汶川地震区崩滑堆积体强度现场直剪试验研究

摘要

以汶川震区漩口一带地震诱发的松散堆积体为研究对象,开展碎石土原状样和重塑样的现场直剪对比试验,探讨不同法向应力、不同粒度组成和不同含水率等条件下碎石土的剪切强度特性.研究结果表明,地质成因和岩土体结构相似、粒度组成不同且级配不良的碎石土的剪切强度特性具有相似性;原状样剪切强度明显高于相同干密度和含水率的重塑样;级配良好的碎石土应变硬化程度略高于级配不良的碎石土,当粒径大于5 mm的粗颗粒含量大于42.9％时,随粗颗粒含量增加,碎石土的内摩擦角增加,而粘聚力则先减小后增大;抗剪强度指标与含水率呈线性负相关关系,随着含水率增高,碎石土抗剪强度降低,其中粘聚力较内摩擦角下降更明显.综合前人研究和本次试验结果,建议汶川震区类似结构组分碎石土天然状态下的剪切强度指标c值取15±3 kPa,ψ值取30°±2°.%In this paper,the earthquake-induced loose sediments near Xuankou,Wenchuan County,Sichuan province are selected to conduct the in-situ direct shear tests of undisturbed gravel soil and remolded soil sample direct shear tests with different situations to explore the shear properties of gravel soils under different vertical pressure,particle size composition and moisture.The study results show that (1) Gravel soils which have similar geological genesis,similar rock mass structure,different size composition and poor gradation have similar shear properties and shear strength.(2) The shear strength of undisturbed gravel soil samples is significantly higher than remolded samples with the same dry density and moisture.(3) Strain hardening strength of well-graded gravel soils is slightly higher than bad-graded gravel soil,when the content of coarse particle whose size is greater than 5 mm is more than 42.9％,friction angle increases with increment of coarse-grained contents,while cohesion decreases firstly and then increases.(4) When moisture content is more than 15.8％,there is a negative correlation between shear strength indexes and moisture content,with gradual increase of moisture,the shear strength of gravel soil will gradually reduce,among which the decrease of cohesion is more remarkable than internal friction angle.Considering others' research and experimental results,we suggest that the gravel soils having similar structure components in Wenchuan earthquake area can select the shear strength indexes c of 15 ± 3kPa and Phi of 30° ± 2°.