An analytical method to study the seismic response of a bridge pier supported on a rigid caisson foundation embedded in a deep soil stratum underlain by a homogeneous half space is developed. The method reproduces the...An analytical method to study the seismic response of a bridge pier supported on a rigid caisson foundation embedded in a deep soil stratum underlain by a homogeneous half space is developed. The method reproduces the kinematic and inertial responses, using translational and rotational distributed Winkler springs and dashpots to simulate the soil-caisson interaction. Closed-form solutions are given in the frequency domain for vertical harmonic S-wave excitation. Comparison with results from finite element （FE） analysis and other available solutions demonstrates the reliability of the model. Results from parametric studies are given for the kinematic and inertial responses. The modification of the fundamental period and damping ratio of the bridge due to soil-structure interaction is graphically illustrated.展开更多
Suction caisson foundations are often subjected to vertical uplift loads,but there are still no wide and spread engineering specifications on design and calculation method for uplift bearing capacity of suction caisso...Suction caisson foundations are often subjected to vertical uplift loads,but there are still no wide and spread engineering specifications on design and calculation method for uplift bearing capacity of suction caisson foundation.So it is important to establish an uplift failure criterion.In order to study the uplift bearing mechanism and failure mode of suction caisson foundation,a series of model tests were carried out considering the effects of aspect ratio,soil permeability and loading mode.Test results indicate that the residual negative pressure at the top of caisson is beneficial to enhance uplift bearing capacity.The smaller the permeability coefficient is,the higher the residual negative pressure will be.And the residual negative pressure is approximately equal to the water head that causes seepage in the caisson.When the load reaches the ultimate bearing capacity,both the top and bottom negative pressures are smaller than Su and both the top and bottom reverse bearing capacity factors are smaller than 1.0 in soft clay.Combined the uplift bearing characteristics of caisson in sandy soil and soft clay,the bearing capacity composition and the calculation method are proposed.It can provide a reference for the engineering design of suction caisson foundation under vertical load.展开更多
Bridge foundations located in deep water are usually subjected to horizontal dynamic loads and moments which may be caused by the wind, waves, earthquake, and the possibility of boat crashing or vehicle braking. Caiss...Bridge foundations located in deep water are usually subjected to horizontal dynamic loads and moments which may be caused by the wind, waves, earthquake, and the possibility of boat crashing or vehicle braking. Caisson foundations based on gravel or sand cushions are a new type of deep-water foundation for bridges, suitable for meizoseismal areas. In this paper, harmonic horizontal excitation tests for the study of the lateral dynamic response of caisson foundations based on cushion layers are described. Different lateral loads and two different cushion types are considered. The results show that the lateral dynamic responses of caisson foundations based on sand and gravel cushions both show strong nonlinear characteristics, and the resonant frequency of the foundation decreases with the increase of the excitation force. The dynamic displacement of a foundation based on a sand cushion is far less than that based on a gravel cushion, and the rate of decrease of the resonant frequency of a foundation based on a gravel cushion is faster than that of a foundation based on a sand cushion under the same conditions. Under dynamic loading the gravel cushion can more effectively dissipate vibration energy and isolate the vibration, than the sand cushion can. A simplified nonlinear analysis method is proposed to simulate the lateral dynamic response of caisson foundations, and the predicted response shows a reasonable match with the results observed in laboratory tests. Scaling laws have also been applied in this small-scale vibration model test to predict the dynamic behavior of the prototype foundation.展开更多
This paper presents an analytical formula for estimating the longitudinal wave forces on a large roundended caisson foundation. The establishment of the formula is based on the superposition of the theoretical formula...This paper presents an analytical formula for estimating the longitudinal wave forces on a large roundended caisson foundation. The establishment of the formula is based on the superposition of the theoretical formula of wave forces on a large circular cylinder and the empirical formula of wave forces on a large rectangular cylinder. With the formula transformed into an inertial force form, a specific inertia coefficient with an exact expression is extracted from the formula. The numerical calculations of the wave forces on round-ended cylinders are carried out by the boundary-element method. The undetermined coefficients in the expression of the inertial coefficient are determined by the numerical results. It is obvious that the numerical values can be well expressed by the computation values from the established formula. By a model experiment carried out in laboratory wave flume, the correctness of the analytical formula is further verified by the measured wave forces on a test model of a round-ended bridge caisson foundation. The comparison shows that the experimental forces can be approximately estimated by this simple calculation method.展开更多
Suction caisson foundation derives most of their uplift resistance from passive suction developed during the pullout movement. It was observed that the passive suction generated in soil at the bottom of the caisson an...Suction caisson foundation derives most of their uplift resistance from passive suction developed during the pullout movement. It was observed that the passive suction generated in soil at the bottom of the caisson and the failure mode of suction caisson foundation subjecting pullout loading behaves as a reverse compression failure mechanism.The upper bound theorems have been proved to be a powerful method to find the critical failure mechanism and critical load associated with foundations, buried caissons and other geotechnical structures. However, limited attempts have been reported to estimate the uplift bearing capacity of the suction caisson foundation using the upper bound solution. In this paper, both reverse failure mechanisms from Prandtl and Hill were adopted as the failure mechanisms for the computation of the uplift bearing capacity of the suction caisson. New equations were proposed based on both failure mechanisms to estimate the pullout capacity of the suction caisson. The proposed equations were verified by the test results and experimental data from published literature. And the two solutions agree reasonably well with the other test results. It can be proved that both failure mechanisms are reasonably and more consistent with the actual force condition.展开更多
To investigate the bearing capacity of a caisson foundation under combined vertical,horizontal and moment loadings,the three-dimensional finite element analyses of a circular caisson foundation in homogenous sandy soi...To investigate the bearing capacity of a caisson foundation under combined vertical,horizontal and moment loadings,the three-dimensional finite element analyses of a circular caisson foundation in homogenous sandy soil subjected to combined loadings are conducted.The caisson model has a depth to breadth ratio equaling one,and a soil-caisson interface friction coefficientμ=0.3.First,the responses of caisson foundations under uniaxial vertical loading V,horizontal loading H and moment loading M are examined.Moreover,the responses of caisson foundations under combined vertical-horizontal V-H,vertical-moment V-M and horizontal-moment H-M load space are studied and presented using normalized failure envelopes generated by the load-controlled method.Subsequently,the bearing behavior of caisson foundations under combined vertical-horizontal-moment V-H-M load space,as well as the kinematic mechanisms accompanying the failure under uniaxial and combined loading,are addressed and presented for different vertical load ratios V/Vu.Finally,three equations that approximate the three-dimensional shape of the failure locus are proposed,which provides a convenient means of calculating the bearing capacity of a caisson foundation subjected to uniaxial and combined vertical,horizontal and moment loadings.展开更多
Because of the computation difficulty of the beating capacity of large underwater caisson foundation on thick overburden layer ground, the geotechnieal software FLAC3D was utilized in the 3D numerical analysis on the ...Because of the computation difficulty of the beating capacity of large underwater caisson foundation on thick overburden layer ground, the geotechnieal software FLAC3D was utilized in the 3D numerical analysis on the bearing capacity of middle pylon foundation. From the computational results, it is concluded that the caisson foundation has a good bearing capacity on thick overburden layer ground and the beating capacity can be improved assuming that the soil near the area of basal comer is reinforced.展开更多
The multi-spring shear mechanism plastic model in this paper is defined in strain space to simulate pore pressure generation and development in sands under cyclic loading and undrained conditions, and the rotation of ...The multi-spring shear mechanism plastic model in this paper is defined in strain space to simulate pore pressure generation and development in sands under cyclic loading and undrained conditions, and the rotation of principal stresses can also be simulated by the model with cyclic behavior of anisotropic consolidated sands. Seismic residual deformations of typical caisson quay walls under different engineering situations are analyzed in detail by the plastic model, and then an index of liquefaction extent is applied to describe the regularity of seismic residual deformation of caisson quay wall top under different engineering situations. Some correlated prediction formulas are derived from the results of regression analysis between seismic residual deformation of quay wall top and extent of liquefaction in the relative safety backfill sand site. Finally, the rationality and the reliability of the prediction methods are validated by test results of a 120 g-centrifuge shaking table, and the comparisons show that some reliable seismic residual deformation of caisson quay can be predicted by appropriate prediction formulas and appropriate index of liquefaction extent.展开更多
As the anchoring foundation of the tension leg platform(TLP),suction caisson foundation is subjected to the long-term vertical pullout loads.But there are few studies on the mechanism of the unloading creep of soft cl...As the anchoring foundation of the tension leg platform(TLP),suction caisson foundation is subjected to the long-term vertical pullout loads.But there are few studies on the mechanism of the unloading creep of soft clay and long-term uplift bearing capacity of suction caisson foundations.To address this problem,unloading creep tests of soft clay were carried out to analyze the strain development with time under different confining pressures.The test results show that the creep curve rapidly develops in the early stage and tends to stabilize in the later stage.The unloading deviator stress is higher,the unloading creep deformation is greater and the soft clay has typical nonlinear creep characteristics.Therefore,by introducing the creep model and considering the influence of the deviator stress,the stress-dependent Merchant model is proposed to describe the unloading creep of soft clay.Then,the stress-dependent Merchant model is extended to a three-dimension constitutive model,and a finite element subroutine is developed to establish a finite element analysis method for analyzing the long-term uplift capacity of suction caisson foundations and validated with the long-term uplift bearing capacity results of caisson model.展开更多
The real-time informational monitoring system is adopted in the construction of middle tower foundation of Taizhou Bridge for the first time. The geometric state of the caisson, the stress of upstream and downstream a...The real-time informational monitoring system is adopted in the construction of middle tower foundation of Taizhou Bridge for the first time. The geometric state of the caisson, the stress of upstream and downstream anchorage cables, underwater topography, the drag forces of the caisson cutting edge and frictional resistances of the sidewall and etc. are monitored in real time. According to the synthesized data analysis and decision-making system, the spatial states of the caisson are adjusted in time to locate and embed the deep water caisson precisely. The offset error of the caisson is less than 30 cm and the vertical error is 1/363 at the final stage. The control technology for construction of large caisson under deep water is concluded and would be helpful for the construction of bridge foundation in the future.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 eq...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
A series of 2D model tests were conducted to assess the foundation stability of composite vertical breakwaters. In this paper, the results from the experimental study are presented conjointly with a formula to estimat...A series of 2D model tests were conducted to assess the foundation stability of composite vertical breakwaters. In this paper, the results from the experimental study are presented conjointly with a formula to estimate the stability number of foundation, which is the most important parameter for evaluation of foundation stability of such structures. The influences of wave height, wave period and the berm width on the stability of compo^ite breakwaters with different armor stone sizes were investigated. Forty-five tests were performed to cover the influences of these parameters. According to the present research, berm width is a significant parameter concerning erosion of armor foundation. As the berm width increases, the amount of berm erosion decreases. Comparisons are made between results of present study and the estimated stability number proposed by Kimura et al. （1994）, which is extension of Tanimoto formula. Results show that the later formula underestimates the stability number. However, by applying an enhancement factor about 1.7 meters to Kimura et al. formula, results correlated with the present experimental results..展开更多
According to the construction method of Taizhou Bridge, numerical simulation is conducted to analyze the vibration of caisson under wind and water flows to determine the main factors of the caisson vibration. Meanwhil...According to the construction method of Taizhou Bridge, numerical simulation is conducted to analyze the vibration of caisson under wind and water flows to determine the main factors of the caisson vibration. Meanwhile, the localization system of caissons and anchors of Taizhou Bridge is modeled in order to summarize the vibration mechanism of caissons under deep-water and jet-flow condition, and further pertinent vibration-control measures are proposed. The obtained results are well verified in engineering practice, and consequently the safety risk of positioning the caisson is reduced.展开更多
基金U.S. Federal Highway Administration Under Grant No. DTFH61-98-C-00094U.S. National Science Foundation Under Grant No. EEC-9701471
文摘An analytical method to study the seismic response of a bridge pier supported on a rigid caisson foundation embedded in a deep soil stratum underlain by a homogeneous half space is developed. The method reproduces the kinematic and inertial responses, using translational and rotational distributed Winkler springs and dashpots to simulate the soil-caisson interaction. Closed-form solutions are given in the frequency domain for vertical harmonic S-wave excitation. Comparison with results from finite element （FE） analysis and other available solutions demonstrates the reliability of the model. Results from parametric studies are given for the kinematic and inertial responses. The modification of the fundamental period and damping ratio of the bridge due to soil-structure interaction is graphically illustrated.
基金the National Key Research and Development Program(Grant No.2017YFC0703408)the National Natural Science Foundation of China(Grant Nos.51678145 and 51478160)the Natural Science Foundation of Jiangsu Province(Grant No.BK20180155).
文摘Suction caisson foundations are often subjected to vertical uplift loads,but there are still no wide and spread engineering specifications on design and calculation method for uplift bearing capacity of suction caisson foundation.So it is important to establish an uplift failure criterion.In order to study the uplift bearing mechanism and failure mode of suction caisson foundation,a series of model tests were carried out considering the effects of aspect ratio,soil permeability and loading mode.Test results indicate that the residual negative pressure at the top of caisson is beneficial to enhance uplift bearing capacity.The smaller the permeability coefficient is,the higher the residual negative pressure will be.And the residual negative pressure is approximately equal to the water head that causes seepage in the caisson.When the load reaches the ultimate bearing capacity,both the top and bottom negative pressures are smaller than Su and both the top and bottom reverse bearing capacity factors are smaller than 1.0 in soft clay.Combined the uplift bearing characteristics of caisson in sandy soil and soft clay,the bearing capacity composition and the calculation method are proposed.It can provide a reference for the engineering design of suction caisson foundation under vertical load.
基金supported by the National Natural Science Foundation of China(Nos.51808220 and 51822809)the Natural Science Foundation of Jiangxi Province(Nos.20192BAB216036 and 20181BCB24011)the Science and Technology Research Project of the Education Department of Jiangxi Province(No.GJJ180340),China。
文摘Bridge foundations located in deep water are usually subjected to horizontal dynamic loads and moments which may be caused by the wind, waves, earthquake, and the possibility of boat crashing or vehicle braking. Caisson foundations based on gravel or sand cushions are a new type of deep-water foundation for bridges, suitable for meizoseismal areas. In this paper, harmonic horizontal excitation tests for the study of the lateral dynamic response of caisson foundations based on cushion layers are described. Different lateral loads and two different cushion types are considered. The results show that the lateral dynamic responses of caisson foundations based on sand and gravel cushions both show strong nonlinear characteristics, and the resonant frequency of the foundation decreases with the increase of the excitation force. The dynamic displacement of a foundation based on a sand cushion is far less than that based on a gravel cushion, and the rate of decrease of the resonant frequency of a foundation based on a gravel cushion is faster than that of a foundation based on a sand cushion under the same conditions. Under dynamic loading the gravel cushion can more effectively dissipate vibration energy and isolate the vibration, than the sand cushion can. A simplified nonlinear analysis method is proposed to simulate the lateral dynamic response of caisson foundations, and the predicted response shows a reasonable match with the results observed in laboratory tests. Scaling laws have also been applied in this small-scale vibration model test to predict the dynamic behavior of the prototype foundation.
基金the Technology Project of Ministry of Transport of China(No.2011318494150)
文摘This paper presents an analytical formula for estimating the longitudinal wave forces on a large roundended caisson foundation. The establishment of the formula is based on the superposition of the theoretical formula of wave forces on a large circular cylinder and the empirical formula of wave forces on a large rectangular cylinder. With the formula transformed into an inertial force form, a specific inertia coefficient with an exact expression is extracted from the formula. The numerical calculations of the wave forces on round-ended cylinders are carried out by the boundary-element method. The undetermined coefficients in the expression of the inertial coefficient are determined by the numerical results. It is obvious that the numerical values can be well expressed by the computation values from the established formula. By a model experiment carried out in laboratory wave flume, the correctness of the analytical formula is further verified by the measured wave forces on a test model of a round-ended bridge caisson foundation. The comparison shows that the experimental forces can be approximately estimated by this simple calculation method.
基金financially supported by the National Key Research and Development Program(Grant No.2017YFC0703408)the National Natural Science Foundation of China(Grant Nos.51678145 and 51878160)
文摘Suction caisson foundation derives most of their uplift resistance from passive suction developed during the pullout movement. It was observed that the passive suction generated in soil at the bottom of the caisson and the failure mode of suction caisson foundation subjecting pullout loading behaves as a reverse compression failure mechanism.The upper bound theorems have been proved to be a powerful method to find the critical failure mechanism and critical load associated with foundations, buried caissons and other geotechnical structures. However, limited attempts have been reported to estimate the uplift bearing capacity of the suction caisson foundation using the upper bound solution. In this paper, both reverse failure mechanisms from Prandtl and Hill were adopted as the failure mechanisms for the computation of the uplift bearing capacity of the suction caisson. New equations were proposed based on both failure mechanisms to estimate the pullout capacity of the suction caisson. The proposed equations were verified by the test results and experimental data from published literature. And the two solutions agree reasonably well with the other test results. It can be proved that both failure mechanisms are reasonably and more consistent with the actual force condition.
基金The National Natural Science Foundation of China(No.51808112,51878160,51678145)the Natural Science Foundation of Jiangsu Province(No.BK20180155)。
文摘To investigate the bearing capacity of a caisson foundation under combined vertical,horizontal and moment loadings,the three-dimensional finite element analyses of a circular caisson foundation in homogenous sandy soil subjected to combined loadings are conducted.The caisson model has a depth to breadth ratio equaling one,and a soil-caisson interface friction coefficientμ=0.3.First,the responses of caisson foundations under uniaxial vertical loading V,horizontal loading H and moment loading M are examined.Moreover,the responses of caisson foundations under combined vertical-horizontal V-H,vertical-moment V-M and horizontal-moment H-M load space are studied and presented using normalized failure envelopes generated by the load-controlled method.Subsequently,the bearing behavior of caisson foundations under combined vertical-horizontal-moment V-H-M load space,as well as the kinematic mechanisms accompanying the failure under uniaxial and combined loading,are addressed and presented for different vertical load ratios V/Vu.Finally,three equations that approximate the three-dimensional shape of the failure locus are proposed,which provides a convenient means of calculating the bearing capacity of a caisson foundation subjected to uniaxial and combined vertical,horizontal and moment loadings.
基金National Science and Technology Support Program of China(No.2009BAG15B02)"333 High-level Personnel Training Project"Special Funded Projects in Jiangsu Province
文摘Because of the computation difficulty of the beating capacity of large underwater caisson foundation on thick overburden layer ground, the geotechnieal software FLAC3D was utilized in the 3D numerical analysis on the bearing capacity of middle pylon foundation. From the computational results, it is concluded that the caisson foundation has a good bearing capacity on thick overburden layer ground and the beating capacity can be improved assuming that the soil near the area of basal comer is reinforced.
基金supported by the Research Foundation of Jiangsu University of Science and Technology for Introducing Talents(Grant No. 35280901)
文摘The multi-spring shear mechanism plastic model in this paper is defined in strain space to simulate pore pressure generation and development in sands under cyclic loading and undrained conditions, and the rotation of principal stresses can also be simulated by the model with cyclic behavior of anisotropic consolidated sands. Seismic residual deformations of typical caisson quay walls under different engineering situations are analyzed in detail by the plastic model, and then an index of liquefaction extent is applied to describe the regularity of seismic residual deformation of caisson quay wall top under different engineering situations. Some correlated prediction formulas are derived from the results of regression analysis between seismic residual deformation of quay wall top and extent of liquefaction in the relative safety backfill sand site. Finally, the rationality and the reliability of the prediction methods are validated by test results of a 120 g-centrifuge shaking table, and the comparisons show that some reliable seismic residual deformation of caisson quay can be predicted by appropriate prediction formulas and appropriate index of liquefaction extent.
基金financially supported by the National Natural Science Foundation of China (Grant Nos. 51878160, 51678145, and52078128)
文摘As the anchoring foundation of the tension leg platform(TLP),suction caisson foundation is subjected to the long-term vertical pullout loads.But there are few studies on the mechanism of the unloading creep of soft clay and long-term uplift bearing capacity of suction caisson foundations.To address this problem,unloading creep tests of soft clay were carried out to analyze the strain development with time under different confining pressures.The test results show that the creep curve rapidly develops in the early stage and tends to stabilize in the later stage.The unloading deviator stress is higher,the unloading creep deformation is greater and the soft clay has typical nonlinear creep characteristics.Therefore,by introducing the creep model and considering the influence of the deviator stress,the stress-dependent Merchant model is proposed to describe the unloading creep of soft clay.Then,the stress-dependent Merchant model is extended to a three-dimension constitutive model,and a finite element subroutine is developed to establish a finite element analysis method for analyzing the long-term uplift capacity of suction caisson foundations and validated with the long-term uplift bearing capacity results of caisson model.
基金National Science and Technology Support Program of China ( No. 2009BAG15B02)Key Programs for Science and Technology Development of Chinese Transportation Industry( No. 2008-353-332-150)
文摘The real-time informational monitoring system is adopted in the construction of middle tower foundation of Taizhou Bridge for the first time. The geometric state of the caisson, the stress of upstream and downstream anchorage cables, underwater topography, the drag forces of the caisson cutting edge and frictional resistances of the sidewall and etc. are monitored in real time. According to the synthesized data analysis and decision-making system, the spatial states of the caisson are adjusted in time to locate and embed the deep water caisson precisely. The offset error of the caisson is less than 30 cm and the vertical error is 1/363 at the final stage. The control technology for construction of large caisson under deep water is concluded and would be helpful for the construction of bridge foundation in the future.
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.
文摘A series of 2D model tests were conducted to assess the foundation stability of composite vertical breakwaters. In this paper, the results from the experimental study are presented conjointly with a formula to estimate the stability number of foundation, which is the most important parameter for evaluation of foundation stability of such structures. The influences of wave height, wave period and the berm width on the stability of compo^ite breakwaters with different armor stone sizes were investigated. Forty-five tests were performed to cover the influences of these parameters. According to the present research, berm width is a significant parameter concerning erosion of armor foundation. As the berm width increases, the amount of berm erosion decreases. Comparisons are made between results of present study and the estimated stability number proposed by Kimura et al. （1994）, which is extension of Tanimoto formula. Results show that the later formula underestimates the stability number. However, by applying an enhancement factor about 1.7 meters to Kimura et al. formula, results correlated with the present experimental results..
基金National Science and Technology Support Program of China ( No. 2009BAG15B02) Key Programs for Science and Technology Development of Chinese Transportation Industry( No. 2008-353-332-150)
文摘According to the construction method of Taizhou Bridge, numerical simulation is conducted to analyze the vibration of caisson under wind and water flows to determine the main factors of the caisson vibration. Meanwhile, the localization system of caissons and anchors of Taizhou Bridge is modeled in order to summarize the vibration mechanism of caissons under deep-water and jet-flow condition, and further pertinent vibration-control measures are proposed. The obtained results are well verified in engineering practice, and consequently the safety risk of positioning the caisson is reduced.
