In order to effectively improve the horizontal bearing capacity of pile foundations,this study proposes post-expanded arm grouting technology and associated pile foundations.The horizontal bearing characteristic of th...In order to effectively improve the horizontal bearing capacity of pile foundations,this study proposes post-expanded arm grouting technology and associated pile foundations.The horizontal bearing characteristic of the post-expanded arm grouting pile was explored through model tests.The test results indicate that the post-expanded arm grouting pile can increase the contact area between the pile and soil,and can improve the strength of the soil.The horizontal bearing capacity of the post-expanded arm grouting pile was approximately 3 times that of the conventional pile.It also shows that the larger the plate diameter ratio or grouting volume,the higher the horizontal bearing capacity of the post-expanded arm grouting pile.The maximum bending moment of the post-expanded arm grouting pile was located at the pile plate,and the displacement zero point of the new pile was higher than that of the conventional pile.The soil resistance at the pile plate was significantly higher than that of conventional piles,indicating that the pile plate effectively enhances the soil resistance.The improved p-y curve model and horizontal bearing capacity calculation method for the post-expanded arm grouting pile were proposed by considering the pile plate diameter factor.This method was finally verified by experimental results.The results of this study can provide a reference for calculating the horizontal bearing capacity of the post-expanded arm grouting pile.展开更多
To study the dynamic response rules of pile foundations of mega-bridges over faults in strong seismic areas,a finite element model of the pile foundation-soil-fault interaction of the Haiwen Bridge is established.The ...To study the dynamic response rules of pile foundations of mega-bridges over faults in strong seismic areas,a finite element model of the pile foundation-soil-fault interaction of the Haiwen Bridge is established.The 0.2-0.6 g peak acceleration of the 5010 seismic waves is input to study the effect of the seismic wave of different intensities and the distance changes between the fault and the pile foundation on the dynamic response of the pile body.The results show that the soil layer covering the bedrock amplifies the peak pile acceleration,and the amplifying effect decreases with increasing seismic wave intensity.However,bedrock has less of an effect on peak acceleration.The relative pile displacement shows the mechanical properties of elastic long piles.The pile foundation generates a large bending moment at the bedrock face and the upper soil layer interface,and a large shear force at the pile top and the soft-hard soil body interface.The relative displacement,bending,and shear bearing characteristics of the pile foundations on the upper and lower plates of the fault are significantly different.The deformation characteristics are affected by faults in a region ten times the pile diameter.Analysis of the dynamic p-y curves shows that the soil resistance on the pile side of the lower plate at the same depth is greater than that of the upper plate.Sensitivity of the dynamic response of pile foundations on either side of the fault to the effects of seismic intensity and distance between the pile foundation and the fault:distance l seismic intensity q.展开更多
Although the load applied to pile foundations is usually a combination of vertical and lateral components,there have been few investigations on the behavior of piles subjected to combined loadings.Those few studies le...Although the load applied to pile foundations is usually a combination of vertical and lateral components,there have been few investigations on the behavior of piles subjected to combined loadings.Those few studies led to inconsistent results with regard to the effects of vertical loads on the lateral response of piles.A series of three-dimensional(3D) finite differences analyses is conducted to evaluate the influence of vertical loads on the lateral performance of pile foundations.Three idealized sandy and clayey soil profiles are considered:a homogeneous soil layer,a layer with modulus proportional to depth,and two-layered strata.The pile material is modeled as linearly elastic,while the soil is idealized using the Mohr-Coulomb constitutive model with a non-associated flow rule.In order to confirm the findings of this study,soils in some cases are further modeled using more sophisticated models(i.e.CYsoil model for sandy soils and modified Cam-Clay(MCC) model for clayey soils).Numerical results showed that the lateral resistance of the piles does not appear to vary considerably with the vertical load in sandy soil especially at the loosest state.However,the presence of a vertical load on a pile embedded in homogeneous or inhomogeneous clay is detrimental to its lateral capacity,and it is unconservative to design piles in clays assuming that there is no interaction between vertical and lateral loads.Moreover,the current results indicate that the effect of vertical loads on the lateral response of piles embedded in twolayered strata depends on the characteristics of soil not only surrounding the piles but also located beneath their tips.展开更多
Geotechnical engineering deals with materials（e.g. soil and rock） that, by their very nature, exhibit varied and uncertain behavior due to the imprecise physical processes associated with the formation of these mate...Geotechnical engineering deals with materials（e.g. soil and rock） that, by their very nature, exhibit varied and uncertain behavior due to the imprecise physical processes associated with the formation of these materials. Modeling the behavior of such materials in geotechnical engineering applications is complex and sometimes beyond the ability of most traditional forms of physically-based engineering methods. Artificial intelligence（AI） is becoming more popular and particularly amenable to modeling the complex behavior of most geotechnical engineering applications because it has demonstrated superior predictive ability compared to traditional methods. This paper provides state-of-the-art review of some selected AI techniques and their applications in pile foundations, and presents the salient features associated with the modeling development of these AI techniques. The paper also discusses the strength and limitations of the selected AI techniques compared to other available modeling approaches.展开更多
Liquefaction has b e e n a m ain cause o f dam ag e to civil en g in eerin g stru ctu res in seism ically active areas.The effects o f dam ag e o f liquefaction o n d eep foundations are v ery d estructive. Seism ic b...Liquefaction has b e e n a m ain cause o f dam ag e to civil en g in eerin g stru ctu res in seism ically active areas.The effects o f dam ag e o f liquefaction o n d eep foundations are v ery d estructive. Seism ic beh av io r o f pilefoundations is w idely discussed by m any researchers for safer an d m ore econom ic design purposes. Thisp a p e r p resen ts a p se u d o -static m eth o d for analysis o f piles in liquefiable soil u n d e r seism ic loads. A freefieldsite resp o n se analysis using th ree-d im en sio n al （3D） num erical m odeling w as p erfo rm ed to d e te rmine kin em atic loads from lateral g ro u n d disp lacem en ts an d inertial loads from vib ratio n o f th e supe rstru ctu re . The effects o f various p aram eters, such as soil layering, k in em atic and inertial forces,b o u n d ary con d itio n o f pile h ead an d gro u n d slope, o n pile resp o n se w e re studied. By com paring th enum erical results w ith th e centrifuge te s t results, it can be concluded th a t th e use o f th e p-y curves w ithvarious d eg rad atio n factors in liquefiable sand gives reasonable results.展开更多
The bearing capacity of pile foundations is affected by the temperature of the frozen soil around pile foundations.The construction process and the hydration heat of cast-in-place(CIP)pile foundations affect the therm...The bearing capacity of pile foundations is affected by the temperature of the frozen soil around pile foundations.The construction process and the hydration heat of cast-in-place(CIP)pile foundations affect the thermal stability of permafrost.In this paper,temperature data from inside multiple CIP piles,borehole observations of ground thermal status adjacent to the foundations and local weather stations were monitored in warm permafrost regions to study the thermal influence process of CIP pile foundations.The following conclusions are drawn from the field observation data.(1)The early temperature change process of different CIP piles is different,and the differences gradually diminish over time.(2)The initial concrete temperature is linearly related with the air temperature,net radiation and wind speed within 1 h before the completion of concrete pouring;the contributions of the air temperature,net radiation,and wind speed to the initial concrete temperature are 51.9%,20.3%and 27.9%,respectively.(3)The outer boundary of the thermal disturbance annulus is approximately 2 m away from the pile center.It took more than 224 days for the soil around the CIP piles to return to the natural permafrost temperature at the study site.展开更多
The pile-soil system interaction computational model in liquefaction-induced lateral spreading ground was established by the finite difference numerical method.Considering an elastic-plastic subgrade reaction method,n...The pile-soil system interaction computational model in liquefaction-induced lateral spreading ground was established by the finite difference numerical method.Considering an elastic-plastic subgrade reaction method,numerical methods involving finite difference approach of pile in liquefaction-induced lateral spreading ground were derived and implemented into a finite difference program.Based on the monotonic loading tests on saturated sand after liquefaction,the liquefaction lateral deformation of the site where group piles are located was predicted.The effects of lateral ground deformation after liquefaction on a group of pile foundations were studied using the fmite difference program mentioned above,and the failure mechanism of group piles in liquefaction-induced lateral spreading ground was obtained.The applicability of the program was preliminarily verified.The results show that the bending moments at the interfaces between liquefied and non-liquefied soil layers are larger than those at the pile＇s top when the pile＇s top is embedded.The value of the additional static bending moment is larger than the peak dynamic bending moment during the earthquake,so in the pile foundation design,more than the superstructure＇s dynamics should be considered and the effect of lateral ground deformation on pile foundations cannot be neglected.展开更多
Two major earthquakes in Alaska, namely the 1964 Great Alaska Earthquake and the 2002 Denali Earthquake, occurred in winter seasons when the ground crust was frozen. None of the then-existing foundation types was able...Two major earthquakes in Alaska, namely the 1964 Great Alaska Earthquake and the 2002 Denali Earthquake, occurred in winter seasons when the ground crust was frozen. None of the then-existing foundation types was able to withstand the force from the lateral spreading of frozen crust. This paper presents results from the analysis of pile foundations in frozen ground overlying lique- fiable soil utilizing the Beam-on-Nonlinear-Winlder-Foundation （BNWF） （or p-y approach）. P-multipliers were applied on tradi- tional sandy soil p-y curves to simulate soil strength degradation during liquefaction. Frozen soil p-y curves were constructed based on a model proposed in a recent study and the frozen soil mechanical properties obtained from testing of naturally frozen soils. Pile response results from the p-y approach were presented along with those from fluid-solid coupled Finite Element （FE） modeling for comparison purpose. Finally, the sensitivity of pile response to frozen soil parameters was investigated and a brief discussion is presented.展开更多
In recent years,offshore wind turbines have rap-idly developed,and many pile foundations installed earlier are now approaching decommissioning.Thus,the efficient removal of pile foundations has become a critical issue...In recent years,offshore wind turbines have rap-idly developed,and many pile foundations installed earlier are now approaching decommissioning.Thus,the efficient removal of pile foundations has become a critical issue for the sustainable development of offshore wind energy.To ad-dress this issue,this paper systematically investigates three methods for the recovery of pile foundations using physical model experiments:water injection+lifting,air injection+lifting,and air retention+water injection.The experimental results show that the water injection+lifting method exhibits remarkable advantages in recovering large-diameter and in-clined pile foundations;however,realigning inclined piles during recovery remains challenging,and a risk of pile over-turning exists.The air injection+lifting method proves ef-fective for realigning inclined piles but presents a risk of air expulsion failure,which may affect the continuity and stabil-ity of the recovery process.By contrast,the air retention+water injection method combines the characteristics of water injection and air injection techniques,effectively avoiding air expulsion failure and exhibiting pronounced displacement jumps during pile uplift.These findings provide a valuable reference for future decommissioning practices of offshore wind pile foundations,offer important engineering applica-tion value,and contribute positively to the sustainable devel-opment of the offshore wind industry.展开更多
Under the combination of currents and waves, seabed scour occurs around offshore wind turbine foundations, which affects the stability and safe operation of offshore wind turbines. In this study, physical model experi...Under the combination of currents and waves, seabed scour occurs around offshore wind turbine foundations, which affects the stability and safe operation of offshore wind turbines. In this study, physical model experiments under unidirectional flow, bidirectional flow, and wave-current interactions with different flow directions around the pile group foundation were first conducted to investigate the development of scour around the pile group foundation.Additionally, a three-dimensional scour numerical model was established via the open-source software REEF3D to simulate the flow field and scour around the prototype-scale foundation. The impact of flow on scour was discussed.Under unidirectional flow, scour equilibrium was reached more quickly, with the maximum scour depth reaching approximately 1.2 times the pile diameter and the extent of the scour hole spanning about 4.9 times the pile diameter.Compared with those under unidirectional flow, the scour depths under combinations of currents and waves, as well as bidirectional flow, were slightly smaller. However, the morphology of scour holes was more uniform and symmetrical. The numerical simulation results show good agreement with the experimental data, demonstrating the impact of varying flow directions on the velocity distribution around the foundation, the morphology of scour holes, and the location of the maximum scour depth.展开更多
In congested cities such as Sydney,competition for underground space escalates within the built environment because various assets require finite geotechnical strength and support.Specific problems such as damage to b...In congested cities such as Sydney,competition for underground space escalates within the built environment because various assets require finite geotechnical strength and support.Specific problems such as damage to buildings may develop when high-rise buildings on piled foundations are subject to ground movements as tunnels are constructed.This paper focuses on the risks of tunneling beneath Sydney’s Martin Place and how buildings are subject to additional loads caused by tunneling.The key objective of this study is to improve the understanding of tunnel-rock-pile interactions and to encourage sustainable development.A finite element model is developed to predict the interaction between tunnel construction and piled foundations.The tunnel,rock,and pile components are studied separately and are then combined into a single model.The ground model is based on the characteristics of Hawkesbury Sandstone and is developed through a desktop study.The piles are designed using Australian Standards and observations of high-rise buildings.The tunnel construction is modeled based on the construction sequence of a tunnel boring machine.After combining the components,a parametric study on the relationship between tunnel location,basements,and piles is conducted.Our findings,thus far,show that tunneling can increase the axial and flexural loads of piles,where the additional loading exceeds the structural capacity of some piles,especially those that are close to basement walls.The parametric study reveals a strong relationship between tunnel depth and lining stresses,while the relationship between tunnel depth and induced pile loads is less convincing.Furthermore,the horizontal tunnel position relative to piles shows a stronger relationship with pile loads.Further research into tunnel-rock-pile interactions is recommended,especially beneath basements,to substantiate the results of this study.展开更多
The aim of this study is to propose a new detection method for determining the damage locations in pile foundations based on deep learning using acoustic emission data.First,the damage location is simulated using a ba...The aim of this study is to propose a new detection method for determining the damage locations in pile foundations based on deep learning using acoustic emission data.First,the damage location is simulated using a back propagation neural network deep learning model with an acoustic emission data set acquired from pile hit experiments.In particular,the damage location is identified using two parameters:the pile location(PL)and the distance from the pile cap(DS).This study investigates the influences of various acoustic emission parameters,numbers of sensors,sensor installation locations,and the time difference on the prediction accuracy of PL and DS.In addition,correlations between the damage location and acoustic emission parameters are investigated.Second,the damage step condition is determined using a classification model with an acoustic emission data set acquired from uniaxial compressive strength experiments.Finally,a new damage detection and evaluation method for pile foundations is proposed.This new method is capable of continuously detecting and evaluating the damage of pile foundations in service.展开更多
Currently,the pile foundation underpinning technology is widely used when underground transportation infrastructure passes through existing buildings or structures in urban areas.This study aims to investigate stress ...Currently,the pile foundation underpinning technology is widely used when underground transportation infrastructure passes through existing buildings or structures in urban areas.This study aims to investigate stress transfer mechanisms in pile foundations during an underpinning process as well as the influence of shield tunnel construction on pile stability.To this end,the pile foundation underpinning technology used in China’s Shenzhen Metro Line 10 crossing through the bridge pile foundation group of the Guangzhou-Shenzhen highway was analyzed in detailed.The refined numerical simulation of the pile foundation underpinning and shield tunnel construction processes were conducted using the fast Lagrangian analysis of continua in 3 dimensions(FLAC3D)software.The results demonstrate that after the pile foundation underpinned,the previous bridge load system of bridge panel→pile foundation→bearing soil would transform into a bridge panel→existing pile foundation→new underpinning pile→deep bearing soil stratum structure.The overlying load on the underpinned pile could be effectively transferred to a new underpinning pile.In the process of underpinning and tunnel excavation,the settlement and deformation of the foundation can improve the tip resistance and shaft friction of piles,which in turn,can reduce the maximum principal stress in the pile foundation group.The deformation of the bridge pile foundation is mainly caused by ground loss and excavation disturbance generated during shield tunneling as the settlement induced by pile foundation underpinning accounts for approximately 20%-30% of the total settlement.The reduction effects of settlement deformation,lateral displacement,and principal stress are mainly manifested in underpinning piles,while the non-underpinning pile exhibits minimal variation.Meanwhile,the deformation of the segment lining structure of the shield tunnel primarily occurs near the underpinning area of the pile foundation,and it is mainly settlement deformation with a small horizontal displacement.展开更多
The torsional low strain integrity test(TLSIT),known for its advantages such as a smaller detection blind zone,improved identification of shallowly buried defects,stable phase velocity for signal interpretation,and be...The torsional low strain integrity test(TLSIT),known for its advantages such as a smaller detection blind zone,improved identification of shallowly buried defects,stable phase velocity for signal interpretation,and better adaptability for existing pile testing.However,it lacks a comprehensive understanding of the authentic three-dimensional(3D)strain wave propagation mechanism,particularly wave reflection and transmission at defects.To address this gap,a novel 3D theoretical framework is introduced in this context to model the authentic 3D wave propagation during the TLSIT.The proposed approach is validated by comparing its results with those obtained from 3D finite element method(FEM)simulations and simplified 1D(one-dimensional)and 3D analytical solutions.Additionally,a parametric study is conducted to enhance insights into the formation mechanism of high-frequency interference observed during the TLSIT.Finally,a defect identification study is performed to provide guidance for interpreting the wave spectrum in terms of defect characteristics.展开更多
Time-dependent characteristics(TDCs)have been neglected in most previous studies investigating the deviation mechanisms of bridge pile foundations and evaluating the effectiveness of preventive measures.In this study,...Time-dependent characteristics(TDCs)have been neglected in most previous studies investigating the deviation mechanisms of bridge pile foundations and evaluating the effectiveness of preventive measures.In this study,the stress-strain-time characteristics of soft soils were illustrated by consolidation-creep tests based on a typical engineering case.An extended Koppejan model was developed and then embedded in a finite element(FE)model via a user-material subroutine(UMAT).Based on the validated FE model,the time-dependent deformation mechanism of the pile foundation was revealed,and the preventive effect of applying micropiles and stress-release holes to control the deviation was investigated.The results show that the calculated maximum lateral displacement of the cap differs from the measured one by 6.5%,indicating that the derived extended Koppejan model reproduced the deviation process of the bridge cap-pile foundation with time.The additional load acting on the pile side caused by soil lateral deformation was mainly concentrated within the soft soil layer and increased with the increase in load duration.Compared with t=3 d(where t is surcharge time),the maximum lateral additional pressure acting on Pile 2#increased by approximately 47.0%at t=224 d.For bridge pile foundation deviation in deep soft soils,stress-release holes can provide better prevention compared to micropiles and are therefore recommended.展开更多
There is growing engineering concern about the base heave and post uplift phenomena in deep excavation in soft clay,which may pose a risk of instability of retaining systems.The purpose here is to conduct a detailed c...There is growing engineering concern about the base heave and post uplift phenomena in deep excavation in soft clay,which may pose a risk of instability of retaining systems.The purpose here is to conduct a detailed case study on the post uplift observed in a 17.6-meterdeep braced excavation of a subway station in thick soft clay(total thickness up to 42 m)in Shanghai.In this case,a large uplift up to 87 mm unexpectedly developed for the post founded on a 30-meter-long pile foundation.Efforts were first made to examine the complex relationships between the post uplift with the excavation depth(H),Terzaghi’s safety factor against base heave(Fs)and maximum deflection of retaining wall.A simplified approach for soil-post-strut interaction analysis was then proposed and used for quantitative research.The working characteristics of the long pile foundation under low safety factor against base heave(Fs<1.5)are summarized as following:(a)the back-analyzed neutral plane,where soil uplift equals the post uplift,lies at approximately 0.68 times the pile length from the pile top;(b)deep soil movement below the neutral plane results in the observed post uplift;(c)strut reaction plays a minor role in the restriction of post uplift.The influence of base treatment and excavation/construction procedures on post uplift and the principles of pile foundation design are also discussed in this paper.展开更多
In the Shenzhen region,where strong karst development is widely distributed,karst caves pose significant difficulties and risks to pile foundation construction.This paper,based on the Yanba Expressway Municipalization...In the Shenzhen region,where strong karst development is widely distributed,karst caves pose significant difficulties and risks to pile foundation construction.This paper,based on the Yanba Expressway Municipalization Reconstruction Project and referencing previous engineering experiences,proposes the application of sleeve valve pipe grouting technology for pre-treatment of small-to medium-sized and bead-shaped karst caves.Specific implementation measures and construction precautions are presented.Practical results demonstrate that the pre-treated karst cave areas achieved stable soil conditions,providing favorable prerequisites for subsequent pile foundation construction.The method proves convenient and feasible in operation,substantially reducing safety and quality risks during construction.This successful practice offers valuable experience for similar projects.展开更多
The problems noted in the structures built on wooden foundation piles in a lake environment required various works to strengthen over time.This work mainly consists of the recovery of the foundation mass by micropiles...The problems noted in the structures built on wooden foundation piles in a lake environment required various works to strengthen over time.This work mainly consists of the recovery of the foundation mass by micropiles due to the increase in loads on the structures,or the recovery of the foundation mass by injection,which is carried out when voids form between the ground and the wooden foundation elements.The high cost of foundation reinforcement methods led the National Agency for the Development of Tourist Heritage in Benin(ANPT)to replace the wooden foundation piles with reinforced concrete piles in the implementation of the project“reinventing the lakeside city of Ganvié”.This article presents an artisanal technology for the creation of reinforced concrete foundation piles in a lake environment.On-site examples made it possible to evaluate the performance of this artisanal implementation technique.The installation of these piles is carried out following manual drilling,followed by the installation of reinforcement and the pouring of concrete on site.The implementation of reinforced concrete foundation piles in place of the wooden ones studied in this article only impacted the infrastructure of the homes of the lakeside town of Ganviébut not the superstructure,which preserved the old traditional wooden architecture and thatched roofs.Thus,the ambition to move this city of Ganviéfrom the stage of a lake village to that of a floating city is very successful.This will contribute to improving the environment and living conditions of the populations and will promote economic development through tourism.展开更多
To evaluate the responses of fixed and pinned pile groups under torsion, a method is presented to analyze the nonlinear behavior of free-standing pile groups with rigid pile caps. The method is capable of simulating t...To evaluate the responses of fixed and pinned pile groups under torsion, a method is presented to analyze the nonlinear behavior of free-standing pile groups with rigid pile caps. The method is capable of simulating the nonlinear soil response in the near field usingp-y and r-θ curves, the far-field interactions through Mindlin＇s and Randolph＇s elastic solutions, and the coupling effect of lateral resistance on torsional resistance of the individual piles using an empirical factor. Based on comparisons of the solutions for fixed- and pinned-head, 1×2, 2×2, and 3×3 pile groups subjected to torsion, it was found that pile-cap connection significantly influences the torsional capacity of pile groups and the assignment of applied torques in the pile groups. In this study, the applied torques for the pinned-head pile groups are only 44%-64% of those for the corresponding fixed-head pile groups at a twist angle of 2^o. Such a difference is mainly due to the change of the lateral resistances of individual piles in the groups.展开更多
In this paper, using the theory of stochastic analysis of the response to earthquake load, a stochastic analysis method of the response of piled platforms to earthquake load has been established. In the method, the st...In this paper, using the theory of stochastic analysis of the response to earthquake load, a stochastic analysis method of the response of piled platforms to earthquake load has been established. In the method, the strong ground motion is considered as three dimensional stationary white noise process and the pile-soil interaction and water-structure interaction are considered. The stochastic response of a typical platform to earthquake load has been computed with this method and the results compared with those obtained with the response spectrum analysis method. The comparison shows that the stochastic analysis method of the response of piled platforms to earthquake load is suitable for this kind of analysis.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.52208333 and 52378328)China Communications Construction Company Ltd.(Grant No.2023-ZJKJ-01).
文摘In order to effectively improve the horizontal bearing capacity of pile foundations,this study proposes post-expanded arm grouting technology and associated pile foundations.The horizontal bearing characteristic of the post-expanded arm grouting pile was explored through model tests.The test results indicate that the post-expanded arm grouting pile can increase the contact area between the pile and soil,and can improve the strength of the soil.The horizontal bearing capacity of the post-expanded arm grouting pile was approximately 3 times that of the conventional pile.It also shows that the larger the plate diameter ratio or grouting volume,the higher the horizontal bearing capacity of the post-expanded arm grouting pile.The maximum bending moment of the post-expanded arm grouting pile was located at the pile plate,and the displacement zero point of the new pile was higher than that of the conventional pile.The soil resistance at the pile plate was significantly higher than that of conventional piles,indicating that the pile plate effectively enhances the soil resistance.The improved p-y curve model and horizontal bearing capacity calculation method for the post-expanded arm grouting pile were proposed by considering the pile plate diameter factor.This method was finally verified by experimental results.The results of this study can provide a reference for calculating the horizontal bearing capacity of the post-expanded arm grouting pile.
基金funded by National Natural Science Foundation of China Projects(51708040)Hainan Provincial Transportation Science and Technology Project(HNZXY2015-045R)Changan University Central University Basic Research Business Fund Special Funds(No.300102218115).
文摘To study the dynamic response rules of pile foundations of mega-bridges over faults in strong seismic areas,a finite element model of the pile foundation-soil-fault interaction of the Haiwen Bridge is established.The 0.2-0.6 g peak acceleration of the 5010 seismic waves is input to study the effect of the seismic wave of different intensities and the distance changes between the fault and the pile foundation on the dynamic response of the pile body.The results show that the soil layer covering the bedrock amplifies the peak pile acceleration,and the amplifying effect decreases with increasing seismic wave intensity.However,bedrock has less of an effect on peak acceleration.The relative pile displacement shows the mechanical properties of elastic long piles.The pile foundation generates a large bending moment at the bedrock face and the upper soil layer interface,and a large shear force at the pile top and the soft-hard soil body interface.The relative displacement,bending,and shear bearing characteristics of the pile foundations on the upper and lower plates of the fault are significantly different.The deformation characteristics are affected by faults in a region ten times the pile diameter.Analysis of the dynamic p-y curves shows that the soil resistance on the pile side of the lower plate at the same depth is greater than that of the upper plate.Sensitivity of the dynamic response of pile foundations on either side of the fault to the effects of seismic intensity and distance between the pile foundation and the fault:distance l seismic intensity q.
文摘Although the load applied to pile foundations is usually a combination of vertical and lateral components,there have been few investigations on the behavior of piles subjected to combined loadings.Those few studies led to inconsistent results with regard to the effects of vertical loads on the lateral response of piles.A series of three-dimensional(3D) finite differences analyses is conducted to evaluate the influence of vertical loads on the lateral performance of pile foundations.Three idealized sandy and clayey soil profiles are considered:a homogeneous soil layer,a layer with modulus proportional to depth,and two-layered strata.The pile material is modeled as linearly elastic,while the soil is idealized using the Mohr-Coulomb constitutive model with a non-associated flow rule.In order to confirm the findings of this study,soils in some cases are further modeled using more sophisticated models(i.e.CYsoil model for sandy soils and modified Cam-Clay(MCC) model for clayey soils).Numerical results showed that the lateral resistance of the piles does not appear to vary considerably with the vertical load in sandy soil especially at the loosest state.However,the presence of a vertical load on a pile embedded in homogeneous or inhomogeneous clay is detrimental to its lateral capacity,and it is unconservative to design piles in clays assuming that there is no interaction between vertical and lateral loads.Moreover,the current results indicate that the effect of vertical loads on the lateral response of piles embedded in twolayered strata depends on the characteristics of soil not only surrounding the piles but also located beneath their tips.
文摘Geotechnical engineering deals with materials（e.g. soil and rock） that, by their very nature, exhibit varied and uncertain behavior due to the imprecise physical processes associated with the formation of these materials. Modeling the behavior of such materials in geotechnical engineering applications is complex and sometimes beyond the ability of most traditional forms of physically-based engineering methods. Artificial intelligence（AI） is becoming more popular and particularly amenable to modeling the complex behavior of most geotechnical engineering applications because it has demonstrated superior predictive ability compared to traditional methods. This paper provides state-of-the-art review of some selected AI techniques and their applications in pile foundations, and presents the salient features associated with the modeling development of these AI techniques. The paper also discusses the strength and limitations of the selected AI techniques compared to other available modeling approaches.
文摘Liquefaction has b e e n a m ain cause o f dam ag e to civil en g in eerin g stru ctu res in seism ically active areas.The effects o f dam ag e o f liquefaction o n d eep foundations are v ery d estructive. Seism ic beh av io r o f pilefoundations is w idely discussed by m any researchers for safer an d m ore econom ic design purposes. Thisp a p e r p resen ts a p se u d o -static m eth o d for analysis o f piles in liquefiable soil u n d e r seism ic loads. A freefieldsite resp o n se analysis using th ree-d im en sio n al （3D） num erical m odeling w as p erfo rm ed to d e te rmine kin em atic loads from lateral g ro u n d disp lacem en ts an d inertial loads from vib ratio n o f th e supe rstru ctu re . The effects o f various p aram eters, such as soil layering, k in em atic and inertial forces,b o u n d ary con d itio n o f pile h ead an d gro u n d slope, o n pile resp o n se w e re studied. By com paring th enum erical results w ith th e centrifuge te s t results, it can be concluded th a t th e use o f th e p-y curves w ithvarious d eg rad atio n factors in liquefiable sand gives reasonable results.
基金supported by the Natural Science Foundation of China (Grants No.41101065)the State Key Laboratory of Frozen Soil Engineering Funds (SKLFSE-ZT-34,SKLFSE-ZQ-202103).
文摘The bearing capacity of pile foundations is affected by the temperature of the frozen soil around pile foundations.The construction process and the hydration heat of cast-in-place(CIP)pile foundations affect the thermal stability of permafrost.In this paper,temperature data from inside multiple CIP piles,borehole observations of ground thermal status adjacent to the foundations and local weather stations were monitored in warm permafrost regions to study the thermal influence process of CIP pile foundations.The following conclusions are drawn from the field observation data.(1)The early temperature change process of different CIP piles is different,and the differences gradually diminish over time.(2)The initial concrete temperature is linearly related with the air temperature,net radiation and wind speed within 1 h before the completion of concrete pouring;the contributions of the air temperature,net radiation,and wind speed to the initial concrete temperature are 51.9%,20.3%and 27.9%,respectively.(3)The outer boundary of the thermal disturbance annulus is approximately 2 m away from the pile center.It took more than 224 days for the soil around the CIP piles to return to the natural permafrost temperature at the study site.
基金Project(51109208)supported by the National Natural Science Foundation of ChinaProject(2013M531688)supported by the Postdoctoral Science Foundation of China+1 种基金Project(Z012009)supported by the Open Research Fund of State Key Laboratory of Geomechanics and Geotechnical Engineering(Institute of Rock and Soil Mechanics,Chinese Academy of Sciences)Project(CKSF2012054)supported by the Foundation of Changjiang River Scientific Research Institute,China
文摘The pile-soil system interaction computational model in liquefaction-induced lateral spreading ground was established by the finite difference numerical method.Considering an elastic-plastic subgrade reaction method,numerical methods involving finite difference approach of pile in liquefaction-induced lateral spreading ground were derived and implemented into a finite difference program.Based on the monotonic loading tests on saturated sand after liquefaction,the liquefaction lateral deformation of the site where group piles are located was predicted.The effects of lateral ground deformation after liquefaction on a group of pile foundations were studied using the fmite difference program mentioned above,and the failure mechanism of group piles in liquefaction-induced lateral spreading ground was obtained.The applicability of the program was preliminarily verified.The results show that the bending moments at the interfaces between liquefied and non-liquefied soil layers are larger than those at the pile＇s top when the pile＇s top is embedded.The value of the additional static bending moment is larger than the peak dynamic bending moment during the earthquake,so in the pile foundation design,more than the superstructure＇s dynamics should be considered and the effect of lateral ground deformation on pile foundations cannot be neglected.
基金funding from Alaska University Transportation Center (AUTC)the State of Alaska Department of Transportation and Public Facilities (ADOT&PF) under projects AUTC Projects #309011 and #510021
文摘Two major earthquakes in Alaska, namely the 1964 Great Alaska Earthquake and the 2002 Denali Earthquake, occurred in winter seasons when the ground crust was frozen. None of the then-existing foundation types was able to withstand the force from the lateral spreading of frozen crust. This paper presents results from the analysis of pile foundations in frozen ground overlying lique- fiable soil utilizing the Beam-on-Nonlinear-Winlder-Foundation （BNWF） （or p-y approach）. P-multipliers were applied on tradi- tional sandy soil p-y curves to simulate soil strength degradation during liquefaction. Frozen soil p-y curves were constructed based on a model proposed in a recent study and the frozen soil mechanical properties obtained from testing of naturally frozen soils. Pile response results from the p-y approach were presented along with those from fluid-solid coupled Finite Element （FE） modeling for comparison purpose. Finally, the sensitivity of pile response to frozen soil parameters was investigated and a brief discussion is presented.
基金The National Natural Science Foundation of China (No. 52171274)。
文摘In recent years,offshore wind turbines have rap-idly developed,and many pile foundations installed earlier are now approaching decommissioning.Thus,the efficient removal of pile foundations has become a critical issue for the sustainable development of offshore wind energy.To ad-dress this issue,this paper systematically investigates three methods for the recovery of pile foundations using physical model experiments:water injection+lifting,air injection+lifting,and air retention+water injection.The experimental results show that the water injection+lifting method exhibits remarkable advantages in recovering large-diameter and in-clined pile foundations;however,realigning inclined piles during recovery remains challenging,and a risk of pile over-turning exists.The air injection+lifting method proves ef-fective for realigning inclined piles but presents a risk of air expulsion failure,which may affect the continuity and stabil-ity of the recovery process.By contrast,the air retention+water injection method combines the characteristics of water injection and air injection techniques,effectively avoiding air expulsion failure and exhibiting pronounced displacement jumps during pile uplift.These findings provide a valuable reference for future decommissioning practices of offshore wind pile foundations,offer important engineering applica-tion value,and contribute positively to the sustainable devel-opment of the offshore wind industry.
基金financially supported by the National Key Research and Development Program of China (Grant No. 2021YFB2601100)the National Natural Science Foundation of China (Grant No. 51979190)。
文摘Under the combination of currents and waves, seabed scour occurs around offshore wind turbine foundations, which affects the stability and safe operation of offshore wind turbines. In this study, physical model experiments under unidirectional flow, bidirectional flow, and wave-current interactions with different flow directions around the pile group foundation were first conducted to investigate the development of scour around the pile group foundation.Additionally, a three-dimensional scour numerical model was established via the open-source software REEF3D to simulate the flow field and scour around the prototype-scale foundation. The impact of flow on scour was discussed.Under unidirectional flow, scour equilibrium was reached more quickly, with the maximum scour depth reaching approximately 1.2 times the pile diameter and the extent of the scour hole spanning about 4.9 times the pile diameter.Compared with those under unidirectional flow, the scour depths under combinations of currents and waves, as well as bidirectional flow, were slightly smaller. However, the morphology of scour holes was more uniform and symmetrical. The numerical simulation results show good agreement with the experimental data, demonstrating the impact of varying flow directions on the velocity distribution around the foundation, the morphology of scour holes, and the location of the maximum scour depth.
基金Corresponding author at:Hadi Khabbaz,School of Civil and Environmental Engineering,Faculty of Engineering and Information Technology,University of Technology Sydney(UTS),City Campus,PO Box 123,Broadway,NSW 2007,Australia.E-mail addresses:Hadi.Khabbaz@uts.edu.au。
文摘In congested cities such as Sydney,competition for underground space escalates within the built environment because various assets require finite geotechnical strength and support.Specific problems such as damage to buildings may develop when high-rise buildings on piled foundations are subject to ground movements as tunnels are constructed.This paper focuses on the risks of tunneling beneath Sydney’s Martin Place and how buildings are subject to additional loads caused by tunneling.The key objective of this study is to improve the understanding of tunnel-rock-pile interactions and to encourage sustainable development.A finite element model is developed to predict the interaction between tunnel construction and piled foundations.The tunnel,rock,and pile components are studied separately and are then combined into a single model.The ground model is based on the characteristics of Hawkesbury Sandstone and is developed through a desktop study.The piles are designed using Australian Standards and observations of high-rise buildings.The tunnel construction is modeled based on the construction sequence of a tunnel boring machine.After combining the components,a parametric study on the relationship between tunnel location,basements,and piles is conducted.Our findings,thus far,show that tunneling can increase the axial and flexural loads of piles,where the additional loading exceeds the structural capacity of some piles,especially those that are close to basement walls.The parametric study reveals a strong relationship between tunnel depth and lining stresses,while the relationship between tunnel depth and induced pile loads is less convincing.Furthermore,the horizontal tunnel position relative to piles shows a stronger relationship with pile loads.Further research into tunnel-rock-pile interactions is recommended,especially beneath basements,to substantiate the results of this study.
基金This work was supported by a National Research Foundation of Korea(NRF)grant funded by the Korean Government(MSIT)(No.NRF-2019R1G1A1100517)the Fundamental Research Funds for the Central Universities(N170108029)+2 种基金the National Natural Science Foundation of China(Grant Nos.U1602232 and 51474050)China Government Scholarship(201806080061)all of the above-mentioned funding sources and kind help are gratefully acknowledged.
文摘The aim of this study is to propose a new detection method for determining the damage locations in pile foundations based on deep learning using acoustic emission data.First,the damage location is simulated using a back propagation neural network deep learning model with an acoustic emission data set acquired from pile hit experiments.In particular,the damage location is identified using two parameters:the pile location(PL)and the distance from the pile cap(DS).This study investigates the influences of various acoustic emission parameters,numbers of sensors,sensor installation locations,and the time difference on the prediction accuracy of PL and DS.In addition,correlations between the damage location and acoustic emission parameters are investigated.Second,the damage step condition is determined using a classification model with an acoustic emission data set acquired from uniaxial compressive strength experiments.Finally,a new damage detection and evaluation method for pile foundations is proposed.This new method is capable of continuously detecting and evaluating the damage of pile foundations in service.
基金supported by the Key R&D Program of Sichuan Province,China(No.2019YFG0001).
文摘Currently,the pile foundation underpinning technology is widely used when underground transportation infrastructure passes through existing buildings or structures in urban areas.This study aims to investigate stress transfer mechanisms in pile foundations during an underpinning process as well as the influence of shield tunnel construction on pile stability.To this end,the pile foundation underpinning technology used in China’s Shenzhen Metro Line 10 crossing through the bridge pile foundation group of the Guangzhou-Shenzhen highway was analyzed in detailed.The refined numerical simulation of the pile foundation underpinning and shield tunnel construction processes were conducted using the fast Lagrangian analysis of continua in 3 dimensions(FLAC3D)software.The results demonstrate that after the pile foundation underpinned,the previous bridge load system of bridge panel→pile foundation→bearing soil would transform into a bridge panel→existing pile foundation→new underpinning pile→deep bearing soil stratum structure.The overlying load on the underpinned pile could be effectively transferred to a new underpinning pile.In the process of underpinning and tunnel excavation,the settlement and deformation of the foundation can improve the tip resistance and shaft friction of piles,which in turn,can reduce the maximum principal stress in the pile foundation group.The deformation of the bridge pile foundation is mainly caused by ground loss and excavation disturbance generated during shield tunneling as the settlement induced by pile foundation underpinning accounts for approximately 20%-30% of the total settlement.The reduction effects of settlement deformation,lateral displacement,and principal stress are mainly manifested in underpinning piles,while the non-underpinning pile exhibits minimal variation.Meanwhile,the deformation of the segment lining structure of the shield tunnel primarily occurs near the underpinning area of the pile foundation,and it is mainly settlement deformation with a small horizontal displacement.
基金supported by the National Natural Science Foundation of China(Grant Nos.52408407 and 52478373)the‘CUG Scholar’Scientific Research Funds at China University of Geosciences(Grant No.2023082).
文摘The torsional low strain integrity test(TLSIT),known for its advantages such as a smaller detection blind zone,improved identification of shallowly buried defects,stable phase velocity for signal interpretation,and better adaptability for existing pile testing.However,it lacks a comprehensive understanding of the authentic three-dimensional(3D)strain wave propagation mechanism,particularly wave reflection and transmission at defects.To address this gap,a novel 3D theoretical framework is introduced in this context to model the authentic 3D wave propagation during the TLSIT.The proposed approach is validated by comparing its results with those obtained from 3D finite element method(FEM)simulations and simplified 1D(one-dimensional)and 3D analytical solutions.Additionally,a parametric study is conducted to enhance insights into the formation mechanism of high-frequency interference observed during the TLSIT.Finally,a defect identification study is performed to provide guidance for interpreting the wave spectrum in terms of defect characteristics.
基金supported by the Science and Technology Research Project of Jiangxi Education Department(Nos.GJJ2201509,GJJ2201501)the National Natural Science Foundation of China(Nos.51878671,51969018,52378344)+1 种基金the Natural Science Foundation of Jiangxi Province(No.20224BAB204076)the Young Scientific and Technological Talents Sponsorship Project in Ganpo Juncai Support Program(No.2023QT08).
文摘Time-dependent characteristics(TDCs)have been neglected in most previous studies investigating the deviation mechanisms of bridge pile foundations and evaluating the effectiveness of preventive measures.In this study,the stress-strain-time characteristics of soft soils were illustrated by consolidation-creep tests based on a typical engineering case.An extended Koppejan model was developed and then embedded in a finite element(FE)model via a user-material subroutine(UMAT).Based on the validated FE model,the time-dependent deformation mechanism of the pile foundation was revealed,and the preventive effect of applying micropiles and stress-release holes to control the deviation was investigated.The results show that the calculated maximum lateral displacement of the cap differs from the measured one by 6.5%,indicating that the derived extended Koppejan model reproduced the deviation process of the bridge cap-pile foundation with time.The additional load acting on the pile side caused by soil lateral deformation was mainly concentrated within the soft soil layer and increased with the increase in load duration.Compared with t=3 d(where t is surcharge time),the maximum lateral additional pressure acting on Pile 2#increased by approximately 47.0%at t=224 d.For bridge pile foundation deviation in deep soft soils,stress-release holes can provide better prevention compared to micropiles and are therefore recommended.
基金the financial support provided by the Natural Science Foundation of China(Grant No.41972273).
文摘There is growing engineering concern about the base heave and post uplift phenomena in deep excavation in soft clay,which may pose a risk of instability of retaining systems.The purpose here is to conduct a detailed case study on the post uplift observed in a 17.6-meterdeep braced excavation of a subway station in thick soft clay(total thickness up to 42 m)in Shanghai.In this case,a large uplift up to 87 mm unexpectedly developed for the post founded on a 30-meter-long pile foundation.Efforts were first made to examine the complex relationships between the post uplift with the excavation depth(H),Terzaghi’s safety factor against base heave(Fs)and maximum deflection of retaining wall.A simplified approach for soil-post-strut interaction analysis was then proposed and used for quantitative research.The working characteristics of the long pile foundation under low safety factor against base heave(Fs<1.5)are summarized as following:(a)the back-analyzed neutral plane,where soil uplift equals the post uplift,lies at approximately 0.68 times the pile length from the pile top;(b)deep soil movement below the neutral plane results in the observed post uplift;(c)strut reaction plays a minor role in the restriction of post uplift.The influence of base treatment and excavation/construction procedures on post uplift and the principles of pile foundation design are also discussed in this paper.
文摘In the Shenzhen region,where strong karst development is widely distributed,karst caves pose significant difficulties and risks to pile foundation construction.This paper,based on the Yanba Expressway Municipalization Reconstruction Project and referencing previous engineering experiences,proposes the application of sleeve valve pipe grouting technology for pre-treatment of small-to medium-sized and bead-shaped karst caves.Specific implementation measures and construction precautions are presented.Practical results demonstrate that the pre-treated karst cave areas achieved stable soil conditions,providing favorable prerequisites for subsequent pile foundation construction.The method proves convenient and feasible in operation,substantially reducing safety and quality risks during construction.This successful practice offers valuable experience for similar projects.
文摘The problems noted in the structures built on wooden foundation piles in a lake environment required various works to strengthen over time.This work mainly consists of the recovery of the foundation mass by micropiles due to the increase in loads on the structures,or the recovery of the foundation mass by injection,which is carried out when voids form between the ground and the wooden foundation elements.The high cost of foundation reinforcement methods led the National Agency for the Development of Tourist Heritage in Benin(ANPT)to replace the wooden foundation piles with reinforced concrete piles in the implementation of the project“reinventing the lakeside city of Ganvié”.This article presents an artisanal technology for the creation of reinforced concrete foundation piles in a lake environment.On-site examples made it possible to evaluate the performance of this artisanal implementation technique.The installation of these piles is carried out following manual drilling,followed by the installation of reinforcement and the pouring of concrete on site.The implementation of reinforced concrete foundation piles in place of the wooden ones studied in this article only impacted the infrastructure of the homes of the lakeside town of Ganviébut not the superstructure,which preserved the old traditional wooden architecture and thatched roofs.Thus,the ambition to move this city of Ganviéfrom the stage of a lake village to that of a floating city is very successful.This will contribute to improving the environment and living conditions of the populations and will promote economic development through tourism.
基金Project (No. HKUST 6037/01E) supported by the Research GrantsCouncil of Hong Kong SAR, China
文摘To evaluate the responses of fixed and pinned pile groups under torsion, a method is presented to analyze the nonlinear behavior of free-standing pile groups with rigid pile caps. The method is capable of simulating the nonlinear soil response in the near field usingp-y and r-θ curves, the far-field interactions through Mindlin＇s and Randolph＇s elastic solutions, and the coupling effect of lateral resistance on torsional resistance of the individual piles using an empirical factor. Based on comparisons of the solutions for fixed- and pinned-head, 1×2, 2×2, and 3×3 pile groups subjected to torsion, it was found that pile-cap connection significantly influences the torsional capacity of pile groups and the assignment of applied torques in the pile groups. In this study, the applied torques for the pinned-head pile groups are only 44%-64% of those for the corresponding fixed-head pile groups at a twist angle of 2^o. Such a difference is mainly due to the change of the lateral resistances of individual piles in the groups.
文摘In this paper, using the theory of stochastic analysis of the response to earthquake load, a stochastic analysis method of the response of piled platforms to earthquake load has been established. In the method, the strong ground motion is considered as three dimensional stationary white noise process and the pile-soil interaction and water-structure interaction are considered. The stochastic response of a typical platform to earthquake load has been computed with this method and the results compared with those obtained with the response spectrum analysis method. The comparison shows that the stochastic analysis method of the response of piled platforms to earthquake load is suitable for this kind of analysis.
