Three-dimensional numerical simulation of a mechanized twin tunnels in soft ground

The increase in transportation in large cities makes it necessary to construct of twin tunnels at shallow depths. Thus, the prediction of the influence of a new tunnel construction on an already existing one plays a key role in the optimal design and construction of close parallel shield tunnels in order to avoid any damage to the existing tunnel during and after excavation of the new tunnel.Most of the reported cases in the literature on parallel mechanized excavation of twin tunnels have focused on the effects of the ground condition, tunnel size, tunnel depth, surface loads, and relative position between the two tunnels on tunnel behaviour. The numerical investigation performed in this study, using the FLAC^3D finite difference element programme, has made it possible to include the influence of the construction process between the two tunnels. The structural forces induced in both tunnels and the development of the displacement field in the surrounding ground have been highlighted.The results of the numerical analysis have indicated a great impact of a new tunnel construction on an existing tunnel. The influence of the lagged distance between the two tunnels faces has also been highlighted. Generally, the simultaneous excavation of twin tunnels causes smaller structural forces and lining displacements than those induced in the case of twin tunnels excavated at a large lagged distance. However, the simultaneous excavation of twin tunnels could result in a higher settlement above the two tunnels.     

Deformation and mechanical characteristics of tunnel lining in tunnel intersection between subway station tunnel and construction tunnel

Deformations and stress distributions in tunnel intersection areas are more complicated than those in common tunnels. The literature on deformations and stress distributions in tunnel intersections, in which the intersecting tunnel is in a different section, is limited. The Shangxinjie subway station in Chongqing, China, was selected to investigate the deformation, stress and plastic zone responses of a tunnel intersection using numerical simulations. Based on the numerical results, the scopes of influence with respect to the deformation, stresses and possible failure modes of the tunnel lining were further studied. The numerical results show that the deformation in a section close to the tunnel intersection was larger than the deformations in distant sections. Compared with the common section, the crown settlement reached the maximum value at the tunnel intersection, and the maximum rate of increase was approximately 28%. The range of the plastic zone at the tunnel intersection was much larger than that in the other areas, and it was mainly located in the side wall and tunnel crown. In the longitudinal direction, the lengths of the scopes of influence were 2.4 B and 1.6 B with respect to the deformation and stress, respectively. The magnitudes of the internal forces in the longitudinal and circumferential directions were almost equal. The bending moments of the tunnel lining within 135° and 225° significantly changed, but the axial force decreased dramatically. Tensile and compressive failures may occur at the tunnel intersection and in a section 5 m away. Locally thickening the supporting structures is suggested to improve the stability of the tunnel.     

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.     

Cause investigation and verification of lining cracking of bifurcation tunnel at Huizhou Pumped Storage Power Station

A wide range of cracking happens in concrete lining at the crown of the lower adit and high-pressure bifurcation in the water-filled test of bifurcation tunnel at Huizhou Pumped Storage Power Station. Then a field investigation is undertaken to explore the main reason of such prominent lining cracking. Through investigating several possible inducing factors, it is found that mass defects exist in the concrete lining in constructing bifurcation tunnel, and insufficient thickness of concrete lining is probably the main factor causing lining cracks. In order to verify if this conclusion is reasonable, comparative analysis through numerical simulation is utilized to assess the influence of different concrete thicknesses on tunnel stability for the lower adit and high-pressure bifurcation. And then the fracturing process of concrete lining with the increase of internal water pressure during the water-filled test is simulated. The results reveal that the displacements and tensile strains in the lining crown are significantly bigger than other parts of tunnel, with deficiency in concrete thickness considered. It is also concluded that whether the cavities exist or not in the crown, rather than the cavity thickness, is the main factor influencing the values and distributions of the tensile strains and displacements for tunnel lining. Besides, the distribution of tensile-strain-concentrated zones is approximately in good agreement with the in-situ fractured status of concrete lining. Finally, a conclusion can be drawn that deficiency in concrete thickness in the crown is the primary triggering factor for lining cracking.     

Influence of multi-layered soil formation on shield tunnel lining behavior

The recent development of larger shield-driven tunnels has for consequence that the tunnel face consists more frequently of multi-layered formations. However, most tunnel designs are still currently conducted in the homogeneous soil condition. In this study, a series of 1-g plane model tests and FEM analyses were carried out to investigate the influence of the layered soils in terms of their relative stiffness and thickness on the lining behavior (i.e. inner force and convergence). The numerical results were found to agree reasonably well with the results obtained from the model tests. For multi-layered formation, a linear increase of the relative thickness of the sandy layer could reduce non-linearly the magnitude of both the moment and the convergence. The distributions of the bending moment and of the convergence along the tunnel perimeter were found to be strongly dependent on the relative stiffness of the layered formations. However, the multi-layered condition has little effect on the thrust force under the condition of this test. In view of these results, some discussions on the applicability of the widely used homogenized design model for the multi-layered soil condition are finally presented.     

The study of seepage forces acting on the tunnel lining and tunnel face in shallow tunnels

In this paper, the seepage force problems arising from the flow of groundwater into a tunnel were studied. Firstly, the effect of seepage forces acting on the tunnel lining was studied for the case of shallow drainage-type tunnels and these results were compared with the lining stresses developed for waterproof-type tunnels. This model was then reviewed through a comparison with an actual case study of the Seoul Subway Line No. 5. Secondly, the effect of seepage forces on the tunnel face stability was studied. In this study, two factors were considered simultaneously. The first factor considered was the effective stresses acting on the tunnel face, calculated from the upper bound solution of limit analysis and the other factor was the seepage forces, calculated from a numerical analysis under a steady-state of groundwater flow conditions. Consequently, reasonable design concepts applicable to the design of tunnel lining and to the evaluation of the support pressure required for maintaining the stability of the tunnel face were suggested for underwater tunnels.     

双圆盾构隧道衬砌结构受力解析

应用不均衡力矩及侧力、竖力传播法推导了双圆DOT盾构隧道衬砌内力的解析解。结合具体工程实例计算,与同一工况下的数值模拟和现场试验实测数据进行了对比分析。结果表明:解析解的计算结果稍微偏大,数值解最小,而实测值基本是介于二者之间,但三者所反映的内力变化规律基本上是一致的,验证了所推导的解析解的合理性和可靠性。此外,基于解析解分析了双圆盾构隧道衬砌结构计算中各种设计参数对计算结果的敏感性,研究表明:对于中浅埋双圆盾构隧道,拱背土压力的影响不能忽略;并建议将侧向土体抗力系数取为2500～6500 kN/m3,以充分发挥地层的被动抗力作用;在考虑结构受力和合理利用、优化结构断面的基础上,张开角应在30°⁶0°取值。     

圆形隧道装配式衬砌接头刚度模型研究

接头刚度Kθ是装配式衬砌结构设计的一个重要参数。目前 ,Kθ的取值尚无现成的公式或图表可循 ,一般是根据接头受力试验确定。本文通过试验建立了接头的力学模型 ,该模型将接头衬垫和连接螺栓抽象成弹簧 ,根据衬垫材料的压缩回弹曲线 ,建立了接头受力和变形的非线性方程式。为了避免应用中求解非线性方程组 ,本文推导了接头刚度的简化计算公式。应用所建立的模型可以求解接头转角、接缝张开量、螺栓拉力等参数 ,通过与接头受力试验实测数据对比 ,证明计算值和实测值是吻合的。文中还应用模型对各种因素对接头刚度的影响规律进行了模拟 ,所得结果是合理的。     

管片衬砌梁–弹簧广义模型及接头转动非线性模拟

梁–弹簧模型法在盾构管片衬砌设计计算中逐渐得到广泛应用,但现有的梁–弹簧模型无法模拟盾构衬砌管片接头的不连续变形及接头转动刚度的非线性特性。基于此,开展了梁–弹簧模型在衬砌设计中的适用性及非线性接头转动刚度在梁–弹簧模型中的应用研究。研究表明:根据对相邻管片在接头位置结点位移处理的不同,可将梁–弹簧模型分为梁–弹簧连续模型和梁–弹簧不连续模型,后者又称为梁–接头模型,可准确分析盾构管片衬砌的内力及变形。采用梁–弹簧不连续模型求解衬砌内力及变形时:对于线性接头转动刚度模型,可基于卡氏第二定理求解;对于多段线性模型,可基于卡氏第一定理或克–恩定理求解;对于非线性模型,可采用增量–迭代法数值求解。     

公路隧道衬砌渗漏水的防止

针对公路隧道防排水的重要性，提出了公路隧道防排水的设计原则，介绍了隧道的防排水措施、衬砌裂缝的防治措施及公路隧道的衬砌质量控制措施，以确保隧道衬砌质量，从而保证隧道的安全。     

Numerical simulation of the uplift behavior of shield tunnel during construction stage

In this study, a new 3D numerical model that considers the circumferential joint, longitudinal bolt, grout pressure, jacking force and the constraint of shield on the linings is developed to derive deeper insights into the lining uplift behavior during shield tunneling. The numerical analysis is conducted using ANSYS, which is verified by a case history in soft soils. Revealed by both the measurements and calculation results, it is found that the lining uplift due to shield tunneling in soft soils can be divided into three stages: dislocation, stretch and steady deformation stages, respectively. In the dislocation stage, the lining deformation attributes principally to the dislocation deformation between neighboring linings. In the stretch stage, the lining deformation is mainly caused by the stretch deformation of circumferential joints. The major uplift is caused during dislocation stage. Thereafter, the impacts of shield-driving parameters including gradient of grout pressure, jacking force and pre-tightening force of longitudinal bolts on the uplift behavior are investigated by a series of parametric studies. The jacking force during segment preparation and assembly shows the most significant impact on the uplift of the tunnel, while the pre-tightening force of longitudinal bolts shows negligible impact. Finally, the control criterion for lining uplift related to the allowable dislocation and opening angle of circumferential joints is proposed.     

隧道混凝土衬砌裂缝修补工艺

针对渝怀铁路 2 6标段白岩隧道工程某段边墙纵向开裂的现象 ,详细阐述了其修补裂缝的步骤及具体方法 ,指出采用环氧树脂浆液修补 ,并用超声波进行检查 ,社会经济效益显著     

隧道二次衬砌施工探讨

结合焦作至晋城高速公路隧道施工情况，就二次衬砌对初期支护的要求作了介绍，探讨了高压大变形围岩和一般软弱围岩的施工时机以及NTM的应用问题，总结了几点施工体会。     

Simplified nonlinear simulation of shield tunnel lining reinforced by epoxy bonded steel plates

A high-efficiency simplified modeling approach based on fiber-beam elements and discrete elements is proposed for investigating the nonlinear response of shield tunnel reinforced concrete linings. The proposed approach focus on following main features: modeling simplicity and computational efficiency, the considerations of critical material and geometric nonlinearity associated with the entire loading process, including the stage of reinforcing the deformed concrete lining by steel plates. Comparison between the analysis results of the proposed numerical model and the experimental results from the full-scale structural test are presented to validate the developed model. The results show that the proposed model can capture the essential characteristics of the nonlinear load–deformation response of segmental tunnel lining. The modeling approach presents a balance between simplicity and accuracy, and serves as a viable alternative to detailed finite elements analysis.     

浅谈乡宁2号隧道混凝土二次衬砌质量控制

结合山西省临吉高速公路乡宁2号隧道施工,为了保证衬砌混凝土外观质量,在施工过程中采用了全断面衬砌钢模台车和其他各种施工措施,通过实践取得了良好的效果,确保了隧道二衬混凝土外观质量,同时为以后二衬施工质量控制积累经验。     

公路隧道衬砌断面型式模型试验研究

通过室内模型试验,研究了在满足建筑限界、通风等约束条件下3种公路隧道衬砌断面型式(单心圆、尖三心圆、坦三心圆)在不同初始应力场作用下的受力性状。分析了初始应力场及断面型式对衬砌结构受力的影响。经综合比较,给出了较为合理的公路隧道衬砌断面型式。研究结论为今后合理地设计隧道衬砌结构提供了可靠的试验依据。     

盾构隧道衬砌的设计方法分析

针对盾构隧道衬砌管片的内力及变形受多种因素影响的情况,结合工程实例,从衬砌管片方面分析了衬砌的内力及变形,得出衬砌管片的内力及变形随其自身因素变化的一些规律,以供设计人员参考。     

隧道二衬渗漏水浅析

结合多年的隧道施工及管养经验,对隧道二衬出现的渗水情况作了简要介绍,就二次衬砌渗水原因进行了分析,并根据渗水情况给出相应的渗水处治原则和方法,以保证隧道运营安全。     

On numerical simulation of tunnel installation

The design of tunnels requires a proper estimate of surface settlements and lining forces. In engineering practice different design methods tend to be used, varying from simple empirical and analytical formulations to advanced finite element analyses. This paper begins with a review of empirical and analytical analyses for settlements and lining forces placing emphasis on the sequences of excavation and installation of support. Such installation procedures range from open face to closed face tunnelling and they tend to have a significant effect on deformations and lining forces. Hereafter the focus is on two-dimensional FE-analyses; again both for open face and for closed face tunnelling. Results for different installation procedures will be presented on the basis of two case studies. It is shown that installation procedures are most important to be considered in order to arrive at proper predictions for tunnelling settlements, horizontal deformations and lining forces. For the installation of closed face shield tunnelling a novel simulation method is presented, named the grout pressure method. It is shown that the grout pressure method yields the best predictions for both ground movements and structural forces.