Cyclic behavior of reinforced sand under principal stress rotation

Although the cyclic rotation of the principal stress direction is important,its effect on the deformation behavior and dynamic properties of the reinforced soil has not been reported to date.Tests carried out on large-scale hollow cylinder samples reveal that the cyclic rotation of the principal stress direction results in significant variations of strain components(ε_z,ε_r,ε_θ and γ_(zθ)) with periodic characteristics despite the deviatoric stress being constant during tests.This oscillation can be related to the corresponding variations in the stress components and the anisotropic fabric that rotate continuously along the principal stress direction.Sand under rotation appears to develop a plastic strain.Similar trends are observed for reinforced sand,but the shear interaction,the interlocking between particles and reinforcement layer,and the confinement result in significant reductions in the induced strains and associated irrecoverable plastic strains.Most of the strains occur in the first cycle,and as the number of cycles increases,the presence of strains becomes very small,which is almost insignificant.This indicates that the soil has reached anisotropic critical state(ACS),where a stable structure is formed after continuous orientation,realignment and rearrangement of the particles accompanied with increasing cyclic rotation.Rotation in the range of 60°-135° produces more induced strains even in the presence of the reinforcement,when compared with other ranges.This relates to the extension mode of the test in this range in which σ_θσ_z and to the relative approach between the mobilized plane and the weakest horizontal plane.Reinforcement results in an increase in shear modulus while it appears to have no effect on the damping ratio.Continuous cycles of rotation result in an increase in shear modulus and lower damping ratio due to the densification that causes a decrease in shear strain and less dissipation of energy.     

基层模量对重载交通沥青路面受力特性的影响分析

基层模量的取值将直接影响到路面结构的受力特性,它是是路面设计的重要力学参数之一。本文系统分析基层模量变化对重载交通沥青路面路表弯沉、基层层底拉应力、底基层层底拉应力的影响,并阐述了其影响规律。结果表明．基层模量对重载交通沥青路面的受力与变形特性具有显著的影响,提高基层模量值将显著减小路表弯沉值底基层层底拉应力,而基层本身的层底拉应力值将增大,需要在路面设计中充分重视。     

公路路面基层用水泥基材料的研制

目前我国公路建设路面基层普遍采用水泥稳定土或砂,而普通水泥不能满足路面基层施工要求,特别是因水泥干缩易引起基层裂缝,导致路面开裂。根据公路路面基层施工需要,开发以粉煤灰为主要原料的新型材料替代目前的普通水泥,该材料不仅满足施工性能需要,而且具有适宜的强度和微膨胀性,可有效地减少路面基层的开裂问题。     

Effect of intermediate principal stress on strength of anisotropic rock mass

The Mohr-Coulomb criterion needs to be modified for highly anisotropic rock material and jointed rock masses. Taking σ₂ into account, a new strength criterion is suggested because both σ₂ and σ₃ would contribute to the normal stress on the existing plane of weakness. This criterion explains the enhancement of strength (σ₂ – σ3) in the underground openings because σ₂ along the tunnel axis is not relaxed significantly. Another cause of strength enhancement is less reduction in the mass modulus in tunnels due to constrained dilatancy. Empirical correlations obtained from data from block shear tests and uniaxial jacking tests have been suggested to estimate new strength parameters. A correlation for the tensile strength of the rock mass is presented. Finally, Hoek and Brown theory is extended to account for σ₂. A common strength criterion for both supported underground openings and rock slopes is suggested.     

波纹钢管廊受力变形特性研究

波纹钢管廊作为传统管廊的替代品,具有运输简单、安装方便、施工快速的特点,可广泛地应用于城市地下工程。通过Flac3D软件,考虑波纹钢管廊与周围填土之间的相互作用,对施工完成后波纹钢管廊的受力变形进行了模拟,研究了波纹钢管廊沿各个坐标轴方向的受力和变形规律,对波峰波谷处的受力变形进行比较。数值模拟结果表明:波峰处的总应变增量较波谷处更大,应把波峰处应变量作为控制指标;波纹钢管廊在土压力下产生了径向收缩和竖向位移,竖向位移约为径向的2倍,且数值都较小;波峰、波谷受力协调,使得波纹钢管廊整体受力较为均匀,共同承担填土荷载作用。     

Effect of polygonal crack grids on deformation characteristics of rock

The writers propose, for analyses, to replace in a rough way the real medium by a set of standard periodic media (in the given case with polygonal crack systems). Based on a simple variant of the principle of equivalent homogeneity, they obtain relations of the deformation characteristics of rock as functions of the properties of undisturbed material and the parameters characterizing cracks and their contact region. A comparison with a parallel-plane crack system is presented.Moscow Civil Engineering Institute (MISI). Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 3, pp. 6–9, May–June, 1993.     

浅析沥青路面就地冷再生底基层混合料配制

以平青乐线K297＋752-K301＋102段冷再生底基层工程为例,介绍了沥青路面全深式就地冷再生底基层混合料配制要点,对冷再生旧料特征,新添骨料性质及相关试验分析步骤作了具体阐述,以期指导实践。     

主应力轴旋转对黄土动模量和阻尼比的影响

对各种不同初始状态下的黄土进行周期扭剪试验,研究主应力轴旋转对其动模量和阻尼比的影响规律,结果表明:黄土的最大动剪切模量随含水率的增大而减小,随着干密度的增大而增大;阻尼比随含水率增大而增大,随干密度的增大而减小。     

聚丙烯土工带塑性变形研究

对目前应用于加筋土工程中的聚丙烯土工带，进行加载拉伸试验，得出聚丙烯土工带的变形特性，并对试验结果进行拟合，得到应力、伸长量和时间的关系方程。     

Experimental investigation of the influence on static and cyclic deformation of structural soft clay of stress level

This paper presents the experimental results performed to study the static and cyclic deformation behavior of undisturbed and remolded soft clays sampling from Xiaoshan. The consolidation tests indicated that the vertical strains of undisturbed soft clay could be divided into three stages with load increasing, however, the remolded clays were almost independent of stress level. The two cut-off points of these three stages are the preconsolidation stress and the structural yielding stress of the original clay, which could be determined by shear wave velocity measurement. The strains developed during cyclic tests of undisturbed and remolded soft clay, both having one turning point under different amplitude of cyclic stress. The strain developed slowly and stayed at a low level at the early stage, but developed quickly in a different way when the turning points were achieved and finally became great. The turning strains changed with different cyclic stress amplitudes, but they almost fell on a linear line whether undisturbed or remolded. Furthermore, the turning points of the remolded clay all fell on the same line of different confining stresses, including which of the undisturbed soft clay under confining pressure was larger than structural yielding stress. It was also found that the deformation characteristic of undisturbed and remolded Xiaoshan clay tend to be consistent when the structure of undisturbed soft clay is damaged. __________ Translated from Chinese Journal of Rock Mechanics and Engineering, 2006, 25(5): 937–944 [译自: 岩石力学与工程学报]     

基于弹塑性本构模型的非饱和膨胀土变形研究

研究了初始含水量一定的条件下,有荷膨胀率与竖向压力半对数成线性关系,与干密度、初始含水量成线性关系,推导出了简单的本构模型,指出该模型是利用室内常规试验可以得到的,能反映研究地区岩土体主要性状的应用型本构模型。     

基于主成分分析法的高性能再生混凝土性能优化设计

影响高性能再生混凝土性能的指标有多种因素,各指标之间由于存在相关性,而难以对其进行比较准确的评价,主成分分析法采用降维的思想把多个变量转化为少数几个互不相关的的主成分,通过对主成分的分析达到对混凝土综合性能的优化设计,以期满足对性能的最优化.实例优化也表明主成分分析法对评价混凝土的综合性能有很好的一致性,满足工程实际对...     

半刚性基层材料抗冲刷性能的研究

半刚性基层材料的抗冲刷性能是评价路面路用性能的一项重要指标,对整个路面特别是沥青路面的强度、使用质量和使用寿命都有十分重要的影响.针对半刚性基层材料常见的冲刷病害,在分析其形成机理的基础上,在室内利用冲刷试验仪研究抗冲刷性能的影响因素,提出了利用10min内冲刷速率作为半刚性基层材料抗冲刷性能的评价指标.     

注浆压力对盾构隧道管片变形及受力特性的影响研究

以深圳地铁7号线为工程背景,通过建立数值计算模型,探究了管片衬砌在非均匀注浆压力作用下的变形及受力情况,结果表明:在非均匀注浆压力的作用下,盾构隧道管片衬砌结构产生明显的上浮现象,管片上浮值较大,管片应力值在可控范围内。     

Effects of fines on the cyclic liquefaction behaviour in unsaturated,well-graded materials

The liquefaction of cargoes of metallic ores during maritime transportation is believed to have caused a number of ships to capsize during the past 30 years. To minimise the risk of liquefaction, shipping standards specify a transportable moisture limit (TML), which is the maximum moisture content for ore cargoes to be loaded onto a ship. However, the mechanics leading to the liquefaction of these cargoes is not well understood. This study uses an unsaturated soil mechanics perspective to understand the cyclic liquefaction behaviour of partially saturated materials, similar in grading to iron ore fines, a metallic ore that is known to liquefy during shipping transportation. Iron ore fines are transported at relatively low densities and have variable gradings containing a wide range of particle sizes and fines contents. Therefore, the effects of the degree of saturation and the fines content on the cyclic liquefaction behaviour of well-graded materials have been investigated by performing unsaturated, compression-only cyclic triaxial tests on samples prepared with four different gradings containing particle sizes from 9.5 mm to 2 μm with fines (<75 μm) contents of 18%, 28%, 40% and 60%. The trends in the data are discussed and used to develop a simple method that can conservatively estimate the number of cycles that samples with different degrees of saturation and fines contents are able to resist. The use of this method to describe the liquefaction behaviour of cargoes containing iron ore fines, in practice, is discussed.