Top structure and basement will confront the risk of being damaged on account of large stress and strain fields incurred by differential uplift and settlement between inner column and diaphragm wall in top-down method...Top structure and basement will confront the risk of being damaged on account of large stress and strain fields incurred by differential uplift and settlement between inner column and diaphragm wall in top-down method. Top-down excavation of the Metro Line 10 in Shanghai was modeled with finite element analysis software ABAQUS and parameters of subsoil were obtained by inverse analysis. Based on the finite element model and parameters, changes in the following factors were made to find more effective methods to restrain differential uplift and settlement: length of diaphragm wall, thickness of jet-grouting reinforcement layer, ways of subsoil reinforcement, sequence of pit excavation, connection between slabs and diaphragm wall or column and width of pit. Several significant results are acquired. The longer the diaphragm wall is, the greater the differential uplift between column and diaphragm wall is. Rigidity of roof slab is in general not strong enough to keep diaphragm wall and column undergoing the same uplift during excavation; Uplift at head of column and differential uplift between column and diaphragm wall decrease when subsoil from-16.6 to-43 m in pit is reinforced through jet-grouting. But, as excavation proceeds to a lower level, benefit from soil reinforcement diminishes. During the process applying vertical load, the larger the depth of diaphragm wall is, the smaller the settlement is at head of column and diaphragm wall, and the greater the differential settlement is between column and diaphragm wall. When friction connection is implemented between column, diaphragm wall and floor slabs, uplifts at head of column and diaphragm wall are larger than those of the case when tie connection is implemented, and so does differential uplift between column and diaphragm wall. The maximum deflection of diaphragm wall decreases by 58% on account of soil reinforcement in pit. The maximum deflection of diaphragm wall decreases by 61.2% when friction connection is implemented instead of tie connection.展开更多
Deep excavation during the construction of underground systems can cause movement on the ground,especially in soft clay layers.At high levels,excessive ground movements can lead to severe damage to adjacent structures...Deep excavation during the construction of underground systems can cause movement on the ground,especially in soft clay layers.At high levels,excessive ground movements can lead to severe damage to adjacent structures.In this study,finite element analyses(FEM)and the hardening small strain(HSS)model were performed to investigate the deflection of the diaphragm wall in the soft clay layer induced by braced excavations.Different geometric and mechanical properties of the wall were investigated to study the deflection behavior of the wall in soft clays.Accordingly,1090 hypothetical cases were surveyed and simulated based on the HSS model and FEM to evaluate the wall deflection behavior.The results were then used to develop an intelligent model for predicting wall deflection using the functional linked neural network(FLNN)with different functional expansions and activation functions.Although the FLNN is a novel approach to predict wall deflection;however,in order to improve the accuracy of the FLNN model in predicting wall deflection,three swarm-based optimization algorithms,such as artificial bee colony(ABC),Harris’s hawk’s optimization(HHO),and hunger games search(HGS),were hybridized to the FLNN model to generate three novel intelligent models,namely ABC-FLNN,HHO-FLNN,HGS-FLNN.The results of the hybrid models were then compared with the basic FLNN and MLP models.They revealed that FLNN is a good solution for predicting wall deflection,and the application of different functional expansions and activation functions has a significant effect on the outcome predictions of the wall deflection.It is remarkably interesting that the performance of the FLNN model was better than the MLP model with a mean absolute error(MAE)of 19.971,root-mean-squared error(RMSE)of 24.574,and determination coefficient(R^(2))of 0.878.Meanwhile,the performance of the MLP model only obtained an MAE of 20.321,RMSE of 27.091,and R^(2)of 0.851.Furthermore,the results also indicated that the proposed hybrid models,i.e.,ABC-FLNN,HHO-FLNN,HGS-FLNN,yielded more superior performances than those of the FLNN and MLP models in terms of the prediction of deflection behavior of diaphragm walls with an MAE in the range of 11.877 to 12.239,RMSE in the range of 15.821 to 16.045,and R^(2)in the range of 0.949 to 0.951.They can be used as an alternative tool to simulate diaphragm wall deflections under different conditions with a high degree of accuracy.展开更多
According to the blasting construction of the diaphragm wall of Puxi approaching section of East Fuxing Road river-crossing tunnel, the monitoring project of the vibration of the existing tun-nel induced by the blasti...According to the blasting construction of the diaphragm wall of Puxi approaching section of East Fuxing Road river-crossing tunnel, the monitoring project of the vibration of the existing tun-nel induced by the blasting construction is put forward, which includes the sensors’ location, moni-tor method and the vibration monitoring system. Based on the monitoring data of the explosion vibration, the vibration wave forms, velocities, acceleration responses, main frequencies and fields of measure points are analyzed under the conditions of three locations and different charge quanti-ties. According to the safety-judging standard of explosion vibration, the conclusion that the exist- ing tunnel is safe under the explosion vibration is then drawn. Furthermore, the spectrum character-istics of three explosion vibrations and the spectrum changing properties of explosion vi-bration wave transmitting in different directions are concluded, which can provide reference to similar projects.展开更多
This paper presents a case study on an ultra-deep diaphragm wall with a depth of 110 m constructed in Ningbo City. The in-situ application shows that using Bauer BC40 cutter machine in conjunction with cutter wheels s...This paper presents a case study on an ultra-deep diaphragm wall with a depth of 110 m constructed in Ningbo City. The in-situ application shows that using Bauer BC40 cutter machine in conjunction with cutter wheels specified for different strata would be qualified for constructing the 110 m diaphragm wall with high efficiency and precision given that the quality of slurry and poured concrete can be guaranteed. The ground settlement can be effectively controlled by using the overlapping construction method. Sliding failure as a whole characterized by pronounced lateral deformation is likely to occur in the upper muddy clay layer due to its high compressibility and sensitivity. In contrast, local collapse of trench walls tends to happen in the sandy silt strata. Furthermore, careful attention should be paid to sandy silt during the entire construction period as the vertical displacement of the sandy silt continues to develop even atter concrete pouring.展开更多
In this paper,a seismic and vibration reduction measure of subway station is developed by setting a segmented isolation layer between the sidewall of structure and the diaphragm wall.The segmented isolation layer cons...In this paper,a seismic and vibration reduction measure of subway station is developed by setting a segmented isolation layer between the sidewall of structure and the diaphragm wall.The segmented isolation layer consists of a rigid layer and a flexible layer.The rigid layer is installed at the joint section between the structural sidewall and slab,and the flexible layer is installed at the remaining sections.A diaphragm wall-segmented isolation layer-subway station structure system is constructed.Seismic and vibration control performance of the diaphragm wall-segmented isolation layer-subway station structure system is evaluated by the detailed numerical analysis.Firstly,a three-dimensional nonlinear time-history analysis is carried out to study the seismic response of the station structure by considering the effect of different earthquake motions and stiffness of segmented isolation layer.Subsequently,the vibration response of site under training loading is also studied by considering the influence of different train velocities and stiffness of the segmented isolation layer.Numerical results demonstrate that the diaphragm wall-segmented isolation layer-subway station structure system can not only effectively reduce the lateral deformation of station structure,but also reduce the tensile damage of the roof slab.On the other hand,the developed reduction measure can also significantly reduce the vertical peak displacements of site under training loading.展开更多
Construction of diaphragm wall panels may cause considerable stress changes in heavily overconsol- idated soil deposits and can induce substantial ground movement. The 3D Lagrangian method was adopted to model the mec...Construction of diaphragm wall panels may cause considerable stress changes in heavily overconsol- idated soil deposits and can induce substantial ground movement. The 3D Lagrangian method was adopted to model the mechanical response of ground, including horizontal normal stress and shear stress, lateral ground displacement and vertical ground surface settlement, during the slurry trenching and concreting of diaphragm wall panels. Numerical results show that slurry trenching leads to horizontal stress relief of ground, reducing the horizontal stress of the ground from initial K0 pressure to hydrostatic betonite pressure. Wet concrete pressure lies between the hydrostatic bentonite pressure and the initial K0 pressure, so it can compensate partially the horizontal stress loss of the ground adjacent to the trench and thus reduce the lateral movement of the trench face as well as the vertical settlement of the ground surface.展开更多
The rectangular closed diaphragm(RCD)wall is a new type of bridge foundation.Compared to barrette foundation,measuring the performance of RCD walls is relatively complicated because of their incorporation of a soil co...The rectangular closed diaphragm(RCD)wall is a new type of bridge foundation.Compared to barrette foundation,measuring the performance of RCD walls is relatively complicated because of their incorporation of a soil core.Using the FLAC3D software,this paper investigates the deformation properties,soil resistance and skin friction of a laterally loaded RCD wall as well as the settlement,axial force and load-sharing ratio of a vertically loaded RCD wall.Special attention is given to the analysis of factors that influence the performance of the soil core.It was found that under lateral loading,the RCD wall behaves as an end-bearing friction wall during the entire loading process.The relative displacement between the wall body and the soil core primarily occurs below the rotation point,and the horizontal displacement of the soil core is greater than that of the wall body.Under vertical loading,the degree of inner skin friction around the bottom of the soil core and the proportion of the loading supported by the soil core increase with increased cross-section size.The wall depth is directly proportional to the loading supported by the outer skin friction and the tip resistance of the wall body and is inversely proportional to the loading borne by the soil core.展开更多
Rectangular-closed-diaphragm-wall foundation is a new type of bridge foundation.Diaphragm wallsoil-cap interaction was studied using a model test.It was observed that the distribution of soil resistance under the cap ...Rectangular-closed-diaphragm-wall foundation is a new type of bridge foundation.Diaphragm wallsoil-cap interaction was studied using a model test.It was observed that the distribution of soil resistance under the cap is not homogeneous.The soil resistance in the corner under the cap is larger than that in the border;and that in the center is the smallest.The distribution of soil resistance under the cap will be more uniform,if the sectional area of soil core is enlarged within a certain range.Due to the existence of cap,there is a“weakening effect”in inner shaft resistance of the upper wall segments,and there is“enhancement effect”in the lower wall segments and in toe resistance.The load shearing percentage of soil resistance under the cap is 10%–20%.It is unreasonable to ignore the effects of the cap and the soil resistance under the cap in bearing capacity calculations.展开更多
There are two major challenges faced by modern society:energy security,and lowering carbon dioxide gas emissions.Thermo-active diaphragm walls have a large potential to remedy one of these problems,since they are a re...There are two major challenges faced by modern society:energy security,and lowering carbon dioxide gas emissions.Thermo-active diaphragm walls have a large potential to remedy one of these problems,since they are a renewable energy technology that uses underground infrastructure as a heat exchange medium.However,extensive research is required to determine the effects of cyclic heating and cooling on their geotechnical and structural performance.In this paper,a series of detailed finite element analyses are carried out to capture the fully coupled thermo-hydro-mechanical response bf the ground and diaphragm wall.It is demonstrated that the thermal operation of the diaphragm wall causes changes in soil temperature,thermal expansion/shrinkage of pore water,and total stress applied on the diaphragm wall.These,in turmn,cause displacements of the diaphragm wall and variations of the bending moments.However,these effects on the performance of diaphragm wall are not significant.The thermally induced bending strain is mainly governed by the temperature differential and uneven thermal expansion/shrinkage across the wall.展开更多
The deformation law of the cellular diaphragm wall in deep foundation pits was studied through numerical simulation.Based on the example of the dock wall in engineering,the full three-dimensional finite element model ...The deformation law of the cellular diaphragm wall in deep foundation pits was studied through numerical simulation.Based on the example of the dock wall in engineering,the full three-dimensional finite element model was used to simulate the excavation of the foundation pit.Interaction between the cellular diaphragm wall and the soil was also taken into account in the calculation.The results indicated that the maximum lateral displacement,which is the evaluation index of sensitivity analysis,appeared on the top of the interior longitudinal wall with an excavation depth of 10 m.The centrifuge model test was carried out to study the deformation regulation for a cellular diaphragm wall.The most sensitive factor was found by adjusting the length of the partition wall,the spacing of the partition wall and the thickness of the wall.In the end,a suggestion was proposed to optimize the cellular diaphragm by adjusting the length of the partition wall.展开更多
The high earth and rockfill cofferdam of Three Gorges Project employs plastic concrete diaphragm walls as seepage barrier. In view of the importance and technical difficulty of the cofferdams, the behavior of plastic ...The high earth and rockfill cofferdam of Three Gorges Project employs plastic concrete diaphragm walls as seepage barrier. In view of the importance and technical difficulty of the cofferdams, the behavior of plastic concrete and the diaphragm walls within the cofferdams was studied. Plastic concrete samples taken from concrete mixer in the dam site were tested by using large triaxial testing apparatus in Tsinghua University. Mechanical properties and parameters of Duncan Chang nonlinear elastic model were obtained. Test results indicated that, comparing with ordinary concrete, the materials have the features of low modulus of deformation and favorable impermeability. The analysis of stresses and deformations of the diaphragm walls was performed by means of finite element method (FEM), using parameters obtained from the result of triaxial tests. Calculation results were discussed.展开更多
When diaphragm wall is used as the permanent vertical bearing structure,design standard of the bored pile adopted has to induce the risk or iste. The vertical load transfer mechanism and bearing capacity of the diaphr...When diaphragm wall is used as the permanent vertical bearing structure,design standard of the bored pile adopted has to induce the risk or iste. The vertical load transfer mechanism and bearing capacity of the diaphragm wall are examined by a field testing program at the site in Shanghai soft clays. Test results indicate that the diaphragm wall almost behaves as a rigid body under the vertical load. It induces that the skin friction and the toe resistance of the wall develop simultaneously. The skin friction resistance carries the large portion of the vertical load,and the toe resistance of the wall provides about 9.2% of vertical bearing load. Toe-grouting technique is found to achieve a remarkable increase in skin friction and toe resistance. The toe resistance of the grouted wall provides about 17.5% of vertical load.展开更多
Light-frame timber buildings are often stabilized against lateral loads by using diaphragm action of roofs, floors and walls. The mechanical behavior of the sheathing-to-framing joints has a significant impact on the ...Light-frame timber buildings are often stabilized against lateral loads by using diaphragm action of roofs, floors and walls. The mechanical behavior of the sheathing-to-framing joints has a significant impact on the structural performance of shear walls. Most sheathing-to-framing joints show nonlinear load-displacement characteristics with plastic behavior. This paper is focused on the finite element modeling of shear walls. The purpose is to present a new shear connector element based on the theory of continuum plasticity. The incremental load-displacement relationship is derived based on the elastic-plastic stiffness tensor including the elastic stiffness tensor, the plastic modulus, a function representing the yield criterion and a hardening rule, and function representing the plastic potential. The plastic properties are determined from experimental results obtained from testing actual connections. Load-displacement curves for shear walls are calculated using the shear connector model and they are compared with experimental and other computational results. Also, the ultimate horizontal load-carrying capacity is compared to results obtained by an analytical plastic design method. Good agreements are found.展开更多
A 2D and 3D kinematically admissible rotational failure mechanism is presented for homogeneous slurry trenches in frictional/cohesive soils.Analytical approaches are derived to obtain the upper bounds on slurry trench...A 2D and 3D kinematically admissible rotational failure mechanism is presented for homogeneous slurry trenches in frictional/cohesive soils.Analytical approaches are derived to obtain the upper bounds on slurry trench stability in the strict framework of limit analysis.It is shown that the factor of safety from a 3D analysis will be greater than that from a 2D analysis.Compared with the limit equilibrium method,the limit analysis method yields an unconservative estimate on the safety factors.A set of examples are presented in a wide range of parameters for 2D and 3D homogeneous slurry trenches.The factor of safety increases with increasing slurry and soil bulk density ratio,cohesion,friction angle,and with decreasing slurry level depth and trench depth ratio,trench width and depth ratio.It is convenient to assess the safety for the homogeneous slurry trenches in practical applications.展开更多
This paper presents a case study on groundwater control and environmental protection during a deep excavation of the foundation pit for the Liyang Road Station of Metro Line 10 in Shanghai.A three-dimensional finite e...This paper presents a case study on groundwater control and environmental protection during a deep excavation of the foundation pit for the Liyang Road Station of Metro Line 10 in Shanghai.A three-dimensional finite element simulation model was constructed to quantify the effects of a dewatering process on the environment around the excavation pit.To understand the decrease in the groundwater level around the foundation pit,the ground settlement and groundwater level were studied.During the excavation,environmental protection methods were used in the design of the optimal watering system to check its detrimental environmental effects.The effects of the diaphragm wall and horizontal barrier system were analyzed by varying their insertion depths and the resulting changes in the ground settlement and groundwater level were studied.It was found that increasing the insertion depth of the diaphragm wall reduced settlement near the excavation site but increased the construction costs.The diaphragm wall used in combination with a horizontal barrier was found to be effective in arresting the decrease in groundwater level and reducing settlement around the excavation site.展开更多
The assessment of the seismic safety of underground structures,either tunnels or large station boxes,should not be overlooked especially in densely populated areas,even with low to moderate seismicity.For underground ...The assessment of the seismic safety of underground structures,either tunnels or large station boxes,should not be overlooked especially in densely populated areas,even with low to moderate seismicity.For underground structures,an important issue is the estimation of the seismic actions acting on the structure;only few experimental evidences are available for multi-level propped walls.For tunnels,it is generally assumed that their seismic behavior in soft ground is governed by the surrounding soil,while the inertial load contribution of the underground structure itself is negligible.In both cases,recent numerical studies proved that advanced dynamic analyses can provide satisfactory interpretation of non-linear soil-structure interaction during earthquakes.In this paper,a real case study,represented by a large open multi-propped excavation and a circular segmented tunnel in a densely urbanized area of the city center in Napoli,has been used to investigate some of the mentioned aspects.Accurate geotechnical characterization and choice of the reference input motions lead to a first estimate of the free-field ground motion,which was subsequently used for pseudo-static decoupled analyses.For the complexity of both excavation geometry and staged construction,a full dynamic analysis was considered neither affordable nor reliable for the multi-propped station box;thus two conventional pseudo-static analyses,applying either a displacement-based or a force-based approach,were carried out.In the case of the tunnel,the seismic increments of internal forces in the lining could be calculated through both a simplified pseudostatic analysis and a full dynamic analysis,showing a satisfying agreement.Overall,the results of the study demonstrated that the seismic increments of internal forces in the diaphragm walls of the station and in the segmented lining of the tunnel were quite significant.The case study encourages improving the reliability of simplified methods based on the more advanced dynamic approaches.展开更多
基金Projects(51208071,51108312) supported by the National Natural Science Foundation of China
文摘Top structure and basement will confront the risk of being damaged on account of large stress and strain fields incurred by differential uplift and settlement between inner column and diaphragm wall in top-down method. Top-down excavation of the Metro Line 10 in Shanghai was modeled with finite element analysis software ABAQUS and parameters of subsoil were obtained by inverse analysis. Based on the finite element model and parameters, changes in the following factors were made to find more effective methods to restrain differential uplift and settlement: length of diaphragm wall, thickness of jet-grouting reinforcement layer, ways of subsoil reinforcement, sequence of pit excavation, connection between slabs and diaphragm wall or column and width of pit. Several significant results are acquired. The longer the diaphragm wall is, the greater the differential uplift between column and diaphragm wall is. Rigidity of roof slab is in general not strong enough to keep diaphragm wall and column undergoing the same uplift during excavation; Uplift at head of column and differential uplift between column and diaphragm wall decrease when subsoil from-16.6 to-43 m in pit is reinforced through jet-grouting. But, as excavation proceeds to a lower level, benefit from soil reinforcement diminishes. During the process applying vertical load, the larger the depth of diaphragm wall is, the smaller the settlement is at head of column and diaphragm wall, and the greater the differential settlement is between column and diaphragm wall. When friction connection is implemented between column, diaphragm wall and floor slabs, uplifts at head of column and diaphragm wall are larger than those of the case when tie connection is implemented, and so does differential uplift between column and diaphragm wall. The maximum deflection of diaphragm wall decreases by 58% on account of soil reinforcement in pit. The maximum deflection of diaphragm wall decreases by 61.2% when friction connection is implemented instead of tie connection.
基金financially supported by the Natural Science Foundation of Hunan Province(2021JJ30679)。
文摘Deep excavation during the construction of underground systems can cause movement on the ground,especially in soft clay layers.At high levels,excessive ground movements can lead to severe damage to adjacent structures.In this study,finite element analyses(FEM)and the hardening small strain(HSS)model were performed to investigate the deflection of the diaphragm wall in the soft clay layer induced by braced excavations.Different geometric and mechanical properties of the wall were investigated to study the deflection behavior of the wall in soft clays.Accordingly,1090 hypothetical cases were surveyed and simulated based on the HSS model and FEM to evaluate the wall deflection behavior.The results were then used to develop an intelligent model for predicting wall deflection using the functional linked neural network(FLNN)with different functional expansions and activation functions.Although the FLNN is a novel approach to predict wall deflection;however,in order to improve the accuracy of the FLNN model in predicting wall deflection,three swarm-based optimization algorithms,such as artificial bee colony(ABC),Harris’s hawk’s optimization(HHO),and hunger games search(HGS),were hybridized to the FLNN model to generate three novel intelligent models,namely ABC-FLNN,HHO-FLNN,HGS-FLNN.The results of the hybrid models were then compared with the basic FLNN and MLP models.They revealed that FLNN is a good solution for predicting wall deflection,and the application of different functional expansions and activation functions has a significant effect on the outcome predictions of the wall deflection.It is remarkably interesting that the performance of the FLNN model was better than the MLP model with a mean absolute error(MAE)of 19.971,root-mean-squared error(RMSE)of 24.574,and determination coefficient(R^(2))of 0.878.Meanwhile,the performance of the MLP model only obtained an MAE of 20.321,RMSE of 27.091,and R^(2)of 0.851.Furthermore,the results also indicated that the proposed hybrid models,i.e.,ABC-FLNN,HHO-FLNN,HGS-FLNN,yielded more superior performances than those of the FLNN and MLP models in terms of the prediction of deflection behavior of diaphragm walls with an MAE in the range of 11.877 to 12.239,RMSE in the range of 15.821 to 16.045,and R^(2)in the range of 0.949 to 0.951.They can be used as an alternative tool to simulate diaphragm wall deflections under different conditions with a high degree of accuracy.
文摘According to the blasting construction of the diaphragm wall of Puxi approaching section of East Fuxing Road river-crossing tunnel, the monitoring project of the vibration of the existing tun-nel induced by the blasting construction is put forward, which includes the sensors’ location, moni-tor method and the vibration monitoring system. Based on the monitoring data of the explosion vibration, the vibration wave forms, velocities, acceleration responses, main frequencies and fields of measure points are analyzed under the conditions of three locations and different charge quanti-ties. According to the safety-judging standard of explosion vibration, the conclusion that the exist- ing tunnel is safe under the explosion vibration is then drawn. Furthermore, the spectrum character-istics of three explosion vibrations and the spectrum changing properties of explosion vi-bration wave transmitting in different directions are concluded, which can provide reference to similar projects.
基金Funded by the National Basic Research Program of China(973 Program,No.2014CB046905)the National Natural Science Foundation of China(Grant Nos.41172249 and 51509186)+1 种基金the State Key Laboratory for Geomechanics and Deep Underground Engineering(No.SKLGDUEK1303)the funding provided by Zhuhai Da Heng Qin Company Limited(Grant No.SG25-2014-173B1)
文摘This paper presents a case study on an ultra-deep diaphragm wall with a depth of 110 m constructed in Ningbo City. The in-situ application shows that using Bauer BC40 cutter machine in conjunction with cutter wheels specified for different strata would be qualified for constructing the 110 m diaphragm wall with high efficiency and precision given that the quality of slurry and poured concrete can be guaranteed. The ground settlement can be effectively controlled by using the overlapping construction method. Sliding failure as a whole characterized by pronounced lateral deformation is likely to occur in the upper muddy clay layer due to its high compressibility and sensitivity. In contrast, local collapse of trench walls tends to happen in the sandy silt strata. Furthermore, careful attention should be paid to sandy silt during the entire construction period as the vertical displacement of the sandy silt continues to develop even atter concrete pouring.
基金supported by the National Natural Science Foundation of China(Grant No.52278476)China Postdoctoral Science Foundation(Grant No.2022M721877).
文摘In this paper,a seismic and vibration reduction measure of subway station is developed by setting a segmented isolation layer between the sidewall of structure and the diaphragm wall.The segmented isolation layer consists of a rigid layer and a flexible layer.The rigid layer is installed at the joint section between the structural sidewall and slab,and the flexible layer is installed at the remaining sections.A diaphragm wall-segmented isolation layer-subway station structure system is constructed.Seismic and vibration control performance of the diaphragm wall-segmented isolation layer-subway station structure system is evaluated by the detailed numerical analysis.Firstly,a three-dimensional nonlinear time-history analysis is carried out to study the seismic response of the station structure by considering the effect of different earthquake motions and stiffness of segmented isolation layer.Subsequently,the vibration response of site under training loading is also studied by considering the influence of different train velocities and stiffness of the segmented isolation layer.Numerical results demonstrate that the diaphragm wall-segmented isolation layer-subway station structure system can not only effectively reduce the lateral deformation of station structure,but also reduce the tensile damage of the roof slab.On the other hand,the developed reduction measure can also significantly reduce the vertical peak displacements of site under training loading.
基金the National Natural Science Foundation of China (No. 50679041)the Shanghai Leading Academic Discipline Project (No. B208)
文摘Construction of diaphragm wall panels may cause considerable stress changes in heavily overconsol- idated soil deposits and can induce substantial ground movement. The 3D Lagrangian method was adopted to model the mechanical response of ground, including horizontal normal stress and shear stress, lateral ground displacement and vertical ground surface settlement, during the slurry trenching and concreting of diaphragm wall panels. Numerical results show that slurry trenching leads to horizontal stress relief of ground, reducing the horizontal stress of the ground from initial K0 pressure to hydrostatic betonite pressure. Wet concrete pressure lies between the hydrostatic bentonite pressure and the initial K0 pressure, so it can compensate partially the horizontal stress loss of the ground adjacent to the trench and thus reduce the lateral movement of the trench face as well as the vertical settlement of the ground surface.
基金The authors gratefully acknowledge the financial support of this work,which was provided by the National Natural Science Foundation of China(Grant Nos.41172260 and 51108393)the Specialized Research Fund for the Doctoral Program of Higher Education(No.20110184110018)the National Basic Research Program of China(No.2008CB425801).
文摘The rectangular closed diaphragm(RCD)wall is a new type of bridge foundation.Compared to barrette foundation,measuring the performance of RCD walls is relatively complicated because of their incorporation of a soil core.Using the FLAC3D software,this paper investigates the deformation properties,soil resistance and skin friction of a laterally loaded RCD wall as well as the settlement,axial force and load-sharing ratio of a vertically loaded RCD wall.Special attention is given to the analysis of factors that influence the performance of the soil core.It was found that under lateral loading,the RCD wall behaves as an end-bearing friction wall during the entire loading process.The relative displacement between the wall body and the soil core primarily occurs below the rotation point,and the horizontal displacement of the soil core is greater than that of the wall body.Under vertical loading,the degree of inner skin friction around the bottom of the soil core and the proportion of the loading supported by the soil core increase with increased cross-section size.The wall depth is directly proportional to the loading supported by the outer skin friction and the tip resistance of the wall body and is inversely proportional to the loading borne by the soil core.
基金supported by the National Basic Research program(2008CB425801)。
文摘Rectangular-closed-diaphragm-wall foundation is a new type of bridge foundation.Diaphragm wallsoil-cap interaction was studied using a model test.It was observed that the distribution of soil resistance under the cap is not homogeneous.The soil resistance in the corner under the cap is larger than that in the border;and that in the center is the smallest.The distribution of soil resistance under the cap will be more uniform,if the sectional area of soil core is enlarged within a certain range.Due to the existence of cap,there is a“weakening effect”in inner shaft resistance of the upper wall segments,and there is“enhancement effect”in the lower wall segments and in toe resistance.The load shearing percentage of soil resistance under the cap is 10%–20%.It is unreasonable to ignore the effects of the cap and the soil resistance under the cap in bearing capacity calculations.
文摘There are two major challenges faced by modern society:energy security,and lowering carbon dioxide gas emissions.Thermo-active diaphragm walls have a large potential to remedy one of these problems,since they are a renewable energy technology that uses underground infrastructure as a heat exchange medium.However,extensive research is required to determine the effects of cyclic heating and cooling on their geotechnical and structural performance.In this paper,a series of detailed finite element analyses are carried out to capture the fully coupled thermo-hydro-mechanical response bf the ground and diaphragm wall.It is demonstrated that the thermal operation of the diaphragm wall causes changes in soil temperature,thermal expansion/shrinkage of pore water,and total stress applied on the diaphragm wall.These,in turmn,cause displacements of the diaphragm wall and variations of the bending moments.However,these effects on the performance of diaphragm wall are not significant.The thermally induced bending strain is mainly governed by the temperature differential and uneven thermal expansion/shrinkage across the wall.
文摘The deformation law of the cellular diaphragm wall in deep foundation pits was studied through numerical simulation.Based on the example of the dock wall in engineering,the full three-dimensional finite element model was used to simulate the excavation of the foundation pit.Interaction between the cellular diaphragm wall and the soil was also taken into account in the calculation.The results indicated that the maximum lateral displacement,which is the evaluation index of sensitivity analysis,appeared on the top of the interior longitudinal wall with an excavation depth of 10 m.The centrifuge model test was carried out to study the deformation regulation for a cellular diaphragm wall.The most sensitive factor was found by adjusting the length of the partition wall,the spacing of the partition wall and the thickness of the wall.In the end,a suggestion was proposed to optimize the cellular diaphragm by adjusting the length of the partition wall.
文摘The high earth and rockfill cofferdam of Three Gorges Project employs plastic concrete diaphragm walls as seepage barrier. In view of the importance and technical difficulty of the cofferdams, the behavior of plastic concrete and the diaphragm walls within the cofferdams was studied. Plastic concrete samples taken from concrete mixer in the dam site were tested by using large triaxial testing apparatus in Tsinghua University. Mechanical properties and parameters of Duncan Chang nonlinear elastic model were obtained. Test results indicated that, comparing with ordinary concrete, the materials have the features of low modulus of deformation and favorable impermeability. The analysis of stresses and deformations of the diaphragm walls was performed by means of finite element method (FEM), using parameters obtained from the result of triaxial tests. Calculation results were discussed.
基金the National Natural Science Foundation of China(No.50679041)the Shanghai Leading Academic Discipline Project(No.B208)
文摘When diaphragm wall is used as the permanent vertical bearing structure,design standard of the bored pile adopted has to induce the risk or iste. The vertical load transfer mechanism and bearing capacity of the diaphragm wall are examined by a field testing program at the site in Shanghai soft clays. Test results indicate that the diaphragm wall almost behaves as a rigid body under the vertical load. It induces that the skin friction and the toe resistance of the wall develop simultaneously. The skin friction resistance carries the large portion of the vertical load,and the toe resistance of the wall provides about 9.2% of vertical bearing load. Toe-grouting technique is found to achieve a remarkable increase in skin friction and toe resistance. The toe resistance of the grouted wall provides about 17.5% of vertical load.
文摘Light-frame timber buildings are often stabilized against lateral loads by using diaphragm action of roofs, floors and walls. The mechanical behavior of the sheathing-to-framing joints has a significant impact on the structural performance of shear walls. Most sheathing-to-framing joints show nonlinear load-displacement characteristics with plastic behavior. This paper is focused on the finite element modeling of shear walls. The purpose is to present a new shear connector element based on the theory of continuum plasticity. The incremental load-displacement relationship is derived based on the elastic-plastic stiffness tensor including the elastic stiffness tensor, the plastic modulus, a function representing the yield criterion and a hardening rule, and function representing the plastic potential. The plastic properties are determined from experimental results obtained from testing actual connections. Load-displacement curves for shear walls are calculated using the shear connector model and they are compared with experimental and other computational results. Also, the ultimate horizontal load-carrying capacity is compared to results obtained by an analytical plastic design method. Good agreements are found.
基金Project (Nos. 41002095,41172251 and 41272317) supported by the National Natural Science Foundation of China
文摘A 2D and 3D kinematically admissible rotational failure mechanism is presented for homogeneous slurry trenches in frictional/cohesive soils.Analytical approaches are derived to obtain the upper bounds on slurry trench stability in the strict framework of limit analysis.It is shown that the factor of safety from a 3D analysis will be greater than that from a 2D analysis.Compared with the limit equilibrium method,the limit analysis method yields an unconservative estimate on the safety factors.A set of examples are presented in a wide range of parameters for 2D and 3D homogeneous slurry trenches.The factor of safety increases with increasing slurry and soil bulk density ratio,cohesion,friction angle,and with decreasing slurry level depth and trench depth ratio,trench width and depth ratio.It is convenient to assess the safety for the homogeneous slurry trenches in practical applications.
基金This research was funded by the Innovative Research Funding of the Science and Technology Commission of Shanghai Municipality(Grant No.18DZ1201102).This financial support is greatly appreciated.
文摘This paper presents a case study on groundwater control and environmental protection during a deep excavation of the foundation pit for the Liyang Road Station of Metro Line 10 in Shanghai.A three-dimensional finite element simulation model was constructed to quantify the effects of a dewatering process on the environment around the excavation pit.To understand the decrease in the groundwater level around the foundation pit,the ground settlement and groundwater level were studied.During the excavation,environmental protection methods were used in the design of the optimal watering system to check its detrimental environmental effects.The effects of the diaphragm wall and horizontal barrier system were analyzed by varying their insertion depths and the resulting changes in the ground settlement and groundwater level were studied.It was found that increasing the insertion depth of the diaphragm wall reduced settlement near the excavation site but increased the construction costs.The diaphragm wall used in combination with a horizontal barrier was found to be effective in arresting the decrease in groundwater level and reducing settlement around the excavation site.
基金This work was carried out as part of WP3‘Tunnels’of the sub-project on‘Earthquake Geotechnical Engineering’,in the framework of the research programme funded by Italian Civil Protection through the ReLUIS Consortium.Dr.Lorenza Evangelista is warmly acknowledged for the help provided in preparing the map in Fig.1.
文摘The assessment of the seismic safety of underground structures,either tunnels or large station boxes,should not be overlooked especially in densely populated areas,even with low to moderate seismicity.For underground structures,an important issue is the estimation of the seismic actions acting on the structure;only few experimental evidences are available for multi-level propped walls.For tunnels,it is generally assumed that their seismic behavior in soft ground is governed by the surrounding soil,while the inertial load contribution of the underground structure itself is negligible.In both cases,recent numerical studies proved that advanced dynamic analyses can provide satisfactory interpretation of non-linear soil-structure interaction during earthquakes.In this paper,a real case study,represented by a large open multi-propped excavation and a circular segmented tunnel in a densely urbanized area of the city center in Napoli,has been used to investigate some of the mentioned aspects.Accurate geotechnical characterization and choice of the reference input motions lead to a first estimate of the free-field ground motion,which was subsequently used for pseudo-static decoupled analyses.For the complexity of both excavation geometry and staged construction,a full dynamic analysis was considered neither affordable nor reliable for the multi-propped station box;thus two conventional pseudo-static analyses,applying either a displacement-based or a force-based approach,were carried out.In the case of the tunnel,the seismic increments of internal forces in the lining could be calculated through both a simplified pseudostatic analysis and a full dynamic analysis,showing a satisfying agreement.Overall,the results of the study demonstrated that the seismic increments of internal forces in the diaphragm walls of the station and in the segmented lining of the tunnel were quite significant.The case study encourages improving the reliability of simplified methods based on the more advanced dynamic approaches.
