摘要
几乎所有土的本构关系模型研究都是以试验得到的土样的应力应变关系曲线为依据的。在此情况下,应力应变关系曲线反映的是土样整体的变形特征,土样被认为是单元体。在土的三轴试验中引入土样全表面变形场(局部变形)测量技术,通过测量在土样表面标定的特征点的变形过程,得到土样表面的局部变形特征。发现土样在发生剪切破坏后,剪切带内和带外的变形特点截然不同。根据剪切带的发生和发展情况,土样的变形可以分成破坏前、破坏和破坏后3个阶段,在不同阶段土样表现出不同的变形性质。在破坏前阶段,土样变形大体均匀,此时整体的应力应变曲线具有代表性;在破坏阶段,土样在某一点(或几个点)开始出现破坏并逐渐发展,最后形成贯穿的剪切带,观测到的变形是剪切带内和剪切带外的土体变形的综合结果;在破坏后阶段,荷载(应力)不再增加,剪切带外的上下两部分土体就像刚体一样变形不再增长,观测到的土样"变形"仅仅来自于土样沿着剪切带的滑动。此时不能根据土样沿剪切带的摩擦滑移直接定义土样应变。土样整体的应力应变关系曲线是土样作为结构体的响应,不是单元体的响应。据此认为:土的本构关系模型研究应该包括土体未发生破坏时的应力应变关系、破坏准则和破坏后沿剪切带的摩擦滑动性质,模型研究的重点在于破坏前阶段的应力应变关系的描述。所谓的临界状态其实是土样沿剪切带的类似于刚体滑动的状态。
Almost all the constitutive models for soils are established on the basis of the stress-strain relationship curve of soil samples. In this case, the stress-strain relationship curve reflects the deformation characteristics of a soil sample as a whole, in which the soil sample is considered as a representative element volume. In this paper, by adopting the deformation field（local deformation） over the entire surface of soil samples in triaxial tests, local deformation characteristics can be obtained by measuring the deformation process at the feature points over the surface of the soil samples. It is found that after the shear failure occurs the deformation feature in the shear band is quite different from that out of the shear band. According to the analysis of the occurrence and development of the shear band, the samples apparently exhibit three states during the tests, i.e., pre-failure, in-failure and post-failure, in correspondence to different deformation features. In the pre-failure state, the deformation of the entire sample is approximately uniform, and the global stress-strain curve is representative. In the failure state, failure occurs from a point（or some points） and develops gradually until the shear band cleaves the sample; in addition, the observed deformation for the entire sample may be the combination of deformations in the failure zones and non-failure zones. In the post-failure state, load（stress） does not continue to increase, and the deformation of the top and bottom blocks out of the shear band also does not continue to increase as a rigid body, and at the same time, the deformation is exclusively owing to the blocks of the sample sliding along the shear band. Therefore, it is not appropriate to define the strain of the sample to result from frictional sliding along the shear band. The stress-strain curve of the entire sample reveals structural response of soil, not an elementary response. So we think that the constitutive models for soils should include the stress-strain relationship of soils in the pre-failure state, failure criterion and frictionalsliding characteristic along the shear band in post-failure state. The important point of establishing the constitutive model is how to describe the stress-strain relationship of soils in the pre-failure state. The so-called ＂critical state＂ is actually a rigid sliding state along the shear failure surface.
出处
《岩土工程学报》
EI
CAS
CSCD
北大核心
2016年第3期385-394,共10页
Chinese Journal of Geotechnical Engineering
基金
国家自然科学基金项目(51309047)
关键词
三轴试验
表面变形场测量
剪切带
应力应变关系
临界状态
triaxial test
measurement of surface deformation field
shear band
stress-strain relationship
critical state
