降雨诱发残积土坡失稳的模型试验

Model Test of Rainfall-induced Residual Soil Slope Failure

为了研究降雨条件对残积土坡坡体内部变形特征及边坡失稳机理的影响,结合自制监测系统、人工降雨试验及数字照相量测技术,开展不同位置、不同坡度、不同密实度边坡的地质力学模型试验,分析雨水入渗对坡体变形、吸力的影响。指出失稳预警因子应从降雨诱发滑坡失稳机理出发,着重考虑边坡关键位置的力学物理量变化。基于坡体变形和吸力时变规律,提出边坡变形发展的3个阶段;基于不同条件下边坡的失稳破坏过程,揭示降雨诱发残积土坡的失稳模式。试验结果表明:边坡上部土体吸力和变形变化幅度较大,速度较快,而下部土体变化幅度较小,速度较慢;陡坡和高密实度边坡抵抗降雨入渗引起的变形能力强于缓坡和低密实度边坡,由于小孔隙结构发生破坏所需的能量远大于大孔隙结构,导致低密实度、缓坡坡体中部产生的变形大于坡体上部;边坡变形发展阶段为初始蠕变阶段、加速发展阶段、滑动破坏阶段;无支护的边坡,失稳预警因子可选择边坡关键位置处的基质吸力;有支护的边坡,应根据支护结构受力(变形)和边坡关键位置处吸力变化特征来选择预警因子;土坡的失稳模式为坡表冲刷→冲沟、切沟侵蚀→坡脚局部坍塌→破坏范围纵横发展→整体失稳,滑动面深度为1~3m,该类滑坡应注重坡脚防护,尽可能降低边坡渐进累积破坏的可能性。研究结果可为构建东南沿海地区降雨诱发滑坡预测模型提供重要依据。

In order to investigate the influences of rainfall on deformation characteristics and slope instability mechanism of the residual soil slope, a real-time monitoring system, artificial rainfall system and digital photogrammetry technology were used to conduct a geo-mechanical modeling test under the different location, different slope angles, different density and different rainfall conditions. Then the influence of rainfall infiltration on body displacement and matric suction was observed. Instability risk factor should be considered from the perspective of instability mechanism of landslide induced by rainfall. The variation of the physical quantity of slope should be paid much attention. Three development phases of slope deformation were proposed on the basis of slope deformation and the changing law of matric suction with time. Meanwhile, by dint of instability failure processes under the different conditions, the rainfall-induced residual soil slope failure mode was revealed. The results show that matric suction and body deformation of slope upper part change greatly, and the speed is fast. However, slope lower part soil change slightly with low speed. Compared with the gentle slope with low density, the anti-deformability of the rainfall infiltration in the steep slope with high density is stronger. As the energy required for the small pore structure destruction is much larger than that of the large pore structure, the deformation in the middle part of the gentle slope with low density is larger than that of the upper part of the slope. Considering the law of soil suction, time variation and body deformation, three stages of slope deformation development are put forward, namely, the initial creep stage, accelerated development stage and sliding failure stage. Meanwhile, the slope instability warning factor should be selected from the instability mechanism of rainfall-induced landslides. Besides, the matric suction of slope key position could be selected as the slope instability warning factor for unsupported slope, whilst the change characteristics of matric suction and supporting structure stresses （deformation） should be considered together as the instability warning factor selection for supported slope. Based on the failure process of the soil slope subjected to rainfall infiltration, the failure mode is observed. It starts from slope surface scouring, and gradually develops into gully erosion. Subsequently, the local failure at the slope toe occurs, and the damage scope extends vertically and horizontally and finishes with a global shallow landslide. The depth of slip surface is 1 to 3m, and this kind of landslide should focus on the slope protection to reduce possibility of slope progressive failure as much as possible. The results provide the reference for constructing a prediction model of landslides induced by rainfall in the southeast coastal areas.