Evaluation of the load on shield tunnel lining in gravel

It is important to evaluate accurately the load acting on a shield tunnel lining to facilitate its economical and rational design. In Japan, the load calculated by Terzaghi's formula, or overburden load, is generally adopted for the design of tunnel segments. However, some previous field measurements have shown that the actual load acting on the shield tunnel lining could be much smaller than that adopted for the design in the case of good ground conditions. In this study, field measurements at two shield tunnel construction sites in gravel were carried out, and the load acting on the shield tunnel lining was evaluated by analyzing the field data to establish the rational design of the shield tunnel segments. The method of treating the dead load of segments in the design was also investigated.     

Development of a prestressed and precast concrete segmental lining

Prestressed & precast concrete segmental lining (P&PCSL) is used for shield tunnels. Its primary feature is that it integrates segments into one ring by introducing prestress in the tunnel circumferential and longitudinal directions. Introducing prestress enables the elimination of bolt joints and reduces the volume of reinforcement, thus reducing the manufacturing cost of precast concrete segments. It also enables quality improvement and labor saving in lining and provides greater adaptability for tunnels with large diameter, where deformation due to dead load is a problem. The P&PCSL has been implemented in three construction projects after undergoing various performance tests and workability verification tests.     

Multi-objective optimization of shield construction parameters based on random forests and NSGA-II

Metro shield construction will inevitably cause changes in the stress and strain state of the surrounding soil, resulting in stratum deformation and surface settlement (SS), which will seriously endanger the safety of nearby buildings, roads and underground pipe networks. Therefore, in the design and construction stage, optimizing the shield construction parameters (SCP) is the key to reducing the SS rate and increasing the safe driving speed (DS). However, optimization of existing SCP are challenged by the need to construct a unified multiobjective model for optimization that are efficient, convenient, and widely applicable. This paper innovatively proposes a hybrid intelligence framework that combines random forest (RF) and non-dominant classification genetic algorithm II (NSGA-II), which overcomes the shortcomings of time-consuming and high cost for the establishment and verification of traditional prediction models. First, RF is used to rank the importance of 10 influencing factors, and the nonlinear mapping relationship between the main SCP and the two objectives is constructed as the fitness function of the NSGA-II algorithm. Second, a multiobjective optimization framework for RF-NSGA-II is established, based on which the optimal Pareto front is calculated, and reasonable optimized control ranges for the SCP are obtained. Finally, a case study in the Wuhan Rail Transit Line 6 project is examined. The results show that the SS is reduced by 12.5% and the DS is increased by 2.5% with the proposed framework. Meanwhile, the prediction results are compared with the back-propagation neural network (BPNN), support vector machine (SVM), and gradient boosting decision tree (GBDT). The findings indicate that the RF-NSGA-II framework can not only meet the requirements of SS and DS calculation, but also used as a support tool for real-time optimization and control of SCP.     

盾构法隧道的纵向受力分析

本文借助等效连续化模型 ,把盾构法隧道假设为弹性地基上的弹塑性梁 ,着重研究了纵向不均匀荷载、不均匀沉降对隧道应力分布以及缝隙张开状况的影响。并以某越江隧道为工程实例 ,分析了隧道的受力变形。     

A simplified 3D model for tunnel construction using tunnel boring machines

This paper includes a presentation of a simplified three-dimensional numerical model for the prediction of soil movement induced during tunnel construction using tunnel boring machines (TBM). The model is based upon the generalization of the convergence-confinement concept to 3D tunnel construction. It uses two parameters (L_dec and α_dec) which stand for the length of the unlined zone and the partial stress release, respectively. The value of the parameter L_dec can be taken equal to the tunnel diameter, while the value of α_dec can be determined by fitting the model to empirical formula, and then adjusted based on settlement registered during tunnel construction.The capacity of the model is illustrated through an application to a shallow tunnel in soft soil. The comparison of the numerical results to those suggested by different authors shows good agreement.     

盾构施工引起地基变位的神经网络预测

通过分析盾构施工引起地基变位的影响因素,在盾构试掘进基础上,提出应用人工神经网络建立地层条件及施工参数与盾构施工引起周围地基变形之间的关系,并分析了人工神经网络技术应用于盾构隧道地表变形预报中的一些关键技术,为盾构法施工中人工神经网络的应用提出一些意见和建议。并对某一地铁工程中实测资料,应用简单的 BP 神经网络进行地表变形预测。     

Automated design of threats and shields under hypervelocity impacts by using successive optimization methodology

In this study, predictive hydrocode simulations are coupled with approximate optimization (AO) methodology to achieve successive design automation for a projectile-Whipple shield (WS) system at hypervelocity impact (HVI) conditions. Successive design methodology is first applied to find the most dangerous threat for a given WS design by varying the shape and orientation of a projectile while imposing constraints on the total projectile mass and radar cross section (RCS). Subsequent optimization procedure is then carried on to improve the baseline WS design parameters. A parametric multi-layered stuffed WS model is considered with varying thicknesses of each layer and variable positions of the inter-layers while having a constraint on the areal density. HVI simulations are conducted by using a non-linear explicit dynamics numerical solver, LS-DYNA. Coupled finite element and smoothed particle hydrodynamics (SPH) parametric models are developed for the predictive numerical simulations. LS-OPT is employed to implement the design optimization process based on response surface methodology. It is found that the ideal spherical projectiles are not necessarily presenting the most dangerous threat compared to the ones with irregular shapes and random orientations, which have the same mass and RCS. Therefore, projectiles with different shapes and orientations should be considered while designing a WS. It is also shown that, successive AO methodology coupled with predictive hydrocode simulations can easily be utilized to enhance WS design.     

盾构法隧道防水堵漏技术

分析隧道渗漏水的机理,总结国内外盾构法隧道防水堵漏的技术方法,并结合上海地铁二号线东昌路－东方路区间隧道施工堵漏,提出了防渗堵漏的技术措施。     

21世纪地铁施工技术展望

展望２１世纪地铁施工的新技术、新工艺,并对区间隧道,地铁车站不同的施工方法进行比较,提出新的开发方向。     

双单元建筑物的换气速度和内部流动的测量

采用示踪气体稀释法对选定的双单元建筑物的换气速度和内部流动进行了测量,以期建立一种实际测量的方法,同时获得一些有用的数据。测量结果表明,选定的建筑物具有令人满意的换气速度,内部流通良好,可满足室内空气质量的要求,但对污染事故的屏蔽能力较差。本工作可以为研究室内空气质量和建筑物屏蔽因子提供一些借鉴。