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15:00-15:20 Investigations in the Field of Long-term Stability of Tunnel Constructions – Focusing on Deterioration of the Support Elements and Resulting Load Distribution Mechanisms S. Lorenz and R. Galler, Montanuniversität Leoben The technical lifetime of underground structures does not only depend on the long-term behavior of individual support elements and material characteristics but also on various boundary conditions, which inﬂuence the entire long-term system behavior of the structure. Thanks to the construction of second tunnel tubes and the corresponding cross passages sampling of support materials such as shotcrete, concrete of the inner lining, rock bolts including sheet membranes is possible. To evaluate the stresses and the supporting effects of the tunnel shells ﬂat-jack tests and different simulations were performed. With these simulations the percentage of the load bearing behavior of the shotcrete shell can be determined. From the results, conclusions for new design approaches for tunnel construction should be generated. New concepts, in which the outer lining is part of the permanent support elements can be considered. This approach would be applicable for conventional as well as mechanical tunneling.
15:20-15:40 ACI Guideline on Design and Construction of Precast Concrete Tunnel Segmental Lining M. Bakhshi and V. Nasri, AECOM Fiber reinforcement has emerged as an alternative to steel bars in precast concrete segments due to advantages such as saving cost and reducing production time while developing a more WTC2016 | SAN FRANCISCO CALIFORNIA, USA MONDAY 25 APRIL robust product with improved handling and long-term durability.
ACI recently drafted a new report as the ﬁrst design guideline on FRC tunnel segments to provide speciﬁc guidance for this emerging technology. This document offers general information on the history of FRC precast segments from tunneling projects throughout the world; a procedure for structural analysis and design based on governing load cases, and a description of the material parameters, tests and analyses required to complete the design. This paper summarizes the design considerations in this ACI guideline prepared by the authors of this paper as the main contributors. Application of this guideline to design of a mid-size tunnel results in elimination of steel bars and reduction of crack width under service loads.
15:40-16:10 Break 16:10-16:30
Concurrent Segment Lining and TBM Design:
A Coordinated Approach for Tunneling Success E. Comis, The Robbins Company and M. Younis and R. Goodfellow, Aldea Services LLC The success of a tunnel project relies on many factors, but one of the most important is also the most overlooked: Coordination by all companies involved during the design stages. This is particularly true of segment design and TBM design. Tunnel lining with segmental rings is usually designed according to the standards of reinforced concrete construction based on a given GBR. But for TBM tunneling, the determination of loads during ring erection, advance of the TBM, earth pressure and bedding of the articulated ring are all part of the design of the lining as well. TBM design can be heavily affected by the segment arrangement, dimension and weight, but these are usually given as a ﬁxed input to the TBM manufacturer—a process that can cause unnecessary complications. The authors propose that the industry evaluate the process as it stands. In order to ﬁnd the optimum between lining design and TBM cost and operational workﬂow, both designs should be ﬁnalized concurrently. This requires coordination between the TBM Manufacturer and Segment Designer from the early stages. The aim of this paper is to evaluate the inﬂuence of the segment lining design on TBM cost and performance, and to provide commentary on existing design guidelines to optimize lining and TBM procurement.
16:30-16:50 Fire Design for the Concrete Lining of the Ohio River Bridges East End Crossing Tunnel W. Chen, Jacobs Engineering A ﬁre design innovation of the concrete lining of the Ohio River Bridges East End Crossing Tunnel has been developed. As a result from a ﬁre suppression and tunnel ventilation system, the project design Heat Release Rate (HRR) was able to be constrained from 300 MW to about 50 MW. With this reduced HRR, concrete lining without passive ﬁre protection may be acceptable, if the tunnel concrete lining will not result in explosive spalling during the designed ﬁre event. Concrete explosive spalling test was proposed to verify this assumption. Since no standard concrete 22 – 28 APRIL | MOSCONE CENTER | WTC2016 ﬁre explosive spalling testing procedure exists, a project speciﬁc testing procedure was developed and ﬁre tests conducted. From ﬁre test results, it is concluded that the proposed tunnel concrete lining, in conjunction with the proposed ﬁre suppressing and ventilation system, will not experience explosive spalling and does not require a passive ﬁre protection system.
16:50-17:10 Performance of Macro Synthetic Fiber Reinforced Tunnel Lining A. Nitschke, Shannon & Wilson, Inc and R. Winterberg, EPC Elasto Plastic Concrete Macro synthetic ﬁber reinforced concrete or shotcrete is seen by many design engineers as offering a viable alternative to steel reinforcement in tunnel linings. The technology is now commonplace for primary and permanent ground support in both mining and civil tunnel applications. It has for instance become the standard form of reinforcement in the Australian mining industry, and has been used for a majority of permanent tunnel linings in recent tunnel construction in Norway. Similarly, macro synthetic ﬁbers are becoming a standard solution for the initial lining in the USA. The use of macro synthetic ﬁber offers innovative solutions, yielding robust and sustainable tunnel lining designs. Citing recent research and actual projects, this paper presents state-of-the-art design considerations for ﬁber reinforced tunnel linings relating to structural and long-term performance. Topics include seismic resistance, crack width control, corrosion and durability as well as sustainment of performance with age.
17:10-17:30 Utilizing Composite Action to Achieve Lining Thickness Efﬁciency for Sprayed Concrete Lined (SCL) Tunnels J. Su and A. Bloodworth, University of Southampton Composite sprayed concrete linings (SCL), consisting of two layers of permanent shotcrete separated by a layer of spray-applied waterprooﬁng membrane, represents the latest development in SCL tunneling, but presents several challenges to designers. This paper aims to address the following issues: (1) how to simulate composite action, (2) behavior of a Composite SCL tunnel, and (3) how to utilize composite action to achieve lining thickness efﬁciency. It ﬁrstly sets out the background to the composite SCL concept, and then presents a strategy for numerical investigation. The main part of the paper is the presentation and discussion of the simulation results, focusing on the lining deformation, load sharing and the safety margin of both linings. Interface stresses are also examined. It is found that signiﬁcant secondary lining thickness reduction may be achieved by utilizing composite action. Challenges for the design of Composite SCL tunnels are brieﬂy discussed at the end.
A Different View on TBM Face Equilibrium in Permeable Ground T. Gerheim Souza Dias and A. Bezuijen, Ghent University The construction of mechanized tunnels in soft ground has evolved signiﬁcantly over the last 20 years, especially in the control of the face pressure and the closure of the soil-lining void to reduce the induced settlements. On the other hand, several mechanisms of the TBM excavation cycle are still not taken into account for routine design calculations, such as the increment of water pressures in front of the tunnel face, the ﬂow of excavation ﬂuids around the shield, the dynamic equilibrium between the grout pressures and the excavation convergence, among others. This paper discusses how these factors, which are routinely considered exceptional, can be easily veriﬁed and incorporated in the state-of-practice of design.
The study deﬁnes a framework where the TBM operational parameters can be assessed together with the induced soil displacements and lining forces for different project conditions. The compliance of the model with ﬁeld measurements is presented.
Interaction Modeling in Mechanized Tunneling G. Meschke, Institute for Structural Mechanics In the presentation selected results from the Collaborative Research Center “Interaction Models for Mechanized Tunneling” installed at the Ruhr-University Bochum, Germany, are summarized. Numerical and experimental research is concerned with
i) the characterization of the in-situ and the disturbed ground conditions in the vicinity of the cutting wheel including advance exploration methods, ii) interactions between the grout and the surrounding soil and novel segmental lining designs with enhanced robustness, iii) computational simulation of soil excavation and material transport, tunnel drive and involved logistics processes, and real time prognosis models to support the TBM steering, and iv) risk analysis in urban tunneling. These research themes are each supported by computational models and are all included in an SFB overreaching tunnel information model (TIM).
Structural Design of Composite Shell Linings J. Jäger, BeMo Tunnelling A composite shell lining typically consists of an outer permanent sprayed concrete shell, a water prooﬁng layer and an inner sprayed or cast concrete shell. There is very little published literature on the actual structural design of composite linings, although composite linings are becoming more and more popular. Composite action of the outer shell initially carrying short term ground loads and the “unloaded” inner shell require nonlinear concrete modelling to be able to assess the bearing capacity of the composite lining structure adequately. The composite action interfaces between the waterprooﬁng membrane and the inner and outer shells can be considered either by simpliﬁed closed form solutions as well as numerical models. Strength and stiffness parameters related to those models govern interaction of inner and outer shell. As those parameters ﬁnd their way into the material speciﬁcations their signiﬁcance regarding the overall structural behaviour has to be critically analysed.
22 – 28 APRIL | MOSCONE CENTER | WTC2016 Posters (Continued) Proposal of the TFI (Tunnel Face stability Index) Based on the Critical Shear Strain Theory T. Sasaki, S. Morimoto, and M. Shinji, Yamaguchi University The tunnel face stability is the most important issue in NATM. If the material properties of ground become clear from the ﬁeld survey, tunnel face behavior can be predicted using numerical simulation before tunnel construction. But the estimation of the safety of tunnel face is difﬁcult especially the ground is very weak like a urban area.
In this study, numerical analysis of tunnel excavation on very weak ground conditions like a low cohesion and low internal friction angle were carried out. The relationship between the average strain distribution of the tunnel face and the overburden was compared. And it estimates the strain of the tunnel face comparing the critical shear strain obtained by the ground properties. We called the allowable overburden which calculated satisfying the critical shear strain of the ground as TFI (Tunnel face stability Index). Finally, the design chart of the allowable overburden of various cohesion and friction angle of the ground is proposed. It is useful in the preliminary tunnel design stage to judge the necessity of additional counter measure against the normal tunnel support patterns.
Assessment of TBM Gripper Performance in the Bedded Sedimentary Rock of Sydney, Australia D. Oliveira, Jacobs and University of Wollongong One of the key drivers for the selection of a mechanized tunneling method in good quality rock masses is a good excavation advance rate. In order to achieve satisfactory advance rates, a good geotechnical performance of the rock grippers in main beam open tunnel boring machines (TBM) is required, besides other factors related to ground support and the performance of the cutter head.
One well known potential issue of TBM grippers is associated with the bearing capacity of the tunnel side walls while crossing fault zones or poor rock masses in general. Such a mechanism is similar to that of footings on rock and perhaps the most common problem associated with gripper performance. Depending on the quality of the rock, the rock under the gripper contact may experience signiﬁcant damage and crushing (Error: Reference source not found), eventually affecting the TBM advance rate due to a lack of tunnel wall reaction/support. Such a mechanism is primarily dependent on rock quality, applied loads and gripper size.
Primary-Secondary Lining Interactions for Sprayed Concrete Lined Tunnels Using Sprayed Waterprooﬁng Membrane J. Su and M. Uhrin, Mott MacDonald Spray applied waterprooﬁng membrane has recently been used in many high proﬁle SCL tunnel projects. Its use with permanent primary and secondary lining introduces complex primary-secondary lining interaction, which is an issue that has previously not been fully investigated and understood. This paper aims to address this issue by presenting a series of numerical analyses on a typical shallow SCL tunnel in soft ground adopting validated modelling approach and interface design parameters. Three different assumptions on the interface are made: (a) compression WTC2016 | SAN FRANCISCO CALIFORNIA, USA MONDAY 25 APRIL only, (b) compression and tension and (c) compression, tension and shear. The results show that the assumptions of spray applied waterprooﬁng membrane behaviour have a signiﬁcant impact on the primary-secondary lining interactions. It would be not conservative to ignore the interface tensile and shear bonds during the design. This paper explains the rationale behind these conclusions and discusses the design implications.