基于压力拱理论的水下隧道合理覆岩厚度研究

建立了水下隧道流固耦合数值模型，通过正交试验优化计算方案，分析土岩复合地层和全断面岩层拱顶竖直方向上围岩压力拱的成拱规律，并据此提出以成拱临界板厚为判据求解水下隧道合理覆岩厚度的思路，建立水下隧道合理覆岩厚度回归模型，并通过BP神经网络模型对回归模型进行评价与校验，结合佛莞城际狮子洋隧道工程，进行了合理覆岩厚度回归模型的应用算例分析。研究表明：土岩复合地层上覆岩层岩性较好时，压力拱高度主要受覆岩厚度影响，上覆岩层岩性较差时，压力拱高度主要受上覆软土厚度影响；压力拱高度随覆岩厚度增加线性增加，达到成拱临界板厚时，逐渐减小随后趋于稳定，上覆岩层岩性越差，成拱临界板厚越大；全断面岩层压力拱高度随覆岩厚度的变化比土岩复合地层平稳。算例分析表明，以成拱临界板厚为判据建立的合理覆岩厚度模型能给出较优的覆岩厚度预测值，可为土岩复合地层水下盾构隧道的设计和施工提供参考。

Reasonable overlying thickness of subaqueous tunnels based on pressure arch theory

With the orthogonal optimisation algorithm, a fluid-solid coupling numerical model for subaqueous tunnels was established to analyse the arching laws of the pressure arch in the vertical direction above the vaults of the soil-rock compound strata and the full-section rock strata. The reasonable overlying thickness of subaqueous tunnels can be further derived based on the critical arching thickness criterion. Subsequently, a regression model for the overlying thickness of the subaqueous tunnel was proposed and further evaluated by BP neural network model. Finally, the regression model was applied to Foguan Shiziyang intercity tunnel to calculate its overlying thickness. The results showed that the height of the pressure arch was mainly affected by the overlying thickness when the lithology of the overlying strata was good, while it was affected by the thickness of soft soil when the lithology of the overlying strata was poor. The height of the pressure arch increased linearly with the increase of the overlying thickness, and then gradually decreased to achieve a stable state when reaching the critical arching thickness. When the lithology of the overlying strata became poorer, the critical arching thickness became greater. The variation of the pressure arch height in the full-section rock strata was less than that in the soil-rock compound strata. The example analysis shows that the reasonable overlying thickness model can be predicted according to the critical arching thickness criterion. Hence, the obtained results can provide references for the design and construction of the subaqueous shield tunnel in the soil-rock compound strata.