考虑降解效应的城市固体废弃物非线性本构模型

基于城市固体废弃物(MSW)的降解及土力学特征,在应力降解模型、等向压缩特性和邓肯-张模型的理论基础上,建立了一个能够描述MSW应力和降解耦合作用的全量非线性本构模型。给出了不同应力状态下单元体体积和轴向变形随时间变化的数学表达,同时给出了所有参数的确定方法。采用该模型对不同龄期和不同围压条件下填埋场现场试样的三轴CD应力-应变曲线以及室内长期一维降解压缩试验进行了模拟。结果表明,模型概念合理、参数明确,能够较全面地描述不同降解龄期垃圾的本构关系,可用于分析填埋场的长期变形。     

考虑纤维加筋作用的城市生活垃圾土弹塑性本构模型

城市生活垃圾土的成分非常复杂,大量纤维材料(如塑料、纺织物、皮革等)的存在使得其力学性质与普通土体之间存在明显差异。现有土体本构模型难以对垃圾土的力学行为进行较好的模拟。对此将垃圾土看作是由纤维材料和泥状物(除纤维材料外剩余的成分)组成的复合体,荷载作用下垃圾土的力学特性取决于纤维材料和泥状物的共同作用,并提出了纤维作用参数R的概念。通过构建新的反映纤维加筋作用的塑性势函数,并依据试验结果推导了纤维作用参数R的演化方程,建立了一个能够合理描述垃圾土力学应力-应变特性的弹塑性本构模型。将垃圾土本构模型的计算结果与三轴排水试验结果和他人模型结果进行比较,发现该模型能较好地反映垃圾土应力-应变特性,尤其是应变水平较大时应力-应变曲线上翘的形状,验证了该模型的合理性和有效性。该模型的建立可为更好地服务于垃圾填埋工程提供理论依据。     

城市固体废弃物的剪切强度机理及本构关系

根据城市固体废弃物（简称MSW）的大三轴固结排水剪试验结果,延伸岩土工程中研究土体的概念和方法,研究MSW的剪切强度机制。MSW与大变形相关的强度特性主要是由于含有大量的纤维状成分所致,在剪切过程中试样总的抗剪能力由剪切面上的摩擦力和纤维状加筋相的拉力所产生。MSW的摩擦强度主要由3部分构成：纤维状成分与土颗粒之间的摩擦,纤维状成分之间的摩擦,和土颗粒之间的摩擦。基于MSW的剪切强度特性,采用邓肯-张本构模型来描述MSW的应力-应变关系。     

考虑初始损伤和蠕变损伤的岩石蠕变全过程本构模型

考虑到天然岩石存在不同程度初始损伤以及蠕变过程中岩石受载后裂隙扩展而导致的新损伤,对具有初始损伤的岩石蠕变特性进行全面描述。根据不闭合结构面应力与法向变形之间的关系,提出裂隙岩石塑性变形体元件,描述岩石蠕变过程中的瞬时塑性变形。引入初始损伤影响因子,建立具有初始损伤的岩石损伤变量演化方程,构建模拟岩石加速蠕变的蠕变损伤体元件。将裂隙岩石塑性变形体和蠕变损伤体与描述瞬时弹性变形和黏弹性变形的广义开尔文模型进行串联组合,形成能够反映具有初始损伤的岩石瞬时弹-塑性变形、稳定蠕变和加速蠕变的蠕变全过程本构模型,提出了进行少量蠕变试验既能解析模型参数的方法,在不同应力水平下模型理论曲线与蠕变试验曲线吻合。     

Study of the mechanical compression behavior of municipal solid waste by temperature-controlled compression tests

Understanding the compression behavior of waste materials is important to the operation and rehabilitation of waste landfill sites. Nevertheless, predicting this behavior is extremely difficult because waste materials are heterogeneous and highly biodegradable. In terms of the mechanism, waste settlement comprises mechanical and biodegradation compressions. This research performs a series of tests to study the mechanical compression behavior of waste materials by using a specifically designed testing device. The device has the ability to keep the temperature low enough to impede the biodegradation of organics, thereby allowing the mechanical compression behavior to be determined. In general, the observed mechanical compression indicates that municipal solid waste (MSW) is very compressible. As the load increases, MSW becomes less compressible because the waste is getting denser. MSW also has a very large creep compression rate, whereby the coefficient of compression of the primary phase is only about 2–8 times that of the creep phase. The magnitude of loading and the elapsed time of loading affect the mechanical compression behavior of MSW. The effects of some parameters on the mechanical behavior are studied herein. MSW with higher dry density had a smaller compressibility. Higher water content also led to a higher compression rate in the primary and creep phases. The waste containing more compressible constituents compressed to a larger extent but with an insignificant increase in the compression rate. The biodegradation of organic constituents did not influence the mechanical compression behavior significantly but increased the rate of creep compression notably. This research also developed a regression relationship between the coefficient of volume compressibility and the dry density of the waste. The prediction of mechanical compression in a field case validated the application of this regression relationship.     

城市固体废弃物本构模型的研究现状及展望

城市固体废弃物(MSW)是由多种无机和有机成分组成的复合材料,具有高压缩性和可降解性。随着时间的变化,基本的物理力学特性发生变化,与传统土体相比,性质差异较大。城市固体废弃物的本构模型对于垃圾填埋场中土工问题的研究极其重要,考虑不同因素的影响,系统总结了国内外一些学者对MSW本构模型的研究现状,指出已有的研究成果主要考虑了荷载引起的瞬时变形、机械蠕变、生物降解、纤维物质的加筋作用等,但这些都是考虑单个因素或者将几个因素简单叠加的本构模型,并未考虑不同因素的耦合作用。结合土体本构模型的发展特点,指出了今后城市固体废弃物本构模型的研究方向和发展趋势：应当综合考虑各种因素对MSW应力-应变关系的影响,从工程实践出发,通过岩土工程、环境工程、化学工程和生物工程等学科的交叉寻求突破,形成考虑生化反应-骨架变形-水气运移-溶质迁移耦合作用的理论框架。     

考虑温度影响的冻土蠕变本构模型

冰作为冻土的基本组成部分,对冻土蠕变的加速蠕变阶段有重要影响。温度通过影响冻土中冰的冻结与融化过程,及其黏塑性流动,引起冻土结构的强化与弱化,从而成为了决定冻土蠕变力学行为的关键因素之一。同时,外部应力也造成冻土的强化与弱化,影响着冻土的蠕变。通过引入硬化因子与损伤因子来考虑温度、应力造成的冻土材料强化与弱化。硬化因子H代表了蠕变过程中强化效应的大小,而损伤因子D则代表了由弱化效应造成的冻土材料相关参数的折减比例,进而提出了适用于冻土的改进西原蠕变本构模型。该模型预测值与试验数据的比较表明：改进的模型不仅能较好地描述初始蠕变阶段、稳定蠕变阶段,而且相比于传统模型,能更好地描述冻土加速蠕变阶段,具有合理性与一定的实用性。     

Permeability and compression characteristics of municipal solid waste samples

Four series of laboratory tests were conducted to evaluate the permeability and compression characteristics of municipal solid waste (MSW) samples. While the two series of tests were conducted using a conventional small-scale consolidometer, the two others were conducted in a large-scale consolidometer specially constructed for this study. In each consolidometer, the MSW samples were tested at two different moisture contents, i.e., original moisture content and field capacity. A scale effect between the two consolidometers with different sizes was investigated. The tests were carried out on samples reconsolidated to pressures of 123, 246, and 369 kPa. Time settlement data gathered from each load increment were employed to plot strain versus log-time graphs. The data acquired from the compression tests were used to back calculate primary and secondary compression indices. The consolidometers were later adapted for permeability experiments. The values of indices and the coefficient of compressibility for the MSW samples tested were within a relatively narrow range despite the size of the consolidometer and the different moisture contents of the specimens tested. The values of the coefficient of permeability were within a band of two orders of magnitude (10⁻⁶–10⁻⁴ m/s). The data presented in this paper agreed very well with the data reported by previous researchers. It was concluded that the scale effect in the compression behavior was significant. However, there was usually no linear relationship between the results obtained in the tests.     

考虑温度影响的花岗岩蠕变全过程本构模型研究

以北山花岗岩为研究对象,采用MTS815岩石力学试验系统开展不同温度条件下的蠕变特性试验研究。考虑温度对花岗岩特征参数的影响,结合岩石蠕变破坏过程中的损伤演化规律,提出了一种新的高温损伤流变元件。通过将高温损伤流变元件代替经典西原模型中Newton元件的方法,构建了能够描述不同温度条件下花岗岩蠕变全过程的本构模型。分析了不同温度条件下花岗岩单轴蠕变试验结果,确定了模型参数,获得了温度对花岗岩蠕变关键参数的影响规律。通过对花岗岩高温蠕变模型进行参数敏感性分析,揭示了弹性模量、黏性系数等关键参数对花岗岩蠕变特性的影响规律,并验证模型在不考虑温度及损伤的影响条件下可退化为经典西原模型。研究表明,建立的花岗岩高温蠕变本构模型可以准确地描述花岗岩典型蠕变全过程的3个阶段,尤其是加速蠕变阶段。黏性系数受损伤的影响越大,花岗岩的稳定蠕变阶段越短,越容易发生加速蠕变。     

软土非线性蠕变压缩模型

从土的力学行为与微观结构相结合的途径探讨滨海软土单向压缩的本构特征,旨在构造一个用于软土一维变形计算的合理形式.据多级加荷压缩试验成果,进一步证明了软土具有非线性蠕变特性;并用幂函数描述了软土压缩蠕变规律,用割线模量法概化了单向压缩的应力-应变的关系.提出了压缩蠕变率(CCR)的概念,并建立与土的结构定量参数(定向概率熵和孔隙分布分维数)、应力比之间的幂函数关系.在此基础上,建议了一个考虑非线性蠕变特性的单向压缩本构模型,并用试验资料初步验证了模型的有效性.建议的模型具有参数少、简便实用之特点,可用于软土地基的沉降计算分析.     

一种横观各向同性岩体蠕变模型

层状岩体由于层理面或者结构面的存在,在力学上具有横观各向同性的特点,现有的各向同性蠕变模型难以全面反映横观各向同性岩体的蠕变力学特性。为构建能够反映横观各向同性岩体的三维蠕变模型,以能反映瞬时应变、减速蠕变和稳态蠕变特征的黏弹性Burgers模型为基础,基于常泊松比假定,在三维各向同性蠕变本构方程的基础上,按照算子替换的方法,将横观各向同性柔度矩阵代替各向同性柔度矩阵,并考虑了平行和垂直层理方向岩体蠕变力学行为的差异性,推导了横观各向同性岩体的三维蠕变本构方程。根据本构方程的特点,提出了根据平行和垂直方向岩体蠕变试验结果进行三维蠕变本构模型中蠕变参数的辨识方法。将提出的模型应用于三轴蠕变试验参数辨识,从而获得了一套完整的三维蠕变参数,并与试验结果进行对比分析,从而验证了所提模型与方法的合理性和有效性。进一步,指出了传统蠕变试验设计方案的局限性,给出了横观各向同性材料蠕变试验设计建议。研究成果为研究岩体三维蠕变机制提供了新思路,可对岩体蠕变试验设计提供相应的科研支撑。     

Modeling elasto-visco-bio-plastic mechanical behavior of municipal solid waste in landfills

Acta Geotechnica - This paper presents a mechanical model for the prediction of short-term and long-term settlement of municipal solid waste in landfills. The load-induced volumetric compression,...     

城市固体垃圾应力-应变-时间关系试验研究

通过室内蠕变试验,研究了城市固体垃圾（MSW）的蠕变变形规律。采用分级加载方式对初始孔隙比为2~4和初始有机物含量在15%~75%的MSW试样进行压缩降解试验。研究发现,应力-应变-时间曲线斜率随着初始孔隙比和初始有机物含量的增加逐渐减小,即材料压缩模量逐渐减小。采用指数模型拟合城市固体垃圾的应力-应变等时曲线,并取得了很好的拟合效果,模型参数简单易求,可反映城市固体垃圾压缩性的大小及其压缩机制。通过对指数模型求导,得到城市固体垃圾的切线压缩模量,切线压缩模量随初始孔隙比和易降解有机物含量的增加呈指数型衰减,初始孔隙比在2~3之间时,初始压缩模量衰减较快,也就是说,在该范围内,初始孔隙比对城市固体垃圾变形影响较大。     

三轴压缩下粉砂质泥岩蠕变本构模型研究

依据粉砂质泥岩三轴压缩蠕变试验结果,分析了岩石的蠕变力学特性。选取线性黏弹性Burgers模型来描述岩石的衰减蠕变和稳定蠕变特性。引入非线性黏塑性元件,将其与Burgers模型串联起来,建立一个新的六元件非线性黏弹塑性Burgers蠕变本构模型。采用非线性Burgers模型来描述岩石的加速蠕变特性。应用Levenberg-Marquardt算法对蠕变试验曲线进行辨识,得出各级应力水平下岩石轴向与径向的蠕变模型参数。对比试验曲线和模型拟合曲线,二者吻合较好,表明线性Burgers模型与非线性Burgers模型可以准确描述岩石3个蠕变阶段的力学特性。模型参数辨识结果表明,在同一级应力水平下岩石轴向与径向的蠕变模型参数各自独立并不统一,模型参数取值时应考虑岩石蠕变的各向异性以及轴向与径向蠕变量、蠕变速率大小的差异。在前7级应力水平下,模型参数应取以轴向应变辨识得到的Burgers模型参数;在第8级应力水平下,模型参数应取以径向应变辨识得到的Burgers模型参数;在破裂应力水平下,模型参数应取以径向应变辨识得到的非线性Burgers模型参数。     

A constitutive model for sand in triaxial compression

Although there is a large number of constitutive models for sand available in the literature it is believed that a fresh approach, striking a balance between complexity and theoretical rigour, is desirable. The approach here has certain conceptual links with the Cam Clay series of elastic–plastic models, but includes the more general starting assumption that the yield function, plastic potential and failure locus should be given quite distinct mathematical expressions. Possible physical bases for the proposed forms are discussed. Ways in which the parameters required to define the model may be determined are suggested and the use of the model is then demonstrated. Firstly, it is shown that, where a limited set of experimental data is available, the model is flexible enough to be able to match the test results. Secondly, it is shown that, where a wide range of test results has been produced, it is possible to determine the model constitutive parameters from a small number of tests and proceed to make satisfactory predictionsfor other, quite different, types of test. The model is developed for sand at a single initial density, but the way in which the constitutive parameters might be expected to vary with density is discussed. The model is described for conditions of triaxial compression, and extension to more general stress states will be needed before it can be put to the test of incorporation in, for example, a finite element program.     

新鲜生活垃圾压缩与直剪联合测定试验研究

在环境土工实验室人工配制了新鲜生活垃圾,采用大型压缩与直剪联合测定仪器,对96个新鲜垃圾试样进行了压缩变形、剪应力及剪应变联合测定试验,研究了垃圾的压缩变形对强度的影响及规律。试样的初始孔隙比分别为2.1、2.5、2.9,试样竖向压力分别为25、50、100、200 kPa,每级压力作用下的时间分别为0、0.25、0.5、1、2、6、12、24 h。试验研究表明,（1）不同压缩时间下剪应力与剪应变的关系符合双曲线模型,模型参数a在0.028～0.144之间,参数b在0.012～0.024之间;（2）不同竖向压力及不同剪应变限值下抗剪强度与竖向压缩应变（压缩时间）的关系可以拟合成多项式的形式,得到了参数的拟合值及相关系数,相关系数在0.63～0.98之间;（3）不同初始孔隙比的抗剪强度与竖向压力的关系符合库仑定律,得到了不同剪应变限值的抗剪强度参数,黏聚力在11.1～34.2 kPa之间,内摩擦角在 11.2°～30.6°之间。     

A simplified analytical model for run-out prediction of flow slides in municipal solid waste landfills

Flow slides in municipal solid waste (MSW) landfills are common geoenvironmental issues in the urban environment and can pose a serious threat to the surrounding population and infrastructure. Prediction of the maximum run-out distance of flow slides in MSW landfills is therefore an essential part of hazard and risk assessment in engineering design. Based on the framework for simple analysis originally developed by Hungr (1995), we propose a simplified analytical model for calculating dam breaks in a plastic fluid along a single inclined base. In the proposed model, a quarter-elliptical shape is used to describe the approximate configuration of the flow slide. Following this step, the physical laws relating to the conservation of mass and energy are used to calculate the potential flow. Of additional note is a boundary condition in mathematics relating to this simplified analytical model, which is also reported in this study. Taking the obvious mobility characteristics of the MSW at point of failure into consideration, a three-phase simplified model along double inclined bases has been further developed for run-out prediction of the flow slide in MSW landfill. The proposed three-phase model is then applied to estimate the maximum run-out distance of two typical flow failures of landfills located in Sarajevo and Bandung, which demonstrate the capability of the proposed simplified analytical model for use in hazard assessments of landfills.     

一种改进的岩石蠕变本构模型

岩石的蠕变曲线通常可以分为衰减蠕变、稳态蠕变和加速蠕变3个阶段。经典的岩石蠕变模型通常包含牛顿黏壶而不是非牛顿黏壶,它们不能描述岩石整个蠕变过程。提出一种改进的岩石蠕变模型,该过程分为3步。首先,用非牛顿黏壶代替Kelvin模型中的牛顿黏壶,给出一种修正的Kelvin模型用来描述衰减蠕变和稳态蠕变。其次,用一种非定常、非牛顿黏壶和塑性体并联的黏塑性体,给出一种经验函数用来描述加速蠕变。再次,用描述瞬时弹性应变的虎克弹簧、修正的Kelvin模型和黏塑性体的串联,给出一种改进的岩石蠕变本构关系及相应的蠕变函数。黏塑性体关闭时,所得蠕变函数可以描述衰减蠕变和稳态蠕变。黏塑性体开启时,蠕变函数可以描述包含加速蠕变在内的3个阶段的岩石蠕变。用给出的蠕变函数拟合了不同应力下的蠕变试验数据,都给出了较好的描述,说明模型具有一定的合理性和适用性。