Variation Characteristics of Mass-Loss Rate in Dynamic Seepage System of the Broken Rocks

Luzhen Wang,Hailing Kong

doi:10.1155/2018/7137601

Abstract

When the collapse column and its adjacent rocks in complex geological structures are disturbed by mining, concomitant fine particle migration, mass loss, and porous structure variation during the water seepage process in broken rocks are the inherent causes for collapse column activation and water inrush. Studying the time-varying characteristics of the mass-loss rate in the dynamic seepage system of the broken rocks is of theoretical importance for the prevention of water inrush from the collapse columns. In this study, the seepage tests of the broken mudstone were carried out using the patented pumping station seepage method, and the time-varying function of the mass-loss rate was generalized. Then, the optimal coefficients in the function of mass-loss rate were computed using the genetic algorithm. At last, the mass-loss rate in the dynamic seepage system of the broken rocks with consideration of the acceleration factor was calculated using Lagrange discrete element method. The results showed that (1) the mass-loss rate was expressed as a time-dependent, exponential function with its coefficient related to the porosity, and its time-varying characteristics were affected by gradation; (2) the time-varying curves with Talbol power exponents less than 0.6 had a rapid change stage and a slow change stage, while the time-varying curves with Talbol power exponents greater than 0.6 had an initial gradual change stage, a rapid change stage and a slow change stage; (3) at the early seepage stage, the mass-loss rate decreased with Talbol power exponent increasing; and (4) after long time seepage, the mass-loss rate was close to zero and unrelated to Talbol power exponent, and the porous structure in broken rocks remained stable with its porosity close to a certain stable value.

Highlights

At present, China is still a country with coal as its major energy source
Taking widely developed collapse columns in the North China coalfield as an example, they are broken rocks with variable porous and fracture structures formed by mixing various broken rock fragments of different sizes, cementing together through muddy and siliceous thin layers on their surfaces and compacting under the selfgravity of collapse columns or ground pressure [4]
The collapse column is widely developed in the North China, which has the characteristic of a complex geological structure

Summary

Introduction

China is still a country with coal as its major energy source. With the gradual exhaustion of its shallow resources, deep excavation of coal resources has become the norm with the mining depth of individual coal mines of down to 1500 m [1]. Deep coal seams are characteristic of a very complex geological structure, such as faults and collapse columns. Their mining is often accompanied with severe water inrush, bringing serious threats to the safe production of coal mines [2, 3]. Taking widely developed collapse columns in the North China coalfield as an example, they are broken rocks with variable porous and fracture structures formed by mixing various broken rock fragments of different sizes, cementing together through muddy and siliceous thin layers on their surfaces and compacting under the selfgravity of collapse columns or ground pressure [4]. Internal pores and fractures of rocks develop and expand, leading to changes in the stress field and the seepage field inside themselves and their adjacent rocks, subsequently, evident alteration of the network of cracks in the confined rocks and the porous structure of the broken rocks, and the formation of water seepage passages

Methods

Results

Conclusion