Study On Water Inrush Mechanism And Early Warning Of Filled Piping-type Disaster And Its Engineering Applications In Tunnels

With the construction of transportation, water conservancy, hydropower and other major infrastructure, especially with the deepening of the western development strategy and the national "Twelfth Five- Year Plan", the focus of major construction projects shifted to the western mountains and the karst area in the extreme complex terrain. China has become the country with the largest scale and difficulty in tunnel construction in the world. In some construction projects, the construction process in high-risk deep tunnel could easily suffered a serious water inrush disaster. In the first 10 years of the 21st century, hundreds of serious geological disasters occurred in the field of transportation and hydropower tunnel construction, among which water inrush and water-induced disasters account for 77.3 percent, causing nearly one thousand casualties, significant economic losses, adverse social impact and serious environmental damage. The root cause of deep tunnels difficult to contain water inrush catastrophe was that the mechanism of water inrush and catastrophic evolution mechanism was extremely complex. We have not yet formed a clear understanding system. It was difficult to form an effective guide to prevention and control disasters.In this paper, the main research object was the water inrush mechanism of the piping type structure. Supported by the project of the Shangjiawan tunnel in Baokang-Yichang expressway, laboratory experiment, theoretical analysis, numerical simulation, model test and field test were used to study piping type structure filling medium hazard penetration failure mechanism and construction disturbance gushing catastrophe evolution and engineering warning mechanism. Some research results and project significances were summarized as follows:(1)Through the statistical analysis of a large number of water inrush cases, especially system arrangements for the Yuhuai railway Yuanliang mountains and the Yiwan railway yunwu mountains tunnel water inrush disasters, the disaster hazard sources were decomposed to the forming, recharge, rich water, filling features of the type. Formative conditions of hazard sources were put forward. For piping disaster hazard sources characteristic of ductility, concealment, hazard, the occurrence regularity and disaster-pregnant mode was revealed. The index system of piping type structure disaster-pregnant judgment evaluation and the classification standard of disaster-pregnant based on the attribute recognition model was provided.(2)Based on the grain size distribution characteristics of filling medium and cementation state, filling medium could be divided into gravel, sand and clay mud three types. Triaxial permeability test system of stress-seepage coupling system was developed, especially the development of the three-dimensional seepage-stress-damage coupling pressure chamber. A perfect seal and loading system was designed. The penetration test of the filling medium simulation under the condition of occurrence was carried out. The seepage characteristics of different kinds of filling medium were systematically analyzed. The seepage failure modes of water gushing type, seepage type and slip type was revealed.(3) Aiming at various seepage failure patterns with different filling media, seepage failure mechanism of piping type disaster structure filler was studied from the experimental phenomena perspective. Gushing type failure could be simplified as pipeline flow, of which flow state was described by Navier-Stokes equation. Seepage type failure includes the overall strength failure of filler body and water erosion expanding. Based on strength conditions and motion equilibrium conditions, starting conditions and develop process of two stages were analyzed respectively. Slippage type failure is overall mechanical failure of filler body under seepage. The thickness of the filling body is an important indicator of its safety, and minimum safe thickness of slippage type failure of filler body is calculated by slices method.(4) In order to study catastrophe evolution mechanism and precursory laws of the seepage failure water-inrush of piping type karst conduit under the influence of construction disturbance and groundwater seepage, the 3D visual fluid-solid coupling test platform, the water-loading control system, and the similar materials of high similarity simulating rocks and the filler in water environment were developed. The 3D large-scale fluid-solid coupling model text of the seepage failure water-inrush of piping type karst conduit of deep long tunnel was carried out based on the water-inrush section of Shangjiawan tunnel in Baokang-Yichang expressway. The process of cracks formation - extension - connection - water inrush was truly reproduced during excavation and water loading. The catastrophe evolution mechanism of fillings seepage failure and precursory characteristics of water inrush under the seepage effects was revealed by analyzing the variation characteristics of displacement, stress and seepage pressure.(5) According to the characteristic of engineering work in exploration design, construction, monitoring, the "three-stage multi-factor" early warning system throughout the whole construction process was founded. The system was based on regional geological information, advanced forecast information, monitoring and measuring information and engineering information correction, and considers the water inrush intensity, alarm location and control time. Eventually, comprehensive early warning mechanism of karst piping water inrush is developed, and various early-warning level of control measures and emergency plans is formulated.(6) Relevant outcomes were applied in Shangjiawan tunnel in Baokang-Yichang expressway, and catastrophe factors for water inrush were analyzed systematically. The reason for repeatedly water inrush occurred in tunnel ZK64+920 section was revealed, that is, water inrush was induced by the over-water karst piping which has good connectivity with surface. According to water inrush comprehensive early warning system, red warning occurs in this region and indicates high water inrush risk. For early warning information, appropriate control programs were proposed and achieve good results. Results of this paper provided guidance for controlling engineering water inrush catastrophe.