| Water inflow,lining water pressure and overburden thickness of submarine tunnels are important issues concerned by tunnel designers.Most of the submarine tunnels in practical engineering are three-hole tunnels with small spacing.Few studies has been done on the influence of water inflow,lining water pressure and small distance tunnel on overburden thickness.In this paper,the seepage of three-hole tunnel and the overlying strata thickness of three-hole submarine tunnel with small spacing were studied.Firstly,the water inflow and lining water pressure of three-hole submarine tunnel were systematically analyzed by theoretical derivation and numerical calculation.The influence of small distance tunnel on overburden thickness was analyzed by numerical calculation.This paper provided a theoretical basis for similar projects in the future.It comes to the following conclusions:(1)Theoretical study on seepage field and overburden thickness of submarine tunnel.Firstly,the analytical solution of seepage field in single-hole submarine tunnel was deduced by using the basic theory of mirror method.Then the basic theory of FLAC3D fluid-solid coupling calculation was introduced.Furthermore,the common methods and criteria for determining the optimum overburden thickness of submarine tunnels were introduced.Finally,according to the engineering analogy method,the initial selection range of overburden thickness was 17m～37m.(2)Analytical solution of seepage field in three-hole submarine tunnel and analysis of its influencing parameters.Due to the pressure relief effect of three-hole submarine tunnels,the seepage field distribution of three-hole submarine tunnels was quite different from that of single-hole tunnels.Based on the theory of mirror method,the analytical solution of seepage field in three-hole submarine tunnel was derived.The analytical solution was degraded to single-hole and double-hole tunnels for theoretical verification.The rationality of analytical solution was verified by numerical calculation.The influence distance of horizontal spacing on tunnel water inflow and lining water pressure was 20 times of tunnel radius,and the water inflow and lining water pressure increased linearly with the increase of burial depth;the anti-seepage performance of initial support was improved,the permeability coefficient of initial support was reduced,the water inflow of tunnel was reduced,and the water pressure after initial support was increased;the water inflow and initial stage of tunnel will be increased by increasing the thickness of grouting ring and decreasing the permeability coefficient.The water pressure decreased in inverse proportion function after support.(3)Study on the optimum overburden thickness of single-hole submarine tunnel under seepage.Using FLAC3D numerical simulation software,the optimum overburden thickness of Jiaozhou Bay Submarine Tunnel was simulated.Comprehensive analysis of tunnel seepage velocity,size and distribution of water pressure in lining,tunnel water inflow,stress disturbance range,plastic zone distribution,tunnel key point displacement.Based on the minimum water inflow criterion and the minimum displacement criterion,the weight function method was used to determine the optimal overburden thickness of single-hole tunnel.(4)Study on the optimum overlying strata thickness of three-hole seabed with small spacing under seepage.Based on the same engineering background as single tunnel,the numerical calculation models of tunnel spacing of 1 times and 0.5 times were established.By comparing the differences of seepage field and surrounding rock stability between single-hole and small-spacing three-hole tunnels with different overburden thickness,the influence of three-hole tunnels on seepage field and optimal overburden thickness was discussed.The results shown that:①Reduction of tunnel spacing with constant overburden thickness can reduce tunnel water inflow,lining water pressure and seepage velocity.At the same time,the stress disturbance range of surrounding rock was enlarged,the phenomenon of stress concentration in middle rock was more severe,the distribution range of plastic zone was enlarged,and the displacement of vault was enlarged.②When the tunnel spacing was unchanged and the thickness of overburden increased,the water inflow decreased rapidly at first and then increased slowly,the water pressure after lining and the maximum seepage point transferred from vault to arch foot.The range of stress disturbance and the vertical stress of the middle rock increased linearly.Excessive burial depth leaded to the penetration of plastic zone in the middle intercalated rock.The vault displacement decreased first and then increased,and there was a minimum value.Using the same judgment method as single tunnel,the optimum overburden thickness of small spacing submarine tunnel was determined to be less than that of single tunnel. |
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