Visualization for Engineering Property of In-Situ Light Weight Soils with Air Foams

The objective of this paper is to evaluate both physical and mechanical properties of in-situ light weight soil with air foams using an industrial X-ray CT scanner. The specimen used in this study was in-situ SGM (Super Geo-Material) which was a light weight soil created by mixing dredged slurry with cement and air foam. This was sampled at the trial construction site of new Kumamoto seaport, Japan. Two different materials of air orientation which were surface active agent and protein were examined at the site. First of all, the effect of different kinds of air foams on the physical property of in-situ light weight soil was discussed using the results of CT scanning, in which the distributions of the density and air foams in the soil were taken into consideration. Furthermore, as a mechanical property, a series of unconfined compression tests was conducted for the in-situ specimen, and the density evolution was also investigated by scanning of the specimen during unconfined compression. Here, the effects of both distribution and size of air foams were also clarified. Finally, the effectiveness of the industrial X-ray CT scanner in geotechnical engineering was confirmed based on all these results.     

Experimental Study on the Cyclic Resistance of a Natural Loess from Northern France

In order to analyze the instability phenomenon observed along the Northern High Speed Line of Réseau Ferré de France (RFF), soil blocks were taken at a site near the railway line, at four different depths (1.2, 2.2, 3.5 and 4.9 m). Cyclic triaxial tests were carried out on saturated and unsaturated soil specimens. The results from tests on initially saturated specimens showed that the soil taken at 2.2 m depth has the lowest resistance to cyclic loading, in relation to its highest porosity and lowest clay fraction. This soil was then studied at unsaturated state with various initial water contents. Unsaturated soil specimens were first subjected to cyclic loadings to decrease their volume. These cyclic loadings were stopped when the volume decrease was approximately equal to the initial pore air volume, or when the pores filled by air were eliminated and the soil was considered to have become saturated. Afterwards, the back-pressure tubing was saturated with de-aired water and cycles were applied under undrained condition. Significant effect of initial water content was evidenced: the lower the initial water content, the higher the cyclic resistance. This can be explained by the densification of the soil during the initial cyclic loadings.     

Effects of particle shape and size distribution on the shear strength behavior of composite soils

The effects of particle shape and size distribution on the constitutive behavior of composite soils with a wide range of particle size were investigated. Two comparable sets of specimens were prepared: (1) mixtures of fines (clay and silt) and an ideal coarse fraction (glass sand and beads), and (2) mixtures of fines and natural coarse fraction (river sand and crushed granite gravels). Direct shear box testing was undertaken on 34 samples and the structure of the shear surfaces, change in volume and water content and the particle shape coefficient of the sheared specimens were examined. The results indicate that the contraction/dilation a specimen exhibits is restrained within the shear zone while the outer zones remain unchanged during shearing. An increased coarse fraction leads to an increase in constant volume shear strength. In addition, increasing elongation or decreasing convexity of the coarse fraction increases the constant volume friction angle. The overall roughness of the shear surface at constant volume state is negatively related to particle smoothness (convexity) and positively related to the area of the shear surface occupied by particles with particular shapes. Two equations are proposed for the estimation of constant volume friction angle based on the proportion and shape coefficient of the coarse fraction. It is hoped this will assist in considering the shear strength of mixed soils when the size of the coarse fraction makes laboratory testing difficult.     

渗透固结试验装置的研制

利用传统的固结仪进行的土工试验可以很好地满足工程需要，但是对软粘土进行深入研究却有明显的不足。通过对固结仪的改装，使其具有以下功能和优点：仪器的密封性能好，可以收集土样固结过程中排出的孔隙水，漏水量小：通过三通阀可以控制排水条件，既可以进行单面排水试验，并在底部量测孔隙水压力的消散规律，也可以进行双面排水试验；可以同时进行固结试验、渗透试验，研究在外加荷载作用下土样的渗透特性。     

Investigation of localized deformation in partially saturated sand under triaxial compression using microfocus X-ray CT with digital image correlation

In this paper, localized deformation in partially saturated sand was investigated quantitatively using microfocus X-ray computed tomography (CT) and an image analysis of the CT images. Triaxial compression tests on a partially saturated dense Toyoura sand specimen were carried out under a low confining pressure and under drained conditions for both air and water. The development of localized deformation was observed macroscopically using microfocus X-ray CT, and the displacement field over the entire specimen was quantified by an image analysis of the CT images with the digital image correlation (DIC) technique. The progressive development of shear bands is discussed with reference to these images. In addition, the region of localization was observed microscopically by partial CT scanning on a micron scale with high spatial resolution. Changes in the particulate structures are also discussed herein. The DIC image analysis of the partial CT images provided a microscopic displacement field and indicated that very fine localized shear deformation developed before the shear bands had become visible in the macroscopic investigation.     

Investigating the mechanism of downslope bentonite erosion in GCL liners using X-Ray CT

Exposed composite GMB-GCL liners are at risk of downslope bentonite erosion caused by the release of low ionic strength condensed water onto the top surface of the GCL following daily solar heating. This paper investigates the use of X-ray computed tomography (X-ray CT) to quantify the thinning of the bentonite layer and the application of X-ray diffraction techniques (XRD) to investigate the changes in clay chemistry (if any) of the bentonite from the virgin GCL to the eroded bentonite. The effect of specimen size and scanning orientation was investigated resulting in a revised testing procedure in which the CT scanning orientation was changed from horizontal to vertical to permit a longer test specimen which was also sealed at the bottom edge to minimise the edge boundary condition. The X-ray CT results provide highly visual evidence that a) bentonite thinning immediately under the upper cover geotextile is the initial location of erosion, and b) the bentonite core erodes at a significantly higher rate when not covered by a geotextile than when covered by a geotextile. These observations indicate that the upper geotextile of the GCL plays a significant role in controlling the rate of bentonite erosion. Finally, a comparison of the virgin and runoff bentonite properties was conducted to investigate potential changes in swell index, X-ray diffraction results, and concentration of Na and Ca cations. The runoff bentonite was observed to had a significantly higher swell index (40?ml/2?g) than the virgin bentonite (28?ml/2?g) and lower Na and Ca concentrations. This finding is consistent with the observation from XRD analyses of the runoff bentonite which illustrate that the clay fraction of the bentonite is preferentially eroded by the application of DI water.     

Influence of physical and geometrical properties of granite and limestone aggregates on the durability of a C20/25 strength class concrete

This paper presents an experimental study to evaluate the influence of physical and geometrical properties of granite and limestone aggregates on the durability of a C20/25 strength class concrete. Different granite and limestone aggregates were collected from seven quarries. Physical, geometrical and mechanical properties of aggregates as well as the rock weathering state were quantify by several tests such as, abrasion, surface hardness, uniaxial compressive strength, ultrasonic pulse velocity, water absorption by capillarity, vacuum water absorption and oxygen permeability.

Using aggregates from each quarry, several C20/25 strength class concrete mixes have been produced, with the same workability and volume proportions. Concrete specimens have been cured under water for 90 days; after that time concrete durability parameters were obtained through tests such as, vacuum water absorption, capillarity water absorption, water permeability and oxygen permeability.

Relevant statistical correlations have been obtained between absorption and permeability test of rock material and rock deterioration state (weathering). Valid statistic correlation was also obtained between durability parameters as well as among aggregates geometrical properties and concrete durability parameters.     

考虑试样特殊区的扰动状态理论合理性细观分析

利用医用CT装置完成实验过程中试样内部的实时定量观测。对基于硬化模型建立的扰动状态理论(DSC)做出细观分析,进一步证明其解决问题的逻辑合理性。利用硬化土和软化土的宏观剪切实验与实时细观CT实验结果对照,指出土体的硬化响应或软化响应与相应CT数统计值变化规律的协调关系。不论材料是否存在特殊区,硬化材料的CT数变化规律和软化材料的CT数变化规律都存在很大的差异性,这个差异性的存在与是否叠加扰动因子相对应。扰动状态理论利用硬化模型并叠加扰动因子得到软化响应。     

Investigation of initial hydration and rehydration of geosynthetic clay liners from sandy subgrades via X-ray computed tomography images

The hydraulic conductivity of geosynthetic clay liners (GCLs) widely used as barrier systems considerably depends on their hydration status after the initial hydration of virgin GCLs and the rehydration of desiccated GCLs. Free hydration tests were performed on virgin and desiccated GCLs over sandy subgrades to compare their hydration level. In addition, high-resolution micro-X-ray computed tomography (CT) images of both GCLs and sandy subgrades with different gravimetric water content (i.e. 15%, 20%, and 25%) after the initial hydration were analyzed for better insights. The results show significant influences of subgrade water content on moisture content and thickness of virgin GCLs. Water loss of sandy subgrades and the time interval necessary for reaching a steady state of desiccated GCLs during rehydration was greater and longer than virgin GCLs during initial hydration. X-ray CT images verified a dense distribution of bentonite particles, macropores, and minor desiccation cracks that existed in poorly-hydrated GCLs over unsaturated sand. On the other hand, the completely saturated sandy subgrade facilitated the hydration of GCLs, leaving a lot of macropores in the sand. The relationship between water distribution and the frequency of macropore generation observed in the upper contact zone of sandy subgrades was also indicated via these X-ray CT images.     

利用废玻璃制备环保型陶瓷透水砖

以废玻璃,陶瓷废料和粘土为主要原料研制环保型陶瓷透水砖,通过对该材料的吸水率、显气孔率、抗折强度、体积密度等性能的测试及SEM分析,结果表明:在合适的工艺参数条件下,可得透水系数为0.10 cm/s,压缩强度为12.1 MPa陶瓷透水砖。通过对该砖的显微结构分析可知:气孔分布比较均匀,透水性较好,满足当前环保的要求。     

水稻秸秆对硫氧镁泡沫轻质保温材料性能的影响

研究了水稻秸秆体积掺量对硫氧镁泡沫轻质保温材料性能的影响,测试了掺水稻秸秆硫氧镁泡沫轻质保温材料的干缩量、吸水率、导热系数、抗压强度、抗折强度,并进行了微观孔结构试验.结果 表明:随着水稻秸秆体积掺量的增加,硫氧镁泡沫轻质保温材料的干缩量、吸水率、导热系数和抗压强度均逐渐降低,抗折强度在一定范围内有所增加;水稻秸秆的理...     

压缩空气泡沫灭浮顶罐密封圈火灾性能研究

为了评估压缩空气泡沫系统用于浮顶罐的技术可行性，通过足尺灭火试验，研究不同供给强度和不同气液比下压缩空气泡沫对浮顶罐密封圈火灾的灭火性能，提出适宜的灭火应用参数。结果表明：在泡沫溶液供给强度为3.4 ~8.0 L/（min·m²）条件下，采用罐壁式压缩空气泡沫释放装置可以快速有效扑灭浮顶罐密封圈火灾，且不发生复燃；泡沫溶液供给强度越大，控灭火速度越快；气液比在8:1~12:1时对控灭火速度略有影响。建议实际工程中泡沫溶液供给强度不低于5 L/（min·m²），气液比不低于8:1，持续供泡时间不低于15 min。     

High-Strengthening of Cement-Treated Clay by Mechanical Dehydration

A technique called the cement-mixing and mechanical dehydration method (CMD) as one of recycling techniques for soft clay slurry is developed. In order to evaluate the effectiveness of the CMD for increasing the strength of soft clay, a series of unconfined compression tests and several durability tests were performed together with the literature review of unconfined compressive strength in cement-treated soils. Moreover, a series of constant strain rate consolidation tests were also performed to evaluate the effects of cement content and dehydration speed on the permeability of cement-treated clay. The following conclusions are obtained: 1) Literature review and theoretical considerations on the shear strength of cement-treated soils show that an additional treatment for the purpose of increasing the density of cement-treated specimen is effective for increasing the shear strength of cement-treated soil. 2) The mechanical dehydration of soft clay with high pressure is accelerated by cement mixing, where the coefficient of consolidation of cement-treated clay increases as the cement content increases. 3) The high-strength specimen having the unconfined compressive strength of more than 20 MPa can be created from soft clay treated by the CMD with the cement content of over 20% and the dehydration pressure of 20 MPa.     

Soil–water–air fully coupling finite element analysis of slope failure in unsaturated ground

In this paper, a program of the finite element method (FEM), named as SOFT, using a finite element–finite difference scheme (FE–FD) for soil–water–air three-phase coupling problems, has been developed based on a rational and simple constitutive model for unsaturated soil proposed by Zhang and Ikariya (2011). In the program, similar to the works by Uzuoka et al. (2009) and Oka et al. (2010b), the FE–FD formulation in saturated condition of soil–water coupling problem, proposed by Oka et al. (1994), has been extended to unsaturated condition in soil–water–air fully coupling scheme, taking the saturation as a state variable. In order to verify the availability of the proposed numerical method, triaxial tests on unsaturated silty clay under fully undrained and unvented conditions, conducted by Oka et al. (2010a), are firstly simulated by the proposed method. The development of pore air pressure and pore water pressure measured in the specimen can be reproduced well by the proposed method. Furthermore, model tests on slope failure in unsaturated Shirasu, carried out by Kitamura et al. (2007), are also simulated by the same numerical method. From the simulation it is known that the slope failure behavior of the model ground observed in the tests can be described, on the whole, with satisfactory accuracy     

基于CT数字体相关法测量红砂岩单轴压缩内部三维应变场

 基于X射线工业CT实时获取单轴压缩过程中红砂岩试件的三维数字体图像,采用数字体相关(digital volume correlation,DVC)法测量、分析受载过程中试件内部三维变形场及应变场。通过位移场和应变场的分析,揭示试件内部应变局部化演变及破坏过程。红砂岩内部结构可以作为散斑结构,成为变形信息的载体,DVC法的精度可达0.05体素;红砂岩变形破坏中存在明显的应变局部化特征,在峰值荷载的68.9%时试件内部出现应变局部化区域,并逐渐发展至试件破坏,局部化区域与试件最终破坏面位置相一致。研究结果表明,DVC法测量结果能够直观地反映出试件内部应变局部化特点及其演化的过程,为岩石内部变形可视化提供了方法。     

Enhancement of mechanical and hydrophobic properties of Adobes for Building Industry by the addition of polymeric agents

Availability, cheapness and thermal insulation properties give adobe an advantage over other building materials in dry regions. On the contrary, its poor compressive strength and high water adsorption are important disadvantages. We report the enhancement on compressive strength and water absorption resistance obtained in this material by the addition of dodecylamine and emulsified asphalt to the clay used for its manufacture. We characterized the adobes by X-ray diffraction, infrared spectrometry, ζ-potential measurements and scanning electronic microscopy. Ultra violet accelerated test, compressive strength test and water absorption tests were also carried out. The results show that adobes with cationic amine and emulsified asphalt improve their compressive strength and lower their water absorption at the time that they preserve their properties under weathering conditions.     

簸箕山大型老滑坡滑动带的结构特征及形成机制试验研究

 上更新世红色黏土岩是黄土高原大型滑坡的易滑地层,对其滑动带的结构特征及形成机制研究较少。在对黏土岩滑动带的组构、构造特征进行解析的基础上,通过三轴应力–应变试验、残余强度试验及滑带土蠕变试验,分析大型滑坡黏土岩滑动带的形成机制。研究表明：(1) 簸箕山黏土岩滑动带发育密集的近水平剪切面,伴随滑带土结构改变的是塑性变形、剪切变形,运动方式上以块体滑动为主;(2) 黏土岩转变为滑带土后,裂隙增多,平均吸水速率达2.7 g/h,其标准岩样单位时间吸水速率是原岩的1.5倍,活性为0.83,比表面积、活性均高于原岩;(3) 与原岩结构改变相应的是强度的衰减,含水率为19.1%时,黏土岩原岩的峰值强度的黏聚力613 kPa,内摩擦角26.7°,簸箕山滑带土长期强度的黏聚力57.4 kPa,内摩擦角20.47°,残余强度的黏聚力8.79 kPa,内摩擦角为17.2°。     

积水入渗稳定时近饱和土中封闭气泡含量 试验研究

含有与大气不相连通的封闭气泡且饱和度接近 100% 的土体称为近饱和土体。通过室内土柱一维积水入渗模型试验,研究了入渗稳定时土壤类型、干密度和初始含水率对近饱和土体中封闭气泡的含量以及气相逸出率的影响,分析了 3 种影响因素对封闭气泡体积的影响趋势和影响机理。试验结果表明：土样孔隙中封闭气泡的体积随土样干密度的增大而减小;当土样初始含水率超过某一临界含水率时,土样孔隙中封闭气泡的逸出随初始含水率的增加显著减少;由于黏性土达到渗流稳定需要的时间较砂性土长,因而砂性土的气相逸出率要明显小于黏性土的气相逸出率。通过试验揭示了实际土体入渗中的一些物理现象,为更好地理解土壤入渗过程和建立数值模拟模型提供了试验数据。     

Influence of natural coarse aggregate size,mineralogy and water content on the permeability of structural concrete

This experimental work discusses the relevance of natural coarse aggregates of different geological sources in the permeability of structural concrete. Good quality granite, basalt, calcareous and marble natural coarse aggregates, obtained from different quarries, were used to produce structural concrete of strength class C30/37. Concretes were produced with constant volume proportions, workability, mixing and curing conditions using different sizes of each aggregate type. Aggregates were mixed in concrete in both dry and water saturated states. Concrete durability parameters, such as capillary water absorption and air permeability, measured at 28 days, were found to be affected by coarse aggregate size and its water content rather than aggregate mineralogy, as discussed.     

预湿陶砂对混凝土板早期湿度分布及发展的影响

研究了室内单面干燥条件下预湿陶砂轻骨料(PSLWA)掺量(体积分数)及水胶比(质量比)对高、中、低强混凝土板28d内部相对湿度(IRH)分布及发展的影响.结果表明:随PSLWA掺量增大,高、中、低强混凝土板湿度饱和期延长,板湿度水平整体提高,湿度下降延缓,板厚方向上湿度梯度减小,湿度饱和区面积比例增大;引入内养护水约60kg/m~3,高、中强混凝土板28d内部相对湿度可维持在92%以上;随基体水胶比降低,PSLWA内养护作用增强,表面干燥影响深度减小;PSLWA不能彻底消除室内单面干燥条件下高、中、低强混凝土板中的表面干燥效应.