浅层蠕动型黄土滑坡机理

摘要

Shallow creeping loess landslides are widely developed on the relatively gentle slopes of gullies.These landslides creep periodically at a low speed along the contact surface between loess and bedrock,posing serious danger to infrastructures nearby,such as buildings,roads and pipelines.A better understanding of the formation mechanism of this sort of slope failure has great implication for geohazard control.The Louyugou landslide,located at the Luoyu gully in Tianshui,Gansu,was targeted as a case study for interpretation of the formation mechanism of shallow creeping loess landslides.Intact mudstone samples,collected from sliding belt of the slope,were tested for shear strength by using direct shear tests and direct shear creep tests.And then with the obtained test data as parameters,simulation of 2 dimensional loess surface flow was performed and slope stability analysis was conducted by using a VB program based on Finite Difference Method.Results showed that the stress-strain behavior of mudstone was of weak strain hardening type.(i.e.yield stress of the mudstone increased slightly with plastic deformation development).The long-term strength values gained by direct shear creep tests (ψ∞ =10.3°,c∞ =12.8 kPa) were much lower than those determined by direct shear test (ψf =11.9°,cf =40.9 kPa),which could be used for explanation of the creeping behavior to some extent.By simulation,it revealed that the rear body of the slope creeps forward gradually whereby relief changes over time,leading to an increasing stability.Nevertheless,the analysis also disclosed that the stability level would decrease significantly due to channel erosion,resulting in periodical downslope creeping,which was entirely consistent with our field observation.In conclusion,our proposed VB program could be used as a tool for assessment of landslide travelling distance.%浅层蠕动型黄土滑坡通常呈面状发育于相对平缓的沟谷两侧,沿黄土-基岩接触面产生周期性低速蠕动,对附近的工厂、道路和管道等设施造成严重破坏.研究这类滑坡的形成机理对其防灾减灾工作具有重要的指导意义.因此本文以甘肃省天水市罗玉沟流域的一个典型浅层蠕动型黄土滑坡为例展开研究.取滑带泥岩样进行直剪和直剪蠕变试验,以试验数据为基本参数,利用VB编程的二维滑坡运动模型模拟该滑坡的演化过程,并分析了滑坡在运动过程中及河流侵蚀下的稳定性.结果表明,泥岩应力-应变曲线呈弱硬化型,破坏后强度不发生衰减,且其长期强度(ψ∞=10.3°、c∞=12.8 kPa)明显低于直剪试验强度(ψf=11.9°、cf=40.9 kPa),有利于滑坡发生蠕动;滑坡演化过程中后缘滑体逐渐向前缘蠕动,滑体稳定系数随之提高,但河流侧蚀又会明显降低其稳定性,导致周期性蠕动下滑;本文采用的二维滑坡运动有限差分模型可较好的模拟这类滑坡的演化过程,可为滑距预测提供依据.