Research On Some Problems Of Rock Pressure Of Caverns At Shallow Depth

With the rapid development of national economy such as the energy sources, communication, national defense municipal engineering,and mine engineering etc,and global environmental protection and the need of sustainable development for the human being, the constructions of underground engineering have got more and more. Recently years, with the development of communication infrastructure has been increased sharply. And there appear more and more tunnels inevitably with the expansion of highways. But there exist some problems in the design and construction in underground project. These problems cause landslide, lining crack or excessive safety, which leads to the large waste of human and material resources. The existing problems which need further research are listed as follow.(1) The twin tunnel, as a new structure style, has obvious dominance in middle and short length tunnel. And its rational load mode is what the designer focuses on.(2) The Code for Design of Road Tunnel (JTG D70-2004) introduce the rock-structure method to the rock pressure calculation of deep seated tunnel for rock class I~IV. But the rock pressure of shallow tunnel are still calculates as loosening load. In fact, the rock displays self-bearing capacity in some shallow buried caverns. How to determine the load ratio beared by the rock itself is the key to optimize design, which is still a puzzle we face today.(3) There are subjective and objective indeterminacies in design by FEM. They are the calculation mode, the calculation parameters, calculation assumption, data and information shortage in design and construction, and etc. The FEM can not give us quantitative designing parameters, but qualitative analysis.And the other problems such as the protection of the plant cover and historic buildings while excavating, integral collapse of the shallow-seated cavern, blow up of the inverted arch also exist.The research is carried on combined with the Key Technologies In The Construction of Twin Tunnel, which is Western Communications Infrastructure Science Project of Ministry of Communications. Through extensive investigation of caverns design and construction, detailed analysis of the measuring data, some achievements are obtained. The research contents and achieved creative work are listed as follow.(1) Presenting a new design and construction method named as multi-arcade tunnels shed method for shallow buried and large span cavern. The new method has many merits such as good stability, minimum excavating quantity, low costs, especially reservation of rock appearance of cavern all around, and protection of plantcover and historical buildings of ground surface, it provides us a useful and new way to escape open excavation.(2) Presenting a new assumption of two slumping arches considering the supporting effects of the middle wall, then establishes the load model of twin tunnel based on the assumption, it settles the groundwork for the further study on th rock pressure of mutil-arch structure in construction process.(3) Giving the distribution ratio of rock pressure under different rock in shallow-seated cavern through analysis of the measured data from mode test and field minitoring in details.(4) Discussing the response of the supporting structure to the excavation under different constrtuction schemes. Some typical construction process is compared on internal force of the lining and the shotconcrete. The time effects with the rock pressure based on long-term measured data is analysised, the mechanical behaviors of the inverted arch are also discussed.