Analysis and Application of the Mechanical Properties of the Karst Collapse Column Fillings

Abstract

The filling material of the karst collapse column (KCC) is easy to be activated by mining. During this process, the mechanical properties of KCC fillings change, and its water resisting capacity constantly deteriorates and thus often leads to water inrush disaster. In this study, the samples of KCC fillings were taken on-site and then were remolded by the consolidation drainage method. The variation laws of the compressive strength, tensile strength, cohesive stress, internal friction angle, and permeability of the filling samples with respect to the consolidation pressure and moisture content were tested and analyzed. Based on an engineering example, the yield and activation and particle loss of the filling material of the KCC are analyzed. A mechanism for the lagging water inrush of KCC in the process of mining is proposed. The main results of the present study can be concluded concisely as follows. (1) The KCC fillings show obvious soft rock characteristics in the process of uniaxial compression and Brazilian split. The ratio of the uniaxial compressive strength to splitting tensile strength is between 12 : 1 and 8 : 1. The larger the consolidation pressure or the smaller the moisture content, the larger the ratio. (2) With the increase of consolidation pressure or the decrease of moisture content, the uniaxial compressive strength, elastic modulus, splitting tensile strength, cohesive stress, and internal friction angle of the filling material of the KCC increase linearly, while its permeability increases exponentially. (3) When the crack field of the surrounding rocks of the stope is connected with the KCC, its filling material will continue to yield, activate, and migrate under the fluid-solid coupling effect and finally result in the lagging water inrush from the KCC.

Mechanism Analysis of Delayed Water Inrush from Karst Collapse Column during Roadway Excavation Based on Seepage Transition Theory: A Case Study in PanEr Coal Mine

“…The gradual development process of water inrush was analyzed from the aspect of fluid-solid coupling through numerical simulation. Due to the influence of high-pressure water seepage and scouring in the rock mass of collapse column, the cracks in the rock mass expanded and the filling materials dissolved until all the cracks were connected [28,29]. Meanwhile, the flow of water inrush was transformed from pore flow to fracture flow, and finally to pipeline flow, which was manifested in a gradual increase in water inrush with a certain lag.…”

Numerical Simulation of Karst Collapse in Qingling Town, Wuhan

“…This model is based on Pu's equilibrium arch theory, the theory of beam and slab force, and equilibrium in Material Mechanics and Elastic Mechanics. The coupling model of the seepage field-stress field is based on the consolidation theory of Terzaghi [1]. The non-coupling model is based on the constitutive relation of rock and soil of Elastic Mechanics.…”

Rock response characteristics in the area of the hidden collapse column induced by mining

“…Feng et al (2018) used self-designed equipment to measure the permeability coefficients of fractured rock and clarified the mechanism of water inrush in the fracture zone of the collapse column. Lin et al (2021) used the consolidation drainage method to remodel karst collapse columns and studied the variation in compressive strength, tensile strength, cohesive force, internal friction angle and permeability with consolidation pressure and water content and proposed the mechanism of hysteresis water inrush in karst collapse columns during the mining process. Zuo et al (2019) established a slip and bending fracture model for collapse columns based on the theory of elastic thin plates and clarified the critical conditions for destabilization of the top floor.…”

“…Unrevealed small hidden collapse columns are difficult to predict and pose a serious threat to the safety of coal mine production (Wang et al, 2014). The rock structure is so complex that theoretical analysis of the rock structure in underground engineering is almost impossible or overly simplified and imprecise (Yang et al, 2007). Numerical simulation has become a powerful analytical calculator and universal material testing machine for underground engineering because of its adaptability to complex conditions and its "memory" function with stress-strain history (Wang and Zhuang, 2018; Kong and Wang, 2018).…”