EPBMs for the North East line project

Fifteen years ago construction started on phase one of the Mass Rapid Transit tunnels in Singapore. Since that time tunnelling technology has advanced considerably. Earth Pressure Balance Machines (EPBMs) are far more commonly used than ever before on tunnelling projects in the Far East, Asia and Europe. For the first time in Singapore full-face tunnelling is being carried out in the Old Alluvium for the construction of North East Line Project (NELP). The TBMs selected for the NELP are, in the main, EPBMs. This paper compares the types of EPBMs chosen for each Contract, highlighting the particular design features of each. The paper also provides an update on the progress of the EPBM tunnelling operations currently being undertaken on the NELP.     

Design of bored tunnel linings for Singapore MRT North East Line C706

The northern section of the bored tunnels of Contract C706 of the Singapore MRT North East Line is located in varying soil conditions ranging from cemented Old Alluvium to very soft marine clay. The bored tunnels will run along Race Course Road, underneath a residential area underpassing several religious temples. The tubes will be constructed by earth pressure balanced shield machines. The paper is presenting the key approaches adopted for the design of the tunnel lining, the assessment of ground movements under the particular circumstances as well as the basic design considerations for the intersection of MRT tunnels with the future tunnels of the Singapore Underground Road System (SURS). In this context, the effect of water pressures in terms of sectional lining forces was studied in detail. A design chart has been developed to determine the sectional forces due to the water pressure load and in relation to the subgrade reaction modulus. An approach to consider the influence of the second tunnel has been developed and its presented in this paper.     

Tunnelling undercrossing existing live MRT tunnels

In conjunction with the government of Singapore’s vision to have efficient and extensive Mass Rapid Transit (MRT) system across Singapore Island, more and more rail tunnels are planned to be constructed in close proximity to sensitive buildings and infrastructures in recent years. This being a particular challenge for major infrastructure works in the urban environment. In contract C937 of Downtown Line Stage 3 (DTL3), twin bored tunnels connect Fort Canning station to Bencoolen Station, under Fort Canning Hill, with the alignment overcrossing the existing North East Line (NEL) rail tunnel, undercrossing North South Line (NSL) and Circle Line (CCL) with clear distance of less than one bored tunnel diameter. This inevitably poses great challenges to tunnelling over and under existing live tunnels without disruption to daily operation of MRT. Further compounding the challenge is the ground condition comprising of Jurong Formation steeply variable sedimentary deposits transitioning into Fort Canning Boulder Bed a colluvial deposit of quartzite boulders in a stiff clay matrix. To successfully negotiate this challenge, requires all involved parties to make contributions in their areas of expertise and work as team together to ensure that the works progress smoothly and as planned. The designer provides an overall approach demonstrating that the work can be safely carried out and provides key parameters for the contractor who carries out the tunnelling with construction control, which in turn is supervised by the supervision engineers ensuring work is carried out safely. The client, who provides the vision in the first place, has overall responsibility for the work providing continuity and ensuring that the component parts of the job are co-ordinated and carried out successfully. In addition, different monitoring levels were also established to reduce the train speed if necessary and also bus bridging service as a contingency measure. This paper summarizes the approach to the tunnelling, key tunnelling parameters during undercrossing of existing live MRT tunnels, instrumentation monitoring as well as measured railway track and structure movements due to proximity tunnelling. It reflects upon the on crucial contributory factors that ensure success within the project and serves as a reference as to how engineering boundaries can be challenged underground.     

Ground response of closely spaced twin tunnels constructed in heavily overconsolidated soils

As part of the City of Edmonton’s light rail transit expansion, twin 6.5 m diameter oval shaped tunnels were constructed using conventional tunnelling methods. The geology of the site consists predominately of a hard, fissured cohesive till unit. The tunnel face construction was sequenced as top header, bench and invert excavations. At its narrowest, the pillar separating the twin tunnels was less than 1.5 m across or 0.23 tunnel diameters. Typically, the minimum pillar spacing required to reduce the interaction between twin, side by side tunnels is one tunnel diameter. Because the tunnel construction was within an urban environment, there was considerable concern with ground loss and excessive surface settlements. This study demonstrates that within similar materials, a pillar width of 0.5 tunnel diameters sufficiently reduces the tunnel interactions and minimize the risk of damage to nearby structures.     

Tunnelling in the Federal Republic of Germany: Analysis for 1985–1986

The author presents the results of a study of tunnelling activity in the Federal Republic of Germany for the years 1985–1986, 1984–1985 and 1983–1984. The study compares six categories of tunnels for each year: underground and commuter railway tunnels; federal railway/long-distance railway tunnels; urban and highway road tunnels; water and other supply tunnels; waste tunnels; and miscellaneous tunnels. Tables and graphs are used to compare overall tunnel drivage length, excavated diameter, means of construction, e.g. mining, cut-and-cover, and placing of contracts as related to excavated volume and drivage length. The author notes that tunnels being constructed as part of the German Federal Railway's program to develop high-speed routes account for the great majority of non-urban traffic tunnel constructions, and that this trend will continue in years to come.     

挪威海底隧道经验在厦门海底隧道建设中的应用

挪威在世界上拥有最多的海底隧道,最近30a共修建了40条海底隧道,总长达240km。尽管大部分隧道位于较好的地层条件,但也遇到与断层相关的复杂地质条件。挪威海底隧道规划与施工中的一个主要特点是封闭可能的渗水,多年的实践发展出一套系统的探测和封闭渗水的方法,挪威所有的海底隧道都应用了这一方法。据此,介绍该方法,同时介绍处理更为复杂地质情况的隧道建设经验,包括防止隧道的进一步坍塌以及所采取的冻结地层方法,进而还讨论有关把挪威海底隧道经验应用到厦门海底隧道规划与建设中的问题。厦门海底隧道某些段所处地质条件较差,极具挑战性。挪威顾问集团专家协助并正参与把挪威经验应用到厦门海底隧道的建设中去。     

Study of ground-tunnel interactions of four shield tunnels driven in close proximity, in relation to design and construction of parallel shield tunnels

In Japan, K yoto City has constructed four subway tunnels that run closely each other. Problems accompanying the closely running tunnels are studied during the planning and design stages prior to construction. A variety of monitoring during the construction stage resulted in the collection of numerous data including the load transmission between tunnels and characteristic behavior of theground during the construction of four tunnels. Aiming at improving the method for the evaluation of the interaction of closely running tunnels, this study attempted to analyze and assess the behavior of the tunnels and the surrounding ground through such data obtained from the above project. This paper describes the characteristics of influence from the thrust of a succeeding tunnel to a preceding tunnel and the analytical expression of the mechanism of ground behavior during the construction of closely running tunnels.     

Evaluating D&B and TBM tunnelling using NTNU prediction models

Drill and Blast (D&B) and Tunnel Boring Machine (TBM) are the two dominating excavation methods in hard rock tunnelling. Selection of the cost effective excavation method for a tunnel is a function of tunnel cross section area, rock conditions, tunnel length, availability of skilled labour and proper equipment, and project schedule. Over the past few decades, major technological development and technical advances have been achieved in both methods. Yet, in many tunnelling projects, choosing the excavation method is still a challenge and requires considering pros and cons of each method and estimating construction time, costs, as well as post construction and operation & maintenance, and related risk in the planning phase. In this study, the productivity and efficiency of the D&B and TBM options for excavating certain size tunnels have been examined. The analysis is based on recent NTNU prediction models for advance rate and unit excavation cost for given ground conditions and tunnel geometry. For excavation of large size tunnels in very hard rock, the D&B method seems to be the cost effective choice irrespective to tunnel geometry. This is compared to smaller long tunnels with good boreability were the TBM has higher advance rate. The tunnel size and rock conditions have higher impact on the TBM performance and costs than for D&B. This refers to lower risk of using D&B where the use of this method is otherwise justified.     

Effects of twin tunnels construction beneath existing shield-driven twin tunnels

This paper presents a case of closely spaced twin tunnels excavated beneath other closely spaced existing twin tunnels in Beijing, China. The existing twin tunnels were previously built by the shield method while the new twin tunnels were excavated by the shallow tunnelling method. The settlements of the existing tunnels and the ground surfaces associated with the new tunnels construction were systematically monitored. A superposition method is adopted to describe the settlement profiles of both the existing tunnels and the ground surfaces under the influence of the new twin tunnels construction below. A satisfactory match between the proposed fitting curves and the measured settlement data of both the existing tunnels and the ground surfaces is obtained. As shown in a particular monitoring cross-section, the settlement profile shapes for the existing tunnel and the ground surface are different. The settlement profile of the existing structure displays a “W” shape while the ground surface settlement profile displays a “U” shape. It is also found that due to the flexibility of the segmental lining, the ground losses obtained from the existing tunnel level and the ground surface level in the same monitoring cross-section are nearly the same.     

大断面顶管通道近接穿越下覆既有地铁隧道数值模拟与现场试验

南京某地下步行通道采用非开挖顶管法施工,顶管近距离穿越既有地铁区间隧道及城市主干道。为了保证隧道及主干道安全,施工前建立三维有限元计算模型,模拟施工全过程,预测施工可能引起的隧道及地表变形。根据数值模拟结果提出针对性控制措施,并制定合理的监测方案,分别对隧道竖向位移、水平位移、径向收敛和地表隆沉进行监测。基于监测数据分析隧道及地表变形规律,明确顶管施工期间隧道及地表变形的3个不同发展阶段。研究表明:隧道竖向位移主要表现为隆起,由通道内出土卸荷所引起,工作井基坑开挖对其影响几乎可以忽略;顶管施工过程中,下覆隧道竖向位移先后经历了初始下沉、隆起增强和隆起稳定3个阶段,地表竖向位移先后经历了隆起增强、隆起减弱和沉降3个阶段;同一监测断面内,地表最大沉降位于通道中心轴线上方,距离通道越远沉降越小;采用微欠挖工艺有效控制了隧道最终隆起和地表最终沉降。     

Planning level tunnel cost estimation based on statistical analysis of historical data

Estimating the construction cost of a tunnel with certain diameter and length during the planning stage of a project is essential and a “must do” to justify the project, but it is a very difficult task. Numerous variables influence the cost of tunnel construction and limited information is available at early stages of design when the possible use of tunnels is being studied. Therefore, there is limited number of models at engineers’ disposal for development of a proper cost estimate in tunneling projects. The focus of this study was to offer a model for estimation of the construction cost of tunnels for various applications in the preliminary stage of a project. The work is based on study of nearly 270 projects and statistical analysis of the recoded construction costs, tunnel size, ground conditions, and tunnel applications. Several cost estimation models are introduced for various tunnel types including waste water, water, and transportation tunnels in soft ground and rock. The model uses commonly available cost indices (CCI and BCI) to adjust the estimated costs for the time and location of the project. The proposed cost models presented in this study can included in a simple program to help users make more accurate and quick cost estimates for their future projects. The models do not deal with construction risk which is an essential part of the study of various methods and should be done through developing a risk registry with related cost of each case before final selection, design, and cost estimation of any tunneling project.     

Monitoring and analysis of results for two strutted deep excavations using vibrating wire strain gauges

As part of the North East Line Mass Rapid Transit Project in Singapore, Contract 704 included the construction of two underground station structures. The excavation for Serangoon Station was in the residual Bukit Timah granite and the excavation for Woodleigh Station was in the residual Old Alluvium material. The temporary retaining structures for both excavations consisted of driven soldier piles and timber lagging supported by steel struts. The excavation for the construction of both stations was monitored in part using vibrating wire strain gauges on the struts. This paper presents the strut monitoring results. A comparison is made with the apparent earth pressure envelopes recommended by Peck. The need to balance continued development with the land constraints in Singapore means that underground structures will continue to be used. The results presented in this paper are relevant in determining the geotechnical parameters for deep excavation retaining walls constructed in these types of materials. It is concluded that the measured earth pressures relate reasonably well to the apparent earth pressure envelopes recommended by Peck.     

Effects of above-crossing tunnelling on the existing shield tunnels

Tunnelling in the dense urban areas frequently results in over-crossing or bypassing the existing tunnels. It is obvious that the over-crossing tunnelling will adversely affect and even damage the existing tunnels if the induced deformation exceeds the capacity of tunnel structures. Increasing concerns have been raised about the interactions between the over-crossing tunnelling and underlying tunnels. In order to obtain a better mechanical understanding of the effects of the over-crossing tunnelling on the existing tunnels and provide a quick but low cost assessment alternative method for evaluating the behavior of underlying tunnels prior to construction, a simplified analytical method is proposed in this study. In this simplified method, the tunnel is simply considered as a continuous Euler-Bernoulli beam with a certain equivalent bending stiffness. The unloading stress at the tunnel location caused by the over-crossing tunnelling is computed through Mindlin’s solution, ignoring the presence of the existing tunnel. Then, the tunnel-soil interaction due to the relief stress is analyzed based on the commonly-accepted Winkler foundation model. The applicability of the presented method is validated by three well-documented case histories. Results of these case studies show a reasonable agreement between the predictions and observations. Finally, a parametric analysis is also preformed to investigate the influences of the different factors on the behavior of the existing tunnels, including clearance distance, advancing distance and multiple tunnels construction.     

重叠隧道的施工力学研究

由于地下空间的不断利用，出现了重叠隧道。这种形式布局的隧道在第1孔隧道完成之后，引起了地层内初始应力的变化，而且由于地层中已有一个相邻的已衬砌隧道，地层的刚度条件不再与单孔隧道的垂直轴对称，第2孔隧道的修建又要对已建的第1孔隧道发生影响。应用ANSYS程序对深圳地铁1期工程中的3种典型的重叠断面的计算表明：重叠隧道地表和拱顶下沉及两隧道间土体的稳定难于控制，上面第1孔隧道易发生结构整体下沉。     

Landtunnel Utrecht at Leidsche Rijn: The conceptualisation of the Dutch multifunctional tunnel

The Landtunnel Utrecht at Leidsche Rijn has become a milestone in Dutch tunnelling because it signifies a remarkable leap forwards in the conceptualisation, awareness and insight into the use of underground space technology and tunnelling for environmental purposes. At the beginning of the 21st century, all motorway tunnels in the Netherlands (with the exception of the Schiphol road tunnel) were subsurface constructions that were built to pass waterways. The Landtunnel Utrecht at Leidsche Rijn is the first aboveground motorway tunnel built to minimise the environmental impact of the road, and it allows development of the largest residential area in the Netherlands: Leidsche Rijn, Utrecht. Implementing the project highlights the difficulties decision makers face when they have to balance safety issues, high costs, multiple environmental issues, complex financing and urban development objectives. With no effective regulation in place and no similar practice to fall back on, the Landtunnel Utrecht (together with Sijtwende and the Green Link A15) breaks ground to allow the use of motorway tunnels for a new and promising application: environmental and spatial integration of motorways in urban areas.     

Building response to tunnelling

Understanding how buildings respond to tunnelling-induced ground movements is an area of great importance for urban tunnelling projects, particularly for risk management. In this paper, observations of building response to tunnelling, from both centrifuge modelling and a field study in Bologna, are used to identify mechanisms governing the soil–structure interaction. Centrifuge modelling was carried out on an 8-m-diameter beam centrifuge at Cambridge University, with buildings being modelled as highly simplified elastic and inelastic beams of varying stiffness and geometry. The Bologna case study presents the response of two different buildings to the construction of a sprayed concrete lining (SCL) tunnel, 12 m in diameter, with jet grouting and face reinforcement.In both studies, a comparison of the building settlement and horizontal displacement profiles, with the greenfield ground movements, enables the soil structure interaction to be quantified. Encouraging agreement between the modification to the greenfield settlement profile, displayed by the buildings, and estimates made from existing predictive tools is observed. Similarly, both studies indicate that the horizontal strains, induced in the buildings, are typically at least an order of magnitude smaller than the greenfield values. This is consistent with observations in the literature. The potential modification to the settlement distortions is shown to have significant implications on the estimated level of damage. Potential issues for infrastructures connected to buildings, arising from the embedment of rigid buildings into the soil, are also highlighted.     

超大直径双线泥水盾构施工的三维数值模拟

以上海长江西路隧道工程为背景,基于适合软土的修正剑桥模型并综合考虑盾构开挖、开挖面泥水压力、盾尾注浆以及盾壳刚度和坡度等因素,建立单台超大直径(=15.43m)泥水盾构往返推进的三维有限元模型。分析不同施工步、不同泥水压力下北线盾构施工对地表沉降以及新建南线隧道的横向位移影响。通过数据分析发现,盾构返回推进时的地表位移规律明显区别于单条隧道施工的情况;盾构的反向推进会造成已建隧道管片的挤压变形以及顺指针的旋转;返回推进时,泥水压力的不同取值对已建隧道的横向位移影响显著。根据数值分析结果提出相应的施工建议:盾构返回施工时适当减小泥水压力;密切监控盾构返回推进时切口断面后1倍刀盘直径范围内已建隧道管片的变形量。     

Finite element analysis of tunnel–soil–pile interaction using displacement controlled model

Significant additional loads could be induced in pile foundations adjacent to new tunnels. Accurate prediction of magnitude and shape of the ground displacements, which define curvature changes, is crucial for the computation of tunnelling induced bending and axial stresses in pile foundations. The finite element simulation of tunnelling by removing forces corresponding to initial stress-state, tend to predict incorrect shape of ground displacement profiles, hence incorrect forces in pile foundations adjacent to tunnels. To overcome this difficulty, this paper describes the development and application of a simple and useful displacement controlled model (DCM) to predict the effects of tunnel excavation on adjacent pile foundations. The DCM simulates tunnelling by applying displacements to the tunnel boundary. A method to determine magnitude and direction of tunnel boundary displacements, based on convergence patterns observed in field and centrifuge test results, is proposed. Back analyses of numerous greenfield tunnel case histories using the DCM indicate good agreement between computed displacement profiles and field/test data. The suitability of the DCM in modelling tunnel–soil–pile interaction problems is demonstrated through back analysis of a centrifuge test and a field case study.     

斯堪的纳维亚硬岩海底隧道工程

论述了北欧海底隧道特别是基岩中开挖的公路隧道的工程经验,目前在北欧已建成25条以上的海底隧道,总长超过100km,大部分在挪威,最长的7.9km,最深的在海平面下264m。所有这些隧道都是用钻爆法进行开挖的。同时,叙述了勘探、规划、设计和施工等诸方面的重要问题,讨论了从这些工程中的经验教训。最后,介绍了规划中的海底隧道,包括长24km、埋深400m的2条隧道。相应地,介绍了其他北欧国家的海底隧道,这些隧道大多也是根据挪威海底隧道的经验进行设计和施工的。     

相邻隧道施工对上海地铁二号线的影响分析

上海明珠线东方路车站附近的区间隧道是相邻于地铁二号线的区间隧道建设的，二者中心线间的最小距离为12.3m。由于距离很近，新隧道的施工对原有的地铁二号线隧道的影响不可避免。讨论了在新隧道施工过程中地铁二号线隧道的位移变化规律；研究了新建的盾构隧道的推进对原有隧道的影响特征，并且，给出了存已有隧道附近建设新隧道的规划和施工建议；同时，用数值模拟手段对隧道变形进行了预测，并将预测结果与实测结果进行了比较。