膨胀土裂隙的工程特性研究

Research on engineering properties of fissures in expansive soil

裂隙是膨胀土的重要特征之一,长期以来,人们常常把分布于膨胀土大气影响深度范围内受干湿循环影响而产生的干缩裂隙与膨胀土地层中特有的原生裂隙混为一谈。在对膨胀土边坡失稳机制的研究中,也忽视了原生裂隙对边坡稳定的重要影响。为研究南水北调中线工程膨胀土地段渠道破坏机制,在河南省南阳市郊建设了一条长为2.05 km试验渠道,通过渠道开挖期间的地质勘察、现场观测和取样试验,以及对现场滑坡体的取样分析,研究了膨胀土裂隙及周边土体的物质成分、密度、含水率和强度特性,结合现场观测资料分析了裂隙与渠道滑坡的关系。研究表明,膨胀土地层中的原生裂隙有两种类型:光滑蜡状裂隙和有一定厚度充填黏土的裂隙。裂隙面上的物质成分与两侧土略有不同,且天然密度低、含水率高,强度远低于相邻土体的强度,一旦地层与边坡倾向一致,将产生沿裂隙面的滑动。

Fissure is one of the important characteristics of expansive soils. Shrinkage fissures induced by the wetting-drying cycle effects and the specific inherent fissures distributed in atmospheric influential depth of expansive soil are often confused. In the study of expansive soil slope failure mechanism, the significant impact of the inherent fissure on slope stability is often ignored. In order to study the failure mechanism of expansive soil in middle route of South-to-North Water Transfer Project, a 2.05 km test channel is constructed on the outskirts of Nanyang, Henan province. Geological survey, field observations and sampling tests during excavation, as well as on-site sampling and analysis of slope failure are conducted to study the material composition of expansive soil fissure and the density, water content and strength characteristics of the surrounding soil. Combined with field observations, the relationship between fissures and channel landslide is analyzed. It is shown that there are two types of inherent fissures for the expansive stratum：one is smooth waxy fissure; and the other is filling clay fissure with a certain thickness. The material composition of the fissure surface is slightly different with the adjacent soil, featured by low natural density and high moisture content;and the intensity is much less than the strength of the adjacent soil. Once the formation is consistent with the slope tendency, it would slide along the fissure surface.