Research On Stability Evaluation Method And Application Of Deep Tunnel

The surrounding rock and support structure instability frequently occurs in the construction of mountain tunnel, which leads to great loss. How to improve the stability evaluation method of tunnel, providing full theory basis for tunnel excavation and supporting design and guaranteeing the project construction safely and smoothly, is a difficult technical problem to the tunnel constructors.Taking the project of "The identification and early warning system for highway tunnel engineering disaster induced from excavation" as the back ground, the deep buried section of Yuanyanghui tunnel was focused in this study. And a series of technological means, such as theoretical analysis, numerical simulation, monitoring measurement, are used to study the stability evaluation method and application of deep rock tunnel under complex conditions. Some innovative results are obtained as follows:(1)It is well known that size effect of rock mass is remarkable, but various rock mass quality classification systems at home and abroad don’t consider this effect. To consider the size effect of rock mass, based on the BQ method, the span correction factor was established to quantify the effect of span on surrounding rock quality and realize the surrounding rock quality evaluation considering the size effect of rock mass. Moreover, based on rough set and uncertainty measure theory, a new method for evaluating tunnel rock quality is established. Both methods were applied to evaluate rock quality and get mutual verification, providing theoretical basis for the research on stability evaluation of deep tunnel.(2)Based on Hoek-Brown failure criterion, the general expression of longitudinal deformation profile (LDP) was established. The functions of LDP which can quantize the difference of spatial excavation effect. LDP with various surrounding rock quality and stress level can be calculated by using these functions, providing theoretical basis for tunnel excavation and supporting design using convergence-confinement method properly.(3)Combined with BQ value, based on the relative limit displacement range given in codes and previous research results, relative limit displacement model of primary support considering effect of multi-factors is established. And the continuous model could provide quantization foundation for the safety evaluation on primary support. (4)Based on above-mentioned outcomes, the method of tunnel excavation footage optimization is established, and is applied to the practical engineering. Combined with the functions of LDP proposed in previous paper, a reasonable footage was calculated by controlling the stability coefficient of the supporting structure and deducing the initial position of primary support. Taking for example LK179+580～LK179+920section of Yuanyanghui tunnel, based on calculation, the reasonable footage was set to1.5m.