兰州大学机构库 >土木工程与力学学院
原状饱和黄土的各向异性边界面模型
Alternative TitleAn Anisotropic Bounding Surface Model for Structured Saturated Loess
马文国
Thesis Advisor王兰民
2017-03-01
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name博士
Keyword原状饱和黄土 边界面塑性模型 结构性 各向异性 孔隙水压力
Abstract

黄土是指第四纪以来在干燥气候和风的作用下形成的沉积物,它是一种具有质地均匀、大空隙、弱胶结和柱状节理发育等性质的特殊土。黄土的颗粒大小介于黏土与细砂之间,颗粒成分主要以粉粒为主,呈浅黄色或黄褐色。主要分布在我国甘肃、陕西、宁夏和山西等地区,空间上有着面积广、厚度大、地层完整和地貌类型复杂等特点,为世界上黄土最为发育的地区。

论文以试验和理论研究为主要目标,以各类土的动割线模量、西安市东三环与地铁三号线交汇处工程场地的原状饱和黄土和宁夏固原六盘山机场东北处石碑村塬上的原状黄土为研究对象。对土的动割线模量和阻尼比之间的关系进行了比较深入的研究。对原状和重塑饱和黄土样本在等向固结和K0固结条件下进行结构性特性试验;同时对西安市东三环与地铁三号线交汇处工程场地的原状饱和黄土在K0偏压固结模式下进行排水、不排水条件下的力学特性试验;对宁夏固原六盘山机场东北处石碑村塬上的原状黄土进行频率为1Hz的循环荷载试验。根据本文建议使用的黄土结构性和各向异性的概念,在各向同性广义剑桥模型的基础上构造了一个考虑原状饱和黄土结构性和各向异性的单面型边界面RSA-MCC模型。利用模型对两处原状饱和黄土的结构性、排水、不排水和循环三轴试验下的应力应变关系和孔隙水压力等内容进行了计算,论文的主要研究内容和成果有如下三个方面:

(1)系统研究了动割线弹性模量E或动割线剪切模量G(因为两者之间存在换算关系,本文不再严格区分,均使用Gsec表示,统称为动割线模量,除非特别声明)和阻尼比λ的力学关系,在弹性阶段土的弹性模量、切线弹性模量和割线弹性模量都是一样的。动割线模量Gsec是一种全量关系,它是描述岩土材料刚度的物理量,本文主要以Gsec来表达动割线模量。而对应应力状态下的λ是岩土材料在振动过程中波动能量耗散的度量,是结构的动力特性之一,是描述岩土材料胶结和致密程度的物理量。首先,利用众多学者认可的结论:动割线模量的倒数1/Gsec和剪应变γ之间一般有较好的线性关系,使用线性回归分析得到回归直线的截距和斜率这两个重要参数。其次,对拥有前面线性关系的Gsec再与阻尼比λ的试验结果进行线性回归分析,也发现Gsec和λ之间也有良好的线性规律,并且通过大量试验结果证实了Gsec和λ之间良好线性关系的可靠性,而先前的文献显示Gsec和λ的关系是非线性的,根据离心模型试验结果证实Gsec比λ更为可靠,这种线性关系为选择正确的Gsec提供了一种简单可行的方法。最后,通过这两个重要参数来优化H-D双曲线模型,预测的Gsec和试验值误差在12%以内。预测和试验结果更为接近,也为评价工程场地的地震安全性提供计算依据。(2)以临界状态土力学和各向同性广义剑桥模型为基本研究框架,对岩土塑性力学的基本试验和理论进行了较为详细的介绍。主要以前面介绍的原状饱和黄土为研究对象,在广义剑桥模型的基础上增加结构性和各向异性参数构造了一个新的边界面模型RSA-MCC。边界面用来表征土体在应力历史下的先期固结程度,构造的单面型RSA-MCC模型没有屈服面的概念。原状饱和黄土使用了三个硬化参量,它们分别是固结压力、结构性参量和各向异性参量,其中:结构性参量使用Rouainia等(2000)提出的方法,而各向异性参量选择Dafalias(2013)建议的旋转硬化参量。RSA-MCC模型的映射中心在初始加载过程中取为应力原点,而在复杂应力条件下进行卸载和反向加载时本文借鉴前人的研究成果将映射中心移动到卸载应力点处。总的塑性模量由边界面处的塑性模量和真实应力与虚应力之间的模量插值函数构成,使得塑性模量在边界面内能够连续变化,而土的塑性应变和硬化或软化也在边界面内随着应力状态的不同而连续变化。(3)论文对西安市东三环与地铁三号线交汇处工程场地的原状饱和黄土进行了等压固结、K0偏压固结模式下的结构性试验和模拟;对K0偏压固结模式下的排水和不排水剪切试验进行了数值模拟。对宁夏固原六盘山机场东北处石碑村塬上的原状黄土饱和固结后再进行双向循环剪切荷载试验结果进行了数值研究。结果显示:新构建的RSA-MCC模型在考虑了结构性和各向异性时对试验结果均有较好的模拟。总之,RSA-MCC模型对原状饱和黄土的静力和动力特性有较好的模拟能力。

Other Abstract

Loess is a kind of sediment formed under the action of dry climate and wind in the Quaternary period. It is a kind of special soil which has the characteristics of uniform texture, large space, weak cementation and columnar joint development. The particle size of loess is between clay and fine sand, and the particle composition is mainly silt, which is light yellow or brown. It is mainly distributed in Gansu, Shaanxi, Ningxia and Shanxi, and has the characteristics of wide area, large thickness, complete formation and complex landform.

For the purpose of theoretical research and practical engineering, this paper takes the experimental and theoretical research as the main research object. Based on the dynamic secant modulus of various soil, the undisturbed saturated loess of the engineering site of intersections of East Third Ring Road and the Subway Line 3 in Xi'an City, the undisturbed loess of Shibei village in the northeast of the Liupanshan Airport in NingXia as the research object. In this paper, the static and cyclic loading tests of undisturbed saturated loess samples under the condition of isotropic consolidation and K0 consolidation are carried out. According to the structure and anisotropy of loess proposed a single side bounding surface plasticity model base on isotropic generalized Cam-clay model, or “RSA-MCC” for short. The stress path, stress-strain relationship and pore water pressure were simulated by RSA-MCC model, the main research contents and results are as follows:

(1) The relationship between G and λ was systematic studied, the G is essentially the secant modulus under the present stress state, and it is a deformation theory of plasticity and may describe the stiffness of geomaterials. Because there is a conversion relationship between the elastic modulus E and the shear modulus G, this paper is no longer strictly differentiated, both using Gsec and as the dynamic secant modulus for short, unless otherwise stated. The shear modulus G and secant shear modulus Gsec of soil at the elastic stage are the same. However, the λ is a measure of wave energy dissipation, it is a physical quantity that describes the cementation and compactness of geomaterials. Firstly, the relationship between 1/ Gsec and dynamic shear strain γ was analysis by linear regression method, the optimized parameters a and b representing the intercept and slope of this regression line. Then, the linear regression analysis of the Gsec with the previous linear relationship and λ also was discovered a good linear relationship by the least square method. However, the all literature show that the relationship between Gsec and λ is nonlinear at large deformation stage. The results show that this linear relationship can overcome the shortcomings of the nonlinear relationship found in the large deformation stage and can predict λ in the hysteresis loop that is not closed case. According to the results of centrifuge model test, it is proved that Gsec is more reliable than λ, which provides a simple and feasible method for selecting the correctly Gsec for further evaluation of seismic safety at engineering sites. Finally, a hyperbolic model was constructed by two optimization parameters a and b, the error between the predicted value and the test value is less than 12%.(2) In the framework of critical state soil mechanics and isotropic generalized Cam-clay model (GCC), the basic theory and experiment of soil plastic mechanics were introduced in detail. A new bounding plasticity model (RSA-MCC) is proposed for the study of the undisturbed saturated loess based on the GCC, the bounding surface is used to characterize the degree of preconsolidation of the soil, and the new RSA-MCC model has no yield surface. Three kinds of hardening parameters are used in the undisturbed saturated loess, which are consolidation pressure pc, structural parameters r and anisotropic parameters α, The structural parameters are obtained by using Rouainia et al. (2000), while the anisotropic parameters are selected by Dafalias (2013) proposed for the typical rotational hardening parameters. The mapping center of RSA-MCC model adopt the origin of stress during the initial loading process, the mapping center moved to the starting point of the unloading stress when unloading and reverse loading. The total plastic modulus is determined by the plastic modulus on the bounding surface and interpolation function between the true stress and virtual stress, this modulus formulation can ensure the plastic modulus can continuously change in the bounding surface. The plastic strain, hardening and softening of the soil also may continuously change in the bounding surface.(3) In this paper, the structure properties of undisturbed and remolded saturated loess are studied under the condition of isotropic and K0 consolidation. RSA-MCC model is used to study the drainage behavior of undisturbed saturated loess under K0 consolidation state, because this kind of state of consolidation to soil structural disturbance is small. The drained and undrained shear tests was carried out to the undisturbed saturated loess of the engineering site of intersections of East Third Ring Road and the Subway Line 3 in Xi'an City, and the two-way cyclic shear loading tests was carried out to the undisturbed saturated loess of Shibei village in the northeast of the Liupanshan Airport in NingXia. The RSA-MCC model is used to simulate the undrained shrear tests and the two-way cyclic shear loading test under K0 consolidation state. The simulation results of stress-strain relationship and pore water pressure are given, the results shown that the new proposed RSA-MCC model is reasonable.

URL查看原文
Language中文
Document Type学位论文
Identifierhttps://ir.lzu.edu.cn/handle/262010/225780
Collection土木工程与力学学院
Recommended Citation
GB/T 7714
马文国. 原状饱和黄土的各向异性边界面模型[D]. 兰州. 兰州大学,2017.
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