Study On The Long-term Stability Of Tunnel-type Anchorage Surrounded By Soft Rock After Reservoir Water Level Rising

The proposed Jijiang Yangtze River bridge plans to use the program of the tunnel-type anchorage on the northern bank. This area's bedrock is mudstone of Jurassic Suining Formation and is mixed up with sandstone in the local formation. The weathering degree of bedrock is moderate. So this tunnel-type anchorage belongs to typical shallow buried and soft rock tunnel-type anchorage. And the Jijiang Yangtze River bridge's single cable is under tension 1.08×105kN in the standard combination. Meanwhile, a part of anchorage and the surrounding rocks on the north shore is under the reservoir water level. If the construction of Xiaonanhai Hydropower Station completes and is in operation, the reservoir water level will further uplifts. But there are water softening and creep characteristics of mudstone under load, the groundwater and its water level will affects the long-term stability of the tunnel-type anchorage. It barely see to construct tunnel-type anchorage under high load in a shallow buried, soft rock and water rich environment at home and abroad. So intensive studying the long-term stability of the tunnel-type anchorage under complex environment, evaluating the feasibility of tunnel-type anchorage program and further expanding the application range of tunnel-type anchorage will be highly significant for highway transportation construction in China.This paper takes the program of the tunnel-type anchorage of Jijiang Yangtze River bridge on the northern bank as the research background. It first designs and implements the scale tunnel-type anchorage model comparison test in the natural state and in water condition under standard design load. And it reveals the creep deformation characteristic of anchorage and surrounding rock system and the influence of groundwater according to the experiment. At the same time, based on the results of indoor and in situ rock mechanics test and scale tunnel-type anchorage model test, creep model of mudstone is identified and creep parameters which is in the natural state or in water condition are inverted respectively by using PSO-LSSVM inversion analysis method. Finally, this article analyses the three-dimensional numerical model of anchorage-surrounding rock system and studies its the long-term stability and the influence after water level rising. The results show that the properties of mudstone is weakened after the reservoir water uplifting. Compared with before the uplift of reservoir water, the creep deformation of anchorage-surrounding rock system increased and but growth rate is low. For the whole anchorage-surrounding rock system, plastic zone appears only in the small range of the front face and back face of anchorage and the surrounding rock of anchorage is largely under elastic working state.