Cement-mixed piles,as countermeasure against liquefaction of silt and sand ground,can improve the shear strength and bearing capacity of foundation soil,meaning cement-mixed piles are capable of resisting displacement...Cement-mixed piles,as countermeasure against liquefaction of silt and sand ground,can improve the shear strength and bearing capacity of foundation soil,meaning cement-mixed piles are capable of resisting displacement when an earthquake happens. However,investigations of cement-mixed piles by experimental methods such as the shaking table test is few and far between. It is especially true for the seismic performance of cement-mixed piles in liquefiable railway foundations in high seismic intensity regions. To this end,a cross-section of the Yuxi-Mengzi railway was selected as the prototype and studied by the shaking table test in this study. The results showed that composite foundation of cementmixed piles was not liquefied when the seismic acceleration was lower than 0. 30g. In the process of acceleration increasing from 0. 30g at 2Hz to 0. 60g at 3Hz,the upper middle silt outside slope toe was partly liquefied. The foundation soil under the shoulders and center of subgrade was far from the initial liquefaction criterion during the test. Cementmixed piles can effectively reduce the embankment settlement and differential settlement. It can be concluded that, the design of cement-mixed piles can ensure the seismic performance of the subgrade,and satisfy the seismic design requirements of the YuxiMengzi railway in areas of VIII degrees seismic fortification intensity.展开更多
A series of investigations were conducted to study the bearing capacity and load transfer mechanism of stiffened deep cement mixed （SDCM） pile. Laboratory tests including six specimens were conducted to investigate ...A series of investigations were conducted to study the bearing capacity and load transfer mechanism of stiffened deep cement mixed （SDCM） pile. Laboratory tests including six specimens were conducted to investigate the frictional resistance between the concrete core and the cementsoil. Two model piles and twenty-four full-scale piles were tested to examine the bearing behavior of single pile. Laboratory and model tests results indicate that the cohesive strength is large enough to ensure the interaction between core pile and the outer cement-soil. The full-scale test results show that the SDCM piles exhibit similar bearing behavior to bored and cast-in-place concrete piles. In general, with the rational composite structure the SDCM piles can transmit the applied load effectively, and due to the addition of the stiffer core, the SDCM piles possess high bearing capacity. Based on the findings of these experimental investigations and theoretical analysi , a practical design method is developed to predict the vertical bearing capacity of SDCM pile.展开更多
Construction of seaside and underground wall bracing often uses stiffened deep cement mixed columns （SDCM）. This research investigates methods used to improve the level of bearing capacity of these SDCM when subject...Construction of seaside and underground wall bracing often uses stiffened deep cement mixed columns （SDCM）. This research investigates methods used to improve the level of bearing capacity of these SDCM when subjected to cyclic lateral loading via various types of stiffer cores. Eight piles, two deep cement mixed piles and six stiffened deep cement mixing piles with three different types of cores, H shape cross section prestressed concrete, steel pipe, and H-beam steel, were embedded though soft clay into medium-hard clay on site in Thailand. Cyclic horizontal loading was gradually applied until pile failure and the hysteresis loops of lateral load vs. lateral deformation were recorded. The lateral carrying capacities of the SDCM piles with an H-beam steel core increased by 3-4 times that of the DCM piles. This field research clearly shows that using H-beam steel as a stiffer core for SDCM piles is the best method to improve its lateral carrying capacity, ductility and energy dissipation capacity.展开更多
The cement mixing (CM) pile is a common method of improving soft offshore ground. The strength growth of CM piles under complex conditions is affected by many factors, especially the cement and moisture contents, and ...The cement mixing (CM) pile is a common method of improving soft offshore ground. The strength growth of CM piles under complex conditions is affected by many factors, especially the cement and moisture contents, and shows significant uncertainty. To investigate the stochasticity of the early strength of CM piles and its impact on the displacement and stability of a seawall, a series of laboratory tests and numerical analyses were carried out in this study. Vane shear tests were conducted on the cement-solidified soil to determine the relationships between the undrained shear strength s_(u) of the cement soil curing in the seawater and the cement content a_(c), as well as the in situ soil moisture content w. It can be inferred that the 24 h undrained shear strength follows a normal distribution. A numerical model considering the random CM pile strength was established to investigate the deformation of the seawall. Due to the uncertainty of CM pile strength, the displacement of the seawall demonstrates a certain discreteness. The decrease of the mean undrained shear strength of CM piles causes a corresponding increase in the average displacement of the seawall. When the mean strength of CM piles is lower than a certain threshold, there is a risk of instability. Furthermore, the heterogeneity of the strength within an individual CM pile also has an impact on seawall displacement. Attention should be paid to the uncertainty of CM pile strength to control displacement and stability.展开更多
This paper presents a reliability-based settlement analysis of T-shaped deep cement mixing(TDM)pile-supported embankments over soft soils.The uncertainties of the mechanical properties of the in-situ soil,pile,and emb...This paper presents a reliability-based settlement analysis of T-shaped deep cement mixing(TDM)pile-supported embankments over soft soils.The uncertainties of the mechanical properties of the in-situ soil,pile,and embankment,and the effect of the pile shape are considered simultaneously.The analyses are performed using Monte Carlo Simulations in combination with an adaptive Kriging(using adaptive sampling algorithm).Individual and system failure probabilities,in terms of the differential and maximum settlements(serviceability limit state(SLS)requirements),are considered.The reliability results for the embankments supported by TDM piles,with various shapes,are compared and discussed together with the results for conventional deep cement mixing pile-supported embankments with equivalent pile volumes.The influences of the inherent variabilities in the material properties(mean and coefficient of variation values)on the reliability of the piled embankments,are also investigated.This study shows that large TDM piles,particularly those with a shape factor of greater than 3,can enhance the reliability of the embankment in terms of SLS requirements,and even avoid unacceptable reliability levels caused by variability in the material properties.展开更多
基金sponsored by the Railway's Research and Development Project of the Ministry of Railways of the People's Republic of the China:Study on Special Subgrade Construction Technology in High Intensity Earthquake Area of the Yuxi-Mengzi Railway
文摘Cement-mixed piles,as countermeasure against liquefaction of silt and sand ground,can improve the shear strength and bearing capacity of foundation soil,meaning cement-mixed piles are capable of resisting displacement when an earthquake happens. However,investigations of cement-mixed piles by experimental methods such as the shaking table test is few and far between. It is especially true for the seismic performance of cement-mixed piles in liquefiable railway foundations in high seismic intensity regions. To this end,a cross-section of the Yuxi-Mengzi railway was selected as the prototype and studied by the shaking table test in this study. The results showed that composite foundation of cementmixed piles was not liquefied when the seismic acceleration was lower than 0. 30g. In the process of acceleration increasing from 0. 30g at 2Hz to 0. 60g at 3Hz,the upper middle silt outside slope toe was partly liquefied. The foundation soil under the shoulders and center of subgrade was far from the initial liquefaction criterion during the test. Cementmixed piles can effectively reduce the embankment settlement and differential settlement. It can be concluded that, the design of cement-mixed piles can ensure the seismic performance of the subgrade,and satisfy the seismic design requirements of the YuxiMengzi railway in areas of VIII degrees seismic fortification intensity.
文摘A series of investigations were conducted to study the bearing capacity and load transfer mechanism of stiffened deep cement mixed （SDCM） pile. Laboratory tests including six specimens were conducted to investigate the frictional resistance between the concrete core and the cementsoil. Two model piles and twenty-four full-scale piles were tested to examine the bearing behavior of single pile. Laboratory and model tests results indicate that the cohesive strength is large enough to ensure the interaction between core pile and the outer cement-soil. The full-scale test results show that the SDCM piles exhibit similar bearing behavior to bored and cast-in-place concrete piles. In general, with the rational composite structure the SDCM piles can transmit the applied load effectively, and due to the addition of the stiffer core, the SDCM piles possess high bearing capacity. Based on the findings of these experimental investigations and theoretical analysi , a practical design method is developed to predict the vertical bearing capacity of SDCM pile.
基金the Thailand Research Fund (TRF) for their financial support to this study
文摘Construction of seaside and underground wall bracing often uses stiffened deep cement mixed columns （SDCM）. This research investigates methods used to improve the level of bearing capacity of these SDCM when subjected to cyclic lateral loading via various types of stiffer cores. Eight piles, two deep cement mixed piles and six stiffened deep cement mixing piles with three different types of cores, H shape cross section prestressed concrete, steel pipe, and H-beam steel, were embedded though soft clay into medium-hard clay on site in Thailand. Cyclic horizontal loading was gradually applied until pile failure and the hysteresis loops of lateral load vs. lateral deformation were recorded. The lateral carrying capacities of the SDCM piles with an H-beam steel core increased by 3-4 times that of the DCM piles. This field research clearly shows that using H-beam steel as a stiffer core for SDCM piles is the best method to improve its lateral carrying capacity, ductility and energy dissipation capacity.
基金supported by the Finance Science and Technology Project of Hainan Province(No.ZDKJ202019)the Key Research and Development Program of Zhejiang Province(No.2021C03014)the Natural Science Foundation of Zhejiang Province(No.LR22E080005),China.
文摘The cement mixing (CM) pile is a common method of improving soft offshore ground. The strength growth of CM piles under complex conditions is affected by many factors, especially the cement and moisture contents, and shows significant uncertainty. To investigate the stochasticity of the early strength of CM piles and its impact on the displacement and stability of a seawall, a series of laboratory tests and numerical analyses were carried out in this study. Vane shear tests were conducted on the cement-solidified soil to determine the relationships between the undrained shear strength s_(u) of the cement soil curing in the seawater and the cement content a_(c), as well as the in situ soil moisture content w. It can be inferred that the 24 h undrained shear strength follows a normal distribution. A numerical model considering the random CM pile strength was established to investigate the deformation of the seawall. Due to the uncertainty of CM pile strength, the displacement of the seawall demonstrates a certain discreteness. The decrease of the mean undrained shear strength of CM piles causes a corresponding increase in the average displacement of the seawall. When the mean strength of CM piles is lower than a certain threshold, there is a risk of instability. Furthermore, the heterogeneity of the strength within an individual CM pile also has an impact on seawall displacement. Attention should be paid to the uncertainty of CM pile strength to control displacement and stability.
基金The authors gratefully acknowledge King Mongkut’s University of Technology Thonburi(KMUTT)and National Research Council of Thailand(NRCT)through grant No.NRCT5-RSA63006 and Thailand Science Research and Innovation(TSRI)under Fundamental Fund 2022(Project:Advanced Construction Towards Thailand 4.0).The authors would also like to acknowledge the financial support provided by King Mongkut’s University of Technology North Bangkok(KMUTNB)and the National Science,Research and Innovation Fund(NSRF)under Contract No.KMUTNB-FF-65-38.The first author also appreciates the financial support through Postdoctoral Fellowship from King Mongkut’s University of Technology Thonburi(KMUTT).
文摘This paper presents a reliability-based settlement analysis of T-shaped deep cement mixing(TDM)pile-supported embankments over soft soils.The uncertainties of the mechanical properties of the in-situ soil,pile,and embankment,and the effect of the pile shape are considered simultaneously.The analyses are performed using Monte Carlo Simulations in combination with an adaptive Kriging(using adaptive sampling algorithm).Individual and system failure probabilities,in terms of the differential and maximum settlements(serviceability limit state(SLS)requirements),are considered.The reliability results for the embankments supported by TDM piles,with various shapes,are compared and discussed together with the results for conventional deep cement mixing pile-supported embankments with equivalent pile volumes.The influences of the inherent variabilities in the material properties(mean and coefficient of variation values)on the reliability of the piled embankments,are also investigated.This study shows that large TDM piles,particularly those with a shape factor of greater than 3,can enhance the reliability of the embankment in terms of SLS requirements,and even avoid unacceptable reliability levels caused by variability in the material properties.
