Experimental Investigation And Numerical Simulation On Quicksand Through Caving Rock Mass Based On Granular Flow Theory

In this paper the special geological conditions of shallow buried depth and thin bedrock in the Yuyang-Shenmu-Fugu mining area is selected as the prototype. The engineering geological model of quicksand in caving zone broken rock mass is generalized. The basic factors that affect quicksand have been identified. The granular flow in fractured rock mass is studied by using a designed quicksand device model. The equation of quicksand movement is summarized. By means of numerical simulation, the specific internal characteristics of quicksand are revealed. The main conclusions are as follows:(1) This paper introduces the regional overview, stratigraphic conditions,engineering geological conditions and hydrogeological conditions of the mining area in Northern Shaanxi Province. It is concluded that the main factors of the occurrence of quicksand disaster are broken rock mass fractures channels and loose aeolian sand layer. Main type of quicksand in the Yuyang-Shenmu-Fugu mining area is quicksand though caving zone. The quicksand channels are the broken rock mass cracks and fractures. The source material is the overlying loose aeolian sand layer.(2) Based on the model of self-designed interior quicksand device, the size of particle, the thickness of the loose layer, the size of the broken rock mass and the height of the caving zone were selected as quicksand factors to design tests. The results show that particles are in a static equilibrium state in cylinder at a certain height and sand falls uniformly; the effect of sand layer thickness on quicksand speed is not obvious. The caving zone rock block has a blocking effect on the quicksand. Along with the increase of the rock block layers, the quicksand velocity presents a decreasing trend. The relationship between rock block layers and quicksand velocity meets the regression equation which is inverse proportion function. The spherical rock stress distribution and distribution of particles blocked effect of quicksand channels are given. Through the analysis of variance, it is concluded that the diameter of the rock mass and the size of the particles have a significant influence on quicksand, and the former is more significant. The ratio between the 3 power of the rock diameter and the 1 power of the particle size is a comprehensive index. With the comprehensive index changes, quicksand velocity presents logarithmic functional relation that the base is greater than 1. Finally, theregression equation of quicksand velocity with the size of particle, the diameter of the rock mass and the number of rock block layers in the caving zone is given.(3)Numerical simulations show that quicksand experiences four movement stages of compaction, uniform fall, turbulent flow and free fall. In the first phase, the quicksand firstly accelerates its speed and then slow down, velocity curve is shown as "V" type. In the second phase, the velocity curve is slightly vibrating at a certain frequency, keeping straight overall. In the third phase, the velocity curve has a large vibration and velocity changes turbulently. When the particles pass through the channals, quicksand velocity increase from top to bottom layer by layer in form of“multi arch” upper area of the channel. The high-speed particles momently experience collision, deceleration, dispersion, and velocity down with a large number of zero velocity fragmented regions after they are blocked by the next layer rock block. Particles show turbulence. The upward face of rock mass meets the maximum density of force and the side face accepts less force. Stress profile presents fan-shaped. The inernal force of paticles is deflected near the channals port,and the flow particles are blocked by the form of the arched force chain.