According to post-seismic observations,spectacular examples of engineering failures can be ascribed to the occurrence of sand liquefaction,where a sandy soil stratum could undergo a transient loss of shear strength an...According to post-seismic observations,spectacular examples of engineering failures can be ascribed to the occurrence of sand liquefaction,where a sandy soil stratum could undergo a transient loss of shear strength and even behave as a“liquid”.Therefore,correct simulation of liquefaction response has become a challenging issue in geotechnical engineering field.In advanced elastoplastic models of sand liquefaction,certain fitting parameters have a remarkable effect on the computed results.However,the identification of these parameters,based on the experimental data,is usually intractable and sometimes follows a subjective trial-and-error procedure.For this,this paper presented a novel calibration methodology based on an optimization algorithm(particle swarm optimization(PSO))for an advanced elastoplastic constitutive model.A multi-objective function was designed to adjust the global quality for both monotonic and cyclic triaxial simulations.To overcome computational problem probably appearing in simulation of the cyclic triaxial test,two interrupt mechanisms were designed to prevent the particles from wasting time in searching the unreasonable space of candidate solutions.The Dafalias model has been used as an example to demonstrate the main programme.With the calibrated parameters for the HN31 sand,the computed results were highly consistent with the laboratory experiments(including monotonic triaxial tests under different confining pressures and cyclic triaxial tests in two loading modes).Finally,an extension example is given for Ottawa sand F65,suggesting that the proposed platform is versatile and can be easily customized to meet different practical needs.展开更多
It is well known that fabric of sand may significantly affect mechanical behaviors and liquefaction resistance of sand.Various optical techniques are currently utilized to visualize the fabric,especially the distribut...It is well known that fabric of sand may significantly affect mechanical behaviors and liquefaction resistance of sand.Various optical techniques are currently utilized to visualize the fabric,especially the distribution of the long axis of soil particles.However,none of these methods provides an ideal solution in laboratory tests and in situ observation.In this study,anisotropy of magnetic susceptibility(AMS)was first proposed as a convenient and efficient way to evaluate the liquefaction of clean sand.At first,investigations with scanning electron microscopy(SEM)and AMS were simultaneously conducted on two groups of soil specimens with different initial fabrics to verify the feasibility of the AMS technique.Then,80 in situ samples were collected to analyze the feature of liquefied and non-liquefied sand layers through AMS tests.It is clearly known from the test results that the natural sedimentary fabric was destroyed during liquefaction and the fabric anisotropy was greatly changed after liquefaction.The feasibility of evaluating soil fabric using the AMS survey was verified by the laboratory tests.Furthermore,the applicability of AMS in detecting liquefied layer in situ was confirmed for the first time.展开更多
Purpose–This study purposes to study the influence of artificial freezing on the liquefaction characteristics of Nanjing sand,as well as its mechanism.Design/methodology/approach–was studied through dynamic triaxial...Purpose–This study purposes to study the influence of artificial freezing on the liquefaction characteristics of Nanjing sand,as well as its mechanism.Design/methodology/approach–was studied through dynamic triaxial tests by means of the GDS dynamic triaxial system on Nanjing sand extensively discovered in the middle and lower reaches of the Yangtze River under seismic load and metro train vibration load,respectively,and potential hazards of the two loads to the freezing construction of Nanjing sand were also identified in the tests.Findings–The results show that under both seismic load and metro train vibration load,freeze-thaw cycles will significantly reduce the stiffness and liquefaction resistance of Nanjing sand,especially in the first freezethaw cycle;the more freeze-thaw cycles,the worse structural behaviors of silty-fine sand,and the easier to liquefy;freeze-thaw cycles will increase the sensitivity of Nanjing sand’s dynamic pore pressure to dynamic load response;the lower the freezing temperature and the effective confining pressure,the worse the liquefaction resistance of Nanjing sand after freeze-thaw cycles;compared to the metro train vibration load,the seismic load in Nanjing is potentially less dangerous to freezing construction of Nanjing sand.Originality/value–The research results are helpful to the construction of the artificial ground freezing of the subway crossing passage in the lower reaches of the Yangtze River and to ensure the construction safety of the subway tunnel and its crossing passage.展开更多
According to the existing problems of liquefaction models of saturated sand that were put forward under dynamic action,on the basis of Handin-Drnevich model,a new calculating model of the dynamic constitutive relation...According to the existing problems of liquefaction models of saturated sand that were put forward under dynamic action,on the basis of Handin-Drnevich model,a new calculating model of the dynamic constitutive relation of saturated sand was put forward.The model was based on the basic hypothesis of instantaneous limit balance according to the basic principle that the stress estate is the destroyed condition was not overstepped.The calculated method of increment nonlinear was referenced and combined with the excellence of the model of distributed particles.The process of vibrating liquefaction of saturated sand was divided into some areas.And the phenomena of shearing dilatation and unloading shrink of saturated sand were considered.On above basic a new calculating constitutive relation model was proposed.There are a few parameters in the model.The physical means of the parameters are very evident and quantized.They could be obtained from the dynamic triaxial test in door.The model was contrasted and validated with the results of the dynamic triaxial test in door.The comparison of the results of the dynamic triaxial test in door and the calculating results of the model indicates that all sorts of phenomenon appearing in the process of liquefaction of saturated sand could be more perfectly reflected by the model.Especially at the initial stage of development of pore water pressure and strain of saturated sand,the results of the dynamic triaxial test in door are consistent with the calculated results of the model very much.But there is some difference between the results at the anaphase of development of pore water pressure and strain.On the path of stress,the calculating and experimenting ultimate state surfaces are almost identical.展开更多
As the offshore wind turbine foundation,the four-bucket jacket foundation has a large stiffness and the structure is difficult to be damaged under seismic load.Nevertheless,the saturated subsoil of the four-bucket jac...As the offshore wind turbine foundation,the four-bucket jacket foundation has a large stiffness and the structure is difficult to be damaged under seismic load.Nevertheless,the saturated subsoil of the four-bucket jacket foundation tends to be liquefied under earthquake,which greatly affects the safety of offshore wind turbine.Therefore,the seismic performance of four-bucket jacket foundation is mainly reflected in the anti-liquefaction capacity of foundation soil.In this paper,the liquefaction resistance of sandy soil of four-bucket jacket foundation for offshore wind turbine is studied.The liquefaction and dynamic response of sandy soil foundation of four-bucket jacket foundation under seismic load are obtained by carrying out the shaking table test,and the influence mechanism of four-bucket jacket foundation on the liquefaction resistance of sandy soil foundation is analyzed.展开更多
This paper describes the improvement effect and mechanism of strengthening a liquefied sand foundation using the cross-vibration wing resonance method,through an indoor model test and numerical simulation.The results ...This paper describes the improvement effect and mechanism of strengthening a liquefied sand foundation using the cross-vibration wing resonance method,through an indoor model test and numerical simulation.The results obtained from the model test showed that a vertical drainage tube was formed during vibration compaction,and finally a crater with a depth of 40 mm and a radius of 150 mm was formed with sloping sides.The sand layer obtained a good improvement effect after resonance vibration,especially in the middle-lower sand deposit.The variation in excess pore water pressure showed different behavior in three stages of the vibration process,and the value after treatment was less than before with a decrease of 18.81%.The vibration energy in the horizontal direction gradually decreased to zero,however the absorption of vibration energy of the soil presented obvious nonuniformity along the depth direction.The results of the numerical simulation were similar to the model test results,including the scope and variation of pore water pressure,and the ground settlement after treatment.展开更多
In this study,a series of undrained cyclic torsional shear tests were conducted to investigate the effect of cyclic loading frequency f on the pre-liquefaction(shearing contractive(SC)period and initial shearing dilat...In this study,a series of undrained cyclic torsional shear tests were conducted to investigate the effect of cyclic loading frequency f on the pre-liquefaction(shearing contractive(SC)period and initial shearing dilative(ISD)period)and post-liquefaction(late shearing dilative(LSD)period)deformation properties of saturated Fujian sand.The secant shear modulus G and damping ratioλin the entire cyclic loading process,and the unloading tangent shear modulus G_(L1)and flow deformation tangent shear modulus GL2 in the ISD and LSD periods were adopted to quantitatively characterize the evolution of hysteresis loop with an increase in shear strain amplitude ca.The test results show that the effect of f on G of saturated Fujian sand in the SC period is not apparent.However,all the G-γ_(a),G_(L1)-γ_(a),and GL2-ca curves in the ISD and LSD periods showed a downward trend with an increase in f.This study also proposes a modified method for calculatingλto compensate for the analytical error caused by the non-closure of hysteresis loop.Compared with the classical curves that mainly applied in geotechnical engineering,theλfirst increases and then decreases with the increase ofγa.Furthermore,theλevaluated by the modified method is approximately 10%–15%more than theλevaluated by the traditional method when theλreaches its peak value.展开更多
基金support provided by the research sponsors through Shanghai Pujiang Program(Grant No.20PJ1417300)ANR(Agence Nationale de la Recherche)ISOLATE is gratefully acknowledged.
文摘According to post-seismic observations,spectacular examples of engineering failures can be ascribed to the occurrence of sand liquefaction,where a sandy soil stratum could undergo a transient loss of shear strength and even behave as a“liquid”.Therefore,correct simulation of liquefaction response has become a challenging issue in geotechnical engineering field.In advanced elastoplastic models of sand liquefaction,certain fitting parameters have a remarkable effect on the computed results.However,the identification of these parameters,based on the experimental data,is usually intractable and sometimes follows a subjective trial-and-error procedure.For this,this paper presented a novel calibration methodology based on an optimization algorithm(particle swarm optimization(PSO))for an advanced elastoplastic constitutive model.A multi-objective function was designed to adjust the global quality for both monotonic and cyclic triaxial simulations.To overcome computational problem probably appearing in simulation of the cyclic triaxial test,two interrupt mechanisms were designed to prevent the particles from wasting time in searching the unreasonable space of candidate solutions.The Dafalias model has been used as an example to demonstrate the main programme.With the calibrated parameters for the HN31 sand,the computed results were highly consistent with the laboratory experiments(including monotonic triaxial tests under different confining pressures and cyclic triaxial tests in two loading modes).Finally,an extension example is given for Ottawa sand F65,suggesting that the proposed platform is versatile and can be easily customized to meet different practical needs.
基金supported by the National Nature Science Foundation of China(Grant No.52208379)which is deeply appreciated.This research was partially supported by the Grant-in-Aid Scientific Research(B)(Grant No.17H03304)Japan Society for the Promotion of Science(JSPS),which is also deeply appreciated.This work was also supported by the Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education,Tongji University,China(Grant No.KLE-TJGE-B2103).
文摘It is well known that fabric of sand may significantly affect mechanical behaviors and liquefaction resistance of sand.Various optical techniques are currently utilized to visualize the fabric,especially the distribution of the long axis of soil particles.However,none of these methods provides an ideal solution in laboratory tests and in situ observation.In this study,anisotropy of magnetic susceptibility(AMS)was first proposed as a convenient and efficient way to evaluate the liquefaction of clean sand.At first,investigations with scanning electron microscopy(SEM)and AMS were simultaneously conducted on two groups of soil specimens with different initial fabrics to verify the feasibility of the AMS technique.Then,80 in situ samples were collected to analyze the feature of liquefied and non-liquefied sand layers through AMS tests.It is clearly known from the test results that the natural sedimentary fabric was destroyed during liquefaction and the fabric anisotropy was greatly changed after liquefaction.The feasibility of evaluating soil fabric using the AMS survey was verified by the laboratory tests.Furthermore,the applicability of AMS in detecting liquefied layer in situ was confirmed for the first time.
基金supported by the National Natural Science Foundation of China(Grant No.U41702299).
文摘Purpose–This study purposes to study the influence of artificial freezing on the liquefaction characteristics of Nanjing sand,as well as its mechanism.Design/methodology/approach–was studied through dynamic triaxial tests by means of the GDS dynamic triaxial system on Nanjing sand extensively discovered in the middle and lower reaches of the Yangtze River under seismic load and metro train vibration load,respectively,and potential hazards of the two loads to the freezing construction of Nanjing sand were also identified in the tests.Findings–The results show that under both seismic load and metro train vibration load,freeze-thaw cycles will significantly reduce the stiffness and liquefaction resistance of Nanjing sand,especially in the first freezethaw cycle;the more freeze-thaw cycles,the worse structural behaviors of silty-fine sand,and the easier to liquefy;freeze-thaw cycles will increase the sensitivity of Nanjing sand’s dynamic pore pressure to dynamic load response;the lower the freezing temperature and the effective confining pressure,the worse the liquefaction resistance of Nanjing sand after freeze-thaw cycles;compared to the metro train vibration load,the seismic load in Nanjing is potentially less dangerous to freezing construction of Nanjing sand.Originality/value–The research results are helpful to the construction of the artificial ground freezing of the subway crossing passage in the lower reaches of the Yangtze River and to ensure the construction safety of the subway tunnel and its crossing passage.
基金Project(59979001) supported by the National Natural Science Foundation of China
文摘According to the existing problems of liquefaction models of saturated sand that were put forward under dynamic action,on the basis of Handin-Drnevich model,a new calculating model of the dynamic constitutive relation of saturated sand was put forward.The model was based on the basic hypothesis of instantaneous limit balance according to the basic principle that the stress estate is the destroyed condition was not overstepped.The calculated method of increment nonlinear was referenced and combined with the excellence of the model of distributed particles.The process of vibrating liquefaction of saturated sand was divided into some areas.And the phenomena of shearing dilatation and unloading shrink of saturated sand were considered.On above basic a new calculating constitutive relation model was proposed.There are a few parameters in the model.The physical means of the parameters are very evident and quantized.They could be obtained from the dynamic triaxial test in door.The model was contrasted and validated with the results of the dynamic triaxial test in door.The comparison of the results of the dynamic triaxial test in door and the calculating results of the model indicates that all sorts of phenomenon appearing in the process of liquefaction of saturated sand could be more perfectly reflected by the model.Especially at the initial stage of development of pore water pressure and strain of saturated sand,the results of the dynamic triaxial test in door are consistent with the calculated results of the model very much.But there is some difference between the results at the anaphase of development of pore water pressure and strain.On the path of stress,the calculating and experimenting ultimate state surfaces are almost identical.
基金financially supported by the National Natural Science Foundation of China(Grant No.52171274).
文摘As the offshore wind turbine foundation,the four-bucket jacket foundation has a large stiffness and the structure is difficult to be damaged under seismic load.Nevertheless,the saturated subsoil of the four-bucket jacket foundation tends to be liquefied under earthquake,which greatly affects the safety of offshore wind turbine.Therefore,the seismic performance of four-bucket jacket foundation is mainly reflected in the anti-liquefaction capacity of foundation soil.In this paper,the liquefaction resistance of sandy soil of four-bucket jacket foundation for offshore wind turbine is studied.The liquefaction and dynamic response of sandy soil foundation of four-bucket jacket foundation under seismic load are obtained by carrying out the shaking table test,and the influence mechanism of four-bucket jacket foundation on the liquefaction resistance of sandy soil foundation is analyzed.
基金National Natural Science Foundation of People′s Republic of China under Grant No.41977241the Scientific Research Foundation of Graduate School of Southeast University under Grant No.YBPY1981。
文摘This paper describes the improvement effect and mechanism of strengthening a liquefied sand foundation using the cross-vibration wing resonance method,through an indoor model test and numerical simulation.The results obtained from the model test showed that a vertical drainage tube was formed during vibration compaction,and finally a crater with a depth of 40 mm and a radius of 150 mm was formed with sloping sides.The sand layer obtained a good improvement effect after resonance vibration,especially in the middle-lower sand deposit.The variation in excess pore water pressure showed different behavior in three stages of the vibration process,and the value after treatment was less than before with a decrease of 18.81%.The vibration energy in the horizontal direction gradually decreased to zero,however the absorption of vibration energy of the soil presented obvious nonuniformity along the depth direction.The results of the numerical simulation were similar to the model test results,including the scope and variation of pore water pressure,and the ground settlement after treatment.
基金supported by the National Outstanding Youth Science Fund Project of the National Natural Science Foundation of China(Grant No.51722801)National Natural Science Foundation of China(Grant No.52078020).
文摘In this study,a series of undrained cyclic torsional shear tests were conducted to investigate the effect of cyclic loading frequency f on the pre-liquefaction(shearing contractive(SC)period and initial shearing dilative(ISD)period)and post-liquefaction(late shearing dilative(LSD)period)deformation properties of saturated Fujian sand.The secant shear modulus G and damping ratioλin the entire cyclic loading process,and the unloading tangent shear modulus G_(L1)and flow deformation tangent shear modulus GL2 in the ISD and LSD periods were adopted to quantitatively characterize the evolution of hysteresis loop with an increase in shear strain amplitude ca.The test results show that the effect of f on G of saturated Fujian sand in the SC period is not apparent.However,all the G-γ_(a),G_(L1)-γ_(a),and GL2-ca curves in the ISD and LSD periods showed a downward trend with an increase in f.This study also proposes a modified method for calculatingλto compensate for the analytical error caused by the non-closure of hysteresis loop.Compared with the classical curves that mainly applied in geotechnical engineering,theλfirst increases and then decreases with the increase ofγa.Furthermore,theλevaluated by the modified method is approximately 10%–15%more than theλevaluated by the traditional method when theλreaches its peak value.
