冻融循环冻土的冲击动态力学性能

以典型冻土为研究对象,通过不同冻融循环次数的冻融循环实验、不同温度的冻结实验以及不同应变率的冲击动态实验,综合研究了冻融循环冻土的冲击动态力学性能。结果表明,冻土存在冻融循环效应,随着冻融循环次数的增加,冻土的峰值应力有一定程度的降低,但在达到临界冻融循环次数后,峰值应力将维持稳定;同时,冻土表现出明显的应变率效应和温度效应,其峰值应力随应变率的增加或温度的降低而增加。通过定义冻融损伤因子,推导满足Weibull分布的冲击损伤,提出了一个基于Z-W-T方程的损伤黏弹性本构模型。该模型可较好地描述冻融循环后冻土的冲击动态力学行为,为研究季节性冻土区冻土的冲击动态破坏提供参考。     

人工冻土力学性能影响因素敏感性分析

为分析人工冻土单轴抗压强度影响因素敏感性,选定人工冻土单轴抗压强度的7 种影响因素,按正交试验设计方案进行大量冻土单轴压缩试验,并采用灰色关联理论对试验结果进行分析,研究分析诸因素敏感性排列顺序. 试验结果表明：在选定的7 种影响因素中,温度为最大敏感因素,其它依次为深度、土性、养护时间、加载速率、含水率和密度,且选定的7 种因素均为重要影响因素,为相关室内试验与工程应用提供依据.     

温度梯度水分扩散系数对非饱和双重孔隙岩体中THM耦合影响的有限元分析

建立了一种饱和–非饱和遍有节理岩体的双重孔隙—裂隙介质热—水—应力耦合模型,并研制出相应的二维有限元程序。通过一个假定的位于非饱和双重孔隙—裂隙岩体中的高放废物地质处置库算例,就温度梯度水分扩散系数不同的三种工况,考察了岩体中的温度、孔隙水压力、饱和度、地下水流速和主应力的变化、分布情况。结果显示：各工况计算域中温度场及应力场基本相同, 当岩体温度梯度水分扩散系数较大时,近场的负孔隙水压力上升到很高的数值,负裂隙水压力有所下降,饱和度亦有相应的变化,当温度梯度水分扩散系数小到一定程度后,其影响也将逐渐消失。     

温度梯度水分扩散对双重孔隙岩体中THM耦合影响的有限元分析

建立了一种饱和-非饱和遍有节理岩体的双重孔隙-裂隙介质热-水-应力耦合模型,并研制出相应的二维有限元程序.通过一个假定的位于非饱和双重孔隙-裂隙岩体中的高放废物地质处置库算例,就温度梯度水分扩散系数不同的三种工况,考察了岩体中的温度、孔隙水压力、饱和度、地下水流速和主应力的变化、分布情况.结果显示:各工况计算域中温度场及应力场基本相同,当岩体温度梯度水分扩散系数较大时,近场的负孔隙水压力上升到很高的数值,负裂隙水压力有所下降,饱和度亦有相应的变化,当温度梯度水分扩散系数小到一定程度后,其影响也将逐渐消失.     

冻结黏土侧限压缩变形的S-M模型

为合理设计冻结壁及确保施工安全,掌握人工冻土侧限条件下压缩变形特性非常必要。对山西省某煤矿深部黏土在不同冻结温度、含水率下,采用分级加载的方式进行侧限一维压缩试验,得到一维压缩应力-时间-轴向压缩变形之间的关系,并根据曲线变化分析可知:同一含水率及加载应力下,温度越低,轴向压缩变形量越小;相同温度下,随着含水率和加载应力的增加,压缩变形量也逐渐增大。引入Singh-Mitchell(S-M)模型,同时考虑温度、含水率和加载应力为模型自变量,建立改进S-M模型,通过对轴向压缩变形取对数的方式计算改进S-M模型参数。将改进S-M模型计算结果与侧限一维压缩变形试验结果进行比较,研究发现:模型计算曲线与试验曲线吻合度较高,模型计算曲线能够反映冻土从初始变形状态到稳定变形状态的变形特性,能准确预测压缩变形曲线的变化趋势,且改进S-M模型涉及参数较少,实际应用价值高。     

基于COMSOL的页岩蠕变过程中固热化耦合响应分析

在已有文献的基础上,建立了固热化耦合控制方程组,包括固体变形方程、能量守恒方程、质量守恒方程。以COMSOL为平台,引入化学反应工程,重点分析了温度梯度、溶质离子浓度的变化过程。化学腐蚀作用对温度的传输过程影响很大,由此引起岩石空隙出现,使岩石温度扩散较快,400h后使温度梯度降低并趋于平稳。温度梯度和化学反应耦合影响时间不同,温度对化学反应的影响在200h后才体现略明显,化学反应对温度梯度影响的时间是在400h后体现明显,温度升高使化学反应速率提高。在巷道蠕变过程中,pH=3的HCl溶液对岩石温度梯度的影响比pH=10的Na OH溶液对温度梯度的影响要强烈,因此岩石在酸性条件下的蠕变变形比在碱性条件下的蠕变变形大。所以多场耦合作用对巷道的稳定具有重要影响,为进一步研究多场耦合作用下深部巷道长期稳定性提供依据。     

大米内水应力和热应力的有限元研究

引言谷粒受到环境变化的影响时,内部会产生裂缝,谷壳会破裂。场土变干,运输,以及人工干燥时发生的气温和空气相对湿度条件的变化,都会导致谷粒的物理损伤。可以推测,由于温度梯度和水分梯度,在谷粒各部分引起程度不同的膨胀和收缩,将在谷粒内部产生应力。因为热传递速率比水分传递的速率高得多,温度梯度和水分梯度的综合效应不好确定。Hcndcrson观察了大米内部的裂痕沿短轴从中心向边上扩展的过程。他指出,在变干的早期阶段,其内应力主要是由温度梯度引起的。Strcmmer      

温度影响下不同含水率细砂中土压力盒测试结果试验研究

在长期的工程监测中,土压力盒的测量精度易受到周围土体环境温度变化的影响。为了提高土压力测量值的可靠度,本文将电阻应变式微型土压力盒埋设于装填有不同含水率细砂的标定桶中,运用冻融循环箱模拟温度变化环境,系统研究了温度循环变化时多个因素对土压力盒测量结果的影响。通过试验研究发现：标定桶内砂土的温度从20°C降低到0°C再升高到20°C的单个冻融过程中,温度对土压力盒测量压力值的影响较大,且得到的温度标定系数为负值,细砂的含水率对土压力盒的温度标定系数的影响相对较弱,采用较小量程的土压力盒以及细砂上部载荷量的增加会使土压力盒的温度敏感性增强;冻融循环次数的增多,会造成土压力盒测量值的损失。     

地表温度对颗粒跃移轨迹的影响

为了研究由地表温度变化引起的向上的垂向气流对沙粒跃移运动的影响,本文给出了考虑近地表温度变化和水平来流风场作用下的沙粒的跃移运动。在定量给出不同时刻的近地表温度和垂向风速的基础上,计算了由于太阳辐射所引起的近地表层垂向气流对沙粒跃移运动的影响,发现:垂向风速在午后可达到1.5m/s并使得沙粒跃移轨迹的最大高度和长度分别增加55.56%和73.68%;同时,与不考虑温度效应的情况不同的是,沙粒跃移轨道最大高度将随粒径变化。     

基于WOA-BP神经网络的超低温冻土抗压强度预测模型研究

为获得超低温冻土抗压强度预测模型, 探究超低温状态下冻土的物理性质及力学性质的变化, 对含水率19%, 22%, 25%和28%的低液限黏土土样进行?180 °C ~ ?10 °C的单轴压缩强度试验, 并测量?80 °C ~ ?10 °C土样的未冻水含量, 建立基于WOA-BP神经网络和BP神经网络的预测模型, 探究含水率、温度、未冻水含量与超低温冻土抗压强度关系. 预测结果表明: 含水率、温度、未冻水含量与超低温冻土抗压强度存在复杂的非线性关系, 特别是在?180 °C ~ ?80 °C区间内, 现有的线性拟合公式已无法准确预测该区间内冻土抗压强度; 基于WOA-BP神经网络预测模型的整体预测效果较好, 其绝对误差平均值为1.167 MPa, 相对误差平均值为7.62%, BP神经网络预测模型的绝对误差平均值为8.462 MPa, 相对误差平均值为47.99%. 基于鲸鱼优化算法的BP神经网络预测模型预测误差明显小于BP神经网络预测模型及线性拟合值, 更接近实测值. 该预测模型具有较高精确度, 能有效解决超低温冻土抗压强度与其影响因素间复杂的非线性关系, 可为人工冻结技术在地层应急工程中的应用提供参考.      

Numerical simulation of coupled heat-fluid transport in freezing soils using finite volume method

A solution procedure using finite volume method has been established for the coupled heat-fluid transport model of freezing soils, and details about determination of the time step interval and discretization at special nodes have been introduced. Comparison between the simulation and the freezing experiments of silica flour and Zhangye loam has been conducted, and the calculated results are in general agreement with the experimental data. The research indicates that the moisture migration in the frozen zone is insignificant, and water mainly migrates from the frozen zone to the vicinity of the moving freezing front; the moving velocity of the freezing front has a great effect on the extent of moisture accumulation to the freezing front, and high extent of accumulation occurs when the freezing front advances slowly. Finally, an apparent heat capacity model has been suggested for the temperature calculation of the soil freezing process in low water content conditions; however, when the moisture migration is significant, water redistribution during the freezing process should be considered.     

Force transmitted below the soil surface by human gait

A force platform, which can provide three dimensional forces and moments on its top surface, was used to study force transmitted by human gait below the soil surface in order to understand detonation of antipersonnel landmines. Soils of varying depth were packed on the top surface of the platform to measure the forces transferred from the soil surface. Experimental variables included subjects (people), soil depth, soil type, moisture content, and compaction level. Soils used in this study were sand and sandy loam. There were medium and high two compaction levels for each soil. Sandy loam soil included two moisture contents; sand tested involved two moisture contents and dry sand. Soil depth varies from 0 (bare platform) to 200 mm. Five subjects with different weights were selected and used in this study.The subsoil force and its duration were measured for different subjects at a depth up to 200 mm. The impulse in subsoil was then calculated and used in evaluating the effect of different subjects on the force transfer in soil. The results indicated that loose soil can transfer larger force to subsoil than dense soil; test results showed that heavier subjects also created larger subsoil forces than lighter ones. Whether the effect of soil depth on subsoil impulse was significant was depended on the soil conditions. For the sand with 5.5% moisture content and bulk density of 1800 kg/m³, soil depth significantly affected subsoil impulses. For the sandy loam soil, the mass of subject increased from 50 to 100 kg resulted in 100% increase in subsoil impulses at all four depths; for the sand, the mass of subject increased from 55 to 100 kg approximately. This resulted in 80% increase in subsoil impulses under all four depths regardless of moisture content and bulk density. The results of this study will helpful for designing new equipment and evaluating existing machines for neutralizing landmines.     

Effect of wetting and drying on soil physical properties

Agricultural soils are subject to seasonal wetting and drying cycles. Effect of drying stress, as influenced by one cycle of wetting and drying, on physical properties of a clay–loam soil was investigated in the laboratory. The physical properties studied were soil bulk density, cone penetration resistance, shear strength, adhesion and aggregate size and stability. Three drying stress treatments were made by wetting air-dried soil of initial moisture content of 12% (on dry weight basis) to three different higher moisture contents, namely 27, 33 and 40%, and then drying each of them back to their original moisture content of 12%. Thus, the soil was subjected to three different degrees of drying stress. The results showed that the soil strength indicated by cone penetration resistance and cohesion, and soil aggregate size, increased with the degree of drying stress. However, the soil bulk density did not change significantly with the drying stress.     

Self-similar solution of a problem of freezing of finely dispersed soils with allowance for moisture migration in thawed and frozen zones

Heat transfer in freezing and thawing soils is accompanied by various processes among which phase transition of moisture and mass transfer should be distinguished in both the thawed and the frozen zones. Their consequence is the formation of ice schlieren and the swelling associated with this. In developing the methods of calculation of moisture migration it was assumed (see, for example, [1, 2]) that the mass transfer occurs only in the thawed part of the soil and is realized predominantly in the liquid phase through the diffusion-film mechanism. It was assumed that the phase conversion of water into ice occurs wholly on the phase interface (the Stefan formulation) and at the same time supplementary conditions for the moisture function are specified on it. Not all these assumptions are valid. In particular, the marked redistribution of moisture in the frozen zone is an important factor in the freezing of moist rocks [3, 4]. This last is also observed in the thawing of dispersed rocks and in frozen samples which are under the influence of a temperature gradient. These phenomena were modeled in [5, 7] on the basis of a single mathematical model which describes the conductive heat transfer, the moisture transfer in thawed and frozen zones, the phase transition of moisture in the temperature range, and the kinetic relaxation effects of moisture crystallization and ice melting. Analysis of the solutions obtained by means of a finite difference method showed that the proposed method of calculation gives results near the experiment. The present paper is devoted to a further study of the model indicated.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp. 113–120, March–April, 1986.     

挡土墙填土边坡水文响应过程分析——以赖屋山挡土墙填土边坡为例

深圳赖屋山的一挡墙表面出现数条裂缝,为了深入研究其变形破坏机制,在挡墙背后填土区布置自动监测仪器,主要包括渗压计、张力计与水分计及固定式测斜仪。通过对渗压计、张力计和水分计的监测数据分析表明：填土内地下水位埋深大,降雨对其影响小; 土体中孔隙压力和体积含水量对强降雨响应随着埋深存在不同程度的滞后性,强降雨入渗深度大于3m,并且在3m处形成瞬态饱和地下水,抗剪强度降低,易于引起边坡的浅层变形破坏。
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Nonisothermal moisture transport in hygroscopic building materials: modeling for the determination of moisture transport coefficients

A mathematical model for calculating the nonisothermal moisture transfer in building materials is presented in the article. The coupled heat and moisture transfer problem was modeled. Vapor content and temperature were chosen as principal driving potentials. The coupled equations were solved by an analytical method, which consists of applying the Laplace transform technique and the Transfer Function Method. A new experimental methodology for determining the temperature gradient coefficient for building materials was also proposed. Both the moisture diffusion coefficient and the temperature gradient coefficient for building material were experimentally evaluated. Using the measured moisture transport coefficients, the temperature and vapor content distribution inside building materials were predicted by the new model. The results were compared with experimental data. A good agreement was obtained.     

冻土力学的研究进展与思考

从冻结土的宏观力学性质,正冻土中的水、热迁移理论,正 冻土的水热力耦合模型四个方面分析综述了国内外冻土力学的发展 历史、研究现状与我国冻土力学研究中存在的问题,指出：（1）当 前冻土力学的研究内容应该从对冻结土的宏观强度与变形性质向更 切合实际工程需要的正冻土、正融土微、细观热、力学耦合性质方 面深化;（2）冻土力学的研究思路应该从对土样纯力学量的试验研 究向土样组构、级配、含水量、饱和度等土性指标在不同负温下对 土样颗粒排列与胶结特性的强度、变形影响机理方面转移;（3）冻 土力学的研究对象也应该从室内冻结试验的研究向具有各种不同水 热交换边界条件与水热迁移内在规律的冻土体发展。     

Soil compaction and over-winter changes to tracked-vehicle ruts, Yakima Training Center, Washington

We monitored two experimental areas at the Yakima Training Center (YTC) in central Washington to measure changes to M1A2 Abrams (M1) tank-rut surface geometry and in- and out-of-rut saturated hydraulic conductivity (K_fs), soil penetration resistance (SPR) and soil bulk density (BD). Profile-meter data show that rut cross-sectional profiles smoothed significantly and that turning ruts did so more than straight ruts. Rut edges were zones of erosion and sidewall bases were zones of deposition. K_fs values were similar in and out of ruts formed on soil with 0–5% moisture by volume, but were lower in ruts formed on soil with about 15% water. Mean SPR was similar in and out of ruts from 0- to 5-cm depth, increased to 2 MPa outside ruts and 4 MPa inside ruts at 10- to 15-cm depth, and decreased by 10–38% outside ruts and by 39–48% inside ruts at the 30-cm depth. Soil BD was similar in and out of ruts from 0- to 2.5-cm depth, and below 2.5 cm, it was generally higher in ruts formed on moist soil with highest values between 10- and 20-cm depth. Conversely, BD in ruts formed on dry soil was similar to out-of-rut BD at all depths. This information is important for determining impacts of tank ruts on water infiltration and soil erosion and for modifying the Revised Universal Soil Loss Equation (RUSLE) and the Water Erosion Prediction Project (WEPP) models to more accurately predict soil losses on army training lands.     

An investigation of the bevameter soil physical measurements in the prediction of soil tool draft

The relationship between the parameters measured during soil testing using the bevameter system and the horizontal forces acting on a simple soil-cutting blade were investigated. Field experiments were conducted on untilled, compacted soil and on recently-tilled soil. On both soils, five sites were randomly chosen and bevameter and draft measurements were performed The parameters measured were modulus of soil deformation, wet and dry bulk density, soil moisture content, tool operating depth, tool operating velocity and horizontal draft. A statistical analysis of the data indicated that a mathematical model for predicting draft should contain the following variables: operating depth, dry bulk density and modulus of deformation. A linear regression analysis of draft versus modulus of deformation showed significance at the 95% confidence level on the untilled sites at all measured depths. A similar analysis of the tilled site indicated significance at the 70 mm depth only. The usefulness of the bevameter deformation modulus as an indicator of draft was found to be limited to shallow depths.