泸定大渡河桥冰碛土的结构及现场剪切试验研究
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摘要
泸定大渡河桥康定岸分布巨厚层冰碛土,为研究土的抗剪强度特性,在不同位置和深度进行了6组现场剪切试验,基于地质勘察和试验结果分析土的结构特征、剪切强度和变形特性及其与土的结构的关系。研究表明:冰碛土的颗粒以粗粒、巨粒粒组为主,骨架颗粒呈悬浮状,混杂、无序堆积,骨架间充填杂基,形成骨架悬浮密实结构。根据颗粒组成和骨架风化程度,划分为骨架悬浮密实结构、软化骨架悬浮密实结构、砂砾土富集结构、大块石包绕结构等4种细观结构类型。冰碛土剪切破坏主要有剪切破碎带、包绕块石边界、锯齿状剪切和切穿软化骨架等4种模式,剪切荷载作用下线弹性变形阶段明显,剪切刚度大,初始屈服历时短。颗粒骨架和杂基形成的悬浮密实结构,是冰碛土强度与变形特性的内在控制因素,剪切荷载作用下骨架颗粒与具有一定胶结的基质间相互作用,剪切破坏时表现为基质的压碎与骨架的变位。骨架颗粒强度、大骨架颗粒分布、基质胶结程度的不同,对冰碛土强度和变形特性都构成一定的影响。土的抗剪强度、剪切刚度和剪胀性随骨架强度和基质胶结程度的提高而增大,而延性随之变差。
A thick layer of moraine sediments exists on the Kangding bank near the Xingkang Bridge over the Daduhe River in Luding along the Ya' an-Kangding Expressway. In order to study the shear strength characteristics of the moraine soils,six groups of field shear tests were carried out at different locations and depths. Based on the geological survey and test results,the structural characteristics,shear strength and deformation characteristics of the marine soils and their relationship with soil structure were analyzed. The results show that the grain size of the moraine soil is mainly composed of coarse grain and huge granular group.Soil skeleton particles are suspended,mixed,disorderly accumulated and filled with matrix between the skeleton,forming a skeleton suspended compact structure. According to the composition of particles and weathering degree of skeleton,four types of mesoscopic structure can be divided,such as the suspended skeleton dense structure,weathered suspended skeleton dense structure,lenticular sand-gravel enrichment structure and boulder enveloped structure. There are four main shear failure modes of moraine soil: shear fracture zone,enclosing boulder boundary,serrated shear and cutting through weathering framework. Under the shear load,the linear elastic deformation stage with large shear stiffness is obvious,and the yield stage is short. The suspension compaction structure formed by grain skeleton and matrix is the internal controlling factor of strength and deformation characteristics of the marine soil. Under the shear loading,the skeleton particles interact with the cemented matrix,when shear failure occurs,the matrix is crushed and the skeleton is dislocated. The strength and deformation characteristics of the marine soils are affected by the strength of skeleton particles,the distribution of large skeleton particles and the degree of matrix cementation. The shear strength,shear stiffness and dilatancy of the marine soils increase with the increasing skeleton strength and matrix cementation,while the ductility decreases.
A thick layer of moraine sediments exists on the Kangding bank near the Xingkang Bridge over the Daduhe River in Luding along the Ya' an-Kangding Expressway. In order to study the shear strength characteristics of the moraine soils,six groups of field shear tests were carried out at different locations and depths. Based on the geological survey and test results,the structural characteristics,shear strength and deformation characteristics of the marine soils and their relationship with soil structure were analyzed. The results show that the grain size of the moraine soil is mainly composed of coarse grain and huge granular group.Soil skeleton particles are suspended,mixed,disorderly accumulated and filled with matrix between the skeleton,forming a skeleton suspended compact structure. According to the composition of particles and weathering degree of skeleton,four types of mesoscopic structure can be divided,such as the suspended skeleton dense structure,weathered suspended skeleton dense structure,lenticular sand-gravel enrichment structure and boulder enveloped structure. There are four main shear failure modes of moraine soil: shear fracture zone,enclosing boulder boundary,serrated shear and cutting through weathering framework. Under the shear load,the linear elastic deformation stage with large shear stiffness is obvious,and the yield stage is short. The suspension compaction structure formed by grain skeleton and matrix is the internal controlling factor of strength and deformation characteristics of the marine soil. Under the shear loading,the skeleton particles interact with the cemented matrix,when shear failure occurs,the matrix is crushed and the skeleton is dislocated. The strength and deformation characteristics of the marine soils are affected by the strength of skeleton particles,the distribution of large skeleton particles and the degree of matrix cementation. The shear strength,shear stiffness and dilatancy of the marine soils increase with the increasing skeleton strength and matrix cementation,while the ductility decreases.
引文
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[3]张晓键,龚辉,艾传井,等.泥质页岩-粉质黏土土石混合填料原位水平推剪试验研究[J].水文地质工程地质,2017,44(3):79-85.[ZHANG X J,GONG H,AI C J,et al. Research on horizontal pushshear in-situ test of pelitic shale-silty clay mixture[J]. Hydrogeology&Engineering Geology,2017,44(3):79-85.(in Chinese)]
[4]杨忠平,雷晓丹,王雷,等.含石量对土石混合体剪切特性影响的颗粒离散元数值研究[J].工程地质学报,2017,25(4):1035-1045.[YANG Z P,LEI X D,WANG L,et al. Impact of stone content to shear properties of soil-rock mixture using particle flow code simulation[J]. Journal of Engineering Geology,2017,25(4):1035-1045.(in Chinese)]
[5]邓华锋,原先凡,李建林,等.土石混合体直剪试验的破坏特征及抗剪强度取值方法研究[J].岩石力学与工程学报,2013,32(增刊2):4065-4072.[DENG H F,YUAN X F,LI J L,et al. Research on failure characteristics and determination method for shear strength of earth-rock aggregate in direct shear tests[J]. Chinese Journal of Rock Mechanics and Engineering,2013,32(Sup 2):4065-4072.(in Chinese)]
[6]袁广祥,尚彦军,林达明.帕隆藏布流域堆积体边坡工程地质特征及稳定性评价[J].工程地质学报,2009,17(2):188-193.[YUAN G X,SHANG Y J,LIN D M. Engineering geological properties and stability analysis of moraine debris slopes in Palong river drainage area along Sichuan-Tibet highway[J].Journal of Engineering Geology,2009,17(2):188-193.(in Chinese)]
[7]方学东,黄润秋.青藏高原典型冰碛土的物理力学特性研究[J].工程地质学报,2013,21(1):123-128.[FANG X D, HUANG R Q. Physical and mechanical properties of typical moraine soil on the Qinghai-Tibet plateau[J]. Journal of Engineering Geology,2013,21(1):123-128.(in Chinese)]
[8]谢春庆,邱延峻.冰碛层水文地质特征及其对工程影响的研究[J].水文地质工程地质,2006,33(5):90-94.[XIE C Q, QIU Y J. Hydrogeological characteristics of glacial till and its influence on engineering[J]. Hydrogeology&Engineering Geology,2006,33(5):90-94.(in Chinese)]
[9]涂国祥,黄润秋,邓辉,等.某巨型冰水堆积体强度特性大型常规三轴试验[J].山地学报,2010,28(2):147-153.[TU G X,HUANG R Q,DENG H,et al. Study on the strength and deformation behavior of a huge outwash deposits on large-scale triaxial tests[J]. Journal of Mountain Research,2010,28(2):147-153.(in Chinese)]
[10]张永双,曲永新,王献礼,等.中国西南山区第四纪冰川堆积物工程地质分类探讨[J].工程地质学报,2009,17(5):581-589.[ZHANG Y S,QU Y X,WANG X L,et al. On the engineering geological classification of quaternary glacial deposits in southwestern mountain area of China[J]. Journal of Engineering Geology,2009,17(5):581-589.(in Chinese)]
[11]何迎红,屈智迥.冰碛土力学性质与微观结构的研究[J].成都科技大学学报,1990(5):57-62.[HE Y H,QU Z J. Mechanical property and microstructure research of glacial till[J]. Journal of Chengdu University of Science and Technology,1990(5):57-62.(in Chinese)]
[12]张咸恭,王思敬,张倬元,等.中国工程地质学[M].北京:科学出版社,2000:69-76.[ZHANG X G,WANG S J,ZHANG Z Y,et al. China engineering geology[M]. Beijing,Beijing Science Press,2000:69-76.(in Chinese)]
[13]徐文杰,胡瑞林,谭儒蛟,等.虎跳峡龙蟠右岸土石混合体野外试验研究[J].岩石力学与工程学报,2006,25(6):1270-1277.[XU W J,HU R L,TAN R J,et al. Study on field test of rock-soil aggregate on right bank of Longpan in Tiger-leaping gorge area[J]. Chinese Journal of Rock Mechanics and Engineering,2006,25(6):1270-1277.(in Chinese)]