基于流固耦合理论水下隧道冻结壁厚度优化研究

水下隧道对冻结壁厚度设计有特殊要求,针对珠机城际轨道交通项目下穿马骝洲水道段联络通道冻结壁设计改进问题,基于流固耦合分析理论,利用有限差分数值计算方法对水下隧道冻结壁稳定性进行研究,通过对不同厚度冻结壁响应情况的对比研究,实现对于冻结壁厚度的优化设计。研究表明:相较无渗流模型,流固耦合模型冻结壁应力分布规律相同,但整体量值增大明显,水的作用不可忽略;水的存在使冻结壁受力趋于"均匀",应力集中现象缓解,但高剪应力区范围扩大,使其剪切破坏风险加大,且冻结壁受力形式有从受压向受拉改变的趋势,对结构稳定不利;冻结壁在流固耦合作用下变形加剧,且随厚度减小而愈发显著,模型厚度达到2.0m以上时变形基本稳定;流固耦合模型塑性区多集中于两侧拱脚区域,3.0 m和2.5 m模型整体完好,2.0 m模型两侧拱脚出现相向发展塑性区,1.5 m模型塑性区厚度接近贯穿,1.0 m冻结壁拱脚已形成明显贯穿破坏;综合选定2.5 m为冻结壁改进厚度,成果直接应用于4#联络通道冻结法施工,经现场监测表明该优化方案有效、可行,对类似工程冻结壁厚度设计具有重要的推广应用价值。

Research on optimization of frozen wall thickness of underwater tunnel based on fluid-solid coupling theory

The design of underwater tunnel has special requirements for the thickness of the frozen wall. To improve the frozen wall design of the contact channel in the Maliuzhou waterway section of the Zhuji Intercity Rail Transit Project, based on the fluid-solid coupling theory, the finite difference method is adopted to analyze the stability of the underwater tunnel numerically. By simulating underwater tunnel with different frozen wall thickness, the responses of underwater tunnel stability to the thickness of frozen wall are discussed and the optimizaitons of frozen wall ticknesses are done. The results of simulation show: compared with the non-permeability model, the fluid-solid coupling model has the same distribution of stress on the frozen wall, but the overall values are obvious larger, which means the effect of water cannot be ignored. Due to the existence of water, the frozen wall tends to be “homogeneous” and the stress concentration phenomenon is alleviated, but the distribution range of high shear stress is expanded, which increases the risk of shear damage, and the frozen wall is changed to be under the tension from the pressure, which decreases structural stability. The deformation of the frozen wall is intensified under influence of the fluid-solid coupling and increase with the decreases of the thickness until the thickness of the model reaches 2.0 m or more, where the deformation of the frozen wall is basically stable. The plastic zones of the fluid-solid coupling models mostly exist at the arched areas on both sides, no plastic zone is formed in the models with 3.0 m and 2.5 m thickness, the plastics are formed in the opposite sides of the model with 2.0 m thickness, the plastic zone is almost going through in the models with 1.5 m thickness, the damage zone is formed obviously at frozen wall arch of the model with 1.0 m thickness. The thickness of 2.5 m is selected as the optimized thickness of the frozen wall. This optimized thickness is directly applied to the design of the No.4 communication channel, which is constructed by a freezing method. Through the on-site monitoring test, the validity and the effectiveness of the optimization scheme are verified, which means this optimization scheme has essential promotion and application value for the design of frozen wall thickness in similar projects.