共查询到16条相似文献，搜索用时 93 毫秒
1.
基于热力学内变量理论,提出能综合考虑毛细滞回效应和非饱和土体积变形影响的土-水特征曲线模型。热力学第二定律推导结果表明：毛细滞回现象和塑性变形本质上是一种耗散行为;吸力和饱和度的变化不仅与流相变化直接相关,而且也受到固相体积变化的约束与影响;土-水特征曲线的流相体积变化与固相变形之间存在相互耦合作用。从微观上阐明滞回现象产生的机制以及变形对吸力的影响,建立了考虑体变及滞回效应的土-水特征曲线一般性模型。然后采用边界面塑性理论,在只增加两个新参数的情况下,建立了一个简化的能描述毛细滞回及塑性孔隙比变化影响的新模型。最后,利用已有试验数据对这一模型进行了验证,结果表明,新模型能考虑土体变形的影响,并能较为准确地描述毛细滞回现象,模型预测结果与已有的试验数据吻合较好。 相似文献
2.
在Wheeler本构模型框架的基础上,提出了一个水力与力学耦合的本构模型。该模型中的土-水特征曲线采用毛细滞回内变量模型,能够更好地描述水力历史变化下毛细滞回现象对非饱和多孔介质变形的影响,同时也可描述非饱和多孔介质变形对渗流的影响。非饱和土的强度不仅与吸力有关,而且受到饱和度的影响。相同的吸力下,土样经过吸湿和脱湿路径的饱和度不同,因此,非饱和土的强度也不同。此模型以体积含水率的塑性变化和体变的塑性变化为硬化参数,不仅能描述基质吸力对非饱和土的强化作用,而且考虑了饱和度对强度及变形的影响。试验结果与模型预测基本吻合,证明该模型能够模拟非饱和土的主要特性。为了简化,此模型是在各向同性荷载下推得的,有待于推广到一般的应力状态 相似文献
3.
非饱和土的水力和力学特性及其弹塑性描述 总被引：6，自引：3，他引：3
简单回顾了非饱和土本构模型研究的发展历程,总结了近几年非饱和土弹塑性本构模型最新研究成果,重点介绍了能统一模拟非饱和土水力性状和力学性状耦合的弹塑性本构模型。通过对建立模型过程中的几个核心问题讨论,较详细地说明该类模型的结构、性能以及相关问题。非饱和土水力性状的滞回性用假定存在饱和度弹性区间的弹塑性过程来模拟;该类耦合模型不仅考虑了吸力对非饱和土水力性状和力学性状的影响,还考虑了饱和度对应力-应变关系和强度的影响以及土体变形对土-水特征曲线的影响。用同一套模型参数,耦合模型可统一预测在吸力控制或含水率控制下沿各种应力路径下非饱和土的水力-力学特性,并简单介绍了膨胀性非饱和土的弹塑性本构模型以及耦合模型在有限元数值计算中的应用。 相似文献
4.
大量的非饱和土干湿循环试验表明,当土体处于吸湿过程直至吸力降低为0 kPa时,土体并不能达到完全饱和状态,还存在一定的残余气体。在高饱和度时,由于残余气体以封闭气泡的形式分布在土体中,土体呈现较大的压缩性,使其与饱和土的性质不同。在这种状态下,现有的非饱和土本构模型预测到的土饱和度为100%,与试验结果存在一定的偏差。为了使本构模型在高饱和度状态时具有较高的精度,对非饱和土的毛细滞回和塑性变形耦合本构模型进行了修正,使其能够考虑残余含气量的影响。通过预测与实测结果比较,证明了新模型能够有效地模拟残余含气量对非饱和土力学特性的影响。 相似文献
5.
热-水-力耦合作用下非饱和土变形特性的弹塑性模拟 总被引：1，自引：0，他引：1
《岩土力学》2017,(4):1060-1068
在已有的非饱和土水-力耦合模型基础上,耦合考虑温度影响,建立了一个热-水-力耦合作用下非饱和土弹塑性本构模型。该模型以土骨架平均应力、修正吸力和温度为应力状态变量,以土骨架应变、饱和度和熵为应变状态变量。通过引入与温度相关的屈服面(LY、TY)以及相应的硬化规律来考虑温度对土体变形的影响。利用建立的模型,对文献中不同吸力和温度条件下的等向压缩和三轴排水剪切试验进行预测,预测结果表明,该模型能够较好地定量描述热-水-力耦合作用下非饱和土的变形特性。 相似文献
6.
多孔介质中的流动问题,与孔隙介质的特性,含水量状态以及含水量的变化历史密切相关。基于毛细循环滞回理论模型,考虑含水量变化历史对土水特征关系的影响,在开发的U-DYSAC2有限元程序中进行了相应的数值实施。在试验给定的初边值条件下进行了非饱和渗流模拟分析,并将模拟结果与实测数据比较,表明在压力边界条件反复变化下,考虑滞回效应能获得更接近实测的结果,证实该模型在模拟各种循环变化条件下非饱和土渗流初边值问题的适用性与必要性。对入渗重分布反复变化条件下非饱和土柱流动的数值模拟表明,考虑滞回与不考虑滞回条件下,含水量、孔隙水压力和湿峰的迁移的预测在入渗后的重分布过程差异较大。考虑滞回效应时,土柱上部的脱湿速率、下部的吸湿速率比不考虑滞回时要低。从而证实了非饱和多孔介质中的土水状态依赖于含水量变化,而且强烈依赖于土体的水力路径变化。因此,循环边界条件变化下,毛细滞回效应在非饱和渗流模拟中的影响显著,必须加以考虑。 相似文献
7.
非饱和土毛细滞回内变量模型的修正 总被引：1，自引：1，他引：0
土-水特征关系是基质吸力和含水率之间关系。在反复干湿循环路径下土-水特征曲线呈现出毛细滞回特性。基于毛细滞回内变量理论和传统的土-水特征关系经验模型,提出了能模拟在任意干湿循环路径下土-水特征关系的修正模型。该模型比原模型增加了一个可逆参数,考虑了含水率的可逆变化,使扫描线在靠近边界线的时候斜率不会无限大,同时保留了原模型精度。通过与文献中的试验结果进行比较,修正模型可以更好地模拟非饱和土的土-水特征关系的循环滞回特性,并讨论了可逆参数的确定方法。 相似文献
8.
《岩土力学》2017,(8):2157-2166
在川西地区,由砂砾石与黏土颗粒构成的混合土路基经常会发生沉降变形问题。对于交通荷载作用下土体中的累积变形,可通过建立循环荷载作用下的动本构模型进行描述。在边界面弹塑性理论的框架内,综合考虑崩坡积混合土非饱和状态和细颗粒含量两大主要影响因素,结合能比较真实描述非饱和土体湿陷性能的LC(loading-collapse)屈服曲线,同时基于可移动映射中心的映射准则,采用经典的修正剑桥模型作为塑性势方程,构建了混合土的非饱和动本构模型,其参数可通过拟合或常规试验获得。通过与试验结果进行对比,该模型不仅可以较好地反映非饱和混合土在静载和循环荷载下的力学特性,而且能够真实地预测土体在加、卸载过程中的滞回特性。其结果可为川西混合土路基沉降变形预测提供理论依据。 相似文献
9.
土-水特征关系是基质吸力和含水率之间的关系。进气值对起点在高饱和度区的脱湿扫描线有较大的影响。Wei等[1]提出了毛细滞回内变量模型,可以对扫描线任意滞回情况进行模拟,但该模型没有考虑进气值的影响,对起点在高饱和度区的脱湿扫描线的模拟与实际情况有一定偏差。基于毛细滞回内变量理论和传统的土-水特征关系经验模型,提出了考虑进气值影响的修正毛细滞回内变量模型。该模型可以考虑进气值对起点在高饱和度区的脱湿扫描线的影响。通过对多种土样的数值模拟计算显示,修正模型较好地解决了原模型对起点在高饱和度区的脱湿扫描线的模拟不能考虑进气值影响的缺点。 相似文献
10.
微观土颗粒及孔隙分布的非均匀性及由此引起的瓶颈效应是造成非饱和土土-水特征曲线(SWCC)滞后效应的主要原因。引入分形理论,考虑非饱和土孔径及渗流路径的微观分形特性,提出了一个用于描述水在非饱和土中渗流的毛细管模型。模型中将非饱和土孔隙简化为一系列具有不同孔径大小的毛细弯管,其孔径大小及弯曲程度假定服从分形规律。在此基础上,推导得了非饱和土的吸湿与脱湿过程的饱和度S_e~-水头高度h来描述土-水特征曲线滞后效应的特征方程以及饱和度S_e~-相对水力传导系数Kr特征方程。与室内观测结果及已有研究的对比表明,该模型相比以往方法,可更好地模拟非饱和土土-水特征曲线的滞后效应。对非饱和土吸湿与脱湿过程滞后效应的本质进行了对比分析,揭示了滞后效应产生的根本原因在于土体中流通孔隙大小的非均匀性。 相似文献
11.
In the last decades, a number of hydro-mechanical elastoplastic constitutive models for unsaturated soils have been proposed. Those models couple the hydraulic and mechanical behaviour of unsaturated soils, and take into account the effects of the degree of saturation on the stress–strain behaviour and the effects of deformation on the soil–water characteristic response with a simple reversible part for the hysteresis. In addition, the influence of the suction on the stress–strain behaviour is considered. However, until now, few models predict the stress–strain and soil–water characteristic responses of unsaturated soils in a fully three-dimensional Finite Element code. This paper presents the predictions of an unsaturated soil model in a Three-dimensional Framework, and develops a study on the effect of partial saturation on the stability of shallow foundation resting on unsaturated silty soil. Qualitative predictions of the constitutive model show that incorporating a special formulation for the effective stress into an elastoplastic coupled hydro-mechanical model opens a full range of possibilities in modelling unsaturated soil behaviour. 相似文献
12.
Several researchers have reported that the mean effective stress of unsaturated soils having a relatively high degree of saturation gradually decreases under fully undrained cyclic loading conditions, and such soils can be finally liquefied like saturated soils. This paper describes a series of simulations of fully undrained cyclic loading on unsaturated soils, conducted using an elastoplastic model for unsaturated soils. This model is a critical state soil model formulated using effective stress tensor for unsaturated soils, which incorporates the following concepts: (a) the volumetric movement of the state boundary surface containing the critical state line owing to the variation in the degree of saturation; (b) the soil water characteristic curve considering the effects of specific volume and hydraulic hysteresis; and (c) the subloading surface concept for considering the effect of density. Void air is assumed to be an ideal gas obeying Boyle's law. The proposed model is validated through comparisons with past results. The simulation results show that the proposed model properly describes the fully undrained cyclic behavior of unsaturated soils, such as liquefaction, compression, and an increase in the degree of saturation. Finally, the effects of the degree of saturation, void ratio, and confining pressure on the cyclic strength of unsaturated soils are described by the simulation results. The liquefaction resistance of unsaturated soils increases as the degree of saturation and the void ratio decrease, and as the confining pressure increases. Furthermore, the degree of saturation has a greater effect on the liquefaction resistance than the confining pressure and void ratio. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
13.
The interparticle bonding effect due to water menisci plays an important role in the hydromechanical coupling properties of unsaturated soils. This paper presents an unsaturated hydromechanical coupling model that considers the influence of matric suction, degree of saturation, and microscopic pore structure on the interparticle bonding effect. The enhanced effective stress and bonding variable are selected as constitutive variables. The bonding variable is correlated with the ratio between unsaturated void ratio and saturated void ratio. The deformation characteristics of unsaturated soils are described based on the bounding surface plasticity theory. A soil–water characteristic model that considers deformation and hydraulic hysteresis is integrated into the constitutive model to achieve hydromechanical coupling. The proposed model can effectively describe the hydromechanical coupling characteristics and the meniscus bonding force of unsaturated bimodal structure soils; the model parameters can be easily obtained through routine experiments. The experimental results of unsaturated isotropic compression, the wetting/drying cycle, and unsaturated triaxial shear tests are used to validate the capability of the proposed model.
相似文献14.
非饱和土土-水特征曲线预估方法研究 总被引：2，自引：0，他引：2
在Wei等[1]基于多相孔隙介质非平衡渗流理论提出的多孔介质热动力学混合物理论模型的基础上,建立了一个能描述不考虑土骨架变形的非饱和土土-水特征曲线动态模型。依据非饱和土土-水特征曲线动态模型,推导出不考虑土骨架变形的气-水两相非饱和土的饱和度演化方程。利用饱和度演化方程并结合多步流动瞬态试验的成果,通过数值反演,提出了一种能利用多步流动瞬态试验数据快速确定非饱和土土-水特征曲线的方法。通过对低液限粉土及低液限黏土的多步流动瞬态试验研究发现,饱和度演化方程能较好地模拟非饱和土在小基质吸力步长变化下饱和度的变化规律。此外,通过对多步流动瞬态试验试样饱和度的模拟确定的非饱和土土-水特征曲线与联合测试系统测得的土-水特征曲线的结果较为一致。 相似文献
15.
This paper presents a three‐dimensional elastoplastic constitutive model for predicting the hydraulic and mechanical behaviour of unsaturated soils. It is based on experimental results obtained from a series of controlled‐suction triaxial tests on unsaturated compacted clay with different initial densities. Hydraulic hysteresis in the water‐retention behaviour is modelled as an elastoplastic process, with the elastic part modelled by a series of scanning curves and the elastoplastic part modelled by the main drying and wetting curves. The effect of void ratio on the water‐retention behaviour is studied using data obtained from controlled‐suction wetting–drying cyclic tests on unsaturated compacted clay with different initial densities. The effect of the degree of saturation on the stress–strain‐strength behaviour and the effect of void ratio on the water‐retention behaviour are considered in the model, as is the effect of suction on the hydraulic and mechanical behaviour. The initial density dependency of the compacted soil behaviour is modelled by experimental relationships between the initial density and the corresponding yield stress and, thereby, between the initial density and the normal compression line. The model is generalized to three‐dimensional stress states by assuming that the shapes of the failure and yield surfaces in the deviatoric stress plane are given by the Matsuoka–Nakai criterion. Model predictions of the stress–strain and water‐retention behaviour are compared with those obtained from triaxial tests with different initial densities under isotropic compression, triaxial compression and triaxial extension, with or without variation in suction. The comparisons indicate that the model accurately predicts the hydraulic and mechanical behaviour of unsaturated compacted soils with different initial densities using the same material constant. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
16.
以饱和度与有效应力为状态变量,通过引入描述不饱和与饱和土孔隙比差的状态变量,将Zhang等提出的饱和土体应力诱导各向异性动弹塑性本构模型推广到不饱和土体中,使其可描述不饱和土在动力循环荷载作用下的力学特性行为。通过对已有不饱和土体在完全不排水条件下的动三轴试验进行理论模拟,验证了所提出不饱和土本构模型的正确性。最后基于所提出本构模型,讨论了在不排水条件下初始饱和度对不饱和土动力特性研究。结果表明,不饱和土在动力荷载作用下,土体的孔隙比将减少,导致饱和度增加;当初始饱和度较高时,不饱和土会转化为饱和土,从而发生液化现象。该研究成果对研究不饱和土在地震等动力荷载作用下的力学特性行为具有重要意义。 相似文献