Piled embankments have many advantages that have been applied in high-speed railway construction engineering.However,the load transfer mechanism of piled embankments,such as soil arching and tension membranes,is still...Piled embankments have many advantages that have been applied in high-speed railway construction engineering.However,the load transfer mechanism of piled embankments,such as soil arching and tension membranes,is still unclear,especially under dynamic loads.To investigate the soil arching and tension membrane under dynamic train loads on high-speed railways,a large-scale piled embankment model test with X-shaped piles as vertical reinforcement was performed,in which twenty-eight earth pressure cells were installed in the piled embankment and an M-shaped wave was adopted to simulate the high-speed railway train load.The results show that dynamic soil arching only occurs when two bogies of a carriage pass by and disappears at other times.The dynamic soil arching and membrane effect are the most significant under the concrete base.The arching height,stress concentration ratio and pile-soil load sharing ratio have a minimal value at 25 Hz.The dynamic soil arching degrades severely at 25 Hz,whose height at 25 Hz is only 0.35 times that at 5 Hz.The arching height fluctuates over a narrow range with increasing loading amplitude.The stress concentration ratio and the pile-soil load sharing ratio increase monotonically as the loading amplitude increases.展开更多
In current underground mining, the stability of the exposed backfill face is a basic issue associated with mining design and has been the subject of considerable research in mining safety and efficiency. In this study...In current underground mining, the stability of the exposed backfill face is a basic issue associated with mining design and has been the subject of considerable research in mining safety and efficiency. In this study, an improved analytical solution for evaluating the safety of vertically exposed faces in backfilling was proposed. Based on a differential slice method, the proposed solution emphasizes the arching effect as having the advantages of more rigor and wider scalability. Feasibility of the proposed solution was validated with classic centrifuge results. Good agreement between compared results indicated that the proposed solution skillfully predicts the behavior of the paste centrifuge model. Additionally, calculation of exposed face safety in sequential filling was presented. The proposed solution has practical significance in mine backfill design.展开更多
To discuss the soil arching effect on the load transferring model and sharing ratios by the piles and inter-pile subsoil in the bidirectionally reinforced composite ground, the forming mechanism, mechanical behavior a...To discuss the soil arching effect on the load transferring model and sharing ratios by the piles and inter-pile subsoil in the bidirectionally reinforced composite ground, the forming mechanism, mechanical behavior and its effect factors were discussed in detail. Then, the unified strength theory was introduced to set up the elastoplastic equilibrium differential equation of the subsoil under the limit equilibrium state. And from the equation, the solutions were derived with the corresponding formulas presented to calculate the earth pressure over and beneath the horizontal reinforced cushion or pillow, the stress of inter-pile subsoil and the pile-soil stress ratio. Based on the obtained solutions and measured data from an engineering project, the influence rules by the soil property parameters (i.e., the cohesion c and internal friction angle φ) and pile spacing on the pile-soil stress ratio n were discussed respectively. The results show that to improve the load sharing ratio by the piles, the more effective means for filling materials with a larger value of φ is to increase the ratio of pile cap size to spacing, while to reduce the pile spacing properly and increase the value of cohesion c is advisable for those filling materials with a smaller value of φ.展开更多
Seismic pile–slope stability analysis and the formation mechanism of soil arching have not been well studied. This study used a threedimensional(3D) finite difference to determine soil and pile parameter changes in t...Seismic pile–slope stability analysis and the formation mechanism of soil arching have not been well studied. This study used a threedimensional(3D) finite difference to determine soil and pile parameter changes in the static and seismic stability of the pile–slope caused by the interaction between stabilizing piles. Pile–slope stability analysis was performed to determine the optimal design of piles along a slope and the corresponding failure mode involving the formation of soil arching around two adjacent piles. The Factor of Safety(FS) of the slope was evaluated using the shear strength reduction method for static and seismic analyses. The results of the analysis show that suitable pile spacing(S) and a suitable pile diameter(D) in the middle of a slope result in the maximum FS for the pile–slope system and the formation of soil arching around two adjacent piles. FS of the pile–slope increased negligibly in the seismic analysis of piles located at the slope crest and toe. An optimized pile diameter and installation location afforded the maximum FS for the slope that corresponded to a specified slope failure mode for different pile locations. A pile spacing S ≤ 2.5D for piles installed in the middle of the slope is suggested for increasing the static and seismic pile–slope stability.展开更多
When the pore pressure in a porous rock changes, stress arching will occur within the rock and the surrounding region. Stress arching ratio is defined as the total stress changes in the porous rock to the pore pressur...When the pore pressure in a porous rock changes, stress arching will occur within the rock and the surrounding region. Stress arching ratio is defined as the total stress changes in the porous rock to the pore pressure change in the region. The region may have the same or different elastic moduli with the surrounding rock, which is usually referred to as inclusion or inhomogeneity. Stress arching is responsible for many geomechanical problems encountered during production or injection; in addition, it is a crucial parameter in stress estimation during field development. This paper aims to present laboratory measurements of vertical stress arching ratio in a material surrounding the inclusion(inhomogeneity).To the authors’ knowledge, few laboratory experiments have been reported on direct measurement of stress arching. The inclusion is a cylindrical sandstone(44 mm in diameter and 50 mm in height)embedded in a larger cylindrical sandstone(150 mm in diameter and 154 mm in height), both of which are made synthetically. These two parts are separated and sealed by a internal polyurethane sleeve.Vertical stress changes are recorded by a mini hydraulic sensor embedded in surrounding rock. Laboratory results are compared to those obtained by numerical models. These models are checked with analytical formulations. The results of numerical models show a good agreement with laboratory data.The numerical results also indicate that the sensor response is affected by elastic properties of the internal sleeve. According to the sensitivity analysis performed, in the absence of the internal sleeve,properties of the inclusion have significant effects on the surrounding stress arching induced.展开更多
The Tunnel Oberau, with a length of 2.9 km, forms the core of the local bypass of Oberau. Between the two massifs Kirchbichl and Mühlberg, the tunnel is situated in the valley of the Gießenbach in alluvial g...The Tunnel Oberau, with a length of 2.9 km, forms the core of the local bypass of Oberau. Between the two massifs Kirchbichl and Mühlberg, the tunnel is situated in the valley of the Gießenbach in alluvial gravel with only a small overlap underneath settlement-sensitive buildings. In this paper, the measures in the tunnel to minimize the settlements of the buildings during the shotcrete excavations are described. Basis for this planning were extensive 3D-FE-calculations. Furthermore, under two buildings a compensation grouting measure was carried out, in order to compensate the occurring settlements. This paper describes how the required time and the amount of injection material (grout) could be reduced during the compensation grouting in highly permeable gravel.展开更多
This study analyzed the passive arching effect under eccentric loading by developing a series of trapdoor discrete numerical models.The numerical models were validated by comparison with laboratory test results.The de...This study analyzed the passive arching effect under eccentric loading by developing a series of trapdoor discrete numerical models.The numerical models were validated by comparison with laboratory test results.The deformation pattern,soil arching ratio,force chain distribution,and coordination number under various surcharge magnitudes and deviation distances were analyzed.The numerical results showed that the deformation diagram of soil particles can be divided into three zones:principal displacement zone,transition zone,and static zone.With an increase in the surcharge magnitude,the range of the principal displacement zone decreased,but the range of the transition region increased.The curve of the soil arching ratio on the trapdoor can be divided into three phases,which can be well characterized by the tangent modulus.The passive arching effect is degraded by a surcharge.The ulti-mate soil arching ratio could be approximated as a W-shaped distribution along the+x-direction.With an increase in the trapdoor displacement,the force chain on the trapdoor gradually expanded outward to form an inverted funnel shape.The most powerful force on the trapdoor was mainly distributed on its edge.The average coordination number decreased gradually as the trapdoor moved upward.展开更多
Shield tunneling and post-tunneling steady seepage are accompanied by stress and displacement variations,which could induce and influence the soil arching effect.Although there are many studies on the tunneling-induce...Shield tunneling and post-tunneling steady seepage are accompanied by stress and displacement variations,which could induce and influence the soil arching effect.Although there are many studies on the tunneling-induced soil arching effect,the research about the effect of seepage on soil arching effect is extremely lacking.In this study,a numerical model is firstly established and verified by field data.Then,a series of numerical models,whose simulation method of steady seepage is verified by adopting the conformal mapping technique,are established to study the soil arching evolution of deep-buried tunneling and post-construction steady seepage.The results indicate that seepage leads to an increase in effective vertical stress,which is consistent with the existing theory.The seepage weakens the soil arching effect resulting in the height of the arch zone reducing from 2.38D(D is the tunnel diameter)to 1.25D.The seepage leads to the further development of ground consolidation settlement,but the differential displacement in the soil mass decreases.The ground reaction curve in the steady seepage condition shows a bigger value than that after excavation.It is reasonable to control the ground loss ratio in the range of 0.5–1.0%,which can minimize overburden pressure with moderate ground deformation.展开更多
As a new type of bridge foundation, Lattice-Shaped Diaphragm Wall (hereinafter for LSDW) is highly concerned in relevant construction area but its research is far from achievement. Based on PFC2D, the soil arching e...As a new type of bridge foundation, Lattice-Shaped Diaphragm Wall (hereinafter for LSDW) is highly concerned in relevant construction area but its research is far from achievement. Based on PFC2D, the soil arching effect of LSDWs is studied thoroughly in this paper and the special attention is given to its influencing factors. It turns out to be that a differential wall-soil settlement can be found at the lower location of soil core of an LSDW which is one of the trigger factors of soil arching; meanwhile, the differential settlement degree can reflect the exertion degree of soil arching; the shape of soil arching is basically a hemisphere which can be explained by the theory proposed by Hewlett and Randolph; normally, the chamber number is a negative factor for the development of soil arching; the soil arching effect is significantly influenced by the distance of two adjacent wall elements and the foundation depth, and a relatively large or small value of these factors is disadvantageous to the exertion of soil arching; in addition, the soil arching effect increase with the growth of stiffness and friction coefficient of particles and the friction coefficient of particles has insignificant influence on the development of soil arching effect compared with particle stiffness.展开更多
Piled embankments are widely used in highway and railway engineering due to their economy and efficiency inovercoming several issues encountered in constructing embankments over weak soils. Soil arching, caused by the...Piled embankments are widely used in highway and railway engineering due to their economy and efficiency inovercoming several issues encountered in constructing embankments over weak soils. Soil arching, caused by the pile-subsoilrelative displacement (△s), plays an important role in reducing the embankment load falling on weak soil, however, the funda-mental characteristics (e.g., formation and features) of soil arching remain poorly understood. In this study, a series of discreteelement method (DEM) modellings are performed to study the formation and features of soil arching with the variation of As inpiled embankments with or without geosynthetic reinforcement. Firstly, calibration for the modelling parameters is carried out bycomparing the DEM results with the experimental data obtained from the existing literature. Secondly, the analysis of the macro-and micro-behaviours is performed in detail. Finally, a parametric study is conducted in an effort to identify the influences of threekey factors on soil arching: the friction coefficient of the embankment fill (f), the embankment height (h), and the pile clear spacing(s-a). Numerical results indicate that △s is a key factor governing the formation and features of soil arching in embankments. Tobe specific, soil arching gradually evolves from two inclined shear planes at a small △s to a hemispherical arch at a relatively largeAs. Then, with a continuous increase in △s, the soil arching height gradually increases and finally approaches a constant value of0.8(s-a) (i.e., the maximum soil arching height). For a given case, the higher the soil arching height, the greater the degree of soilarching effect. The parametric study shows that the friction coefficient of the embankment fill has a negligible influence on theformation and features of soil arching. However, embankment height is a key factor governing the formation and features of soilarching. In addition, pile clear spacing has a significant effect on the formation of soil arching, but not on its features.展开更多
High geostress,a typical attribute of tunnels located at significant depths,is crucial in causing stress-induced failure and influencing the stability of the tunnel crown.This study developed an analytical method for ...High geostress,a typical attribute of tunnels located at significant depths,is crucial in causing stress-induced failure and influencing the stability of the tunnel crown.This study developed an analytical method for the failure mechanism that occurs in deep-buried tunnel roofs,taking into account the influence of geostress.The limit analysis theory was utilized for deriving analytical solutions about the geometry of the collapsing surface and the limit supporting pressure.The collapsing surface obtained by the analytical solution was validated by the findings of the physical model test,which shows a high level of agreement with the actual one.An extensive investigation was done to explore the effects of the lateral pressure coefficients,the tunnel buried depth,the geological conditions of the surrounding rock,the long-short axis ratio,and the size of the tunnel profile.The findings indicate that an increase in the lateral pressure coefficient from 0.5 to 1.5 results in a reduction in the height of the collapsing zone by 2.08 m and the width of the collapsing zone by 1.15 m,while simultaneously increases the limit supporting pressure by 18.9%.The proposed upper bound method accurately determines the limit supporting pressure and the geometry of the collapsing surface,which aligns well with the results acquired through numerical modelling and on-site monitoring in actual engineering applications.The proposed analytical method can serve as a reference for similar crown failure issues of deep-buried tunnels.展开更多
Currently,more than ten ultrahigh arch dams have been constructed or are being constructed in China.Safety control is essential to long-term operation of these dams.This study employed the flexibility coefficient and ...Currently,more than ten ultrahigh arch dams have been constructed or are being constructed in China.Safety control is essential to long-term operation of these dams.This study employed the flexibility coefficient and plastic complementary energy norm to assess the structural safety of arch dams.A comprehensive analysis was conducted,focusing on differences among conventional methods in characterizing the structural behavior of the Xiaowan arch dam in China.Subsequently,the spatiotemporal characteristics of the measured performance of the Xiaowan dam were explored,including periodicity,convergence,and time-effect characteristics.These findings revealed the governing mechanism of main factors.Furthermore,a heterogeneous spatial panel vector model was developed,considering both common factors and specific factors affecting the safety and performance of arch dams.This model aims to comprehensively illustrate spatial heterogeneity between the entire structure and local regions,introducing a specific effect quantity to characterize local deformation differences.Ultimately,the proposed model was applied to the Xiaowan arch dam,accurately quantifying the spatiotemporal heterogeneity of dam performance.Additionally,the spatiotemporal distri-bution characteristics of environmental load effects on different parts of the dam were reasonably interpreted.Validation of the model prediction enhances its credibility,leading to the formulation of health diagnosis criteria for future long-term operation of the Xiaowan dam.The findings not only enhance the predictive ability and timely control of ultrahigh arch dams'performance but also provide a crucial basis for assessing the effectiveness of engineering treatment measures.展开更多
In order to study the residual stress distribution law of welded joints of arch ribs of large-span steel pipe concrete arch bridges,numerical simulation of temperature,stress and strain fields based on ABAQUS for weld...In order to study the residual stress distribution law of welded joints of arch ribs of large-span steel pipe concrete arch bridges,numerical simulation of temperature,stress and strain fields based on ABAQUS for welded joints of arch-ribbed steel tubes using 7-,8-and 9-layer welds is carried out and its accuracy is demonstrated.The steel pipe welding temperature changes,residual stress distribution,different processes residual stress changes in the law,the prediction of post-weld residual stress distribution and deformation are studied in this paper.The results show that the temperature field values and test results are more consistent with the accuracy of numerical simulation of welding,the welding process is mainly in the form of heat transfer;Residual high stresses are predominantly distributed in the Fusion zone(FZ)and Heat-affected zone(HAZ),with residual stress levels tending to decrease from the center of the weld along the axial path,the maximum stress appears in the FZ and HAZ junction;The number of welding layers has an effect on the residual stress distribution,the number of welding layers increases,the residual stress tends to decrease,while the FZ and HAZ high stress area range shrinks;Increasing the number of plies will increase the amount of residual distortion.展开更多
The stability of an arching slope in deformable materials above strong rocks strongly depends on the shape and width of the span.Equations for a free surface problem that incorporate these two parameters were derived ...The stability of an arching slope in deformable materials above strong rocks strongly depends on the shape and width of the span.Equations for a free surface problem that incorporate these two parameters were derived using a simplified two-dimensional arching slope model,and were validated using physical model tests under 1 g and centrifugal conditions.The results are used to estimate the maximum excavation width for a weak claystone slope in a lignite mine,for which we calculate a safety factor of 1.31.展开更多
Predicting the inner displacements of deep vertical shafts during the excavation process has been a difficult task considering the geological,structural,and constructional influences.In fact,the two-dimensional(2D)ana...Predicting the inner displacements of deep vertical shafts during the excavation process has been a difficult task considering the geological,structural,and constructional influences.In fact,the two-dimensional(2D)analytical solution based on the retaining wall model remains insufficient for understanding the actual behavior during an excavation.This is because the deformation of vertical shafts becomes complicated due to the unexpected arching effect brought about by the three-dimensional(3D)flexible displacements occurring in the excavation process.Previous analytical solutions only considered the limit equilibrium.Therefore,the present study deals with a 3D soil-structure simulation by considering the displacements of a cylindrical shaft and the mechanical behavior of the surrounding soil as well as the geometry of the cylindrical structure.Moreover,this mechanical behaviors of the surrounding soil and shaft are controlled by the shaft stiffness;hence,the relationships among the shaft stiffness,mechanical behavior of the surrounding soil(in terms of earth pressure coefficient),and shaft displacement were investigated.A cylindrical model,120 m in depth and 20 m in diameter,was positioned at the center of a sand domain,and each excavation step was performed at an interval depth of 20 m.A 3D finite difference method analysis was applied using the modified Cam-Clay(MCC)model to represent the soil behavior.As a result,the present study provides a new normalized lateral earth pressure theory for excavated shafts by considering the 3D arching effect obtained from parametric studies using various levels of shaft stiffness.From a comparison with the analytical solutions of previous studies(Terzaghi,1943a;Prater,1977;Cheng&Hu,2005),it is found that the previous studies underestimated the earth pressure acting on the cylindrical shaft because they did not consider the accurate arching effect.展开更多
Te year 2021 marks the 120th anniversary of the birth of Liang Sicheng.To celebrate this historical event,the School of Architecture of Tsinghua University began preparations in the fall of 2020 by appointing Liu Chan...Te year 2021 marks the 120th anniversary of the birth of Liang Sicheng.To celebrate this historical event,the School of Architecture of Tsinghua University began preparations in the fall of 2020 by appointing Liu Chang and Wang Nan,two faculty members from the department,to collect and organise various historical materials and exhibits.After 10months of work,‘Te Overarching:A Documenta Celebrating the 120th Anniversary of the Birth of Liang Sicheng’debuted in August 2021 on the 4th foor of Tsinghua University Art Museum(Fig.1).展开更多
基金Natural Science Research Project of Anhui Educational Committee under Grant No.2022AH050844Anhui Provincial Natural Science Foundation of China under Grant No.2008085ME143+1 种基金the Doctoral Foundation of Anhui University of Science and Technology under Grant No.13190018Innovation and Entrepreneurship Training Program for College Students under Grant No.S202110361059。
文摘Piled embankments have many advantages that have been applied in high-speed railway construction engineering.However,the load transfer mechanism of piled embankments,such as soil arching and tension membranes,is still unclear,especially under dynamic loads.To investigate the soil arching and tension membrane under dynamic train loads on high-speed railways,a large-scale piled embankment model test with X-shaped piles as vertical reinforcement was performed,in which twenty-eight earth pressure cells were installed in the piled embankment and an M-shaped wave was adopted to simulate the high-speed railway train load.The results show that dynamic soil arching only occurs when two bogies of a carriage pass by and disappears at other times.The dynamic soil arching and membrane effect are the most significant under the concrete base.The arching height,stress concentration ratio and pile-soil load sharing ratio have a minimal value at 25 Hz.The dynamic soil arching degrades severely at 25 Hz,whose height at 25 Hz is only 0.35 times that at 5 Hz.The arching height fluctuates over a narrow range with increasing loading amplitude.The stress concentration ratio and the pile-soil load sharing ratio increase monotonically as the loading amplitude increases.
基金financially supported by the China Scholarship Council (No. 201506420049)
文摘In current underground mining, the stability of the exposed backfill face is a basic issue associated with mining design and has been the subject of considerable research in mining safety and efficiency. In this study, an improved analytical solution for evaluating the safety of vertically exposed faces in backfilling was proposed. Based on a differential slice method, the proposed solution emphasizes the arching effect as having the advantages of more rigor and wider scalability. Feasibility of the proposed solution was validated with classic centrifuge results. Good agreement between compared results indicated that the proposed solution skillfully predicts the behavior of the paste centrifuge model. Additionally, calculation of exposed face safety in sequential filling was presented. The proposed solution has practical significance in mine backfill design.
基金Project (07JJ4015) supported by the Natural Science Foundation of Hunan Province, China
文摘To discuss the soil arching effect on the load transferring model and sharing ratios by the piles and inter-pile subsoil in the bidirectionally reinforced composite ground, the forming mechanism, mechanical behavior and its effect factors were discussed in detail. Then, the unified strength theory was introduced to set up the elastoplastic equilibrium differential equation of the subsoil under the limit equilibrium state. And from the equation, the solutions were derived with the corresponding formulas presented to calculate the earth pressure over and beneath the horizontal reinforced cushion or pillow, the stress of inter-pile subsoil and the pile-soil stress ratio. Based on the obtained solutions and measured data from an engineering project, the influence rules by the soil property parameters (i.e., the cohesion c and internal friction angle φ) and pile spacing on the pile-soil stress ratio n were discussed respectively. The results show that to improve the load sharing ratio by the piles, the more effective means for filling materials with a larger value of φ is to increase the ratio of pile cap size to spacing, while to reduce the pile spacing properly and increase the value of cohesion c is advisable for those filling materials with a smaller value of φ.
文摘Seismic pile–slope stability analysis and the formation mechanism of soil arching have not been well studied. This study used a threedimensional(3D) finite difference to determine soil and pile parameter changes in the static and seismic stability of the pile–slope caused by the interaction between stabilizing piles. Pile–slope stability analysis was performed to determine the optimal design of piles along a slope and the corresponding failure mode involving the formation of soil arching around two adjacent piles. The Factor of Safety(FS) of the slope was evaluated using the shear strength reduction method for static and seismic analyses. The results of the analysis show that suitable pile spacing(S) and a suitable pile diameter(D) in the middle of a slope result in the maximum FS for the pile–slope system and the formation of soil arching around two adjacent piles. FS of the pile–slope increased negligibly in the seismic analysis of piles located at the slope crest and toe. An optimized pile diameter and installation location afforded the maximum FS for the slope that corresponded to a specified slope failure mode for different pile locations. A pile spacing S ≤ 2.5D for piles installed in the middle of the slope is suggested for increasing the static and seismic pile–slope stability.
文摘When the pore pressure in a porous rock changes, stress arching will occur within the rock and the surrounding region. Stress arching ratio is defined as the total stress changes in the porous rock to the pore pressure change in the region. The region may have the same or different elastic moduli with the surrounding rock, which is usually referred to as inclusion or inhomogeneity. Stress arching is responsible for many geomechanical problems encountered during production or injection; in addition, it is a crucial parameter in stress estimation during field development. This paper aims to present laboratory measurements of vertical stress arching ratio in a material surrounding the inclusion(inhomogeneity).To the authors’ knowledge, few laboratory experiments have been reported on direct measurement of stress arching. The inclusion is a cylindrical sandstone(44 mm in diameter and 50 mm in height)embedded in a larger cylindrical sandstone(150 mm in diameter and 154 mm in height), both of which are made synthetically. These two parts are separated and sealed by a internal polyurethane sleeve.Vertical stress changes are recorded by a mini hydraulic sensor embedded in surrounding rock. Laboratory results are compared to those obtained by numerical models. These models are checked with analytical formulations. The results of numerical models show a good agreement with laboratory data.The numerical results also indicate that the sensor response is affected by elastic properties of the internal sleeve. According to the sensitivity analysis performed, in the absence of the internal sleeve,properties of the inclusion have significant effects on the surrounding stress arching induced.
文摘The Tunnel Oberau, with a length of 2.9 km, forms the core of the local bypass of Oberau. Between the two massifs Kirchbichl and Mühlberg, the tunnel is situated in the valley of the Gießenbach in alluvial gravel with only a small overlap underneath settlement-sensitive buildings. In this paper, the measures in the tunnel to minimize the settlements of the buildings during the shotcrete excavations are described. Basis for this planning were extensive 3D-FE-calculations. Furthermore, under two buildings a compensation grouting measure was carried out, in order to compensate the occurring settlements. This paper describes how the required time and the amount of injection material (grout) could be reduced during the compensation grouting in highly permeable gravel.
基金supported by the National Natural Science Foundation of China(Nos.52090081 and 51938008)Key Research and Development Program of Guangdong Province(No.2019B111105001)the Natural Science Foundation of Shenzhen(No.JCYJ20210324094607020).
文摘This study analyzed the passive arching effect under eccentric loading by developing a series of trapdoor discrete numerical models.The numerical models were validated by comparison with laboratory test results.The deformation pattern,soil arching ratio,force chain distribution,and coordination number under various surcharge magnitudes and deviation distances were analyzed.The numerical results showed that the deformation diagram of soil particles can be divided into three zones:principal displacement zone,transition zone,and static zone.With an increase in the surcharge magnitude,the range of the principal displacement zone decreased,but the range of the transition region increased.The curve of the soil arching ratio on the trapdoor can be divided into three phases,which can be well characterized by the tangent modulus.The passive arching effect is degraded by a surcharge.The ulti-mate soil arching ratio could be approximated as a W-shaped distribution along the+x-direction.With an increase in the trapdoor displacement,the force chain on the trapdoor gradually expanded outward to form an inverted funnel shape.The most powerful force on the trapdoor was mainly distributed on its edge.The average coordination number decreased gradually as the trapdoor moved upward.
基金supported by the National Natural Science Foundation of China(Grant Nos.52090082,51938005,52122807,and 52108318)China Hunan Provincial Science&Technology Department(Grant Nos.2021RC3043 and 2021JJ30119).
文摘Shield tunneling and post-tunneling steady seepage are accompanied by stress and displacement variations,which could induce and influence the soil arching effect.Although there are many studies on the tunneling-induced soil arching effect,the research about the effect of seepage on soil arching effect is extremely lacking.In this study,a numerical model is firstly established and verified by field data.Then,a series of numerical models,whose simulation method of steady seepage is verified by adopting the conformal mapping technique,are established to study the soil arching evolution of deep-buried tunneling and post-construction steady seepage.The results indicate that seepage leads to an increase in effective vertical stress,which is consistent with the existing theory.The seepage weakens the soil arching effect resulting in the height of the arch zone reducing from 2.38D(D is the tunnel diameter)to 1.25D.The seepage leads to the further development of ground consolidation settlement,but the differential displacement in the soil mass decreases.The ground reaction curve in the steady seepage condition shows a bigger value than that after excavation.It is reasonable to control the ground loss ratio in the range of 0.5–1.0%,which can minimize overburden pressure with moderate ground deformation.
文摘As a new type of bridge foundation, Lattice-Shaped Diaphragm Wall (hereinafter for LSDW) is highly concerned in relevant construction area but its research is far from achievement. Based on PFC2D, the soil arching effect of LSDWs is studied thoroughly in this paper and the special attention is given to its influencing factors. It turns out to be that a differential wall-soil settlement can be found at the lower location of soil core of an LSDW which is one of the trigger factors of soil arching; meanwhile, the differential settlement degree can reflect the exertion degree of soil arching; the shape of soil arching is basically a hemisphere which can be explained by the theory proposed by Hewlett and Randolph; normally, the chamber number is a negative factor for the development of soil arching; the soil arching effect is significantly influenced by the distance of two adjacent wall elements and the foundation depth, and a relatively large or small value of these factors is disadvantageous to the exertion of soil arching; in addition, the soil arching effect increase with the growth of stiffness and friction coefficient of particles and the friction coefficient of particles has insignificant influence on the development of soil arching effect compared with particle stiffness.
文摘2019年发表的全球ARCHES试验(NCT02677896)结果显示,与安慰剂(placebo,PBO)+雄激素剥夺治疗(androgen deprivation therapy,ADT)相比,恩扎卢胺+ADT延长了转移性激素敏感性前列腺癌(metastatic hormone-sensitive prostate cancer,mHSPC)患者的总生存期和放射影像学无进展生存期(radiographic progression-free survival,rPFS)^([1])。然而,该试验无中国患者入组。欧洲肿瘤内科学会(European Society for Medical Oncology,ESMO)2023年会议报道了中国ARCHES研究(NCT04076059)的初步结果,这是一项评估恩扎卢胺+ADTvs.PBO+ADT在中国m HSPC患者中的疗效和安全性的多中心、随机、双盲、PBO对照的Ⅲ期试验^([2])。
基金supported by the National Key Research and Development Program of China(2016YFC0800208)the National Natural Science Foundation of China(Nos.51278216,51478201,51308241,and 51608316)
文摘Piled embankments are widely used in highway and railway engineering due to their economy and efficiency inovercoming several issues encountered in constructing embankments over weak soils. Soil arching, caused by the pile-subsoilrelative displacement (△s), plays an important role in reducing the embankment load falling on weak soil, however, the funda-mental characteristics (e.g., formation and features) of soil arching remain poorly understood. In this study, a series of discreteelement method (DEM) modellings are performed to study the formation and features of soil arching with the variation of As inpiled embankments with or without geosynthetic reinforcement. Firstly, calibration for the modelling parameters is carried out bycomparing the DEM results with the experimental data obtained from the existing literature. Secondly, the analysis of the macro-and micro-behaviours is performed in detail. Finally, a parametric study is conducted in an effort to identify the influences of threekey factors on soil arching: the friction coefficient of the embankment fill (f), the embankment height (h), and the pile clear spacing(s-a). Numerical results indicate that △s is a key factor governing the formation and features of soil arching in embankments. Tobe specific, soil arching gradually evolves from two inclined shear planes at a small △s to a hemispherical arch at a relatively largeAs. Then, with a continuous increase in △s, the soil arching height gradually increases and finally approaches a constant value of0.8(s-a) (i.e., the maximum soil arching height). For a given case, the higher the soil arching height, the greater the degree of soilarching effect. The parametric study shows that the friction coefficient of the embankment fill has a negligible influence on theformation and features of soil arching. However, embankment height is a key factor governing the formation and features of soilarching. In addition, pile clear spacing has a significant effect on the formation of soil arching, but not on its features.
基金supported partially by the National Natural Science Foundation of China(42277158,41972277,and U1934212)。
文摘High geostress,a typical attribute of tunnels located at significant depths,is crucial in causing stress-induced failure and influencing the stability of the tunnel crown.This study developed an analytical method for the failure mechanism that occurs in deep-buried tunnel roofs,taking into account the influence of geostress.The limit analysis theory was utilized for deriving analytical solutions about the geometry of the collapsing surface and the limit supporting pressure.The collapsing surface obtained by the analytical solution was validated by the findings of the physical model test,which shows a high level of agreement with the actual one.An extensive investigation was done to explore the effects of the lateral pressure coefficients,the tunnel buried depth,the geological conditions of the surrounding rock,the long-short axis ratio,and the size of the tunnel profile.The findings indicate that an increase in the lateral pressure coefficient from 0.5 to 1.5 results in a reduction in the height of the collapsing zone by 2.08 m and the width of the collapsing zone by 1.15 m,while simultaneously increases the limit supporting pressure by 18.9%.The proposed upper bound method accurately determines the limit supporting pressure and the geometry of the collapsing surface,which aligns well with the results acquired through numerical modelling and on-site monitoring in actual engineering applications.The proposed analytical method can serve as a reference for similar crown failure issues of deep-buried tunnels.
基金supported by the National Natural Science Foundation of China(Grant No.52079046).
文摘Currently,more than ten ultrahigh arch dams have been constructed or are being constructed in China.Safety control is essential to long-term operation of these dams.This study employed the flexibility coefficient and plastic complementary energy norm to assess the structural safety of arch dams.A comprehensive analysis was conducted,focusing on differences among conventional methods in characterizing the structural behavior of the Xiaowan arch dam in China.Subsequently,the spatiotemporal characteristics of the measured performance of the Xiaowan dam were explored,including periodicity,convergence,and time-effect characteristics.These findings revealed the governing mechanism of main factors.Furthermore,a heterogeneous spatial panel vector model was developed,considering both common factors and specific factors affecting the safety and performance of arch dams.This model aims to comprehensively illustrate spatial heterogeneity between the entire structure and local regions,introducing a specific effect quantity to characterize local deformation differences.Ultimately,the proposed model was applied to the Xiaowan arch dam,accurately quantifying the spatiotemporal heterogeneity of dam performance.Additionally,the spatiotemporal distri-bution characteristics of environmental load effects on different parts of the dam were reasonably interpreted.Validation of the model prediction enhances its credibility,leading to the formulation of health diagnosis criteria for future long-term operation of the Xiaowan dam.The findings not only enhance the predictive ability and timely control of ultrahigh arch dams'performance but also provide a crucial basis for assessing the effectiveness of engineering treatment measures.
基金Sponsored by the National Natural Science Foundation of China(Grant No.52268048)the Guangxi Key Technology Research and Development Program(Grant No.GUI-KEAB23026101)the Guangxi Science and Technology Major Special Project(Grant No.GUI-KEAA22068066).
文摘In order to study the residual stress distribution law of welded joints of arch ribs of large-span steel pipe concrete arch bridges,numerical simulation of temperature,stress and strain fields based on ABAQUS for welded joints of arch-ribbed steel tubes using 7-,8-and 9-layer welds is carried out and its accuracy is demonstrated.The steel pipe welding temperature changes,residual stress distribution,different processes residual stress changes in the law,the prediction of post-weld residual stress distribution and deformation are studied in this paper.The results show that the temperature field values and test results are more consistent with the accuracy of numerical simulation of welding,the welding process is mainly in the form of heat transfer;Residual high stresses are predominantly distributed in the Fusion zone(FZ)and Heat-affected zone(HAZ),with residual stress levels tending to decrease from the center of the weld along the axial path,the maximum stress appears in the FZ and HAZ junction;The number of welding layers has an effect on the residual stress distribution,the number of welding layers increases,the residual stress tends to decrease,while the FZ and HAZ high stress area range shrinks;Increasing the number of plies will increase the amount of residual distortion.
基金the National Key Research and Development Program of China(No.2017YFC1501305)the National Major Scientific Instruments and Equipment Development Projects of China(No.41827808)。
文摘The stability of an arching slope in deformable materials above strong rocks strongly depends on the shape and width of the span.Equations for a free surface problem that incorporate these two parameters were derived using a simplified two-dimensional arching slope model,and were validated using physical model tests under 1 g and centrifugal conditions.The results are used to estimate the maximum excavation width for a weak claystone slope in a lignite mine,for which we calculate a safety factor of 1.31.
基金partly supported by Association for Disaster Prevention Research.
文摘Predicting the inner displacements of deep vertical shafts during the excavation process has been a difficult task considering the geological,structural,and constructional influences.In fact,the two-dimensional(2D)analytical solution based on the retaining wall model remains insufficient for understanding the actual behavior during an excavation.This is because the deformation of vertical shafts becomes complicated due to the unexpected arching effect brought about by the three-dimensional(3D)flexible displacements occurring in the excavation process.Previous analytical solutions only considered the limit equilibrium.Therefore,the present study deals with a 3D soil-structure simulation by considering the displacements of a cylindrical shaft and the mechanical behavior of the surrounding soil as well as the geometry of the cylindrical structure.Moreover,this mechanical behaviors of the surrounding soil and shaft are controlled by the shaft stiffness;hence,the relationships among the shaft stiffness,mechanical behavior of the surrounding soil(in terms of earth pressure coefficient),and shaft displacement were investigated.A cylindrical model,120 m in depth and 20 m in diameter,was positioned at the center of a sand domain,and each excavation step was performed at an interval depth of 20 m.A 3D finite difference method analysis was applied using the modified Cam-Clay(MCC)model to represent the soil behavior.As a result,the present study provides a new normalized lateral earth pressure theory for excavated shafts by considering the 3D arching effect obtained from parametric studies using various levels of shaft stiffness.From a comparison with the analytical solutions of previous studies(Terzaghi,1943a;Prater,1977;Cheng&Hu,2005),it is found that the previous studies underestimated the earth pressure acting on the cylindrical shaft because they did not consider the accurate arching effect.
文摘Te year 2021 marks the 120th anniversary of the birth of Liang Sicheng.To celebrate this historical event,the School of Architecture of Tsinghua University began preparations in the fall of 2020 by appointing Liu Chang and Wang Nan,two faculty members from the department,to collect and organise various historical materials and exhibits.After 10months of work,‘Te Overarching:A Documenta Celebrating the 120th Anniversary of the Birth of Liang Sicheng’debuted in August 2021 on the 4th foor of Tsinghua University Art Museum(Fig.1).