【作者】 蔺晓燕；

【导师】 李同录；

【作者基本信息】 长安大学 ， 地质工程， 2013， 博士

【摘要】 灌溉诱发的突发性黄土滑坡-泥流是黄土灌区发育较多的一类地质灾害，对此类滑坡前期研究较少。本文对甘肃省永靖县盐锅峡镇西起方台，东至黑台，南以黄河北岸为界，北以磨石沟为界的黑台和方台两个台塬及其边坡一带进行野外勘查，共发现37个滑坡。依据运动学模型进行分类，其中快速错落式滑坡12个，滑坡-泥流15个，低速蠕动滑坡10个，统计结果表明该区以滑坡-泥流发育数量最多。进一步对各种类型滑坡的发生条件进行对比分析发现，黄土滑坡-泥流的发生具有其地形特点：一般发生在黄土冲沟的沟头，沟头为凹形坡，在自然状态下是稳定的，同时沟道狭窄，两测灌木和草本植被发育，并不具备泥流沟的特征，没有典型滑坡地貌。因此，在通常的地质灾害调查中，很难将这类地貌判定为潜在灾点，且滑坡点位于沟头，受灾点位于沟口或坡下，滑坡灾点不易被人发觉，滑坡方量虽然不大，但转化为泥流后，致灾范围显著扩大。对黑方台黑台西南端永靖电厂北面的斜坡上每1m采取的土样进行物理力学性能测试，得到了不同深度的含水率、液限、塑限、饱和含水率、孔隙比、塑性指数和颗粒组成，确定了该地区的上部地层主要由24m的Q3黄土、20m的Q2黄土及8m的冲积粉质粘土组成，发现了可转化为泥流的黄土结构疏松，孔隙比一般大于0.80，饱和含水率大于液限，下部的冲积粉质粘土为相对隔水层，由此得到了滑坡-泥流发生的物质条件和地下水条件。不同含水率和不同围压下的三轴剪切试验得到了黄土不同应力环境下的三种破坏模型，即劈裂破坏、剪切破坏和鼓胀破坏。在野外调查中发现：边坡坡顶的黄土多发生劈裂破坏，其含水率小，围压小；坡底的黄土多表现为蠕变破坏，土的围压与含水率都很大；处在中部的土有明显的破坏面，为剪切破坏，其围压与含水率介于上述两种情况中间。试验结果与实际相吻合，因此本次试验结果揭示了非饱和黄土的变形破坏特性。同时，对灌区三个土层的饱和原状样进行三轴试验，加孔隙反压致土样破坏的应力路径曲线表明：随着孔隙水压力增加，在p-q坐标上土样的应力路径从起始点向左移，即向破坏线方向移动，孔隙水压力增加致使应力点接近强度线时土样破坏。同时由试验得到了冲积粉质粘土、Q2黄土、Q3黄土的有效残余粘聚力、有效内摩擦角、总残余粘聚力和总残余内摩擦角，试验结果显示总应力值比有效应力低，可见滑坡-泥流的发生具有很大的可能性。室内渗透试验过程中由于土样经过了卸荷回弹，所测得的渗透系数并不是土体真实应力状态下的渗透系数，为此对传统渗透仪进行改装，并以黑方台黄土为研究对象，对不同深度的黄土试样进行不同压力下土的固结-渗透试验，得到了各种土样的固结压力-渗透系数关系曲线，进而得到土样真实应力状态下的渗透系数。对比分析了土的变形及渗透特征，结果表明室内常规变水头渗透试验所得黄土渗透系数较固结-渗透试验所测得数据大25-40倍。在饱和渗透试验的基础上，结合采用张力计测得的土水特征曲线，利用经验公式换算出非饱和渗透系数。将上述三轴试验和渗透试验参数应用到GEO-Studio软件的SEEP/W、SIGMA/W、SLPOE/W模块，对该滑坡-泥流进行渗流分析、应力-应变分析和稳定性计算。分析结果表明：随着灌溉水的入渗，地下水位不断上升，土体的孔隙水压力不断升高，导致土体应力重分布；当水位增加到一定程度，潜在滑动面（带）土体接近饱和，滑带土体的抗剪强度大幅度降低，导致滑坡-泥流发生。K.Sassa基于流体力学的理论推导出三维滑坡运动模型，开发的三维滑坡运动模拟程序LS-RAPID适用于滑坡-泥流和泥石流的运动模拟。本文采用该程序通过对取样点的土进行环剪试验，确定各层土的残余摩擦角、饱和不排水抗剪强度τss，估计孔隙水压力发挥程度Bss，然后进行三维滑坡-泥流运动模拟，得出滑坡-泥流发生时的瞬时速度和稳定时的堆积范围，为滑坡-泥流破坏程度和致灾范围的预测提供了依据。更多还原

【Abstract】 Irrigation-induced slide-flow is one of the most general geological disasters in loessirrigation areas and there is hardly any research of it. Based on the survey and research of thetwo platforms named HeiTai and FangTai, which are located to the north of the Yellow Riverand south of the MoShiGou, there are12quick collapse landslides,15slide-flows,10slowtransitional landslides and no rapid long run-out landslides. Slide-flow distributes the mostextensively and it always originates from the head of the gully which presents the concavetype. Meanwhile, the slope general stays stable under the natural state for its narrow slidingpath and the thick vegetation. During the investigation, this kind of landslide is easily ignoredfor the reason that it doesn’t have the typical physiognomy. At last, the landslide grows in thetop while the effected area in the bottom, when it turns to slide-flow, its destructive scope isexpanded significantly.Through the physical and mechanical test of the soil for every1.0meter taken fromsouthwest of HeiTai, we get the result of the moisture content, liquid limit, plastic limit,saturated moisture content, void ratio, plasticity index and particle composition. The resultshows the three typical stratums, namely24m Q3loess,20m Q2loess and8m alluvial siltyclay.Physical mechanical performance tests were taken on the soil samples which were takenfrom the slope with intervals of1m in the vertical direction. The slope is on the north of theYongjing PowerStation which is located in the southwest end of Heitai. Through the tests, Igot the data of water content, liquid limit, plastic limit, saturated water content, void ratio,plasticity index and grain composition at different height, and find that the upper formationmainly consists of three layers: Q3loess layer of24m, Q2loess layer of20m and alluvial siltyclay layer of8m. I find that the loess that can became mudflow has several characteristics:void ratio bigger than0.8, saturated water content bigger than liquid limit, silty claysubstratum relative impermeable. Thus, we find the ground water condition and physicalcondition of landslide-mud flow.Loess with different moisture content under different confining pressures in three axle shear test should be got three failure models of environment, namely the splitting failure,shear failure and destruction of bulging. The field investigation shows that the top of theslope loess mostly appears splitting failure with low moisture content and small confiningpressure. The loess in bottom of the slope more performance for the creep damage, both ofconfining pressure and moisture content are large. The soil in the middle of the slope oftenappears obvious failure surface of shearing, and value of the confining pressure and watercontent are always between the aforesaid two cases.Test result is in conformity with the actual, so the test results revealed the deformationand failure characteristics of unsaturated soil. The triaxial test shows that with the increasingof the pore pressure, the stress path is turning to the left that is the direction of damage. Wealso measured the effective c’ and and total residual c and of alluvial silty clay, Q2loess,and Q3loess. The result shows that the total stress value is lower than the effective one,suggesting the great possibility of the slide flow.Based on the saturated permeability tests, we used the tensiometer to measure soil-watercharacteristic curve and calculate the unsaturated permeability coefficient using the empiricalformula.The sample usually used in permeability test is unloaded, not in the real stressenvironment. The permeability coefficient we get is not what we want. In order to restore thereal stress environment of the sample, the instruments have been improved. The loess inHeifangtai platform from different depth has been choose as the object of study, and theconsolidation-permeability test under different stress environment have been done. Thecomparative analysis is made on the deformation and permeability of the loess under theeffect of different loads. It turned out that the permeability coefficient obtained from thepenetration test under consolidation is25-40times as high as the one obtained from theconventional penetration test.After that, we make the parameters into SEEP/W, SIG, MA/W, SLPOE/W of GEO-Studiosoftware, to analysis the seepage, stress and stability. The result shows that with the rising ofgroundwater levels, oil pore water pressure is changing, resulting in redistribution of stress.When the water level rising to a certain extent, the potential sliding surface soil is close tosaturation, the landslide occurred.Based on the theory of fluid mechanics and three-dimensional landslide motion model, K.Sassa developed LS-RAPID which is appropriate for the simulation of the landslide, rapidslide-flow and debris flow. By ring shear test on soil sample points, we get the residualfriction angle, saturated undrained shear strength τss, estimating degree of pore waterpressure Bss, then simulate the movement process. From the result, we can get theinstantaneous velocity and scope of accumulation that is close to the actual situation. So thesimulation provides a basis for the prediction of the damage ability and disaster scopes.更多还原