This paper discusses the temporary support design methodology for the largest road caverns ever b... more This paper discusses the temporary support design methodology for the largest road caverns ever built in Australia - the Lutwyche Caverns - part of the Airport Link project in Brisbane, Australia. The Lutwyche Caverns with a maximum excavated span of 27 m form a key component of this major road project, allowing on and off ramps merging with the underground highway. In addition to the two large span caverns, a 15 m soft ground tunnel with 5 m cover above the caverns and two 24 m deep burial chambers for the 12.4 m tunnel boring machines (TBMs) had to be built in record time at Lutwyche. The temporary support design methodology involved the use of a range of analytical approaches, including empirical methods to provide a starting point for design development, key block models to determine the potential influence of discontinuities on excavation stability and 2/3D continuum and discontinuum models to determine the potential influence of adjacent excavations and the proposed construction staging on the design. In addition, probabilistic analysis of potential kinematic instability using a discrete fracture network (DFN) approach was also undertaken to establish the critical block loads for the temporary lining, while the continuum and discontinuum models were used to design the support for the 1.5 m diameter rock pillar at the north end of the northbound cavern. The numerical modelling was undertaken in close conjunction with the contractor to develop the optimal construction sequence, considering the available construction equipment on-site and the overall project program requirements. Part of the presentation will further show the applicability of the developed design during construction (deformations, monitoring field observations) and lessons learned for future cavern construction in Australia.
Since the past 30 years, the research for estimating an accurate prediction of deformations induc... more Since the past 30 years, the research for estimating an accurate prediction of deformations induced by tunneling has been a major engineering challenge all around the world. The in situ measurements have shown that deformations of the soil on the vicinity of a tunnel show a strong evolution with time. Three essential phenomena, actually, can be related to this evolution : the evolution with time of the distance to the working face, the distance of the lining to the working face and the viscous effets occurring in the soil. The objective of this thesis is to propose a procedure for predicting the deformations induced by tunneling, by taking into account these three essential phenomena, particularly the third phenomenon. Therefore, in this study, a constitutive model for the time-dependent behaviour of cohesive soil has been developed within the framework of elastoplasticity-viscoplasicity and critical state soil mechanics. The consideration of viscoplastic characteristic sets the cur...
In urban areas, tunnels for services and transport are usually excavated in the near-surface zone... more In urban areas, tunnels for services and transport are usually excavated in the near-surface zone, which often exhibits poor geotechnical characteristics. In this case, the design of a tunnel requires ground deformations to be controlled so as to avoid damage to buildings and to ensure the safety of the workforce. Empirical methods of evaluating displacement caused by tunnelling have not always proved suitable in sensitive urban areas. The goal of this paper is to analyse the influence of strain-softening of soil on settlement due to tunnelling in soft ground by numerical methods.
This paper discusses the temporary support design methodology for the largest road caverns ever b... more This paper discusses the temporary support design methodology for the largest road caverns ever built in Australia - the Lutwyche Caverns - part of the Airport Link project in Brisbane, Australia. The Lutwyche Caverns with a maximum excavated span of 27 m form a key component of this major road project, allowing on and off ramps merging with the underground highway. In addition to the two large span caverns, a 15 m soft ground tunnel with 5 m cover above the caverns and two 24 m deep burial chambers for the 12.4 m tunnel boring machines (TBMs) had to be built in record time at Lutwyche. The temporary support design methodology involved the use of a range of analytical approaches, including empirical methods to provide a starting point for design development, key block models to determine the potential influence of discontinuities on excavation stability and 2/3D continuum and discontinuum models to determine the potential influence of adjacent excavations and the proposed construction staging on the design. In addition, probabilistic analysis of potential kinematic instability using a discrete fracture network (DFN) approach was also undertaken to establish the critical block loads for the temporary lining, while the continuum and discontinuum models were used to design the support for the 1.5 m diameter rock pillar at the north end of the northbound cavern. The numerical modelling was undertaken in close conjunction with the contractor to develop the optimal construction sequence, considering the available construction equipment on-site and the overall project program requirements. Part of the presentation will further show the applicability of the developed design during construction (deformations, monitoring field observations) and lessons learned for future cavern construction in Australia.
Since the past 30 years, the research for estimating an accurate prediction of deformations induc... more Since the past 30 years, the research for estimating an accurate prediction of deformations induced by tunneling has been a major engineering challenge all around the world. The in situ measurements have shown that deformations of the soil on the vicinity of a tunnel show a strong evolution with time. Three essential phenomena, actually, can be related to this evolution : the evolution with time of the distance to the working face, the distance of the lining to the working face and the viscous effets occurring in the soil. The objective of this thesis is to propose a procedure for predicting the deformations induced by tunneling, by taking into account these three essential phenomena, particularly the third phenomenon. Therefore, in this study, a constitutive model for the time-dependent behaviour of cohesive soil has been developed within the framework of elastoplasticity-viscoplasicity and critical state soil mechanics. The consideration of viscoplastic characteristic sets the cur...
In urban areas, tunnels for services and transport are usually excavated in the near-surface zone... more In urban areas, tunnels for services and transport are usually excavated in the near-surface zone, which often exhibits poor geotechnical characteristics. In this case, the design of a tunnel requires ground deformations to be controlled so as to avoid damage to buildings and to ensure the safety of the workforce. Empirical methods of evaluating displacement caused by tunnelling have not always proved suitable in sensitive urban areas. The goal of this paper is to analyse the influence of strain-softening of soil on settlement due to tunnelling in soft ground by numerical methods.
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Papers by Ardie Purwodihardjo