静三轴试验中水泥土力学特性及本构模型研究

通过不排水三轴压缩试验对水泥土的力学特性进行研究,重点分析了围压与水泥掺入比对水泥土体强度、孔压及刚度的影响。试验结果表明,随着围压与水泥掺入比的增加,水泥土体的强度与刚度均增加,而孔压随之减少;随着轴应变的增加,刚度逐渐减少。而在加载初期,刚度衰减较快,随着轴应变的继续增加曲线渐趋平缓,衰减现象并不明显;随着无量纲化偏应力的增加,无量纲化刚度逐渐减少,并且两者为曲线关系。通过对水泥土的刚度软化规律进行描述,得到了修正的邓肯-张模型。通过对试验曲线进行回归分析确定了模型参数。与实测数据对比发现,该修正模型不仅可以较好地模拟水泥土的应力-应变关系,还体现了水泥土应变软化型曲线的特点。     

A bond failure criterion for DEM simulations of cemented geomaterials considering variable bond thickness

A series of micromechanical tests were conducted to investigate the bond failure criterion of bonded granules considering the effect of bond thickness, with the aim of enhancing the bond contact model used in the distinct element simulations of cemented geomaterials. The granules were idealized in a two‐dimensional context as one pair of aluminum rods bonded by resin epoxy or cement. The mechanical responses of nearly 500 rod pairs were tested under different loading paths to attain the yield loads of bonded granules at variable bond thickness. This study leads to a generic bond failure criterion incorporating the effect of the bond thickness. The results show that the bond compressive resistance largely decreases with increasing bond thickness owing to the presence of the confinement at the bond‐particle interface. The strength envelopes obtained from the combined shear compression tests and combined torsion compression tests have identical functional form, and they decrease in size with increasing bond thickness but remain unchanged in shape. Given the same cementation material, the generic bond strength envelope in a three‐dimensional contact force space under different loading paths remains the same in shape but shrinks with the increase of bond thickness. Copyright © 2014 John Wiley & Sons, Ltd.     

A theoretical–experimental approach to elastic and strength properties of artificially cemented sand

Evaluating the behavior parameters of soils and soil-binder mixes by means of theoretical models that are supported by laboratory tests still remains a key challenge in foundation design. In this context, the paper investigates some aspects of the mechanical behavior of artificially cemented sands (ACS) by means of experimental characterization and micromechanics-based modeling. Particular emphasis is given to the increase in elastic stiffness and strength brought by cementation. Based on the concept of a fictitious continuum medium and the homogenization theory, the effective elastic properties of ACS are evaluated using the Mori–Tanaka and self-consistent schemes. The elastic micromechanical approach is supported by bender element tests. Finally, the effective strength properties of ACS are assessed by means of micromechanics-based failure criterion formulated within the context of non-associated plasticity. Validation and calibration of the theoretical model are achieved by comparison with data from unconfined compression tests.     

Inherent heterogeneity of sediments in Dhahran, Saudi Arabia — a case study

The behavior and properties of sediments depend on their compositional characteristics and formation processes, as well as the environmental conditions during their geological history, i.e. post-formation processes. A vertical cut made in a hill in Dhahran, Saudi Arabia, reveals a vivid picture of the inherent heterogeneity of sediments that have been deposited at different geological ages. A review of the geology of the area, as well as laboratory tests, help to determine the possible causes of the variability of soil types and properties in the area. Laboratory tests include basic geotechnical tests, chemical tests, X-ray diffraction analysis, scanning electron microscopy, and thermal analysis. These tests are used to identify different rock types and soils from the face of the cut. The results of this study indicate that the material from this cut varies from clayey shale and limestone rock (Tertiary, lower Eocene) formed some 52 M.Y. to calcite-cemented sand and pure calcite rock formed in the Quaternary age.     

橡胶水泥土动力特性的试验研究

通过动三轴试验,研究了橡胶水泥土复合试样的动强度、动弹性模量和阻尼比等动力参数的变化规律,着重研究了橡胶粉掺量、围压和应变3个主要因素的影响并分析了内在机理。在围压不变的情况下,随着橡胶粉掺量的增大,橡胶水泥土复合试样动强度降低。围压越大,动强度越高,受橡胶粉掺量的影响越小。随着围压的增大,动弹性模量增大而阻尼比减小;随着橡胶粉掺量的增加,动弹性模量减小而阻尼比增大。通过数据拟合,得到了橡胶水泥土动弹性模量和阻尼比的计算公式。橡胶粉可以提高水泥土吸收能量的能力,采用橡胶水泥土作为地基处理材料时,能够起到减震的作用。     

封闭不良天然气孔突水过程的水文地球化学特征

为了查清封闭不良天然气孔突水过程中充水水源的变化规律,开展了气孔出水水文地球化学特征研究。结果表明：“大53”天然气孔突水过程中TDS浓度逐渐降低,初期为SO₄·Cl—Na型水,位于Piper三线图右端部,来自直罗组;中期TDS浓度降至500多mg/L,属于HCO₃·SO₄·Cl—Na型水,位于Piper三线图右端偏下,来自白垩系;期间煤层底部涌出高TDS的SO₄·Cl—Na型水,该水样点位于三线图右端偏上。气孔处理过程中,水样中γ（Ca）/γ（Na）系数均远大于其他水样,且HCO₃^- 未检出,为煤层顶板直罗组水化学特征,表明阻隔了2^-1煤层与白垩系含水层和2煤—6煤含水层的水力联系。取距离阈值20,分层聚类分析可以将水样分为白垩系水和侏罗系水,距离阈值5又可将侏罗系含水层水细分为直罗组2段、直罗组1段和2煤—6煤含水层水,实现了对气孔突水过程中充水水源变化规律的准确判别。     

胶结充填体压缩破坏前兆多参数表征

借助自主设计的由加载控制系统、应变采集系统、电阻同步采集系统以及红外成像系统等组成的多参数、同步监测系统,研究了充填体在单轴压缩过程中的应力-应变、电阻率以及温度变化规律,分析了充填体在破坏失稳应力-应变、电阻率以及热效应异常前兆特征,并对比了不同监测信息对同一事件破坏的敏感度和差异性。结果表明：充填体的电阻率和热红外信息时空演化进程与其压缩变形破坏整个过程基本相符,且具有明显的阶段性;在整个加载破坏过程中,观测到的电阻率前兆信息点要早于热红外前兆点、应力前兆点;与应力-应变、温度变化相比,电阻率变化规律具有明显的反对称性;电阻率变化规律能详细地表现充填体受压过程中每个阶段内部结构变化特征,而热红外信息则主要体现充填体塑性屈服前的表面结构温度演化特性。运用多参数评价充填体加载破坏前兆特征,能克服单纯考虑某一参数变化方法预警可信度低、错误率高的缺点。该方法是一种能全面、精准地掌握采场充填体稳定状态的有效方法。     

Effects of anisotropic permeability on stabilization and pore water pressure distribution of poorly cemented stratified rock slopes

Slopes composed of stratified and poorly cemented rocks that fail during heavy rainfalls are typical in the outer zone of Taiwan's Western Foothills. This study investigates how hydraulic conductivity anisotropy influences pore water pressure (PWP) distributed in stratified, poorly cemented rock slopes and related slope stability through numerical simulation. The notion of representing thin alternating beds of stratified, poorly cemented rocks as an equivalent anisotropic medium for ground‐water flow analysis in finite slopes was validated. PWP was then derived in a modelled slope comprising an anisotropic medium with suitable boundary conditions. Simulation results indicate the significance of the principal directions of hydraulic conductivity tensor and the anisotropic ratio on PWP estimation for anisotropic finite slopes. For a stratified, poorly cemented rock slope, estimating PWP utilizing a phreatic surface with isotropic and hydrostatic assumptions will yield incorrect results. Stability analysis results demonstrate that hydraulic conductivity anisotropy affects the slope safety factor and slip surface pattern. Consequently, steady‐state groundwater flow analysis is essential for stratified, poorly cemented rock slopes when evaluating PWP distribution and slope stability. This study highlights the importance of hydraulic conductivity anisotropy on the stability of a stratified, poorly cemented rock slope. Copyright © 2006 John Wiley & Sons, Ltd.     

金刚石薄膜涂层硬质合金的耐磨性试验研究

为表征金刚石薄膜涂层硬质合金的耐磨性能,引入了“耐磨系数”指标。利用自行设计的试验装置,在设定的试验条件下,对金刚石薄涂层硬质合金等３种不同材料试件的磨耗比进行对比试验,并对试验结果进行讨论。     

Shaft capacity of pre-bored grouted planted nodular pile under various overburden pressures in dense sand

Abstract

This paper presents the results of a series of model tests performed to study the shaft capacity of pre-bored grouted planted nodular (PGPN) pile in dense sand. The influence of the vertical overburden pressure on the shaft capacity of the PGPN pile is also investigated based on the test results. The test piles were equipped with strain gauges to measure the axial loads during the loading process, moreover, a foam plate was buried beneath pile tip to eliminate the influence of tip resistance on the shaft capacity. Some conclusions can be drawn based on the test results: the peak skin friction of PGPN pile increases with the increase of vertical overburden pressure applied on the foundation soil, while the rate of increase decreases with the increasing overburden pressure; the surface of the pile–soil interface of PGPN pile is relatively rough, and significant dilatant increase in lateral stress occurs during the loading process.