Effect of water salinity on Atterberg limits of El-Hodna sabkha soil

Sabkha soils are recent saline sediments widely distributed in Algeria and other countries. As they are characterised by low strength and high compressibility, they are considered to be difficult foundation soils that pose special problems for design and construction engineering. This study deals with the effect of salts on the determination of the water content and Atterberg limits of sabkha soils. The tests were performed using distilled water, natural sabkha brine and saline solutions with different salt concentrations. The results indicate that the liquid and plastic limits decrease with pore fluid salinity when the conventional water content procedure is used, but increase when the fluid content method is used. Also, the results revealed that the oven-drying time of saline soils is highly affected by the size of soil clods and surface salt precipitation.     

考虑渗透性的水–土压力计算方法

在弱渗透性黏性土中,水–土压力的计算采用“水土分算”还是“水土合算”一直是学术界和工程界有争论的问题。上述两种土压力计算方法只考虑了极端情况,没有充分考虑土体的物理特性,计算结果差异很大。笔者根据不同土具有不同渗透性这一基本物理特性,提出考虑渗透性的水–土压力计算方法,该方法概念明确,适用范围更广,可以实现从无黏性土到黏性土的水–土压力计算且具有连续性 ,最后通过算例验证了该方法的合理性。     

中国红土的微结构和工程性质

为了研究红土的高强度、低压缩和高孔隙的工程特性,我们系统地分析了我国各类红土的物理力学性质,物质成分和微结构特征。我们发现红土强度主要来源于粒间残存或新生的化学键力、晶质氧化铁的胶结力和胶态含水氧化铁的影响。长期处于湿润条件下,赋存于孔隙溶液中的游离胶态氧化铁,虽能对粘土表面斥力起一定抑制作用,但还是不能完全阻止红粘土的胀缩行为。     

基于透明土的取土管贯入扰动变形试验研究

在岩土工程勘察取样过程中,取土管的贯入会引起土体的扰动变形,影响到对土体物理力学性质的准确评价。为了研究取土管贯入过程中土体扰动变形特性,基于透明土及PIV技术,开发了相应的取土管贯入模型试验系统,进行了取土管的贯入试验,得到了在取土管贯入过程中土体扰动变形场的分布特性。试验结果表明:土体扰动变形随着取土管贯入深度增大而增大,管外土体主要表现为斜向上的隆起变形;管内土体主要为向上的隆起变形,在深度方向最大变形位于取土管中间部位;不同截面处土体其变形规律基本一致,截面间土体剪切变形较小。     

A glacial terrain map of britain for engineering purposes

The engineering importance of superficial soils in Britain cannot be overemphasized. They range in age from Quaternary to Recent and vary from overconsolidated bouldery silty clays: tills, through normally consolidated clays, laminated clays, silts, sands and gravels, to peats and organic soils. Associated with the superficial soils are superficial structures involving both soil and rock and resulting from glacial and periglacial activity. For engineering construction, these structures may give rise to problematic grround conditions. For ground conditions resulting from glacial and periglacial conditions four generalised terrain models are presented as annotated block diagrams. These diagrams represent subglacial terrain, supraglacial terrain, glaciated valley terrain and periglacial terrain. The four terrain models are supported by maps illustrating the distribution of superficial engineering soils, the distribution of predominant glacial terrain types and selected periglacial features. The distinctive terrain types each have both characteristic topography and subsurface conditions. If the landforms and hence the terrain types can be identified, then the geometry and character of the subsurface—both soils and bedrock conditions—can be generally predicted. By recognising these terrain types the character of subsurface ground conditions can be generalised for large areas. The value of this approach to ground engineering lies in its use as an engineering geological mapping tool and as a rapid guide to likely subsurface conditions.     

三峡库区膨胀土的发现和研究

在三峡库区地质调查中 ,遇到了一种工程性质不良、易于导致滑坡等地质灾害的粘土 ,通过对物质组成、水理和物化性质的测试 ,按粘土膨胀势判别的国家标准 ,它们为弱膨胀性粘土 ,而按国外流行的WilliamsandDonaldson( 1980 )粘土膨胀势判别法 ,它们介于mediumexpansion与highexpansion势粘土之间。通过采用XRD技术对粘土矿物定量测试 ,表明主要膨胀性粘土矿物为中等混层比的I/S混层矿物。综合野外调查和室内测试结果 ,研究了它们的成因、分布和成灾机理 ,提出了治理措施。三峡库区膨胀土的发现和研究对我国膨胀土形成发展规律的认识和对三峡库区移民迁建工程规划以及地基边坡处理有重要的理论和实际意义。     

苏丹膨胀土的工程性质与处理方法

以苏丹Munga地区某输电线路岩土工程勘察项目为背景,分析了该区膨胀土的工程性质,并针对该区膨胀土的胀缩性能提出了膨胀土危害的防灾思路,建立了该区膨胀土塑性指数与液限的相关方程,对膨胀力与初始含水量的相关性进行了分析,研究成果对该地区工程建设地基基础设计及我国膨胀土的研究具有一定参考价值。     

基坑支挡结构设计若干问题探讨

根据基坑开挖应力路径的室内试验和现场实测数据,从土工试验方法、土体强度指标、地基土水平反力系数等方面分析了现在基坑工程支挡结构设计存在的一些问题。研究成果如下:支挡结构设计参数的获取应考虑主动区及被动区地基土的应力路径,并恢复地基土的固结状态。基坑开挖后主动区和浅部被动区土体抵抗剪切破坏的能力大于以常规CU强度指标的计算结果,这有利于工程安全;深部被动区土体抵抗剪切破坏的能力小于以常规CU强度指标的计算结果,对于地基土被动抗力发挥较大的工程,需验算嵌固深度,确保被动抗力小于极限被动土压力。定义了被动区基坑开挖"强影响区",并给出了该区域深度的计算方法。以相应应力路径下的土体割线模量值作为地基土水平反力系数,讨论推导了作用于支挡结构上的分布土反力与支挡结构水平位移的计算公式,其计算结果更接近工程实际。本次研究对以变形控制为主的基坑设计具有较好的指导意义。     

Gibson地基模型参数的一种实用确定方法

Gibson地基在理论上可以考虑土体模量沿深度的变化，但工程应用中一直存在相关参数难以确定的问题。基于压缩试验成果和魏汝龙割线模量法双曲线模型，探讨提出确定单层和成层Gibson地基参数的实用新方法。该方法对压缩性状服从双曲线模型的土体较为适用。通过对浙江沿海地区若干典型工程的试验结果分析，结果初步表明地表处剪切模量为零的狭义Gibson地基在实际工程中几乎不存在。结合真空堆载联合预压加固软基的工程实例，对比分析了成层Gibson地基模型在沉降分析中的应用。新方法确定的成层Gibson地基模型不仅应用简便，而且可以显著地提高地基沉降预测结果的精度。在地基有效加固深度不是特别深厚的情况下，Gibson地基模型能较好地改进不能考虑模量随埋深变化的传统模型。     

The relationship between the geology and the lateritic engineering soils in the northern environs of Akure,Nigeria

Two contiguously occurring brownish to reddish residual soils in the northern environs of Akure, Nigeria, which show definite relationships in their physical and engineering properties to their parent rocks, have been studied. The parent rocks are coarse porphyritic granite and fine, to medium grained basic charnockite respectively. For each soil, the profile development, clay mineralogy, texture, consistency and the compaction characteristics are investigated. The test results show that the differences in physical and engineering properties are conditioned fundamentally by the parent rock, with drainage and other environmental conditions being practically identical. Although the two soils are both usually described as “lateritic”, the engineering properties of the soils considered on a comparative basis have established the coarse granite derived soil as superior to the charnockite derived soil as road base of fill material generally.     

红层残积土工程特性与应用

湘北红层残积土具有特殊的工程地质特性,作为基础持力层时,其指标选择存在不小难度。通过工程实测资料分析,对红层残积土地基承载力的确定及变形特征进行了讨论,提出了确定红层残积土地基承载力和变形模量的方法。     

纤维石灰土工程性质的试验研究

为了解决石灰改良引发的填筑土脆性破坏的问题,本文提出了将分散的聚丙烯纤维丝掺入到石灰土中的设想,并对不同纤维和石灰掺量的6组土样分别进行了无侧限抗压试验、剪切试验、膨胀率试验和收缩试验。试验结果表明,纤维的掺入不仅提高了石灰土的强度,而且还增强了石灰土的塑性,使其破坏形式从脆性破坏转变为塑性破坏。此外,在胀缩性方面,纤维的掺入减小了石灰土的膨胀性,但增加了收缩性。研究表明,纤维的强抗拉性是导致石灰土工程性质改变的主要因素。因此,纤维和石灰的混合掺入可以为填筑土工程性质的改良提供一个更加有效的方法。     

深土冻土力学的研究现状与思考

人工冻结技术在深部地下工程施工中的广泛使用,使人们更加迫切地认识到对深土冻土力学研究的必要性。本文 通过分析目前国内外对深部岩土工程的认识,在前人对深土及深土冻土理解的基础上,考虑深土冻土形成过程的特殊性及受力特点,从新的角度给出了深土冻土及深土冻土力学的概念,阐述了深土冻土力学的主要研究内容。最后通过对深土冻土力学研究现状的分析,从深土冻土室内物理力学试验研究、大型模型模拟研究、理论模型研究以及工程应用等四个角度讨论了目前室内进行深土冻土力学研究所面临的主要问题。     

湿干循环下压实膨胀土裂隙扩展规律研究

裂隙特征作为膨胀土裂隙性研究的基础,其定量化描述有助于膨胀土工程性质的深入探究。以膨胀土平面裂隙为研究对象,使用数码摄影获取多次湿干循环下的裂隙扩展图像,采用优化和改进的裂隙图像处理及裂隙特征提取方法,分析所获得的膨胀土裂隙各特征参数。结果表明：室内压实膨胀土表面裂隙率随着湿干循环次数增加而增大,且第二次湿干循环对裂隙率影响最为显著;裂隙发育峰值条数在第一次湿干循环后最多,总长度最大,而三次湿干循环后的裂隙条数和总长度较为相近;裂隙宽度随湿干循环次数增加而增大,且第二次湿干循环影响最为显著;同时,第一次湿干循环中主裂隙发育最明显,在第二次和第三次中宽度发育趋于均匀;通过裂隙方向玫瑰花图发现,裂隙主要沿着初始方向扩展,直至下一次湿干循环;裂隙发育方向在第一次湿干循环中是随机的,而在第二次与第三次中有较高相似性,表明湿干循环对裂隙发育方向的影响也主要发生在第二次。     

膨胀土渠道边坡的破坏与防治对策

膨胀土边坡的破坏在工程中极为常见,它是岩土工程的一个难题。当前对其破坏形式和破坏机理仍未形成统一的认识,影响了问题的解决。在对膨胀土地层结构分析的基础上,通过两个大型的现场试验,并结合许多滑坡实例,概括出膨胀土坡两种典型的滑动形式,即浅表层的膨胀型滑动(塌坡)和中深部的裂隙性滑坡,对膨胀土边坡的破坏有了新的认识。并分析了滑动的机理和影响因素,并对相应的处治对策提出了建议。     

软弱地层联络通道冻结法施工温度及位移场全程实测研究

研究软弱地层联络通道冻结法施工的冻结温度场、解冻温度场、冻胀融沉发展规律,是解决其冻胀及工后融沉预测与控制的前提。以软土隧道联络通道冻结法工程为背景,对冻结温度场、解冻温度场、地表变形、深层土体冻胀融沉及温度变化规律等进行了全程实测,对冻结壁的形成及解冻全过程进行了分析。结果表明:冻结过程温度变化规律可分为温度快速下降、降温减慢、降温速度加快、土体温度稳定、维护冻结等5个阶段。解冻期间,土体温度经历快速回升、0℃附近稳定、温度持续回升3个阶段。冻结圆柱交圈是产生迅速冻胀的临界时间点,冻胀主要发生在冻结18~45 d;联络通道解冻15 d,部分土体温度达到0℃附近,冻土进入相变阶段,因此应在15 d后开始融沉跟踪注浆;入土深度越大土体相变阶段持续时间越长,粉土融沉主要发生在解冻前2个月,其完全解冻需要100 d左右,此为跟踪注浆至少应持续时间。深部土体温度、冻胀融沉位移均随深度增大呈线性递增。实测拱顶冻结壁处最大冻胀及融沉位移分别是对应地表冻胀、融沉量的3.6倍、4.9倍。地表冻胀融沉槽为联络通道中线两侧符合拟正态分布规律,其影响范围约为隧道底部埋深的1.2倍。     

A new strength criterion for structured soils

Existing strength criteria are mostly formulated to describe the mechanical properties of reconstituted soils. However, the engineering characteristics of structured soils are different from those of reconstituted soils in many aspects, especially in their strength properties. Thus, the influence of soil structure (bonding and fabric) on the mechanical properties of structured soils cannot be correctly described. By analyzing the breakage mechanism of natural soils, the structured soils can be conceptualized as binary medium materials consisting of bonded blocks and weakened bands. On this basis, a new strength criterion is proposed for structured soils. The expressions of the strength criterion on both meridian and deviator planes are given to describe the strength properties of structured soils on these planes. The proposed strength criterion is compared with available test data under conventional and true triaxial stress conditions in the literature. It is observed that the proposed strength criterion agrees well with the test data.     

一个预测路堤沉降的新经验公式模型

大量工程实践验证表明，无论是一级荷载还是多级荷载下的指数曲线模型，均可对地基沉降进行较好地预测，但也存在不足之处。先基于绝对时间坐标系下的软土次压缩计算修正式子，提出耦合软土流变项的新型指数曲线模型，并采用数学中最优化技术，根据前期沉降实测资料对模型中参数进行反演。实例计算表明：该模型对沉降预测精度高，能较合理地反应出土颗粒骨架的蠕变过程，且能给出不同时刻的次压缩量，在实际工程上具有一定的参考价值。     

Reappraisal of the Activity of Clays. Activity Chart

The proposed activity chart, which aims to classify soils (<425 μm) using the Atterberg limits, differs from the plasticity chart recently proposed by the author because the inorganic soils with platey clay minerals are classified (in addition to clay percentage) on the basis of their activity rather than on the degree of plasticity as a function of the liquid limit value, currently used by the standards. This is because soils that have the same liquid limit value may have very different characteristics because of both the amount and type of clay minerals contained in the soils. On the activity chart, the silt and the clay zones are subdivided (by two straight lines) in three new groups (low activity, medium activity and high activity) making it possible to classify inorganic soils with platey clay minerals (or their fraction) <425 μm on the basis of the amount and type of clay minerals they contain. The activity chart adapted to predict residual shear behaviour of cohesive soils is also shown. Finally, the distinction between coarse-grained soils and fine-grained soils based on their percentage of clay (<2 μm), might be useful in characterizing and predicting soils' engineering behaviour.     

油水二相体对油污染土电阻率特性的影响

为研究油类污染粉质黏土的电阻率特性,室内分别拌制了不同含水率、不同含油率的柴油、煤油污染土试样,采用四电极方法对不同状态下的污染土体电阻率进行了测试。试验结果显示,两种油污染土有相似的变化规律,即在相同的含水率下,均表现为电阻率随着含油率的增加而线性增大;在相同的含油率下,随着含水率、水饱和度的增加而呈幂函数关系减小。为了分析油、水二相体对电阻率的影响,引入了体积含湿率、油水饱和度两个指标,发现在相同的水饱和度下,电阻率随体积含湿率的增加而线性增大;在相同的体积含湿率下,电阻率随油水饱和度的增加而幂函数关系减小。进一步分析表明,电阻率与体积含湿率间存在线性相关关系,与油水饱和度间存在幂函数相关关系,两种油污染土的电阻率与体积含湿率、油水饱和度间的关系可以用同一公式表达。