非饱和高压实膨润土水化的数值模拟

高压实膨润土是核废料处置的首选缓冲回填材料。使用Code—Bright软件对侧限条件下高压实膨润土的室内注水试验进行了数值模拟。数值模型中的非饱和渗流特性参数即土一水特征曲线参数由室内试验确定。数值模型中使用的膨润土非饱和弹塑性本构模型参数由膨润土的常规非饱和三轴力学模型试验得到。数值模拟结果和实测结果的比较可以反分析出膨润土的固有渗透系数。对数值模型的研究有助于加深对膨润土非饱和渗流特性的认识。数值模型计算得到的吸力分布和实测结果基本吻合。     

高压实膨润土水分特征曲线的测定

本文介绍了在极高吸力工况下，介质吸力与含水率关系的测定工作，由于传统的测量方法此时的不适用性，本文研究采用保持密闭空间定湿度的饱和盐溶液方法，进行了高压实膨润土吸力－含水率关系的测定，测量结果显示，对于高压实膨润土，给定吸力情况下的最终含水率与试样初始干密度及初始含水率无关，这个结果对于研究非饱和状态下水分迁移有极其重要的意义。     

圆饼状高压实膨润土膨胀力各向异性特征研究

针对作为我国缓冲/回填材料的高压实高庙子膨润土,采用自主研制的膨胀力-渗透性一体化测试仪器开展膨胀力试验,分别测定圆饼状试样的轴向膨胀力和径向膨胀力发展规律,研究试样初始干密度、初始吸力和尺寸效应对其膨胀力各向异性特征的影响。试验结果显示,轴向膨胀力和径向膨胀力均随着试样初始干密度的增加呈指数增大,膨胀力各向异性特征愈加显著。轴向膨胀力和径向膨胀力均随着试样初始吸力的增加而呈减小趋势;相同初始吸力条件下,径向膨胀力均大于轴向膨胀力,但是膨胀力各向异性系数随着初始吸力增大而不断减小。试样尺寸对膨胀力有显著影响,增加试样高度,轴向膨胀力不断增加,径向膨胀力增加到某一数值后不再随高度增加,膨胀力各向异性系数随着试样高度的增加逐渐减小。最后,基于膨润土膨胀机理、压实效应和尺寸效应,分析了膨胀力各向异性特征的形成机理。     

侧限状态下高压实高庙子膨润土非饱和渗透性的试验研究

高放废弃物深地质处置库中,由高压实膨润土形成的人工屏障,起着阻障围岩中地下水渗入内库并引起核素迁移以及库内高放废物的辐射扩散的作用。因此,有必要研究侧限状态下高压实膨润土的非饱和渗透性能。采用瞬时截面法试验研究了侧限状态下高压实高庙子膨润土的非饱和渗透特性。结果表明:侧限状态下,干密度为1.7g/cm3的高压实高庙子膨润土的非饱和渗透系数,数值为1.13×10-13～8.41×10-15m/s,且与土中吸力呈非单一增减关系。当土中吸力约为68MPa时,非饱和渗透系数最小;吸力大于68MPa时,其非饱和渗透系数随着吸力的增加而增加;而当吸力小于68MPa时,非饱和渗透系数随着土中吸力的增加而减小。     

自由膨胀条件下高压实砂–膨润土混合物非饱和渗透特征

选择合适的配合比,使得膨润土–石英砂混合物在增加导热性能和强度的同时,又能满足渗透性要求并维持适当的膨胀力,是混合型缓冲/回填材料研究的关键。采用瞬时截面法,通过试验研究了干密度1.9 g/cm³、配合比为7∶3的高庙子膨润土–石英砂混合物的非饱和渗透特性。结果表明,所测非饱和渗透系数主要集中在2.1×10^-15～1.0×10^-13 m/s,且趋势上随吸力的增大而减小但变化较为平缓;与自由膨胀条件下、纯膨润土试样的非饱和渗透系数相比,混合物渗透系数稍有增大,但变化幅度不太明显。石英砂的加入,改善了混合物的导热性能,且仍然基本符合缓冲/回填材料的低渗透性要求。     

非饱和砂土坡面降雨非正交入渗试验与数值模拟研究

传统降雨入渗分析仅以降雨强度在坡面上的正交分量作为边界条件,不符合实际降雨非正交入渗规律。为了研究非饱和砂土的非正交入渗规律性,采用自行研制的室内降雨试验装置对非饱和砂土坡面进行了一系列不同降雨强度、坡角和孔隙比的降雨入渗试验,并对应地进行了正交入渗条件下的数值模拟。测量了入渗率、出渗速率及砂土储水增量随时间变化的关系曲线,分析了雨强、坡角和孔隙比对试验结果的影响。试验结果显示各试验中均无坡面径流现象,与正交入渗边界理论差异显著。通过分析非饱和砂土在传统坡面降雨正交入渗边界条件下的入渗率、出渗速率及砂土储水增量等数值模拟结果与对应的降雨入渗试验结果的差异,证明按正交入渗边界理论计算得到的砂土坡面土体含水率、入渗能力及坡面边界条件转化的判别机制均与实际情况不符。     

降雨条件下非饱和土中污染物迁移的数值模拟

利用溶质传递方程与非饱和土非稳态渗流方程联立耦合,建立了非饱和土污染物迁移模型.采用有限元数值分析的方法,模拟了土体非饱和带中污染物在降雨条件下的迁移过程,研究了无降雨、连续降雨和间断降雨条件下土体非饱和带中孔隙水压力和含水量变化以及污染物的迁移规律.研究结果表明,非饱和带污染物浓度随着时间增加逐渐增大,达到峰值后逐渐...     

粘土岩饱和-非饱和渗流应力耦合模型及数值模拟研究

岩体中饱和-非饱和渗流、应力耦合行为对工程岩体的强度和稳定性有十分重要的影响。基于粘土岩实验室非饱和渗流试验的结果，将考虑塑性应变硬化的非饱和渗流、应力耦合模型、Hoek—Brown非饱和渗流、应力耦合模型应用于模拟某粘土岩竖井，研究其在开挖、通风、衬砌支护及长期运营期围岩内渗流从初始饱和→非饱和→近饱和的过程，以及竖井的非饱和流动区域大小对水力学参数（Biot固结系数、饱和度与毛细孔隙压力、水相的相对渗透系数与饱和度）的敏感性。结果表明：水力学参数对非饱和渗流的影响区域非常显著，尤其是水相的相对渗透系数与饱和度的关系。力学模型的差异对非饱和区的影响几乎可以忽略不计。     

大型贮灰场的三维饱和–非饱和瞬变流数值模拟及非饱和参数试验

基于Narasimhan T N的理论,研究了大型复杂工程问题的三维饱和–非饱和瞬变流数值模型,编制了相应的计算机程序。成功地对占地1.1km×1.0km×72m的大型不规则域--上冶峪干贮灰场进行了历时87 d的饱和–非饱和瞬变流数值模拟,演绎了场内粉煤灰体的含水率、饱和度和孔隙水压力在洪水、降雨、排渗和蒸发等作用下,随时间变化的规律和过程。同时,还进行了特殊工程材料--粉煤灰的水分特征曲线和非饱和渗透系数K(h)的试验。     

双孔隙压实膨润土的细观导热模型

压实膨润土导热系数是评价核废料处置库散热安全以及计算温度场分布的关键指标,准确预测不同条件下压实膨润土导热系数对于处置库的安全设计具有重要意义.数值模拟是预测土体导热系数的有效途径之一,然而,由于压实膨润土双孔隙结构的复杂性,基于细观数值模拟的压实膨润土导热模型较少.建立了一种适用于双孔隙压实膨润土导热系数的细观模型,...     

Thermal-Mechanical Behavior of Compacted GMZ Bentonite

The THM behavior of compacted GMZ bentonite has been investigated using a suction-temperature controlled isotropic cell. The results obtained were compared with the existing results on other reference bentonites (MX80, FEBEX, FoCa, and Kunigel-V1). It has been observed that the coefficient of thermal expansion of the compacted GMZ bentonite is 2×10^-4°C^-1, similar to the values of compacted MX80 and FEBEX bentonites. The heating tests of the GMZ bentonite also show that the suction is an important parameter that governs the thermal volumetric behavior of unsaturated soils. Unlike temperature, suction has a significant effect on the compressibility parameters. Examination of the mineralogy of various bentonites showed that a good correlation can be generally established between the montmorillonite content and the cations exchange capacity (CEC) or the specific surface area (S). Nevertheless, both the basic geotechnical properties and the swelling potential seem to depend not only on the montmorillonite content but also on other factors such as the nature of base exchangeable cations. The quartz content of the GMZ bentonite is relatively high (11.7%). This could explain its relatively large values of thermal conductivity.     

Experimental Study on the Behavior of Unsaturated Compacted Silt Under Triaxial Compression

Most of the experimental investigations conducted on unsaturated soil have been performed under a constant air pressure. Changes in air pressure during deformation are in some cases important in practice. For example, in order to explain the stability problems of embankments during earthquakes and seepage flow, and grounds containing gas associated with the dissociation of methane hydrates, it is necessary to consider the interaction between the soil and the pore fluids. In the present study, we carried out fully undrained tests as well as drained tests, namely, constant water and constant air shearing tests. We performed the fully undrained tests using an air-controlled valve to measure the pore air pressure. For the stress variables of the unsaturated soil, skeleton stress values were used to describe the experimental results. From triaxial compression tests on silty soil, we found that the initial suction, the confining pressure, and the strain rate of unsaturated soil strongly influence the stress-strain behavior of unsaturated silt.     

邯郸非饱和膨胀土的干燥收缩试验研究

基质吸力和净平均应力的增大均可引起土体的压缩变形。针对物理性质不同的4种非饱和膨胀土体结合试样收缩曲线和土水特征曲线分析了土体干燥过程中基质吸力和孔隙比的关系。试验结果表明:土体干燥收缩过程中随着基质吸力的增大试样不断发生收缩,当基质吸力增大到某一定值时,基质吸力的增大对试样收缩变形无明影响,称此基质吸力为缩限吸力。并且不同性质土体的缩限吸力不相同,缩限吸力值与土体的塑性指数密切相关。在干燥收缩过程中,当试验的饱和度减小到85%时试样完成了绝大部分收缩,当试验饱和度达到70%时土样的孔隙比基本保持不变。     

高庙子膨润土的土水特征曲线与渗透系数

在土水特征测定试验的基础上,分析了历史上提出的各种模拟土水特征曲线的方程与试验结果的拟合程度.在非饱和渗透系数试验结果的基础上,分析了由分维理论得到的非饱和渗透系数模拟方程与试验结果的拟合程度.得出以下结论:Fredlund and Xing土水特征曲线方程对于试验结果有较好的模拟效果;Brooks和Corey土水特征曲线方程与试验结果的曲线形状更为接近,但在模拟接近309MPa的吸力段的土水曲线时与试验结果有偏差.分维理论的修正公式能更好模拟非饱和渗透系数.     

A Three-Dimensional Elastoplastic Model for Unsaturated Compacted Soils with Hydraulic Hysteresis

This paper presents a three-dimensional elastoplastic model for predicting the hydraulic and stress-strain-strength behaviour of unsaturated soils. The model is generalized using the transformed stress method to three-dimensional stress states by assuming that the shapes of the failure surface and the yield surface in the deviatoric plane of the average skeleton stress space are given by the SMP criterion. Hydraulic hysteresis in the water-retention behaviour is modeled as an elastoplastic process with the elastic region of the saturation degree decreasing with increasing suction in the S_r-log s plane. The effect of void ratio on the water-retention behaviour is studied using test data obtained from controlled-suction triaxial tests on unsaturated compacted clay. The effect of change in degree of saturation on the stress-strain-strength behaviour and the effect of change in void ratio on the water-retention behaviour are taken into consideration in the model, in addition to the effect of suction on the hydraulic and mechanical behaviour. Model predictions of the stress-strain and water-retention behaviour are compared with those obtained from triaxial tests on unsaturated soil along isotropic compression, triaxial compression and triaxial extension stress paths with or without variation in suction. The comparisons indicate that the model has well predicting capabilities to reproduce the hydraulic and mechanical behaviour of unsaturated soils under three-dimensional stress states.     

非饱和黄土受压过程中结构变化的CT描述(英文)

The triaxial compression tests of compacted loess samples with different lateral pressures arc mmducted with a new set of modified triaxial compression apparatus which. With the new apparatus, the soil sample can be scanned with CT machine at the same time during compression process. The different damage process of compacted loess ssmple is directly observed for the first time with CT images and CT numbers. The initiation mechanisms of soil micro-crack during different processes are analyzed with CT images.     

诱导缝防水体系在水化热作用下的数值模拟研究

钢筋混凝土结构有效的防水设计是大型盾构隧道明挖段的重点。以珠海三通道南线工程为背景,分析混凝土等效龄期水化热的温度作用,建立三维模型,应用扩展有限单元法(XFEM)对比分析在考虑热力耦合条件下的新型反应性丁基橡胶钢板止水带和传统钢板止水带对于裂缝扩展的影响,评估不同防水体系的工作状态。结果表明:新型反应性丁基橡胶钢板止水带对于裂缝扩展的控制效果优于传统钢板止水带,考虑温度变化的作用后,结构裂缝开展宽度有明显增大,但随着结构受力逐渐趋于平衡,裂缝扩展也趋于稳定。此外,针对不同截面部分损失率下的裂缝扩展情况进行分析,裂缝开展的宽度均随着截面部分损失率的增大而增大,因此在考虑防水效果的基础上,需控制因埋设防水部材而造成的截面部分损失率。     

地埋管换热器周围非饱和土壤热湿迁移数值模拟

本文在极坐标下建立了地埋管换热器周围非饱和土壤的热湿迁移数学模型与纯导热数学模型,采用有限体积法对两种模型进行了数值求解。模拟结果表明,向土壤中排热会使得钻孔壁附近的含湿量降低。当土壤初始含湿量较大时,土壤中湿分迁移对土壤热物性基本上没有影响,纯导热模型与热湿迁移模型模拟土壤与地埋管换热器之间的换热现象时基本一致;当土壤初始含湿量较小时,热作用对钻孔壁附近的湿迁移影响较为显著,土壤热物性会随之发生变化,此时纯导热模型与热湿迁移模型计算差值较大。