Macroscopic Deformation/failure Caused By Mining Of Hard Soil Under Reservoir And Application

In coal mine, a huge layer of hard soil that cut off the upper aquifers and lower mining areas is always emphasized as the key aquifuge. This hard soil layer are make up of Quaternary and Neogene soil, which all have some properties that rock and soil have. It was careful protected during mining according to its deformation/failure characteristics.This paper Basing on the geological prototype of unconsolidated formations and thin bedrocks under reservoir of Quandian coal mine in Henan province, the geological, hydrogeological and engineering geological conditions of study area are analyzed. Discrimination、classification and engineering geological properties of hard soil are also analyzed. Bedrock thickness 、 caving thickness and hard soil lithologic are selected to establish orthogonal test table to conduct simulation experiment. Macroscopic deformation failure is summarized, and mechanism is also analyzed. At the same time, hydrolysis and conductivity experiment of hard soil are conducted, and different characteristics of water stability and stages of water-soil interaction are got. Basing on clay content 、stucture and clay mineral content, the mechanism is analyzed. The main conclusions are shown as follows.(1) Macroscopic deformation failure and mechanism is summarized by experiment. 9 engineering geological simulation experiments are conducted basing on different bedrock thickness、caving thickness and hard soil lithologic. It can be got that the deformation failure of hard soil is similar to bedrock. Horizontal and vertical cracks will appear in mining and deformation failure expression is an arch, which includes 4 stages. Shaly hard soil’s plasticity is high to formate beam(plate) more easily, and sandy hard soil is relatively loose to fail more easily. Their properties of deformation failure are different. The important order of relevant factors is bedrock thickness、caving thickness and hard soil lithologic. The equation can be got. The deformation failure and mechanism of hard soil are explained by pressure-balanced arch, and mechanical model of pressure-balanced arch is also established.(2) Water stability and difference are analyzed by experiment. It can be summarized 3 water stability types: non-disintegration after soaking with water Ⅰ,weak disintegration Ⅱ, strong disintegration Ⅲ. From conductivity test, it can be taken that absolute increment of conductivity and TDS variates consistent with time regularly. And it can be divided into three stages, in the first ten minutes waswater-soil interaction quickly(Ⅰ), 10 ~ 120 min for medium speed section(Ⅱ), 120 ~1440 min was slow(Ⅲ). The mechanism of different water stability is analyzed from clay content 、stucture and clay mineral content. It can be obtained that the higher the clay content, the better the water stability and the weaker the disintegration; the more the fracture, the weaker the water stability and the better the disintegration; the higher content of montmorillonite, kaolinite and illite, the weaker the water stability characteristics and the better the disintegration.(3) Basing on macroscopic deformation failure and water stability of hard soil under reservoir, feasibility of mining is studied in study area.