Study On Deformation And Failure Of Rock Surrounding Shallow Goaf Under Water And Dynamic Loads

With the rapid development of economy, the traffic infrastructure construction is increasing, many local railways, highways are inevitable to go through goaf. Therefore, the effect of dynamic loads on deformation and failure of goaf is researched for providing a reliable basis to stability evaluation and project management, the research has also significant to ensure the safe operation of the railway in the design period. In this paper, laboratory experiments, theoretical analysis and numerical simulation method are adopted, then the effect of water and dynamic train load on deformation and failure of goaf are studied. The main content and results are given in the following:(1) Deformation and failure evolution process of mine strata in shallow coal goaf and characteristics of relatively stable state are observed by simulation experiment of similar material. The final mined strata is basically divided into’two belts", i.e. caving zone and fracture zone. In order to eliminate the "re-activation" of caving zone, semi filling and grouting treatment method for goaf is proposed. The strength of goaf is determined by the slurry mixing experiment, and the failure modes of concrete pile body and the instability conditions of falling rock cemented are analyzed by combining with the structure characteristics of slurry cementing.(2) The test of mechanical properties of rock specimen indicates that the compressive and shear strength of rock is decreased with the increase of water content, but the degree of influence is different for different type rock, actually, little effect on the strength of hard rock, and larger effect on weak rock. The relationship between elastic modulus and water content is deduced by combining with the test and formula of relationship between elastic modulus and compressive strength of concrete. The rock density, damping ratio and damping coefficients are function of water content, and formula of relationship between them and water content can be deduced by linear fitting method for measured values.(3) The roof strata of area mined out and pile body are selected as a system, and the mechanical model is established and analyzed. According to the function of physical parameters of rock and water content, the total potential energy function of the goaf with the action of water is deduced. Then the sufficient mechanics condition of system catastrophe is given by using the cusp catastrophe theory, and the effect of damage failure mechanism and stability is analyzed.(4) The coupling dynamic model of train-pathway-subgrade is established for considering that goaf be affected easily by water and surface train load. The overlying strata of shallow goaf and running train are modeled by ANSYS software, and the dynamic equations are solved by the transient solver. The effect of vertical displacement for surface of goaf is analyzed under the condition of different span and water content, the effect of vertical displacement of strata for the vertical profiles in middle of goaf and the stress and strain of rock surrounding goaf are also analyzed for the same conditions.