The main purpose of using geothermal energy piles(GEPs)is to enable the exploitation of geothermal energy for meeting the heating/cooling demands of buildings efficiently.However,the installation process of convention...The main purpose of using geothermal energy piles(GEPs)is to enable the exploitation of geothermal energy for meeting the heating/cooling demands of buildings efficiently.However,the installation process of conventional GEPs is inconvenient compared with that of traditional foundation piles.The pre-bored grouted planted geothermal energy pile(PGP GEP)is an innovative technology to simplify the installation process.Most investigations of in-situ experiments for conventional GEPs have focused on summer conditions.An in-situ test for a PGP GEP was conducted to analyze the temperature changes and thermo-mechanical characteristics under winter conditions.The results show that the average temperature of the pile decreased by 5.1℃,and the pile exhibited a general trend of high temperatures at both ends and low temperatures in the middle.In mechanics,strong pile end restraints resulted in smaller observed axial strain and higher axial thermal-induced force in the pile ends than at the middle of the pile.展开更多
This paper develops a semi-analytical solution for pile penetration in natural soft clays using the strain path method(SPM).The stress-strain behavior of soils is characterized by the S-CLAY1S model,which can capture ...This paper develops a semi-analytical solution for pile penetration in natural soft clays using the strain path method(SPM).The stress-strain behavior of soils is characterized by the S-CLAY1S model,which can capture the anisotropic evolution and destructuring nature of soft clays.By integrating the S-CLAY1S model into the theoretical framework of the SPM,a set of ordinary differential equations is formulated with respect to the vertical coordinate of soil particles.The distribution of excess pore water pressure(EPWP)following pile installation is approximated through one-dimensional(1D)radial integration around the pile shaft.The distribution of stresses and EPWP,along with the evolution of fabric anisotropy within the soil surrounding the pile,is presented to illustrate the response of pile penetration in natural soft clays.The proposed solution is validated against existing theoretical solutions using the SPM and cavity expansion method(CEM),along with experimental data.The findings demonstrate that the SPM reveals lower radial effective stresses and EPWP at the pile shaft than that of CEM.Pile penetration alters the soil's anisotropic properties,inducing rotational hardening and affecting post-installation stress distribution.Soil destructuration eliminates bonding among particles near the pile,resulting in a complete disruption of soil structure at the pile surface,which is particularly pronounced for higher initial soil structure ratios.Minimal variation was observed in the three principal stresses and shear stress on the cone side surface as the angle increased from 18°to 60°,except for a slight reduction in EPWP.展开更多
A shaking table test was performed to investigate the different responses of piles with and without cement-soil reinforcement,considering both inertial and kinematic interactions.A comparison of the dynamic shear stre...A shaking table test was performed to investigate the different responses of piles with and without cement-soil reinforcement,considering both inertial and kinematic interactions.A comparison of the dynamic shear stress−strain hysteresis curves of soil profiles on the pile side with and without cement-soil reinforced piles indicates that cement-soil reinforced piles not only bear more tremendous shear stress but also have smaller strains under the action of cyclic shear stress.Furthermore,the cement-soil on the pile side not only shares part of the shear stress and modifies the bending moment distribution but also significantly enhances the resistance of the pile-side soil,reducing the lateral displacement of the superstructure.Cement-soil reinforcement reduced shear strains,inhibited sand liquefaction,and reduced superstructure displacements by 27%−47%(instantaneous)and 40%−65%(permanent).The proportion of horizontal load sharing between cement-soil reinforcement and saturated sand is considered,along with the change pattern of the subgrade reaction after sand liquefaction.An equivalent subgrade reaction calculation method is proposed,which accounts for the horizontal load-sharing ratios of soils with two different strengths.The test results indicate that the pile stress and displacement,estimated using the equivalent subgrade reaction,are in good agreement with the observed results.展开更多
To reveal the bearing capacity of the X-section pile group in coral sand, a series of model load tests are conducted.The testing results are presented as load-settlement curves, pile-soil stress ratios, distributions ...To reveal the bearing capacity of the X-section pile group in coral sand, a series of model load tests are conducted.The testing results are presented as load-settlement curves, pile-soil stress ratios, distributions of side friction and axial force, and load-sharing ratio between side and tip resistances. The reliability and accuracy of the numerical simulation model are verified by comparing the results of the model test. Comparative analysis between X-section and circular section piles with the same cross-sectional area indicates that the bearing capacity of the X-section pile group is much larger than that of the circular pile group. The axial force of X-section piles is smaller while the peak skin friction is larger than that of circular piles at the same depth. The skin friction of the core pile is the largest,followed by the side pile and the corner pile is the smallest when the load is relatively small;however, it is converse when the load is larger than 10 k N. Compared with piles in silica sand, the pile in coral sand has a lower bearing capacity, and the sand breakage leads to the steep drop failure of pile foundation. Moreover, pile positions under the raft have less effect on the load-share differences among corner, side and core piles in coral sand. This study provides a reference for the construction of pile foundations in coral sand.展开更多
To reveal the bearing capacity of the X-section concrete piles pile raft foundation in silica sand,a series of vertical load tests are carried out.The X-section concrete piles are compared with circular section pile w...To reveal the bearing capacity of the X-section concrete piles pile raft foundation in silica sand,a series of vertical load tests are carried out.The X-section concrete piles are compared with circular section pile with the same section area.The load−settlement curves,axial force and skin friction,strain on concave and convex edge of the pile,pile-sand stress ratio,distributions of side and tip resistance are presented.The results show that bearing capacity of the X section concrete pile raft foundation is much larger than that of the circular pile raft foundation.Besides,compared with the circular pile,the peak axial force of X-section piles under raft is deeper and smaller while the neutral point of X-section concrete pile is deeper.Moreover,the strain on the concave edge is much larger than that on the convex edge of the pile,and the convex edge has more potential in bearing capacity as the vertical load increases.The X-section pile has higher pile-sand stress ratios and load-sharing between side resistance and tip resistance.Above all,the X-section concrete pile can significantly increase the bearing capacity of pile-raft foundations in silica sand.展开更多
Stress waves propagate along vertical,radial and circumferential directions when a non-uniformly distributed load is applied at one end of a three-dimensional shaft.As a result,the receiving signals are usually mixed ...Stress waves propagate along vertical,radial and circumferential directions when a non-uniformly distributed load is applied at one end of a three-dimensional shaft.As a result,the receiving signals are usually mixed with undesired interference components,often featuring as high-frequency fluctuations.Previous studies have revealed that sectional geometry(shape and size)greatly affects the high-frequency interference.In this study,low strain dynamic testing on full-scale X-section concrete is conducted in order to investigate the influences of high-frequency interference on velocity responses at the pile head.Emphasis is placed on the frequency and peak value of interference waves at various receiving points.Additionally,the effects of the geometrical,and mechanical properties of the pile shaft on high-frequency interference are elaborated on through the three-dimensional finite element method.The results show that the measured wave is obscured by interference waves superposed by two types of high-frequency components.The modulus and cross-sectional area are contributing factors to the frequency and peak value of the interference waves.On the other hand,the position with the least interference is determined,to some extent,by the accurate shape of the X-section.展开更多
A series of small-scale 1g X-section cast-in-place concrete(XCC)pile-penetration model tests were conducted to study the effects of soil density and pile geometry on the lateral responses of an existing pile and the v...A series of small-scale 1g X-section cast-in-place concrete(XCC)pile-penetration model tests were conducted to study the effects of soil density and pile geometry on the lateral responses of an existing pile and the variations in surrounding soil stress.The results showed that the bending patterns of existing XCC piles varied with penetration depth.The lateral response of the existing pile was sensitive to the change in relative density and pile geometry.For example,the bending moment of the existing pile increased along with these parameters.The development of the radial stressσ′r/σ′v0 of the soil around an existing pile showed different trends at various depths during the penetration of the adjacent pile.Moreover,the change in radial stress during the penetration of the XCC pile did not exhibit the“h/R effect”that was observed in the free-field soil,due to the shielding effect of the existing piles.The peak value of radial stressσ′r_max/σ′v0 decreased exponentially as the radial distance r/R increased.The attenuation ofσ′r_max/σ′v0 with r/R in the loose sand was faster than in the medium-dense or dense sands.Theσ′r_max/σ′v0 at the same soil location increased with the cross-section geometry parameter.展开更多
Spiral pile foundations,as a promising type of foundation,are of significant importance for the development of offshore wind energy,particularly as it moves toward deeper waters.This study conducted a physical experim...Spiral pile foundations,as a promising type of foundation,are of significant importance for the development of offshore wind energy,particularly as it moves toward deeper waters.This study conducted a physical experiment on a three-spiral-pile jacket foundation under deep-buried sandy soil conditions.During the experiment,horizontal displacement was applied to the structure to thoroughly investigate the bearing characteristics of the three-spiral-pile jacket foundation.This study also focused on analyzing the bearing mechanisms of conventional piles compared with spiral piles with different numbers of blades.Three different working conditions were set up and compared,and key data,such as the horizontal bearing capacity,pile shaft axial force,and spiral blade soil pressure,were measured and analyzed.The results show the distinct impacts of the spiral blades on the compressed and tensioned sides of the foundation.Specifically,on the compressed side,the spiral blades effectively enhance the restraint of the soil on the pile foundation,whereas on the tensioned side,an excessive number of spiral blades can negatively affect the structural tensile performance to some extent.This study also emphasizes that the addition of blades to the side of a single pile is the most effective method for increasing the bearing capacity of the foundation.This research aims to provide design insights into improving the bearing capacity of the foundation.展开更多
Precast driven piles are extensively used for infrastructure on soft soils,but the buildup of excess pore water pressure associated with pile driving is a challenging issue.The process of soil consolidation could take...Precast driven piles are extensively used for infrastructure on soft soils,but the buildup of excess pore water pressure associated with pile driving is a challenging issue.The process of soil consolidation could take several months.Measures are sought to shorten the drainage path in the ground,and permeable pipe pile is a concept that involves drainage channels at the peak pore pressure locations around the pile circumference.Centrifuge tests were conducted to understand the responses of permeable pipe pile treated ground,experiencing the whole pile driving,soil consolidating,and axially loading process.Results show that the dissipation rate of pore pressures can be improved,especially at a greater depth or at a shorter distance from the pile,since the local hydraulic gradient was higher.Less significant buildup of pore pressures can be anticipated with the use of permeable pipe pile.For this,the bearing capacity of composite foundation with permeable pipe pile can be increased by over 36.9%,compared to the case with normal pipe pile at a specific time period.All these demonstrate the ability of permeable pipe pile in accelerating the consolidation process,mobilizing the bearing capacity of treated ground at an early stage,and minimizing the set-up effect.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
Understanding the factors triggering slope failure is essential to ensure the safety of buildings and transportation infrastructure on slopes. Specifically,the failure of stabilizing piles due to groundwater migration...Understanding the factors triggering slope failure is essential to ensure the safety of buildings and transportation infrastructure on slopes. Specifically,the failure of stabilizing piles due to groundwater migration and freeze–thaw(FT) cycles is a significant factor causing slope failure. This study aims to investigate the transmedia seepage characteristics at slope–concrete stabilizing pile interface systems by using silty clay and concrete with varying microstructure characteristics under FT cycles. To this end, a self-developed indoor test device for transmedia water migration, combined with a macro-meso-micro multiscale testing approach, was used to analyze the laws and mechanisms of transmedia seepage at the interface systems. The effect of the medium's microstructure characteristics on the transmedia seepage behavior at the interface systems under FT cycles was also assessed. Results indicated that the transmedia water migration exhibited particularity due to the migration of soil particles and the low permeability characteristics of concrete. The water content in the media increased significantly within the range of 1/3–2/3 of the height from the interface for soil and within 5 mm from the interface for concrete.FT cycles promoted the increase and penetration of cracks within the medium, enhancing the permeability of the slope-concrete stabilizing pile interface systems.With the increase in FT cycles, the porosity inside the medium first decreased and then increased, and the porosity reached the minimum after 25 FT cycles and the maximum after 75 FT cycles, and the water content of the medium after water migration was positively correlated with the porosity. FT cycles also significantly influenced the temporal variation characteristics of soil moisture and the migration path of water in concrete. The study results could serve as a reference for related research on slope stability assessment.展开更多
A simplified analytical approach is proposed for predicting the load-displacement behavior of single piles in unsaturated soils considering the contribution from the nonlinear shear strength and soil stiffness influen...A simplified analytical approach is proposed for predicting the load-displacement behavior of single piles in unsaturated soils considering the contribution from the nonlinear shear strength and soil stiffness influenced by matric suction.This approach includes a Modified Load Transfer Model(MLTM)that can predict the nonlinear relationships between the shear stress and pile-soil relative displacement along the pile shaft,and between the pile base resistance and base settlement.The proposed model is also extended for pile groups to incorporate the interaction effects between individual piles.The analytical approach is validated through a comparative analysis with the measurements from two single pile tests and one pile group test.In addition,a finite element analysis using 3D modeling is carried out to investigate the behavior of pile groups in various unsaturated conditions.This is accomplished with a user-defined subroutine that is written and implemented in ABAQUS to simulate the nonlinear mechanical behavior of unsaturated soils.The predictions derived from the proposed analytical and numerical methods compare well with the measurements of a published experimental study.The proposed methodologies have the potential to be applied in geotechnical engineering practice for the rational design of single piles and pile groups in unsaturated soils.展开更多
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
Reliability analysis of soil slopes under rainfall is an important task for landslide risk assessment.Previous studies rarely contribute to the probabilistic analysis of slope stability under rainfall with reinforceme...Reliability analysis of soil slopes under rainfall is an important task for landslide risk assessment.Previous studies rarely contribute to the probabilistic analysis of slope stability under rainfall with reinforcement.A new method is suggested for reliability analysis of soil slopes stabilized with piles under rainfall.First,an efficient numerical model is exploited for slope stability analysis,where two types of slope failure modes,i.e.,plastic flow and local failure are considered.To address the blocking effect of piles during seepage analysis,the equivalent hydraulic conductivity of the pile area is estimated according to the effective medium theory.The stabilizing force of piles is investigated by an analytical approach.For saving computational effort,the response surface is established based on a multi-class classification model to predict two types of slope failure modes.Finally,uncertainties in soil parameters and rainfall events are both modelled,and the failure probability of soil slopes within a given time period is assessed through Monte Carlo simulation.An illustrative example is used to demonstrate the performance of the suggested method.It is found that the slope is mainly controlled by local failure.As the pile spacing increases,the likelihood of plastic flow significantly increases.As the piles are located near the slope crest,plastic flow is effectively prevented and the slope is better stabilized against rainfall.If rainfall uncertainties are not considered,the slope failure probability is significantly overestimated.Overall,this study can provide a useful guidance for the design of pile-stabilized slopes against rainfall infiltration.展开更多
With the increasing construction of port facilities,cross-sea bridges,and offshore engineering projects,uplift piles embedded in marine sedimentary soft soil are becoming increasingly necessary.The load-displacement c...With the increasing construction of port facilities,cross-sea bridges,and offshore engineering projects,uplift piles embedded in marine sedimentary soft soil are becoming increasingly necessary.The load-displacement curve of uplift piles is crucial for evaluating their uplift bearing characteristics,which facilitates the risk evaluation,design,and construction of large infrastructural supports.In this study,a load-displacement curve model based on piezocone penetration test(CPTU)data is proposed via the load transfer method.Experimental tests are conducted to analyze the uplift bearing characteristics and establish a correlation between the proposed model and CPTU data.The results of the proposed load-displacement curve are compared with the results from numerical simulations and those calculated by previous methods.The results show that the proposed curves appropriately evaluated the uplift bearing characteristics and improved the accuracy in comparison with previous methods.展开更多
Anti-slide piles are commonly used to stabilise high and steep slopes in earthquake-prone areas in southwestern China.Herein,we investigate the impact of initial damage on the seismic performance of anti-slide piles.F...Anti-slide piles are commonly used to stabilise high and steep slopes in earthquake-prone areas in southwestern China.Herein,we investigate the impact of initial damage on the seismic performance of anti-slide piles.For this purpose,we selected a representative slope adjacent to the Jiuzhaigou Bridge in the Sichuan–Qinghai Railway;we employed a three-dimensional dynamic finite element method combined with the local stiffness reduction approach to simulate three different initial-damage scenarios:intact,slightly damaged and heavily damaged.The dynamic displacement,bending moment and shear stress responses of the piles were comprehensively analysed.Using wavelet packet energy spectrum(WPES)analysis,we introduced two indices:the damage index(DPERV)and its increment(|△DPERV|).The results showed that both the initial damage and seismic energy control the peak dynamic response of the piles.Specifically,high initial damage accelerates stiffness degradation,leading to large horizontal displacements,whereas intact piles sustain high bending moments and shear forces.The distribution of|△DPERV|along a pile reveals three post-earthquake performance stages(i.e.minor,moderate and severe),which agree well with the observed mechanical response characteristics and form the basis for targeted reinforcement strategies.The main innovation of this study is the combined use of initial-damage simulation with WPES analysis,thereby establishing a quantitative diagnostic framework(DPERV and|△DPERV|)for anti-slide piles.This framework determines the non-linear relationship between seismic response and damage evolution and provides a rapid,usable tool for health monitoring and post-earthquake decision-making in landslide-prone mountainous railway areas.展开更多
This study investigates the load-bearing capacity of open-ended pipe piles in sandy soil, with a specific focus on the impact of soil plug constraints at four levels(no plug, 25% plug, 50% plug, and full plug). Levera...This study investigates the load-bearing capacity of open-ended pipe piles in sandy soil, with a specific focus on the impact of soil plug constraints at four levels(no plug, 25% plug, 50% plug, and full plug). Leveraging a dataset comprising open-ended pipe piles with varying geometrical and geotechnical properties, this research employs shallow neural network(SNN) and deep neural network(DNN) models to predict plugging conditions for both driven and pressed installation types. This paper underscores the importance of key parameters such as the settlement value,applied load, installation type, and soil configuration(loose, medium, and dense) in accurately predicting pile settlement. These findings offer valuable insights for optimizing pile design and construction in geotechnical engineering,addressing a longstanding challenge in the field. The study demonstrates the potential of the SNN and DNN models in precisely identifying plugging conditions before pile driving, with the SNN achieving R2 values ranging from0.444 to 0.711 and RMSPE values ranging from 24.621% to 48.663%, whereas the DNN exhibits superior performance, with R2 values ranging from 0.815 to 0.942 and RMSPE values ranging from 4.419% to 10.325%. These results have significant implications for enhancing construction practices and reducing uncertainties associated with pile foundation projects in addition to leveraging artificial intelligence tools to avoid long experimental procedures.展开更多
The M-shaped multi-row pile foundation retaining structure represents an enhanced version of conventional multi-row anti-sliding support systems.To date,the implementation of M-shaped pile configurations in foundation...The M-shaped multi-row pile foundation retaining structure represents an enhanced version of conventional multi-row anti-sliding support systems.To date,the implementation of M-shaped pile configurations in foundation pit excavations has not been extensively investigated,with particularly scant research focusing on their load-bearing mechanisms and stress redistribution characteristics.Furthermore,numerical modeling methodologies for such geometrically optimized pile networks remain underdeveloped compared to practical engineering applications,creating a notable research-practice gap in geotechnical engineering.A comparative finite element analysis was systematically conducted using ABAQUS software to establish three distinct excavation support configurations:single-row cantilever retaining structures,three-row cantilever configurations,and M-shaped multi-row pile foundation systems.Subsequent numerical simulations enabled quantitative comparisons of critical performance indicators,including pile stress distribution patterns,lateral displacement profiles,and bending moment diagrams across different structural typologies.The parametric investigation revealed characteristic mechanical responses associated with each configuration,establishing corresponding mechanical principles governing the interaction between pile topology and soil-structure behavior towers.The findings of this study provide critical references for the design optimization of M-shaped multi-row pile foundation retaining systems.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
A full-scale research study was conducted during the bored tunnelling of the Klang Valley Mass Rapid Transit-Putrajaya Line beneath an existing building structure in Kuala Lumpur,Malaysia.The primary objective was to ...A full-scale research study was conducted during the bored tunnelling of the Klang Valley Mass Rapid Transit-Putrajaya Line beneath an existing building structure in Kuala Lumpur,Malaysia.The primary objective was to investigate the tunnel-soil-pile interaction at various stages of tunnel excavation.This study combined field measurements and three-dimensional(3D)numerical analysis to understand the transient effects of TBM tunnelling on a loaded pile.An experimental pile was instrumented with vibrating wire strain gauges,an inclinometer,and distributed fibre optic sensors using Brillouin optical time domain analysis.The pile was pre-loaded and continuously monitored in real-time throughout the tunnel construction process.The 3D finite element modelling was used to simulate the pile’s transient responses based on actual tunnel boring machine(TBM)driving data.The study revealed that the zone of influence due to tunnelling effects extended from y¼2D to y¼4D,with the peak effect observed at y¼1D to 1.5D,where D represents the tunnel diameter.The analysis of axial load patterns highlighted transient responses,including tensile loads below the tunnel invert,which propagated upward and subsided due to negative skin friction.The maximum downdrag load observed reached 56%e71%of the pile’s working load.Additionally,pile movement patterns indicated outward deflections as the TBM approached and a return toward the tunnel post-passage,aligning with the predicted behaviour in a negative face loss scenario.This validated numerical framework provides a solid foundation for further parametric studies and enhances the understanding of tunnel-soil-pile interactions.展开更多
文摘The main purpose of using geothermal energy piles(GEPs)is to enable the exploitation of geothermal energy for meeting the heating/cooling demands of buildings efficiently.However,the installation process of conventional GEPs is inconvenient compared with that of traditional foundation piles.The pre-bored grouted planted geothermal energy pile(PGP GEP)is an innovative technology to simplify the installation process.Most investigations of in-situ experiments for conventional GEPs have focused on summer conditions.An in-situ test for a PGP GEP was conducted to analyze the temperature changes and thermo-mechanical characteristics under winter conditions.The results show that the average temperature of the pile decreased by 5.1℃,and the pile exhibited a general trend of high temperatures at both ends and low temperatures in the middle.In mechanics,strong pile end restraints resulted in smaller observed axial strain and higher axial thermal-induced force in the pile ends than at the middle of the pile.
基金support from the National Natural Science Foundation of China(Grant No.42407256)the State Key Laboratory of Hydraulics and Mountain River Engineering,China(Grant No.SKHL2113)the Sichuan Science and Technology Program(Grant No.2024YFHZ0341).
文摘This paper develops a semi-analytical solution for pile penetration in natural soft clays using the strain path method(SPM).The stress-strain behavior of soils is characterized by the S-CLAY1S model,which can capture the anisotropic evolution and destructuring nature of soft clays.By integrating the S-CLAY1S model into the theoretical framework of the SPM,a set of ordinary differential equations is formulated with respect to the vertical coordinate of soil particles.The distribution of excess pore water pressure(EPWP)following pile installation is approximated through one-dimensional(1D)radial integration around the pile shaft.The distribution of stresses and EPWP,along with the evolution of fabric anisotropy within the soil surrounding the pile,is presented to illustrate the response of pile penetration in natural soft clays.The proposed solution is validated against existing theoretical solutions using the SPM and cavity expansion method(CEM),along with experimental data.The findings demonstrate that the SPM reveals lower radial effective stresses and EPWP at the pile shaft than that of CEM.Pile penetration alters the soil's anisotropic properties,inducing rotational hardening and affecting post-installation stress distribution.Soil destructuration eliminates bonding among particles near the pile,resulting in a complete disruption of soil structure at the pile surface,which is particularly pronounced for higher initial soil structure ratios.Minimal variation was observed in the three principal stresses and shear stress on the cone side surface as the angle increased from 18°to 60°,except for a slight reduction in EPWP.
基金Project(52078129)supported by the National Natural Science Foundation of ChinaProject(MTF2023009)supported by the Open Project of Key Laboratory of Transport Industry of Comprehensive Transportation Theory(Nanjing Modern Multimodal Transportation Laboratory),ChinaProject(2242024K40037)supported by the Fundamental Research Funds for the Central Universities,China。
文摘A shaking table test was performed to investigate the different responses of piles with and without cement-soil reinforcement,considering both inertial and kinematic interactions.A comparison of the dynamic shear stress−strain hysteresis curves of soil profiles on the pile side with and without cement-soil reinforced piles indicates that cement-soil reinforced piles not only bear more tremendous shear stress but also have smaller strains under the action of cyclic shear stress.Furthermore,the cement-soil on the pile side not only shares part of the shear stress and modifies the bending moment distribution but also significantly enhances the resistance of the pile-side soil,reducing the lateral displacement of the superstructure.Cement-soil reinforcement reduced shear strains,inhibited sand liquefaction,and reduced superstructure displacements by 27%−47%(instantaneous)and 40%−65%(permanent).The proportion of horizontal load sharing between cement-soil reinforcement and saturated sand is considered,along with the change pattern of the subgrade reaction after sand liquefaction.An equivalent subgrade reaction calculation method is proposed,which accounts for the horizontal load-sharing ratios of soils with two different strengths.The test results indicate that the pile stress and displacement,estimated using the equivalent subgrade reaction,are in good agreement with the observed results.
基金financially supported by the National Key Research and Development Program of China (Grant No. 2016YFE0200100)the National Natural Science Foundation of China (Grant Nos. 51878103 and 41831282)。
文摘To reveal the bearing capacity of the X-section pile group in coral sand, a series of model load tests are conducted.The testing results are presented as load-settlement curves, pile-soil stress ratios, distributions of side friction and axial force, and load-sharing ratio between side and tip resistances. The reliability and accuracy of the numerical simulation model are verified by comparing the results of the model test. Comparative analysis between X-section and circular section piles with the same cross-sectional area indicates that the bearing capacity of the X-section pile group is much larger than that of the circular pile group. The axial force of X-section piles is smaller while the peak skin friction is larger than that of circular piles at the same depth. The skin friction of the core pile is the largest,followed by the side pile and the corner pile is the smallest when the load is relatively small;however, it is converse when the load is larger than 10 k N. Compared with piles in silica sand, the pile in coral sand has a lower bearing capacity, and the sand breakage leads to the steep drop failure of pile foundation. Moreover, pile positions under the raft have less effect on the load-share differences among corner, side and core piles in coral sand. This study provides a reference for the construction of pile foundations in coral sand.
基金Project(51878103)supported by the National Natural Science Foundation of ChinaProject(2016YFE0200100)supported by the National Key Research and Development Program of China。
文摘To reveal the bearing capacity of the X-section concrete piles pile raft foundation in silica sand,a series of vertical load tests are carried out.The X-section concrete piles are compared with circular section pile with the same section area.The load−settlement curves,axial force and skin friction,strain on concave and convex edge of the pile,pile-sand stress ratio,distributions of side and tip resistance are presented.The results show that bearing capacity of the X section concrete pile raft foundation is much larger than that of the circular pile raft foundation.Besides,compared with the circular pile,the peak axial force of X-section piles under raft is deeper and smaller while the neutral point of X-section concrete pile is deeper.Moreover,the strain on the concave edge is much larger than that on the convex edge of the pile,and the convex edge has more potential in bearing capacity as the vertical load increases.The X-section pile has higher pile-sand stress ratios and load-sharing between side resistance and tip resistance.Above all,the X-section concrete pile can significantly increase the bearing capacity of pile-raft foundations in silica sand.
基金National Natural Science Foundation of China under Grant Nos.51622803 and 51878103China Postdoctoral Science Foundation under Grant No.2021M692689。
文摘Stress waves propagate along vertical,radial and circumferential directions when a non-uniformly distributed load is applied at one end of a three-dimensional shaft.As a result,the receiving signals are usually mixed with undesired interference components,often featuring as high-frequency fluctuations.Previous studies have revealed that sectional geometry(shape and size)greatly affects the high-frequency interference.In this study,low strain dynamic testing on full-scale X-section concrete is conducted in order to investigate the influences of high-frequency interference on velocity responses at the pile head.Emphasis is placed on the frequency and peak value of interference waves at various receiving points.Additionally,the effects of the geometrical,and mechanical properties of the pile shaft on high-frequency interference are elaborated on through the three-dimensional finite element method.The results show that the measured wave is obscured by interference waves superposed by two types of high-frequency components.The modulus and cross-sectional area are contributing factors to the frequency and peak value of the interference waves.On the other hand,the position with the least interference is determined,to some extent,by the accurate shape of the X-section.
基金supported by the National Natural Science Foundation of China(Nos.52308352,52238009,and 52108321)the Jiangxi Provincial Natural Science Foundation of China(No.20232BAB214082)+1 种基金the Open Research Fund Program of Guangdong Key Laboratory of Earthquake Engineering and Application Technology(No.2020B1212060071)the Science&Technology Project of the Education Department of Jiangxi Province(No.GJJ2200681),China.
文摘A series of small-scale 1g X-section cast-in-place concrete(XCC)pile-penetration model tests were conducted to study the effects of soil density and pile geometry on the lateral responses of an existing pile and the variations in surrounding soil stress.The results showed that the bending patterns of existing XCC piles varied with penetration depth.The lateral response of the existing pile was sensitive to the change in relative density and pile geometry.For example,the bending moment of the existing pile increased along with these parameters.The development of the radial stressσ′r/σ′v0 of the soil around an existing pile showed different trends at various depths during the penetration of the adjacent pile.Moreover,the change in radial stress during the penetration of the XCC pile did not exhibit the“h/R effect”that was observed in the free-field soil,due to the shielding effect of the existing piles.The peak value of radial stressσ′r_max/σ′v0 decreased exponentially as the radial distance r/R increased.The attenuation ofσ′r_max/σ′v0 with r/R in the loose sand was faster than in the medium-dense or dense sands.Theσ′r_max/σ′v0 at the same soil location increased with the cross-section geometry parameter.
基金The National Natural Science Foundation of China(No.52171274).
文摘Spiral pile foundations,as a promising type of foundation,are of significant importance for the development of offshore wind energy,particularly as it moves toward deeper waters.This study conducted a physical experiment on a three-spiral-pile jacket foundation under deep-buried sandy soil conditions.During the experiment,horizontal displacement was applied to the structure to thoroughly investigate the bearing characteristics of the three-spiral-pile jacket foundation.This study also focused on analyzing the bearing mechanisms of conventional piles compared with spiral piles with different numbers of blades.Three different working conditions were set up and compared,and key data,such as the horizontal bearing capacity,pile shaft axial force,and spiral blade soil pressure,were measured and analyzed.The results show the distinct impacts of the spiral blades on the compressed and tensioned sides of the foundation.Specifically,on the compressed side,the spiral blades effectively enhance the restraint of the soil on the pile foundation,whereas on the tensioned side,an excessive number of spiral blades can negatively affect the structural tensile performance to some extent.This study also emphasizes that the addition of blades to the side of a single pile is the most effective method for increasing the bearing capacity of the foundation.This research aims to provide design insights into improving the bearing capacity of the foundation.
基金supported by the National Natural Science Foundation of China(Grant Nos.52168046 and 52178321)the Natural Science Foundation of Guangxi Province,China(Grant No.2021AC18019).
文摘Precast driven piles are extensively used for infrastructure on soft soils,but the buildup of excess pore water pressure associated with pile driving is a challenging issue.The process of soil consolidation could take several months.Measures are sought to shorten the drainage path in the ground,and permeable pipe pile is a concept that involves drainage channels at the peak pore pressure locations around the pile circumference.Centrifuge tests were conducted to understand the responses of permeable pipe pile treated ground,experiencing the whole pile driving,soil consolidating,and axially loading process.Results show that the dissipation rate of pore pressures can be improved,especially at a greater depth or at a shorter distance from the pile,since the local hydraulic gradient was higher.Less significant buildup of pore pressures can be anticipated with the use of permeable pipe pile.For this,the bearing capacity of composite foundation with permeable pipe pile can be increased by over 36.9%,compared to the case with normal pipe pile at a specific time period.All these demonstrate the ability of permeable pipe pile in accelerating the consolidation process,mobilizing the bearing capacity of treated ground at an early stage,and minimizing the set-up effect.
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financially supported by Jilin Provincial Natural Science Foundation (No.20220101164JC)。
文摘Understanding the factors triggering slope failure is essential to ensure the safety of buildings and transportation infrastructure on slopes. Specifically,the failure of stabilizing piles due to groundwater migration and freeze–thaw(FT) cycles is a significant factor causing slope failure. This study aims to investigate the transmedia seepage characteristics at slope–concrete stabilizing pile interface systems by using silty clay and concrete with varying microstructure characteristics under FT cycles. To this end, a self-developed indoor test device for transmedia water migration, combined with a macro-meso-micro multiscale testing approach, was used to analyze the laws and mechanisms of transmedia seepage at the interface systems. The effect of the medium's microstructure characteristics on the transmedia seepage behavior at the interface systems under FT cycles was also assessed. Results indicated that the transmedia water migration exhibited particularity due to the migration of soil particles and the low permeability characteristics of concrete. The water content in the media increased significantly within the range of 1/3–2/3 of the height from the interface for soil and within 5 mm from the interface for concrete.FT cycles promoted the increase and penetration of cracks within the medium, enhancing the permeability of the slope-concrete stabilizing pile interface systems.With the increase in FT cycles, the porosity inside the medium first decreased and then increased, and the porosity reached the minimum after 25 FT cycles and the maximum after 75 FT cycles, and the water content of the medium after water migration was positively correlated with the porosity. FT cycles also significantly influenced the temporal variation characteristics of soil moisture and the migration path of water in concrete. The study results could serve as a reference for related research on slope stability assessment.
基金financially supported by NSERC,CanadaDiscovery Grant 2020(Grant No.5808).
文摘A simplified analytical approach is proposed for predicting the load-displacement behavior of single piles in unsaturated soils considering the contribution from the nonlinear shear strength and soil stiffness influenced by matric suction.This approach includes a Modified Load Transfer Model(MLTM)that can predict the nonlinear relationships between the shear stress and pile-soil relative displacement along the pile shaft,and between the pile base resistance and base settlement.The proposed model is also extended for pile groups to incorporate the interaction effects between individual piles.The analytical approach is validated through a comparative analysis with the measurements from two single pile tests and one pile group test.In addition,a finite element analysis using 3D modeling is carried out to investigate the behavior of pile groups in various unsaturated conditions.This is accomplished with a user-defined subroutine that is written and implemented in ABAQUS to simulate the nonlinear mechanical behavior of unsaturated soils.The predictions derived from the proposed analytical and numerical methods compare well with the measurements of a published experimental study.The proposed methodologies have the potential to be applied in geotechnical engineering practice for the rational design of single piles and pile groups in unsaturated soils.
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supported by the National Key Research and Development Program of China(Grant No.2021YFB2600504)the National Natural Science Foundation of China(Grant No.42072302)the Postdoctoral Fellowship Program of CPSF(Grant No.GZB20240533).
文摘Reliability analysis of soil slopes under rainfall is an important task for landslide risk assessment.Previous studies rarely contribute to the probabilistic analysis of slope stability under rainfall with reinforcement.A new method is suggested for reliability analysis of soil slopes stabilized with piles under rainfall.First,an efficient numerical model is exploited for slope stability analysis,where two types of slope failure modes,i.e.,plastic flow and local failure are considered.To address the blocking effect of piles during seepage analysis,the equivalent hydraulic conductivity of the pile area is estimated according to the effective medium theory.The stabilizing force of piles is investigated by an analytical approach.For saving computational effort,the response surface is established based on a multi-class classification model to predict two types of slope failure modes.Finally,uncertainties in soil parameters and rainfall events are both modelled,and the failure probability of soil slopes within a given time period is assessed through Monte Carlo simulation.An illustrative example is used to demonstrate the performance of the suggested method.It is found that the slope is mainly controlled by local failure.As the pile spacing increases,the likelihood of plastic flow significantly increases.As the piles are located near the slope crest,plastic flow is effectively prevented and the slope is better stabilized against rainfall.If rainfall uncertainties are not considered,the slope failure probability is significantly overestimated.Overall,this study can provide a useful guidance for the design of pile-stabilized slopes against rainfall infiltration.
基金supported by the China Postdoctoral Science Foundation(Grant No.2024M760734)National Science Fund for Distinguished Young Scholars(Grant No.42225206)the National Natural Science Foundation of China(Grant Nos.41877231 and 42072299).
文摘With the increasing construction of port facilities,cross-sea bridges,and offshore engineering projects,uplift piles embedded in marine sedimentary soft soil are becoming increasingly necessary.The load-displacement curve of uplift piles is crucial for evaluating their uplift bearing characteristics,which facilitates the risk evaluation,design,and construction of large infrastructural supports.In this study,a load-displacement curve model based on piezocone penetration test(CPTU)data is proposed via the load transfer method.Experimental tests are conducted to analyze the uplift bearing characteristics and establish a correlation between the proposed model and CPTU data.The results of the proposed load-displacement curve are compared with the results from numerical simulations and those calculated by previous methods.The results show that the proposed curves appropriately evaluated the uplift bearing characteristics and improved the accuracy in comparison with previous methods.
基金financially supported by the National Key R&D Program of China(No.2024YFC3012701)the National Natural Science Foundation of China(No.42307269)+1 种基金the Growth of Young Scientific and Technological Talents of Guizhou Educational Commission[Qianjiaoji,Grant No.[2024]348]the Foundation Research Project of Kaili University(No.YTH-TD20253I)。
文摘Anti-slide piles are commonly used to stabilise high and steep slopes in earthquake-prone areas in southwestern China.Herein,we investigate the impact of initial damage on the seismic performance of anti-slide piles.For this purpose,we selected a representative slope adjacent to the Jiuzhaigou Bridge in the Sichuan–Qinghai Railway;we employed a three-dimensional dynamic finite element method combined with the local stiffness reduction approach to simulate three different initial-damage scenarios:intact,slightly damaged and heavily damaged.The dynamic displacement,bending moment and shear stress responses of the piles were comprehensively analysed.Using wavelet packet energy spectrum(WPES)analysis,we introduced two indices:the damage index(DPERV)and its increment(|△DPERV|).The results showed that both the initial damage and seismic energy control the peak dynamic response of the piles.Specifically,high initial damage accelerates stiffness degradation,leading to large horizontal displacements,whereas intact piles sustain high bending moments and shear forces.The distribution of|△DPERV|along a pile reveals three post-earthquake performance stages(i.e.minor,moderate and severe),which agree well with the observed mechanical response characteristics and form the basis for targeted reinforcement strategies.The main innovation of this study is the combined use of initial-damage simulation with WPES analysis,thereby establishing a quantitative diagnostic framework(DPERV and|△DPERV|)for anti-slide piles.This framework determines the non-linear relationship between seismic response and damage evolution and provides a rapid,usable tool for health monitoring and post-earthquake decision-making in landslide-prone mountainous railway areas.
文摘This study investigates the load-bearing capacity of open-ended pipe piles in sandy soil, with a specific focus on the impact of soil plug constraints at four levels(no plug, 25% plug, 50% plug, and full plug). Leveraging a dataset comprising open-ended pipe piles with varying geometrical and geotechnical properties, this research employs shallow neural network(SNN) and deep neural network(DNN) models to predict plugging conditions for both driven and pressed installation types. This paper underscores the importance of key parameters such as the settlement value,applied load, installation type, and soil configuration(loose, medium, and dense) in accurately predicting pile settlement. These findings offer valuable insights for optimizing pile design and construction in geotechnical engineering,addressing a longstanding challenge in the field. The study demonstrates the potential of the SNN and DNN models in precisely identifying plugging conditions before pile driving, with the SNN achieving R2 values ranging from0.444 to 0.711 and RMSPE values ranging from 24.621% to 48.663%, whereas the DNN exhibits superior performance, with R2 values ranging from 0.815 to 0.942 and RMSPE values ranging from 4.419% to 10.325%. These results have significant implications for enhancing construction practices and reducing uncertainties associated with pile foundation projects in addition to leveraging artificial intelligence tools to avoid long experimental procedures.
文摘The M-shaped multi-row pile foundation retaining structure represents an enhanced version of conventional multi-row anti-sliding support systems.To date,the implementation of M-shaped pile configurations in foundation pit excavations has not been extensively investigated,with particularly scant research focusing on their load-bearing mechanisms and stress redistribution characteristics.Furthermore,numerical modeling methodologies for such geometrically optimized pile networks remain underdeveloped compared to practical engineering applications,creating a notable research-practice gap in geotechnical engineering.A comparative finite element analysis was systematically conducted using ABAQUS software to establish three distinct excavation support configurations:single-row cantilever retaining structures,three-row cantilever configurations,and M-shaped multi-row pile foundation systems.Subsequent numerical simulations enabled quantitative comparisons of critical performance indicators,including pile stress distribution patterns,lateral displacement profiles,and bending moment diagrams across different structural typologies.The parametric investigation revealed characteristic mechanical responses associated with each configuration,establishing corresponding mechanical principles governing the interaction between pile topology and soil-structure behavior towers.The findings of this study provide critical references for the design optimization of M-shaped multi-row pile foundation retaining systems.
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.
文摘A full-scale research study was conducted during the bored tunnelling of the Klang Valley Mass Rapid Transit-Putrajaya Line beneath an existing building structure in Kuala Lumpur,Malaysia.The primary objective was to investigate the tunnel-soil-pile interaction at various stages of tunnel excavation.This study combined field measurements and three-dimensional(3D)numerical analysis to understand the transient effects of TBM tunnelling on a loaded pile.An experimental pile was instrumented with vibrating wire strain gauges,an inclinometer,and distributed fibre optic sensors using Brillouin optical time domain analysis.The pile was pre-loaded and continuously monitored in real-time throughout the tunnel construction process.The 3D finite element modelling was used to simulate the pile’s transient responses based on actual tunnel boring machine(TBM)driving data.The study revealed that the zone of influence due to tunnelling effects extended from y¼2D to y¼4D,with the peak effect observed at y¼1D to 1.5D,where D represents the tunnel diameter.The analysis of axial load patterns highlighted transient responses,including tensile loads below the tunnel invert,which propagated upward and subsided due to negative skin friction.The maximum downdrag load observed reached 56%e71%of the pile’s working load.Additionally,pile movement patterns indicated outward deflections as the TBM approached and a return toward the tunnel post-passage,aligning with the predicted behaviour in a negative face loss scenario.This validated numerical framework provides a solid foundation for further parametric studies and enhances the understanding of tunnel-soil-pile interactions.
