四川理县欢喜村冰水堆积体降雨条件下变形机理研究
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摘要
四川理县欢喜村具有干暖河谷气候特征,降雨量少、蒸发量大,冰水堆积体在降雨作用下的变形特征及机理与以往降雨型滑坡有较大差异。通过水土化学试验、矿物成分检测、电镜扫描(SEM)、降雨模拟-现场中剪试验等手段查明冰水堆积物遇水结构损伤机理,以及由此引起的强度衰减特征及幅度,在此基础上,采用SEEP/W模块分析堆积体降雨条件下地下水浸润、饱和特征及孔隙水压力变化趋势,结合地质环境条件归纳总结堆积体变形机理及过程。研究表明:冰水堆积物遇水后,细粒组分内矿物(以石膏为主)溶解、颗粒重排列共同导致充填细粒土结构弱化、损伤,进一步发展促使大颗粒间相互作用程度减弱,加之粒间水的润滑、软化最终引起土体整体强度大幅度衰减,其中c值降低20.6%,φ值降低34.1%,c值下降幅度弱于φ值;此外,研究区特殊的地质环境条件导致缓坡段降雨入渗效果优于陡坡段,饱和时间、范围、深度的不同形成土体强度差异变化,加之前缘良好的临空条件,导致坡体近前缘端表层易朝临空方向产生蠕滑变形,变形体后缘形成拉张裂缝,并为降雨入渗提供通道,多次降雨-蠕滑变形累积作用使变形体前缘锁固段减小,形成失稳破坏。
The deformation mechanism and characteristics of outwash deposit body under rainfall condition are different from those of rainfall-induced landslides. The study area is featured with characteristics of dry and warm valley climate,with small rainfall amount but large evaporation. Through water-soil chemical effect tests,mineral composition detection,scanning electron microscopy( SEM),rainfall simulation and medium scale in-situ shear test,the structural damage mechanism of outwash deposit in water is examined,and the characteristics and amplitude of strength attenuation are also investigated. On this basis,the infiltration and saturation characteristics of groundwater and the change trend of pore water pressure are analyzed by using SEEP/W module. The deformation mechanism and process of outwash deposit body are concluded in summary in line with geoenvironmental conditions. Research results unveil that when outwash deposit contacts with water,the dissolution of mineral( mainly gypsum) together with the rearrangement of mineral particles weakens the soil structure,which further develops and mitigates the interactions among large particles,and finally results in the dramatic attenuation of overall soil strength under the lubrication and softening effect of water: the value of cohesion declines by 20. 6%,and internal friction angle by34.1%. Moreover,due to the special geological condition of the study area,the effect of rainfall infiltration in gentle slope is better than that in steep slope; and the differences in saturation time,range and depth brings about the variation of soil strength. Besides,favorable free surface gives rise to creep deformation in the direction of the free surface in the front edge and tensile cracks in the back edge of deformed body,providing passage for rainfall infiltration. Cumulative creep deformation diminishes the locked segment in the front edge of deformed body,and finally induces instability.
The deformation mechanism and characteristics of outwash deposit body under rainfall condition are different from those of rainfall-induced landslides. The study area is featured with characteristics of dry and warm valley climate,with small rainfall amount but large evaporation. Through water-soil chemical effect tests,mineral composition detection,scanning electron microscopy( SEM),rainfall simulation and medium scale in-situ shear test,the structural damage mechanism of outwash deposit in water is examined,and the characteristics and amplitude of strength attenuation are also investigated. On this basis,the infiltration and saturation characteristics of groundwater and the change trend of pore water pressure are analyzed by using SEEP/W module. The deformation mechanism and process of outwash deposit body are concluded in summary in line with geoenvironmental conditions. Research results unveil that when outwash deposit contacts with water,the dissolution of mineral( mainly gypsum) together with the rearrangement of mineral particles weakens the soil structure,which further develops and mitigates the interactions among large particles,and finally results in the dramatic attenuation of overall soil strength under the lubrication and softening effect of water: the value of cohesion declines by 20. 6%,and internal friction angle by34.1%. Moreover,due to the special geological condition of the study area,the effect of rainfall infiltration in gentle slope is better than that in steep slope; and the differences in saturation time,range and depth brings about the variation of soil strength. Besides,favorable free surface gives rise to creep deformation in the direction of the free surface in the front edge and tensile cracks in the back edge of deformed body,providing passage for rainfall infiltration. Cumulative creep deformation diminishes the locked segment in the front edge of deformed body,and finally induces instability.
引文
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[11]杜杰,冯文凯,石豫川,等.汶川地震对望月寨滑坡稳定性影响研究[J].岩土力学,2010,31(3):856-862.
[12]黄家华,冯文凯,王琦,等.遇水作用下冰水堆积体角砾土微观结构与抗剪强度[J].水文地质工程地质,2016,43(5):149-154.
[13]曾琳洁.基于SWCC的小岐村冰碛堆积体斜坡强度及稳定性研究[D].成都:成都理工大学,2014.
[2] FENG Wen-kai,ZENG Lin-jie,LI Wen-san. Study on the Dynamic Characteristics and Stability Analysis Method of Glaciofluvial Deposits in Dry and Warm Valley[C]∥Global View of Engineering Geology and the Environment:Proceedings of the International Symposium and 9thAsian Regional Conference of IAEG. September 24-25,2013:135-140.
[3] FENG Wen-kai,HUANG Run-qiu,LIU Han-chao. The Deformation Characteristics and Engineering Properties of Large Glacial Tills in the Upper Reaches of the Minjiang River[C]∥Proceeding of the 11th IAEG Congress,Auckland,New Zealand,September 5-10,2010.
[4]林鸿州,于玉贞,李广信,等.降雨特性对土质边坡失稳的影响[J].岩石力学与工程学报,2009,28(1):198-204.
[5]黄润秋. 20世纪以来中国的大型滑坡及其发生机制[J].岩石力学与工程学报,2007,26(3):433-454.
[6]高华喜,殷坤龙.降雨与滑坡灾害相关性分析及预警预报阀值之探讨[J].岩土力学,2007,28(5):1055-1060.
[7]魏来.降雨诱发滑坡预测模型研究[D].重庆:重庆交通大学,2013.
[8]谢剑明.降雨对滑坡灾害的作用规律研究[D].武汉:中国地质大学(武汉),2004.
[9]庞学勇,包维楷,吴宁.岷江上游干旱河谷气候特征及成因[J].长江流域资源与环境,2008,17(增1):46-53.
[10]张一平,段泽新,窦军霞.岷江上游干暖河谷与元江干热河谷的气候特征比较研究[J].长江流域资源与环境,2005,14(1):76-82.
[11]杜杰,冯文凯,石豫川,等.汶川地震对望月寨滑坡稳定性影响研究[J].岩土力学,2010,31(3):856-862.
[12]黄家华,冯文凯,王琦,等.遇水作用下冰水堆积体角砾土微观结构与抗剪强度[J].水文地质工程地质,2016,43(5):149-154.
[13]曾琳洁.基于SWCC的小岐村冰碛堆积体斜坡强度及稳定性研究[D].成都:成都理工大学,2014.
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