Effect of Freezing Conditions on the Shear Strength of Soils Frozen Together with Materials

The relationship between the strength of soils frozen together with materials on the roughness of their surface is analyzed under different temperature conditions. The formation of an ice interlayer at the contact between the frozen soil and material, and its effect on the adfreezing strength are investigated.     

正常使用状态下部分预应力砼叠合梁刚性计算新方法的探讨

分析了二次受力情况下部分预应力砼叠合梁的受力特点,探讨了这种构件刚度的计算方。结果表明,在正常使用状态下由于预制断面上“荷载预应力”的残存,增大了断面的有效受压区面积,从而提高了叠合构件的初期抗弯刚度。研究结果给出的刚度计算方法,合理地解决了“二次受力”叠合梁在正常使用状态下的刚度计算问题,其计算结果与试验结果吻合较好。     

Strength Characteristics of Frozen Saline Soils

Methods for determination of the strength characteristics of frozen saline soils (FSS) are examined. The shear parameters C _lt and _lt for typical soils of the Yamal Peninsula are determined over a broad range of negative temperatures (from – sign;1 to – sign;8°C) and salinities (from 0 to 1.5%). Proposed tabular data on strength characteristics of FSS make it possible to use them in calculations to determine limiting loads on bed soils.     

矩形钢管和矩形钢管混凝土T形不等宽受拉节点 轴向刚度

为获得T形节点轴向刚度简化计算公式,根据节点受力特点,提出了适用于矩形钢管节点的平面框架模型和适用于矩形钢管混凝土节点的固端梁模型,并推导得到了2类节点的节点轴向刚度理论公式; 运用有限元方法对节点轴向刚度理论公式中的节点域有效长度l_eff进行参数分析,拟合得到l_eff简化计算公式; 将节点轴向刚度理论公式与试验及有限元结果进行了对比,并分析了主管内填混凝土对节点轴向刚度的影响。结果表明:主管高宽比和主管宽厚比对l_eff的影响较小,不予考虑; l_eff与主管宽度和支管高宽比均呈线性关系,且随之增大而增大; l_eff与支主管宽度比β呈非线性关系,且随之增大而减小; 2类节点的轴向刚度理论公式计算结果与试验结果及有限元结果均吻合较好; 主管内填混凝土可以提高节点轴向刚度,提高系数k_c/h随着主管高宽比的增大而增大,随着β的增大呈现先增大后减小的规律,且当β=0.6～0.7时提高最大。     

人工冻土帷幕的冻结过程研究

人工冻土帷幕具有广泛的应用前景。研究表明,冻土的均匀性和冻结状态是影响人工冻土帷幕强度的重要指标。冻结方向、受力方向、冻结时间影响下的冻结锋面发展情况和温度场规律是描述冻土力学性能差异的四个重要特征。该文通过分析这些指标和特征,完善了人工冻土帷幕的分析计算内容,有助于验证冻结时间、冻结位置等重要工程指标的正确性。     

冻融循环作用下混凝土受压本构特征研究

采用混凝土棱柱体试件,通过快速冻融试验方法,对经受冻融损伤的混凝土受压性能进行了试验研究,分析了冻融循环次数、混凝土等级、相对动弹性模量对混凝土受压性能的影响,通过碟簧耗能装置,得到了完整的应力-应变关系试验结果.将冻融次数和混凝土等级作为参数,回归试验结果,提出了冻融循环后受压性能的计算公式以及适用于立方体抗压强度为20～50 MPa的冻融循环作用下混凝土的应力-应变全曲线方程,并将曲线控制参数与相对动弹性模量和混凝土等级建立关系.结果表明:碟簧耗能装置起到了吸收机械能量的作用,是应力-应变关系试验成功的重要保证.随着冻融循环次数的增加,受压应力-应变曲线趋于扁平;受压峰值应力降低,受压峰值应变、受压极限应变增大,三者随冻融循环的变化关系均近似线性;随着混凝土等级的提高,冻融对于混凝土材料的影响下降.此外,结合所建立的破坏准则所得到的数值分析结果与试验曲线有较好的一致性.     

预应力混凝土构件冻融环境下疲劳数值模拟

基于冻融与疲劳耦合作用下混凝土弹性模量衰减模型、冻融损伤的混凝土疲劳本构模型以及钢筋的疲劳本构方程,通过ANSYS综合各模型的材料参数,模拟预应力混凝土受弯构件在冻融与疲劳交替作用下的疲劳性能,并与试验结果进行对比.结果表明:数值模拟的预应力混凝土构件弯曲挠度和上边缘的应变与试验结果吻合较好,所得结果可为实际工程中冻融环境下预应力混凝土疲劳性能的数值模拟提供有效方法.     

Testing Methods for Hydro-Mechanical Characteristics of Unsaturated Soils Subjected to One-Dimensional Freeze-Thaw Action

This paper proposes new testing methods for evaluating the effects of freeze-thaw action on the deformation-strength characteristics and the water retention-permeability characteristics of granular materials under unsaturated conditions. A triaxial apparatus and a permeability apparatus for unsaturated soils, with cooling systems to control the temperature of soil specimens and use the pressure membrane method instead of the pressure plate method, were newly developed in order to examine the hydro-mechanical behavior of unsaturated soils subjected to the freeze-thaw sequence, as experienced by in-situ soils in cold regions. Results indicate that the proposed testing methods with these newly developed test apparatuses are highly useful in the evaluation of the effect of freeze-thaw action on the hydro-mechanical behavior of unsaturated granular materials and in the reduction of total testing time.     

The influence of Anisotropic Stiffness on the Consolidation of Peat

An analytical solution for the consolidation problem of an axially loaded triaxial sample including anisotropy in stiffness is presented. The solution shows that anisotropy in stiffness strongly influences the consolidation process. The influence of anisotropy in stiffness is found in the initial pore pressure reaction, in the Mandel-Cryer effect and in the consolidation coefficient. Measurements on conventional sized peat samples appear not to correspond to the analytical solution. Besides drain resistance, literature presents two other explanations for this fact. These explanations are tested in a large scale test set-up. It is found that induced permeability changes have a strong influence. The possibility of using the Mandel-Cryer effect for assessment of stiffness parameters of peat introduces extra parameters to describe the variations in permeability. For strongly over-consolidated samples, leading to a nearly constant permeability the analytical solution fits perfectly to measurements.     

Strain Rate Dependency of Cohesive Soils in Consolidation Settlement

It has been revealed from the long term consolidation test that the e-logp relation is linearly shifted with decrease in the strain rate in logarithm scale. The minimum strain rate measured by the conventional long term consolidation test is at most in the order of 10^-9s^-1. Question arises whether such a shift of the e-logp relation continues at even the infinite small strain rate, for example, smaller than 10^-9s^-1. To investigate the strain rate dependency of cohesive soil, the relaxation test was carried out for Osaka Pleistocene clays. It may be considered that in relaxation test, recoverable strain decreases due to decrease in acting pressure, and the irrecoverable strain equally increases, because the total strain remains constant. In this paper, assuming that the isotaches model can be applied to the irrecoverable strain, the strain rate dependency at very small strain rate was obtained from a series of relaxation tests. In this investigation the “strain rate dependency ratio” (SRDR) is defined as the ratio of the stress in the same ε or e under the objective strain rate, based on the strain rate of 3.3×10^-6s^-1. It is revealed that the SRDR at infinite small strain rate is about 0.7.     

二维渗透各向异性多层地基Biot固结分析

从二维渗透各向异性Biot固结问题的基本控制方程出发,对时间t进行Laplace变换,对坐标x进行Fourier变换,构造出Laplace-Fourier变换域内的常微分方程,利用Cayley-Hamilton定理推导出单层地基的传递矩阵。根据传递矩阵的性质,并结合层间连续条件和边界条件,求得了二维渗透各向异性多层地基Biot固结问题在Laplace-Fourier变换域内的解,通过Laplace-Fourier逆变换可求得该问题物理域内的真实解。编制了相应的计算程序,并对数值计算结果进行了比较和分析。计算结果表明:土的渗透各向异性对固结过程中的地表位移有比较显著的影响。     

多层饱和地基三维Biot固结问题的一个理论解

从直角坐标系下三维饱和弹性土体的控制方程出发,通过引入中间变量和积分变换,构造出一组有6个参量的状态方程和一组有2个参量的状态方程,求得单层土Biot固结问题的传递矩阵;将传递矩阵应用于多层体系中的每一层,结合边界条件和连续条件,得到多层土Biot固结问题变换域内的解;通过相应的积分逆变换,求得该问题物理域的真实解.同时,对求得的解进行分析以验证其正确性.     

珠海软土次固结特性试验研究

对广东珠海某大桥地基软土进行一系列一维次固结试验,通过分析土体在不同含水率及加卸载条件下次固结系数的变化规律,研究了珠海地基软土的次固结特性。结果表明:软土在次固结过程中,随着固结围压的增大,次固结系数逐渐增大;软土次固结过程受土体含水率的影响;卸载再加载后土体次固结系数呈减小趋势。试验及分析结果对工程实际具有一定的指导意义。     

Analysis of Results of Consolidation Tests of Saturated Clayey Soils

It is shown that the dependence of soil deformation on the distance to the drainage boundary, which is noted by a number of experimenters for the stage of secondary consolidation, is explained by incorrect interpretation of test data. Laboratory results demonstrating an apparent lack of creep in the stage of primary consolidation are explained by characteristic features of the generalized consolidation equations and relationships between their parameters.__________Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 3, pp. 7–10, May–June, 2005.     

某输气管道沿线冻土的分布及其工程特性研究

根据某输气管道沿线冻土分布地段的工程实践,通过分析总结,在阐述冻土分布和工程性能的基础上,结合原有管道在该地段的工程病害,提出冻土的主动保护及预防措施。建议在冻土工程中,应科学勘察、掌握冻土的分布规律及工程特性,管道不宜直接埋设在季节性冻土层内,在冻胀区,可在管道周围回填粗砂、中砂、炉渣、碎石等非冻胀性散粒材料或采取其他有效措施。在施工过程中应选择合理的施工期,施工期间应避免水流浸入管沟。     

Verification of Compatibility of Isotropic Consolidation Characteristics of Soils to Multiplicative Decomposition of Deformation Gradient

It is verified that the linear relation of logarithmic volumetric strain vs. logarithm of pressure derived from the linear relation of both logarithms of volume and pressure (Hashiguchi, 1974) for isotropic consolidation of soils is exactly compatible to the multiplicative decomposition of deformation gradient (Lee, 1969) which would be one of the fundamental requirements for constitutive equations describing the finite elastoplastic deformation. On the other hand, it is emphasized that the adoption of the linear relation of void ratio vs. logarithm of pressure is impertinent for the constitutive equation describing the finite deformation although it is most widely used for constitutive equations of soils.     

白垩系地层冻结壁冻融全过程温度场现场实测研究

目前西部地区矿井建设普遍采用冻结法凿井,但对白垩系地层冻结特性了解不清,特别是融化过程尚未有可靠资料作为参考.文章以西部地区某在建井筒选择代表性地层为研究对象,开展冻结壁温度场冻结、融化全过程现场实测,通过二者结果对比,得出西部地区冻结壁温度场冻融过程分布规律,为以后类似地层冻结法凿井提供参考.