首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 15 毫秒
1.
In current geoenvironmental practice, design engineers usually require that soil liners in waste landfills be compacted within a specified range of water content and dry unit weight. This specification is based primarily on the need to achieve a minimum dry unit weight for factors controlling the performance of compacted soil liners most especially the hydraulic conductivity, k. In this study, lateritic soil treated with up to 10% bentonite, prepared at various compaction states (dry of optimum, optimum and wet of optimum moisture content) was compacted with four compactive efforts (i.e., the reduced British Standard Light, British Standard Light, West African Standard, and British Standard Heavy) to simulate the range of compaction energies expected in the field. Prepared soil mixtures were permeated with water and specimens that yielded the permissible limit of k????1?×?10?9?m/s were enclosed in an envelope (known as the acceptable zone) on the water content?Cdry unit weight curve. It was observed that compaction conditions resulting in moisture content slightly wet of optimum led to the lowest values of k and that the shapes and boundaries of the acceptable zones gradually increased in extent, shifting to wet side of optimum moisture content as the bentonite content increased to 10%. This approach provides good control over the quality of compacted soils and has great potential for field application.  相似文献   

2.
砂-膨润土混合屏障材料渗透性影响因素研究   总被引：2，自引：0，他引：2  
膨润土因具有渗透性低、阳离子交换能力高等优点被认为是最适合高放废物深地质处置库中屏障系统的缓冲材料,工程实践发现随着水化过程的进行,纯高压实膨润土强度不断降低,并最终影响到工程屏障系统功能的发挥。针对这一问题,在膨润土中加入一定比例的石英砂,可以有效地提高工程屏障的热传导特性、压实性、力学强度和长期稳定性,降低工程造价。本文研究了影响砂-膨润土混合物渗透性的主要因素,包括膨润土含量、粒径分布、含水量和干密度、压实方法以及膨润土类型等。结果表明,砂土混合物渗透性主要受膨润土的渗透性控制,渗透系数随着膨润土含量和干密度的增加而减小,当膨润土含量超过某一界限值后,继续增加膨润土含量对降低渗透系数的作用有限;细颗粒和级配良好的混合物渗透系数小,当土体内部发生渗透侵蚀将增大渗透系数;最优含水量条件下压实得到的渗透系数最低,高于最优含水量压实得到的渗透系数比低于最优含水量压实得到的渗透系数要小。  相似文献   

3.
Compacted soil–bentonite mixtures are finding wide application as buffer material for waste repositories for their favorable self-sealing qualities. The swelling properties of such materials which serve as a measure of their self-sealing capabilities and, thus, the efficiency of the repository in sealing off their contents from the environment are closely related to the chemistry of the leachate that emanate from the wastes. For this reason, the swelling parameters (namely swelling potential and pressure) of compacted lateritic soil–bentonite mixtures under consideration for use as barrier in municipal waste landfill were evaluated. Series of swelling potential and pressure tests were performed using variable content (0–10 %) of bentonite at predetermined optimum moisture content. Soil mixtures were compacted with British Standard Heavy compactive effort and saturated with processed tap water as well as three leachate solutions of varying ionic strength that were generated in active open dump landfills. Experimental results showed that swelling potential based on the free swell together with the maximum swell pressures of compacted soil mixtures measured at equilibrium increased approximately linearly with increase in the amount of bentonite when inundated with processed tap water and the three leachate solutions. On the other hand, these swelling parameters decreased as the ionic strength of the leachate solutions measured by their electrical conductivity increased for the various soil mixtures. These results provide an insight into the swelling behavior and the possible degradation in the efficiency of the proposed lateritic soil–bentonite mixtures in relation to their use as buffer material in waste landfills.  相似文献   

4.
A reddish brown lateritic soil treated with up to 15% blast furnace slag was compacted with three compactive efforts, (standard Proctor, West African Standard and modified Proctor) with moulding water contents ranging between 10 and 20% of weight of dry mixture. Compacted samples were extruded and allowed to dry in the laboratory for 30 days with measurements taken every 5 days to monitor volumetric changes due to drying. Four specimens compacted on the wet side of optimum using standard proctor effort; at the various slag treatments after 10 days of drying were subjected to four cycles of drying and three cycles of wetting. The results obtained showed that the changes in mass and volumetric shrinkage were rapid within the first 5 days of drying. These changes were proportional to the moulding water contents and were unaffected by the compactive effort. The volumetric shrinkage strain increased with increasing moulding water content and compactive efforts. As the water content relative to the optimum increased towards the wet side, the volumetric shrinkage strain increased and it decreased towards the dry side. For all compaction energies, the initial degree of saturation increased and regardless of the slag content, the volumetric shrinkage strain increased. As the slag content increased, the initial degree of saturation at which the permissible 4% volumetric shrinkage occurred increased. Slag content had marginal effects on the volumetric shrinkage strain as no clear trend was established. For each slag treatment the volumetric shrinkage strain did not vary significantly with increasing number of drying cycles.  相似文献   

5.
为了探究土体干缩开裂问题,文章采用ERT技术,对黏性土开展了一维干缩开裂动态监测试验。配制初始状态饱和 的泥浆试样,在自然条件下干燥,采用ERT技术获得试样干燥过程中的电阻值变化。结合试样的电阻值图像和裂隙图像, 对土体干缩开裂规律进行了分析。研究结果表明：在干燥蒸发初期,土体电阻值随时间增加缓慢减小,其原因在于土体干 燥收缩导致土颗粒间接触面积增大,颗粒水化膜变薄,进而使得土颗粒表面双电层导电性增强。随着干燥继续进行,气体 进入土体内部,土体由初始饱和状态转变为非饱和状态,电阻值转为缓慢增加。当土体产生裂隙时,裂隙周围土体电阻值 急剧增大,而未发育裂隙的土体电阻依然保持缓慢增加的趋势。通过对比试样电阻值变化曲线和裂隙图像,发现两者所呈 现的裂隙发育位置和状态存在良好的一致性。因此,ERT技术能对干燥过程中土体裂隙发育进行有效的动态监测,准确掌 握裂隙发育的时空动态信息,并且能提前预测裂隙发育的可能位置,为研究极端干旱气候作用下土体的工程性质响应提供 了理想手段。  相似文献   

6.
Long term competent performance of liner systems is a critical issue in the design and construction of waste repositories due to adverse interactions associated with leachate generated by wastes. This study was conducted to verify the efficacy of fly ash stabilization in enhancing compatibility between lateritic soil and municipal waste leachate. Applications investigated include soil mixtures containing 0, 5, 10, 15, and 20% fly ash compacted at approximately 2% wet of optimum moisture content with modified proctor energy. Baseline hydraulic conductivity was first established at every level of fly ash content by permeating soil mixtures with tap water before permeation with leachate in a compaction mould permeameter using the falling head test method. Results show that the trend in hydraulic conductivity of specimen containing 0% fly ash was characterized by a gradual but erratic decrease which may suggests partial entry of the leachate cations into the double layer. Conversely, specimens containing fly ash showed a general trend consisting of an initial drop in k (up to an order of magnitude) that was followed by slight decrease sustained until k stabilized and later terminated. Above 10% fly ash content, the relatively high values of k observed was not connected with the reactivity of the soil mixtures with leachate, rather it may be attributed to excessive fly ash content that altered their textural and hydraulic properties. The result of this study is potentially significant in the assessment of fly ash as a compatibility enhancing agent which can be admixed in barrier materials that are susceptible to adverse reactions with the liquid to be contained.  相似文献   

7.
This study evaluates the applicability of residually derived lateritic soil stabilized with cement kiln dust (CKD), a waste product from the cement manufacturing process as liner in waste repositories. Lateritic soil sample mixed with 0–16 % CKD (by dry weight of the soil) was compacted with the British Standard Light, West African Standard and British Standard Heavy compaction efforts at water contents ranging from the dry to wet of optimum moistures. Geotechnical parameters such as Atterberg limits, compaction characteristics, hydraulic conductivity, unconfined compressive strength and volumetric shrinkage strain were determined. Results indicate that the plasticity index, the maximum dry unit weight and hydraulic conductivity together with the volumetric shrinkage decreased with increased amount of CKD while the optimum moisture content and unconfined compressive strength increased with higher CKD content for all the efforts. When measured properties were compared with standard specifications adopted by most environmental regulatory agencies for the construction of barrier systems in waste containment structures, the resulting values showed substantial compliance. Besides developing an economically sustainable liner material, the present study demonstrated effective utilization of an industrial by-product otherwise considered as waste by the producers, in addition to a systematic expansion in the use of the lateritic soil for geotechnical works.  相似文献   

8.
高放废物地质处置库缓冲/回填材料的重要作用之一是传导和散失高放废物衰变热,在膨润土中添加石英砂、石墨、花岗岩岩屑等导热性能较好的添加剂是提高缓冲/回填材料导热性能的主要方法。选用北山花岗岩岩屑为添加剂,与高庙子钠基膨润土GMZ01组成混合材料,制备不同含水率、不同密度的试样。使用Hot Disk TPS2500s热常数分析仪测定样品的导热系数,分析其与花岗岩岩屑含量、干密度、饱和度等参数的关系,并运用多种混合物热传导模型分析预测导热系数。研究结果表明,花岗岩岩屑能够有效提高缓冲/回填材料的导热性能,混合材料的导热系数分别与其饱和度、气体体积存在线性关系;Maxwell方程能够较好预测北山花岗岩岩屑-膨润土混合材料的导热系数。  相似文献   

9.
废旧轮胎胶粉用于填埋场衬垫材料改性,是提高衬垫系统有效性和扩展废旧轮胎资源化利用途径的一种手段。以高岭土作为黏性土的代表,开展废旧轮胎胶粉-高岭土混合土的力学和水力学性质试验,重点探讨胶粉掺量及尺寸对混合土渗透性、压缩性和收缩性的影响规律。研究表明,废旧轮胎胶粉-高岭土混合土的渗透系数、压缩系数、回弹指数、固结系数和体缩率等均随胶粉掺入比的增加而增大。高岭土及混合土的无侧限抗压强度大于200kPa,50kPa和200kPa压力下渗透系数满足≤1.0×10-7cm·s-1的要求,均属于中压缩性土,且体缩率小于体积应变合格值4%。与30目胶粉相比,12目胶粉-高岭土混合土压缩性和回弹量较小、固结系数较大,胶粉尺寸对无侧限抗压强度、体缩率和渗透系数的影响不显著。在本文试验条件下,为提高黏土衬垫对有机污染物的吸附能力并满足渗透性、强度及变形的要求,12目25%胶粉改性黏土可作为填埋场黏土衬垫材料。  相似文献   

10.
于响  孙德安  孙文静 《岩土力学》2015,36(5):1339-1346
膨润土因具有湿胀、干缩特性,其水力-力学性质易受干湿循环的影响。采用饱和盐溶液蒸汽平衡法研究了干湿循环对压实高庙子钙基膨润土持水特性的影响。对相同条件下制作的试样进行0～6次干湿循环,选取其中的原试样（0次）、循环3次和6次试样,进行蒸汽平衡法试验,测定其土-水特征曲线。同时,在0～6次干湿循环过程中,对每一次脱湿后试样表面采集图像,用数字图像处理技术提取了收缩及裂隙开展区域,分析得到收缩率与裂隙率。试验结果表明：随着干湿循环次数的增加（0→3次时）,土-水特征曲线向下平移、持水性下降、孔隙比增大、平均骨架应力减小,试样烘干时收缩率和裂隙率增加明显;但随着循环次数的继续增加（3→6次时）,持水性、收缩率和裂隙率趋于稳定。  相似文献   

11.
The effects of post-compaction residual lateral stress and salt concentration in the hydrating fluid on swelling pressures of compacted MX80 bentonite is brought out in this paper. In order to release the residual lateral stresses, following the static compaction process during preparation of specimens, compacted bentonite specimens were extruded from the specimen rings and then inserted back prior to testing them for swelling pressures in isochoric condition. The swelling pressure tests were carried out at several dry densities of the bentonite with distilled water and solutions of NaCl (0.1 and 1.0 M) as the hydrating fluids. With water, the test results showed that specimens that underwent extrusion and insertion processes exhibited about 10–15 % greater swelling pressures as compared to the specimens those that were compacted and tested. The influence of saline solutions was found to reduce the swelling pressure of the bentonite, but their impact was less significant at high compaction dry densities.  相似文献   

12.
This study investigates the performance of an optimum compacted bentonite/sand mixture seal for the isolation of underground waste repositories. Engineering geological tests such as compaction, flow, swelling, mechanical and shear strength tests have been conducted to select an optimum mixture and to recommend a stable bentonite/sand seal length-to-radius ratio (L/a) as far as the factor of safety (F) is concerned. The results of the compaction permeameter tests led to a recommendation to select an optimum compacted bentonite/sand mixture possessing a bentonite content of about 20% to satisfy the minimum regulatory hydraulic conductivity requirement. Engineering geological analysis of the seal/rock mechanical interaction with regard to reduce the possibility of seal slip led to a recommendation to utilize a seal L/a of at least 25.  相似文献   

13.
饱和膨润土及其与砂混合物的压缩变形特性   总被引：1，自引：0，他引：1  
孙文静  孙德安  孟德林 《岩土力学》2009,30(11):3249-3255
对用不同制样方法得到的饱和膨润土及其与砂混合物进行了压缩试验。试验结果表明,饱和膨润土的压缩曲线呈双线性,不同于普通黏土的压缩曲线。压缩试验中量测了侧向应力,由此得到的饱和膨润土的静止侧向压力系数值较一般黏土的数值要大。对膨润土与砂混合物的击实样进行了由非饱和到饱和状态的浸水试验,并得出试验过程中侧向应力的变化规律。由于浸水饱和的试样和抽真空饱和的试样在较高压力时压缩曲线趋于一致,可采用快速抽真空饱和的方法进行试验研究,以缩短非饱和混合物击实样浸水饱和所需时间。引入骨架孔隙比的概念,用来判断膨润土与砂混合物中砂骨架是否形成,得出影响混合物压缩特性的决定因素。  相似文献   

14.
The paper presents the results of an experimental study on the effects of the initial water content and dry density on the soil–water retention curve and the shrinkage behavior of a compacted Lias-clay. The initial conditions after compaction (initial water content and initial dry density) have been chosen on the basis of three Proctor tests of different compaction efforts. According to the eight chosen initial conditions clay samples have been compacted statically. The relation between total suction and water content was determined for the drying path starting from the initial conditions without previous saturation of the specimens. A chilled-mirror dew-point hygrometer was used for the suction measurements. For the investigation of the shrinkage behavior cylindrical specimens were dried to desired water contents step-by-step without previous saturation. The volume of the specimens was measured by means of a caliper. Based on the test results the influence of different initial conditions on the soil suction and the shrinkage behavior is analyzed. The soil–water retention curves obtained in terms of the gravimetric water content are independent of the initial dry density. At water contents above approximately 11–12.5% a strong influence of the compaction water content is observed. At smaller water contents, the soil–water retention curve is independent of the compaction water content. The results of the shrinkage tests show that the influence of the compaction dry density on the shrinkage behavior is negligible. Similar to the drying behavior of saturated samples a primary and a residual drying process could be distinguished. The primary drying process is strongly influenced by the initial water content. In contrast, the rate of the volume change of the residual drying process is unaffected by the initial water content.  相似文献   

15.
In this study, an investigation was performed to determine if lime-stabilized sand–bentonite mixtures are appropriate for the construction of sanitary landfills liners. For this aim, the hydraulic conductivity tests were conducted in the laboratory on sand–bentonite mixtures and lime-stabilized sand–bentonite mixtures to evaluate the effect of wetting–drying cycles. The hydraulic conductivity tests were performed to see if their hydraulic conductivities are affected by wetting–drying cycles. First series of specimens have been prepared as a mixture of sand and bentonite only. In the first series of specimens, sand was mixed with bentonite in proportions of 20, 30, 40, and 50 %. In the second series of the specimens, lime in proportions of 1, 2 and 3 % by weight was added to the mixtures of sand–bentonite in proportions of 20, 30, 40, and 50 %. From the results of the tests, it was observed that while optimum water content increased, maximum dry density decreased with addition of lime to the sand–bentonite mixtures. Generally, the hydraulic conductivity increased with the addition of lime to the mixtures but at low percentages of lime (1–2 %), however, slight decreases in k were recorded. It was also observed that the wetting–drying cycles on the permeability test indicate cure effect on specimens with addition of lime which resulted in decreased the hydraulic conductivity.  相似文献   

16.
In the present study, influence of wetting–drying cycles on swelling pressures of sand–bentonite mixtures used in the construction of sanitary landfills to have an impermeable liner was investigated before and after lime treatment of the mixtures. Swelling pressure tests were conducted to see if the swelling pressures were affected by wetting–drying cycles. First series of specimens were prepared as a mixture of sand and bentonite only. In the first series of specimens, sand was mixed with bentonite in various proportions with their optimum water contents and compacted by using standard proctor energy. In the second series of the specimens, lime in various proportions was added to the mixtures of sand–bentonite. Then, the sand–bentonite mixtures stabilized by lime were compacted with the standard proctor energy at their optimum moisture contents. Five wetting–drying cycles were performed on each specimen and values of swelling pressures were measured at the end of each cycle. Results of swelling pressure tests indicated that the swelling pressure is decreased when lime is added to the mixtures. In addition, decrements were observed on swelling pressures by wetting–drying cycles. The results of the experiments of this investigation showed that the beneficial effect of lime stabilization to control the swelling pressures was partly lost by the wetting–drying cycles. However, the test results indicated that the swelling pressures of the specimens made of sand–bentonite mixtures stabilized by lime were lower than the swelling pressures of the specimens made of only sand–bentonite mixtures.  相似文献   

17.
The thermal property is one of the key properties for the design of the high-level radioactive waste (HLW) repository. In this study, the thermal properties transient automatic tester (HPP-F) is uesd to study the thermal conductivity of multiphase composite buffer/backfill material including the type B-Z and B-Z-P (Here B、Z、P represents bentonite、zeolite and pyrite respectively,the same as in the following.) in different dry density and moisture conditions. The results show that for the same moisture content (dry density), thermal conductivity of specimens increases as the dry density (moisture content) increases. As a result, the type B-Z-P which is highly compacted of 1.8 g/cm3 in dry density and 17.65% in moisture content performs well, it meets the requirements of the IAEA and is easy to be compacted ,so it can be recommend as a alternative material of high level radioactive waste disposal repository buffer/backfilling materials.  相似文献   

18.
Specimens prepared from three lateritic soil samples were subjected to drying under laboratory conditions. Volumetric shrinkage strains were measured at the end of the drying period. Results of this study indicate that, for the lateritic soils tested, volumetric shrinkage strains are influenced by soil composition and compaction conditions. Volumetric shrinkage strain increased with higher compaction water content. The influence of compaction water content on measured volumetric shrinkage strain was more pronounced in specimens with higher fines content. A regression equation was developed from the data to estimate volumetric shrinkage strain given the compaction water content relative to optimum, plasticity index, fines content and compactive effort.  相似文献   

19.
Compacted soil–bentonite liners, consisting of a sandy soil mixed with bentonite as backfill, are used extensively as engineered barriers for contaminant containment. This paper studies the valorization of local materials containing calcareous sand, tuff obtained from Laghouat region (in the South Algeria), to associate with bentonite in order to improve their hydraulic characteristics for use as landfill liner material. Firstly, a geotechnical characterization of mixtures chooses from a fixed percentage to 10% bentonite and different percentages of calcareous sand and tuff so that they are complementary to 90% by not 10%. Thereafter, the determination of saturated hydraulic conductivity at falling-head permeability (Kv) and oedometer (Kid, indirect Measure) tests of all compacted mixtures at Optimum Normal Proctor have been carried out using both permeates by tap water and a landfill leachate in order to simulate long-term conditions. The results showed that the saturated hydraulic conductivity of tap water is relatively lower than the one saturated by leachate in the falling-head test, unlike the oedometer test. The B10CS20T70 mixture has satisfied the hydraulic conductivity criterion of bottom barriers (i.e. water permeated: kv20° = 1.97 × 10?9 and kid from 7 × 10?9 to 1.83 × 10?10 < 10?9m/s; leachate permeated: kv20° = 2.91 × 10?9 and kid from 7 × 10?9 at 1.44 × 10?10 < 10?9 m/s). Finally, a comparison between direct measurements of the saturated hydraulic conductivity by triaxial (Kd) test and oedometer test (Kid) in the range of effective stress applied 100–800 kPa led to propose equations of correlations between these two methods. In conclusion, adopted formulation B10CS20T70 perfectly meets the regulatory requirements in force and constitutes an economic product based on available local materials for engineers barriers.  相似文献   

20.
Analysis of Swelling and Shrinkage Behavior of Compacted Clays   总被引：2，自引：0，他引：2  
The impact of the variation in compaction condition on the swelling and shrinkage behavior of three soils has been examined. Two natural soils, namely red soil and black cotton soil, and one artificially mixed soil sample of commercial bentonite with well-graded sand, were studied. Compaction curve for Standard Proctor conditions were plotted and four compaction conditions were selected. Experimental results showed that clay mineralogy dominates over compaction conditions in influencing the swelling and shrinkage behavior of the tested soils. Monitoring of void ratio (e)−water content (w) relations during shrinkage showed that soil specimens generally shrunk in three distinct linear stages. A small reduction in void ratio occurred on reduction in water content during the first shrinkage stage and was termed as initial shrinkage. In second stage, void ratio decreased rapidly with reduction in water content and was termed as primary shrinkage. In third and final stage, reduction in water content is accompanied by a marginal change in void ratio and it’s called residual shrinkage. Irrespective of initial compaction conditions studied, the transition from primary to residual shrinkage for all the specimens occurred within a narrow range of water content (10–15%).  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号