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1.
This paper presents a fully coupled finite element formulation for partially saturated soil as a triphasic porous material, which has been developed for the simulation of shield tunnelling with heading face support using compressed air. While for many numerical simulations in geotechnics use of a two‐phase soil model is sufficient, the simulation of compressed air support demands the use of a three‐phase model with the consideration of air as a separate phase. A multiphase model for soft soils is developed, in which the individual constituents of the soil—the soil skeleton, the fluid and the gaseous phase—and their interactions are considered. The triphasic model is formulated within the framework of the theory of porous media, based upon balance equations and constitutive relations for the soil constituents and their mixture. An elasto‐plastic, cam–clay type model is extended to partially saturated soil conditions by incorporating capillary pressure according to the Barcelona basic model. The hydraulic properties of the soil are described via DARCY 's law and the soil–water characteristic curve after VAN GENUCHTEN . Water is modelled as an incompressible and air as a compressible phase. The model is validated by means of selected benchmark problems. The applicability of the model to geotechnical problems is demonstrated by results from the simulation of a compressed air intervention in shield tunnelling. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
2.
对于大面积浅层风化土边坡,当下部含有浅水位或不透水基岩层时大降雨将导致下部气体被封闭。随着湿润峰的下移,气压不断增大。封闭气压力不仅降低了雨水在边坡土体的入渗率,而且对边坡的稳定有显著影响。通过分析封闭气压力的形成和相关理论,提出取 大小的气压力头来研究边坡的稳定性（Hc为一水头值,与土体孔隙尺寸分布有关; hd为土体进气值水头）。结合非饱和土的Mohr-Coulomb破坏准则和极限平衡法,将封闭气压力引入到边坡的稳定分析中,建立了考虑气压力影响下的稳定分析模型。与传统的不考虑气压力的稳定分析方法作对比,提出了气压力影响率概念。研究表明,封闭气压力显著降低了边坡的安全系数,传统的无限边坡稳定计算方法偏于危险。研究结果对无限边坡的强降雨安全预报具有较好的指导作用。 相似文献
3.
The paper describes a multi-phase, multi-scale rational method for modeling and predicting free-field wave propagation and the weakening and liquefaction of near-surface soils. The one-dimensional time-domain model of a soil column uses the discrete element method (DEM) to track stress and strain within a series of representative volume elements (RVEs), driven by seismic rock displacements at the column base. The RVE interactions are accomplished with a time-stepping finite-difference algorithm. The method applies Darcy’s principle to resolve the momentum transfer between a soil’s solid matrix and its interstitial pore fluid. Different algorithms are described for the dynamic period of seismic shaking and for the post-shaking consolidation period. The method can analyze numerous conditions and phenomena, including site-specific amplification, down-slope movement of sloping ground, dissolution or cavitation of air in the pore fluid, and drainage that is concurrent with shaking. Several refinements of the DEM are described for realistically simulating soil behavior and for solving a range of propagation and liquefaction factors, including the poromechanic stiffness of the pore fluid and the pressure-dependent drained stiffness of the grain matrix. The model is applied to four sets of well-documented centrifuge studies. The verification results are favorable and highlight the importance of the pore fluid conditions, such as the amount of dissolved air within the pore water.
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.
A new constitutive formulation for simulating the behaviour of nearly saturated sands under seismic loads is presented. The formulation is based on combining the Henry's law for dissolution of gas in water, the ideal or perfect gas law and the law of conservation of mass. The effects of transient air dissolution in water on the compressibility of partially saturated soils are also taken into account. The model was calibrated based on numerical simulations of isotropically consolidated cyclic triaxial tests conducted on partially saturated samples of Toyoura sand. A multi‐yield plasticity soil constitutive model implemented in the finite element code DYNAFLOW was used for these numerical simulations. It is shown that the formulation proposed here is able to reasonably predict the soil cyclic undrained behaviour at various degrees of saturation (95% and higher). Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
6.
我国高寒山地区广泛发育连片冰碛土堆积边坡,因其普遍具有级配宽、分选差、孔隙率大等特点,在复杂构造地貌条件和冻融条件影响下,往往会发生剧烈的水-热-质交换而产生富冰滞水润滑效应,进而诱发冰碛土界面型滑坡灾害。冰碛土界面型滑坡对该区域工程建设具有重大的潜在风险,而系统掌握高寒山地区冰碛土水热迁移及聚冰冻胀孕灾机制是实现该类地质灾害科学防控的基础性工作。据此,首先研究了冰碛土的粒度组成和结构特征,明确了冰碛土存在典型的“二粒组”的组构特征;而后,围绕冻融作用下冰碛土水热迁移及聚冰冻胀规律研究现状予以深入剖析,厘清了冰碛土的多相多场迁移机制及聚冰冻胀特性;最后,围绕冰碛土边坡孕灾演化过程开展研究,阐明了内部富冰带成因及滞水促滑失稳机制。研究表明：(1)冰碛土的典型组构特征为其水-热-质多相多场迁移提供了前提条件,也是诱发局部化聚冰冻胀的重要因素;(2)冰碛土因剧烈水热迁移产生的定向化界面聚冰现象,而界面效应是诱发边坡失稳的“源生地”,探究冰碛土边坡失稳问题应重点关注富冰带发育特征及其促滑失稳机制;(3)高寒山地区冰碛土边坡的孕灾机制主要受两种模式控制：(1)混态水-热迁移聚冰效应;(2)富冰带... 相似文献
7.
A coupled two‐phase fluid flow and elastoplastic deformation model for unsaturated soils: theory,implementation, and application 
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下载免费PDF全文 Although numerous numerical models have been proposed for simulating the coupled hydromechanical behaviors in unsaturated soils, few studies satisfactorily reproduced the soil–water–air three‐phase coupling processes. Particularly, the impacts of deformation dependence of water retention curve, bonding stress, and gas flow on the coupled processes were less examined within a coupled soil–water–air model. Based on our newly developed constitutive models (Hu et al., 2013, 2014, 2015) in which the soil–water–air couplings have been appropriately captured, this study develops a computer code named F2Mus3D to investigate the coupled processes with a focus on the above impacts. In the numerical implementation, the generalized‐α time integration scheme was adopted to solve the equations, and a return‐mapping implicit stress integration scheme was used to update the state variables. The numerical model was verified by two well‐designed laboratory tests and was applied for modeling the coupled elastoplastic deformation and two‐phase fluid flow processes in a homogenous soil slope induced by rainfall infiltration. The simulation results demonstrated that the numerical model well reproduces the initiation of a sheared zone at the toe of the slope and its propagation toward the crest as the rain infiltration proceeds, which manifests a typical mechanism for rainfall‐induced shallow landslides. The simulated plastic strain and deformation would be remarkably underestimated when the bonding stress and/or the deformation‐dependent nature of hydraulic properties are ignored in the coupled model. But on the contrary, the negligence of gas flow in the slope soil results in an overestimation of the rainfall‐induced deformation. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
8.
坡体地下水是影响边坡稳定的主要因素,将水排出往往能够阻止滑坡的启动。通过应用基本理论和模型试验对高压充气法应用在边坡排水工程中的可行性进行研究分析。结果表明：将高压充气排水法应用在边坡排水工程中是可行的,且适用于土体中最大孔径大于5.0 μm的边坡;气驱水过程存在初始充气气压且存在上限值;气排水速度与土体渗透系数和充气气压成正比、与水头高度和孔隙通道半径成反比;气排水过程中土体大孔隙通道内产生优先流现象。 相似文献
9.
Nadia Laredj Hanifi Missoum Karim Bendani Mustapha Maliki 《Arabian Journal of Geosciences》2011,5(5):935-942
Knowledge of transport processes of heat and moisture in soils of arid zones is vital to understanding the environmental and economic impacts of many activities: agriculture, waste disposal, geoenvironmental practices and earth sciences. Through extensive review and study on the different aspects of coupled transfer processes in swelling porous media, a general mathematical model for coupled heat, moisture, air flow and deformation problems in clayey soils is proposed in a consistent and unified manner. The model is characterized by the presence of a deformable solid matrix filled with two fluid phases (liquid water and air). In the proposed model, both pore water and air transfers are assumed to be governed by the generalized Darcy’s law. Fully coupled, non-linear partial differential equations are established and then solved by using a Galerkin weighted residual approach in space domain and an implicit integrating scheme in time domain. The obtained model has been finally validated by means of some case tests for the prediction of the thermo-hydro-mechanical behaviour of unsaturated swelling soils. The calculated relative errors between experimental and numerical results are 3% for temperature and 7% for stresses. Consequently, the developed numerical model predicts satisfactory results, compared to experimental test measures. The model is applicable to two-dimensional problems with various initial and boundary conditions; non-linear soil parameters can be easily included in this model. 相似文献
10.
This paper presents a semi-analytical solution to one-dimensional consolidation of viscoelastic unsaturated soils with a finite thickness under oedometric conditions and subjected to a sudden loading. The solution is obtained by using Lee’s correspondence principle based on the semi-analytical solution to one-dimensional consolidation of elastic unsaturated soils. The boundary contains the top surface permeable to water and air and the bottom impermeable to water and air. A typical example is given to show the evolution of excess pore-air and pore-water pressures as well as the total degree of consolidation of the soil layer with time for different ratios of air–water permeability coefficient, elastic modulus and viscoelastic coefficient. The one-dimensional consolidation behavior of viscoelastic unsaturated soil is discussed according to the semi-analytical solution. These results contribute to a better understanding of the consolidation behavior of viscoelastic unsaturated soils. 相似文献
11.
竖向应力及干密度对砾石土土-水特征曲线的影响研究 总被引：1，自引：0，他引：1
利用SWC-150 Fredlund土-水特征曲线压力仪,对不同干密度的砾石土进行不同竖向应力作用下的土-水特征试验,探讨了干密度和竖向应力对土-水特征曲线(SWCC)的影响。采用Fredlund & Xing三参数模型对试验所得的土-水特征曲线进行最小二乘法拟合,获得了土-水特征曲线的模型参数,并探讨了其变化规律。随着竖向应力及干密度的增大,模型参数n增大,m减小。除吸湿阶段拟合参数a随干密度略微减小外,其余情况a随竖向应力和干密度密度的增大而增大。结合土-水特征曲线拟合函数,分析研究了竖向应力和干密度对土-水特征曲线的进气值或进水值以及斜率的影响规律,提出了土-水特征曲线的进气值或进水值以及过渡段斜率与竖向应力和干密度的定量关系。结果表明：进气值或进水值与竖向应力和干密度呈线性关系,但吸湿阶段的进水值随干密度变化不明显;土-水特征曲线的斜率与竖向应力呈双曲线关系,与干密度呈直线关系。 相似文献
12.
非饱和土体中的部分气体极容易在入渗过程中被封闭在孔隙或裂隙中,形成互不连通的与外界隔绝的封闭气泡。封闭气泡的存在阻碍了水相的流动,使土体的渗透性能降低,从而对土体的入渗速率产生不可忽视的影响。在分析前人研究成果的基础上,结合室内一维积水入渗试验结果,初步探讨了封闭气泡的形成原因,及其对土体入渗性能的影响机制,对研究非饱和土中水气二相流规律有重要指导意义。试验结果表明：积水入渗时,土体中存在封闭气泡,封闭气泡的含量与土性、干密度和初始含水率等有关。干密度越大,封闭气泡占据孔隙空间越大,阻渗作用越明显,干密度相同时,黏性土中封闭气泡对入渗的阻碍作用较砂性土明显;初始含水率较小时,封闭气泡含量相对较大。由于封闭气泡的存在,入渗稳定时的传输区土体含水率只有土样饱和含水率的80 %左右。 相似文献
13.
针对盐碱化土壤地表蒸发速率研究的不足,以表层土壤为研究对象,采用土壤蒸发试验和数学模型相结合的方法分析了溶质势对地表蒸发速率的影响。结果表明:当土壤中盐分没有沉淀结晶时,溶质势是盐分引起地表蒸发速率降低的主要原因;溶质势越低,蒸发速率下降比例越大,该下降比例与溶质势有近似线性关系,但同时还受到空气温度与相对湿度、土壤温度以及土壤基质势等因素的影响;当表层土壤存在水盐补给时,地表蒸发速率总是变化趋向于水分补给速率,但含盐土壤蒸发速率变化较慢,而且若补给水分中含盐,那么其稳定蒸发速率会低于水分补给速率。 相似文献
14.
The Barcelona basic model cannot predict the mechanical behaviour of unsaturated expansive soils, whereas the Barcelona expansive model (BExM) can only predict the stress–strain behaviour of unsaturated expansive soils without the water‐retention behaviour being incorporated. Moreover, the micro‐parameters and the coupling function between micro‐structural and macro‐structural strains in the BExM are difficult to determine. Experimental data show that the compression curves for non‐expansive soils under constant suctions are shifted towards higher void ratios with increasing suction, whereas the opposite is true for expansive soils. According to the observed water‐retention behaviour of unsaturated expansive soils, the air‐entry value increases with density, and the relationship between the degree of saturation and void ratio is linear at constant suction. According to the above observation, an elastoplastic constitutive model is developed for predicting the hydraulic and mechanical behaviour of unsaturated expansive soils, based on the existing hydro‐mechanical model for non‐expansive unsaturated soil. The model takes into consideration the effect of degree of saturation on the mechanical behaviour and that of void ratio on the water‐retention behaviour. The concept of equivalent void ratio curve is introduced to distinguish the plastic potential curve from the yield curve. The model predictions are compared with the test results of an unsaturated expansive soil, including swelling tests under constant net stress, isotropic compression tests and triaxial shear tests under constant suction. The comparison indicates that the model offers great potential for quantitatively predicting the hydraulic and mechanical behaviour of unsaturated expansive soils. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
15.
非饱和粘性土中气体渗透特征 总被引：1，自引：0，他引：1
由于气体的进入形成了非饱和带,饱和土层中的气体渗透实质上是非饱和渗透问题。本文借助基于多孔介质气体渗流理论并考虑气体压缩性的、描述非饱和土中气体渗流运动的本构方程,试验研究了上海地区饱和粘性土层中的气体渗透规律。结果表明,饱水粘性土层中,气体渗透存在起始压力值,数值为100～200kPa, 与上海地区粘土的非饱和进气值较为接近;气体渗透速度与外界所施加的压力平方差梯度之间存在明显的分段特征。后者可能与在充满结合水的微孔隙通道中,只有一部分结合水在气压梯度的作用下发生流动,从而形成气体通道,施加的外力越大,形成的气体通道也越大,气体渗流也越明显。非饱和粘性土中气体渗透规律的研究,对于饱和粘土中的气压法施工,具有重要的理论与工程实践意义。 相似文献
16.
滨海盐渍土的固化方法及固化土的偏应力-应变 总被引：2，自引：0，他引：2
滨海盐渍土可使用水泥、石灰、粉煤灰和高分子材料SH固土剂单独及联合固化,以提高土的强度、抗变形能力和水稳性。为研究各种固化方法固化盐渍土的抗变形能力和偏应力-应变特征,通过三轴UU压缩试验得到盐渍土和6种固化盐渍土的偏应力-应变曲线。曲线显示：水泥＋石灰类固化土呈应变软化型、石灰＋粉煤灰类固化土呈应变软化型、石灰类固化土呈应变硬化型。掺入SH固土剂,提高了固化土的浸水前后的强度,同时也增强了固化土的水稳性。掺入SH固土剂使固化土达到偏应力峰值所需的应变增加,即抗变形能力增强;0.9%SH固土剂+12%石灰+36%粉煤灰固化土具有适中的强度、良好的弹性变形和水稳性的优点,作为轻质路堤填料使用,还可减少滨海地区软土路基的沉降量,这使其成为滨海盐渍土的6种固化方案中的最适宜方案。 相似文献
17.
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
18.
膨润土缓冲材料热传导特性的研究,对于高放废物深地质处置系统的安全评价至关重要。基于串、并联原理,通过将土体孔隙划分为与固相基质并联和串联两部分,提出了考虑矿物成分、颗粒亲水性、孔隙率及饱和度等因素的非饱和膨润土有效热传导系数的4种预测形式,建立了基于4种形式线性组合的有效热传导特性预测模型。详细讨论了模型参数的确定方法,并讨论了孔隙率、饱和度和孔隙结构、颗粒亲水性等因素对土体有效热传导特性的影响。基于MX-80膨润土和高庙子膨润土热传导特性试验成果,对模型的预测性能进行了验证。结果表明,由于膨润土颗粒尺寸较小且具有亲水特性,孔隙内的空气与水宜采用并联描述。研究成果对于非饱和膨润土的导热性能以及工程屏障系统的THM耦合数值模拟研究具有一定的参考价值。 相似文献
19.
分析了土壤表面积水入渗过程中压缩气体对土体结构的影响理论,并通过二维土柱入渗试验对其进行了分析及验证。在积水深度为2.8 cm的条件下,对2个初始含水量、3个孔隙率下的土柱进行了试验,测量出其在试验过程中的气体压力和入渗量,并同时观察土体结构的变化。理论和试验结果表明,气体出现突破之前,土壤内气体压缩产生的气压对湿润区土体的顶托作用会破坏土体的平衡,从而在湿润锋处产生水平裂缝,破坏入渗土体的连续性。试验还发现,入渗过程中土体结构变化大小受土壤初始结构和含水率的影响,初始结构越牢固、含水量越大,结构和气压变化越小,根据结构变化不同,可以划分出两种不同的试验过程。同时入渗土体内出现裂缝时,气压的减渗作用尤为显著,甚至会导致试验过程的停止。 相似文献
20.
An analytical solution for rainfall infiltration into an unsaturated infinite slope and its application to slope stability analysis 总被引：1，自引：0，他引：1
Surficial slope failures in residual soils are common in tropical and subtropical regions as a result of rainfall infiltration. This study develops an analytical solution for simulating rainfall infiltration into an infinite unsaturated soil slope. The analytical solution is based on the general partial differential equation for water flow through unsaturated soils. It can accept soil–water characteristic curve and unsaturated permeability function of the exponential form into account. Numerical simulations are conducted to verify the assumptions of the analytical solution and demonstrate that the proposed analytical solution is acceptable for the coarse soils with low air entry values. The pore‐water pressure (pwp) distributions obtained from the analytical solution can be incorporated into a limit equilibrium method to do infinite slope stability analysis for a rain‐induced shallow slip. The analysis method takes into account the influence of the water content change on unit weight and hence on factor of safety. A series of analytical parametric analyses have been performed using the developed model. The analyses indicate that when the residual soil slope, consisting of a completely decomposed granite layer underlain by a less permeable layer, is subjected to a continuous heavy rainfall, the loss of negative pwp and the reduction in factor of safety were found to be most significant for the shallow soil layer and during the first 12 h. The antecedent and subsequent rainfall intensity, depth of a less permeable layer and slope angle all have a significant influence on the pwp response and hence the slope stability. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献