三轴压缩下锚固岩石−砂浆结构面力学特性与强度预测模型

Mechanical properties and strength prediction model of anchored rock-mortar structural plane under triaxial compression

  • 摘要: 矿山锚喷支护的岩壁−混凝土喷层是一种典型的岩石−砂浆加锚异性结构面,为了探究锚喷支护的岩壁−喷层界面的力学行为,开展了三轴压缩下岩石−砂浆无锚与加锚异性结构面试件力学特性试验研究。采用MTS 815岩石力学试验系统进行了三轴压缩下岩石−砂浆无锚与加锚异性结构面试件力学特性研究,试验围压为10、15、20、25 MPa这4个系列,岩石−砂浆异性结构面设置为等腰三角形锯齿状,起伏角为30°、45°及60°。分析了锚杆锚固及围压对岩石−砂浆异性结构面力学特性及破坏模式的影响,同时对压缩试验过程中的声发射信号进行监测,并对破裂后结构面进行三维形貌扫描,最后建立了加锚倾斜异性结构面岩石的抗压强度预测模型。结果表明:岩石−砂浆异性结构面试件的峰值强度随围压以及结构面起伏角度的增加而增加,砂浆基体主导了岩石−砂浆无锚异性结构面试件的偏应力−应变曲线的走势。加锚后岩石−砂浆异性结构面试件的峰值强度提升明显,且试件承受塑性变形的能力大幅提升,在试件发生破裂后依旧能承受较大应力,偏应力−应变曲线呈现双峰值特性。对比加锚前后的岩石−砂浆异性结构面试件的破坏模式,发现无锚试件沿异性结构面剪切滑移破坏,在锚固后试件呈现“X”状共轭剪切破坏。对比加锚前后的岩石−砂浆异性结构面试件在三轴压缩下的声发射特性,发现试件锚固后的声发射信号在加载前期较稀疏,但在试件发生宏观破裂后振铃计数信号更密集,这代表锚固后在试件发生宏观破裂前锚杆很好地限制了试件内部微小裂隙的产生,在发生宏观破裂后锚杆更好地使结构面本身性能得到发挥。在对破裂后结构面进行三维形貌扫描后,发现岩石结构面磨损小于砂浆结构面,锚固后结构面磨损程度减小。将试验结果与强度预测模型结果对比,在不同结构面粗糙度下,其预测强度平均误差为6.64%,验证了预测模型的可靠性。

     

    Abstract: The rock wall-concrete shotcrete layer, which is supported by anchor and shotcrete in a mining environment, represents a typical example of an anisotropic structural plane anchored by rock mortar. The objective of this study is to investigate the mechanical behaviour of the rock wall-spray layer interface supported by bolting and shotcreting. To this end, the findings of an experimental study on the mechanical properties of rock-mortar non-anchor and anchored anisotropic structural plane specimens under triaxial compression are presented herein. The mechanical properties of rock-mortar unanchored and anchored anisotropic structural plane specimens under triaxial compression were investigated utilising the MTS 815 rock mechanics test system. The confining pressure of the test was set at 10, 15, 20 and 25 MPa. The rock-mortar anisotropic structural plane is defined as an isosceles triangular serrated surface. The undulating angles are 30°, 45°, and 60°. This study analyses the influence of bolt anchorage and confining pressure on the mechanical properties and failure mode of rock-mortar structural planes. Additionally, the acoustic emission signal in the compression test process is analysed. Subsequently, the three-dimensional morphology of the structural plane following fracture is scanned. Finally, the compressive strength prediction model of rock with anchored inclined anisotropic structural plane is established. The findings indicate that the peak strength of rock-mortar anisotropic structural plane specimens exhibits an increase with the rise in confining pressure and undulation angle of the structural plane. The mortar matrix exerts a dominant influence on the trend observed in the deviatoric stress-strain curve of rock-mortar non-anchor anisotropic structural plane specimens. Following the anchoring process, the peak strength of the rock-mortar anisotropic structural plane specimen is demonstrably enhanced, accompanied by a notable increase in the specimen’s capacity to withstand plastic deformation. Following the fracture of the specimen, it was observed that the material was still capable of withstanding significant stress. Additionally, the deviatoric stress-strain curve exhibited double-peak characteristics. A comparative analysis of the failure modes exhibited by rock-mortar anisotropic structural plane specimens, both before and after anchoring, reveals that the unanchored specimens display shear slip failure along the anisotropic structural plane. Conversely, specimens that have been anchored demonstrate “X”-shaped conjugate shear failure. Comparing the acoustic emission characteristics of rock-mortar anisotropic structural plane specimens before and after anchoring under triaxial compression, it is found that the acoustic emission signal of the specimen after anchoring is sparse in the early stage of loading, but the ringing count signal is more intensive after the macroscopic fracture of the specimen, which means that the bolt after anchoring is very good before the macroscopic fracture of the specimen, which limits the generation of small cracks inside the specimen. After the macroscopic fracture, the bolt better exerts the performance of the structural plane itself. Three-dimensional morphological scanning of the structural plane following fracture revealed that the degree of wear on the rock structural plane was less than that observed on the mortar structural plane. Furthermore, the degree of wear on the structural plane was found to decrease following anchoring. Comparing the test results with the strength prediction model results, the average error of the predicted strength under different structural surface roughness is 6.64%, which verifies the reliability of the prediction model.

     

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