Numerical simulation of the creation and performance of extruded concrete linings in microtunnelling

Microtunnelling traditionally utilises pipe-jacked or segmental lining systems, however when employed over long, continuous distances, which may include changes in depth and direction, both lining systems have associated limitations that would reduce the drive rate of the TBM and increase the costs of the project. The use of an extruded lining system could circumvent a number of these limitations and make such an undertaking economically viable. A numerical model has been developed to simulate the extrusion of a tunnel lining from a microtunnelling TBM. The model was created in Plaxis (3-D Tunnel), a commercially available finite element modelling package. A methodology was developed and tested to approximate the movement of a TBM and the curing of the extruded lining, both of which are time-based phenomena. The extruded materials were subsequently investigated, using published strength-curing time for a normal strength concrete and a polymer concrete, for two drive rates. The outcome of the modelling suggests that the relationship between the developing stiffness and time in the early phases of curing is critical if an extruded lining system is to be deployed behind a TBM without slowing its drive rate.     

试论节理对隧道开挖和衬砌的影响

本文采用文献[1]中的接触摩擦单元对在具有节理和弱软介质中隧道开挖和衬砌进行了有限元模拟。考虑了三种情况:(1) 无节理影响的弹塑性分析;(2) 有一条节理带和软弱夹层影响的弹塑性分析;(3) 双节理和软弱夹层影响的弹塑性分析。通过计算,表明节理的存在,使隧道衬砌的变形和受力状况恶化。     

软弱围岩中的新型双层复合衬砌的受力特性研究及渗水风险分析

 某输水隧洞位于河床的软弱砂岩中,其双层复合预应力衬砌结构形式新颖,受力条件复杂。为了解这种新型双层复合预应力衬砌的工作性态和受力特性,分别采用现场1∶1仿真模型试验方法、三维非线性有限元数值分析方法,并将数值分析结果与仿真试验进行对比分析。有限元分析按照仿真模型试验中管片拼装、分层填土、内衬浇筑、内衬预应力张拉以及内衬充水加压的实际过程模拟,计算中考虑衬砌与土体的耦合效应,通过外衬变形反分析调整土体计算参数,采用基于直接约束的接触迭代算法模拟管片与管片之间、内衬与外衬之间的多重接触与传力。研究结果显示,无论是结构变形、缝隙开度还是结构应力,有限元分析与仿真试验规律一致,数值接近,两种方法相互验证了这种具有多重复杂接触边界的非连续变形柔性结构的受力特性,明确了内、外衬的传力机制;在此基础上,进一步分析高压内水外渗对结构安全性的影响以及预防措施,其研究成果可供类似工程参考。     

A method to estimate concrete hydraulic conductivity of underground tunnel to assess lining degradation

The determination of the degradation state of underground concrete tunnels is a crucial issue for maintaining and monitoring the performance of these infrastructures. In particular, if the tunnel is totally or partially submerged, concrete deterioration and consequent changes in both lining thickness and hydraulic conductivity can have dramatic effects on the amount of water inflow, leading to an increase in maintenance costs as well as to possible interruption of the infrastructure serviceability. The hydraulic conductivity of the concrete lining is here proposed as a proxy of the overall degradation state of the structure, being this property directly correlated to porosity and to the presence of interconnected fissures and cracks.The aim of this study is to propose a simple and completely non-destructive method to estimate the hydraulic conductivity of tunnel lining concrete. Provided the availability of easy-to-collect in situ geometrical and hydrogeological data (i.e. tunnel geometry, water inflow, water table level), the method relies on a back analysis to estimate the hydraulic conductivity of the concrete, performed via the finite element method to solve the seepage equations in porous media. Ground Penetration Radar technique is coupled to the modelling approach to gain accurate data about the current lining thickness.The proposed method has been applied to the study of a real case of underground tunnel, used to prove the model reliability. Moreover, once estimated the hydraulic conductivity and thickness of the concrete, the model can be used to generate curves linking the total water inflow in the tunnel as a function of the groundwater level variations, allowing a real-time monitoring of the current hydraulic state of the infrastructure.This methodology, which can be considered of general validity and easy to be extended for the study of any underground tunnel, provides a simple and effective tool useful to prioritize maintenance works and to evaluate the consequences of different hydraulic scenarios.     

Structural effects of concrete lining for concrete-lined corrugated steel pipes

This article presents the results of an analytical study on the structural behaviour of buried concrete-lined corrugated steel pipe (CLCSP). CLCSP combines the hydraulic characteristics of concrete pipe with an extended service life compared to unlined corrugated pipe. It is typically factory manufactured and shipped to the jobsite for roadway drainage applications. However, recent investigations have also demonstrated the ability to rehabilitate deteriorating metal culverts using a spray-on mortar lining approach. Since the primary intent of the concrete liner of manufactured CLCSP is to prevent abrasion and corrosion and improve the hydraulic performance, design guides for metal culverts lined with concrete have not been developed. A better understanding of the structural significance and the effect of the concrete lining on the strength of CLCSP is therefore needed. This study evaluated the structural effects of the concrete lining in CLCSP using finite element analysis and detailed soil modelling and proposes a design methodology for CLCSP.     

庆阳地区黄土窑洞的病害分析及防治

利用室内试验结合有限元模拟的方法进行计算分析,得到了窑洞病害的防治措施:通过崖面砌筑护面墙较好的解决了窑洞崖面风化剥落的问题,并提高了窑脸的整体强度。通过洞内砌筑夯实土坯和加筋土抹面等围护结构,解决了窑洞干缩裂缝和不均匀掉块等问题,使窑洞洞壁的受力更均匀,变形在围护结构的弹性变形范围内。     

盾构施工隧道衬砌内力及地表沉降计算

讨论盾构法施工时隧道衬砌内力及其附近地表沉降的有限元计算。包括土工结构建造过程的有限元模拟方法，模拟隧道衬砌的Ｍｉｎｄｌｉｎ曲梁单元，施工过程中洞室超挖量的数值处理方法等。最后通过一实际问题的计算表明本文所建议方法是有效的，并讨论了一些有关的问题。     

Dynamic responses and damage analyses of tunnel lining and errant large vehicle during collision

Collision accidents between errant vehicles and tunnels occur frequently, causing serious loss of life and property as well as the damage to the tunnel lining. Damage analysis of the tunnel lining under collision loads is still a lack of research at present. Based on dynamic finite element method, this study simulates and analyzes the interaction between errant large vehicles and tunnel lining structure and their dynamic response processes under various collision cases. It is noted that the lining structure mainly suffers tensile damage and its value increases with the increases of the collision angle and the vehicle speed. The larger the vehicle speed and the collision angle are, the bigger accelerations the passengers experience. A series of in-situ damage detections and sampling tests of the tunnel lining in a real collision accident that occurred in the Panlong Tunnel on Jinghu Highway in China in 2009 strongly approve the numerical simulation results. This study provides technical supports to the optimal design and operations management of tunnels.     

A holistic numerical approach to simulating the thermal and mechanical behaviour of a tunnel lining subject to fire

Conventional heat transfer analysis for the prediction of fire-induced damage in a tunnel is performed without consideration of the spalling and dehydration of concrete, meaning that the fire-induced damage of concrete may be underestimated. This study proposes a new model that is able to simulate structural loss during a fire by eliminating the elements exceeding a pre-determined critical temperature in a finite element analysis. The important parameters for the application of the proposed element elimination model include the critical temperature chosen as the element elimination criterion and the changes of the combined heat transfer coefficients, which are dependent on element size and the time–temperature history during a fire, respectively. These parameters are derived from a series of parametric studies based on real fire experiments using a high-temperature furnace. In order to verify the applicability of thermo-mechanical coupling analysis using the proposed model, the fire-induced damage of an unreinforced concrete tunnel lining was estimated with a focus on the spalling depth, temperature distribution, and equivalent stress in the remaining part of the concrete lining under RABT and RWS fire scenarios.     

考虑衬砌接头的土-盾构隧道有限元模型初探

本文作者详细推导了由梁单元和衬砌接头单元组成的混合单元的刚度矩阵,形成了考虑衬砌拉头的土－盾构隧道有限元模型。利用有限元法计算了考虑衬砌接头和不考虑衬砌接头两种情况下衬砌的内力和衬砌的变形。由计算可知,衬砌接头对衬砌的轴力和位移影响相对较小,但对衬砌的弯矩影响较大,因此在盾构隧道的抗震设计中必须考虑衬砌接头的影响,否则将使设计趋于保守。     

Advanced model for predicting the fire response of concrete filled tubular columns

In this work, a nonlinear finite element three-dimensional model is presented and validated in order to study the behaviour of axially loaded concrete filled tubular (CFT) columns with circular cross-section exposed to fire. A realistic sequentially coupled nonlinear thermal-stress analysis is conducted for a series of columns available in the literature. The model is validated by comparing the simulation results with the real fire resistance tests. By means of this model, and extensive sensitivity analysis is performed over a wide range of aspects concerning the finite element modelling of the problem under study, including new key factors not studied previously. Based on this sensitivity analysis several modelling recommendations are given in this paper, which will be useful for future research work. The validated numerical model is furthermore employed to study and discuss the Eurocode 4 Part 1–2 simple calculation model, which is deeply analysed in this paper.     

Effect of large excavation on deformation of adjacent MRT tunnels

A large excavation of approximately 140 m wide, 200 m long and 15 m deep was made close to two Mass Rapid Transit (MRT) tunnels of 6 m diameter with invert depth of 15–27 m. In view of the scale and distance of excavation, significant effects on the MRT tunnels were expected. The paper presents the monitoring of the tunnel deformations during the excavation. A sophisticated monitoring system using a motorised total station was installed in the MRT tunnels to monitor their displacements and to ensure that the stringent requirements for safeguarding the tunnels were not violated during any part of the excavation works. The paper also presents the modelling of the excavation using a finite element program. The results obtained were reasonably close to the monitoring results. It was found that the stiffness of the tunnel lining has significant influence on the displacement and distortion of tunnels caused by an adjacent excavation. A stiffer lining undergoes less displacement and distortion but is likely to experience significantly greater bending moments.     

The effect of erosion voids on existing tunnel linings

Erosion voids may develop around buried infrastructures due to several reasons including water infiltration into leaking joints, dissolution of Karst limestone, and dynamic loading caused by construction related activities. This study evaluates the effect of erosion voids developing in the close vicinity of existing tunnels on the circumferential stresses in the lining. A series of simplified void geometries are defined beside and under the lining. Elasto-plastic finite element analyses are performed to study how those voids influence thrust forces and bending moments in the lining. The role of other factors such as the lining flexibility and in situ stress conditions is also investigated. Depending on the flexibility ratio between the lining and the surrounding soil, the void size can have a significant impact on the circumferential stresses in the tunnel lining. A void under the invert leads to decrease in the magnitude of bending moment, and for large void size, the moments can reverse sign. This preliminary study suggests that efforts to arrest the growth of erosion voids at the invert and springline should be made before the voids reach this size. All results presented are theoretical in nature, and physical testing is needed to evaluate the performance of these calculations.     

地铁换乘车站结构内力计算分析

以某地铁岛车站主结构单拱、单柱复合衬砌结构为研究对象,采用三维有限元分析方法对其进行分析计算。根据地下工程有限元分析的原则和要求,利用有限元软件MIDAS/GTS计算分析了主体结构荷载效应的最不利组合。同时,根据其主要控制截面,建立了有限元分析模型,在受力条件下进行了有限元分析,得到了相应的计算结果。     

地下衬砌的变几何应力分析

根据地下衬砌边砌筑边受载的特点,针对空间轴对称的衬砌结构和荷载的情形,给出了变几何应力的解析解。文中讨论了采用Ｆｏｕｒｉｅｒ级数和Ｆｏｕｒｉｅｒ－Ｂｅｓｓｅｌ级数展开的方法求解在任意轴对称荷载作用下有限长空心圆柱问题的过程和步骤。最后,将地下衬砌的变几何与不变几何的应力分析结果作了比较。     

土中爆炸衬砌有限元数值模拟

对土中爆炸砂浆形成的爆炸衬砌应用Hsieh-Ting-Chen破坏准则进行了有限元数值模拟,获得在不同水容量情况下衬砌工作时的应力和变形情况,分析了爆破衬砌随水容变化下的安全情况,解决了爆炸衬砌这种新型结构形式的简化数值模拟问题。     

Numerical investigation into the composite behaviour of over-deformed segmental tunnel linings strengthened by bonding steel plates

Bonding steel plate has been used as a strengthening approach to repair disrupted segmental lining of operational tunnels. This paper introduces numerical investigation into the composite behaviour of the initially deformed segmental tunnel linings strengthened by bonding steel plates using finite element modelling. Cohesive zone modelling was used to simulate the interface bonding behaviour between the segmental linings and steel plates. The full history of the tunnel behaviour before and after strengthening were simulated, where the segmental tunnel lining is initially loaded to create some deformation, then after bonding steel plate, the strengthened tunnel is reloaded until failure occurs. By comparing the results with experimental data from the literature, the proposed model was proved to be capable of simulating the strengthened lining behaviour and able to capture the strengthening failure process in terms of the interface debonding. Subsequently, the segmental lining response and interface shear stress distribution and propagation were analysed to interpret the interaction and failure mechanism of the steel plate strengthened segmental linings. The influence of the initial deformation and the steel plate thickness were investigated and discussed in terms of the strengthened stiffness and capacity. It has been found that the interface shear stress concentration occurred at the positions of the segment joints, where bond damage first initiated. The ultimate failure of the steel plate strengthening happened suddenly once a local debonding zone close to the segmental joint was formed. In addition, the predicted results indicate that a delay in strengthening would result in an increase in strengthened capacity but a decrease in strengthened stiffness. By using thicker steel plates, the strengthened stiffness was improved, while the strengthened capacity could be improved only if the thickness was relatively thin.     

爆破施工对新喷射混凝土的损伤影响分析

根据混凝土损伤理论,利用有限元数值模拟技术,研究了地下工程掘进爆破施工产生的空气冲击波荷载对早期新喷射混凝土衬砌结构的损伤影响,并定量地给出了衬砌结构的最大损伤值。分析了不同混凝土喷层厚度、掘进循环进尺、循环作业时间、爆破装药量等因素对混凝土损伤的影响,总结了各种因素下新喷射混凝土结构损伤发展变化的规律,为地下工程掘进爆破施工和早期喷射混凝土衬砌结构的设计提供了重要的参考依据。     

连拱隧道衬砌厚度对结构安全影响分析

基于有限元分析了不同厚度下衬砌结构的受力特征,通过对比总结了衬砌结构安全系数随厚度的变化规律,得到了连拱衬砌厚度的合理取值。分析结果可以为连拱隧道衬砌工程设计提供参考。     

衬砌背后空洞对隧道结构的影响分析及综合评价方法

本文选取隧道典型病害——衬砌背后的空洞,作为研究对象。通过对病害断面进行数值模拟分析,对隧道衬砌背后不同位置、不同范围的空洞以及拱顶存在空洞下隧道衬砌在不同围岩等级进行有限元模拟,得出衬砌内力和位移,通过分析得到其对衬砌影响的程度及规律。对衬砌结构健康级别评价划分,从而采取不同的应对措施。