南阳膨胀土渠道滑坡破坏特征与演化机制研究

为了解河南南阳地区膨胀土渠道边坡滑坡机制,基于南水北调中线工程南阳段19个滑坡的现场调研统计结果,选取南阳段TS105+400处右岸滑坡为典型实例,开挖探槽揭露滑坡内部结构,对该区膨胀土渠道滑坡的破坏特征及演化机制进行了研究。结果显示,该区滑坡多发生在al+pl2Q地层;边坡的稳定性受中上部土体中的垂直节理及坡脚充填强膨胀土的缓倾长大裂隙共同控制,滑动面由后缘陡倾裂隙及前缘缓倾长大裂隙组成。开挖卸荷导致垂直节理张开,垂直节理向下可延伸3 m以上,破坏边坡土体整体性,且充当水分出入边坡的主要通道;坡面以下深度4⁸ m存在一个高湿度带,带内土体强度小,发育滑动面。气候造成的胀缩循环、开挖卸荷导致边坡垂直节理张开并向深部发展,对边坡土体的强度衰减作用明显,当垂直裂隙与前缘缓倾裂隙贯通后,发生强(久)降雨,裂隙充水软化,即诱发边坡失稳。

Study of failure characteristics and evolution mechanism of canal slope of Nanyang expansive soil

In order to understand the mechanism of expansive soil canal slope slide, a study is conducted based on the statistical results of 19 landslides at the Nanyang Section of Middle Route of South-to-North Water Transfer Project. The right bank landslide at TS105+400 is selected as typical landslide. Excavating trench exposes internal structure of landslide. A series of geological survey has been done to study the characteristics and evolution mechanism of expansive soil landslide in the area by excavating trench slides. The results show that, most landslides in the area occurred in the strata. Slope stability is jointly controlled by vertical joints in the upper layer soil and the gently dipping big fissures at the toe of the slope, which are filled with highly expansive clay. Sliding surface is composed of the steep tilting cracks at the trailing edge of slope and big gently dipping fractures at the toe of slope. Excavation unloading effect causes the vertical joints’ opening. These joints can extend more than 3 meters into the slope, which destroys the integrity of the slope soil and serves as the main channel for water to go in and out of the slope; there is a high humidity area 4 to 8 meters below the surface of slope. Soil within the area is weak and the sliding surface develops in it. Wetting and drying cycles caused by climate and excavation unloading lead to the vertical crack to open and propagation deep into slope. This effect causes a dramatic attenuation of soil strength. The vertical cracks connected with the big gently dipping fissures at the toe of the slope eventually. The slope slides after these fissure and crack are filled with water after the occurrence of strong lasting precipitation.