Piled embankments,which offer many advantages,are increasingly popular in construction of high-speed railways in China.Although the performance of piled embankment under static loading is well-known,the behavior under...Piled embankments,which offer many advantages,are increasingly popular in construction of high-speed railways in China.Although the performance of piled embankment under static loading is well-known,the behavior under the dynamic train load of a high-speed railway is not yet understood.In light of this,a heavily instrumented piled embankment model was set up,and a model test was carried out,in which a servo-hydraulic actuator outputting M-shaped waves was adopted to simulate the process of a running train.Earth pressure,settlement,strain in the geogrid and pile and excess pore water pressure were measured.The results show that the soil arching height under the dynamic train load of a high-speed railway is shorter than under static loading.The growth trend for accumulated settlement slowed down after long-term vibration although there was still a tendency for it to increase.Accumulated geogrid strain has an increasing tendency after long-term vibration.The closer the embankment edge,the greater the geogrid strain over the subsoil.Strains in the pile were smaller under dynamic train loads,and their distribution was different from that under static loading.At the same elevation,excess pore water pressure under the track slab was greater than that under the embankment shoulder.展开更多
As a special geological phenomenon, the character of collapsible loess foundation is collapsible when penetrated by water. This character leads to the soil losing load bearing capacity largely and may lead to foundati...As a special geological phenomenon, the character of collapsible loess foundation is collapsible when penetrated by water. This character leads to the soil losing load bearing capacity largely and may lead to foundation failure. Pile is a popular foundation used in collapsible loess. The squeezed branch and plate pile is a new type of pile developed in recent years and has not be used in a project before. In this paper three squeezed branch and plate piles are tested in collapsible loess after immersion processing. The results may be used for reference in similar construction project, and to provide theoretical references for de- signing of the squeezed branch and plate piles in engineering practice.展开更多
Horizontal impedance functions of inclined single piles are measured experimentally for model soil-pile systems with both the effects of local soil nonlinearity and resonant characteristics.Two practical pile inclinat...Horizontal impedance functions of inclined single piles are measured experimentally for model soil-pile systems with both the effects of local soil nonlinearity and resonant characteristics.Two practical pile inclinations of 5掳 and 10掳 in addition to a vertical pile embedded in cohesionless soil and subjected to lateral harmonic pile head loadings for a wide range of frequencies are considered.Results obtained with low-to-high amplitude of lateral loadings on model soil-pile systems encased in a laminar shear box show that the local nonlinearities have a profound impact on the horizontal impedance functions of piles.Horizontal impedance functions of inclined piles are found to be smaller than the vertical pile and the values decrease as the angle of pile inclination increases.Distinct values of horizontal impedance functions are obtained for the 'positive' and 'negative' cycles of harmonic loadings,leading to asymmetric force-displacement relationships for the inclined piles.Validation of these experimental results is carried out through three-dimensional nonlinear finite element analyses,and the results from the numerical models are in good agreement with the experimental data.Sensitivity analyses conducted on the numerical models suggest that the consideration of local nonlinearity at the vicinity of the soil-pile interface influence the response of the soil-pile systems.展开更多
Piled embankments have many advantages that have been applied in high-speed railway construction engineering.However,the load transfer mechanism of piled embankments,such as soil arching and tension membranes,is still...Piled embankments have many advantages that have been applied in high-speed railway construction engineering.However,the load transfer mechanism of piled embankments,such as soil arching and tension membranes,is still unclear,especially under dynamic loads.To investigate the soil arching and tension membrane under dynamic train loads on high-speed railways,a large-scale piled embankment model test with X-shaped piles as vertical reinforcement was performed,in which twenty-eight earth pressure cells were installed in the piled embankment and an M-shaped wave was adopted to simulate the high-speed railway train load.The results show that dynamic soil arching only occurs when two bogies of a carriage pass by and disappears at other times.The dynamic soil arching and membrane effect are the most significant under the concrete base.The arching height,stress concentration ratio and pile-soil load sharing ratio have a minimal value at 25 Hz.The dynamic soil arching degrades severely at 25 Hz,whose height at 25 Hz is only 0.35 times that at 5 Hz.The arching height fluctuates over a narrow range with increasing loading amplitude.The stress concentration ratio and the pile-soil load sharing ratio increase monotonically as the loading amplitude increases.展开更多
Bi-directional static loading test adopting load cells is widely used around the world at present, with increase in diameter and length of deep foundations. In this paper, a new simple conversion method to predict the...Bi-directional static loading test adopting load cells is widely used around the world at present, with increase in diameter and length of deep foundations. In this paper, a new simple conversion method to predict the equivalent pile head load-settlement curve considering elastic shortening of deep foundation was put forward according to the load transfer mechanism. The proposed conversion method was applied to root caisson foundation in a bridge and to large diameter pipe piles in a sea wind power plant. Some new load cells, test procedure, and construction technology were adopted based on the applications to different deep foundations, which could enlarge the application scopes of bi-directional loading test. A new type of bi-directional loading test for pipe pile was conducted, in which the load cell was installed and loaded after the pipe pile with special connector has been set up. Unlike the conventional bi-directional loading test, the load cell can be reused and shows an evident economic benefit.展开更多
To gain insight into the inelastic behavior of piles, the response of a vertical pile embedded in dry sand and subjected to cyclic lateral loading was studied experimentally in centrifuge tests conducted in Laboratoir...To gain insight into the inelastic behavior of piles, the response of a vertical pile embedded in dry sand and subjected to cyclic lateral loading was studied experimentally in centrifuge tests conducted in Laboratoire Central des Ponts et Chaussees. Three types of cyclic loading were applied, two asymmetric and one symmetric with respect to the unloaded pile. An approximately square-root variation of soil stiffness with depth was obtained from indirect in-flight density measurements, laboratory tests on reconstituted samples, and well-established empirical correlations. The tests were simulated using a cyclic nonlinear Winkler spring model, which describes the full range of inelastic phenomena, including separation and re-attachment of the pile from and to the soil. The model consists of three mathematical expressions capable of reproducing a wide variety of monotonic and cyclic experimentalp-y curves. The physical meaning of key model parameters is graphically explained and related to soil behavior. Comparisons with the centrifuge test results demonstrate the general validity of the model and its ability to capture several features of pile-soil interaction, including: soil plastification at an early stage of loading, "pinching" behavior due to the formation of a relaxation zone around the upper part of the pile, and stiffness and strength changes due to cyclic loading. A comparison of the p-y curves derived from the test results and the proposed model, as well as those from the classical curves of Reese et al. (1974) for sand, is also presented.展开更多
In order to study the infl uence of pile spacing on the seismic response of piled raft in soft clay, a series of shaking table tests were conducted by using a geotechnical centrifuge. The dynamic behavior of accelerat...In order to study the infl uence of pile spacing on the seismic response of piled raft in soft clay, a series of shaking table tests were conducted by using a geotechnical centrifuge. The dynamic behavior of acceleration, displacement and internal forces was examined. The test results indicate that the seismic acceleration responses of models are generally greater than the surrounding soil surface in the period ranges of 2–10 seconds. Foundation instant settlements for 4×4 and 3×3 piled raft (with pile spacing equal to 4 and 6 times pile diameter) are somewhat close to each other at the end of the earthquake, but reconsolidation settlements are greater for 3×3 piled raft. The seismic acceleration of superstructure, the uneven settlement of the foundation and the maximum bending moment of pile are relatively lower for 3×3 piled raft. Successive earthquakes lead to the softening behavior of soft clay, which causes a reduction of the pile bearing capacity and thus loads are transferred from the pile group to the raft. For the case of a 3×3 piled raft, there is relatively smaller change of the load sharing ratio of the pile group and raft after the earthquake and the distribution of maximum bending moments at the pile head is more uniform.展开更多
The pile group with elevated cap is widely used as foundation of offshore structures such as turbines, power transmission towers and bridge piers, and understanding its behavior under cyclic lateral loads induced by w...The pile group with elevated cap is widely used as foundation of offshore structures such as turbines, power transmission towers and bridge piers, and understanding its behavior under cyclic lateral loads induced by waves, tide water and winds, is of great importance to designing. A large-scale model test on 3×3 pile group with elevated cap subjected to cyclic lateral loads was performed in saturated silts. The preparation and implementation of the test is presented. Steel pipes with the outer diameter of 114 mm, thickness of 4.5 mm, and length of 6 m were employed as model piles. The pile group was cyclic loaded in a multi-stage sequence with the lateral displacement controlled. In addition, a single pile test was also conducted at the same site for comparison. The displacement of the pile cap, the internal forces of individual piles, and the horizontal stiffness of the pile group are presented and discussed in detail. The results indicate that the lateral cyclic loads have a greater impact on pile group than that on a single pile, and give rise to the significant plastic strain in the soil around piles. The lateral loads carried by each row of piles within the group would be redistributed with loading cycles. The lateral stiffness of the pile group decreases gradually with cycles and broadly presents three different degradation patterns in the test. Significant axial forces were measured out in some piles within the group, owing to the strong restraint provided by the cap, and finally lead to a large settlement of the pile group. These findings can be referred for foundation designing of offshore structures.展开更多
In the near future, several offshore wind farms are planned to be built in the North Sea. Therefore, jacket and tripod constructions with mainly axially loaded piles are suitable as support structures. The current des...In the near future, several offshore wind farms are planned to be built in the North Sea. Therefore, jacket and tripod constructions with mainly axially loaded piles are suitable as support structures. The current design of axial bearing resistance of these piles leads to deviant results regarding the pile resistance when different design methods are adopted. Hence, a strong deviation regarding the required pile length must be addressed. The reliability of a design method can be evaluated based on a model error which describes the quality of the considered design method by comparing measured and predicted pile bearing resistances. However, only few pile load tests are reported with regard to the boundary conditions in the North Sea. This paper presents 6 large-scale axial pile load tests which were incorporated within a new model error approach for the current design methods used for the axial bearing resistance,namely API Main Text method and cone penetration test(CPT)-based design methods, such as simplified ICP-05, offshore UWA-05, Fugro-05 and NGI-05 methods. Based on these new model errors, a reliabilitybased study towards the safety was conducted by performing a Monte-Carlo simulation. In addition,consequences regarding the deterministic pile design in terms of quality factors were evaluated. It is shown that the current global safety factor(GSF) prescribed and the partial safety factors are only valid for the API Main Text and the offshore UWA-05 design methods; whereas for the simplified ICP-05,Fugro-05 and NGI-05 design methods, an increase in the required embedded pile length and thus in the GSF up to 2.69, 2.95 and 3.27, respectively, should be considered to satisfy the desired safety level according to DIN EN 1990 of b ? 3.8. Further, quality factors for each design method on the basis of all reliability-based design results were derived. Hence, evaluation of each design method regarding the reliability of the pile capacity prediction is possible.展开更多
In order to find out the bearing behavior of super-long piles located in deep soft clay over stiff layers around Dongting Lake, China, a test pile was first designed with the field loading test finished afterward. Bas...In order to find out the bearing behavior of super-long piles located in deep soft clay over stiff layers around Dongting Lake, China, a test pile was first designed with the field loading test finished afterward. Based on the measured test results, load transfer mechanism and bearing behavior of the pile shaft were discussed in detail. Then, by introducing a bi-linear model for shaft friction and the tri-linear model for pile tip resistance, respectively, the governing differential equation of pile soil system was set up by the load transfer method with the analytical solutions derived as well, taking into account the effect by stratified feature and various bearing conditions of subsoil, material nonlinearity, and the sediment under pile tip. Furthermore, formulas to determine the axial capacity of super-long piles by the pile top settlement were advised and applied to analyze the test pile. Good agreement between the predicted load settlement variations and the measured data is obtained to verify the validity of the present method. The results also show that, the axial bearing capacity of super-long piles should be controlled by the allowable pile top settlement, and buckling stability of the pile shaft should be paid attention as well.展开更多
The existing studies have primarily focused on the effect of cyclic load characteristics(namely,cyclic load ratio and amplitude ratio)on cyclic lateral response of monopiles in sand,with little attention paid to the e...The existing studies have primarily focused on the effect of cyclic load characteristics(namely,cyclic load ratio and amplitude ratio)on cyclic lateral response of monopiles in sand,with little attention paid to the effect of pile−soil relative stiffness(K_(R)).This paper presents a series of 1-g cyclic tests aimed at improving understanding of the cyclic lateral responses of monopiles under different pile−soil systems.These systems are arranged by two model piles with different stiffness,including four different slenderness ratios(pile embedded length,L,normalized by diameter,D)under medium dense sand.The K_(R)-values are calculated by a previously proposed method considering the real soil stress level.The test results show that the lateral accumulation displacement increases significantly with the increment of the K_(R)-value,while the cyclic secant stiffness performs inversely.The maximum pile bending moment increases with the cycle number for the rigid pile−soil system,but shows a decreasing trend in the flexible system.For an uppermost concern,an empirical model is proposed to predict the accumulated displacement of arbitrary pile−soil systems by combining the results from this study with those from previous experimental investigations.The validity of the proposed model is demonstrated by 1-g and centrifuge tests.展开更多
Based on Mindlin stress solution, a numerical computational method was proposed to calculate the stresses in the ground induced by side friction and the resistance of Y-shaped vibro-pile. The improved Terzaghi's a...Based on Mindlin stress solution, a numerical computational method was proposed to calculate the stresses in the ground induced by side friction and the resistance of Y-shaped vibro-pile. The improved Terzaghi's and ЪерезанцевВГ's methods for ultimate bearing capacity evaluation were proposed by considering the stress strength induced by friction resistance at pile head level of Y-pile. A new method to calculate the ultimate bearing capacity of Y-pile was also proposed based on the assumptions of soil failure mode at the tip of Y-pile and the use of Mohr-Coulomb soil yield criterion and Vesic compressive correction coefficient with the induced stresses in the ground. Based on the comparisons with the field static load test results, it is found that the improved Terzaghi's method gives higher ultimate capacity, while the other two methods shows good agreement with the field results.展开更多
Experiments about working mechanism and mechanical characteristics of the DX model pile foundation under lateral dynamic and static loading were conducted by using a model system of the dynamic frozen soil-pile intera...Experiments about working mechanism and mechanical characteristics of the DX model pile foundation under lateral dynamic and static loading were conducted by using a model system of the dynamic frozen soil-pile interaction. The horizontal displacement-force relationship of the pile head and bending moment distribution along the body in frozen soils of different temperatures were discussed. According to test results, both the horizontal disp!acement-force relationship of the DX pile head and bending moment distribution of the DX pile body are smaller than that of equal-diameter piles under same lateral loads. The piles with different plate positions show different displacements and bending moments. This phenomenon is mainly related to the soil temperature and bearing plates locations. Thus, dynamic response analysis of the pile foundation should be taken into account.展开更多
A set of serf-developed apparatus for foundation physical model were utilized to conduct model tests of the multi-element composite foundation with a steel pipe pile and several gravel piles. Some load-bearing charact...A set of serf-developed apparatus for foundation physical model were utilized to conduct model tests of the multi-element composite foundation with a steel pipe pile and several gravel piles. Some load-bearing characteristics of the multi-element Composite foundation, including the curves of foundation settlement, stresses of piles, pile-soil stress ratio, and load-sharing ratio of piles and soil, were obtained to study its working performances in silty sand soil. The experimental results revealed that the multi-element composite foundation with steel pipe pile and gravel pile contributed more than the gravel pile composite foundation in improving the bearing capacity of the silty fine sand.展开更多
The horizontal bearing behavior of a single batter pile(SBP)is vital to its application in practical engineering;however,the horizontal responses of SBPs change with the directions of horizontal loads,and this phenome...The horizontal bearing behavior of a single batter pile(SBP)is vital to its application in practical engineering;however,the horizontal responses of SBPs change with the directions of horizontal loads,and this phenomenon is rarely investigated.Therefore,the directional differences in the horizontal bearing behaviors of SBPs are investigated in this study.Four model tests are conducted to preliminarily examine the effects of the skew angle of horizontal loads on the horizontal bearing capacities and distributions of the bending moments of the SBPs.Subsequently,the differences in the responses of the SBPs under horizontal loads in various directions at full scale are analyzed comprehensively via finite-element(FE)analysis.The effects of the skew angle on SBP-soil interaction are discussed.Moreover,an empirical design method is proposed based on the FE analysis results to predict the bearing ratios of SBPs in medium-dense and dense sand while considering the effects of the skew angle,batter angle,and pile diameter.The method is confirmed to be effective,as confirmed by the close agreement between the predicting results with the model test(reported in this study)and centrifuge model test results(reported in the literature).展开更多
基金National Natural Science Foundation of China under Grant Nos.51622803,51378177 and 51420105013the 111 Project under Grant No.B13024
文摘Piled embankments,which offer many advantages,are increasingly popular in construction of high-speed railways in China.Although the performance of piled embankment under static loading is well-known,the behavior under the dynamic train load of a high-speed railway is not yet understood.In light of this,a heavily instrumented piled embankment model was set up,and a model test was carried out,in which a servo-hydraulic actuator outputting M-shaped waves was adopted to simulate the process of a running train.Earth pressure,settlement,strain in the geogrid and pile and excess pore water pressure were measured.The results show that the soil arching height under the dynamic train load of a high-speed railway is shorter than under static loading.The growth trend for accumulated settlement slowed down after long-term vibration although there was still a tendency for it to increase.Accumulated geogrid strain has an increasing tendency after long-term vibration.The closer the embankment edge,the greater the geogrid strain over the subsoil.Strains in the pile were smaller under dynamic train loads,and their distribution was different from that under static loading.At the same elevation,excess pore water pressure under the track slab was greater than that under the embankment shoulder.
文摘As a special geological phenomenon, the character of collapsible loess foundation is collapsible when penetrated by water. This character leads to the soil losing load bearing capacity largely and may lead to foundation failure. Pile is a popular foundation used in collapsible loess. The squeezed branch and plate pile is a new type of pile developed in recent years and has not be used in a project before. In this paper three squeezed branch and plate piles are tested in collapsible loess after immersion processing. The results may be used for reference in similar construction project, and to provide theoretical references for de- signing of the squeezed branch and plate piles in engineering practice.
文摘Horizontal impedance functions of inclined single piles are measured experimentally for model soil-pile systems with both the effects of local soil nonlinearity and resonant characteristics.Two practical pile inclinations of 5掳 and 10掳 in addition to a vertical pile embedded in cohesionless soil and subjected to lateral harmonic pile head loadings for a wide range of frequencies are considered.Results obtained with low-to-high amplitude of lateral loadings on model soil-pile systems encased in a laminar shear box show that the local nonlinearities have a profound impact on the horizontal impedance functions of piles.Horizontal impedance functions of inclined piles are found to be smaller than the vertical pile and the values decrease as the angle of pile inclination increases.Distinct values of horizontal impedance functions are obtained for the 'positive' and 'negative' cycles of harmonic loadings,leading to asymmetric force-displacement relationships for the inclined piles.Validation of these experimental results is carried out through three-dimensional nonlinear finite element analyses,and the results from the numerical models are in good agreement with the experimental data.Sensitivity analyses conducted on the numerical models suggest that the consideration of local nonlinearity at the vicinity of the soil-pile interface influence the response of the soil-pile systems.
基金Natural Science Research Project of Anhui Educational Committee under Grant No.2022AH050844Anhui Provincial Natural Science Foundation of China under Grant No.2008085ME143+1 种基金the Doctoral Foundation of Anhui University of Science and Technology under Grant No.13190018Innovation and Entrepreneurship Training Program for College Students under Grant No.S202110361059。
文摘Piled embankments have many advantages that have been applied in high-speed railway construction engineering.However,the load transfer mechanism of piled embankments,such as soil arching and tension membranes,is still unclear,especially under dynamic loads.To investigate the soil arching and tension membrane under dynamic train loads on high-speed railways,a large-scale piled embankment model test with X-shaped piles as vertical reinforcement was performed,in which twenty-eight earth pressure cells were installed in the piled embankment and an M-shaped wave was adopted to simulate the high-speed railway train load.The results show that dynamic soil arching only occurs when two bogies of a carriage pass by and disappears at other times.The dynamic soil arching and membrane effect are the most significant under the concrete base.The arching height,stress concentration ratio and pile-soil load sharing ratio have a minimal value at 25 Hz.The dynamic soil arching degrades severely at 25 Hz,whose height at 25 Hz is only 0.35 times that at 5 Hz.The arching height fluctuates over a narrow range with increasing loading amplitude.The stress concentration ratio and the pile-soil load sharing ratio increase monotonically as the loading amplitude increases.
基金Supported by the National Natural Science Foundation of China (50908048)the Priority Academic Program Development (PAPD) Project of JiangsuHigher Education Institutions
文摘Bi-directional static loading test adopting load cells is widely used around the world at present, with increase in diameter and length of deep foundations. In this paper, a new simple conversion method to predict the equivalent pile head load-settlement curve considering elastic shortening of deep foundation was put forward according to the load transfer mechanism. The proposed conversion method was applied to root caisson foundation in a bridge and to large diameter pipe piles in a sea wind power plant. Some new load cells, test procedure, and construction technology were adopted based on the applications to different deep foundations, which could enlarge the application scopes of bi-directional loading test. A new type of bi-directional loading test for pipe pile was conducted, in which the load cell was installed and loaded after the pipe pile with special connector has been set up. Unlike the conventional bi-directional loading test, the load cell can be reused and shows an evident economic benefit.
基金EU Fifth Framework Program: Environment, Energy and Sustainable Development Research and Technological Development Activity of Generic Nature: The Fight Against Natural and Technological Hazards, Research Project QUAKER Under Contract No. EVG1–CT–2002–00064
文摘To gain insight into the inelastic behavior of piles, the response of a vertical pile embedded in dry sand and subjected to cyclic lateral loading was studied experimentally in centrifuge tests conducted in Laboratoire Central des Ponts et Chaussees. Three types of cyclic loading were applied, two asymmetric and one symmetric with respect to the unloaded pile. An approximately square-root variation of soil stiffness with depth was obtained from indirect in-flight density measurements, laboratory tests on reconstituted samples, and well-established empirical correlations. The tests were simulated using a cyclic nonlinear Winkler spring model, which describes the full range of inelastic phenomena, including separation and re-attachment of the pile from and to the soil. The model consists of three mathematical expressions capable of reproducing a wide variety of monotonic and cyclic experimentalp-y curves. The physical meaning of key model parameters is graphically explained and related to soil behavior. Comparisons with the centrifuge test results demonstrate the general validity of the model and its ability to capture several features of pile-soil interaction, including: soil plastification at an early stage of loading, "pinching" behavior due to the formation of a relaxation zone around the upper part of the pile, and stiffness and strength changes due to cyclic loading. A comparison of the p-y curves derived from the test results and the proposed model, as well as those from the classical curves of Reese et al. (1974) for sand, is also presented.
基金National Natural Science Foundation of China under Grand No.41372274
文摘In order to study the infl uence of pile spacing on the seismic response of piled raft in soft clay, a series of shaking table tests were conducted by using a geotechnical centrifuge. The dynamic behavior of acceleration, displacement and internal forces was examined. The test results indicate that the seismic acceleration responses of models are generally greater than the surrounding soil surface in the period ranges of 2–10 seconds. Foundation instant settlements for 4×4 and 3×3 piled raft (with pile spacing equal to 4 and 6 times pile diameter) are somewhat close to each other at the end of the earthquake, but reconsolidation settlements are greater for 3×3 piled raft. The seismic acceleration of superstructure, the uneven settlement of the foundation and the maximum bending moment of pile are relatively lower for 3×3 piled raft. Successive earthquakes lead to the softening behavior of soft clay, which causes a reduction of the pile bearing capacity and thus loads are transferred from the pile group to the raft. For the case of a 3×3 piled raft, there is relatively smaller change of the load sharing ratio of the pile group and raft after the earthquake and the distribution of maximum bending moments at the pile head is more uniform.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51225804 and U1234204)the Zhejiang Electric Power Design Institute
文摘The pile group with elevated cap is widely used as foundation of offshore structures such as turbines, power transmission towers and bridge piers, and understanding its behavior under cyclic lateral loads induced by waves, tide water and winds, is of great importance to designing. A large-scale model test on 3×3 pile group with elevated cap subjected to cyclic lateral loads was performed in saturated silts. The preparation and implementation of the test is presented. Steel pipes with the outer diameter of 114 mm, thickness of 4.5 mm, and length of 6 m were employed as model piles. The pile group was cyclic loaded in a multi-stage sequence with the lateral displacement controlled. In addition, a single pile test was also conducted at the same site for comparison. The displacement of the pile cap, the internal forces of individual piles, and the horizontal stiffness of the pile group are presented and discussed in detail. The results indicate that the lateral cyclic loads have a greater impact on pile group than that on a single pile, and give rise to the significant plastic strain in the soil around piles. The lateral loads carried by each row of piles within the group would be redistributed with loading cycles. The lateral stiffness of the pile group decreases gradually with cycles and broadly presents three different degradation patterns in the test. Significant axial forces were measured out in some piles within the group, owing to the strong restraint provided by the cap, and finally lead to a large settlement of the pile group. These findings can be referred for foundation designing of offshore structures.
基金the European Union funded project Integrated Research Project Wind (IRPWind, European Union Seventh Framework Program under Grant No. 609795)
文摘In the near future, several offshore wind farms are planned to be built in the North Sea. Therefore, jacket and tripod constructions with mainly axially loaded piles are suitable as support structures. The current design of axial bearing resistance of these piles leads to deviant results regarding the pile resistance when different design methods are adopted. Hence, a strong deviation regarding the required pile length must be addressed. The reliability of a design method can be evaluated based on a model error which describes the quality of the considered design method by comparing measured and predicted pile bearing resistances. However, only few pile load tests are reported with regard to the boundary conditions in the North Sea. This paper presents 6 large-scale axial pile load tests which were incorporated within a new model error approach for the current design methods used for the axial bearing resistance,namely API Main Text method and cone penetration test(CPT)-based design methods, such as simplified ICP-05, offshore UWA-05, Fugro-05 and NGI-05 methods. Based on these new model errors, a reliabilitybased study towards the safety was conducted by performing a Monte-Carlo simulation. In addition,consequences regarding the deterministic pile design in terms of quality factors were evaluated. It is shown that the current global safety factor(GSF) prescribed and the partial safety factors are only valid for the API Main Text and the offshore UWA-05 design methods; whereas for the simplified ICP-05,Fugro-05 and NGI-05 design methods, an increase in the required embedded pile length and thus in the GSF up to 2.69, 2.95 and 3.27, respectively, should be considered to satisfy the desired safety level according to DIN EN 1990 of b ? 3.8. Further, quality factors for each design method on the basis of all reliability-based design results were derived. Hence, evaluation of each design method regarding the reliability of the pile capacity prediction is possible.
基金Project(50908084)supported by the National Natural Science Foundation of ChinaProject(200815)supported by the Transportation Science and Technology Program of Hunan Province,ChinaProject(531107040620)supported by the Growth Plan for Young Teachers of Hunan University,China
文摘In order to find out the bearing behavior of super-long piles located in deep soft clay over stiff layers around Dongting Lake, China, a test pile was first designed with the field loading test finished afterward. Based on the measured test results, load transfer mechanism and bearing behavior of the pile shaft were discussed in detail. Then, by introducing a bi-linear model for shaft friction and the tri-linear model for pile tip resistance, respectively, the governing differential equation of pile soil system was set up by the load transfer method with the analytical solutions derived as well, taking into account the effect by stratified feature and various bearing conditions of subsoil, material nonlinearity, and the sediment under pile tip. Furthermore, formulas to determine the axial capacity of super-long piles by the pile top settlement were advised and applied to analyze the test pile. Good agreement between the predicted load settlement variations and the measured data is obtained to verify the validity of the present method. The results also show that, the axial bearing capacity of super-long piles should be controlled by the allowable pile top settlement, and buckling stability of the pile shaft should be paid attention as well.
基金This work was financially supported by the National Natural Science Foundation of China(Grant Nos.51808112,51878160,and 52078128)the Natural Science Foundation of Jiangsu Province(Grant No.BK20180155).
文摘The existing studies have primarily focused on the effect of cyclic load characteristics(namely,cyclic load ratio and amplitude ratio)on cyclic lateral response of monopiles in sand,with little attention paid to the effect of pile−soil relative stiffness(K_(R)).This paper presents a series of 1-g cyclic tests aimed at improving understanding of the cyclic lateral responses of monopiles under different pile−soil systems.These systems are arranged by two model piles with different stiffness,including four different slenderness ratios(pile embedded length,L,normalized by diameter,D)under medium dense sand.The K_(R)-values are calculated by a previously proposed method considering the real soil stress level.The test results show that the lateral accumulation displacement increases significantly with the increment of the K_(R)-value,while the cyclic secant stiffness performs inversely.The maximum pile bending moment increases with the cycle number for the rigid pile−soil system,but shows a decreasing trend in the flexible system.For an uppermost concern,an empirical model is proposed to predict the accumulated displacement of arbitrary pile−soil systems by combining the results from this study with those from previous experimental investigations.The validity of the proposed model is demonstrated by 1-g and centrifuge tests.
文摘Based on Mindlin stress solution, a numerical computational method was proposed to calculate the stresses in the ground induced by side friction and the resistance of Y-shaped vibro-pile. The improved Terzaghi's and ЪерезанцевВГ's methods for ultimate bearing capacity evaluation were proposed by considering the stress strength induced by friction resistance at pile head level of Y-pile. A new method to calculate the ultimate bearing capacity of Y-pile was also proposed based on the assumptions of soil failure mode at the tip of Y-pile and the use of Mohr-Coulomb soil yield criterion and Vesic compressive correction coefficient with the induced stresses in the ground. Based on the comparisons with the field static load test results, it is found that the improved Terzaghi's method gives higher ultimate capacity, while the other two methods shows good agreement with the field results.
基金supported by the Fundamental Research Funds for the Central Universities of China (Grant No.2011JBM269)the State Key Development Programof Basic Research of China (973 Project No.2012CB026104)the College Students Technology Innovation Experiment project in Beijing Jiaotong University
文摘Experiments about working mechanism and mechanical characteristics of the DX model pile foundation under lateral dynamic and static loading were conducted by using a model system of the dynamic frozen soil-pile interaction. The horizontal displacement-force relationship of the pile head and bending moment distribution along the body in frozen soils of different temperatures were discussed. According to test results, both the horizontal disp!acement-force relationship of the DX pile head and bending moment distribution of the DX pile body are smaller than that of equal-diameter piles under same lateral loads. The piles with different plate positions show different displacements and bending moments. This phenomenon is mainly related to the soil temperature and bearing plates locations. Thus, dynamic response analysis of the pile foundation should be taken into account.
基金The National Natural Science Foundation of China (No.50478090)
文摘A set of serf-developed apparatus for foundation physical model were utilized to conduct model tests of the multi-element composite foundation with a steel pipe pile and several gravel piles. Some load-bearing characteristics of the multi-element Composite foundation, including the curves of foundation settlement, stresses of piles, pile-soil stress ratio, and load-sharing ratio of piles and soil, were obtained to study its working performances in silty sand soil. The experimental results revealed that the multi-element composite foundation with steel pipe pile and gravel pile contributed more than the gravel pile composite foundation in improving the bearing capacity of the silty fine sand.
基金supported by the National Natural Science Foundation of China(Grant Nos.52178358,52108349,and 51779217)the Key Project of the Natural Science Foundation of Zhejiang Province(No.LXZ22E080001).
文摘The horizontal bearing behavior of a single batter pile(SBP)is vital to its application in practical engineering;however,the horizontal responses of SBPs change with the directions of horizontal loads,and this phenomenon is rarely investigated.Therefore,the directional differences in the horizontal bearing behaviors of SBPs are investigated in this study.Four model tests are conducted to preliminarily examine the effects of the skew angle of horizontal loads on the horizontal bearing capacities and distributions of the bending moments of the SBPs.Subsequently,the differences in the responses of the SBPs under horizontal loads in various directions at full scale are analyzed comprehensively via finite-element(FE)analysis.The effects of the skew angle on SBP-soil interaction are discussed.Moreover,an empirical design method is proposed based on the FE analysis results to predict the bearing ratios of SBPs in medium-dense and dense sand while considering the effects of the skew angle,batter angle,and pile diameter.The method is confirmed to be effective,as confirmed by the close agreement between the predicting results with the model test(reported in this study)and centrifuge model test results(reported in the literature).