Research On Physical Model Experiment Of Metro Tunnel Crossing Ground Fissures And A New Supporting Technology

Xi'an Subway was built in ground fissure stratum. As ground fissures move, the lining structure of tunnel will have a significant additional stress and uneven settlement, while deformation crack will occur relatively dislocation displacement and the impermeable structure will lapse. To revelate the law of rock pressure, lining structure's internal forces and uneven settlement under the conditions of ground fissure have important practical significance to take effective measures and guarantee the normal operation of subway tunnel.Targeted in Xi'an Subway Line 2 between Xiaozhai Station and Bali Village Station through f8 ground fissures and combined with practical engineering design methods and specific engineering measures, the interaction mechanism between lining and wall rock in the activities of the orthogonal and oblique ground fissure was studied by physical model experiment. In the first place, this paper developes a tunnel model test apparatus which crossing ground fissures based on the geometric similarity ratio 50:1 scale. The device uses compressed air to simulate different way of loading depth of tunnel surrounding rock stress field, and simulates the activities of the orthogonal and 45°oblique ground fissure by controlling the take-off and landing control panel. In addition, auxiliary measurement devices are desinged, including self-developed Flexible-Membrane-Hydraulic earth pressure cell and mechanical lining structure uneven settlement measurement system. Then, soil-formation conditions, orthogonal or 45°oblique ground fissures, sub-seam lining structure and stress field of 0.05MPa, 0.10MPa and 0.15MPa were simulated, and model test was carried out. Finally, get understanding as follows.First, lining structure's uneven settlement has changed markedly within a distance of 20m in the hanging wall and 18m in the foot wall under the movement of orthogonal ground fissure. Another, the lining structure's uneven displacement in the hanging wall gradually decreases with increasing of the the distance from ground fissure. While the lining's displacement was slowly decreasing trend on both sides of 45°oblique ground fissure, and its uneven settlement has changed markedly within a distance of 30m in the hanging wall and 22m in the foot wall.Second, as to the development of fracture dislocation displacement, the tunnel arch and bottom arch in the hanging wall will show signs of weakening of the role, at the same time the earth pressure of the side wall may increase, while the earth pressure and lining's compressive stress of the tunnel arch and bottom arch in the foot wall will increase. And the maximum value of the earth pressure increment occurred near the ground fissure in the foot wall. As a result of the interaction between sections lining structure and rock and soil Wai, the earth pressure of the tunnel arch in the foot wall emerges in volatility.Third, compared to the ground fissure, oblique ground fissure has an even greater impact on the subway tunnel and more likely cause damage to subway tunnel or generate off air between the bottom arch and rock at the hanging wall. Another, the lining structure's uneven displacement variation is similar in different rock stress field, and the greater the stress field of rock, the more remarkable wai rock pressure and stress of lining structure caused by fracture dislocation.Fourth, the lining is in a force state similar to "beam" which is oblique crossing ground fissures, and produce rotation displacement within the longitudinal profile. What's more, the earth pressure of the tunnel arch in the hanging wall and the tunnel arch and bottom arch in the foot wall all increase, also do the lining's internal forces, which is larger than those in the orthogonal ground fissure case and will cause the destruction of lining. So, this section lining's strength and rigidity should be strengthened during designing. Accordingly, the earth pressure and the internal forces of bottom arch in the hanging wall are significantly reduced, and generate off air when the dislocation displacement reached 100cm.Finally, addressing the problem of ground fissures's long-term slowly movement, growth of lining structure's additional stress and development of uneven settlement deformation, and using asphalt concrete material with rheology, crack resistance, impermeability, a supporting technology of asphalt concrete composite lining structures was proposed in this paper. The supporting technology is made by pouring an asphalt concrete lining structure between the tunnel initial lining and second lining, which able to adapt to the activities of ground fissures without creating cracks, continue to play its anti-seepage capacity, improve the subway tunnel secondary lining's environmental stress and weaken the external load on the subway tunnel including ground fissure's activity or earthquakes. This supporting technology has the advantage of low cost, easy construction, simple structure, durability and easy to repair, and can be presented as the reference to structural design and prevention measures of metro tunnel passing through the ground fissure active zone, which has strong practical significance.