水底隧道饱水地层衬砌作用荷载研究

与山岭隧道所不同，采用矿山法修建水底隧道，二次衬砌将承受很大外水压力，特别是穿越饱水破碎地层时，具有很大的施工风险。以厦门翔安海底隧道为工程背景，针对F4风化深槽地层，研究不同水位条件下，衬砌荷载与排放流量及排放方式之间相关关系。研究得出：当控制排放量为全排条件流量1/3左右时，可卸掉80%外水压力；从环境和经济角度考虑，可将出现拐点折减系数0.2作为水底隧道限量排放的设计基准值；从支护结构体系组成考虑，对于F4强风化深槽破碎围岩，必须施作注浆圈，才可以保证在水压、土压共同作用下衬砌结构安全，结果显示施作注浆圈能够减少衬砌作用荷载30%～40%，提高安全系数几乎一倍；从主体结构受力特征看，水底隧道最不利受力位置在墙脚和仰拱，因此，无论是防水型还是排水型隧道，均应对仰拱形式及支护参数加强设计。

Study of load of lining under condition of saturated stratum for underwater tunnels

Being different from general mountain tunnel by NATM, the lining of underwater tunnels built by mining method may be sustained heavy external water pressure; and underwater tunnels are more affected geological uncertainties and risks, particularly when passing through the saturated stratum such as the weathering deep slot stratum F4 in Xiamen undersea tunnel. Based on fluid-mechanical interaction model for saturated ground conditions, the three dimensional numerical analyses are conducted to investigate the relationships between the pressure behind the lining and the discharge water inflow for different drainage conditions. The results show that the water pressure trapped behind the support depends on the discharge capacity of the drainage system relative to the water inflow from the ground, even the reduction of 80% external water pressure is obtained while the discharge water flow being controlled about one-third of the full water inflow from the ground. From the view of reasonable design of seismic water loads behind the lining, the reduction coefficient of 0.2 is regarded as the acceptable level for controlled drainage underwater tunnel. The emphasis is placed on introduction of grouting circle in support system for weathering deep slot stratum F4，but if competent ground conditions are anticipated to be encountered during underwater tunnel construction; then grouting circle may not necessarily be required. In view of the disadvantageous distribution of deformation and internal forces occurred in the invert, particularly in the corner position of invert connected with the side-wall; therefore, whether it is waterproof-type tunnel or drainage-type tunnel, more attention is paid on design of invert form and support.