Study on the theory and methods of bolt-shotcrete support for weak surrounding rock based on reliability analysis

The evaluation of stability and reliability of support system for tunnel weak surrounding rock are difficult issues of concern in rock and soil engineering. Aiming at the problem of parameter design and reliability evaluation of tunnel weak surrounding rock and bolt-shotcrete support system, the deformation, failure mechanism and physical mechanical properties of weak surrounding rock are analyzed as well as the mechanism of bolt-shotcrete support in soft rock is studied. And the reliability analysis equation of bolt-shotcrete support in two kinds of weak surrounding rock (nearly horizontal layered mechanics medium and continuum mechanics medium) is established. The quantitative soft rock supporting theory is introduced into the reliability analysis equation. The calculation formula of two important design parameters of anchoring force and bolt spacing in bolt-shotcrete support is established. Finally an engineering example is adopted to prove the rationality of the calculation results. Therefor this paper provides theoretical basis and design method for supporting structure design and reliability evaluation of tunnel weak surrounding rock.