山西清徐—太谷地区地裂缝形成机理

山西清徐—太谷地区是中国地质灾害高发区之一, 地质灾害类型主要有活动断裂、滑坡、地震、地裂缝等。通过对该区开展地面路线地质调查、物探、水文工程钻探等工作, 将地裂缝划分为山前地裂缝和盆地中部地裂缝2类。山前地裂缝主要与断陷盆地盆-山转换带的活动断层有关, 其盆地上基底构造层岩石组合具有软硬相间的"二元结构"特征, 由厚层状砂岩和薄层状粉砂质泥岩组成, 这种"二元结构"在外在因素(如暴雨、地震等)的诱发作用下, 软质层容易产生层间滑动, 导致地裂缝等地质灾害。盆地中部地裂缝除与可能的隐伏断裂有关外, 主要与清徐—太谷地区地下水过度开采有关。水文工程钻探揭露了该断陷盆地中多个含水层, 每个含水层结构中的上下层为不透水的厚大粘土层或粉砂质粘土层, 中间含水层为粉砂或细砂层。当地下水过量开采时, 水位降低, 含水层受上覆地层重力作用影响, 发生沉降形成地裂缝。清徐—太谷地区上更新统粉质泥岩中常可见少量白色膏盐团斑, 推测是造成本区地下水质普遍偏咸的原因。

The formation mechanism of ground fissures in Qingxu-Taigu area,Shanxi Province

Qingxu-Taigu area, Shanxi Province is one of the high incidence of geological disasters in China, the main types of geological disasters are active fault, landslide, earthquake, ground fissure and so on.This article based on the ground route geology survey, geophysical prospecting and hydrological engineering drilling, preliminarily divided the ground fissures in this area into two categories, which are the ground fissures nearby mountain and the ground fissures in central basin.The ground fissures nearby mountain are mainly associated with the active fault in the transition zone between the mountain and the graben basin, the underlying bedrock of the basin shows the characteristics of "dual structure" mainly consisting of the thick layer of sandstone and thin bedded silty mudstone, which is very easy to produce interlayer slip and lead to geological disasters such as ground fissures induced by the external factors(such as heavy rain and earthquake, etc.).The ground fissures in central basin are mainly related to groundwater overexploitation besides the possible concealed faults under the basin.The results of hydro-engineering drilling show that there are multiple aquifers in the central basin.The aquifers closed by impermeable thick clay layer or silty clay layer are usually composed of silty sands or fine sands.When the groundwater in central basin is overexploited, the water level will decrease, and the aquifer will sink to form ground fissure by the gravity of overlying strata.In addition, a small amount of white salts are often found in the Upper Pleistocene silty mudstone that may be the reason for the general saltiness of underground water in this area