前伏不同角度富水溶洞下节理隧道最小防突层厚度研究

Study on minimum anti-outburst layer thickness of joint tunnel with forward water-rich karst cave at different angles

为研究前伏不同角度富水溶洞下节理隧道最小防突层厚度,基于断裂力学和弹性力学理论,分析节理裂隙在开挖扰动和岩溶水压共同作用下的扩展起裂机理,建立隧道围岩节理翼裂纹扩展模型,将防突层厚度分为扰动带厚度和节理带厚度,提出含节理隧道掌子面最小防突层厚度计算方法;根据算例分析不同方位溶洞下节理长度、节理倾角、掌子面开挖大小等参数对最小防突层厚度的影响规律。结果表明:掌子面最小防突层厚度随溶洞方位角增大先增大后减小,在方位角为30°时出现峰值;防突层厚度受节理几何特征影响明显,防突层厚度随节理长度增大而增大,防突层厚度随节理倾角增大先增大,在达到峰值厚度后开始减小;溶洞方位角超过25°时,开挖半径对最小防突层厚度影响显著。该结论对岩溶地区的节理隧道开挖安全施工具有参考意义。

In order to study the minimum anti-outburst layer thickness of joint tunnel with forward water-rich karst cave at different angles,based on the theory of fracture mechanics and elastic mechanics,the mechanism of joint crack propagation and initiation under the combined action of excavation disturbance and karst water pressure was analyzed.A crack propagation model for the joint wing of tunnel surrounding rock was established,and the thickness of anti-outburst layer was divided into the thickness of disturbance zone and the thickness of joint zone,then a calculation method of the minimum anti-outburst layer thickness on the heading face of joint tunnel was proposed.According to the calculation example,the influence of joint length,joint dip angle and excavation size of heading face on the minimum thickness of anti-outburst layer under different orientations of karst cave was analyzed.The results showed that the minimum thickness of anti-outburst layer on the heading face increased first and then decreased with the increase of azimuth angle of karst cave,and the peak value appeared when the azimuth angle was 30°.The thickness of anti-outburst layer was obviously affected by the geometric characteristics of the joint.The thickness of anti-outburst layer increased with the increase of joint length,and it first increases with the increase of the joint inclination,and then begins to decrease after reaching the peak thickness.When the azimuth angle of karst cave exceeded 25°,the effect of excavation radius on the minimum anti-outburst layer thickness was significant.The conclusion has reference significance for the safe construction of joint tunnel in karst area.