Water Seal Failure Mechanism And Long-term Service Performance Prediction Of Subsea Tunnel Segment Structure

With the vigorous implementation of the national ocean development strategy and the strategy of strengthening the country in transportation,a large number of undersea tunnels will be put into operation in the next few years.The high concentration of ion erosion,high water pressure,and complex geological conditions in the marine environment is extremely unfavorable for the long-term service performance of the tunnel.Segment joints are the weak link of the prefabricated tunnel structure.Under the action of complex marine environment such as tension,bending and torsion,it is easy to cause the uneven settlement of tunnel structure,segment joint opening and stagging.At the same time,the EPDM rubber elastic gasket will age and stress relaxation.These will lead to engineering problems such as water leakage,which will seriously affect traffic safety.Aiming at the problems of unclear water-stop failure mechanism and difficulty in calculating the amount of seepage water in subsea tunnel segment structures,this paper studies the effects of shear dislocation and erosion degradation on the resistance of segment structures through theoretical analysis,numerical simulation,laboratory tests,and model tests.The attenuation law of bending performance was revealed,and the mechanism of mechanical performance deterioration of elastic gasket was revealed.On this basis,the leakage mechanism of the sealing interface of the elastic gasket with segment structure was clarified,and a calculation method of leakage flow at the sealing interface considering the surface topography was proposed,which revealed the nonlinear and rapid growth law of tunnel leakage during the service period.This paper finally established a calculation model of tunnel leakage flow during the service period considering shear dislocation and erosion deterioration and realized the long-term leakage flow prediction of the tunnel.The main research work and innovation achievements are as follows:(1)The opening deformation law of segment structure after the dislocation.A test system that can apply a shear force to the segment structure first and then apply the bending moment was developed,and the whole process simulation of the staggered opening of the segment structure was realized.In this paper,the shear-bending mechanical performance test of segment structure was carried out,and the failure process,vertical displacement-bending moment relationship,opening amount-bending moment relationship,bending stiffness,and crack propagation process of segment structure under the action of staggered platform bending moment were analyzed.The staggered segment structure exhibited three-stage progressive failure characteristics under the action of bending moment,which were the initial opening stage of the joint,the initial crack stage of the segment,and the ultimate bearing stage.The staggered platform leaded to an increase in the opening of the segment structure,which has a significant attenuation effect on the ultimate bearing capacity and bending stiffness of the segment structure.(2)The opening deformation law of segment structure after the deterioration.Based on the corrosion theory of reinforced concrete,a steel corrosion model that can describe the concrete cover before and after cracking was determined,and a calculation model of the elastic modulus decay of reinforced concrete considering the service time was proposed.On this basis,the compressive damage model of concrete,considering the attenuation of elastic modulus,was used to establish the flexural mechanical model of the segment structure in-service period.The calculation results showed that with the increase of the erosion age,the opening amount,closing amount,and rotation angle of the segment structure joints increased rapidly,and the flexural stiffness of the segment structure decreased sharply.(3)Deterioration mechanism of mechanical properties of elastic gaskets with segment structure.The compressive stress-hydrothermal aging accelerated test of EPDM rubber was carried out,and the attenuation law of long-term mechanical properties such as pre-compression and aging time on rubber compression set and stress-strain characteristics was studied.A structural model was used to predict the long-term mechanical properties and residual properties of rubber.The long-term mechanical properties of the elastic gasket considering the spatial structure were studied,and the stress concentration phenomenon,compression set characteristics,and compression force-compression relationship of the elastic gasket with different cross-section forms were systematically analyzed,which revealed the mechanical property deterioration mechanism of the elastic sealing gasket of the tunnel segment structure during the service period.(4)The segment structure elastic gasket seals the leakage mechanism of the interface.Based on the rough surface topography parameters of the elastic gasket and the geometric characteristics of the asperities,the contact mechanics model of the sealing interface was established,and the influence of the contact stress and surface topography on the sealing interface closure was analyzed.Combined with the structural characteristics of the sealing interface,the leakage mechanism of the sealing interface was clarified.The fluid flow criterion of the leakage channel was established,and a calculation method for the leakage flow of the sealing interface considering the surface topography was proposed.The water leakage test at the sealing interface was carried out,and the influence law of joint opening and staggering on the critical leakage pressure and leakage flow was revealed.The results were compared with the theoretical values,and verified the rationality of the theory.(5)Model test of tunnel water leakage during the service period.A model test system for tunnel seepage water was developed,which simulates uneven settlement through local overloading,and reduces the elastic modulus of heating segments to simulate seawater erosion and deterioration.It realized the simulation of the equivalent service life of the submarine tunnel and revealed the nonlinear growth law of tunnel water leakage with service period.The deformation of the tunnel annular joint can be approximately divided into three stages with the service life,namely the nonlinear fast growth stage,the linear growth stage,and the nonlinear slow growth stage.The joint action of the deformation of the tunnel annular seam and the stress relaxation of the elastic gasket aggravated the leakage of water at the sealing interface.(6)Prediction of tunnel leakage flow during the service period.The longitudinal deformation calculation model of the tunnel considering shear dislocation and erosion deterioration was established,and the nonlinear growth law of the annular joint opening and dislocation amount of the segment structure with the service life was studied.Based on the theory of advanced seepage mechanics,a calculation model of tunnel leakage flow during service life was established considering shear dislocation and erosion deterioration.It realized the prediction of the leakage flow of the tunnel during the service period.Compared with the model test results,the rationality and accuracy of the calculation model were verified.For the submarine tunnel project of Qingdao Metro Line 8,long-term service performance was predicted.The result showed that it meeted the requirement of underwater tunnel waterproof specification.