Abstract
We study the structural instability mechanism and effect of a multi-echelon support in very-deep roadways. We conduct a scale model test for analysing the structural failure mechanism and the effect of multi-echelon support of roadways under high horizontal stress. Mechanical bearing structures are classified according to their secondary stress distribution and the strength degradation of the surrounding rock after roadway excavation. A new method is proposed by partitioning the mechanical bearing structure of the surrounding rock into weak, key and main coupling bearing stratums. In the surrounding rock, the main bearing stratum is the plastic reshaping and flowing area. The weak bearing stratum is the peeling layer or the caving part. And the key bearing stratum is the shearing and yielding area. The structural fracture mechanism of roadways is considered in analysing the bearing structure instability of the surrounding rock, and multi-echelon support that considers the structural characteristics of roadway bearings is proposed. Results of the experimental study indicate that horizontal pressure seriously influences the stability of the surrounding rock, as indicated by extension of the weak bearing area and the transfer of the main and key bearing zones. The falling roof, rib spalling, and floor heave indicate the decline of the bearing capacity of surrounding rock, thereby causing roadway structural instability. Multi-echelon support is proposed according to the mechanical bearing structure of the surrounding rock without support. The redesigned support can reduce the scope of the weak bearing area and limit the transfer of the main and key bearing areas. Consequently, kilometre-deep roadway disasters, such as wedge roof caving, floor heave, and rib spalling, can be avoided to a certain degree, and plastic flow in the surrounding rock is relieved. The adverse effect of horizontal stress on the vault, spandrel and arch foot decreases. The stability of the soft rock surrounding the roadways is maintained.
Highlights
The gradual development of the Chinese mining industry has entered the kilometre-deep mining stage
Scholars employ classical elastic–plastic mechanics on surrounding rock to analyse the instability of shallow roadways
The instability of deep roadways often results from the structural fracture [8], which cannot be sufficiently explained in the light of the classical elastic–plastic mechanical analysis method for surrounding rock [9]
Summary
The gradual development of the Chinese mining industry has entered the kilometre-deep mining stage. Scholars employ classical elastic–plastic mechanics on surrounding rock to analyse the instability of shallow roadways. The instability of deep roadways often results from the structural fracture [8], which cannot be sufficiently explained in the light of the classical elastic–plastic mechanical analysis method for surrounding rock [9]. Whether by means of theoretic deducing or experimentation, the above-mentioned researchers all believe that it is necessary to partition a roadway into different bearing stratums but they are different only in partition methods and rationale They have failed to consider factors such as non-uniform stress field, shear failure, and the relationship between mechanical bearing structure and quantitative support design of the surrounding rock. The effect of the proposed multi-echelon support on the stability of deep excavation roadways is determined by examining the rupture degree of rock and surveying the loose circle by in-situ and numerical simulation
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