Abstract
A mixture of fault gouge and rubble taken out from a fault zone is used to prepare a S-RM (Soil-Rock Mixture) sample with rock block proportions of 20%, 30%, 40%, 50%, 60% and 70%, respectively. A GDS triaxial test system is used accordingly to measure the seepage characteristics of such samples under different loading and unloading confining pressures in order to determine the variation law of the permeability coefficient. The test results show that: (1) The permeability coefficient of the S-RM samples decreases as the pressure increases, and the decrease rate of this coefficient in the initial stage of confining pressure loading is obviously higher than in the semi-late period; (2) The permeability coefficient at different confining pressure levels presents a common trend as the rock block proportion is increased, i.e., it decreases first then it increases (the permeability coefficient of the sample with rock block proportion 40% being the smallest, 70% the largest); (3) In the stage of confining pressure unloading, the recovery degree of the permeability coefficient grows with the increase of rock block proportion (the recovery rate of S-RM sample with rock block proportion 70% reaches 50.2%); (4) In the stage of confining pressure loading and unloading, the sensitivity of the permeability coefficient to the rock block proportion displays the inverse “Z” variation rule (when rock block proportion reaches 60%, the sensitivity is highest); (5) In the stage of confining pressure loading, the relationship between the permeability coefficient and confining pressure can be described by an exponential relationship.
Highlights
Among the water inrush accidents in mine roadway and stope, the water inrush accidents caused by faults account for 41% and 45%, respectively [1–3], it can be seen that the water inrush in fault fracture zone has a very serious impact on mine safety mining [4–6]
Through field investigation and research, it is found that continuous mixture of fault breccia and fault gouge with different thickness is developed in most fault fracture zones, which makes the seepage characteristics of faults basically depend on the seepage characteristics of soil-rock mixture in fault fracture zones [7–10]
When the rock block proportion continues to increase from 40% (40%–70%), the block stone in the soil-rock mixture sample gradually transits to the dominant position, the main seepage channel of the sample is surrounded by the block stone, with large porosity, and forms a large permeability drop at the soil-rock interface, resulting in the permeability coefficient of soil-rock mixture rose rapidly
Summary
Among the water inrush accidents in mine roadway and stope, the water inrush accidents caused by faults account for 41% and 45%, respectively [1–3], it can be seen that the water inrush in fault fracture zone has a very serious impact on mine safety mining [4–6]. Zhou et al [24] carried out permeability test with self-made constant head permeameter to study the effects of gravel content, pore ratio and particle shape on the permeability coefficient of soil-rock mixture at different levels. The soil-rock mixture in the fault fracture zone is a mixture of clay like fine mineral particles (fault gouge) and rock breccia filled in the fault fracture zone or between the two walls of the fault [28] formed by crushing, repeated grinding and underground circulating diffusion solution during fault dislocation, it has high compactness and permeability and is the main place for seepage and disaster of mine water, there are few reports on its seepage characteristics. The soil samples taken from the fault fracture zone are made into soil-rock mixture plastic samples with different rock block proportion, and the permeability coefficient under different confining pressure levels is measured by GDS triaxial test system to study the stress seepage coupling characteristics of soil-rock mixture in the fault fracture zone
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