Earth Fissure Formation Mechanism Under The The Role Of Water And Its Numerical Simulation

It is accepted that water is the most important factor to the formation and development of the ground fissures. But the specific mechanism is a controversial question. The reasons are the complex mechanism of water-soil action and different geological environmental conditions. It has important scientific significance and social value to carry out the research on the comprehensive formation mechanism of the ground fissures by the action of water.In this paper, the main works done are as follows. Firstly, the types and modes of water-soil action are studied. Formation mechanism of the flow of soil material and the changes of physico-mechanical properties and geological environment are summaried. Secondly, formation mechanism of the ground fissures under the role of water is researched by theoretical analysis and numerical simulation. Thirdly, through analysizing the ground fissures in xi’an city and shuanghuaishu village of sanyuan, the validity of theoretical mode is verified. And some traditional understandings are explained scientificly.The main work and innovative results are as follows:(1) Based on the theory of random medium, the ground fissures caused by extractive are studied. The results show that the crush zone would be formed in settlement central area and the tension zone would be formed in settlement fringe area owing to extractive function. The strain of tension area in the biggest curvature change of the subsidence funnel reaches the maximum value, so the tension-cracks are developed from top to bottom.(2) Based on the theory of Mohr-Coulmb considering the accidentally stress, the ground fissures caused by extractive are studied. The results show that different subsidence produced under the action of extractive would generate additional couple stress role in the soil mass unit. The role makes the unit stress present the asymmetric feature and causes the Mohr-round to deflect. The possibility of soil shear failure is increased and the shear-cracks are developed.(3) Based on the theory of damage of weak surface and plastic sliding, activities of the ground fissures are researched firstly. The results show that the ground fissures developed on the basis of early fractures are very easy to damage again and to slide along the fracture surface under the action of extractive and other disturbing forces, because the ability of weak surface to resistant deformation and failure is poor. The effect is the main factor to the formation and development of the ground fissures developed on the basis of early fractures in xi’an city.(4) Through the establishment of numerical calculation model considering water-soil coupling and the prior fracture, the author simulates the development of single fissure under the action of extractive and analyzes the sensitivity of influence factors. The results show that the prior fracture has effect of induction, isolation and enlargement. And the parameters of ground fissures, such as internal friction angle and dip angle, are sensitive strongly to the activities of the ground fissures.(5) Through the analysis of hydrology, geology, geomorphic conditions of the ground fissure in jitai village of xi’an city, the author establishes a fine calculation model including two ground fissures.The calculation results are in good agreement with the actual. Model calculation verifies many problems and some new understandings are achieved:①The activities of ground fissures in xi’an city are relate to extractive directly. But the main activities are the damagement of weak surface and slippage effect under the control of subjacent faults. Descend funnel by extractive and different subsidence caused by stratigraphic differences are just the minor factors.②Ridge-depression physiognomy in xi’an has certain effection to the development of ground fissures. The big relative elevation of ridge-depression physiognomy develops quickerly in advance, but they have little difference in the total magnitudes.(6) The formation mechanism of ground fissures by the action of superficial water includes failure mechanism caused by collapse of loess, failure mechanism caused by erosion and corrosion, failure mechanism caused by hydraulic pressure, failure mechanism caused by water loss shrinkage, and so on. Through analysizing the ground fissures in shuanghuaishu village of sanyuan caused by rainstorm, the results show that the ground fissures caused by the comprehensive function of fracturing effect, scouring effect, drag traction effect during rainstorm under preponderant controlling role of concealed ground fissures, incuding water-blocking and water-interception role, permeability and strong seepage role.