无、有荷膨胀率试验，并采用SEM扫描电镜、MIP压汞仪和XRD衍射仪分析了二者共同作用下试样微结构及矿物成分的演变规律。结果表明：橡皮膜约束对低围压的测试结果影响显著，须校正；做膨胀土边坡稳定性分析时，宜用经校正围压方法获得的应力圆拟合双线形强度线确定计算参数，以获得与实际坍滑破坏较吻合的计算结果。获得了浅表层边坡土体强度具有非线性性质，并认为该特性是因土固有的膨胀性本质所致；揭示了膨胀土吸湿膨胀与粘聚力的严重衰减是引起边坡浅层坍滑的重要原因，得到了不同降雨条件对边坡浅层坍滑的影响。弄清了酸雨作用下膨胀土微观结构和矿物成分变化特性，揭示了酸雨入渗对膨胀土的微观作用机理，并阐明了其对膨胀土强度特性影响的劣化机理。