Stability Analysis Of RockMass Of Crossing Tunnels

In order to meet the demands of usage function, the crossing tunnels are usually constructed in underground engineering. With more free surface and more complicated state of stress in the cross section, the crossing tunnels become weak in underground engineering. It's difficult to obtain the analytic solution of stress and deformation in rockmass of crossing tunnels because of complicated boundary conditions. It is not easy to find it in any research report regarding this problem, therefore, the stability analysis of crossing tunnels needs to be studied.A project requires excavation of complex caves in sandy gravel rock which exists more cross sections and weak stratum, so the stability of the cross section during the excavation is a key issue concerned by engineering design and construction staffs.The paper studies the stability of crossing tunnels in sandy gravel from theoretical analysis, numerical simulation and model experiment taken the project as the background, and with sandy gravel rock and crossing tunnels at the core. Firstly, the main failure mechanism of tunnel is induced from the general destruction characteristics of tunnel. On the basis of it, the failure mechanism of crossing tunnel in sandy gravel rock is analysed considering the property of stratum and the characteristic of structure. Secondly, The distributing characteristic of stress and deformation in rockmass of single tunnel and crossing tunnels is simulated by using finite element method. Through comparison, the characteristic of response in rockmass of crossing tunnel is fully understood.Thirdly, distributing law of stress and deformation in rock mass of crossing tunnel and destruction characteristics are verified by similar model experiment. Finally, the stress and deformation in rock mass of crossing tunnel with different section shape and excavation sequence is simulated by using numerical experiment. The reasonable section shape and excavation sequence of crossing tunnel are selected according to comprehensive assessment. Three conclusions are reached after research.1.The distribution law of stress and deformation in rockmass of crossing tunnels is that the plastic radius in rockmass of crossing tunnels is longer than that of single tunnel, and the tension stress exists in apex of arch and floor of crossing tunnel. The direction of tension stress is toward horizontal.2.The destruction characteristic of crossing tunnels is that the weakest part of crossing tunnels exists in four wall around corner. The destruction style is fracture flaking and shear slip. The failure mechanism is fracture and shear failure caused by compression stress concentration.3.When the height of arch is higher than or equal to the half of span, the crossing tunnel is more stable. When different tunnels cross over, excavation one after another could be more stable than that of at the same time, and could be even better if start from the small size one to the large one.The achievements of the paper provide scientific reference for design and construction of the crossing tunnel in sandy gravel rock.