Study On Durability Of Subsea Tunnel Concrete Structure

This paper comprehensively analyzes moisture and chloride’s migration mechanism based on subsea tunnels’form and environmental condition with high water pressure and chloride content. Moisture, chloride migration patterns and life prediction inside and outside subsea tunnel in chloride environment are studied by integrating experimental investigation with theoretical analysis. In consideration of higher construction cost, lower maintainability and higher maintainee expense, and to be sure of normal performance in100years service lifespan, durability and service-life forecast theory need to be studied urgently. Therefore, this paper’s research will be of great value for reference in durability study of subsea tunnel.The contents and achievements of this paper mainly include:(1) A self-made pressure control device is designed according to pilot program to study the migrations features moisture and chloride in concrete under the pressure head. The effect of pressure, pressure time, strength grade, water cement ratio, chloride diffusion coefficient, saturation degree, solution concentration and other factors on moisture and chloride’s migration is analyzed. Through experimental measurement, chloride diffusion coefficient and water saturation in concrete with different water cement ratio are obtained. The chloride diffusion coefficient increases with water cement ratio and with high growth rate when water cement ratio in the range of0.3-0.38.(2) With the introduction of relative permeability (saturation degree) kT, theoretical models of pressure and flow velocity changes with time in concrete are built based on Darcy’s law theoretical equation considering pressure and pressure model various with position in lining concrete. Flow rate changes over time are always a peak first, then declined and stabilized. Flow rate in superficial layer is greater than deep. Theoretical analysis also shows that the pressure promote water flow rate. Flow rate is greater in concrete with lower strength grade, higher water cement ratio or higher saturation degree.(3) The moisture penetration depth theoretical model is obtained based on flow rate model using integral. Analyze penetration depth and compare with experimental value with good agreement. Penetration depth is always larger with the increase of time and the increasing degree is lower in the latter part. Pressure has a promotion effect on penetration depth. Strength grade is inversely proportional to penetration depth. While water cement ratio is the opposite. Theoretical values and experimental values are in good agreement during discussion all the factors.(4) A chloride migration theoretical model considering coupling effect of pressure penetration and diffusion is established combining with flow rate model and compared with experimental value with good consistence. Superficial layer in concrete has higher chloride concentration, decline extent with position and towards stability in the deep. Pressure promotes the migration of chloride to deep. Strength grade is inversely proportional to chloride concentration. Concrete with higher saturation degree or chloride diffusion coefficient has higher chloride concentration. With higher environmental chloride concentration and longer pressure time, the chloride concentration in concrete will be improved.(5) As relative humidity h is the main parameters, the chloride migration equation under the coupling of diffusion and convection is establishment considering binding capacity and carbonization combined with the moisture diffusion nonlinear equation. Finite difference method and Matlab are used to analyzed these equations. Relative humidity at every position increases over time and finally stabilized. But the stable humidity values can’t be equal to the ambient humidity. The chloride concentration is accumulated over time and the chloride concentration in shallow layer is always higher than the deep one. Concrete with high strength grade impede moisture and chloride migration, so that the accumulation reduced. Ambient humidity can greatly affect the ion transport. The greater environmental humidity is, the more chloride accumulation concentration is.(6) The lifetime of subsea tunnel is defined as the smaller one of the outside life and the inside life. As long as one of them damaged, it’s the end of the subsea tunnel. Life prediction model of subsea tunnel is obtained combined with lateral and inner model. Use these models to analyze Zhoushan Shenjiamen subsea tunnel and prove this tunnel can meet the requirement of design life with100years.