不同钻孔深度下应力扰动对泥岩力学特性的影响

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

针对巷道围岩强度测试中泥岩取芯率低、常忽略应力扰动影响和应力扰动分区困难的3个问题,开展了理论分析、现场实测、试验研究。为获得不同深度处泥岩强度,采用钻孔触探法进行原位测定。基于钻孔触探法边界面上受集中力模型,理论分析应力扰动程度与探针临界压力的关系,结合钻孔窥视、RQD、实验室矿物成分、单轴抗拉强度等分析手段,对比研究了不同钻孔深度下泥岩强度变化规律,并进行了应力扰动分区。结果表明:①探针在集中力作用下产生主动承载区、辐射剪切区、被动承载区,巷道浅部扰动程度较大,泥岩容易出现“拉-压”滑移破坏。当被动承载区处于巷道浅部位置时,滑移变得更为容易,探针临界压力较低,导致所测泥岩强度偏低;当被动承载区处于巷道深部位置时,泥岩处于“压-压”受力状态抑制滑移活动,探针压力增加,泥岩力学强度增加。②泥岩取芯率低的位置,一处为泥岩与砂质泥岩互层且胶结性较弱位置,另一处为黏土含量高且厚度较大位置。③采用强力短锚索技术,增加顶板支护强度,减少应力扰动程度,浅部泥岩力学强度增加了71%~76%。④随着距巷道表面深度的增加,现场所测抗压强度和实验室所测抗拉强度数据离散程度均减少,根据二者比值关系,划分了应力充分扰动区、部分扰动区、未扰动区。实验研究应力扰动对泥岩力学特征的影响,对于泥岩从实验室到现场强度换算具有重要参考意义。

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 that①the 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.②The 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.③Using 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%.④With 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.