膨胀土长期强度特性试验研究

发布时间：2018-06-19 21:08

本文选题：膨胀土 + 非线性流变　；参考：《中南林业科技大学》2013年硕士论文

【摘要】：膨胀土是一种典型的非饱和土,具有高塑性、多裂隙性和反复胀缩性等灾害性地质土特点。在我国的广大地域分布着层厚、埋深和形态不同的膨胀土,给工程建设带来了诸多困扰。实际工程中许多路堤、边坡、坝基等由于膨胀土流变特性而产生失稳和变形等问题,特别是所产生的强度破坏具有长期潜在的危险。因此基于土流变学理论,开展对膨胀土的非线性剪切蠕变和长期强度特性的研究,建立相关的分析模型和理论,是解决膨胀土工程在长期荷载作用下的强度和变形问题的前提,对指导膨胀土灾害治理具有重要的工程意义。本文在综合分析国内外对土流变研究的基础上,吸取了国内外在流变学特别是土流变学方面的最新研究成果,依托国家自然科学基金项目“膨胀土非线性流变特性研究”(项目编号：50978097),以及湖南省科技厅资助项目“膨胀土非线性流变特性本构模型研究”(项目编号：2010SK3047)等科研课题,开展了南宁膨胀土长期强度特性展开研究。通过室内流变试验、流变理论分析和数值计算,论文主要取得了以下结论及创新成果： (1)南宁膨胀土非线性剪切蠕变特性及模型研究 1)膨胀土的剪切蠕变曲线分为衰减蠕变和非衰减蠕变。当水平剪应力较低时,蠕变曲线进入衰减阶段,呈衰减型蠕变；当水平剪应力较高时,剪切蠕变曲线分为衰减阶段、等速阶段和加速阶段,呈非衰减蠕变。 2)根据剪切蠕变曲线可得剪应力-应变等时曲线,可知膨胀土的应变随着时间的发展而增加；等时曲线是一簇曲线,水平剪应力较低时为线性,随着水平剪应力的增大呈非线性；水平剪应力恒定时,竖向应力大的等时曲线非线性程度越明显。说明膨胀土的剪切蠕变不仅是时间的函数,还与应力水平有关,亦即膨胀土的剪切蠕变具有非线性蠕变特点。 3)通过对膨胀土非线性剪切蠕变特性的试验研究和分析,基于0RIGIN数值分析与拟合,建立了非线性的蠕变经验模型,该模型的理论值和试验值的拟合度较高,能准确的描述膨胀土的非线性剪切蠕变特点,丰富了土的非线性流变研究理论,也为膨胀土在长期荷载作用下的变形计算提供了理论论据。 (2)南宁膨胀土长期强度特性及理论模型研究 1)通过对膨胀土的剪切蠕变试验,同时可对其进行长期强度特性研究。由试验得到的长期强度曲线发现,膨胀土的长期强度极限小于瞬时强度,随着时间的发展,膨胀土的长期强度逐渐降低。 2)南宁膨胀土的长期强度发展可分为两个不同的阶段：前期阶段土的强度在短时间内降低很快；后期阶段膨胀土的强度在很长时间内缓慢降低并逐渐趋近于某一稳定的长期强度极限。 3)在直剪试验条件下,膨胀土的长期抗剪强度与竖向应力有关,长期强度在不同时间的发展均服从库伦强度定律。竖向应力越大,同一时刻膨胀土的长期强度也越大。 4)由于膨胀土的强度随时间降低,根据莫尔-库伦条件可得到不同时刻的粘聚力和内摩擦角。通过研究发现,膨胀土的粘聚力和内摩擦角随时间的发展而降低,粘聚力的变化较为明显,随时间变化大,而内摩擦角的变化较小,受时间的影响较小。 5)通过对膨胀土长期强度曲线的分析,运用数值分析软件对曲线进行拟合,对不同竖向荷载下的参数进行回归,建立了能描述膨胀土的长期强度发展的非线性经验模型t=f(σ,t)。经验证该,该模型能较好地反映出南宁膨胀土在长期荷载作用下强度随时间的变化规律,能直观、快捷的得出长期强度的相关参数,且根据该模型得到的理论值和试验结果高度吻合。开展膨胀土长期强度特性研究,建立相关理论和模型,进一步丰富了土流变学理论,也为膨胀土工程的长期强度和变形分析提供可靠的理论依据,具有广泛的工程应用价值。
[Abstract]:Expansive soil is a typical unsaturated soil, which has the characteristics of high plasticity, multi fracture and repeated expansion and shrinkage. In the vast area of China, the expansive soil with thick layer, deep buried depth and different shape has brought many troubles to the construction. Many embankments, slopes and dam foundations in practical engineering are due to the rheological characteristics of expansive soil. The problems of instability and deformation, especially the resulting strength failure, have long potential risks. Therefore, based on the theory of soil rheology, the study of nonlinear shear creep and long-term strength characteristics of expansive soils and the establishment of relevant analytical models and theories are the solutions to the strength and deformation of expanded soil under long-term load. The premise of the problem is of great engineering significance for the management of the expansive soil disaster. Based on the comprehensive analysis of the soil rheology at home and abroad, this paper draws the latest research achievements in the field of rheology, especially the soil rheology at home and abroad, and relies on the National Natural Science Fund Item "Research on the nonlinear rheological properties of expansive soil" (project). Numbered: 50978097) and the research subject of "nonlinear rheological characteristic constitutive model of expansive soil" (project number: 2010SK3047), which is funded by the Hunan provincial science and technology department. The long-term strength characteristics of Nanning expansive soil are carried out. The following conclusions are obtained by the laboratory rheology test, rheological theory analysis and numerical calculation. And the results of innovation:
(1) nonlinear shear creep characteristics and model study of Nanning expansive soil
1) the shear creep curve of expansive soil is divided into attenuating creep and non attenuated creep. When the horizontal shear stress is low, the creep curve enters the attenuation stage and assumes the attenuating creep. When the horizontal shear stress is high, the shear creep curve is divided into the attenuation stage, the isokinetic stage and the acceleration stage are non attenuated creep.
2) according to the shear creep curve, the shear stress strain isochronous curve can be obtained, and the strain of the expansive soil increases with the development of time; the isochronous curve is a cluster curve, the horizontal shear stress is linear when the stress is low, and it is nonlinear with the increase of the horizontal shear stress, and the higher the vertical stress is constant, the more nonlinear degree of the isochronous curve is the higher vertical stress. It is obvious that shear creep of expansive soil is not only a function of time, but also related to the stress level, that is, the shear creep of expansive soil has nonlinear creep characteristics.
3) based on the experimental study and analysis of the nonlinear shear creep characteristics of expansive soil, a nonlinear creep empirical model is established based on 0RIGIN numerical analysis and fitting. The theoretical value of the model is well fitted to the test value, which can accurately describe the nonlinear shear creep characteristics of expansive soil and enrich the theory of Nonlinear Rheological Study of soil. It also provides a theoretical basis for the deformation calculation of expansive soil under long term loading.
(2) long-term strength characteristics and theoretical model of Nanning expansive soil
1) through the shear creep test of expansive soil, the long-term strength characteristics of the expansive soil can be studied at the same time. The long-term strength curve obtained from the test shows that the long-term strength limit of the expansive soil is less than the instantaneous strength. With the development of time, the long-term strength of expansive soil decreases gradually.
2) the long-term strength development of Nanning expansive soil can be divided into two different stages: the strength of soil in the early stage decreases rapidly in a short time, and the strength of expansive soil decreases slowly in the later stage and gradually approaches to a certain stable long-term strength limit.
3) under the condition of direct shear test, the long-term shear strength of expansive soil is related to the vertical stress, and the development of long term strength obeys the law of Kulun strength at different time. The greater the vertical stress is, the longer the long-term strength of expansive soil is at the same time.
4) because the strength of the expansive soil decreases with time, the cohesion and internal friction angle can be obtained at different times according to the Mohr Kulun condition. Through the study, it is found that the cohesion and internal friction angle of the expansive soil decrease with the development of time, the change of cohesive force is more obvious, the change of the internal friction angle is smaller and the influence of the time is smaller. Smaller.
5) through the analysis of the long-term strength curve of the expansive soil, the curve is fitted by numerical analysis software, and the parameters under different vertical loads are regressed, and a nonlinear empirical model t=f (sigma, t) which can describe the long-term strength development of expansive soil is established. It is proved that this model can better reflect the long-term load of Nanning expansive soil in the long term load. With the changing law of the strength with time, the relative parameters of the long term strength can be obtained intuitively and quickly, and the theoretical values obtained according to the model are in good agreement with the experimental results.
The study of the long-term strength characteristics of expansive soil, the establishment of relevant theories and models, further enriches the theory of soil rheology, and provides a reliable theoretical basis for the analysis of long term strength and deformation of expansive soil engineering, and has extensive engineering application value.
【学位授予单位】：中南林业科技大学
【学位级别】：硕士
【学位授予年份】：2013
【分类号】：TU443

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