考虑气相硬化的准饱和黏土弹塑性模型     

周容名  翁效林  李林  侯乐乐 《岩土力学》2022,43(11):2963-2972

假定准饱和黏土由饱和基质（土骨架和水）和封闭气体组成,采用饱和基质塑性体应变和气体塑性体应变作为硬化参数以反映准饱和黏土的塑性硬化行为,在综合考虑气体溶解系数随温度和水中含盐量变化、预固结应力随封闭气体的变化等关键因素的基础上,基于临界状态土力学理论提出了可以反映封闭气体气压变化对准饱和黏土力学影响的弹塑性本构模型。模型共计10个材料参数,均可通过等向压缩试验和三轴剪切试验获得。通过与已有试验数据对比分析,结果显示本模型可以较好地模拟准饱和黏土在不排水应力路径下的应力-应变关系、孔隙水压力发展以及饱和度的演变规律;所建立模型形式简单,参数易于确定,为准饱和黏土地基中岩土工程问题的设计、计算及灾变控制提供了重要的理论基础。  相似文献   

基于耗散能量的饱和黄土动孔压模型     

简涛  孔令伟  柏巍  舒荣军 《岩土力学》2023,(8):2238-2248

通过一系列不排水动三轴试验探究了饱和黄土振动液化过程中孔隙水压力和累积耗散能量的演化模式,并讨论了围压、动应力幅值和固结应力比对其演化过程的影响。结果表明：饱和黄土的孔隙水压力和耗散能量随着循环荷载作用逐渐累积。固结围压抑制孔隙水压力增长而消耗更多能量;更大的动应力幅值使得孔隙水压力增长更快而消耗能量更少;等压固结下,孔隙水压力增长至围压从而触发初始液化,而偏压固结下,通常先达到振动液化应变标准而孔隙水压力并没有增长至围压水平,并且固结应力比越大,液化时孔隙水压力越小,消耗能量也更少。归一化孔隙水压力u/σ₀’与累积耗散能量W/W_f之间关系受围压、循环应力比和固结应力比影响较小,可统一用双曲线模型表示。  相似文献   

一种改进的自适应Wallis滤波算法     

王博  张永军  陈奇 《测绘科学》2015,40(5):95-98

针对影像增强过程中的边缘扩张、灰度过饱和及"块效应"等问题,文章提出了一种改进的自适应Wallis滤波算法:结合影像特征提取的实践应用,在影像局部范围内进行灰度均值和方差的统计,能够较好地实现自适应的判断二值分割阈值,利用迭代的方法,可以有效保证影像在增强处理下的保真度。最后以几组典型影像为例,证明该方法相对于传统方法较好地保证了影像增强后的影像质量,处理效率较高、应用面广。  相似文献   

濮阳3286 m岩盐勘探深井高密度钻井液工艺          下载免费PDF全文

靳廷朝 《探矿工程》2015,42(3):29-32

濮阳岩盐普查项目ZK0401孔设计孔深3280 m。在该孔钻探取心施工中,结合地层水敏性、地层压力及地温特点,试验采用了耐高温、高密度饱和盐水钻井液,并配以适宜取心钻探工艺,成功地实施了连续岩盐取心,实际终孔孔深3286 m,收到了良好的效果。重点介绍了钻井液体系配方的优选及钻井液工艺技术措施。  相似文献   

Effective transfer properties of partially saturated geomaterials with interfaces using the immersed interface method     

Duc Phi Do  Dashnor Hoxha 《国际地质力学数值与分析法杂志》2013,37(18):3237-3257

The present work aims at introducing an efficient numerical approach based on the immersed interface method to estimate the effective thermal conductivity and permeability of geomaterials as porous media with either perfect or debonded interfaces. The first part deals with the problem of the overall thermal properties of a medium containing perfectly bonded inclusions. The evolution of the homogenized properties with respect to the properties of individual constituents, the volume fraction, the spatial distribution, and the shape of inclusions is highlighted. The second part of the paper is devoted to the case of imperfectly bonded inclusions. An extension of the immersed interface method in this context makes it possible to study other aspects that have an influence on the effective properties such as the interfacial resistance and the size of inclusions. The application of the proposed numerical tool to some porous rocks in partially saturated condition shows good agreement with the available experimental results and demonstrates the performance and the flexibility of the developed procedure.Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Study of the soil–atmosphere moisture exchanges through convective drying tests in non‐isothermal conditions     

Pierre Gerard  Angélique Léonard  Jean‐Pierre Masekanya  Robert Charlier  Frédéric Collin 《国际地质力学数值与分析法杂志》2010,34(12):1297-1320

This paper deals with the moisture exchanges occurring between soils and the surrounding atmosphere. Convective drying tests are performed on Awans silts at different drying temperatures and air relative humidities in order to reproduce the natural drying conditions. The experiments improve the understanding of the vapour transfers kinetics between the soil samples and the atmosphere. The experimental results are analysed assuming that the transfers take place in a boundary layer existing at the surface of the porous medium. The influence of the thermal conditions on the evaporation is also taken into account. In our model, coupled vapour and energy exchanges are controlled by mass and heat transfer coefficients characterizing the boundary layer. These coefficients are determined from the drying experiments. The modelling of the drying tests in non‐isothermal conditions is performed in order to validate the formulation of the vapour and heat exchanges. The numerical results present a good agreement with the kinetic of the materials desaturation determined during the tests. The analysis of the moisture transport mechanisms into the sample and at the boundary shows that at the beginning of the test, the drying is first achieved by the transport of moisture in its liquid form and its evaporation at the sample outer boundary in contact with the atmosphere. In a second step, vapour diffusion becomes predominant into the sample and it corresponds to the most important decrease of relative humidity. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Modeling of dynamic cohesive fracture propagation in porous saturated media     

A. R. Khoei  O. R. Barani  M. Mofid 《国际地质力学数值与分析法杂志》2011,35(10):1160-1184

In this paper, a mathematical model is presented for the analysis of dynamic fracture propagation in the saturated porous media. The solid behavior incorporates a discrete cohesive fracture model, coupled with the flow in porous media through the fracture network. The double‐nodded zero‐thickness cohesive interface element is employed for the mixed mode fracture behavior in tension and contact behavior in compression. The crack is automatically detected and propagated perpendicular to the maximum effective stress. The spatial discretization is continuously updated during the crack propagation. Numerical examples from the hydraulic fracturing test and the concrete gravity dam show the capability of the model to simulate dynamic fracture propagation. The comparison is performed between the quasi‐static and fully dynamic solutions, and the performance of two analyses is investigated on the values of crack length and crack mouth opening. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Stiffness Degradation of Undisturbed Saturated Soft Clay in Yangtze Estuary under Complex Stress Conditions     

栾茂田  刘功勋  王忠涛  郭莹 《海洋工程》2010,(3):523-538

Stiffness degradation will occur due to the generation of accumulated pore pressure in saturated soft clays under cyclic loading. The soil static-dynamic multi-purpose triaxial and torsional shear apparatus in Dalian University of Technology was employed to perform different types of test on saturated soft marine clay in the Yangtze estuary. Undisturbed samples of the clay were subjected to undrained cyclic vertical and torsional coupling shear and cyclic torsional shear after three-directional anisotorpic consolidation with different initial consolidation parameters. Investigated were the effects of the initial orientation angle of the major principal stress, initial ratio of deviatoric stress, initial coefficient of intermediate principal stress and continuous rotation of principal stress axes on the stiffness degradation. It is found that the degradation index decreases (or degradation degree increases) significantly with increasing initial orientation angle of the major principal stress and initial ratio of deviatoric stress. Compared to the effects of the initial orientation angle of the major principal stress and initial ratio of deviatoric stress, the effect of initial coefficient of intermediate principal stress is less evident and this trend is more clearly reflected by the results of the cyclic torsional shear tests than those of the cyclic coupling shear tests. At the same cycle number, the degradation index obtained from the cyclic torsional shear test is higher than that from the cyclic coupling shear test. The main reason is that the continuous rotation in principal stress directions during cyclic coupling shear damages the original structure of the soil more than the cyclic torsional shear does. Based on a series of experiments, a mathematical model for stiffness degradation is proposed and the relevant parameters are determined.  相似文献   

Measurement Method Has a Larger Impact Than Spatial Scale For Plot-Scale Field-Saturated Hydraulic Conductivity (Kfs) After Wildfire and Prescribed Fire in Forests     

Brian A. Ebel 《地球表面变化过程与地形》2019,44(10):1945-1956

Wildfires raise risks of floods, debris flows, major geomorphologic and sedimentologic change, and water quality and quantity shifts. A principal control on the magnitude of these changes is field-saturated hydraulic conductivity (K_fs), which dictates surface runoff generation and is a key input into numerical models. This work synthesizes 73 K_fs datasets from the literature in the first year following fire at the plot scale (≤ 10 m²). A meta-analysis using a random effects analysis showed significant differences between burned and unburned K_fs. The reductions in K_fs after fire, expressed by the ratio of K_{fs Burned}/K_{fs Unburned}, were 0.46 (95% confidence interval of 0.31-0.70) combining wildfire and prescribed fire and 0.3 (95% confidence interval of 0.13-0.71) for wildfire. No significant differences for K_fs were observed between wildfire and prescribed fire or moderate and high fire severity. Both K_fs magnitude and variability depended more on measurement method than measurement support area at the plot scale, with methods applying head ≥0.5 cm producing larger estimates of K_fs. It is recommended that post-fire efforts to characterize K_fs for modeling or process-based interpretations use methods that reflect the dominant infiltration processes: tension infiltrometers and simulated rainfall methods when soil matrix flow dominates and ponded head methods when macropore flow is critical. Published 2019. This article is a U.S. Government work and is in the public domain in the USA.  相似文献   

地震作用下不同厚度饱和砂土中直群桩结构动力响应试验研究   总被引：1，自引：0，他引：1       下载免费PDF全文

李雨润  陈华斌  强东峰  邹泽 《地震工程学报》2019,41(4):834-839,852

基于振动台试验,设计制作2×2直群桩结构相似模型,通过输入一定峰值加速度的迁安波,对非液化砂土、300 mm厚饱和砂土和380 mm厚饱和砂土中群桩承台横向动力响应特性展开研究。研究结果表明:在迁安波输入下,非液化砂土中群桩承台加速度和位移时程与台面输入时程相比,其波形变化规律与峰值大小没有明显差异;而对于两种不同厚度饱和砂土中承台加速度放大较多,承台位移峰值较台面位移峰值相差不大。在300 mm饱和砂土中群桩承台加速度峰值较台面输入放大了约1.35倍,在380 mm饱和砂土中承台加速度峰值放大了1.42倍,说明在相同输入条件下,较厚的饱和砂土层在发生液化后群桩承台的动力响应更加显著。  相似文献