The rapid growth in railway infrastructure and the construction of high-speed heavy-haul rail network,especially on ground that is basically unsuitable,poses challenges for geotechnical engineers because a large part ...The rapid growth in railway infrastructure and the construction of high-speed heavy-haul rail network,especially on ground that is basically unsuitable,poses challenges for geotechnical engineers because a large part of the money invested in the development of railway lines is often spent on track maintenance.In fact around the world,the mud pumping of subgrade fines is one of the common reasons why track performance deteriorates and track stability is hindered.This article presents a series of laboratory tests to examine following aspects of mud pumping:(1)the mechanisms of subgrade fluidisation under undrained condition,(2)the effects of mud pumping on the engineering characteristics of ballast,and(3)the use of vertical drains to stabilize subgrade under cyclic loads.The undrained cyclic triaxial testing on vulnerable soft subgrade was performed by varying the cyclic stress ratio(CSR)from 0.2 to 1.0 and the loading frequency f from 1.0 to 5.0 Hz.It is seen from the test results that for a specimen compacted at an initial dry density of 1790 kg/m3,the top portion of the specimen fluidises at CSR=0.5,irrespective of the applied loading frequency.Under cyclic railway loading,the internal redistribution of water at the top of the subgrade layer softens the soil and also reduces its stiffness.In response to these problems,this paper explains how the inclusion of vertical drains in soft subgrade will help to prevent mud pumping by alleviating the build-up of excess pore pressures under moving train loads.展开更多
Stabilising soft marine clay and estuarine soils via vacuum preloading has become very popular in Australasia over the past decades because it is a cost-effective and time-efficient approach.In recent times,new land o...Stabilising soft marine clay and estuarine soils via vacuum preloading has become very popular in Australasia over the past decades because it is a cost-effective and time-efficient approach.In recent times,new land on areas outside but adjacent to existing port amenities,the Fisherman Islands at the Port of Brisbane(POB),was reclaimed to cater for an increase in trade activities.A vacuum preloading method combined with surcharge to stabilise the deep layers of soil was used to enhance the application of prefabricated vertical drains(PVDs).This paper describes the performance of this combined surcharge fill and vacuum system under the embankment and also compares it with a surcharge loading system to demonstrate the benefits of vacuum pressure over conventional fill.The performance of this embankment is also presented in terms of field monitoring data,and the relative performance of the vacuum together with non-vacuum systems is evaluated.An analytical solution to radial consolidation with time-dependent surcharge loading and vacuum pressure is also presented in order to predict the settlement and associated excess pore water pressure(EPWP)of deposits of thick soft clay.展开更多
The typical shear behaviour of rough joints has been studied under constant normal load/stress (CNL) boundary conditions, but recent studies have shown that this boundary condition may not replicate true practical s...The typical shear behaviour of rough joints has been studied under constant normal load/stress (CNL) boundary conditions, but recent studies have shown that this boundary condition may not replicate true practical situations. Constant normal stiffness (CNS) is more appropriate to describe the stress-strain response of field joints since the CNS boundary condition is more realistic than CNL. The practical implications of CNS are movements of unstable blocks in the roof or walls of an underground excavation, reinforced rock wedges sliding in a rock slope or foundation, and the vertical movement of rock-socketed concrete piles. In this paper, the highlights and limitations of the existing models used to predict the shear strength/behaviour of joints under CNS conditions are discussed in depth.展开更多
In recent years, reconstituted small samples have often been used to assess the performance of radial consolidation due to prefabricated vertical drains(PVDs), but the permeability and compressibility of samples of un...In recent years, reconstituted small samples have often been used to assess the performance of radial consolidation due to prefabricated vertical drains(PVDs), but the permeability and compressibility of samples of undisturbed soil often differ from those of the remoulded ones. The problem seems more complex in marine environment due to the presence of random coarse particles including gravels, shells and natural partings. Performing small-scale laboratory experiment with reconstituted samples, especially in marine environment, cannot predict the exact soil behaviour in the field. This paper describes an experimental programme that measures radial consolidation using a conventional Rowe cell and a largescale consolidometer, where the samples of undisturbed soil obtained from a site along the Pacific Highway(north of Sydney) were compared using measured settlements and excess pore pressures.Moreover, this paper highlights the implications of the smear effect and sample size influence, which are imperative in translating the laboratory testing practices to actual real-life behaviour. The effect of vacuum pressure on the coefficient of radial consolidation of a large-scale undisturbed test specimen is also discussed. The paper demonstrates that the extent of smear zone in the field can be very similar to the large-scale laboratory consolidation test using a scaled-down drain and mandrel, but considerably different from the data obtained for small laboratory specimens.展开更多
基金This research was supported by the Australian Government through the Australian Research Council’s Linkage Projects funding scheme(Project LP160101254)the Industrial Transformation Training Centre for Advanced Technologies in Rail Track Infrastructure(ITTC),University of WollongongThe financial and technical support from SMEC-Australia and ARTC(Australian Rail Track Corporation)is acknowledged.
文摘The rapid growth in railway infrastructure and the construction of high-speed heavy-haul rail network,especially on ground that is basically unsuitable,poses challenges for geotechnical engineers because a large part of the money invested in the development of railway lines is often spent on track maintenance.In fact around the world,the mud pumping of subgrade fines is one of the common reasons why track performance deteriorates and track stability is hindered.This article presents a series of laboratory tests to examine following aspects of mud pumping:(1)the mechanisms of subgrade fluidisation under undrained condition,(2)the effects of mud pumping on the engineering characteristics of ballast,and(3)the use of vertical drains to stabilize subgrade under cyclic loads.The undrained cyclic triaxial testing on vulnerable soft subgrade was performed by varying the cyclic stress ratio(CSR)from 0.2 to 1.0 and the loading frequency f from 1.0 to 5.0 Hz.It is seen from the test results that for a specimen compacted at an initial dry density of 1790 kg/m3,the top portion of the specimen fluidises at CSR=0.5,irrespective of the applied loading frequency.Under cyclic railway loading,the internal redistribution of water at the top of the subgrade layer softens the soil and also reduces its stiffness.In response to these problems,this paper explains how the inclusion of vertical drains in soft subgrade will help to prevent mud pumping by alleviating the build-up of excess pore pressures under moving train loads.
基金the support of the Port of Brisbane Pty LtdCoffey Geotechnicsresearch funding from the Australia Research Council
文摘Stabilising soft marine clay and estuarine soils via vacuum preloading has become very popular in Australasia over the past decades because it is a cost-effective and time-efficient approach.In recent times,new land on areas outside but adjacent to existing port amenities,the Fisherman Islands at the Port of Brisbane(POB),was reclaimed to cater for an increase in trade activities.A vacuum preloading method combined with surcharge to stabilise the deep layers of soil was used to enhance the application of prefabricated vertical drains(PVDs).This paper describes the performance of this combined surcharge fill and vacuum system under the embankment and also compares it with a surcharge loading system to demonstrate the benefits of vacuum pressure over conventional fill.The performance of this embankment is also presented in terms of field monitoring data,and the relative performance of the vacuum together with non-vacuum systems is evaluated.An analytical solution to radial consolidation with time-dependent surcharge loading and vacuum pressure is also presented in order to predict the settlement and associated excess pore water pressure(EPWP)of deposits of thick soft clay.
文摘The typical shear behaviour of rough joints has been studied under constant normal load/stress (CNL) boundary conditions, but recent studies have shown that this boundary condition may not replicate true practical situations. Constant normal stiffness (CNS) is more appropriate to describe the stress-strain response of field joints since the CNS boundary condition is more realistic than CNL. The practical implications of CNS are movements of unstable blocks in the roof or walls of an underground excavation, reinforced rock wedges sliding in a rock slope or foundation, and the vertical movement of rock-socketed concrete piles. In this paper, the highlights and limitations of the existing models used to predict the shear strength/behaviour of joints under CNS conditions are discussed in depth.
基金the Australian Research Council (ARC) Centre of Excellence in Geotechnical Science and Engineering and the Centre for Geomechanics and Railway Engineering (CGRE) of University of Wollongong (UOW) for the financial support
文摘In recent years, reconstituted small samples have often been used to assess the performance of radial consolidation due to prefabricated vertical drains(PVDs), but the permeability and compressibility of samples of undisturbed soil often differ from those of the remoulded ones. The problem seems more complex in marine environment due to the presence of random coarse particles including gravels, shells and natural partings. Performing small-scale laboratory experiment with reconstituted samples, especially in marine environment, cannot predict the exact soil behaviour in the field. This paper describes an experimental programme that measures radial consolidation using a conventional Rowe cell and a largescale consolidometer, where the samples of undisturbed soil obtained from a site along the Pacific Highway(north of Sydney) were compared using measured settlements and excess pore pressures.Moreover, this paper highlights the implications of the smear effect and sample size influence, which are imperative in translating the laboratory testing practices to actual real-life behaviour. The effect of vacuum pressure on the coefficient of radial consolidation of a large-scale undisturbed test specimen is also discussed. The paper demonstrates that the extent of smear zone in the field can be very similar to the large-scale laboratory consolidation test using a scaled-down drain and mandrel, but considerably different from the data obtained for small laboratory specimens.