Field measurement study of the relation between mining pressure and axial boltload

Using non-destructive testing technique for axial bolt load,large amounts of field measurements have been performed on the variation of the axial bolt load with mining advance in mining disturbancezones of a working face. It was found that an obvious correspondence between the variation of axial bolt load and the abutment pressure distribu- tion in front of theface exist. Given a mine in Shanxi Province as an example,the measured data of axial bolt load in the belt entry of the face show that axial bolt load varies considerably in the zone from 0 to 20 m before the working face owing to heave mining disturbance. Within the zone of 5 m before the face,a releasing area of the abutment pres- sure exists and the axial bolt load drops. The abutment pressure is concentrated in the zone from about 5 m to 20 m in front of the faceand theaxial bolt load increases correspondingly;moreover,the bolts’ peak-load is located at about 10 m from the face. In the zone of about 20 m far away from the face,the abutment pressure keeps stably and theaxial bolt load is not likely to change quickly. After the failure of main roof,the axial load of roof bolts decreases considera- bly in the releasing area of the abutment pressure,meanwhile the peak value of the axial bolt load declines violently and its location leaps forwards. The research results demonstrate that the variation of the axial bolt load and the abutment pressure distribution are in good correspondence,meanwhile the failure of main roof can be effectively reflected on the dynamic response of theaxial bolt load.