应力路径分析在岩土工程中的应用

本文简单回顾了应力路径分析的研究历史，阐述了总应力路径和有效应力路径的关系、功用和方法。并以常见的岩土工程问题为例进行分析，得出土的应力－应变依赖于应力路径，应力路径的分析将推动岩土工程学科向前发展的结论。     

考虑应力路径影响下砂土的三维本构模型

应力路径是影响土的应力-应变关系的一个重要因素。通过对一组砂土（日本Toyoura砂）三轴试验结果的详细分析,揭示了应力路径对剪应变及体积应变的影响规律,进而建立了能反映应力路径影响的应力-应变增量本构模型,提出的统一硬化参数反映了其剪胀特性,引入的变换应力能反映三维应力-应变特性。     

应力路径对砂土变形特性影响的细观机制研究

在对已有试验结果进行分析基础上,从细观角度研究了砂土变形机制。通过对简化的颗粒单元体的受力及变形分析,推导了主应力比与θ的关系以及孔隙比与θ的关系。结果表明,颗粒单元体变形过程中主应力比与孔隙比有着对应的关系,这与"应力路径对塑性体应变的影响主要是由应力比引起的"的试验结论是一致的。从细观角度分析了应力路径(主要是主应力比)影响砂土变形的过程。研究表明,砂土体中存在着大孔隙以及两种基本状态的颗粒单元体结构孔隙,它们是控制砂土变形特性的关键因素,大孔隙受应力路径影响不大,而颗粒单元体结构孔隙则与应力路径密切相关,主要表现为主应力比对塑性体应变的影响;从细观角度分析了峰值应力比与相变应力比的关系,即初始孔隙比越小,相变应力比越低,峰值应力比越高,这与宏观试验结果是一致的。     

黏土的应力路径本构模型

根据黏土应力-应变曲线的特点及其应力路径的相关特性,将作者所建立的砂土应力路径本构模型扩展用于黏土,建立了黏土的应力路径本构模型,利用变换应力方法将SMP准则用于黏土的应力路径本构模型,使模型得到了合理的三维化。黏土的应力路径模型与修正剑桥模型相比,在双向加载A区和卸载D区二者完全相同;在单向加载B区和F区,两种模型均可计算塑性应变;特别是在C区和E区,黏土的应力路径模型可计算塑性应变,而修正剑桥模型的塑性应变为0。通过与修正剑桥模型比较和对藤森黏土试验结果的预测,反映了黏土应力路径本构模型描述黏土在不同应力路径条件下应力-应变特性的优越性。     

砂土应力路径本构模型的试验验证

建立了砂土应力路径本构模型,揭示了应力路径影响砂土应力-应变关系的本质,在平均应力p变化不大的条件下主要是剪应力比的影响。当使用该模型计算应力-应变关系时,将应力路径线性化,分别计算等平均应力p路径和等应力比 路径上的应变。利用试验对模型所引用的关系式 进行验证,试验结果和 的理论值较为吻合,证明了模型引用关系式 的合理性。并利用模型对复杂路径下砂土的应力-应变关系进行预测,对模型预测与试验结果进行比较,结果表明模型可以合理地考虑复杂应力路径对砂土应力-应变关系的影响。     

不同应力路径下砂土的神经网络弹塑性本构模型研究

基于多种应力路径下砂土的加载、卸载和再加载过程的三轴排水试验数据，研究了三种应力路径对屈服面的影响，其结果表明，不同应力路径对砂土的本构模型有着不可忽视的作用。在此基础上，建立了砂土的弹塑性神经网络模型，对相应路径下的本构关系进行了学习。实例分析表明，该模型能够很好地描述具体应力路径下的本构关系，神经网络建模方法具有方便、容错性强的特点，对岩土力学快速、高效数值方法的进一步发展具有重要的参考价值。同时，在这种弹塑性应力-应变关系中，笔者并没有使用塑性势函数，这在目前的弹塑性本构关系的建模中是一种新的尝试。     

应力路径对黄土固结不排水剪强度的影响

用总应力法研究了应力路径对陇西Q3原状黄土的固结不排水剪强度的影响。试验基于正交设计,考虑了含水率、固结比、固结末径向应力和剪切路径4个因子、4种水平。试验结果表明,当黄土各向异性程度较小时应力路径对黄土的固结不排水抗剪强度有一定影响;基于正交设计的黄土三轴固结不排水剪试验的破坏点与普通三轴固结不排水剪试验（均压固结常规剪切）得到的破坏点处于一个条带内。黄土强度随含水率的变化规律与普通三轴固结不排水剪试验的相同。     

杭州湾浅层储气砂土应力路径试验研究

利用GDS非饱和三轴试验系统开展了杭州湾储气砂土主动压缩、被动压缩、主动伸长与被动伸长等4种应力路径试验研究,以论证应力路径对非饱和砂土的变形性状与强度特性影响。结果表明,在卸荷应力路径被动压缩与被动伸长下非饱和砂土的应力-应变曲线呈明显的应变软化性状,而加荷应力路径主动压缩与主动伸长则分别表现为轻度应变软化及显著应变硬化变形特征;非饱和砂土的强度参数在卸荷与加荷应力路径中也存在差异,前者的有效凝聚力高于后者,而内摩擦角则相反;但其表观凝聚力与基质吸力关系在不同应力路径下均可用乘幂函数 有效描述,而试验参数a、b值不同,公式 可合理地用于表述非饱和砂土的强度特性。     

岩土材料的各向异性强度准则

岩土材料的强度往往表现出很强的各向异性,而已有的各向同性强度准则不能够描述这一特性。提出一个岩土材料的各向异性强度准则。为了描述材料的各向异性,引入了一个由应力张量和组构张量的联合不变量表达的各向异性参数。该参数可以描述加载方向和材料组构方向的夹角。强度准则是基于材料在子午面和偏平面上的破坏特性而建立的,这为描述广义的材料强度各向异性提供了方便。与原各向同性强度准则相比,各向异性强度准则只引入了两个新的模型参数,而且所有的模型参数都可以通过常规的室内试验结果确定。该准则的预测结果与砂土、黏土、天然黏土和岩石的试验结果比较表明,它能够很好地描述岩土材料强度的各向异性     

高水材料的水化硬化反应机理的研究

高水材料是８０年代才问世的一种新型材料。它以铝酸钙或硫铝酸钙等为甲料（分别称为高铝型甲料和硫铝型甲料）,以石灰、石膏和外加剂等为乙料,经磨细、均化等工艺而制成的甲、乙两种固体粉料。使用时,加大量的水配制成浆液,用管道将其送到使用地点,混合后的浆液便很快凝固。由于该材料可在水灰比２－５∶１的情况下浇注成型,又有速凝早强等特点,所以称为高水材料。研究高水材料的水化硬化机理,对全面深入地了解其性能与应用有重要意义。１　单矿物水化铝酸一钙（ＣＡ）是高铝型甲料的主要矿物,与水反应可得到一系列结晶良好的水化…     

Automatic substepping integration of the subloading tij model with stress path dependent hardening

This paper discusses the numerical integration of the subloading tij model. This is an elastoplastic model with stress path dependent hardening, which can predict the behaviour of normally consolidated clays or loose sands, as well as of over-consolidated clays or dense sands, with a small number of material parameters. Three features distinguish the subloading tij model from the conventional ones: (a) the use of a modified stress space given by tensor t_ij; (b) the split of the plastic strain increments in two components leading to a stress path dependent hardening; and (c) the use of two yield surfaces (subloading yield surface and normal yield surface). This last feature is based on the concept of sub-yielding stress states and adds an extra internal strain-like hardening variable, related to the relative density state, which demands its own evolution law. The three characteristics above greatly improve the prediction capabilities of the model, with respect to those of the well-known Cam clay model, at the cost of only two additional parameters. Nonetheless, the numerical integration of the constitutive equations of subloading tij model is a bit challenging, mainly due to the stress path dependent hardening. In order to integrate the equations of subloading tij model in the same way as for any conventional model, the authors reformulated its equations in a simpler and direct manner. Here, these equations are integrated using multi-step explicit schemes, such as modified-Euler and Runge–Kutta–Dormand–Price, with automatic error control. Simple forward-Euler scheme is also used for the sake of comparison. The results show that the modified-Euler scheme is more accurate as well as faster than the other schemes analysed over a wide range of error tolerance. Besides, the automatic feature of these schemes is a great convenience for the users of numerical codes.     

Rotational kinematic hardening model for three‐dimensional stress reversals in sand

A kinematic hardening mechanism has previously been proposed to capture the behavior of soil during large stress reversals in the triaxial plane. This mechanism is now extended to the principal stress space. It incorporates rotation and intersection of yield surfaces to achieve a consistent and physically rational fit with experimentally observed soil behavior during large three‐dimensional stress reversals. An existing elasto‐plastic model with isotropic hardening is used as the basic framework to which the rotational kinematic hardening mechanism has been added. The new combined model preserves the behavior of the isotropic hardening model under monotonic loading conditions, and the extension from isotropic to rotational kinematic hardening under three‐dimensional conditions is accomplished without introducing new material parameters. The framework of the model is presented here with some comparisons between theoretical and experimental directions of strain increment vectors to indicate the potential of the model. Copyright © 2008 John Wiley & Sons, Ltd.     

应力路径对黄土结构性的影响

利用SLB–1型应力应变控制式三轴剪切渗透试验仪,对陕西杨凌黄土进行了应力控制的常规三轴压缩、减压三轴压缩和等p应力路径的各向等压固结不排水三轴试验,探讨和分析应力路径对黄土结构性的影响。试验结果表明：不同应力路径下,随着初始围压的增大,黄土的结构性参数并不是一味地不断增大,而是在300 kPa时有一个峰值,且当黄土的含水率较高时,其结构性参数相对较小。     

标准砂小应变特性的应力路径三轴试验研究

通过应力路径三轴试验,将标准砂样分别K0固结和等向固结到平均球应力150 kPa,在p-q平面内沿0o,45o,90o,135o,180o,225o,270o,315o应力路径方向进行16组试样的应力应变关系试验研究,对当前应力路径、前期应力路径、应力路径旋转条件下1 %范围内剪应变和体积应变规律进行了对比分析。由试验曲线整理得到的剪切模量和体积模量随应力路径变化规律与已有的Bothkennar黏土试验结果类似。     

On the validity of the flow rule postulate for geomaterials

This paper is concerned with a fundamental assumption in the theory of plasticity: the direction of plastic strain increments is independent of the loading (stress) increment direction. This assumption, also known as plastic flow rule postulate, works quite well for metal‐like materials. However, geomaterials such as sand present deformational mechanisms that are distinctive from those of metals when they are loaded. As such, we hereby examine the validity of this postulate for granular media accounting for their discrete nature. This is accomplished by analysing the mechanical behaviour of a cubic assembly of polydispersed spherical articles using a particle flow code. An extension to Gudehus' response envelope to three‐dimensional conditions is used to study the incremental character and influence of loading direction on the behaviour of these materials. It is found that plastic flow in granular media is governed by both current state variables and incremental loading direction and magnitude, especially under non‐axisymmetric stress conditions. The flow rule postulate of plasticity remains valid only in axisymmetric and biaxial conditions. We also verified that the plastic response might be significantly influenced by the stress path (or history) taken prior to loading. These findings raise the question of whether or not classic elastoplastic models based on the above postulate will have serious shortcomings, especially in true‐triaxial conditions. Copyright © 2013 John Wiley & Sons, Ltd.