Usually, the collapsible loess widely distributed across the world can serve as a type of foundation soil that meets its strength requirement after dense compaction and elimination of collapsibility. However, many pro...Usually, the collapsible loess widely distributed across the world can serve as a type of foundation soil that meets its strength requirement after dense compaction and elimination of collapsibility. However, many problems such as cracks and differential settlement still occur in loess roads in the seasonally frozen ground regions after several years of op- eration. Many studies have demonstrated that these secondary or multiple collapses primarily result from the repeated freezing-thawing, wetting-drying, and salinization-desalinization cycles. Therefore, we conducted a research program to （1） monitor the in-situ ground temperatures and water content in certain loess roads to understand their changes, （2） study the effects of freezing-thawing, wetting-drying, and salinization-desalinization cycles on geotechnical properties and micro-fabrics of compacted loess in the laboratory, and （3） develop mitigative measures and examine their engineered effectiveness, i.e., their thermal insulating and water-proofing effects in field and laboratory tests. Our results and advances are reviewed and some further research needs are proposed. These findings more clearly explain the processes and mechanisms of secondary and multiple collapse of loess roads. We also offer references for further study of the weakening mechanisms of similar structural soils.展开更多
Loess is prone to collapse upon wetting due to its open metastable structure,which poses a considerable threat to the environment,construction processes and human life.In this study,double oedometer tests and scanning...Loess is prone to collapse upon wetting due to its open metastable structure,which poses a considerable threat to the environment,construction processes and human life.In this study,double oedometer tests and scanning electron microscopy and mercury intrusion porosimetry analyses were conducted on loess from Yan’an to study the macroscopic and microscopic characteristics of loess wetting deformation and the underlying mechanism.The wetting collapse of loess under loading depends on the changes in different microstructure levels and elements.This collapse chain reaction is manifested by the dissipation,scattering and recombination of the cementation,deformation and reorganization of the particles,blocking of the pore channels,decrease in the dominant size and volume of unstable macropores(>14μm)and abundant mesopores(2.5-14μm),increase in the volume of small pores(0.05–2.5μm),and volume contraction at the macroscale.This process is dependent on the initial water content,stress level and wetting degree.These findings can facilitate collapsible loess hazard prevention and geological engineering construction.展开更多
湿陷性黄土在卸荷状态下的湿陷量与恒压下不同,通过试验从宏观与微观角度研究了卸荷作用下黄土湿陷量与微观结构变化情况。对铜川地区黄土进行湿陷性试验,测得不同埋深处恒压与卸荷的湿陷性系数,对比恒压与卸荷、湿陷系数的差异性,并结...湿陷性黄土在卸荷状态下的湿陷量与恒压下不同,通过试验从宏观与微观角度研究了卸荷作用下黄土湿陷量与微观结构变化情况。对铜川地区黄土进行湿陷性试验,测得不同埋深处恒压与卸荷的湿陷性系数,对比恒压与卸荷、湿陷系数的差异性,并结合电镜扫描(scanning electron microscope,SEM)与图像分析系统PCAS(particles and cracks analysis system)观测分析湿陷性黄土微观结构变化,得到不同埋深、卸荷量下微观参数孔隙面积占比、概率熵与平均形状系数等变化特征。结果表明:卸荷将有效提高湿陷起始压力,减少湿陷性的发生,相较于恒压条件下改变了湿陷性黄土孔隙面积、颗粒分布、排列方式等;微观结构主要以片状和蜂窝结构为主,随埋深与卸荷量增加,孔隙由疏到密、细小孔隙占比增加;概率熵逐渐增大、颗粒排列混乱且定向性变差,均一化程度降低;卸荷作用下黄土的湿陷系数、埋深与卸荷量有很强的相关性。展开更多
新疆北疆地区某输水明渠工程跨越大面积湿陷性黄土区域,湿陷性黄土经多年降雨、蒸发及季节气温交替变化后力学特性衰减严重,极易造成渠基塌陷及渠坡滑动破坏等工程现象。为深入探究其劣化机制,通过开展干湿-冻融循环条件下湿陷性黄土的...新疆北疆地区某输水明渠工程跨越大面积湿陷性黄土区域,湿陷性黄土经多年降雨、蒸发及季节气温交替变化后力学特性衰减严重,极易造成渠基塌陷及渠坡滑动破坏等工程现象。为深入探究其劣化机制,通过开展干湿-冻融循环条件下湿陷性黄土的直剪、压缩及其微观扫描试验,从宏-微观两个尺度分析其剪切强度、压缩特性的劣化规律及其损伤物理机制。研究结果表明(1)直剪试验:随着干湿-冻融循环次数的增加,峰值抗剪强度呈急速减小-速率减缓-趋于稳定3阶段发展趋势;黏聚力呈指数形式减少,第1次循环减小幅度最大,5次循环后趋于稳定状态,劣化度达到44.55%;内摩擦角变化幅度在2.1°以内,最大劣化度为7.04%,受干湿-冻融循环的影响较小。(2)压缩试验:压缩曲线可依据固结压缩屈服应力σ_(k)分为弹性变形和弹塑性变形两阶段,σ_(k)随循环次数增加前移;压缩系数、压缩指数与循环次数呈指数、幂函数形式减小,土体的整体压缩性减小;回弹指数与循环次数呈线性正相关。(3)微观结构:通过微观电镜扫描(scanning electron microscope,简称SEM)试验分析,在循环作用下,大孔隙减小,中、小孔隙增加,排列方式趋于无序状;大粒径颗粒逐渐转化为中、小颗粒,形态趋向于拟圆形;利用关联度分析发现孔隙大小及其角度是影响剪切强度的主要因素;引入Pearson相关系数发现颗粒形态及孔隙大小对压缩指标的影响程度最大。展开更多
基金supported by the National Key Basic Research Program of China (973 Program) (No. 2012CB026106)the Science and Technology Major Project of Gansu Province (No. 143GKDA007)+2 种基金the West Light Foundation of CAS for Dr. G. Y. Lithe Program for Innovative Research Group of the Natural Science Foundation of China (No. 41121061)the Foundation of the State Key Laboratory of Frozen Soils Engineering of CAS (No. SKLFSE-ZT-11)
文摘Usually, the collapsible loess widely distributed across the world can serve as a type of foundation soil that meets its strength requirement after dense compaction and elimination of collapsibility. However, many problems such as cracks and differential settlement still occur in loess roads in the seasonally frozen ground regions after several years of op- eration. Many studies have demonstrated that these secondary or multiple collapses primarily result from the repeated freezing-thawing, wetting-drying, and salinization-desalinization cycles. Therefore, we conducted a research program to （1） monitor the in-situ ground temperatures and water content in certain loess roads to understand their changes, （2） study the effects of freezing-thawing, wetting-drying, and salinization-desalinization cycles on geotechnical properties and micro-fabrics of compacted loess in the laboratory, and （3） develop mitigative measures and examine their engineered effectiveness, i.e., their thermal insulating and water-proofing effects in field and laboratory tests. Our results and advances are reviewed and some further research needs are proposed. These findings more clearly explain the processes and mechanisms of secondary and multiple collapse of loess roads. We also offer references for further study of the weakening mechanisms of similar structural soils.
基金supported by the Major Program of National Natural Science Foundation of China(No.41790441)the National Natural Science Foundation of China(No.41807234,41907235)the Fundamental Research Funds for the Central Universities,CHD(300102269203)。
文摘Loess is prone to collapse upon wetting due to its open metastable structure,which poses a considerable threat to the environment,construction processes and human life.In this study,double oedometer tests and scanning electron microscopy and mercury intrusion porosimetry analyses were conducted on loess from Yan’an to study the macroscopic and microscopic characteristics of loess wetting deformation and the underlying mechanism.The wetting collapse of loess under loading depends on the changes in different microstructure levels and elements.This collapse chain reaction is manifested by the dissipation,scattering and recombination of the cementation,deformation and reorganization of the particles,blocking of the pore channels,decrease in the dominant size and volume of unstable macropores(>14μm)and abundant mesopores(2.5-14μm),increase in the volume of small pores(0.05–2.5μm),and volume contraction at the macroscale.This process is dependent on the initial water content,stress level and wetting degree.These findings can facilitate collapsible loess hazard prevention and geological engineering construction.
文摘湿陷性黄土在卸荷状态下的湿陷量与恒压下不同,通过试验从宏观与微观角度研究了卸荷作用下黄土湿陷量与微观结构变化情况。对铜川地区黄土进行湿陷性试验,测得不同埋深处恒压与卸荷的湿陷性系数,对比恒压与卸荷、湿陷系数的差异性,并结合电镜扫描(scanning electron microscope,SEM)与图像分析系统PCAS(particles and cracks analysis system)观测分析湿陷性黄土微观结构变化,得到不同埋深、卸荷量下微观参数孔隙面积占比、概率熵与平均形状系数等变化特征。结果表明:卸荷将有效提高湿陷起始压力,减少湿陷性的发生,相较于恒压条件下改变了湿陷性黄土孔隙面积、颗粒分布、排列方式等;微观结构主要以片状和蜂窝结构为主,随埋深与卸荷量增加,孔隙由疏到密、细小孔隙占比增加;概率熵逐渐增大、颗粒排列混乱且定向性变差,均一化程度降低;卸荷作用下黄土的湿陷系数、埋深与卸荷量有很强的相关性。
文摘新疆北疆地区某输水明渠工程跨越大面积湿陷性黄土区域,湿陷性黄土经多年降雨、蒸发及季节气温交替变化后力学特性衰减严重,极易造成渠基塌陷及渠坡滑动破坏等工程现象。为深入探究其劣化机制,通过开展干湿-冻融循环条件下湿陷性黄土的直剪、压缩及其微观扫描试验,从宏-微观两个尺度分析其剪切强度、压缩特性的劣化规律及其损伤物理机制。研究结果表明(1)直剪试验:随着干湿-冻融循环次数的增加,峰值抗剪强度呈急速减小-速率减缓-趋于稳定3阶段发展趋势;黏聚力呈指数形式减少,第1次循环减小幅度最大,5次循环后趋于稳定状态,劣化度达到44.55%;内摩擦角变化幅度在2.1°以内,最大劣化度为7.04%,受干湿-冻融循环的影响较小。(2)压缩试验:压缩曲线可依据固结压缩屈服应力σ_(k)分为弹性变形和弹塑性变形两阶段,σ_(k)随循环次数增加前移;压缩系数、压缩指数与循环次数呈指数、幂函数形式减小,土体的整体压缩性减小;回弹指数与循环次数呈线性正相关。(3)微观结构:通过微观电镜扫描(scanning electron microscope,简称SEM)试验分析,在循环作用下,大孔隙减小,中、小孔隙增加,排列方式趋于无序状;大粒径颗粒逐渐转化为中、小颗粒,形态趋向于拟圆形;利用关联度分析发现孔隙大小及其角度是影响剪切强度的主要因素;引入Pearson相关系数发现颗粒形态及孔隙大小对压缩指标的影响程度最大。
