Influence of stress disturbance on the mechanical characteristics of mudstone with different borehole depths

In order to overcome the problems of low core-taking ratio of mudstone, neglect on the influence of stress disturbance and the difficulty of division of stress disturbance in the strength test of surrounding rock of roadway, the theoretical analysis, field measurement and experimental research were carried out in this study.To obtain the strength of mudstone at different depths, the borehole penetration method was used for in-situ measurement.The relationship between the degree of stress disturbance and the critical pressure of the probe was theoretically analyzed based on the concentrated force model on the boundary surface of the borehole penetration method.The variation law of mudstone strength under different drilling depths was studied by in-situ drilling peeking, RQD analysis, laboratory mineral composition and tensile strength analysis, and the stress disturbance partitioning was carried out.The results show that ① the probe generates the active bearing zone, the radiative shear zone and the passive bearing zone under the action of concentrated force.The shallow disturbance of the roadway is large, and the mudstone is prone to "tension-compress" slippage damage.When the zone is in the shallow position of the roadway, the slip becomes easier, the critical pressure of the probe is lower, and the measured mudstone strength is lower.When the passive bearing zone is in the deep position of the roadway, the mudstone is under the compress-compress state to restrain the slip activity, resulting in the increase of probe pressure, and the increase of mudstone mechanical strength.② The locations with low core rate include the location at mudstone and sandy mudstone interbed with weak cementation, and the other location is at the high clay content.③ Using strong short anchor cable technology to increase the strength of roof support and reduce the degree of stress disturbance, the mechanical strength of shallow mudstone increases by 71%-76%.④ With the increase of surface depth from the roadway, the degree of dispersion of the measured compressive strength and the measured tensile strength data in the laboratory are reduced.According to the ratio of the two, the stress full disturbance zone, the partial disturbance zone and the undisturbed zone are divided.The experimental study on the influence of stress disturbance on the mechanical characteristics of mudstone has a reference significance for the conversion of mudstone strength from laboratory to site.