Experimental Study on Roof Cutting Characteristics and Anchorage Control Mechanism of Gob-side Entry Retaining
Author:Zuo Heng Jie
Supervisor:jiang yu jing
Gob-side entry retaining(GER),which is an important direction for the development of coal mining,can not only significantly improve the efficiency of coal mining,but also effectively control the dynamic disasters,such as coal and gas outburst,rock burst and so on.Currently,the control of surrounding rocks of GER has two aspects of particularity.On the one hand,the high stress concentrates caused by the large-scale suspension which can easily result in the large deformation and failure of the surrounding rocks;it is very important for the stress optimization of surrounding rocks to study the lateral roof-cutting characteristics of the gob-side entry retaining.On the other hand,the roof strata rotate to the gob and it leads to the notable shear-dislocation,and thereby resulting in the instability of the GER;so we study the anchorage effect with shear stress for controlling the stability of surrounding rocks in gob-side entry retaining.Hence,in this paper,the field observations,theoretical analysis,numerical simulation,and laboratory test are used to study the roof cutting characteristics and anchorage control mechanism of gob-side entry retaining.The main study results are as follows:(1)Failure characteristics and control of surrounding rocks of gob-side entry retainingBased on the failure analysis of the surrounding rocks of GER in field,the stability control mechanism of the surrounding rocks is revealed.Moreover,by using the UDEC software,the movement of overlying strata,the deformation and stress distribution of the surrounding rocks caused by roof cutting is simulated,and then control effect and mechanism of surrounding rocks with roof-cutting in gob-side entry retaining are analyzed.Then,the relationship between "roof cutting","roof caving" and "roof support" of gob-side entry retaining is discussed.(2)Effect of joint-cutting length on lateral roof cutting in gob side entry retainingThe effect of joint-cutting length on lateral roof cutting in gob side entry retaining is studied by establishing a roof model of lateral rock in gob-side entry retaining and carrying the shear test with fractured rock block,and the influence of joint-cutting length on the support strength of cutting roof and the failure characteristics of joint-cutting plane is revealed.(3)Effect of joint-cutting roughness on lateral roof slipping in gob side entry retainingConsidering the effect of the roughness of the side roof fracture surface on the caving characteristics of the slit rock beam,based on the shear test of the structural plane with different roughness,the relationship between the cutting effect and the roof slipping is quantitatively studied,and the roughness effect of the joint-cutting plane on the lateral roof-slipping is revealed.(4)Shear characteristics of surrounding rocks with heterosexual plane in gob-side entry retainingThe relationship between the shear failure of the roof and the stability of the surrounding rocks is analyzed;and the shear characteristics and failure mechanism of roof with the heterosexual plane and sandwich structure plane are obtained through the shear tests.The internal mechanism of shear dislocation and separation of roof in gob side entry retaining is revealed.(5)Anchorage effect of surrounding rocks with heterosexual plane of gob-side entry retainingConsidering the effect of the heterosexual plane on the shear characteristics of the anchorage system,the anchorage effect of the roof is revealed according to the shear tests and numerical simulation.It is pointed out that the anchorage support will cause damage to the anchorage system and the effect of anchorage system on shear capacity is not significant with the low strength of any side of the rock.