Experimental study on mechanical behavior of roof-coal pillar structure body under different loading rates

In order to study the mechanical behavior of roof-coal pillar structure body under different loading rates,the uniaxial compression tests with different loading rates were carried out on the sandstone roof -coal pillar structure bodies. Also the acoustic emission (AE) monitoring technique,digital video camera system and scanning electron mi- croscope were used to investigate the effects of loading rate on the mechanical behavior of roof-coal pillar structure body. The results show that with the decrease of the loading rate,the macro-failure initiation strength,uniaxial com- pressive strength and elastic modulus of the structure body integrally decrease. However,both the uniaxial compressive strength and elastic modulus show an increasing trend at the loading rate of 1×10-5 mm / s. Moreover,when the horizon- tal additional stress produced by native defects in coal body is larger than the tensile strength of coal body,the macro- failure initiation of the structure body will occur. And the macro-failure initiations under different loading rates all oc- cur in the coal body as the forms of tension crack combined with partial ejection or spalling of varying degrees. Additionally,the failures of structure bodies mainly occur in the coal body and no obvious damage is observed for roof sand- stone. And the splitting ejection failure mainly occurs in the coal body. At a high loading rate,the elastic energy stored in the entity bearing structure of the coal body will be rapidly released through the macro-tensile crack as a releasing channel. Thus,the failure under a high loading rate is sudden and violent. The rebound deformation of roof sandstone is also severe. The coal becomes more broken than that at a low loading rate. Finally,the fracture surface of the structure body under a high loading rate is irregularity with a lacerated shape. The fracture surface becomes smooth with the de- crease of loading rate. An obvious saw tooth region is found in the fracture surface under a low loading rate. The occlu- sal frictions of steps in the saw tooth region resist the failure of the structure body in a certain extent and the structure body shows a relative ductile failure.