The recently developed elasto-viscoplastic Creep-SCLAY1S model has been used in conjunction with PLAXIS 2D to investigate the effectiveness of vibro-replacement in a creep-prone clay. The Creep-SCLAY1S model accounts ...The recently developed elasto-viscoplastic Creep-SCLAY1S model has been used in conjunction with PLAXIS 2D to investigate the effectiveness of vibro-replacement in a creep-prone clay. The Creep-SCLAY1S model accounts for anisotropy, bonding, and destructuration, and uses the concept of a constant rate of viscoplastic multiplier to calculate creep strain rate. A comparison of settlement improvement factors with and without creep indicates that ‘total’ settlement improvement factors （primary plus creep） are lower than their ‘primary’ counterparts （primary settlement only）. The lowest settlement improvement factors arise for analyses incorporating the effect of bonding and destructuration. Examination of the variations of vertical stress with time and depth has indicated that vertical stress is transferred from the soil to the column as the soil creeps. This results in additional column yielding. In addition, the radial and hoop stresses in the soil are lower for the ‘creep’ case. The reduced radial stresses lead to additional column bulging and hence more settlement, whereas the hoop stress reductions appear to be a secondary effect, caused by additional plastic deformation for the ‘creep’ case.展开更多
The popularity of trenchless techniques as a means of utility pipeline installation in urban environments,specifically microtunnelling/pipe-jacking,has increased in recent years due to its minimally-disruptive nature ...The popularity of trenchless techniques as a means of utility pipeline installation in urban environments,specifically microtunnelling/pipe-jacking,has increased in recent years due to its minimally-disruptive nature and reduced carbon footprint in comparison to conventional open-cut excavation methods.The response of pipes during the jacking process is complex and is governed by several factors,including ground conditions,the amount and distribution of lubrication,pipe and annulus size,pipeline misalignments and jacking force eccentricity,among others.Design practice remains based on empirical equations and previous drives through similar geology,resulting in uncertainty in jacking force estimates,thereby restricting adoption of the technique.In order to improve our understanding of the pipe-jacking process,pipes incorporating sensors providing real-time measurements of earth pressures,pore water pressures,axial strains and hoop strains can be used;but the number of such studies reported in the literature is small and the potential of instrumentation on routine projects is largely untapped.Moreover,jacking pipe monitoring practice lags behind the state-of-the-art instrumentation techniques used for monitoring other geotechnical infrastructure.The purpose of this paper is to provide a thorough review of learnings from instrumented pipe-jacking case studies and other supporting research,as well as to propose potential solutions to research gaps in the current state of design practice and field monitoring of pipe jacking projects.展开更多
In recent years,there has been an increased resort to microtunnelling/pipe-jacking as a means of constructing underground conduits(for water,sewage,gas,and other utilities)to avoid on-street disruption in urban areas....In recent years,there has been an increased resort to microtunnelling/pipe-jacking as a means of constructing underground conduits(for water,sewage,gas,and other utilities)to avoid on-street disruption in urban areas.In this paper,technical details of two 1200 mm internal diameter microtunnels in silty sand totalling over 550 m in length are discussed.While average skin friction values are extremely low for both drives suggesting effective lubrication practice,differences in normalised bentonite volumes appear to be responsible for differences in skin friction.Full or near full buoyancy of the pipeline has been demonstrated for the majority of the drive.The frictional stress increase after a stoppage is shown to depend on not only the stoppage duration but also on the normalised lubrication volume.Interpretation of data in the manner presented in the paper is an important means of assimilating experience of microtunnelling in different ground conditions.展开更多
基金the funding provided by the Irish Research Council(IRC) for the research into stone column behaviour in creep-prone soilspart of CREEP(Creep of Geomaterials,PIAP-GA-2011-286397) project supported by the European Community through the programme Marie Curie Industry-Academia Partnerships and Pathways(IAPP) under the 7th Framework ProgrammeThe support from the BIG(Better Interaction in Geotechnics) project from the Swedish Transport Administration
文摘The recently developed elasto-viscoplastic Creep-SCLAY1S model has been used in conjunction with PLAXIS 2D to investigate the effectiveness of vibro-replacement in a creep-prone clay. The Creep-SCLAY1S model accounts for anisotropy, bonding, and destructuration, and uses the concept of a constant rate of viscoplastic multiplier to calculate creep strain rate. A comparison of settlement improvement factors with and without creep indicates that ‘total’ settlement improvement factors （primary plus creep） are lower than their ‘primary’ counterparts （primary settlement only）. The lowest settlement improvement factors arise for analyses incorporating the effect of bonding and destructuration. Examination of the variations of vertical stress with time and depth has indicated that vertical stress is transferred from the soil to the column as the soil creeps. This results in additional column yielding. In addition, the radial and hoop stresses in the soil are lower for the ‘creep’ case. The reduced radial stresses lead to additional column bulging and hence more settlement, whereas the hoop stress reductions appear to be a secondary effect, caused by additional plastic deformation for the ‘creep’ case.
基金funded by the Science Foundation Ireland Research Centre in Applied Geosciences(SFI-iCRAG),with Ward and Burke Construction Limited as the industry partner.
文摘The popularity of trenchless techniques as a means of utility pipeline installation in urban environments,specifically microtunnelling/pipe-jacking,has increased in recent years due to its minimally-disruptive nature and reduced carbon footprint in comparison to conventional open-cut excavation methods.The response of pipes during the jacking process is complex and is governed by several factors,including ground conditions,the amount and distribution of lubrication,pipe and annulus size,pipeline misalignments and jacking force eccentricity,among others.Design practice remains based on empirical equations and previous drives through similar geology,resulting in uncertainty in jacking force estimates,thereby restricting adoption of the technique.In order to improve our understanding of the pipe-jacking process,pipes incorporating sensors providing real-time measurements of earth pressures,pore water pressures,axial strains and hoop strains can be used;but the number of such studies reported in the literature is small and the potential of instrumentation on routine projects is largely untapped.Moreover,jacking pipe monitoring practice lags behind the state-of-the-art instrumentation techniques used for monitoring other geotechnical infrastructure.The purpose of this paper is to provide a thorough review of learnings from instrumented pipe-jacking case studies and other supporting research,as well as to propose potential solutions to research gaps in the current state of design practice and field monitoring of pipe jacking projects.
基金The first author is funded by an Irish Research Council Enterprise Partnership Scheme(IRC-EPS)Postgraduate Scholarship,with Ward and Burke Construction Limited as the industry partner.The third author is supported by the Royal Academy of Engineering(U.K.)under the Research Fellowship Scheme.
文摘In recent years,there has been an increased resort to microtunnelling/pipe-jacking as a means of constructing underground conduits(for water,sewage,gas,and other utilities)to avoid on-street disruption in urban areas.In this paper,technical details of two 1200 mm internal diameter microtunnels in silty sand totalling over 550 m in length are discussed.While average skin friction values are extremely low for both drives suggesting effective lubrication practice,differences in normalised bentonite volumes appear to be responsible for differences in skin friction.Full or near full buoyancy of the pipeline has been demonstrated for the majority of the drive.The frictional stress increase after a stoppage is shown to depend on not only the stoppage duration but also on the normalised lubrication volume.Interpretation of data in the manner presented in the paper is an important means of assimilating experience of microtunnelling in different ground conditions.
