考虑非饱和效应的跨海隧道衬砌混凝土氯离子非线性对流-扩散侵蚀模型及其求解方法

A non-linear chloride convection-diffusion model and solution method for undersea tunnel lining concrete considering unsaturated effect

为准确预测跨海隧道衬砌内部氯离子含量,本文提出了一个考虑非饱和效应的跨海隧道衬砌混凝土氯离子非线性对流-扩散侵蚀模型。首先,分别引入Langmuir等温吸附结合模型、幂函数型非饱和扩散方程和VG-Mualem水分传输模型,依次考虑氯离子结合效应、混凝土内部非饱和扩散以及非饱和水分渗透作用对氯离子传输的影响,建立非饱和状态下的隧道衬砌混凝土氯离子侵蚀理论模型;其次,基于有限差分原理提出模型的数值求解方法,并验证求解方法的有效性;最后,通过试验分析模型的可靠性,开展参数讨论。研究结果表明:在非饱和状态下,水分渗透对混凝土内离子输运有双重促进作用,使得混凝土内部的饱和度、扩散系数和渗透系数均随时间增加而逐渐增大;在外水压作用早期,混凝土内部处于非饱和状态时,混凝土内部的毛细压力对离子传输效率的影响占主导作用,且呈现出显著的正相关性;饱和渗透系数越大,溶质流速越快,氯离子传输效率也更高。本文提出的基于有限差分原理的数值求解方法是有效的,建立的非饱和状态下隧道衬砌混凝土氯离子非线性对流-扩散侵蚀模型具有可靠性,可用于分析混凝土内部非饱和状态时的氯离子传输规律。

To accurately predict chloride ion content within the lining of a subsea tunnel,a non-linear convection-diffusion erosion model for the unsaturated effect in the concrete lining of the subsea tunnel was proposed.Firstly,the influences of chloride ion binding effects,unsaturated diffusion within the concrete and unsaturated moisture infiltration on chloride ion transport were sequentially considered by introducing Langmuir isotherm adsorption,a power-law unsaturated diffusion equation and the VG−Mualem moisture transport model,which enabled the development of a theoretical model for chloride ion erosion in the unsaturated state of tunnel lining concrete.Secondly,a numerical solution method for the model was proposed based on the finite difference principle,and the effectiveness of the solution method was also validated.Finally,the reliability of the model was analyzed through experimental comparisons,and discussions on parameter analysis were conducted.The results show that water infiltration under unsaturated conditions has a dual promoting effect on ion transport in concrete,which gradually increases the saturation,diffusion coefficient,and permeability coefficient of concrete over time.At the early stage of external water pressure,when the concrete is in an unsaturated state,the capillary pressure inside the concrete dominates the ion transport efficiency and shows a significant positive correlation.The higher the permeability coefficient under saturation,the higher the solute flow rate and the higher the efficiency of chloride ion transport.The proposed numerical method based on the finite difference principle is effective.The established nonlinear convection-diffusion erosion model of chloride ions in unsaturated tunnel lining concrete is reliable and it can be used to analyze the transport law of chloride ions in unsaturated concrete.