Behavior of sand–rubber particle mixtures: experimental observations and numerical simulations

A series of laboratory experiments and numerical simulations are conducted to explore the characteristics of mixtures composed of sand and rubber particles of the same median diameter. The mixtures are prepared with different volumetric sand fractions (sf = V_sand/V_total). The experiment focuses on assessing the strain level on the characteristics of the mixture with the volume fraction of each component. Numerical simulations using the discrete element method are performed to obtain insight into the microscale behavior and internal mechanism of the mixtures. The experimental results show that the behavior of the mixtures is dependent on the relative sand and rubber particles composition with variation in the strain levels. The numerical simulation reveals the effect of the soft rubber particle inclusion in the mixture on the micromechanical parameters. In low sand fraction mixtures, a high shear stress along the contact is mobilized, and the stress state is driven to a more anisotropic condition because of the relatively high particle friction angle of the rubber. The rubber particles play different roles with the strain level in the mixture, including increasing the coordination number and controlling plasticity of the mixture in a small strain, preventing buckling of the force chain in an intermediate strain, and leading to contractive behavior in a large strain. Copyright © 2014 John Wiley & Sons, Ltd.     

Directional properties of small strain shear stiffness in soils

A compiled database of shear wave velocity measurements in a variety of clays, silts and sands shows directional hierarchies between downhole (V_sVH), standard crosshole (V_sHV), and rotary crosshole (V_sHH) tests. The special in situ database has been collected from 33 well-documented geotechnical test sites. Expressions relating the small-strain shear modulus in terms of effective confining stress level, stress history and void ratio are explored for each of these three modes of directional shear wave velocity. The relationships are separated initially into soil groups (intact clays, fissured clays, sands and silts), and then generalised to consider all soil types together.     

岩石力学实验在地应力测试中的应用

介绍了应力解除法的基本原理、测试步骤及计算过程,采用实验室测得的弹性模量、泊松比及现场应力解除获得的三维膨胀变形数据,由线性虎克定律即可计算出应力解除前岩体中应力的大小和方向。以济宁煤田安居煤矿为例,获得3个测点的最大主应力、中间主应力及最小主应力的大小、方向、倾角,总结了安居煤矿井底车场附近的原岩应力分布规律。     

土体非线性参数变异性与地表响应的概率关系

场地土体非线性参数存在明显的变异性,因而与其相关的许多岩土工程问题都会受到其变异性的影响。采用数值模拟的方法研究了场地土非线性参数概率与场地地表加速度反应谱概率之间的关系。结果表明,场地土体动剪切模量比概率水平与场地地表加速度反应谱概率水平的关系随周期频段的变化而变化,粘性土在0.01 s～0.8 s周期内,无粘性土在0.02 s～0.7 s周期内,两者基本呈线性关系;场地土体阻尼比概率水平与地表加速度反应谱概率水平存在良好的对应关系,二者概率水平一致,且与反应谱的频段无关;在0.01 s～6.0 s周期频段内,无粘性土和粘性土的阻尼比概率与地表反应谱概率水平呈明显的线性关系。     

Prediction of long-term settlement on soft clay using shear wave velocity and damping characteristics

This paper presents a method of calculating long-term settlement of a loaded pad on soft clay at Klang, Selangor, Malaysia where the soil model is treated as an anelastic material of viscoelastic property. Initially, an elastic shear modulus (G) value from shear wave velocity profiles of the seismic tests from spectral analysis of surface wave (SASW) and continuous surface wave (CSW) tests was obtained. A value of damping (D) at an equivalent elastic strain is then calculated from the hysteresis of the plate load tests corrected to equivalent strain using the Damping–Strain formula. The calculated elastic settlement and its equivalent damping are then used to calculate the long-term settlement by applying the generalised viscoelastic formula. Comparisons to traditional methods of settlement predictions were made and the viscoelastic formula has shown better agreement to the observed settlement. Further modification of the settlement formula is introduced to improve the settlement accuracy to 10%.     

考虑变形模量劣化的应变软化模型在FLAC3D中的开发与验证

FLAC3D软件中的应变软化本构模型是通过抗剪强度参数劣化来实现的,没有考虑变形模量劣化造成的影响。针对这一问题,采用了变形模量劣化的损伤本构模型,详细推导了劣化损伤本构模型的差分格式,研究该模型在FLAC3D中二次开发的流程,在VC++环境下实现了劣化损伤本构模型在FLAC3D中的二次开发;通过与深埋圆形洞室应变软化数值解算例对比,进一步验证了该模型弹塑性和损伤的力学性质,分析了变形模量劣化对围岩变形特性的影响。由于该模型能够反映围岩的劣化损伤特性和大变形特点,因此在工程应用中有一定的实用价值。     

基于MODISEVI序列典型指标组合的土地覆盖分类研究

以2008年经Savitzky-Golay滤波技术平滑处理的MODIS EVI时间序列数据为数据源,采用支持向量机分类法对年EVI矢量模、年EVI最大值和年EVI最小值3个指标组成的影像进行土地覆盖分类,并利用验证样本对分类结果进行精度评价.试验结果表明:采用选用的3个指标不仅能减少分类的数据量、加快分类速度,而且还能...     

交互式航磁异常切线法系统研制

人机交互航磁异常切线法系统模拟手工切线法计算磁性体顶面埋深的流程,充分发挥解释人员的经验和智慧,同时利用计算机善于计算、查表以及图形处理的强大能力,实现了单测线和多测线显示、缩放以及平移,局部异常特征线和特征点自动绘制、交互修改、磁性体形态参数、深度、宽度以及磁化强度的自动查表计算,特征线和特征点、计算结果显示、保存等实用功能,极大地提高了航磁异常深度计算的可视化程度,减轻了解释人员的劳动强度,提高了工作效率,同时为个别异常的精细解释提供了不同方法.该系统采用面向对象设计方法,以VC++作为开发工具,可运行于各类Win32平台之上.     

土体动剪切模量及其衰减特性现场试验研究

如何获取土体动模量原位衰减曲线是研究天然土层在循环动荷载下的动变形特性课题中亟待解决的难题。为此,本文自制了一套地震动参数现场试验系统,依据动剪切模量原位测试原理获得了不同深度土体在小应变范围内的动模量原位衰减曲线。试验数据表明:当剪应变小于4×10^－5时,土体变形处于线性阶段;当剪应变大于4×10^－5时,土体归一化动剪切模量G/G_max衰减加快,以塑性变形为主。同时,当向土层施加的垂向静荷载越大,归一化动剪切模量值G/G_max与对数剪应变值logγ_d之间的关系会逐渐上移,但直线段斜率值不变。相关成果可为试验场地的动模量取值提供一定参考。     

Random field characterization of uniaxial compressive strength and elastic modulus for intact rocks

Rock properties exhibit spatial variabilities due to complex geological processes such as sedimentation,metamorphism, weathering, and tectogenesis. Although recognized as an important factor controlling the safety of geotechnical structures in rock engineering, the spatial variability of rock properties is rarely quantified. Hence, this study characterizes the autocorrelation structures and scales of fluctuation of two important parameters of intact rocks, i.e. uniaxial compressive strength(UCS) and elastic modulus(EM).UCS and EM data for sedimentary and igneous rocks are collected. The autocorrelation structures are selected using a Bayesian model class selection approach and the scales of fluctuation for these two parameters are estimated using a Bayesian updating method. The results show that the autocorrelation structures for UCS and EM could be best described by a single exponential autocorrelation function. The scales of fluctuation for UCS and EM respectively range from 0.3 m to 8.0 m and from 0.3 m to 8.4 m.These results serve as guidelines for selecting proper autocorrelation functions and autocorrelation distances for rock properties in reliability analyses and could also be used as prior information for quantifying the spatial variability of rock properties in a Bayesian framework.