In order to reduce the risk associated with water seepage in an underground rock cavern project inSingapore, a reliable hydro-geological model should be established based on the in situ investigationdata. The key chal...In order to reduce the risk associated with water seepage in an underground rock cavern project inSingapore, a reliable hydro-geological model should be established based on the in situ investigationdata. The key challenging issue in the hydro-geological model building is how to integrate limitedgeological and hydro-geological data to determine the hydraulic conductivity of the fractured rockmasses. Based on the data obtained from different stages （feasibility investigation stage, constructionstage, and post-construction stage）, suitable models and methods are proposed to determine the hydraulicconductivities at different locations and depths, which will be used at other locations in thefuture. 2015 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.展开更多
This paper shares some experiences of developing a good metro network in Singapore. After providing a background of the local land transportation scene, the paper provides a chronological discussion of the metro devel...This paper shares some experiences of developing a good metro network in Singapore. After providing a background of the local land transportation scene, the paper provides a chronological discussion of the metro development in Singapore where the characteristics of each new metro line was briefly discussed. The next part of the paper shares some features and initiatives through developing the Singapore metro system over the years, such as funding arrangement, bringing artworks to transit stations, integrated planning between road and rail, integration between transit facilities with non-transit developments, barrier-free accessibility and improving connectivity to the metro stations, and transforming transport nodes into lifestyle hubs. Finally, the paper concludes by discussing the challenges on the land transport system in Singapore and the way forward.展开更多
Ground losses due to tunneling would induce settlement of nearby raft foundations.To study the change in behavior of the raft foundations over time due to tunnel excavation in soft clay,a series of centrifuge model te...Ground losses due to tunneling would induce settlement of nearby raft foundations.To study the change in behavior of the raft foundations over time due to tunnel excavation in soft clay,a series of centrifuge model tests were conducted.The results reveal that the raft stiffness has a significant influence on the development of the gap between the raft and the ground.The width of the gap beneath the flexible foundation would increase over time,leading to a further increase in tensile strain after excavation,whereas the gap for raft foundations with a large stiffness would reduce with time,causing a gradual decrease in tensile strain.The modification factor(MF)design approach is also evaluated with the test results and demonstrates that the MF design approach would underestimate the tensile strain of the flexible raft and provide a relatively conservative prediction for larger stiffnesses.展开更多
Determining the location and boundary of underground obstructions and/or anomalies is a common problem and often a great chal-lenge for tunneling and underground construction.In this study,geotechnical investigations(...Determining the location and boundary of underground obstructions and/or anomalies is a common problem and often a great chal-lenge for tunneling and underground construction.In this study,geotechnical investigations(penetration tests and borehole drilling/sam-pling)and geophysical investigations(surface wave method and cross-hole seismic method)were conducted with the aim of identifying the location and boundary of rock obstructions in Changi East,Singapore.The surface wave method is frequently used in the sites with lateral homogeneity in previous studies,but its application in the sites with rock obstructions is rare.The experimental results of this study indicate that the surface wave method is also able to determine the upper surface of rock obstructions,but difficult to identify the lateral and bottom boundaries of rock obstructions.To improve the precision of detection,the full waveform inversion(FWI)method was used to process the data from the cross-hole seismic survey.The results indicate that the inversion precision of P-wave is higher than that of S-wave.The horizontal and vertical ranges of rock obstructions in the P-wave inversion results are 14–26 m and 7.5–11.0 m respectively,roughly consistent with the results of penetration tests(about 15–25 m)and borehole log(8.85–10.80 m).This result proves that the sequential application of first-arrival time analysis and FWI can effectively delineate the boundary of rock obstruc-tions.Finally,the results of various detection methods were analyzed and compared in this study.Considering the advantages of various methods,we propose a cost-effective and high-precision workflow containing both geotechnical and geophysical investigations.展开更多
In densely built-up Singapore,relatively stiffsecant-bored piles and diaphragm walls are commonly used in cut-and-cover works to minimize the impact of ground movement on the adjacent structures and utilities.For exca...In densely built-up Singapore,relatively stiffsecant-bored piles and diaphragm walls are commonly used in cut-and-cover works to minimize the impact of ground movement on the adjacent structures and utilities.For excavations in stiffresidual soil deposits,the asso-ciated wall deflections and ground settlements are generally smaller than for excavations in soft soil deposits.However,if the residual soil permeability is high and the underlying rock is highlyfissured or fractured,substantial groundwater drawdown and associated seepage-induced settlement may occur.In this study,the excavation performance of four sites in residual soil deposits with maximum excavation depths between 20 and 24 m is presented.The maximum wall deflections were found to be relatively small compared to the significantly larger maximum ground settlements,owing to the extensive lowering of the groundwater table.In this paper,details of the subsurface conditions,excavation support system,field instrumentation,and observed excavation responses are presented,with particular focus on the large groundwater drawdown and associated ground settlement.Specific issues encountered during the excavation,as well as the effectiveness of various groundwater control measures,are discussed.The case studies will provide useful references and insights for future projects involving braced excavations in residual soil.展开更多
Underground space utilization is becoming increasingly essential for modern metropolitan cities such as Singapore.Mapping a soil/rock interface using traditional borehole investigation methods is expensive and difficu...Underground space utilization is becoming increasingly essential for modern metropolitan cities such as Singapore.Mapping a soil/rock interface using traditional borehole investigation methods is expensive and difficult,owing to the numerous physical constraints within a built-up city.Boreholes are often far apart,resulting in many unforeseen ground conditions during subsequent excavation.Geophysical methods are sometimes employed as possible alternatives for fast,economical,and efficient bedrock surveys.The goal of this study is to investigate the practical details of applying microtremor array measurement(MAM)as a non-invasive surface wave survey for mapping soil/rock interfaces in Singapore.Critical configurations in field data acquisition are examined,and practical recommendations for array construction are provided.In addition,30 in situ MAM tests are carried out for two major geological formations in Singapore.From the results,a standard shear wave velocity(V_(s))of 500 m/s is found to be suitable for interpreting the soil/rock interface,for the Bukit Timah Granite and Jurong formations.However,the method does not predict well when soft Kallang formation deposits are present.Other limitations are also discussed in the later parts of this paper.Conclusions and practical recommendations are discussed,providing constructive guidance to the industry.The proposed Vs-based method and associated guidelines and limitations can be used to create a digital geological database and are especially useful for rock profiling in an urban environment.展开更多
In this paper,the co-rotational total Lagrangian forms of finite element formulations are derived to perform elasto-plastic analysis for plane steel frames that either experience increasing external loading at ambient...In this paper,the co-rotational total Lagrangian forms of finite element formulations are derived to perform elasto-plastic analysis for plane steel frames that either experience increasing external loading at ambient temperature or constant external loading at elevated temperatures.Geometric nonlinearities and thermal-expansion effects are considered.A series of programs were developed based on these formulations.To verify the accuracy and efficiency of the nonlinear finite element programs,numerical benchmark tests were performed,and the results from these tests are in a good agreement with the literature.The effects of the nonlinear terms of the stiffness matrices on the computational results were investigated in detail.It was also demonstrated that the influence of geometric nonlinearities on the incremental steps of the finite element analysis for plane steel frames in the presence of fire is limited.展开更多
文摘In order to reduce the risk associated with water seepage in an underground rock cavern project inSingapore, a reliable hydro-geological model should be established based on the in situ investigationdata. The key challenging issue in the hydro-geological model building is how to integrate limitedgeological and hydro-geological data to determine the hydraulic conductivity of the fractured rockmasses. Based on the data obtained from different stages （feasibility investigation stage, constructionstage, and post-construction stage）, suitable models and methods are proposed to determine the hydraulicconductivities at different locations and depths, which will be used at other locations in thefuture. 2015 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.
文摘This paper shares some experiences of developing a good metro network in Singapore. After providing a background of the local land transportation scene, the paper provides a chronological discussion of the metro development in Singapore where the characteristics of each new metro line was briefly discussed. The next part of the paper shares some features and initiatives through developing the Singapore metro system over the years, such as funding arrangement, bringing artworks to transit stations, integrated planning between road and rail, integration between transit facilities with non-transit developments, barrier-free accessibility and improving connectivity to the metro stations, and transforming transport nodes into lifestyle hubs. Finally, the paper concludes by discussing the challenges on the land transport system in Singapore and the way forward.
基金financial support from the Natural Science Foundation of Shanghai(Grant No.23ZR1468500)the National Natural Science Foundation of China(Grant No.51738010)Singapore Housing and Development research grant on tunnel-foundation interaction(Research project number R-302-000-086-490).
文摘Ground losses due to tunneling would induce settlement of nearby raft foundations.To study the change in behavior of the raft foundations over time due to tunnel excavation in soft clay,a series of centrifuge model tests were conducted.The results reveal that the raft stiffness has a significant influence on the development of the gap between the raft and the ground.The width of the gap beneath the flexible foundation would increase over time,leading to a further increase in tensile strain after excavation,whereas the gap for raft foundations with a large stiffness would reduce with time,causing a gradual decrease in tensile strain.The modification factor(MF)design approach is also evaluated with the test results and demonstrates that the MF design approach would underestimate the tensile strain of the flexible raft and provide a relatively conservative prediction for larger stiffnesses.
基金support from China Scholarship Council(CSC)(Grant No.201906260173)the National Science Foundation of Jiangsu Province,China(Grants No.BK20221148)Fundamental Research Funds for the Central Universities,China(Grant No.XJ2021008101).
文摘Determining the location and boundary of underground obstructions and/or anomalies is a common problem and often a great chal-lenge for tunneling and underground construction.In this study,geotechnical investigations(penetration tests and borehole drilling/sam-pling)and geophysical investigations(surface wave method and cross-hole seismic method)were conducted with the aim of identifying the location and boundary of rock obstructions in Changi East,Singapore.The surface wave method is frequently used in the sites with lateral homogeneity in previous studies,but its application in the sites with rock obstructions is rare.The experimental results of this study indicate that the surface wave method is also able to determine the upper surface of rock obstructions,but difficult to identify the lateral and bottom boundaries of rock obstructions.To improve the precision of detection,the full waveform inversion(FWI)method was used to process the data from the cross-hole seismic survey.The results indicate that the inversion precision of P-wave is higher than that of S-wave.The horizontal and vertical ranges of rock obstructions in the P-wave inversion results are 14–26 m and 7.5–11.0 m respectively,roughly consistent with the results of penetration tests(about 15–25 m)and borehole log(8.85–10.80 m).This result proves that the sequential application of first-arrival time analysis and FWI can effectively delineate the boundary of rock obstruc-tions.Finally,the results of various detection methods were analyzed and compared in this study.Considering the advantages of various methods,we propose a cost-effective and high-precision workflow containing both geotechnical and geophysical investigations.
文摘In densely built-up Singapore,relatively stiffsecant-bored piles and diaphragm walls are commonly used in cut-and-cover works to minimize the impact of ground movement on the adjacent structures and utilities.For excavations in stiffresidual soil deposits,the asso-ciated wall deflections and ground settlements are generally smaller than for excavations in soft soil deposits.However,if the residual soil permeability is high and the underlying rock is highlyfissured or fractured,substantial groundwater drawdown and associated seepage-induced settlement may occur.In this study,the excavation performance of four sites in residual soil deposits with maximum excavation depths between 20 and 24 m is presented.The maximum wall deflections were found to be relatively small compared to the significantly larger maximum ground settlements,owing to the extensive lowering of the groundwater table.In this paper,details of the subsurface conditions,excavation support system,field instrumentation,and observed excavation responses are presented,with particular focus on the large groundwater drawdown and associated ground settlement.Specific issues encountered during the excavation,as well as the effectiveness of various groundwater control measures,are discussed.The case studies will provide useful references and insights for future projects involving braced excavations in residual soil.
基金Land Transport Authority Singapore to fund this research project,using the land transportation innovation fund project:non-invasive geophysical study for bedrock evaluation(Award Number:R-302-000-164-490).
文摘Underground space utilization is becoming increasingly essential for modern metropolitan cities such as Singapore.Mapping a soil/rock interface using traditional borehole investigation methods is expensive and difficult,owing to the numerous physical constraints within a built-up city.Boreholes are often far apart,resulting in many unforeseen ground conditions during subsequent excavation.Geophysical methods are sometimes employed as possible alternatives for fast,economical,and efficient bedrock surveys.The goal of this study is to investigate the practical details of applying microtremor array measurement(MAM)as a non-invasive surface wave survey for mapping soil/rock interfaces in Singapore.Critical configurations in field data acquisition are examined,and practical recommendations for array construction are provided.In addition,30 in situ MAM tests are carried out for two major geological formations in Singapore.From the results,a standard shear wave velocity(V_(s))of 500 m/s is found to be suitable for interpreting the soil/rock interface,for the Bukit Timah Granite and Jurong formations.However,the method does not predict well when soft Kallang formation deposits are present.Other limitations are also discussed in the later parts of this paper.Conclusions and practical recommendations are discussed,providing constructive guidance to the industry.The proposed Vs-based method and associated guidelines and limitations can be used to create a digital geological database and are especially useful for rock profiling in an urban environment.
基金This work was sponsored by the National Natural Science Foundation of China(Grant No.10972162).This support is gratefully acknowledged.
文摘In this paper,the co-rotational total Lagrangian forms of finite element formulations are derived to perform elasto-plastic analysis for plane steel frames that either experience increasing external loading at ambient temperature or constant external loading at elevated temperatures.Geometric nonlinearities and thermal-expansion effects are considered.A series of programs were developed based on these formulations.To verify the accuracy and efficiency of the nonlinear finite element programs,numerical benchmark tests were performed,and the results from these tests are in a good agreement with the literature.The effects of the nonlinear terms of the stiffness matrices on the computational results were investigated in detail.It was also demonstrated that the influence of geometric nonlinearities on the incremental steps of the finite element analysis for plane steel frames in the presence of fire is limited.
