白鹤滩水电站左岸坝基边坡柱状节理玄武岩出露且易松弛，对边坡安全稳定影响较大。为了解坝基柱状 节理玄武岩在爆破开挖后松弛深度的变化规律及发展趋势，以坝基650～660ｍ高程边坡柱状节理试验区为研究对 象，利用声波孔检测不同区域、不同支护条件下岩体松弛深度。通过分析检测成果得出如下结论：地质条件对柱状 节理玄武岩的松弛深度有影响；预应力锚杆在一定时间内能压密松弛岩体，其防松弛作用好于砂浆锚杆。

The mechanisms and mechanical processes of water bursts caused by tensile-shear failure and compression-shear failure of fractures in karst tunnel construction are analyzed according to the hydraulic fracturing principle. Results show that the critical hydraulic pressure of water burst is affected by trend and location of fractures and other factors. Through analyzing the distribution characteristics and gradient of water pressure in the process of fracture propagation, the critical water pressure of tensile-shear failure is revealed greater than that of compression-shear failure. And the crack extension is discontinuous under the action of hydraulic fracturing. The research results are of significance for the prevention and treatment of water burst in the process of tunnel construction.