In the process of shield tunneling through soft soil layers,the presence of confined water ahead poses a significant threat to the stability of the tunnel face.Therefore,it is crucial to consider the impact of confine...In the process of shield tunneling through soft soil layers,the presence of confined water ahead poses a significant threat to the stability of the tunnel face.Therefore,it is crucial to consider the impact of confined water on the limit support pressure of the tunnel face.This study employed the finite element method(FEM)to analyze the limit support pressure of shield tunnel face instability within a pressurized water-containing layer.Subsequently,a multiple linear regression approach was applied to derive a concise solution formula for the limit support pressure,incorporating various influencing factors.The analysis yields the following conclusions:1)The influence of confined water on the instability mode of the tunnel face in soft soil layers makes the displacement response of the strata not significant when the face is unstable;2)The limit support pressure increases approximately linearly with the pressure head,shield tunnel diameter,and tunnel burial depth.And inversely proportional to the thickness of the impermeable layer,soil cohesion and internal friction angle;3)Through an engineering case study analysis,the results align well with those obtained from traditional theoretical methods,thereby validating the rationality of the equations proposed in this paper.Furthermore,the proposed equations overcome the limitation of traditional theoretical approaches considering the influence of changes in impermeable layer thickness.It can accurately depict the dynamic variation in the required limit support pressure to maintain the stability of the tunnel face during shield tunneling,thus better reflecting engineering reality.展开更多
Soil aggregate stability is an important index that reflects soil quality and anti-erosion ability and strongly affects soil processes and functions.Bedrock strata dips(dip and anti-dip slopes)and land use types prima...Soil aggregate stability is an important index that reflects soil quality and anti-erosion ability and strongly affects soil processes and functions.Bedrock strata dips(dip and anti-dip slopes)and land use types primarily influence soil aggregate stability,whereas the detailed mechanisms are unclear in karst trough valley.Therefore,to explore the effects of bedrock strata dip and land use type on soil aggregate stability in karst trough valleys,soils were collected from five major land use types(abandoned land,grassland,pepper fields,corn fields and forest)on dip and anti-dip slopes.The soil was fractionated into macroaggregates and microaggrates using dry and wet sieving analysis.The soil particle size distribu-tions in the macroaggregates and microaggregates were measured in conventional laboratories.The results showed significant differences in soil aggregate stability among different bedrock strata dips,slope positions,and land use types(P<0.05).The variation ranges of macroaggregates and micro-aggregates in the pepper fields of the dip slope were higher than those on the anti-dip slope.Comparing all land use types,the forest of the anti-dip slope had>0.25 mm water-stable aggregates(85.31%)and mean weight diameter(2.67 mm)on the upper slope compared to that in the other slope positions of the dip slope.In addition,the dip slope had a higher percentage of aggregate destruction(35.57%)than the anti-dip slope(29.81%),and the soil erodibility factor value of the natural forest of the dip/anti-dip slope was significantly lower than that of the other land use types(P<0.05).When the content of large macroaggregates was larger,the soil macroaggregate weight was greater.When the failure rate of the soil aggregates was lower,the stability of the soil structure was better.Overall,these results suggest that natural forests can significantly improve the stability of soil aggregates,thereby improving soil erosion resistance.Therefore,natural recovery measures should be implemented on dip/anti-dip slopes of karst trough valleys.展开更多
基金Project(ZDRW-ZS-2021-3)supported by the Key Deployment Projects of Chinese Academy of SciencesProjects(52179116,51991392)supported by the National Natural Science Foundation of China。
文摘In the process of shield tunneling through soft soil layers,the presence of confined water ahead poses a significant threat to the stability of the tunnel face.Therefore,it is crucial to consider the impact of confined water on the limit support pressure of the tunnel face.This study employed the finite element method(FEM)to analyze the limit support pressure of shield tunnel face instability within a pressurized water-containing layer.Subsequently,a multiple linear regression approach was applied to derive a concise solution formula for the limit support pressure,incorporating various influencing factors.The analysis yields the following conclusions:1)The influence of confined water on the instability mode of the tunnel face in soft soil layers makes the displacement response of the strata not significant when the face is unstable;2)The limit support pressure increases approximately linearly with the pressure head,shield tunnel diameter,and tunnel burial depth.And inversely proportional to the thickness of the impermeable layer,soil cohesion and internal friction angle;3)Through an engineering case study analysis,the results align well with those obtained from traditional theoretical methods,thereby validating the rationality of the equations proposed in this paper.Furthermore,the proposed equations overcome the limitation of traditional theoretical approaches considering the influence of changes in impermeable layer thickness.It can accurately depict the dynamic variation in the required limit support pressure to maintain the stability of the tunnel face during shield tunneling,thus better reflecting engineering reality.
基金financially supported by the National Science Foundation(42107355,42167044,42007045)Guizhou University Cultivation Project(Guizhou University Cultivation[2019]No.10)+2 种基金China Postdoctoral Science Foundation(2020M673296)the Scientific research project of Chongqing Science and Technology Commission(CSTB2022NSCQ-MSX1053)the Science and technologyprojecot of Chongqing Education Commission(KJQN202100518).
文摘Soil aggregate stability is an important index that reflects soil quality and anti-erosion ability and strongly affects soil processes and functions.Bedrock strata dips(dip and anti-dip slopes)and land use types primarily influence soil aggregate stability,whereas the detailed mechanisms are unclear in karst trough valley.Therefore,to explore the effects of bedrock strata dip and land use type on soil aggregate stability in karst trough valleys,soils were collected from five major land use types(abandoned land,grassland,pepper fields,corn fields and forest)on dip and anti-dip slopes.The soil was fractionated into macroaggregates and microaggrates using dry and wet sieving analysis.The soil particle size distribu-tions in the macroaggregates and microaggregates were measured in conventional laboratories.The results showed significant differences in soil aggregate stability among different bedrock strata dips,slope positions,and land use types(P<0.05).The variation ranges of macroaggregates and micro-aggregates in the pepper fields of the dip slope were higher than those on the anti-dip slope.Comparing all land use types,the forest of the anti-dip slope had>0.25 mm water-stable aggregates(85.31%)and mean weight diameter(2.67 mm)on the upper slope compared to that in the other slope positions of the dip slope.In addition,the dip slope had a higher percentage of aggregate destruction(35.57%)than the anti-dip slope(29.81%),and the soil erodibility factor value of the natural forest of the dip/anti-dip slope was significantly lower than that of the other land use types(P<0.05).When the content of large macroaggregates was larger,the soil macroaggregate weight was greater.When the failure rate of the soil aggregates was lower,the stability of the soil structure was better.Overall,these results suggest that natural forests can significantly improve the stability of soil aggregates,thereby improving soil erosion resistance.Therefore,natural recovery measures should be implemented on dip/anti-dip slopes of karst trough valleys.
