动载下3条断续裂隙岩样的裂缝贯通机制

采用含3条断续预制裂隙的类砂岩模型试样进行单轴动力加载试验,对不同裂隙空间位置条件下断续裂隙岩体中裂隙的贯通机制进行了研究。静、动荷载下的对比研究成果显示：不同空间位置的裂隙贯通方式存在较大差异,且对动载的响应不同;动载下分支裂纹扩展及贯通具有惯性效应,即动载下裂尖次生共面、次生倾斜裂纹起裂后易朝原起裂方向快速发展,动载下易在两预制裂隙内端部产生直接贯通。这与静载下岩桥处的贯通常通过分支裂纹拐折扩展、相连不同,这也是导致裂隙试样中低应变速率下强度增大（即速率效应）的主要原因。同时,试验结果也表明：含裂隙试样静、动荷载下裂隙间的多次贯通是导致其呈现出渐进破坏特征的主要原因。     

刚性动力荷载作用下地基动力反应的若干问题

研究了地基表面在刚性动力荷载作用下的动力反应,给出了柱坐标解。在此基础上获得一个实用的地基动力刚度。定性地讨论了地基刚度和阻尼及其相互关系。并提出一个求取地基动力刚度和粘滞系数的实用化方法。     

地铁行车荷载作用下淤泥质黏土累积特性的试验研究

中国上海地区地铁隧道一般位于第④层淤泥质黏土层中,在地铁行车荷载作用下隧道周围土体变形引起隧道轴线沉降,有些区段隧道轴线沉降量已超过20cm,引起了一系列环境地质问题.本文以上海第④层原状淤泥质黏土为研究对象,通过室内循环三轴试验,模拟地铁运营过程中产生的振动荷载,研究荷载作用下上海淤泥质黏土的累积应变、孔隙水压力及再...     

马兰黄土动强度及其微结构变化实验

黄土斜坡灾害已经成为黄土地区农村城镇化及交通建设的瓶颈,是当前地质灾害领域的研究热点.因震(振)动影响而降低黄土强度、改变黄土自身结构形态的研究是揭示黄土斜坡灾变机理的基础.基于GDS试验系统,采用应变控制等效正弦波逐级加载方式,进行马兰黄土动三轴试验;利用扫描电镜,观察马兰黄土试验前后微结构变化.试验结果表明:马兰黄...     

海底泉对在海底有限延伸的越流含水层系统中地下水潮汐效应的增强作用

海底泉在滨海地下水排泄过程中起着重要的作用。本文给出了含有一个海底泉的在海底延伸的越流承压含水层系统中地下水水头在海潮作用下波动的近似解析解。该含水层顶底板隔水且向海底延伸有限距离。假设含水层的海底露头被一层隔水层覆盖,海底泉由一个渗透性很好的完全穿透海底含水层硕板的圆柱体渗漏天窗（海底泉孔）来表示。近似解析解中包含了6个参数：承压含水层的海潮传播参数,海底泉孔中心到海岸线的距离,表示泉的圆柱体的等效半径,海底泉孔中心到含水层海底露头处的距离,承压含水层的海潮载荷效率和弱透水层的越流。分析表明,如果海底泉孔中心到海岸线的距离远大于泉孔的等效半径,且海底泉孔中心到含水层海底露头处的距离远大于泉孔的等效半径时,解析解的近似误差可以忽略。然后本文讨论了解析解的两个基本性质,分析了海底泉对海底地下水水头波动的影响。     

Design of shallow foundations under tensile loading for transmission line towers: An overview

Tensioned foundations are common in civil engineering applications such as transmission towers, harbors, offshore structures, basement slabs under pressure, industrial equipment, etc. Procedures for the design of tensioned foundations are discussed in this paper, including specific recommendations for more common transmission tower foundations. Starting from a distinction between shallow and deep modes of failure, the paper presents the most common failure mechanisms for shallow failure in tension, including procedures for calculation of foundation tensile capacity under vertical and inclined loading. Emphasis is given to the influence of the strength of the compacted backfill compared to the strength of the natural soil, including presentation of results of full-scale loading tests.     

压重顶进框构下穿高铁引起桥墩变形及控制技术

以某高速公路下穿京沪高铁工程为例,提出一种基于"卸载-加载平衡"理念的压重顶进框构方案,并对高铁桥墩变形及控制技术进行研究。结果表明,高速公路在高铁桥下开挖10 m深,开挖体量近10万方。采用压重顶进框构方案,施工中边顶进、边监测、边通过框顶堆土、桥下堆土、框内留土等措施加载压重,可有效控制高铁的隆起变形。在通车运营3个月后,高铁相邻桥墩累计最大差异沉降为2.7mm,距离规范限值留有46%的余量,满足规范要求。轨检表明,无砟轨道平顺性满足运营要求。对比分析表明,数值模型中粉质黏土压缩模量可采用P0~P0+100 kPa(P0为土体自重应力)应力区间对应的模量值,卸载模量可取为压缩模量的3~5倍。     

基于小波函数的锚杆拉拔全过程分析

基于小波函数伸缩平移的特性,建立了能反映锚杆界面黏结?软化?滑动力学特性的剪应力?位移非线性本构模型,克服了三折线软化界面模型需要分段分析的复杂性。结合锚固体荷载传递的力学微分方程,推导了锚杆拉拔荷载?位移曲线的解析表达式,并提出了锚固体位移、轴力、周边剪应力的数值计算方法和步骤。通过算例分析,得到不同张拉位移作用下的锚固段位移、轴力和剪应力分布,获得的锚杆拉拔荷载?位移和锚杆轴向力分布计算值与实测值进行了对比分析,验证了该方法的有效性。该方法能准确地反映锚杆在不同荷载下的传力机制,模拟锚杆从弹性工作状态到塑性滑移的全过程。最后,通过参数分析,得到了锚杆锚固长度、轴向刚度以及锚固界面本构参数对锚固效果的影响规律。     

Quantitative prediction of discrete element models on complex loading paths

The ability of discrete element models to describe quantitatively (and not only qualitatively) the constitutive behaviour of a dense sand is assessed in this paper. Two kinds of 3D discrete models are considered. Both consider spheres as elementary particles. Nevertheless, the first model implements a contact law with rolling resistance whereas the second takes into account clumps made of two spheres. The discrete models are calibrated and validated from mechanical tests performed on a dense Hostun sand with a true triaxial apparatus. The calibration is carried out from axisymmetric drained compression tests, while the validation is discussed from monotonic and cyclic stress proportional loading paths and from a circular stress path in the deviatoric stress plane. The quality of the predictions of the discrete models are evaluated by comparison with the predictions given with advanced phenomenological constitutive relations, mainly an incrementally non-linear relation. Predictions given by the discrete models are remarkable, particularly when it is put in perspective with respect to the very few number of mechanical tests required for their calibration. However, these results and conclusions were reached in enabling conditions, and some limitations of such discrete models should be kept in mind.     

Limitations of suction‐controlled triaxial tests in the characterization of unsaturated soils

Behavior of unsaturated soils is influenced by many factors, and the influences of these factors are usually coupled together. Suction‐controlled triaxial (SCTX) tests are considered to allow researchers to investigate influences of individual variables on unsaturated soils under specified stress path with controls of stresses, pore water, and air pressures. In the past 50 years, SCTX testing method has been established as a standard approach to characterize constitutive behavior of unsaturated soils. Most important concepts for modern unsaturated soil mechanics were developed upon results from the SCTX tests. Among these, one of the most important contributions in the constitutive modeling of elasto‐plastic behavior for unsaturated soils is the Barcelona basic model (BBM) proposed by Alonso et al. in 1990. The BBM successfully explained many features of unsaturated soils and received extensive acceptance. However, the SCTX tests are designed based upon the divide‐and‐conquer approach in which an implicit assumption is used: soil behavior is stress‐path independent. However, it is well‐established that unsaturated soil behavior is elasto‐plastic and stress‐path dependent. It is found that the SCTX tests in fact cannot control the stress path of an unsaturated soil during loading. This incapability, in combination with complicated loading/collapse behavior of unsaturated soils, makes the SCTX tests for characterizing unsaturated soil questionable. This paper discusses the limitations of the SCTX tests in the characterization of unsaturated soils. A possible solution to the problem was proposed based on a newly developed modified state surface approach. The discussions are limited for isotropic conditions. Copyright © 2015 John Wiley & Sons, Ltd.