岩溶基底隧道拱顶沉陷三段四层关键技术研究

为有效治理岩溶基底城市隧道拱顶地层沉陷地质灾害，在充分探明沉陷区水文地质、工程地质特征的基础上，提出了“三段四层控制技术”，将治理区划分为沉陷区重点加固段、影响区次重点加固段和超前加固段；再根据治理深度和治理顺序进一步把沉陷区重点加固段分为顶部阻浆层、拱顶止浆垫层、拱顶加固层和中间加固层，研究了每段、每层注浆加固机理、浆液类型选择和控制注浆参数。研究成果表明，采用孔内复合止浆技术满足不同深度地层分段注浆为主、垂直孔和定向斜孔相结合，充填注浆、劈裂-挤密注浆相结合，以速凝浆液为主、单液水泥浆为辅，严格控制安全注浆参数，是“三段四层控制技术”安全有效注浆的技术关键，该技术方案在岩溶基底城市隧道拱顶地层沉陷地质灾害治理方面，取得了较好的注浆加固效果，有良好的推广应用价值。 

Study on "three-section and four-layer" reinforcement technology of tunnel vault subsidence in the karst basement

In order to effectively control the geological disaster of tunnel vault subsidence in the karst basement, the "three-section and four-layer" control technology is proposed, based on the full analysis of engineering geology and hydrogeological characteristics of the subsidence stratum. In this technology, the treatment area is divided into the key reinforcement section, the sub-key reinforcement section of the affected area and the pre-excavated reinforcement section. According to the treatment depth and order, the key reinforcement section of the subsidence area is divided into the top slurry barrier layer, the vault cushion layer of slurry-stopping, the vault reinforcement layer and the intermediate reinforcement layer. In terms of grouting mechanism, filling grouting and splitting-compacting grouting are adopted in both the top slurry barrier layer and the intermediate reinforcement layer. The alternate mode with filling-splitting-compacting grouting is implemented in the intermediate reinforcement layer, and the filling grouting mode is adopted in the vault cushion layer of slurry-stopping. Splitting-compacting grouting is conducted in both the pre-excavated reinforcement section and the sub-key reinforcement section in the affected area. In order to reduce the leakage of grout in the top slurry barrier layer and vault cushion layer of slurry-stopping, C-GT quick setting mixed grout is selected, and the initial setting time of the grout is controlled at 30-50 seconds, while the final grouting pressure is no more than 0.5 MPa and 0.8 MPa. In order to realize the effective diffusion of slurry in the vault reinforcement layer and intermediate reinforcement layer, the initial setting time of C-GT mixed slurry is extended to 50-90 seconds, even up to 150 seconds, and the final grouting pressure is up to 0.8-1.2 MPa. To improve the slurry diffusion and overall reinforcement strength of the pre-excavated reinforcement layer and the sub-key reinforcement layer in the affected area, the alternate and continuous grouting mode of single and double cement slurry is implemented based on the high consolidation strength of single cement slurry and the quick setting characteristics of C-GT mixed slurry. The above-mentioned technology is the key to the success of grouting reinforcement. Besides, the combined grout-stopping method is used to effectively deal with the segmented grout-stopping at the place where the hole wall collapses and shrinks, and the diameter of borehole is greatly oversized. Hence, the isolated grouting at different depths of those four layers is realized. The directional inclined hole is used to effectively avoid the hidden underground pipeline, and the grouting pipe is used as the pipe roof to improve the shear resistance of stratum. Combined with grouting, this technology can effectively improve the overall strength and stability of the reinforcement stratum by tunnel vault grouting. Research results indicate that "the three-section and four-layer" treatment scheme is the basis to effectively control the subsidence of soil overlying the tunnel. The combined grout-stopping technology in the hole is the guarantee to meet the requirement of segmented grouting at different depths. The combination of vertical hole and directional inclined hole and of filling grouting and splitting-compacting grouting, taking quick setting slurry as the primary part supplemented with single cement slurry, and the strict control of safe grouting parameters are the technical keys of safe and effective grouting. The application of the above technology has achieved good grouting reinforcement effect and hence should be popularized.