【作者】 黄翔；

【导师】 张振华；

【作者基本信息】 合肥工业大学 ， 水工结构工程， 2018， 硕士

【摘要】 三峡库区马家沟滑坡抗滑桩施工完成以后,在水库蓄水运行过程中,桩身与桩后滑体间产生开裂现象(发育一条贯穿型裂缝)。以往关于马家沟滑坡抗滑桩体系变形机制的研究,认为桩后滑体的作用力是导致该滑坡抗滑桩产生变形的主要原因,但该观点并不能合理地解释抗滑桩与桩后滑体间的开裂变形现象。为了弄清马家沟滑坡抗滑桩与桩后滑体间产生开裂变形的内在机制,本文选取马家沟滑坡抗滑桩嵌固段红砂岩为研究对象,模拟水库蓄水初期至抗滑桩与桩后滑体间产生开裂变形期间的真实蓄水运行过程,进行红砂岩在此过程中不同时刻的(单)三轴压缩试验以及劈裂试验;建立马家沟滑坡典型剖面的数值网格模型,基于饱和-非饱和渗流理论,采用GEO-STUDIO软件对该滑坡在水库蓄水初期至滑坡抗滑桩体系产生开裂变形期间的地下水渗流场进行计算分析;基于流固耦合理论,采用FLAC3D软件对该滑坡在水库蓄水初期至滑坡抗滑桩体系产生开裂变形期间的变形过程进行数值模拟计算;最后基于上述研究结果,探讨马家沟滑坡抗滑桩与桩后滑体间产生开裂变形的内在机制。研究所获得的结果如下:(1)自主研发了能较真实地模拟湿干变化环境作用下的岩石抗拉强度测试装置(SGPL-2016),为马家沟滑坡抗滑桩嵌固段位置的红砂岩在水库蓄水初期至滑坡抗滑桩体系产生开裂变形期间的库水浸泡作用下的抗拉强度测试提供了设备基础。(2)水库蓄水初期至滑坡抗滑桩与桩后滑体产生开裂变形期间,马家沟滑坡嵌固段红砂岩在库水浸泡作用下的物理力学参数劣化明显,与天然状态试样(未浸泡)相比,浸泡75天后的红砂岩试样的峰值抗压强度(0 MPa、2 MPa、4MPa)分别降低67.96%、60.89%、59.34%,抗拉强度降低58.95%,黏聚力和内摩擦角分别降低61.06%、13.71%。(3)水库蓄水初期至滑坡抗滑桩与桩后滑体产生开裂变形期间,马家沟滑坡前缘涉水段(滑坡前缘坡脚位置)的浸润线受库水位下降的影响较大,变化较明显;库水位下降初期,浸润线与水平方向夹角较小,呈水平状态;随着库水位不断降低,浸润线与水平方向夹角不断增大,滑坡体内的地下水向外渗流产生较大的渗流力。(4)水库蓄水初期至滑坡抗滑桩与桩后滑体产生开裂变形期间,一方面,抗滑桩嵌固段红砂岩受库水浸泡作用的影响,宏观力学强度劣化明显,使得抗滑桩嵌固效果减弱;另一方面,由于滑体渗透系数较小,使得库水位下降过程中坡体内地下水位下降速度明显缓于坡外库水位的下降速度,滑坡体内外形成了较大的水位差并产生了指向坡外的较大的渗透力,在坡内渗透力的作用下,桩前滑体的变形快速增大,抗滑桩的桩前支撑作用大大减弱,使得抗滑桩的变形也快速增大,且大于桩后滑体的变形,导致两者变形不协调,从而在抗滑桩与桩后滑体间产生开裂现象。(5)马家沟滑坡抗滑桩嵌固段红砂岩在水库蓄水运行过程中受库水浸泡作用影响强度劣化(弱化)是引起抗滑桩与桩后滑体间产生开裂的主要原因,而库水下降作用引起的坡内渗透力在此过程中起一定的促进作用。因此,在水库岸坡加固支护设计时应考虑库水浸泡作用对嵌固段岩体(岩石)强度的影响,采用受库水浸泡作用影响劣化(弱化)后的强度参数及变形参数进行抗滑桩的设计,而不应仅考虑其在饱和状态下的强度参数和变形参数。更多还原

【Abstract】 After the completion of anti-slide pile construction on Majiagou landslide in the Three Gorges Reservoir area,penetrating cracks emerging between pile and sliding mass behind the pile due to their disharmonious deformation under water level fluctuations of the Three Gorges Reservoir.Previous studies on the deformation mechanism of the anti-slide piles in Majiagou landslide mainly focused on the deformation of the landslide under the influence of inducing factors(rainfall,water level fluctuating,and so on),and these studies show that thrust is the main reason for deformation of landslide anti-slide pile.However,this view of point cannot explain how the cracks develop.In order to study the development of the cracks,red sandstone samples from embedded section of the anti-slide piles in Majiagou landslide were taken for triaxial and splitting tests under long-term immersion conditions to obtain compressive and tensile strength of the sandstone.The groundwater seepage fields during the period between the moment of initial impoundment and the time of cracks appearing are simulated by GEO-STUDIO software based on the theory of saturated-unsaturated seepage.The deformation of the landslide during development of the cracks are calculated using FLAC3 D software based on the theory of fluid-solid coupling.At last,the developing mechanism of the cracks is discussed based on the results of above tests and numerical simulations.The main study results are summarized as follows:(1)In order to simulate the conditions of the sandstone samples from the embedded section in Majiagou landslide undergoing wetting-drying cycles more reasonably,the test system for rock tensile strength is developed independently to test tensile strengths of the sandstone samples during the period of water level fluctuations of Three Gorges Reservoir.s.(2)During the period of the cracks developing,the physical and mechanical parameters of the sandstone samples degraded obviously after a long time immersion.The peak compressive strength of the sandstone samples immersed for 75 days under confining pressures of 0 MPa,2 MPa and 4MPa decreased by 67.96%,60.89% and 59.34% respectively;the tensile strength decreased by 58.95%,the cohesion and internal friction angles decreased by 61.06% and 13.71%,respectively.(3)During the period of the development of the cracks,the saturation line at the toe of landslide is greatly affected by the decrease of reservoir water level.In the early stage of water level decline,the angle between the saturation line and horizontal direction is small.As the decreasing of reservoir water level,the angle increases continuously,and so do the difference of water head between the underground water table in the landslide and the reservoir water level,which make a large seepage force pointing outside landslide.(4)On the one hand,macroscopic mechanical strength of the sandstone in embedded section of the anti-slide piles degraded obviously due to its long-term immersing,which make the resistance of sandstone in the front of the pile reduced and the effects of embedding weakened during the period of the development of the cracks.On the other hand,the descending speed of underground water table in landslide is obviously slower than that of reservoir water level due to small permeability coefficient of the sliding mass,resulting in a great difference of water heads inside and outside of the landslide,then a large seepage force pointing outward the landslide is produced.The deformation of the sliding mass in the front of the piles increases under the action of the seepage forces.Finally,the supporting effect of the anti-slide piles greatly weakened.Cracks were gradually developing with the combined effects of strength deterioration of the sandstone in embedded section and decline of reservoir water level.(5)The strength deterioration of the sandstone in embedded section of the anti-slide piles after long-time immersion is the main reason for the development of the cracks,and the deformation of sliding mass in the front of the pile promoted the development of this progress.Hence,the effect of the long-time immersion on the strength of rocks in embedded section of anti-slide piles should be taken into account for anti-slide pile design.In other words,we should not only determine the strength parameters in saturated state of the rocks in embedded section,but also need to obtain the strength parameters of the rocks after long-time immersion in reservoir water.更多还原