干湿循环作用下膨胀土剪切蠕变特性及长期强度研究

发布时间：2018-02-08 08:04

  本文关键词： 干湿循环 膨胀土 剪切蠕变 蠕变模型 长期强度　出处：《长沙理工大学》2015年硕士论文　论文类型：学位论文

【摘要】：干湿循环作用对膨胀土的内部结构造成了一定程度的损伤,为了进一步研究干湿循环作用下膨胀土应力-应变状态的规律、剪切蠕变模型及土体的长期强度参数衰减规律,建立符合工程实际并合理反映膨胀土蠕变性状的本构模型及确定模型参数,使之能预测膨胀土的蠕变特性,本文进行了不同法向压力下干湿循环作用第0次、2次、4次、6次后膨胀土的室内剪切蠕变试验,通过对剪切蠕变试验曲线的数据分析与整理,对百色膨胀土的剪切蠕变机理进行了研究,构建了半经验半理论的膨胀土剪切蠕变模型,该模型参数物理意义明确,不仅能描述土体的衰减蠕变和等速蠕变阶段,也能对加速蠕变阶段进行描述,能全面反映土体流变粘弹塑性特性且参数较易辨识,其准确性得到了较好的验证。主要得出了以下几点结论:(1)在相同的应力路径下,经干湿循环作用后的土样瞬时变形及累积变形均大于未经干湿循环作用的土样,且变形随干湿循环次数的增加而增大。干湿循环作用对土样的蠕变特性产生了明显影响,其瞬时强度和长期强度也较循环前大幅降低。(2)由剪应变-时间曲线的分析可知,百色膨胀土的非线性蠕变呈现出弹性、黏弹性、黏塑性、黏弹塑性的特征。(3)膨胀土的剪切蠕变变形可分为三个阶段:衰减蠕变阶段、等速蠕变阶段、加速蠕变阶段。在蠕变过程中存在三个剪应力特征值:τ_1、τ_2、τ_f,在低剪应力水平τ_iτ_1时,土体仅发生瞬时变形,但蠕变速率不断减小,最后收敛,无蠕变现象。剪应力继续增大至τ_2τ_i≥τ_1时,土体开始产生蠕变,为衰减蠕变阶段;当剪应力水平τ_2≥τ_iτ_f时,土体开始以恒定的速度发生蠕变,为等速蠕变阶段;当剪应力水平τ_i≥τ_f时,土体进入加速蠕变阶段,迅速失稳破坏。(4)建立了半经验半理论剪切蠕变模型,拟合了模型参数。经验证,该模型的拟合值与蠕变试验得到的实测值较吻合,可为百色地区的工程建设提供了可靠的土体蠕变变形计算依据。(5)干湿循环作用将导致膨胀土的瞬时强度和长期强度大幅衰减,且长期强度的衰减幅度较瞬时强度更大。(6)瞬时强度与长期强度大小的排序依次为:干湿循环作用6次后土体长期强度干湿循环作用6次后土体瞬时强度未经干湿循环作用的土体长期强度未经干湿循环作用的土体瞬时强度。干湿循环作用导致土体瞬时强度和长期强度衰减,其衰减程度随干湿循环作用次数的增加而增大。
[Abstract]:In order to study the stress-strain state of expansive soil under dry-wet cycle, shear creep model and attenuation law of long-term strength parameters of expansive soil are studied in order to further study the stress-strain state of expansive soil under dry-wet cycle. In order to predict the creep characteristics of expansive soil, a constitutive model and model parameters are established, which accord with the engineering practice and reflect the creep behavior of expansive soil reasonably. In this paper, the indoor shear creep tests of expansive soil under different normal pressures under dry and wet cycles were carried out, and the data of shear creep test curves were analyzed and sorted out. The shear creep mechanism of Baise expansive soil is studied, and a semi-empirical and semi-theoretical shear creep model of expansive soil is constructed. The physical meaning of the parameters of the model is clear, which can not only describe the stage of attenuation creep and constant velocity creep of soil. The accelerated creep stage can also be described, and the rheological viscoelastic-plastic properties of soil can be fully reflected, and the parameters can be easily identified, and its accuracy is well verified. The following conclusions are drawn: 1) under the same stress path, The instantaneous deformation and cumulative deformation of soil samples treated by dry and wet cycles are larger than those of soil samples without dry and wet cycles, and the deformation increases with the increase of dry and wet cycles. The creep characteristics of soil samples are obviously affected by dry and wet cycles. Its instantaneous strength and long-term strength are also significantly reduced compared with those before cycling. (2) from the analysis of the shear strain-time curve, it can be seen that the nonlinear creep of Baise expansive soil shows elasticity, viscoelasticity and viscoplasticity. The shear creep deformation of expansive soil can be divided into three stages: attenuated creep stage, isokinetic creep stage and accelerated creep stage. There are three eigenvalues of shear stress in the creep process: 蟿 _ 1, 蟿 _ 2, 蟿 _ f, and 蟿 _ I 蟿 _ 1:00 at low shear stress level. There is only instantaneous deformation in soil, but creep rate decreases continuously, and finally converges without creep phenomenon. The shear stress continues to increase to 蟿 _ 2 蟿 _ I 鈮，

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