膨胀土干湿循环试验和超固结性与结构性本构模型研究

发布时间：2018-05-24 21:29

本文选题：膨胀土 + 干湿循环　；参考：《广西大学》2014年硕士论文

【摘要】：膨胀土对在其分布区域内的工程建设产生不利影响。例如,在湿热交替频繁气候条件下膨胀土路基的不均匀沉陷、隆起和开裂,膨胀土边坡的滑溜、坍塌及滑坡,膨胀土地基上房屋的开裂等工程地质灾害。因此,研究膨胀土在干湿循环条件下的压缩特性和建立能够反映膨胀土力学特性的本构模型对膨胀土区域的工程建设有着重要的理论和实际意义。为此,本文以南宁膨胀土的原状样、重塑样、干湿循环样为试验对象,对其做了相关的基本物理力学试验和一维固结试验研究,然后建立了反映膨胀土超固结性的本构模型和反映膨胀土超固结性、结构性的本构模型。随后利用有限元分析软件的子程序接口编制了对应于上述模型的材料子程序,建立了适用于超固结土、结构性土的数值模拟平台。基于数值模拟平台进行了系列数值模拟试验,验证了上述模型以及对应子程序的精度与稳定性。最后,对比本文模型和其他模型模关于Fujinomori黏土与Boom黏土的模拟结果及试验数据。上述试验研究表明,干湿循环效应使得膨胀土产生了一种特殊的结构性,该结构性对膨胀土压缩特性的影响与结构性对土压缩特性的影响相反,故此在本文中被称为“负结构性”,具体表现为：膨胀土循环样在固结压力小于“负结构性”屈服应力之前,压缩性不受干湿循环效应的影响；当固结压力大于该应力时,压缩性随“负结构性”的衰减而增强；在“负结构性,,随固结压力的增加被完全破坏后,压缩性不再受干湿循环效应的影响。在本构模型研究方面,针对膨胀土的超固结性本文建立了改进超固结状态参量下负荷面模型。该模型能够准确描述超固结土在三轴压缩试验过程中的孔隙比与有效应力变化规律、变形特征、应力-应变关系等特性,且能更为连续平滑地模拟实际超固结七的弹塑性应力-应变关系。同时,该模型相对UH模型能够更准确地刻画重超固结Fujinomori黏土的应力-应变关系、应变软化以及峰值强度与残余强度等特征。为反映超固结性与结构性对膨胀土的影响,本文建立了改进状态变量上下负荷面模型。该模型模拟的应力路径、超孔隙水压力变化、应力-应变关系等完全符合超固结土及结构性土力学行为的一般规律。同时,该模型能准确描述Boom原状黏土与Fujinomori黏土的应力-应变的非线性、应变软化以及峰值强度与残余强度等特征。此外,该模型相对Nakai和Hinokio模型能更准确地反映主应力旋转效应的影响。本文通过建立考虑超固结性、结构性影响的本构模型,扩充了有限元软件的材料子程序库,为文中的两个本构模型在实际工程中的应用奠定了基础,随着对膨胀土超固结性、结构性的进一步科学的定性定量研究,上述两个本构模型的实际应用指日可待。
[Abstract]:Expansive soil has an adverse effect on engineering construction in its distribution area. For example, engineering geological disasters such as uneven subsidence, uplift and cracking of expansive soil subgrade, slippage, collapse and landslide of expansive soil slope, cracking of house on expansive soil foundation, etc. Therefore, it is of great theoretical and practical significance to study the compression characteristics of expansive soil under dry-wet cycle and to establish a constitutive model which can reflect the mechanical properties of expansive soil. Therefore, in this paper, the basic physical and mechanical tests and one-dimensional consolidation tests of the expansive soil in Nanning were carried out, including the undisturbed sample, the remolded sample and the dry wet cycle sample. Then a constitutive model reflecting the overconsolidation of expansive soil and a constitutive model reflecting the overconsolidation and structure of expansive soil are established. Then the material subroutine corresponding to the above model is compiled by using the subroutine interface of the finite element analysis software, and a numerical simulation platform for the overconsolidated and structural soils is established. A series of numerical simulation experiments are carried out based on the numerical simulation platform to verify the accuracy and stability of the above model and the corresponding subroutine. Finally, the simulation results and experimental data of Fujinomori clay and Boom clay are compared with other models. The experimental results show that the dry and wet cycle effect makes expansive soil produce a special structure. The influence of this structure on the compression characteristics of expansive soil is opposite to that of the structural effect on soil compression characteristics. Therefore, it is called "negative structure" in this paper, which shows that the compressibility of expansive soil cyclic sample is not affected by dry-wet cycle effect before the consolidation pressure is less than "negative structural" yield stress, and when the consolidation pressure is greater than this stress, the compressibility of the expansive soil is not affected by the dry and wet cycle effect before the consolidation pressure is less than the negative structural yield stress. The compressibility increases with the attenuation of "negative structure", and when the "negative structure" is completely destroyed with the increase of consolidation pressure, the compressibility is no longer affected by the effect of dry-wet cycle. In terms of constitutive model, an improved load surface model for the overconsolidation of expansive soils is established in this paper. The model can accurately describe the variation law of void ratio and effective stress, deformation characteristics and stress-strain relationship of overconsolidated soil during triaxial compression test. Furthermore, the elastoplastic stress-strain relationship of the actual over-consolidated seven can be simulated more smoothly and continuously. Compared with UH model, the model can describe the stress-strain relationship, strain softening, peak strength and residual strength of heavily overconsolidated Fujinomori clay more accurately. In order to reflect the influence of overconsolidation and structure on expansive soil, an improved upper and lower load surface model of state variables is established in this paper. The stress path, excess pore water pressure and stress-strain relationship simulated by this model fully accord with the general law of mechanical behavior of overconsolidated soil and structural soil. At the same time, the model can accurately describe the stress-strain nonlinearity, strain softening, peak strength and residual strength of Boom and Fujinomori clay. In addition, the model can reflect the effect of principal stress rotation more accurately than Nakai and Hinokio models. In this paper, the material subprogram library of the finite element software is expanded by establishing a constitutive model considering the overconsolidation and structural effects, which lays a foundation for the application of the two constitutive models in the practical engineering. Further scientific qualitative and quantitative studies on the structure of the above two constitutive models can be applied in the near future.
【学位授予单位】：广西大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU443;TU411

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