求取现场黄土饱和渗透系数的双环入渗法

土体渗透性参数的测定是解决与水有关的岩土工程问题的关键所在。为使现场原状土体饱和渗透系数的测定更为准确,通过一种易于安装和固定的防蒸发型双环入渗仪,研究黄土的入渗规律与特点,试验结果表明:黄土的入渗分区可分为饱和区、湿润区与干土区,其中饱和区的入渗深度约占总入渗深度的1/2,而湿润区土体的饱和度在70%以上,这一特征与Green-Ampt入渗模型的假设较为接近,但在应用基于Green-Ampt模型的规范法（SL237-042-1999）求取黄土的饱和渗透系数时,发现该法会高估黄土的饱和渗透系数。因此,结合Green-Ampt入渗模型与土水特征曲线主要增湿路径的特点,提出了能合理测定现场黄土饱和渗透系数的双环入渗法,对Green-Ampt入渗模型参数加以修正,即直接采用干土区的初始基质吸力水头值,且该值由张力计实测或由主要增湿曲线求得;需采用入渗试验前期的平均入渗率;所对应的湿润锋发展深度需经由水分传感器实测而得。研究结果表明该法能合理估算现场黄土的饱和渗透系数。     

Three-dimensional numerical modelling of the behaviour of a pile subjected to cyclic lateral loading

This paper presents a finite element simulation of the behaviour of a vertical pile subjected to a cyclic lateral loading. First, the choice of a suitable constitutive model is discussed. The analytical solution of the model equations for a monotonic triaxial compression is given, and the model is compared with monotonic and cyclic triaxial tests on dry Fontainebleau sand. Simulations of tests carried out on a model pile with the geotechnical centrifuge of the French Public Works Research Laboratory (LCPC) were then performed with the model parameters derived from the triaxial tests. Results are in good agreement with experiments.     

An assessment of miniaturised electrical imaging equipment to monitor pollution plume evolution in scaled centrifuge modelling

This paper demonstrates the capabilities and limitations of a miniaturised electrical imaging technique (resistivity tomography) developed at Cardiff University to image contaminant plumes in scaled centrifuge models of the vadose zone. For this purpose a generic model of contaminant infiltration into unsaturated sand was designed. The imaging technique produces two-dimensional contoured plots of the resistivity distribution before and during contaminant infiltration experiments. During the experiments, dyed NaCl solution was released into the model and the change in resistivity associated with the contaminant plume evolution was imaged as a function of time and g-level. Capillary pressure was monitored constantly by matrix potential probes (tensiometers) in order to investigate the effect of capillary forces on plume evolution. Tests at 1g (static conditions) and 10g are described in this paper. Comparison of resulting two-dimensional tomography with observed plume geometry at the end of the 1g test showed this imaging technique to be highly effective.

Contaminant plume evolution in the unsaturated sand model was observed to be mainly gravity-driven, with plume migration and geometry being strongly affected by a tenfold increase in gravity in the centrifuge experiment. It is concluded that miniaturised electrical imaging can be a useful tool for monitoring pollution plume evolution during centrifuge tests, but when plume evolution is rapid, the time taken to interrogate each array restricts the effectiveness of the technique in monitoring changes in plume geometry. However, in such cases, resistivity tomography does provide valuable information on residual levels of contaminant fluid retained within the soil after passage of the plume.     

地震作用下自由场中饱和砂土的应力-应变推导

水平自由场地震响应分析是岩土地震工程实践的重要内容之一。利用香港科技大学土工离心机上的双向振动台,进行了饱和砂土自由场在水平双向地震作用下的动力模型试验。根据应力和应变的定义以及达朗贝尔原理,由试验观测的土体加速度、位移和孔隙水压力数据直接推导得到不同深度处砂土的应力和应变,揭示了振动过程中饱和砂土的应力路径和应力-应变关系演化过程,以及与超静孔隙水压力发展的联系。     

Geological features and landslide mechanisms of an unstable coastal slope (Petacciato, Italy)

On the basis of geological and geomorphological surveys, landslide phenomena are analysed on a slope along a stretch of the Adriatic coast, near Petacciato (Molise, Italy).

Locally, a blue clay sequence of Pleistocene outcrops, stratified with silty-sandy layers; bedding dips 3–8°NE and the slope has a similar attitude. This sequence evolves upwards to sands and conglomerates, with thickness of up to 40 m, on which the built-up area is located.

Several episodes of landslide reactivation occurred in the past century, involving the zone between the built-up area and the sea, along a coastal slope of over 2000 m long and 200 m high. Important roads and railway lines have been heavily damaged as well as the town itself.

The typology of the movement is a rotational–translational slide; the displacement reaches tens of centimetres at each reactivation episode along the entire coastal slope, extending well beyond the shore line.

Detailed studies already exists, but different mechanism failures have been proposed to explain the landslide phenomena. In this study, a new failure mechanism is proposed, (sudden spreading of Terzaghi, K., Peck, R.B., 1948. Soil Mechanics in Engineering Practice. Wiley and Sons New York) and analytical approaches have been adopted to evaluate the slope stability, based on the geotechnical and monitoring data and the geometrical and geological features of the slope.     

潜水自然防护性能的评价及效果分析

本文以大量的水文地质勘探结果为依据,引用了水文地质参数:隔、透水层的厚度(A、B)和渗透系数(K_1、K_2)。对研究区非饱和带进行统计计算,求出该带的垂直自然防护性能指数。同时选择饱和带特征参数导水系数(T),计算出潜水自然防护性能总指数后,对潜水自然防护性能进行评价。     

饱和钙质砂爆炸响应动力特性试验研究

钙质砂是一种特殊的海洋沉积物,开展钙质砂在爆炸作用下动力响应特性研究具有重要的理论意义和工程实用价值。通过室内小型爆炸试验,研究饱和钙质砂在爆炸作用下土压力、孔隙水压力和质点振动加速度等参数的变化规律。结果表明：饱和钙质砂中爆炸应力波随距离增大而衰减,但随爆心距增大衰减速度呈减小趋势;随试样相对密度增大爆炸应力波的衰减速度趋缓;爆炸引起的超孔隙水压力在10～30 ms内到达峰值,在前3 min内快速消散,消散幅度达90％以上;双发雷管微差起爆相对于单发起爆,最大单段起爆药量相同,但微差起爆由于爆炸应力波的叠加,使得钙质砂动力响应加剧。与相同试验条件下石英砂爆炸响应对比表明,相同测点处钙质砂动力响应弱于石英砂,应力波在钙质砂中衰减速度远比石英砂快,说明饱和钙质砂对爆炸应力波有着极强的吸收和衰减作用;爆炸近区钙质砂颗粒大量破碎,形成爆炸破碎和压缩区,形成这几个区域所耗损的爆炸冲击能量大约占总能量的25％左右。     

岩土工程试验研究中的若干新进展

介绍了在非饱和土、数值分析、测试技术和土工合成材料工程应用方面的成就。关于非饱和土方面,指出了加强非饱和土基本试验研究工作的紧迫性;关于数值分析方面,认为流形元法为连续和非连续变形的力学分析提供了一个统一的方法,应加强在岩体力学和土力学中的开发与应用;关于岩土力学的测试技术,需密切注意近年高新技术在岩土领域的引进和推广;对于土工合成材料,应加强机制的研究,注意在应用中掌握有关原理,最后对岩土工程研究中当前存在的问题和今后发展作了简单的评述     

冻结滞水形成机制的探讨

资料表明，冻结滞水形成机制是在冬季的冻结作用下，包气滞冻土层内产生氢键吸附能，饱和水汽压差和气管薄膜等机制构成冻结势。它具用奶强的吸附能凝聚水分，全副钨气带水和潜水液态，汽态向冻结层迁移富集；形成季节性固态地下水。在冻结期间包气带水盐具有明显倒置分带性：冻结滞水带；过渡水分带；支持毛管水汽化输水带。     

Modelling coupled heat and contaminant transport in groundwater

This paper presents the results of a research programme conducted on the geotechnical centrifuge at The University of Western Australia to investigate coupled heat and contaminant transport in the soil surrounding a buried waste source. The phenomena which govern heat and contaminant transport through porous media are discussed, the principles of geotechnical centrifuge modelling are outlined, and relevant scaling laws that govern the relationship between a centrifuge model and the prototype, with respect to the problem of coupled waste transport, are presented. A model test, simulating two-dimensional migration from a buried heat and contaminant source, is described, and the results from four model tests are presented. The experimental data show that hydraulic instability is responsible for the transport of contaminant in the soil around the source and that the mode of instability is determined by the magnitude of the effective Rayleigh number.     

饱和度-压力曲线法预测柴油在毛细带中形成的透镜体厚度

轻非水相液体（LNAPL）进入到地下环境中,首先在非饱和带进行垂向迁移,到达毛细带后在地下水面以上形成饱和透镜体。准确预测LNAPL渗漏在毛细带形成的透镜体厚度,对于LNAPL的去除及污染含水层的修复具有重要的指导意义。通过模拟实验测定了水-油两相吸湿及脱湿曲线,采用水-油饱和度-压力曲线拟合出了吸湿及脱湿进入压力。根据透镜体达到稳定状态时脱湿、吸湿压力水头之间的关系,建立了透镜体厚度的预测计算方法,并以中砂和粗砂为例,预测出实验条件下柴油在毛细带形成透镜体稳定时的厚度分别为4.61 cm和1.29 cm。通过室内模拟槽实验,测得柴油在中砂和粗砂中迁移时形成的透镜体厚度分别为5.30 cm和1.50 cm。预测与实验结果的相对误差分别为13.0%和14.0%。误差产生的主要原因为脱湿与吸湿曲线是在非干燥情况下测得,从而导致预测的透镜体厚度偏小。     

非饱和含黏土砂毛细上升试验研究

采用MP406水分传感器、WM-1负压计和DT80数据记录仪等设备,开发了一套毛细上升试验系统,对非饱和含黏土砂做了3个不同初始含水率的毛细上升试验,得到了试样各个断面的含水率和吸力随时间的变化规律。研究表明：初始含水率对毛细上升高度和上升速度有显著影响,本套系统可测定毛细上升的实际高度,在土样渗透系数未知的情况下可对不同土样测定其毛细上升的最大高度;可根据湿润锋运动速度、土样含水率变化和吸力变化数值,确定非饱和土渗水系数,从而避免了渗透系数确定费时、费力的困难;可由吸力预测试样的渗水系数,只需测定该土的土-水特征曲线或进行吸力量测即可确定出该土在这一吸力下的渗水系数;并拟合出不同初始含水率试样的湿润锋随时间变化规律     

三轴试验中砂土刚度的统计和回归分析及应用

砂土的密度和应力状态对其刚度有很大的影响。计算岩土工程中许多硬化土体模型都是基于邓肯−张模型得出的,没有考虑到密度对砂土刚度的影响。而在极致密或松散的砂土的三轴压缩过程中,剪切应变的上升会引起密度的显著变化。为了评估粒径分布、密度及应力状态对砂土刚度的影响,使用统计和回归方法对来自莫斯科和明斯克的15个建筑工地的962个土壤样本的各向同性三轴试验数据进行分析。基于密度和应力状态参数的影响,提出了评估不同粒径砂土刚度的经验方程。对来自欧洲、印度和美国的冲积土和陆地土试验的比较分析表明,其砂土的刚度与莫斯科和明斯克的砂土在同一范围。所提出的方程可用于初步估计有限元法计算里的刚度参数,也可应用于岩土工程模型（允许考虑刚度的变化、水平和垂直分布）。此外,还提出了基于邓肯−张模型的半经验关系。当密度的变化影响土的刚度时,该半经验关系可为受到大变形和（或）复杂加载路径影响的松散和非常致密的砂土提供更为真实的结果。一般来说,岩土工程师可将获得的结果应用于更为复杂的土体模型设计中。     

包气带非水相污染物迁移离心模型研究中的相似比例关系

非水相污染物在包气带中的迁移是一个复杂的物理、化学及生物过程 ,离心模型是解决该问题的有效途径之一。采用理论分析和数值分析的方法 ,对两种湿润历史条件下 ,二相与三相体系中 ,毛细上升高度、达到毛细平衡所需要的时间以及迁移距离等与离心加速度之间的关系进行了研究 ,提出了存在于包气带非水相污染物迁移离心模型研究中的相似比例关系     

Application of electrical imaging to leachate plume evolution studies under in-situ and model conditions

Electrical imaging (resistivity tomography) is increasingly used as a geophysical exploration technique in contaminated land research. The present work demonstrates the efficiency of electrical imaging in monitoring pollution plume evolution under both in-situ and model conditions. The in-situ campaign was done at an unlined landfill site situated in the city of Patras, Hellas. A partially saturated zone of alluvial fan deposits underlies the site, which retards leachate percolation to the underlying water table. Electrical imaging provided details of the internal structure of the waste tip, and confirmed the presence of a leachate plume beneath the base of the landfill. This field data component provided the constraints for the design of a generic model of contaminant infiltration into partially saturated sand. The aim was to study leachate plume evolution in a laboratory environment. For this purpose, a miniaturised resistivity tomography technique, developed at Cardiff University, was used to image the resistivity distribution before during and after contaminant infiltration. Comparison of resulting two-dimensional tomography with observed plume geometry at the end of the test showed the miniaturised electrical imaging technique to be highly effective. Experiment showed that contaminant evolution taking place in the model was gravity-driven, with capillary water in the vadose zone being displaced by the denser contaminant solution.     

碎石桩复合地基的抗液化特性探讨

饱和砂土地震液化问题是岩土地震工程中一个重要的研究课题。在多种可行的防治液化措施中 ,最普遍的方法是采用碎石桩复合地基。本文结合目前国内外碎石桩复合地基的抗液化研究的最新进展 ,对碎石桩的密实、排水减压和减震作用做了较详细的评述 ,最后还提出碎石桩复合地基抗液化特性需要进一步研究的问题     

Scaling Laws and Experimental Modelling of Contaminant Transport Mechanism through Soils in a Geotechnical Centrifuge

This paper presents the results of a research program conducted on the geotechnical centrifuge to investigate contaminant transport mechanism through the soil mass. The mechanism that governs contaminant transport through soil mass is discussed, the principles of geotechnical centrifuge modelling are outlined, and relevant scaling laws that govern the relationship between a centrifuge model and the prototype, with respect to the problem of contaminant transport, are presented. Modelling of models has been established to validate the experimental results. It has been concluded that the geotechnical centrifuge can be used as an experimental tool to simulate field scale problems.     

爆炸离心模型试验研究进展与展望

由于能量比尺和原型应力模拟的优势,采用离心机进行爆炸试验具有无可比拟的优越性。在简要介绍土工离心机的发展历程的基础上,对爆炸离心模型试验较关注的问题--模型箱、爆炸源、离心模型比尺、数据采集、科氏加速度等方面的研究进行了归纳,对已有的研究领域进行总结并对以后的发展提出了自己的看法--模型箱设计需考虑防风措施、能量比尺仍需采取更精确方法验证、需制作稳定性好及质量有保证的微型炸药源等     

西辽河平原地下水补给植被的临界埋深

许多地区地下水是生态稳定的重要支撑或补充,确定地下水补给地表植被的临界埋深对地下水管理和生态安全至关重要。以西辽河平原为例,主要研究成果如下:①根据地下水补给植被原理划分包气带水分运动结构,描述地下水补给植被的作用机理和物理过程,定义地下水补给植被的临界埋深及相关物理概念。②根据植被根系吸收潜水蒸发的物理机制,地下水面附近由毛管水上升形成的潜水影响层是临界埋深计算的关键。③推导土壤毛管有效孔径计算推理公式,通过构建土壤微结构模型求解推理公式中的孔隙特征参数,解决毛管水最大上升高度的精确计算难题;④结合不同群落植被根系层厚度,形成地下水补给植被的临界埋深计算模型。⑤通过野外调查和观测试验实证,表明计算结果可靠,研究成果在科尔沁草原得到了及时应用。     

砂土中隧道开挖对邻近桩基竖向影响的简化计算方法

基于砂土中隧道开挖引起的土体竖向位移经验公式,分析隧道开挖对邻近桩基础的竖向影响。采用两阶段计算方法,将邻近桩基础视为竖向被动桩,依据砂土中隧道开挖引起地表及地表以下土体产生的沉降槽,考虑桩土相互作用的非线性,得到砂土中隧道开挖对邻近桩基础轴力影响的简化计算方法,并与土工离心试验结果进行对比,验证了该方法的合理性。在研究过程中,分析了隧道覆盖层厚度、隧道直径、隧道与桩之间的距离、隧道土体损失率、桩长、桩径等因素。研究结果表明,桩身轴力随着覆盖层厚度的增加而减小,随隧道直径和土体损失率的增大而增加;隧道与桩之间距离为2.5倍隧道直径时对轴力的影响最大;随着桩长、桩径的增加,桩身轴力逐渐增加。