The section of shield tunnel of the Chengdu Metro line passes primarily through sandy cobble strata. There are many buildings with spread foundations along the lines. Shield tunnel construction will disturb the ground...The section of shield tunnel of the Chengdu Metro line passes primarily through sandy cobble strata. There are many buildings with spread foundations along the lines. Shield tunnel construction will disturb the ground, causing displacement or stress to adjacent spread foundations. Based on the similarity theory, a laboratory model test of shield tunnel driving was carried out to study the influence of shield tunnel excavation on the displace ment of adjacent spread foundation. The results show that foundation closer to the tunnel has greater displacement or settlement than that further away. The horizontal dis placement is small and is influenced greatly by the cutting face. The displacement along the machine driving direction is bigger and is significantly affected by the thrust force. Settlement occurs primarily when shield machine passes close to the foundation and is the greatest at that time. Uneven settlement at the bottom of the spread foundation reaches a maximum after the excavation ends. In a numerical simulation, a particle flow model was con structed to study the impact of shield tunnel excavation on the stresses in the ground. The model showed stress con centration at the bottom of the spread foundation. With the increasing ground loss ratio, a loose area appears in the tunnel dome where the contact force dropped. Above the loose area, the contact force increases, forming an arch shaped soil area which prevents the loose area from expanding to the ground surface. The excavation also changed the pressure distribution around spread foundation.展开更多
To elucidate the wear mechanisms of the scraper in shield tunneling through sandy pebble strata,this study aims to achieve high efficiency and low wear during the tunneling process.We evaluate the operational paramete...To elucidate the wear mechanisms of the scraper in shield tunneling through sandy pebble strata,this study aims to achieve high efficiency and low wear during the tunneling process.We evaluate the operational parameters and tool wear characteristics of a 9-m diameter spoke-type shield machine used on the Beijing Daxing Airport Line.The analysis focuses on the wear values of the scrapers and rippers,wear of the scraper in different wear forms,and scraper wear relative to the position of the rippers obtained from the field.The study yielded the following conclusions.The wear values of scrapers on different spokes vary significantly owing to ripper protection.The wear of the scrapers can be categorized into six types:tooth chipping,local damage of teeth,wear of side teeth,wave-type of wear,wear on intermediate teeth,and flat wear,with the majority exhibiting wear on the side and intermediate teeth.The 0°spoke maintained the initial shape of the scrapers,making it more suitable for tunneling in sandy pebble strata.Based on the differences in the relative positions of the ripper and scraper,a model is proposed to determine the ripper plowing influence area.It was found that this area depends on the geological conditions of the soil;thus,the influence angle of ripper plowing in the considered sandy pebble strata is determined to be between 35°and 50°.The results obtained in this study provide a theoretical reference for optimizing scraper layouts in shield construction,even when operating under varying geological conditions.展开更多
In order to investigate the influence of face instability for tunnels with different burial depths in sandy cobble strata on earth pressure and the instability region,geomechanical model tests and numerical simulation...In order to investigate the influence of face instability for tunnels with different burial depths in sandy cobble strata on earth pressure and the instability region,geomechanical model tests and numerical simulations were performed.The continuous excavation method was adopted to reduce the pressure of the soil bin and restore the real engineering situation.Earth pressure in three directions of the obser-vation section in front of the tunnel face was monitored during the tunneling of the shield.Evolutions of the lateral stress ratios at dif-ferent stages were also investigated.The instability area of the shield tunnel face in sandy cobble strata with different burial depth ratios during the instability stage was obtained based on the change ratio of earth pressure and compared with existing researches.The earth pressure began to change when the excavation was one shield diameter away from the observation section,and when the excavation reached the observation section,the earth pressure decreased significantly.The burial depth of shield tunnel in the sandy cobble strata has a significant impact on the evolution of soil arch and the size of the failure area.The numerical simulation of the continuum medium cannot reflect the stress redistribution characteristics of the granular body like sandy cobble strata,and the failure area or stress distur-bance area obtained by the model test is larger than the numerical simulation result.Existing methods have deviations in analyzing the failure area of shield tunnel face in sandy cobble strata.It provides not only guidance for shield tunnel excavation engineering in sandy cobble strata,but also a reference for the theoretical research on failure areas.展开更多
Earth pressure balance(EPB)shield tunneling in sandy cobble strata often encounters challenges such as muck stagnation,severe tool wear,difficulties in chamber pressure control,and low excavation efficiency.To address...Earth pressure balance(EPB)shield tunneling in sandy cobble strata often encounters challenges such as muck stagnation,severe tool wear,difficulties in chamber pressure control,and low excavation efficiency.To address these issues,this study proposes a novel gradient stress construction strategy based on rigid wall boundaries by integrating the finite difference method(FDM)and the discrete element method(DEM),and establishes a refined FDM-DEM coupled shield tunneling model.Using this model,the pressure distribution and load transfer mechanisms at the excavation face and within the chamber,as well as the motion trajectories,velocities,and spatial distribution of muck particles,are analyzed in detail.The results indicate that:(1)The pressure at the cutterhead spokes is lower than that at the cutterhead openings;the muck pressure within the chamber exhibits significant radial gradient variations,with distinct differences between the left and right sides.(2)The average pressure in the upper regions of both the left and right sides of the chamber is nearly equal,with a stable pressure transmission coefficient of approximately 0.8.An under-pressure advancement strategy is recommended to avoid ground heave.(3)The muck particles follow spiral trajectories,forming dual-vortex stagnation zones in the central region of the cutterhead(0-0.2D,where D denotes the cutterhead diameter)and the support column region of the chamber(0-0.25D).The installation of radial mixing rods on the cutterhead shaft is suggested to improve muck flowability.This study provides new insights for optimizing cutterhead and chamber design,offering significant implications for enhancing the efficiency of shield tunneling construction.展开更多
基金funded by the National Natural Science Foundation of China (Nos. 51278422 and 50925830)the National 973 Plan Topics of China (No. 2010CB732105)+1 种基金the National Science and Technology Pillar Program of China (No. 2012BAG05B03)the Sichuan Youth Science and Technology Foundation, China (No. 2012JQ0021)
文摘The section of shield tunnel of the Chengdu Metro line passes primarily through sandy cobble strata. There are many buildings with spread foundations along the lines. Shield tunnel construction will disturb the ground, causing displacement or stress to adjacent spread foundations. Based on the similarity theory, a laboratory model test of shield tunnel driving was carried out to study the influence of shield tunnel excavation on the displace ment of adjacent spread foundation. The results show that foundation closer to the tunnel has greater displacement or settlement than that further away. The horizontal dis placement is small and is influenced greatly by the cutting face. The displacement along the machine driving direction is bigger and is significantly affected by the thrust force. Settlement occurs primarily when shield machine passes close to the foundation and is the greatest at that time. Uneven settlement at the bottom of the spread foundation reaches a maximum after the excavation ends. In a numerical simulation, a particle flow model was con structed to study the impact of shield tunnel excavation on the stresses in the ground. The model showed stress con centration at the bottom of the spread foundation. With the increasing ground loss ratio, a loose area appears in the tunnel dome where the contact force dropped. Above the loose area, the contact force increases, forming an arch shaped soil area which prevents the loose area from expanding to the ground surface. The excavation also changed the pressure distribution around spread foundation.
基金Supported by Beijing Municipal Natural Science Foundation of China(Grant No.8252017)National Natural Science Foundation of China(Grant Nos.51608521,52178375)Beijing Urban Construction Group Co.,Ltd.
文摘To elucidate the wear mechanisms of the scraper in shield tunneling through sandy pebble strata,this study aims to achieve high efficiency and low wear during the tunneling process.We evaluate the operational parameters and tool wear characteristics of a 9-m diameter spoke-type shield machine used on the Beijing Daxing Airport Line.The analysis focuses on the wear values of the scrapers and rippers,wear of the scraper in different wear forms,and scraper wear relative to the position of the rippers obtained from the field.The study yielded the following conclusions.The wear values of scrapers on different spokes vary significantly owing to ripper protection.The wear of the scrapers can be categorized into six types:tooth chipping,local damage of teeth,wear of side teeth,wave-type of wear,wear on intermediate teeth,and flat wear,with the majority exhibiting wear on the side and intermediate teeth.The 0°spoke maintained the initial shape of the scrapers,making it more suitable for tunneling in sandy pebble strata.Based on the differences in the relative positions of the ripper and scraper,a model is proposed to determine the ripper plowing influence area.It was found that this area depends on the geological conditions of the soil;thus,the influence angle of ripper plowing in the considered sandy pebble strata is determined to be between 35°and 50°.The results obtained in this study provide a theoretical reference for optimizing scraper layouts in shield construction,even when operating under varying geological conditions.
基金the financial support provided by Natural Science Foundation of China(Grant Nos.51978019,52278382)Beijing Natural Science Foundation,China(Grant No.8222004).
文摘In order to investigate the influence of face instability for tunnels with different burial depths in sandy cobble strata on earth pressure and the instability region,geomechanical model tests and numerical simulations were performed.The continuous excavation method was adopted to reduce the pressure of the soil bin and restore the real engineering situation.Earth pressure in three directions of the obser-vation section in front of the tunnel face was monitored during the tunneling of the shield.Evolutions of the lateral stress ratios at dif-ferent stages were also investigated.The instability area of the shield tunnel face in sandy cobble strata with different burial depth ratios during the instability stage was obtained based on the change ratio of earth pressure and compared with existing researches.The earth pressure began to change when the excavation was one shield diameter away from the observation section,and when the excavation reached the observation section,the earth pressure decreased significantly.The burial depth of shield tunnel in the sandy cobble strata has a significant impact on the evolution of soil arch and the size of the failure area.The numerical simulation of the continuum medium cannot reflect the stress redistribution characteristics of the granular body like sandy cobble strata,and the failure area or stress distur-bance area obtained by the model test is larger than the numerical simulation result.Existing methods have deviations in analyzing the failure area of shield tunnel face in sandy cobble strata.It provides not only guidance for shield tunnel excavation engineering in sandy cobble strata,but also a reference for the theoretical research on failure areas.
基金supported by the National Science Fund for Distinguished Young Scholars of China(Grant No.52425807)the Science Foundation of Sichuan Province,China(Grant No.2024NSFTD0013)+2 种基金the Sichuan“Top Youth”Special Program for Outstanding Young Science and Technology Talent(DQ202403)the National Natural Science Foundation of China(Grant No.52478418)the National Natural Science Foundation of China Youth Fund(Grant No.52408441).
文摘Earth pressure balance(EPB)shield tunneling in sandy cobble strata often encounters challenges such as muck stagnation,severe tool wear,difficulties in chamber pressure control,and low excavation efficiency.To address these issues,this study proposes a novel gradient stress construction strategy based on rigid wall boundaries by integrating the finite difference method(FDM)and the discrete element method(DEM),and establishes a refined FDM-DEM coupled shield tunneling model.Using this model,the pressure distribution and load transfer mechanisms at the excavation face and within the chamber,as well as the motion trajectories,velocities,and spatial distribution of muck particles,are analyzed in detail.The results indicate that:(1)The pressure at the cutterhead spokes is lower than that at the cutterhead openings;the muck pressure within the chamber exhibits significant radial gradient variations,with distinct differences between the left and right sides.(2)The average pressure in the upper regions of both the left and right sides of the chamber is nearly equal,with a stable pressure transmission coefficient of approximately 0.8.An under-pressure advancement strategy is recommended to avoid ground heave.(3)The muck particles follow spiral trajectories,forming dual-vortex stagnation zones in the central region of the cutterhead(0-0.2D,where D denotes the cutterhead diameter)and the support column region of the chamber(0-0.25D).The installation of radial mixing rods on the cutterhead shaft is suggested to improve muck flowability.This study provides new insights for optimizing cutterhead and chamber design,offering significant implications for enhancing the efficiency of shield tunneling construction.
