宽级配粗粒土的内部侵蚀试验及其稳定性判别

强降雨入渗条件下宽级配粗粒土中的细颗粒会由于孔隙流体的作用发生内部侵蚀。细颗粒的运移改变了土体的微观结构,土体的水力、力学性质随之变化。利用自行研发的刚性壁渗流侵蚀实验装置,对颗粒粒径介于0.002～10 mm的9种间断及连续颗粒级配粗粒土试样进行渗流侵蚀试验,提出一种新的基于试验的内部稳定性判别标准。实验结果表明:对于宽级配粗颗粒土,内部侵蚀改变了土体的渗透系数,最终导致渗透系数下降;粗颗粒的缺失导致内部稳定性降低,渗流作用下,连续颗粒级配土也可能是内部不稳定土;侵蚀土颗粒累计质量可以度量土体内部稳定性,在容许水力梯度范围内侵蚀量超过总质量5%的土体可划分为内部不稳定土;Kezdi几何标准更适用于评价宽级配粗粒土的内部稳定性。     

Estimating the groutability of granular soils: a new approach

This paper evaluates different parameters that affect the grouting of soil, and presents a new approach to predict the groutability of granular soil. An accurate prediction of the groutability of granular soils has always been complicated due to the effects of different soil parameters. We know that these parameters are the grain-size of soil and cement-based grouts, the relative density and fine contents of soil, the water/cement ratio of grout mixture and grouting pressure, which directly affect the groutability of soil media. However, the relative density, fine contents of soil, the water/cement ratio, and grouting pressure are seldom considered as the prediction of groutability. In order to study the effects of the parameters on groutability, an alternative empirical formula to estimate the groutability of granular soils is presented in this paper and supported by experimental results obtained from the grouted sand samples prepared with various relative densities. The newly developed approach will help for the more accurate prediction of the groutability in granular soils and may also be used to provide first-hand information about the groutability of soils.     

胶结土力学特性与强度分析

通过对土料人工处理,可以使其力学特性和强度大为提高,从而有助于建筑物的兴建。通过添加不同含量的水泥,制备了人工胶结土样。然后进行了三轴试验来探讨胶结土的力学特性和强度特点,试验结果表明水泥含量不同导致的颗粒胶结对胶结土的应力—应变、孔压发展、体积变形特性和抗剪强度有很大的影响。最后建议了一个胶结土的抗剪强度表达式,并与实验结果进行对比,表明所建议的抗剪强度表达式具有较好的适用性。     

水泥加固砂性土微观特征试验研究

通过电动体视显微镜微观试验手段,研究了不同水泥掺量下水泥加固砂性土加载前后微观特征,并分析了水泥加固砂性土孔隙的形状系数、定向角和孔径大小等参数的变化规律,揭示了水泥砂性加固土体强度及承载机制的演化特征。结果表明:(1)水泥砂性加固土在加载前后孔径分布和孔隙形状系数在水泥掺量5%~10%范围内同时存在剪缩和剪胀;但水泥掺量高(＞10%)的加固土加载后整体宏观表现为剪胀;(2)在加载条件下,水泥加固砂性土体的颗粒或团粒会发生定向滑移或转动,并在一定程度上孔隙长轴的方向会发生改变。且孔隙定向角分布形式逐步由均匀向集中转变,孔隙分布呈现显著的定向性。     

Effect of grain size on the strength of cubes made from lateritic soils

Lateritic soils are known to be available in large quantities and in different types all over Nigeria, in particular, and in most tropical countries all over the world in general. This paper reports the results of the investigations carried out on the grain size effect on the strength properties of the cubes made from lateritic soils without cement stabilization. This is with the view to recommending the production of blocks from graded lateritic soils in supplementing sandcrete blocks in the building construction industry, especially for low-cost or rural housing.Sieve analysis of soil samples collected from three different locations has been carried out. It is on the basis of the results obtained that five different grain sizes of each soil sample have been chosen for this investigation. The compressive strenghts of cubes made from each grain size range have been established. The relationship between the strength characteristics of the cubes and the sources of the lateritic soils used for making the cubes has also been investigated. It is found that the finer grained samples had more strength. This finding could have been predicted due to the additional cohesiveness from finer elements in the clay zone.     

Triaxial shear behavior of a cement-treated sandegravel mixture

A number of parameters, e.g. cement content, cement type, relative density, and grain size distribution,can influence the mechanical behaviors of cemented soils. In the present study, a series of conventionaltriaxial compression tests were conducted on a cemented poorly graded sandegravel mixture containing30% gravel and 70% sand in both consolidated drained and undrained conditions. Portland cement usedas the cementing agent was added to the soil at 0%, 1%, 2%, and 3% （dry weight） of sandegravel mixture.Samples were prepared at 70% relative density and tested at confining pressures of 50 kPa, 100 kPa, and150 kPa. Comparison of the results with other studies on well graded gravely sands indicated moredilation or negative pore pressure in poorly graded samples. Undrained failure envelopes determinedusing zero Skempton抯 pore pressure coefficient 餉 ？0？criterion were consistent with the drained ones.Energy absorption potential was higher in drained condition than undrained condition, suggesting thatmore energy was required to induce deformation in cemented soil under drained state. Energy absorptionincreased with increase in cement content under both drained and undrained conditions.
2014 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.     

结构性砂土力学特性三维离散元分析

利用离散元法对结构性砂土的三轴试验进行了三维数值模拟并对其宏观特性进行了分析。首先将考虑胶结尺寸(宽度和厚度)的三维胶结接触模型导入离散元软件PFC3D中,对结构性砂土数值试样进行三轴试验数值模拟;然后对比分析离散元模拟与室内试验结果;最后从宏观力学角度对试验结果进行了分析。离散元模拟结果表明:结构性砂土与无胶结松散砂土表现不同,其在低围压时表现出应变软化和体积剪胀特征,并随胶结含量的增加或围压的减少而愈发显著,在高围压时则呈应变硬化和体积剪缩现象;低平均应力时,随胶结含量的增加,试样峰值内摩擦角、黏聚力以及内摩擦角均增加,其中黏聚力增加较为明显,随着平均应力的增加,峰值强度包线逐渐趋向于无胶结土。     

南阳中膨胀土水泥改性的室内试验研究

取南水北调中线工程南阳段自由膨胀率77%的中膨胀土,开展了一系列不同水泥掺灰率和不同龄期下,压实度为98%试样的物理力学特性试验。通过对素膨胀土与改性膨胀土的胀缩性、界限含水率、级配及无侧限抗压强度的对比,揭示了掺灰率及养护龄期对膨胀土改性效果的影响。试验结果表明:(1)随掺灰率的增加,改性膨胀土的胀缩性指标及反映黏土亲水性的液限和塑性指数均降低、胶粒含量减小、级配曲线随趋于平缓、无侧限抗压强度和弹性模量增加;合理的掺灰率应取6%;(2)随养护龄期的增加,胀缩性指标、液限、塑性指数、胶粒含量减小,无侧限抗压强度和弹性模量则增大。     

Anisotropic swelling in black cotton soil

The influence of initial moisture content and the nature of granular material on the anisotropic swell behaviour in black cotton soil has been examined. It was observed that the amount and rate of swelling are guided by the initial particle orientation. For samples compacted with moisture below the optimum value, the variation in swelling trends in vertical and horizontal directions is a result of the particle arrangement, the pressure exerted by the air in the voids and also the subsequent expulsion of the same. In samples compacted with moisture content above the optimum, the initial dispersed state of the particles guides the anisotropy. The swelling in such samples is considerable in directions transverse to the particle orientation. At optimum moisture levels, because of the minimal differences in the particle arrangement for samples in vertical and horizontal directions, the swelling is similar in both cases and as such no anisotropic behaviour was noticed. Increasing presence of granular component in the soil reduces the rate of swelling, protracts the time for completion of swelling and also reduces the anisotropic behaviour. Reduction in the grain size of the granular material facilitates quick swelling. The variations in such samples for vertical and horizontal directions are explained on the basis of packing in the system and the constraints imposed by sand grains on osmotic swelling. Since similar variables exist in field conditions, the present study enables an understanding of their role in the anisotropic swell behaviour of black cotton soils.     

水泥土搅拌桩止水帷幕工程特性研究

水泥土搅拌桩作为基坑止水帷幕已经得到了广泛应用,为了更深入的理解作为止水帷幕的水泥土的工程特性,通过对不同水泥掺入量的水泥土无侧限抗压强度和渗透系数的室内试验研究,利用CBR-1承载比试验仪和TSS-2柔性壁三轴渗透仪对水泥土进行了无侧限抗压强度和渗透试验,分析了养护龄期及水泥掺入量对水泥土的无侧限抗压强度和渗透系数的影响。试验结果表明,水泥土的无侧限抗压强度随养护龄期和水泥掺入量的增大而增大,并通过曲线的拟合,得出了无侧限抗压强度的预测公式;渗透系数随养护龄期和水泥掺入量的增大而减少,通过数据对比得出28天之后水泥土渗透系数主要是受水泥掺入量的影响。     

氯化镁对水泥土早期强度的影响研究

通过水泥加固不同含量的氯化镁污染土室内28 d抗压强度、X射线衍射（XRD）和微观扫描电镜试验（SEM）,研究了氯化镁对水泥土的早期强度影响机理。XRD分析结果表明：氯化镁参与反应生成的M-S-H、M-A-H、氯化钙结晶、轻质氯化镁结晶和水化氯铝酸钙等产物对水泥土产生分解与结晶的复合作用；SEM图象分析表明：氯化镁使水泥土的孔径分布发生改变,当氯化镁含量较低时,水泥土中的水泥水化产物与结晶物将颗粒连结在一起,形成较强的结构联结,使其孔隙率变小,对水泥土的强度增长有利；随着氯化镁含量增大,土颗粒周围的凝胶物被分解,使水泥土的孔隙率增大与胶结程度下降,对水泥土的强度不利。     

基于裂离参量的粒状土颗粒破碎量化方法

以粒组为分析对象,将颗粒破碎引起粒状土级配变化的过程划分为3个阶段。在此基础上,针对单个粒组与粒状土整体的颗粒破碎情况分别提出了裂离比R_k与加权裂离率B_d的新概念。在进行等比级数简化假设的基础上,给出了两者的计算方法。研究已有文献中搜集的21组颗粒破碎试验资料发现：在所研究的围压范围内,对于不同粒状土材料,B_d-均呈现出线性关系。且对于多数试验结果,该关系存在一个明显的斜率折点。综合考虑围压、母岩强度与原始级配对B_d的影响发现,对于灰岩、角砾岩、砂岩料等不同粒状土材料,B_d的变化规律具有归一性。整理已有试验资料中不同粒状土的加权裂离率B_d与破碎率B_g发现,B_d与B_g间存在一定的指数化关系。最后通过优势分析,指出基于裂离参量的粒状土颗粒破碎量化方法有其自身的特点与优势,具备广阔的研究前景。     

污水环境对水泥土力学性能的影响试验研究

由于多数地下水泥土工程直接与地下腐蚀性介质环境接触,必将导致水泥土材料的逐步劣化甚至失效破坏。以某市区工地附近明渠排放的污水作为侵蚀性介质,制作了不同水泥掺量的水泥土试件,通过对比试验,研究了污水环境和清水环境下不同水泥掺量、不同龄期的水泥土抗压强度和抗剪强度。结果表明,在污水或清水环境下,相同水泥掺量水泥土30 d 龄期的抗压强度几乎相等,随着龄期的增加其抗压强度均逐步增大,但污水环境下其抗压强度增长的幅度明显小于清水环境,90 d 后清水环境的水泥土抗压强度不再增长,而污水环境的抗压强度开始降低;污水环境和清水环境下的水泥土内摩擦角和黏聚力随龄期、水泥掺量的增加均逐步增大,污水环境下龄期90 d后的内摩擦角和黏聚力均开始降低。     

Laboratory study of an injected granular soil with polymer grouts

Soil or rock mass with low strength or high permeability may not be appropriate for an excavation project or for use as a structural support. These soils or rock mass can cause severe damages to overlying structures, because of their considerable distress. Therefore, a suitable ground improvement technique is needed for deep excavations in order to confront these problems. The increase in strength and durability, as well as the reduction in compressibility and porosity are the main aims of a ground improvement technique. Grouting is the commonly used method to meet the above requirements. In recent years, various types of water soluble polymers are used as additives in cement grouts to improve the soil properties. The main objective of this laboratory project was to investigate the use of such materials for the improvement of physical and mechanical properties of a granular soil. Grouts were prepared by using cement, clay, water in different percentages along with an amount of acrylic resin or methyl methacrylate co-polymer emulsion. These two substances are the most widely used non-toxic additives in concrete structures and applications due to their significant contribution to the improvement of physical and mechanical properties of mortars or concretes. Grouting experiments were performed through 10-cm diameter and 150-cm height columns, filled with granular soil with particle size distribution of 2 – 12.7 mm. The experimental results reveal that the addition of latexes in thick pure cement grouts improves substantially the physical and mechanical properties of the injected soil.     

水泥加固酸污染土无侧限强度特征

污染土是利用水泥固化处理后,土体的强度得到提高。针对该项技术,采用水泥固化法处理酸污染土,通过两种试验方案,对水泥加固酸污染土的无侧限抗压强度特性进行研究。试验所用酸污染土用浓硫酸配置人工制备而成,并考虑了不同水泥掺量、不同硫酸浓度和不同龄期对水泥加固酸污染土强度的影响。试验表明:水泥固化酸污染土的强度与水泥掺量和硫酸含量有密切关系,二者共同作用决定其强度的变化。在一定硫酸浓度(2~16g/kg)条件下,伴随硫酸含量的升高,水泥掺量较低时,无侧限抗压强度整体呈明显下降的趋势;水泥掺量较高时,无侧限抗压强度呈缓慢上升的趋势。随着水泥掺量提高,土样的无侧限抗压强度达到峰值时所对应的硫酸含量也逐渐变大。     

高应力粒状土中球形孔的扩张问题

考虑粒状土在高应力下的应力－尖变－体变关系和非线性强度特性，依据扩张过程中的能量守恒和体变平衡原理，给出扩极限压力的解答，用于估算临界深度以下静力触探或桩尖的贯入阻力。分析表明，扩孔极限压力取决于粒状土的应力－应变－体变关系和强度特性，与上覆土压力在大小无关。计算结果表明，考虑曲线型强度包线将减小扩孔极限压力，与中密砂土的静力触探贯入阻力经验值对比，初步证实了该理论的正确性。     

聚丙烯纤维和水泥加固软土的强度特性

在软土中加入水泥能有效提高软土的工程力学性能,是一种常见的软基处理方法。但在一些特定条件下,水泥加固软土的强度存在偏低的现象,无法满足工程要求。提出将聚丙烯纤维的物理加筋作用同水泥的化学加固作用相结合,通过开展室内试验,在水泥土中加入适量的聚丙烯纤维,分别研究软土初始含水量(35%～70%)、纤维掺量(0～0.3%)和长度(6～19mm)对纤维加筋水泥土强度的影响,并对影响机理进行探讨。试验结果表明:当水泥掺量为15%时,水泥土的强度受初始含水量的影响非常明显,最优含水量为55%;纤维的加入能有效提高水泥土的强度,强度值随纤维掺量的增加而增加;当纤维长度为12mm时,其加筋效果得到最大发挥;纤维的加入降低了水泥土的脆性,提高了水泥土的断裂破坏韧性,对提高工程的安全性和稳定性有一定意义。     

Über den Einfluß der Kornverteilungskurve auf das dynamische und das kumulative Verhalten nichtbindiger Böden

On the influence of the grain size distribution curve on the dynamic and the cumulative behaviour of non-cohesive soils. This paper presents experimental studies on non-cohesive soils on the influence of the grain size distribution curve on the dynamic soil properties and the accumulation of residual deformations under cyclic loading. It is shown that the dynamic shear modulus is not influenced by the mean grain diameter but decreases strongly with the non-uniformity. For a non-uniform soil the common empirical formulas overestimate the dynamic shear modulus by up to 70%. Also the residual deformations under cyclic loading depend significantly on the grain size distribution curve. They are larger for fine-grained soils. Under cyclic loading non-uniform soils densify much faster than uniform soils.     

深厚砂性土地基竖向高频振动致密机理及地基加固设计

高频振动致密是一种地基处理的新技术。该法应用高频振动锤在振动探杆顶施加竖向激振力,在振动杆轴周围产生剪切波(S波)及压缩波(P波),在高频振动力的作用下,土体中的振动探杆由此上下反复振动,在S波和P波的作用下,最终逐步地提高其周围土体密实度。在详细介绍该法的加固机理、施工原理以及与振冲法区别的基础上,提出适用于该法处理的土质条件并采用颗粒离散元分析结果进行分析说明以及相应的设计和检测方法。最后指出了该技术有待于进一步研究的几个理论问题。     

Chemical analysis and X-ray diffraction assessment of stabilized expansive soils

The long-term viability of many construction projects is heavily dependent on the soundness of the underlying subgrade soil which needs to be capable of supporting loads from structures without undergoing excessive deformation or volume changes. However, in certain locations geotechnical engineers face repeated problems in the design of substructures due to the presence of expansive soils. Light structures are especially susceptible to damage in such situations which can result in cracks in walls, beams, columns and on-grade slabs. One extensively used way of overcoming such problems is to improve the soil by stabilizing it with cement and/or lime which prevents this unwanted behavior. Most previous research conducted on expansive soils focused on studying the effects of treatment on the physical properties of the soil without detailed examination of the physicochemical mechanism of the process, although some studies surveyed the effect of the treatment using cement and lime on the mineralogical composition and newly formed pozzolanic compounds. In this research the mineralogical changes due to lime and cement additions to two different expansive soils from Saudi Arabia, in particular, were investigated using X-ray diffraction. The results of this work indicate that addition of lime or cement to the soils tested resulted in the formation of pozzolanic compounds, namely, calcium silicate hydrate and calcium aluminate hydrate together with calcite (CaCO₃). The soil improvements are compared for cement and lime. Changes in potassium, aluminum and silicon were also determined and interpreted in terms of the soil mineralogy. It was concluded that pozzolanic compounds play a significant role in reducing the swelling and increasing the strength.