Investigating Structural Damage And Mechanisms Induced By Water Inflow And Seepage Erosion During Shield Tunnelling

The accidents of water inflow may be possibly induced by improper construction process during shield tunneling through silty sand layer under high water pressure,while the seepage force in this kind of soil layer may induce seepage failure in which fine particles are gradually removed due to the loose characteristic of gap-graded soil and the high hydraulic gradient.These accidents would result in large ground settlement and structural damage.In a worst-case senario,the tunnel might collapse due to such construction accidents.However,the structural damage induced by water inflow or seepage erosion has not been adequately investigated in the literature,and its damage mechanisms haven’t been identified.Three-dimensional tunneling models were established by employing the FiniteElement program ABAQUS.The objective was to investigate the influence of water inflow from excavation face or seepage erosion between segment joints on ground settlement and structural damage during shield tunneling.Firstly,the numerical approaches were reliably validated by a series of experimental results from the literatures.And then the influences of large water inflow from excavation face on the ground settlement and structural damage were investigated,followed by the effect of seepage erosion on the ground settlement and structural damage.Lastly,the relationship between the erosion-induced structural damage and lining displacement parameters was established.The main research contents and results are drawn as follows:(1)The three-dimensional shield tunneling method was reliably validated by comparing the ground settlement of field datas and numerical results.The concrete damage was simulated by a new approach with high efficiency and good convergence,and the numerical results agreed well with the experimental ones.Based on an experiment of segment joints,four numerical methods were adopted to simulate the joints bolt,and the numerical results presented a good consistence with the experiment results.Based on the seepage erosion experiments,a simplified numerical approach was proposed to qualitatively model the effects of seepage erosion,the results of which were in good agreement with those of the seepage erosion experiments.(2)The effects of water inflow from excavation face on the ground settlement and structural damage were investigated,and then the structural damage was clarified and the countermeasure was proposed to alleviate the lining damage.It was the horizontal unloading of surrounding soil that resulted in lining damage on the tunnel side.Larger water inflow or smaller lateral earth pressure coefficient would lead to a higher lining damage.The value of lining damage would be smaller when sufficient water flowed toward the excavation face to compensate for large water loss.Continuous grouting was proved to be an effective countermeasure to alleviate the lining damage.(3)The effect of seepage erosion between segment joints on the ground settlement and structural damage was investigated.The structural damage mechanisms induced by different erosion region were clarified.The seepage erosion process had significant influence on the ground settlement,and resulted in large deformation and damage of segmental linings.Both erosion-induced lateral unloading and soil arching effect contributed to lining damage and deformation as seepage erosion occurred on the tunnel side.As seepage erosion occurred on the tunnel crown or invert,the lining rings were pushed unward or downward due to erosion-induced unloading.A larger erosion region resulted in a larger structural response.A larger increase of eroded soil permeability would result in a less structural damage.(4)Based on the sophisticated joint bolt model,the relationship between erosioninduced structural damage and lining displacement parameters was established.The longitudinal bolt force could be identified by the axially deflection angle.The number of yielding bolts could be identified by the average vertical convergence rate of linings,and the maximal lining damage could be identified by the maximal vertical convergence rate.