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Conventional Tunneling Challenges In The Himalayas: A Case Study R. Kumar Khali and S. Yalal, Hindustan Construction Company Limited Himalayan geology poses the most challenging ground conditions almost anywhere in the world, one of the reasons thereof is their evolution as the youngest mountain chains. They are demonstratively rising faster than any mountain elsewhere. The composition is also younger, and consequently less well consolidated than the other older fold belts. This is consistent with the fact that they constitute one of the most active of the plate margin zones rising at a rate that is almost double the Andes, which is in turn three times that of the Alps. Thus, stress conditions (Magnitude and variations) can potentially be more extreme and adverse on a Himalayan tunneling project. Tunnel excavation under the Himalayan Mountains will pose signiﬁcantly more challenges than an equal length and equal cover drive almost anywhere in the world. These WTC2016 | SAN FRANCISCO CALIFORNIA, USA MONDAY 25 APRIL in-depth-tunneling difﬁculties through high mountainous terrains have posed major challenges for application of traditional drill and blast (D&B) and NATM methods. Handling such adverse geology at any depth is always problematic and generally leads, if not adequately foreseen, to the signiﬁcant tunneling delays.
40 Years of Experience in the Use of Umbrella Arch Method in Tunneling: Problems and Solutions S. Pelizza, Emeritus Politecnico Di Torino and C. Alessio and G. Kalamaras, Ak Ingegneria Geotecnica SRL The umbrella arch method provides a short support of the tunnel vault just ahead of the excavation face. The method foresees the drilling and installation of peripheral, sub-horizontal steel pipes in the ground, followed by their grouting. The umbrella arch method is also known as forepoling, steel pipe umbrella, reinforced protective umbrella or simply “umbrella”. The umbrella arch method does not have a static function because the immediate stabilization of tunnel section is entrusted to the internal shell of steel ribs and shotcrete. The “umbrella” provides a pre-support of the excavation which has to be stable for an adequate length and duration permitting the installation of the next steel rib and shotcrete under conditions of safety (Figure 1). The umbrella-arch provides pre-reinforcement of poor ground around the tunnel perimeter in a simple and ﬂexible manner that is adaptable to different ground conditions. In fact, it is possible to vary the number and length of pipes, the distance between them, their diameter and thickness as well as the overlapping length of two succeeding umbrella arches.
The versatility of the umbrella arch technique allows its application to: clay deposits, granular alluvial deposits, moraine and debris materials even when containing large blocks, heavily jointed, foliated and tectonically disturbed rock masses. Static dimensioning of the umbrella arch is not the subject of the article. Reference is given to the works of Galletto et al. 2002 and Peila 1994 regarding the dimensioning of the steel pipe umbrella.
Technical Issues and necessary Design Adaptations during Construction of Concrete Plugs for Hydrocarbon Underground Storages P. Deschamps, Geostock During the last decades, many underground facilities for the storage of hydrocarbons have been excavated worldwide and the technology is fully mature. Similarly to other underground structures, the initial basic design has to be adapted along with the work progress, in order to cope with the actual site conditions and in particular the geology, hydrogeology and associated rockmass quality.
In addition, Client’s or underground Contractor’s constraints (such as resources availability, schedule or cost impact) may vary from design to construction and require last minute adjustments. Engineers are required to introduce ﬂexibility and anticipation of unexpected situations (similar to the above-mentioned) while conceiving large underground facilities. Although most of the cases require only minor adaptations, crucial parts of the facility have sometimes to be considerably modiﬁed and reviewed. This article will present four cases evidencing how the design of one of these essential structures – the concrete plug – has been adjusted during site implementation without impairing the initial performances.
22 – 28 APRIL | MOSCONE CENTER | WTC2016 Posters (Continued) Performance of Reinforced Ribs of Shotcrete (RRS) under Different Stress Regimes P. Chryssanthakis, Norwegian Geotechnical Institute The aim of this study is to give a better understanding for the performance of the composite material RRS and the synergy effect of its components under different stress regimes and while an excavation face advances during tunneling. The lower part of the Q-system scale (i.e. Q-values of 0.4 or less for a tunnel span of 10m) is commonly used for tunnel applications in softer rock formations. This is implied in the updated Q-chart, where the dimensioning of rock support by using Reinforced Ribs of Shotcrete (RRS) comprises the use of ﬁber reinforced shotcrete, S(fr), rock bolts and shotcreted beams reinforced with steel rebars. In this study, an effort has been made to simulate RRS in a numerical code and to study its behaviour in a real case study. A double tube, triple lane tunnel in weathered tuff has been chosen as reference material for testing RRS under changing load. A rather extensive parametric study has been run by using the same key input rock mass parameters and three different in situ stress regimes (σH/σv =2,σH/σv =1 and σH/σv =0.5). Changes have only been made to the RRS key input parameters in order to simulate the changing loads during the face excavation process in tunneling. The critical part of this numerical modelling work that is under investigation in this study under each stress regime, is the period just after the excavation: i.e 4 hours; 16 hours after excavation; and ﬁnally after the complete curing (28 days) of the cement based components.
The RRS are installed in three consecutive numerical steps as follows: a) the application of S(fr) on the rock surface in order to even it up for the RRS application; b) radial bolting; and c) installation of the reinforcing steel rebars, that form the reinforced beam. The results are varying and are strongly dependent on the imposed
stress regime and they show in general the following tendencies:
The axial forces on S(fr) show that S(fr) is almost overloaded during the ﬁrst 4 hours in all 3 stages.
Numerical Feasibility Study on Ground Deformation Caused by Enlargement of Shallow Box Tunnel Y. Cha, G. Cho and E. Hong, KAIST Rapid population growth and scarcity of space have led many developed cities to bury supply facilities. In line with this, utility tunnels have been employed in Korea since the 1970s. However, approximately 70% of structures were installed more than 20 years ago, in response to the issue of ageing, tunnel enlargement has been proposed. The aim of this study is to investigate geo-mechanical behavior due to tunnel enlargement. Tunnel enlargement methods have been researched to suggest a optimal method. A ﬁnite element analysis is conducted to evaluate ground behavior by the expansion of internal space. Vertical displacement and settlement trough width are investigated according to ground stiffness and different enlargement size. It was determined that displacement is affected by the enlargement size and ground stiffness. Based on the deformation results obtained from the numerical analysis, it is possible to predict ground behavior and stability upon tunnel enlargement.
Case Histories and Difﬁcult Ground Chair: R. Robinson, Shannon & Wilson, USA ITA Co-chair: R. Dimmock, ITAtech Lining & Waterprooﬁng Leader, UK 14:00-14:20 “They Want to Dig a 100 Foot Hole in Front of My House for Two Years!” Community Mitigation and Outreach for DC Water’s First Street Tunnel W. P. Levy and C. M. Ray, District of Columbia Water and Sewer Authority; T. Lindberg, McKissack & McKissack and J. Carl, Greeley and Hansen The District of Columbia Water and Sewer Authority (DC Water) is implementing its $2.6 billion DC Clean Rivers Project to reduce combined sewer overﬂows to the District’s receiving waterbodies and mitigate chronic sewer ﬂooding in District neighborhoods. The First Street Tunnel project is a major component of the DC Clean Rivers Project, designed to mitigate sewer ﬂooding and basement backups in the District’s historic and densely populated Bloomingdale neighborhood. Bloomingdale has been historically affected by sewer ﬂooding and was severely impacted by four storms in the summer of 2012 that caused signiﬁcant damage to homes, the environment and public property. As a result, DC Water accelerated the design and construction of the First Street Tunnel in order to mitigate the effect storms have on the undersized sewers serving the neighborhood. The infrastructure designed to mitigate ﬂooding, including the tunnel, are located within the highly urbanized neighborhood – with some structures being less than ten feet from residents front door steps. The success of a large public works project of this magnitude and in this unique location depends on a well informed and supportive public. With the local community impacted by ﬂooding but concerned about heavy construction impacts, this paper details the components of a successful public outreach plan and lessons learned throughout the design and construction process. Early identiﬁcation of community mitigation, working cooperatively with stakeholders and frequent dissemination of accurate information required the project team to establish a culture of problem solving collaboration with the community.
14:20-14:40 Tunnelling Under the Fraser River at 6 Bar – Design and Construction of the Port Mann Main Water Supply Tunnel S. Robillard, McMillen Jacobs Associates; S. Skelhorn, McNally Construction Inc; T. Langmaid, Mott MacDonald and A. Mitchell, Metro Vancouver The Port Mann Main Water Supply Tunnel project provides a critical water main crossing of the Fraser River for the owner, Greater Vancouver Water District (Metro Vancouver). The project consists of 22 – 28 APRIL | MOSCONE CENTER | WTC2016 two 60-metre-deep slurry panel shafts and a 1-kilometre-long, 3.5metre excavated diameter tunnel located near Vancouver, British Columbia, Canada. The initial tunnel lining is a precast steel ﬁber reinforced segmental lining. The ﬁnal lining is a 2.1-metre-diameter welded steel pipe. This paper describes the challenges encountered during tunnel construction and the solutions implemented.
Key challenges include earth pressure balance tunnelling at up to 6 bar pressure—the highest to date in Canada—a water-crossing without surface access for the majority of the tunnel drive, ground freezing from a river platform for a critical TBM intervention, and boring through cobbles and boulders in dense glacial till.
14:40-15:00 Pressurized Face Tunneling under Very High Groundwater Heads S. W. Hunt, CH2M A paper called “Global Experience with Soft Ground and Weak Rock Tunneling under Very High Groundwater Heads” was presented at the North American Tunneling 2006 conference (Holzhäuser et.al 2006). It summarized global experience on nine projects with tunneling that experienced groundwater heads ranging from 5.5 to 11 bar.
Since then, additional projects have been completed with groundwater heads ranging from 7 to 15 bar. Of these, the high pressure tunneling experience on the Lake Mead Intake No. 3 project in Nevada and on the Eurasia Tunnel (Istanbul Strait Crossing) had the greatest lengths at face pressure over 7 bar. Experience with sustained pressurized face tunneling at groundwater heads over 7 bar and risk management observations are the focus of this paper.
15:00-15:20 Reliability of Swelling Pressure Testing for Tunnel Support Evaluation B. Nilsen, Norwegian University of Science and Technology (NTNU) Weakness zones or faults containing clay-rich gouge represent one of the most challenging rock mass conditions to be encountered during tunneling. In Norway, such conditions count for a large part of the rock support costs, and in cases where the rock support has been insufﬁcient, serious instability and cave-in have in many cases been the result. Most commonly, such cave-in has occurred after water ﬁlling of hydropower tunnels, but in some cases it has also occurred in tunnels under excavation and in completed “dry” tunnels. To avoid instability, two important requirements have to be fulﬁlled: The location of the weakness zone and it’s character have to be identiﬁed in time and the rock support has to be sufﬁcient to withstand the loading caused by the zone.
An incident which really brought the problems related to swelling clay into focus was the cave-in at the Hanekleiv road tunnel in
2006. Here, rock fall from the roof as shown in Figure 1 occurred unexpectedly about 10 years after the tunnel was completed. Fortunately this happened at a time with very little trafﬁc, and nobody was injured. This incident emphasized the signiﬁcance of the issue of swelling clay, although it was found to be caused also by gravitational collapse of the clay-rich gouge material of the weakness zone, and not related to swelling only (Nilsen et al. 2007).