The motion of pore water directly influences mechanical properties of soils, which are variable during creep. Accurate description of the evolution of mechanical properties of soils can help to reveal the internal beh...The motion of pore water directly influences mechanical properties of soils, which are variable during creep. Accurate description of the evolution of mechanical properties of soils can help to reveal the internal behavior of pore water. Based on the idea of using the fractional order to reflect mechanical properties of soils, a fractional creep model is proposed by introducing a variable-order fractional operator, and realized on a series of creep responses in soft soils. A comparative analysis illustrates that the evolution of mechanical properties, shown through the simulated results, exactly corresponds to the motion of pore water and the solid skeleton. This demonstrates that the proposed variable-order fractional model can be employed to characterize the evolution of mechanical properties of and the pore water motion in soft soils during creep. It is observed that the fractional order from the proposed model is related to the dissipation rate of pore water pressure.展开更多
The main objective of this study was to investigate creep characteristics and construct a suitable constitutive model for soft soils in offshore areas.Soft soil samples were obtained to evaluate the physical and mecha...The main objective of this study was to investigate creep characteristics and construct a suitable constitutive model for soft soils in offshore areas.Soft soil samples were obtained to evaluate the physical and mechanical properties.Additionally,a triaxial creep test was conducted by applying different axial deviator stresses under three confining pressures to analyze the creep characteristics and establish a creep constitutive model suitable.It was found that the physical and mechanical properties of soft soils at different depths are significantly different,and the physical properties have a significant correlation with compression modulus and compression coefficient.The soft soils creep mainly present linear viscoelasticity under low axial stress,while it shows nonlinear viscoplasticity characteristics when the axial deviator stress is greater than the yield stress.The correlation coefficient R2 of Merchant model fitting curves are significantly larger than that of Burgers model.The Burgers model fitting curves have a large deviation from the actual creep characteristics under smaller axial deviator stress and the parameters are also inconsistent with the internal creep mechanism.The Kelvin body in Merchant model can better simulate attenuation creep characteristics of soft soils,but it cannot exhibit nonlinear viscoplasticity creep characteristics.Furthermore,a combination of Merchant model and power function empirical model can dramatically characterize the linear viscoelasticity and nonlinear viscoplasticity creep behaviors of offshore soft soils,with a correlation coefficient above 0.94.Verification of the combined constitutive model indicates that it has excellent credibility and applicability in offshore areas.展开更多
This study was designed to enhance the soft clayey soil treatment effects using an innovative mechanochemically activated geopolymer(GP)through the optimized inclusion of nano-metakaolin(NM)and polypropylene fiber.The...This study was designed to enhance the soft clayey soil treatment effects using an innovative mechanochemically activated geopolymer(GP)through the optimized inclusion of nano-metakaolin(NM)and polypropylene fiber.The study also investigated the possible improvements in the binding ability of GP stabilization under different curing regimes.To this end,binders including lime alone,LG(slag-based geopolymer),LGNM(nano-modified LG with NM)and LGNMF(LGNM/fiber)mixture were separately added to soft soil samples.The fabricated composites were then subjected to a set of macro and micro level tests.The results indicated that,adding LG binary with a 20%NM replacement can lead to a significant increase(by nearly 21 times)in soil strength and a remarkable decline(about 70%)in the compression index.In fact,NM can play a great role in accelerating the rate of hydration reactions and forming a densely packed fabric,which staggeringly improve the soil hydromechanical attributes.It was also observed that raising the curing temperature will effectively augment the polymerization kinetics,leading to a substantial increase(~2 times)in the soil solidification process.However,the stabilized composites containing NM may reveal a brittle nature under more intense stress.Such a potential drawback seems to be resolved by the integration of fibers within the matrix.LGNM combined with fiber would boost(≥10 times)the energy absorption capacity of the soil,notably enhancing its residual strength.Overall,LGNMF may not only feature a broader range of benefits(inc.economic,technical,environmental)compared to traditional binders but also promote the ductility of the GP materials.展开更多
The objective of this study is to propose an artificial neural network(ANN)model to predict the excavation-induced tunnel horizontal displacement in soft soils.For this purpose,a series of finite element data sets fro...The objective of this study is to propose an artificial neural network(ANN)model to predict the excavation-induced tunnel horizontal displacement in soft soils.For this purpose,a series of finite element data sets from rigorously verified numerical models were collected to be utilized for the development of the ANN model.The excavation width,the excavation depth,the retaining wall thickness,the ratio of the average shear strength to the vertical effective stress,the ratio of the average unloading/reloading Young’s modulus to the vertical effective stress,the horizontal distance between the tunnel and retaining wall,and the ratio of the buried depth of the tunnel crown to the excavation depth were chosen as the input variables,while the excavation-induced tunnel horizontal displacement was considered as an output variable.The results demonstrated the feasibility of the developed ANN model to predict the excavation-induced tunnel horizontal displacement.The proposed ANN model in this study can be applied to predict the excavation-induced tunnel horizontal displacement in soft soils for practical risk assessment and mitigation decision.展开更多
A new triaxial apparatus was designed and manufactured. It is able to applysurcharge and combined vacuum-surcharge pressures on soil samples, and allows for monitoring ofexcess pore-water pressure, axial strain or set...A new triaxial apparatus was designed and manufactured. It is able to applysurcharge and combined vacuum-surcharge pressures on soil samples, and allows for monitoring ofexcess pore-water pressure, axial strain or settlement, and volumetric strain during the process ofconsolidation. Tests were performed using the apparatus on undisturbed soft clayey soil samples,which were collected from Wenzhou, Zhejiang Province, China, at average natural water content 72. 5%. The consolidation behavior of theclay has no rigorous difference, whether it is consolidatedunder the vacuum, surcharge, or combined vacuum-surcharge preloading. The study shows that somephysical properties of the soft clayey soils are changed and mechanical properties are improved tosupport excessive loads transferred to the soil foundation due to construction.展开更多
Time-dependent characteristics(TDCs)have been neglected in most previous studies investigating the deviation mechanisms of bridge pile foundations and evaluating the effectiveness of preventive measures.In this study,...Time-dependent characteristics(TDCs)have been neglected in most previous studies investigating the deviation mechanisms of bridge pile foundations and evaluating the effectiveness of preventive measures.In this study,the stress-strain-time characteristics of soft soils were illustrated by consolidation-creep tests based on a typical engineering case.An extended Koppejan model was developed and then embedded in a finite element(FE)model via a user-material subroutine(UMAT).Based on the validated FE model,the time-dependent deformation mechanism of the pile foundation was revealed,and the preventive effect of applying micropiles and stress-release holes to control the deviation was investigated.The results show that the calculated maximum lateral displacement of the cap differs from the measured one by 6.5%,indicating that the derived extended Koppejan model reproduced the deviation process of the bridge cap-pile foundation with time.The additional load acting on the pile side caused by soil lateral deformation was mainly concentrated within the soft soil layer and increased with the increase in load duration.Compared with t=3 d(where t is surcharge time),the maximum lateral additional pressure acting on Pile 2#increased by approximately 47.0%at t=224 d.For bridge pile foundation deviation in deep soft soils,stress-release holes can provide better prevention compared to micropiles and are therefore recommended.展开更多
This study uses Steel Slag Coarse Aggregate (SSCA) as a mixture replacement, preamble material to improve soft soils, which is economic, and has good effect environment. Recently, the development and utilization of by...This study uses Steel Slag Coarse Aggregate (SSCA) as a mixture replacement, preamble material to improve soft soils, which is economic, and has good effect environment. Recently, the development and utilization of by-product, waste and recycle materials must be studied and investigated as a source of improved material for soft soils as, an economic and good effect environmental. The study analyzes effects of both replaced mixtures, (SSCA) or (TSCA) on improved soil bearing capacity and expected settlement after verifying the model. Numerical modeling of the one of real store loaded strip using, PLAXIS, 2D, strain deformation behavior to achieve field visible and measured deformations of untreated soft soil. Numerical studies were devolved to investigate geomechanics parameters improved to compare between using (SSCA) or (TSCA) as, replacement mixture. Results demonstrate that using (SSCA) improved compressibility and strength of shallow soft soil layer significantly than using (TCSA) mixture, while (SSCA) improved strip footing ultimate bearing capacity, (UBC), by 84.4% compared with increase of 20.5% when using (TCSA) mixture at the same thickness. In addition, the study highlights the effective (SSCA) replacement thickness ranges between (0.65 ~ 0.80) footing width.展开更多
The coastal region of Fujian contains numerous existing stone masonry structures,many of which are constructed on soft soil sites.Previous studies have shown that the soil-structure interaction(SSI)effect on soft soil...The coastal region of Fujian contains numerous existing stone masonry structures,many of which are constructed on soft soil sites.Previous studies have shown that the soil-structure interaction(SSI)effect on soft soil foundations can prolong the structure's natural vibration period and enhance its seismic response.We develops a soilstructure interaction system model and a comparative rigid foundation model using the finite element software LS-DYNA to investigate the impact of SSI on the dynamic characteristics and seismic response of stone structures.The results indicate that the SSI effect alters stone structures'dynamic properties and seismic response.This alteration is evident in the extended natural vibration period,which reduces overall stiffness,increases interstory displacement angles,and slightly decreases the acceleration response.Under both SSI and FIX systems,the structural failure mode is characterized by the external collapse of the second-story stone walls,which causes the roof stone slabs to lose support and fall,leading to overall collapse.The FIX system demonstrates better structural integrity and stability with slower crack development.In contrast,the SSI system exhibits cracks that appear earlier and develop more rapidly,causing more severe damage.The research findings provide a theoretical basis for the seismic reinforcement of existing stone structures on soft soil foundations.展开更多
The accumulative shear deformation of soft clays under cyclic loads is considered as pseudo-static creep. A pseudo-static elasto-plastic cyclic creep model is developed based on the visco-elasto-plastic theory. The pa...The accumulative shear deformation of soft clays under cyclic loads is considered as pseudo-static creep. A pseudo-static elasto-plastic cyclic creep model is developed based on the visco-elasto-plastic theory. The parameters in the model are determined by cyclic triaxial soil tests. A method for analyzing the stability of offshore soft foundation under wave loads is given by combining the model with pseudo-static creep analysis. An example is analyzed by the method. The results show that the horizontal and vertical stability of foundations under wave loads can be analyzed by it and the analytical results are qualitatively consistent with the observed failure modes of shallow foundations.展开更多
The reinforcement effects of geosynthetics in thick soft subsoil case and thin soft subsoil case are studied in this paper,and a Duncan Chang nonlinear numerical model based on the finite element method (FEM) is deve...The reinforcement effects of geosynthetics in thick soft subsoil case and thin soft subsoil case are studied in this paper,and a Duncan Chang nonlinear numerical model based on the finite element method (FEM) is developed.Moreover,an important conclusion that the thickness of soft subsoil affects greatly the geotechnical behavior of geosynthetic reinforced embankments is drawn.A series of embankment built on soft subsoil is calculated using the FEM program.The results of the computer program,such as the lateral displacements,settlements,and stress level and shear stresses in the subsoil,are presented in great detail and the comparison of those results disposes clearly the huge discrepancy of reinforce benefit between the thick subsoil embankment and thin subsoil embankment.Reinforcement mechanism of geosynthetics is also discussed in this paper and several conclusions are reached.This paper also gives recommendations for design.展开更多
The effect of the consolidation stress σc and the consolidation ratio kc on the cyclic degradation relation is studied by cyclic triaxial tests of soft clay. The results show that the normalized relation among the c...The effect of the consolidation stress σc and the consolidation ratio kc on the cyclic degradation relation is studied by cyclic triaxial tests of soft clay. The results show that the normalized relation among the cyclic modulus, the damping ratio, the accumulative deviatoric strain and the cyclic degradation parameter can be established if the cyclic stress ratio and initial shear stress ratio are used as normalized parameters. Thereby the reasonable method is supplied to measure and apply cyclic parameters of soft clay.展开更多
The use of geotextiles as a reinforcement material for improving the factor of safety against slope failure in embankments built on soft clay is becoming a common practice. This work is intended to help understand the...The use of geotextiles as a reinforcement material for improving the factor of safety against slope failure in embankments built on soft clay is becoming a common practice. This work is intended to help understand the effect of the geotextile reinforcement has on such embankments and to provide a design aid for civil engineers that enables them to quickly estimate the factor of safety against slope failure. Seventy four different cases were modelled and analyzed using a finite element software, GeoStudio 2018 R2. The results showed that the optimum improvement was achieved when using a single layer of geotextile reinforcement placed at the base of the embankment, by which the factor of safety increased by up to 40%. Adding a second layer, a third layer and a fourth layer, increases the safety factor by 2.5%, 1% and 0.5% respectively. Different charts for different heights of embankments were presented to aid in finding the most suitable slope angle and number of reinforcement layers required to achieve a certain safety factor.展开更多
In view of the characteristics of soft soil deep foundation pit for the construction and geotechnical characteristics of the special medium,it is difficult to calculate theoreti- cally accurately structural deformatio...In view of the characteristics of soft soil deep foundation pit for the construction and geotechnical characteristics of the special medium,it is difficult to calculate theoreti- cally accurately structural deformation of the foundation pit,so in the course of excavation on the construction of the information is particularly important.The analysis and compari- son of several popular non-linear forecasting methods,combined with the actual projects, set up a grey theoretical prediction model,time series forecasting model,improved neural network model to predict deformation of the foundation pit.The results show that the use of neural network to predict with high accuracy solution,it is the foundation deformation prediction effective way in underground works with good prospects.展开更多
Construction issues of high-speed rail infrastructures have been increasingly concerned worldwide,of which the subgrade settlement in soft soil area becomes a particularly critical problem.Due to the high compressibil...Construction issues of high-speed rail infrastructures have been increasingly concerned worldwide,of which the subgrade settlement in soft soil area becomes a particularly critical problem.Due to the high compressibility and low permeability of soft soil,the post-construction settlement of the subgrade is extremely difficult to control in these regions,which seriously threatens the operation safety of high-speed trains.In this work,the significant issues of high-speed railway subgrades in soft soil regions are discussed.The theoretical and experimental studies on foundation treatment methods for ballasted and ballastless tracks are reviewed.The settlement evolution and the settlement control effect of different treatment methods are highlighted.Control technologies of subgrade differential settlement are subsequently briefly presented.Settlement calculation algorithms of foundations reinforced by different treatment methods are discussed in detail.The defects of existing prediction methods and the challenges faced in their practical applications are analyzed.Furthermore,the guidance on future improvement in control theories and technologies of subgrade settlement for high-speed railway lines and the corresponding challenges are provided.展开更多
A series of researches were carried out for the soil samples in the Pearl River Delta under the action of consolidation loads,such as the quantitative analyses of the pore scale,shape and size distributions of micro-s...A series of researches were carried out for the soil samples in the Pearl River Delta under the action of consolidation loads,such as the quantitative analyses of the pore scale,shape and size distributions of micro-structure units,with an environmental scanning electron microscope (ESEM),a mercury intrusion analyzer and a mineral diffractometer. The experimental results show that the consolidation pressures remarkably change the pore sizes and distribution characteristics of the silt,thus changing its compressibility and permeability. This can be proved by the fact that,in the earlier stage with a consolidation pressure of p<200 kPa,the pore sizes are greater and the compressibility and permeability coefficients are larger. However,they rapidly decrease with the increase in consolidation pressure. And in the later stage with a consolidation pressure of p>200 kPa,the pore sizes are smaller and the compressibility and permeability coefficients are less. Therefore,the empirical formulas of compression coefficient and permeability coefficient vs consolidation load and average pore diameter are deduced.展开更多
Soft clays are problematic soils as they present high compressibility and low shear strength.There are several methods for improving in situ conditions of soft clays.Based on the geotechnical problem’s geometry and c...Soft clays are problematic soils as they present high compressibility and low shear strength.There are several methods for improving in situ conditions of soft clays.Based on the geotechnical problem’s geometry and characteristics,the in situ conditions may require reinforcement to restrain instability and construction settlements.Granular columns reinforced by geosynthetic material are widely used to reduce settlements of embankments on soft clays.They also accelerate the consolidation rate by reducing the drainage path’s length and increasing the foundation soil’s bearing capacity.In this study,the performance of encased and layered granular columns in soft clay is investigated and discussed.The numerical results show the significance of geosynthetic stiffness and the column length on the embankment settlements.Furthermore,the results show that granular columns may play an important role in dissipating the excess pore water pressures and accelerating the consolidation settlements of embankments on soft clays.展开更多
Abundant practical evidences have indicated that the soil progressively loses its structural configuration under construction disturbance and this can result in long-term macro deformation.The fundamental understandin...Abundant practical evidences have indicated that the soil progressively loses its structural configuration under construction disturbance and this can result in long-term macro deformation.The fundamental understanding of soil microstructure evolution subject to construction disturbance is necessary for controlling disturbance in excavation projects and minimizing ground settlement.The microstructure of Shanghai soft soil is investigated in this study.The laboratory isotropic compression tests are respectively performed on the virgin soil and the reconstructed Shanghai soft soil to investigate the macro deformation of soil under disturbance.Discrete element method model is used to study the micro particle level responses of soil under disturbance.The laboratory tests and numerical simulations provide theoretical basis for construction disturbance mitigation to ensure safety and stability of excavation projects.展开更多
Finite element method was performed to investigate the influences of beam stiffness, foundation width and cushion thickness on the beating capacity of beam foundation on underlying weak laminated clay. The comparison ...Finite element method was performed to investigate the influences of beam stiffness, foundation width and cushion thickness on the beating capacity of beam foundation on underlying weak laminated clay. The comparison between numerical results and results from field test including plate-bearing test and foundation settlement observation shows reasonable agreement. According to the numerical results, the beam width, length, cross section and cushion thickness were optimized. The results show that the stresses in subgrade soil decrease greatly with increasing the cushion thickness and width of foundation. However, the foundation settlement and influencing depth of displacement also increase correspondingly under conditions of relatively thinner cushion thickness. For the foundations on underlying weak layer, increasing foundation width merely might be inadequate for improving the bearing capacity, and the appropriate width and cushion thickness depend on the response of subgrade. A comparison between rigid and flexible beams was also discussed. The influence of a flexible beam foundation on subgrade is relatively smaller under the same loading conditions, and the flexible beam foundation appears more adaptable to various subgrades. The proposed flexible beam foundation was adopted in engineering. According to the calculation results, beam width of 2.4 m and cushion thickness of 0.8 m are proposed, and a flexible beam foundation is applied in the optimized design, which is confirmed reasonable by the actual engineering.展开更多
The flow characteristics of foundation soils subjected to train loads can present engineering hazards in highspeed railways.In order to verify the feasibility of blending coarse sand in modifying soft subsoil,undraine...The flow characteristics of foundation soils subjected to train loads can present engineering hazards in highspeed railways.In order to verify the feasibility of blending coarse sand in modifying soft subsoil,undrained pulling sphere tests were carried out and the train loads were simulated through localized and cyclic vibration at various frequencies.Laboratory testing results indicate that the fl ow characteristics of soft soil can be signifi cantly enhanced by high-frequency vibration;meanwhile the continuous increase in fl ow characteristics caused by cyclic vibration may be an important reason for the long-term settlement of soft subsoil.The infl uence of sand content on fl ow characteristics is also studied in detail,and it is shown that the addition of coarse sand can weaken the fl ow characteristics of soft soil induced by sudden vibration at lower than 50 Hz.Under the condition of cyclic vibration,the growth of the fl ow characteristics of sand-clay mixtures is mainly caused by the fi rst-time vibration in the cycle,and the increase in sand content can make the fl ow characteristics present a faster convergent tendency.展开更多
In recent years, reconstituted small samples have often been used to assess the performance of radial consolidation due to prefabricated vertical drains(PVDs), but the permeability and compressibility of samples of un...In recent years, reconstituted small samples have often been used to assess the performance of radial consolidation due to prefabricated vertical drains(PVDs), but the permeability and compressibility of samples of undisturbed soil often differ from those of the remoulded ones. The problem seems more complex in marine environment due to the presence of random coarse particles including gravels, shells and natural partings. Performing small-scale laboratory experiment with reconstituted samples, especially in marine environment, cannot predict the exact soil behaviour in the field. This paper describes an experimental programme that measures radial consolidation using a conventional Rowe cell and a largescale consolidometer, where the samples of undisturbed soil obtained from a site along the Pacific Highway(north of Sydney) were compared using measured settlements and excess pore pressures.Moreover, this paper highlights the implications of the smear effect and sample size influence, which are imperative in translating the laboratory testing practices to actual real-life behaviour. The effect of vacuum pressure on the coefficient of radial consolidation of a large-scale undisturbed test specimen is also discussed. The paper demonstrates that the extent of smear zone in the field can be very similar to the large-scale laboratory consolidation test using a scaled-down drain and mandrel, but considerably different from the data obtained for small laboratory specimens.展开更多
基金supported by the Natural Science Foundation of Jiangsu Province of China(Grant No.BK2012810)the Fundamental Research Funds for the Central Universities(Grant No.2009B15114)
文摘The motion of pore water directly influences mechanical properties of soils, which are variable during creep. Accurate description of the evolution of mechanical properties of soils can help to reveal the internal behavior of pore water. Based on the idea of using the fractional order to reflect mechanical properties of soils, a fractional creep model is proposed by introducing a variable-order fractional operator, and realized on a series of creep responses in soft soils. A comparative analysis illustrates that the evolution of mechanical properties, shown through the simulated results, exactly corresponds to the motion of pore water and the solid skeleton. This demonstrates that the proposed variable-order fractional model can be employed to characterize the evolution of mechanical properties of and the pore water motion in soft soils during creep. It is observed that the fractional order from the proposed model is related to the dissipation rate of pore water pressure.
基金supported by the National Natural Science Foundation of China(NSFC)(No.U2433210)Safety Capability Development Program of CAAC(ADSA0346)Innovation Capability Support Program of Shaanxi(2024RS-CXTD-43).
文摘The main objective of this study was to investigate creep characteristics and construct a suitable constitutive model for soft soils in offshore areas.Soft soil samples were obtained to evaluate the physical and mechanical properties.Additionally,a triaxial creep test was conducted by applying different axial deviator stresses under three confining pressures to analyze the creep characteristics and establish a creep constitutive model suitable.It was found that the physical and mechanical properties of soft soils at different depths are significantly different,and the physical properties have a significant correlation with compression modulus and compression coefficient.The soft soils creep mainly present linear viscoelasticity under low axial stress,while it shows nonlinear viscoplasticity characteristics when the axial deviator stress is greater than the yield stress.The correlation coefficient R2 of Merchant model fitting curves are significantly larger than that of Burgers model.The Burgers model fitting curves have a large deviation from the actual creep characteristics under smaller axial deviator stress and the parameters are also inconsistent with the internal creep mechanism.The Kelvin body in Merchant model can better simulate attenuation creep characteristics of soft soils,but it cannot exhibit nonlinear viscoplasticity creep characteristics.Furthermore,a combination of Merchant model and power function empirical model can dramatically characterize the linear viscoelasticity and nonlinear viscoplasticity creep behaviors of offshore soft soils,with a correlation coefficient above 0.94.Verification of the combined constitutive model indicates that it has excellent credibility and applicability in offshore areas.
文摘This study was designed to enhance the soft clayey soil treatment effects using an innovative mechanochemically activated geopolymer(GP)through the optimized inclusion of nano-metakaolin(NM)and polypropylene fiber.The study also investigated the possible improvements in the binding ability of GP stabilization under different curing regimes.To this end,binders including lime alone,LG(slag-based geopolymer),LGNM(nano-modified LG with NM)and LGNMF(LGNM/fiber)mixture were separately added to soft soil samples.The fabricated composites were then subjected to a set of macro and micro level tests.The results indicated that,adding LG binary with a 20%NM replacement can lead to a significant increase(by nearly 21 times)in soil strength and a remarkable decline(about 70%)in the compression index.In fact,NM can play a great role in accelerating the rate of hydration reactions and forming a densely packed fabric,which staggeringly improve the soil hydromechanical attributes.It was also observed that raising the curing temperature will effectively augment the polymerization kinetics,leading to a substantial increase(~2 times)in the soil solidification process.However,the stabilized composites containing NM may reveal a brittle nature under more intense stress.Such a potential drawback seems to be resolved by the integration of fibers within the matrix.LGNM combined with fiber would boost(≥10 times)the energy absorption capacity of the soil,notably enhancing its residual strength.Overall,LGNMF may not only feature a broader range of benefits(inc.economic,technical,environmental)compared to traditional binders but also promote the ductility of the GP materials.
基金the financial support from National Natural Science Foundation of China(Grant Nos.52108381,52090082,41772295,and 51978517)Innovation Program of Shanghai Municipal Education Commission(Grant No.2019-01-07-00-07-456 E00051)+1 种基金Shanghai Science and Technology Committee Program(Nos.20dz1201404 and 21DZ1200601)key innovation team program of innovation talents promotion plan by MOST of China(No.2016RA4059).
文摘The objective of this study is to propose an artificial neural network(ANN)model to predict the excavation-induced tunnel horizontal displacement in soft soils.For this purpose,a series of finite element data sets from rigorously verified numerical models were collected to be utilized for the development of the ANN model.The excavation width,the excavation depth,the retaining wall thickness,the ratio of the average shear strength to the vertical effective stress,the ratio of the average unloading/reloading Young’s modulus to the vertical effective stress,the horizontal distance between the tunnel and retaining wall,and the ratio of the buried depth of the tunnel crown to the excavation depth were chosen as the input variables,while the excavation-induced tunnel horizontal displacement was considered as an output variable.The results demonstrated the feasibility of the developed ANN model to predict the excavation-induced tunnel horizontal displacement.The proposed ANN model in this study can be applied to predict the excavation-induced tunnel horizontal displacement in soft soils for practical risk assessment and mitigation decision.
文摘A new triaxial apparatus was designed and manufactured. It is able to applysurcharge and combined vacuum-surcharge pressures on soil samples, and allows for monitoring ofexcess pore-water pressure, axial strain or settlement, and volumetric strain during the process ofconsolidation. Tests were performed using the apparatus on undisturbed soft clayey soil samples,which were collected from Wenzhou, Zhejiang Province, China, at average natural water content 72. 5%. The consolidation behavior of theclay has no rigorous difference, whether it is consolidatedunder the vacuum, surcharge, or combined vacuum-surcharge preloading. The study shows that somephysical properties of the soft clayey soils are changed and mechanical properties are improved tosupport excessive loads transferred to the soil foundation due to construction.
基金supported by the Science and Technology Research Project of Jiangxi Education Department(Nos.GJJ2201509,GJJ2201501)the National Natural Science Foundation of China(Nos.51878671,51969018,52378344)+1 种基金the Natural Science Foundation of Jiangxi Province(No.20224BAB204076)the Young Scientific and Technological Talents Sponsorship Project in Ganpo Juncai Support Program(No.2023QT08).
文摘Time-dependent characteristics(TDCs)have been neglected in most previous studies investigating the deviation mechanisms of bridge pile foundations and evaluating the effectiveness of preventive measures.In this study,the stress-strain-time characteristics of soft soils were illustrated by consolidation-creep tests based on a typical engineering case.An extended Koppejan model was developed and then embedded in a finite element(FE)model via a user-material subroutine(UMAT).Based on the validated FE model,the time-dependent deformation mechanism of the pile foundation was revealed,and the preventive effect of applying micropiles and stress-release holes to control the deviation was investigated.The results show that the calculated maximum lateral displacement of the cap differs from the measured one by 6.5%,indicating that the derived extended Koppejan model reproduced the deviation process of the bridge cap-pile foundation with time.The additional load acting on the pile side caused by soil lateral deformation was mainly concentrated within the soft soil layer and increased with the increase in load duration.Compared with t=3 d(where t is surcharge time),the maximum lateral additional pressure acting on Pile 2#increased by approximately 47.0%at t=224 d.For bridge pile foundation deviation in deep soft soils,stress-release holes can provide better prevention compared to micropiles and are therefore recommended.
文摘This study uses Steel Slag Coarse Aggregate (SSCA) as a mixture replacement, preamble material to improve soft soils, which is economic, and has good effect environment. Recently, the development and utilization of by-product, waste and recycle materials must be studied and investigated as a source of improved material for soft soils as, an economic and good effect environmental. The study analyzes effects of both replaced mixtures, (SSCA) or (TSCA) on improved soil bearing capacity and expected settlement after verifying the model. Numerical modeling of the one of real store loaded strip using, PLAXIS, 2D, strain deformation behavior to achieve field visible and measured deformations of untreated soft soil. Numerical studies were devolved to investigate geomechanics parameters improved to compare between using (SSCA) or (TSCA) as, replacement mixture. Results demonstrate that using (SSCA) improved compressibility and strength of shallow soft soil layer significantly than using (TCSA) mixture, while (SSCA) improved strip footing ultimate bearing capacity, (UBC), by 84.4% compared with increase of 20.5% when using (TCSA) mixture at the same thickness. In addition, the study highlights the effective (SSCA) replacement thickness ranges between (0.65 ~ 0.80) footing width.
基金jointly sponsored by Fujian Province construction science and technology development research project(2023-B-07,2023-K-47,2022-K-118)。
文摘The coastal region of Fujian contains numerous existing stone masonry structures,many of which are constructed on soft soil sites.Previous studies have shown that the soil-structure interaction(SSI)effect on soft soil foundations can prolong the structure's natural vibration period and enhance its seismic response.We develops a soilstructure interaction system model and a comparative rigid foundation model using the finite element software LS-DYNA to investigate the impact of SSI on the dynamic characteristics and seismic response of stone structures.The results indicate that the SSI effect alters stone structures'dynamic properties and seismic response.This alteration is evident in the extended natural vibration period,which reduces overall stiffness,increases interstory displacement angles,and slightly decreases the acceleration response.Under both SSI and FIX systems,the structural failure mode is characterized by the external collapse of the second-story stone walls,which causes the roof stone slabs to lose support and fall,leading to overall collapse.The FIX system demonstrates better structural integrity and stability with slower crack development.In contrast,the SSI system exhibits cracks that appear earlier and develop more rapidly,causing more severe damage.The research findings provide a theoretical basis for the seismic reinforcement of existing stone structures on soft soil foundations.
基金National Natral Science Foundation of China(Grant No.59679018)
文摘The accumulative shear deformation of soft clays under cyclic loads is considered as pseudo-static creep. A pseudo-static elasto-plastic cyclic creep model is developed based on the visco-elasto-plastic theory. The parameters in the model are determined by cyclic triaxial soil tests. A method for analyzing the stability of offshore soft foundation under wave loads is given by combining the model with pseudo-static creep analysis. An example is analyzed by the method. The results show that the horizontal and vertical stability of foundations under wave loads can be analyzed by it and the analytical results are qualitatively consistent with the observed failure modes of shallow foundations.
文摘The reinforcement effects of geosynthetics in thick soft subsoil case and thin soft subsoil case are studied in this paper,and a Duncan Chang nonlinear numerical model based on the finite element method (FEM) is developed.Moreover,an important conclusion that the thickness of soft subsoil affects greatly the geotechnical behavior of geosynthetic reinforced embankments is drawn.A series of embankment built on soft subsoil is calculated using the FEM program.The results of the computer program,such as the lateral displacements,settlements,and stress level and shear stresses in the subsoil,are presented in great detail and the comparison of those results disposes clearly the huge discrepancy of reinforce benefit between the thick subsoil embankment and thin subsoil embankment.Reinforcement mechanism of geosynthetics is also discussed in this paper and several conclusions are reached.This paper also gives recommendations for design.
文摘The effect of the consolidation stress σc and the consolidation ratio kc on the cyclic degradation relation is studied by cyclic triaxial tests of soft clay. The results show that the normalized relation among the cyclic modulus, the damping ratio, the accumulative deviatoric strain and the cyclic degradation parameter can be established if the cyclic stress ratio and initial shear stress ratio are used as normalized parameters. Thereby the reasonable method is supplied to measure and apply cyclic parameters of soft clay.
文摘The use of geotextiles as a reinforcement material for improving the factor of safety against slope failure in embankments built on soft clay is becoming a common practice. This work is intended to help understand the effect of the geotextile reinforcement has on such embankments and to provide a design aid for civil engineers that enables them to quickly estimate the factor of safety against slope failure. Seventy four different cases were modelled and analyzed using a finite element software, GeoStudio 2018 R2. The results showed that the optimum improvement was achieved when using a single layer of geotextile reinforcement placed at the base of the embankment, by which the factor of safety increased by up to 40%. Adding a second layer, a third layer and a fourth layer, increases the safety factor by 2.5%, 1% and 0.5% respectively. Different charts for different heights of embankments were presented to aid in finding the most suitable slope angle and number of reinforcement layers required to achieve a certain safety factor.
基金the Educational Department of Liaoning Province Through Scientific Research Project(20060051)National Natural Science Foundation of China(50604009)Universities Excellent Talents Support Plan to Train Foundation of Liaoning(RC-04-13)
文摘In view of the characteristics of soft soil deep foundation pit for the construction and geotechnical characteristics of the special medium,it is difficult to calculate theoreti- cally accurately structural deformation of the foundation pit,so in the course of excavation on the construction of the information is particularly important.The analysis and compari- son of several popular non-linear forecasting methods,combined with the actual projects, set up a grey theoretical prediction model,time series forecasting model,improved neural network model to predict deformation of the foundation pit.The results show that the use of neural network to predict with high accuracy solution,it is the foundation deformation prediction effective way in underground works with good prospects.
基金National Natural Science Foundation of China(No.51778485).
文摘Construction issues of high-speed rail infrastructures have been increasingly concerned worldwide,of which the subgrade settlement in soft soil area becomes a particularly critical problem.Due to the high compressibility and low permeability of soft soil,the post-construction settlement of the subgrade is extremely difficult to control in these regions,which seriously threatens the operation safety of high-speed trains.In this work,the significant issues of high-speed railway subgrades in soft soil regions are discussed.The theoretical and experimental studies on foundation treatment methods for ballasted and ballastless tracks are reviewed.The settlement evolution and the settlement control effect of different treatment methods are highlighted.Control technologies of subgrade differential settlement are subsequently briefly presented.Settlement calculation algorithms of foundations reinforced by different treatment methods are discussed in detail.The defects of existing prediction methods and the challenges faced in their practical applications are analyzed.Furthermore,the guidance on future improvement in control theories and technologies of subgrade settlement for high-speed railway lines and the corresponding challenges are provided.
基金Project(2008ZA11) supported by State Key Laboratory of Subtropical Building Science in South China University of Technology, ChinaProject(20080430815) supported by China Postdoctoral Science Foundation
文摘A series of researches were carried out for the soil samples in the Pearl River Delta under the action of consolidation loads,such as the quantitative analyses of the pore scale,shape and size distributions of micro-structure units,with an environmental scanning electron microscope (ESEM),a mercury intrusion analyzer and a mineral diffractometer. The experimental results show that the consolidation pressures remarkably change the pore sizes and distribution characteristics of the silt,thus changing its compressibility and permeability. This can be proved by the fact that,in the earlier stage with a consolidation pressure of p<200 kPa,the pore sizes are greater and the compressibility and permeability coefficients are larger. However,they rapidly decrease with the increase in consolidation pressure. And in the later stage with a consolidation pressure of p>200 kPa,the pore sizes are smaller and the compressibility and permeability coefficients are less. Therefore,the empirical formulas of compression coefficient and permeability coefficient vs consolidation load and average pore diameter are deduced.
文摘Soft clays are problematic soils as they present high compressibility and low shear strength.There are several methods for improving in situ conditions of soft clays.Based on the geotechnical problem’s geometry and characteristics,the in situ conditions may require reinforcement to restrain instability and construction settlements.Granular columns reinforced by geosynthetic material are widely used to reduce settlements of embankments on soft clays.They also accelerate the consolidation rate by reducing the drainage path’s length and increasing the foundation soil’s bearing capacity.In this study,the performance of encased and layered granular columns in soft clay is investigated and discussed.The numerical results show the significance of geosynthetic stiffness and the column length on the embankment settlements.Furthermore,the results show that granular columns may play an important role in dissipating the excess pore water pressures and accelerating the consolidation settlements of embankments on soft clays.
文摘Abundant practical evidences have indicated that the soil progressively loses its structural configuration under construction disturbance and this can result in long-term macro deformation.The fundamental understanding of soil microstructure evolution subject to construction disturbance is necessary for controlling disturbance in excavation projects and minimizing ground settlement.The microstructure of Shanghai soft soil is investigated in this study.The laboratory isotropic compression tests are respectively performed on the virgin soil and the reconstructed Shanghai soft soil to investigate the macro deformation of soil under disturbance.Discrete element method model is used to study the micro particle level responses of soil under disturbance.The laboratory tests and numerical simulations provide theoretical basis for construction disturbance mitigation to ensure safety and stability of excavation projects.
基金Projects(50778181, 51178472) supported by the National Natural Science Foundation of China Project(2007045) supported by the Transportation Department of Hunan Province,China
文摘Finite element method was performed to investigate the influences of beam stiffness, foundation width and cushion thickness on the beating capacity of beam foundation on underlying weak laminated clay. The comparison between numerical results and results from field test including plate-bearing test and foundation settlement observation shows reasonable agreement. According to the numerical results, the beam width, length, cross section and cushion thickness were optimized. The results show that the stresses in subgrade soil decrease greatly with increasing the cushion thickness and width of foundation. However, the foundation settlement and influencing depth of displacement also increase correspondingly under conditions of relatively thinner cushion thickness. For the foundations on underlying weak layer, increasing foundation width merely might be inadequate for improving the bearing capacity, and the appropriate width and cushion thickness depend on the response of subgrade. A comparison between rigid and flexible beams was also discussed. The influence of a flexible beam foundation on subgrade is relatively smaller under the same loading conditions, and the flexible beam foundation appears more adaptable to various subgrades. The proposed flexible beam foundation was adopted in engineering. According to the calculation results, beam width of 2.4 m and cushion thickness of 0.8 m are proposed, and a flexible beam foundation is applied in the optimized design, which is confirmed reasonable by the actual engineering.
基金Natural Science Foundation of Jiangsu Province of China under Grant No.BK2012810
文摘The flow characteristics of foundation soils subjected to train loads can present engineering hazards in highspeed railways.In order to verify the feasibility of blending coarse sand in modifying soft subsoil,undrained pulling sphere tests were carried out and the train loads were simulated through localized and cyclic vibration at various frequencies.Laboratory testing results indicate that the fl ow characteristics of soft soil can be signifi cantly enhanced by high-frequency vibration;meanwhile the continuous increase in fl ow characteristics caused by cyclic vibration may be an important reason for the long-term settlement of soft subsoil.The infl uence of sand content on fl ow characteristics is also studied in detail,and it is shown that the addition of coarse sand can weaken the fl ow characteristics of soft soil induced by sudden vibration at lower than 50 Hz.Under the condition of cyclic vibration,the growth of the fl ow characteristics of sand-clay mixtures is mainly caused by the fi rst-time vibration in the cycle,and the increase in sand content can make the fl ow characteristics present a faster convergent tendency.
基金the Australian Research Council (ARC) Centre of Excellence in Geotechnical Science and Engineering and the Centre for Geomechanics and Railway Engineering (CGRE) of University of Wollongong (UOW) for the financial support
文摘In recent years, reconstituted small samples have often been used to assess the performance of radial consolidation due to prefabricated vertical drains(PVDs), but the permeability and compressibility of samples of undisturbed soil often differ from those of the remoulded ones. The problem seems more complex in marine environment due to the presence of random coarse particles including gravels, shells and natural partings. Performing small-scale laboratory experiment with reconstituted samples, especially in marine environment, cannot predict the exact soil behaviour in the field. This paper describes an experimental programme that measures radial consolidation using a conventional Rowe cell and a largescale consolidometer, where the samples of undisturbed soil obtained from a site along the Pacific Highway(north of Sydney) were compared using measured settlements and excess pore pressures.Moreover, this paper highlights the implications of the smear effect and sample size influence, which are imperative in translating the laboratory testing practices to actual real-life behaviour. The effect of vacuum pressure on the coefficient of radial consolidation of a large-scale undisturbed test specimen is also discussed. The paper demonstrates that the extent of smear zone in the field can be very similar to the large-scale laboratory consolidation test using a scaled-down drain and mandrel, but considerably different from the data obtained for small laboratory specimens.
