扰动诱发高应力卸荷岩体破坏特征实验研究

Experimental study on the failure characteristics of high stress unloading rock mass induced by disturbance

为研究扰动诱发不同中间主应力单面卸荷岩体破坏特征,通过真三轴扰动卸荷测试系统和声发射监测系统,进行了不同中间主应力卸荷实验及卸荷扰动实验,研究了中间主应力对单面卸荷岩石强度特征、演变规律及破裂模式的影响,分析了中间主应力σ_(2)方向扰动作用后卸荷岩石的力学特性。结果表明:在一定范围内,随着中间主应力的增大,卸荷岩石的稳定性和峰值强度都有所增强,但较大的中间主应力会逐渐弱化岩石的承载能力;随着中间主应力的增大,卸荷岩石的开裂模式由张拉-剪切破坏逐渐转变成张拉-劈裂破坏;在σ_(2)≤30 MPa时,声发射信号经历了平静、持续出现伴随小幅突增、陡升高峰、持续低峰、大幅突增破坏;在σ_(2)>30 MPa时,声发射信号经历了平静、持续出现、多低峰、持续升高、突增破坏;不同类型扰动作用后卸荷岩石的破坏差异明显,中频中幅扰动后卸荷面形成明显V型破坏坑,分形维数最大,中频中幅扰动不仅加速了约束力小的卸荷面附近的小裂纹发育成核,同时也加速了远离卸荷面的大裂纹之间的连接贯通;扰动对岩石承载能力的损伤为中频中幅>高频低幅>低频高幅;工程建设时,不能简单增加σ_(2)从而增强围岩承载能力,还要综合考虑σ_(2)的增大会加剧卸荷岩体破坏时的剧烈程度,减少爆破和机械等对围岩的扰动,不能只单一地改变扰动源的频率或振幅。

In order to study the failure characteristics of single-sided unloading rock mass with different intermediate principal stress induced by disturbance,a true triaxial disturbance unloading test system and an acoustic emission monitoring system were used to carry out different intermediate principal stress unloading experiments and unloading disturbance experiments.The influence of principal stress on the strength characteristics,evolution law,and fracture mode of single-sided unloaded rock was analyzed.Furthermore,the mechanical properties of unloaded rock after disturbance inσ_(2) direction were analyzed.The results show that with the increase of the intermediate principal stress,the stability and peak strength of the unloaded rock are enhanced,but a larger one will gradually weaken the rock bearing capacity.With the increase of stress,the cracking mode of unloading rock gradually changes from tension-shear failure to tension-fracturing failure.Besides,atσ_(2)≤30 MPa,the acoustic emission of rock failure experiences calm and continues to appear accompanied by a small sudden increase and a steep rise,continuous low peak,and large sudden increase of damage.Afterσ_(2)>30 MPa,the signal experiences calm,continuous appearance,multiple low peaks,and continuous rising damage.Moreover,the failure of unloaded rocks after different types of disturbances is significantly different.After the medium-frequency and medium-amplitude disturbances,the unloading surface forms obvious V-shaped failure pits,and the fractal dimension of the debris is the largest.Therefore,the mid-frequency and mid-amplitude disturbance not only accelerates the nucleation of small cracks near the unloading surface with small constraining force,but also accelerates the connection between large cracks far away from the unloading surface.The damage of bearing capacity is medium frequency medium amplitude>high frequency low amplitude>low frequency high amplitude.During engineering construction,σ_(2) cannot be simply increased to enhance the surrounding rock bearing capacity.Besides,it must also be considered comprehensively that the increase ofσ_(2) will increase the severity of unloading rock mass failure.To reduce the disturbance of surrounding rock caused by blasting and machinery,the frequency or amplitude of disturbance source cannot be changed alone.