Abstract
Tests of the effects of uniaxial compression on the structural behavior of fractured coals were conducted. The structural behavior is different from the material behavior of intact samples and the discontinuous behavior based on the block theory. It is a macro response of continuous-discontinuous behavior in coal with varied fracture structure geometry, and includes the material behavior with cracking and contact behavior with sliding. The structural behavior is studied based on the complete stress-strain curve, the material parameters, i.e. elastic modulus, Poisson’s ratio, and compression strength, and the structural integrity parameters, i.e. longitudinal and shear wave velocity, and the physical parameter, i.e. density. All the parameters are compared with the different fracture patterns. Various types of parameter degradation damage are defined to describe the structural characteristics with the different fracture patterns. They shows the effective relation of damage with strength. Furthermore, the mechanisms of the structural modulus degradation, structural failure deformation, and structural strength evolution are discussed. The results show that the post-peak behavior can be defined as the structural behavior. With the structural formation-reloading failure cycle, the mutual conversion changes between structural geometry instability and stability, and the characteristics are stress drops or stress platforms generated by structural rebalance. It is pointed out that the post-peak unloading is a macro response of the structural geometry. It includes the recovery of elastic strain and structural resilience strain, and structural stress drop.
Highlights
The fractured or jointed rock nature of excavated coal, the complex composition [1,2] as well as the fracture or crack distribution [3,4,5,6] are all likely to deteriorate its macro- and meso-mechanical behavior
The tension failure and the slippage failure on the fracture surface occurred simultaneously in the main direction dominated fractures (MDF) and simple cross fractures (SCF) coal, which indicates the transition from material to structural failure
Fractured coal samples with various different fracture patterns were prepared for the uniaxial compression test
Summary
The fractured or jointed rock nature of excavated coal, the complex composition [1,2] as well as the fracture or crack distribution [3,4,5,6] are all likely to deteriorate its macro- and meso-mechanical behavior. The structural geometry of crack networks may dominate the macro behavior, which cannot be connected to the intact coal without fractures. Most studies focus separately on the material behavior with cracking or contact behavior by the block theory with sliding. It is important to directly understand the continuous-discontinuous behavior based on the fractured coal nature. Some important work [7,8] is based on the intact coal only [9], without considering the fractured coal. With the evolution of stress fields [10,11], the generation of new fractures will deteriorate the mechanical behavior [12]
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