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1.
A mixture of the MX80 bentonite and the Callovo-Oxfordian (COx) claystone were investigated by carrying out a series of experiments including determination of the swelling pressure of compacted samples by constant-volume method, pre-swell method, zero-swell method and swell–consolidation method. Distilled water, synthetic water and humidity controlled vapour were employed for hydration. Results show that upon wetting the swelling pressure increases with decreasing suction; however, there are no obvious effects of synthetic water chemistry and hydration procedure on the swelling behaviour in both short and long terms. For the same initial dry density, the swelling pressure decreases with increasing pre-swell strain; whereas there is a well defined logarithmic relation between the swelling pressure and final dry density of the sample regardless of the initial dry densities and the experimental methods. It was also found that swelling pressure depends on the loading-wetting conditions as a consequence of the different microstructure changes occurred in different conditions. Furthermore, it was attempted to elaborate a general relationship between the swelling pressure and the final dry density for various reference bentonites. 相似文献
2.
Pre-compacted MX80 bentonite/Callovo-Oxfordian (COx) claystone mixture has been proposed to backfill and seal the underground galleries for radioactive waste disposal in France. While emplacing these pre-compacted blocks, technological voids are created between the blocks and the host rock and among the blocks themselves. It is expected that homogenization process will take place over time for the structure constructed with pre-compacted blocks upon hydration. This study investigated the boundary friction effect on such a process. Results showed that after the filling of technological voids, the soil far from the technological voids would swell further, while those near the voids would be compressed under the welling pressure generated by the soil behind, resulting in an increase in homogeneity in terms of dry density distribution. However, this homogenization process would stop after a certain time. Further examination showed that the homogenization process ended when the maximum boundary friction force became equal to or higher than the vector sum of swelling forces in the radial direction. Based on the force equilibrium and the mass conservation, the final dry density distribution was estimated. Comparison between the estimation and the measurement showed a good agreement, indicating the relevance of the identified mechanism related to boundary friction. 相似文献
3.
本文在前人基础上改进渗透装置,通过自制多功能膨胀渗透仪在氮气加压为1.0 MPa条件下,测得沸石-膨润土-硫铁矿、凹凸棒石-膨润土-硫铁矿两组混合物在不同膨润土含量、压制载荷、压实密度、出水时间等条件下的渗透系数。实验结果表明:集成回填材料的渗透系数随时间的变化不大,基本满足达西定律。同一干密度和含水率条件下,不同混合物随着膨润土含量的增加,其渗透系数降低。膨润土含量占沸石混合物或者凹凸棒石混合物比例不小于60%时,二者混合物的渗透系数均满足高放废物处置中回填材料渗透系数小于7×10-10m/s的要求。但同等条件下,由于沸石为非粘性矿石,其具有孔隙大、渗透性好等特点,因此天然地下水在沸石混合物中比在凹凸棒石混合物中渗透得快。同一干密度和含水率条件下,不同混合物压实制样的载荷越大,其渗透系数越小,反之越大。压制载荷在50~100 MPa间时,混合物的渗透系数变化不大。通过进行混合物不同配比、不同影响因素对渗透特性影响的研究,为我国新型缓冲回填材料在未来地下工程中施工提供一定的理论依据。 相似文献
4.
膨胀力是膨胀岩土地区工程设计和施工中的重要参数,目前常用的膨胀力试验方法主要有膨胀反压法、平衡加压法和加压膨胀法3种。膨胀力大小容易受试验方法的影响。为了研究试验方法对膨胀力的影响,以延吉膨胀岩为研究对象,采用上述3种方法开展了不同初始含水率试样的膨胀力试验,分析比较了3种试验方法的特点和适用范围。结果表明,膨胀力具有强烈的水-力路径效应,3种方法确定的膨胀力存在较大差异,膨胀反压法测得的膨胀力最大,加压膨胀法最小;3种方法确定的膨胀力与初始含水率之间存在明显的线性负相关关系,随着试样初始含水率的增加,不同方法得到的膨胀力与初始含水率的关系曲线逐渐靠拢,水-力路径对膨胀力试验结果的影响逐渐减弱,每一种方法有其自身的特点和特定的适用范围,膨胀力测试应该根据实际工况选择合适的试验方法。 相似文献
5.
本文研究了我国高放废物地质处置库缓冲／回填材料－内蒙古高庙子膨润土的压实、膨胀力和膨胀变形特性。实验结果表明，膨润土样品的压实密度与压制压力和蒙脱石含量有关，膨胀力与样品压实密度和蒙脱石含量有关，样品在荷载作用下膨胀变形明显减小。 相似文献
6.
Buffer/backfill material is an important engineering barrier in a deep geological repository of high-level radioactive waste (HLW). Its thermo-hydro-mechanical (THM) performance is very important for the safe and stable operation of the HLW repository system. Natural graphite powder mixed with sodium bentonite forms a buffer/backfill material that can dissipate heat quickly and provide strong isolation. In this paper, the THM characteristics of bentonite–sand–graphite–polypropylene fiber (BSGF) mixtures, used as a buffer/backfill material, were studied through a series of laboratory tests. The influence of graphite and polypropylene fiber contents on thermal conductivity, swelling pressure, hydraulic conductivity, and strength properties of BSGF mixtures with different sand contents was analyzed. Experimental results indicated that the graphite content, the maximum graphite mesh number, and the initial dry density of bentonite–graphite mixtures influenced the thermal conductivity of bentonite–graphite mixtures. The addition of polypropylene fiber was found to enhance the shear strength and inhibit cracking without significantly affecting the expansivity, permeability, and thermal conductivity of the BSGF mixtures. This study provides a new buffer/backfill material that can improve the stability, functionality, and thermal efficiency of the HLW repository. 相似文献
7.
Bentonite pellet mixtures are considered as one of the candidate sealing materials for deep geological disposals of radioactive waste. One of the particularities of this material is the initial heterogeneous distribution of pellets and porosity within the mixture, leading to complex hydro-mechanical behaviour. In this paper, the hydro-mechanical properties of GMZ bentonite pellet mixtures were investigated in the laboratory by carrying out water retention tests on pellet mixtures under constant-volume condition and single pellets under free swelling condition, as well as a infiltration test on a column specimen of pellet mixture. In the infiltration test, the relative humidity and radial swelling pressure were monitored at five heights, the axial swelling pressure was also recorded. The instantaneous profile method was applied to determine the unsaturated hydraulic conductivities. Results show that, in high suction range (>?10 MPa) the water retention curve of pellet mixture under constant-volume condition was comparable to that of a single pellet under free swelling condition, while in low suction range (<?10 MPa) the latter exhibits a much higher water retention capacity. Due to clogging of large pores, the unsaturated hydraulic conductivity decreases as suction decreases to around 25 MPa. However, with further suction decrease, the hydraulic conductivity increases continuously until the value at saturated state, as in the case of most unsaturated soils. The radial swelling pressure at different heights develops with local sudden increase and decrease, which was attributed to local rearrangement of pellets upon wetting. By contrast, as the axial swelling pressure was measured on the global surface of the specimen, it develops in a more regular fashion. 相似文献
8.
与纯膨润土相比,混合型缓冲回填材料（膨润土与石英砂混合物）能够实现防渗阻隔能力、热传导性能、力学强度和可施工性能的最佳组合。选用高庙子钠基膨润土（GMZ001）为缓冲回填材料的主料,添加不同比例的石英砂,对掺砂比分别为0、10%、20%、30%、40%和50%的膨润土-砂混合物压实试样进行室内试验。结果表明,混合物的液限、塑限随掺砂率的增大而线性降低;膨胀力随时间呈指数增长。初始含水率较大时,最大膨胀力随初始含水率的增大略有降低。掺砂率一定时,最大膨胀力随初始干密度指数增长。提出了有效黏土密度的概念,建立了一定初始含水率条件下,任意掺砂率和初始干密度的高庙子膨润土-砂混合物最大膨胀力归一化模型,为混合型缓冲回填材料膨胀力的预测与控制提供了依据。 相似文献
9.
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
10.
运用自行研制的膨胀仪对膨润土加砂混合物进行了一系列膨胀力及膨胀应变等膨胀特性的试验研究,分析了膨胀力随时间的变化规律、两向膨胀力之间的关系和膨胀应变与时间及吸水量之间的关系。试验研究表明,膨润土加砂混合物的最大膨胀力以及最大膨胀应变主要取决于混合物的最初干密度和膨润土含量,并且随着二者的增大而增大;膨润土加砂混合物的水平膨胀力与竖向膨胀力之比随着混合物干密度的增大减小,并且与干密度近似成线性关系;不同膨润土含量的膨润土加砂混合物的膨胀应变与时间成双曲线关系,与吸水量近似呈S型曲线关系,并且其最大膨胀应变与膨润土含量存在指数关系。试验结果对高放废物深处置库中的缓冲回填材料设计具有一定的参考价值。 相似文献
11.
膨润土具有遇水膨胀的特性,是高放核废料深地质处置库理想的缓冲回填材料。膨胀特性是其作为缓冲材料最重要的性能之一,同时受多方面因素的影响。本文以我国首选缓冲材料高庙子膨润土为研究对象,以含水率和干密度为控制变量,以恒体积法为试验方法,研究了高压实高庙子膨润土的水化膨胀特性,采用压汞试验法(MIP)对膨润土微观结构进行了研究,并以此对水化膨胀特性进行了解释。膨胀力试验结果表明,高庙子膨润土的膨胀力发展形式和最大膨胀力均受试样含水率和干密度影响,干密度较小时,水化曲线呈明显的双峰结构,干密度较大时,水化曲线形态与含水率相关,随着含水率增大,双峰结构逐渐消失。MIP试验结果表明,高庙子膨润土的孔径分布同样受含水率和干密度影响,随着含水率和干密度降低,集合体间大孔隙体积增多。膨润土的水化膨胀曲线受集合体间大孔隙影响显著。大孔隙较多时,膨润土集合体能迅速膨胀形成临时结构,当膨胀力超过临时结构的极限荷载时发生坍塌,膨胀力回落,内部结构重组后继续水化达到最大膨胀力,因此其水化膨胀曲线呈明显的双峰结构。随着大孔隙量减少,水化膨胀曲线由双峰结构演变成一条平滑曲线。 相似文献
12.
目前测量土体膨胀力的主要方法有膨胀反压法、加压膨胀法、平衡加压法和恒体积法。基于测量膨胀力的恒体积法,利用TST-55型渗透仪、高精度压力传感器和数采系统改进了测量土体膨胀力的装置,并研究了膨胀土的膨胀特性。试验结果表明,土样初始含水率和干密度对土体的极限膨胀力都有显著的影响,并建立了极限膨胀力与两者之间的关系式;较低初始含水率时,不同干密度的土样在膨胀力达到峰值之后,都有不同幅度的降低,随着干密度的增大而降低的越多,并且发现极限膨胀力降低值与干密度之间在双对数坐标轴上存在线性关系;而在较高初始含水率时,不同干密度的土样在膨胀力达到峰值之后,会保持平稳趋势。极限膨胀力的对数与初始含水率之间具有很好的线性关系,土样吸水量的对数与初始含水率以及干密度均有着很好的线性关系。 相似文献
13.
膨润土颗粒混合物是高放废物深地质处置库中的一种缓冲/回填材料,掌握其堆积性质与水-力特性是开展处置库安全性能评估的关键基础。本文全面回顾和总结了近年来国内外学者对膨润土颗粒混合物的堆积性质、持水特性、结构特征、渗透特性、胀缩特性及本构模型等方面的研究进展与取得的成果,展望了几个值得进一步研究的问题。结果表明,颗粒混合物的堆积性质与粒径级配密切相关;湿化过程中,颗粒混合物由初始松散结构逐渐转变为胶结融合结构,孔隙结构逐渐趋于均一化,并伴随着颗粒破碎和错动,进而影响其水-力特性。考虑到处置库实际运营环境的复杂性,颗粒混合物的原位填充技术以及多场(热-水-力-化)耦合条件下颗粒混合物的水-力特性是今后值得深入研究的方向。 相似文献
14.
将建筑废渣按一定比例与黏土掺合形成的渣土混合料用作填筑材料,具有显著的社会经济与环保效益。为了揭示渣土混合料的压实特性,利用击实试验研究渣料含量和初始级配对渣土混合料压实性能及颗粒破碎特性的影响。研究结果显示,与黏土相比,渣土混合料的最优含水率较低而最大干密度较高,尽管渣料的初始级配有所不同,渣土混合料的最优含水率随掺渣量的增加而减小,最大干密度随掺渣量的增加而先增后减,并存在着一个约为30%的最优掺渣量;击实作用下渣料颗粒的相对破碎率随掺渣量的增加而增加,与初始级配均匀的渣料相比,相同掺渣量下初始级配不均匀渣料的相对破碎率较小,但受渣料初始颗粒大小的影响不大;与初始较小颗粒渣料的混合料相比,初始较大颗粒渣料的混合料的最大干密度较大,表明宽级配的渣土混合料压实性能较好。渣土混合料的压实特性通过结合掺渣量、颗粒破碎特性与渣土混合料结构响应分析得到合理解释。 相似文献
15.
This report describes the application and field compaction of a tunnel backfill, which consists of a mixture of commercial Na bentonite (MX 80) powder and suitably graded ballast material. The ballast material consists of quartz-rich sand and feldspar rich filler. Important characteristics for the tunnel backfill are low permeability, low compressibility and a certain swelling potential. 相似文献
16.
ABSTRACTThis paper presents the effectiveness of xanthan gum (XG) biopolymer in stabilising the expansive soil. The XG biopolymer is mixed with expansive soil in different proportions such as 0%, 0.2%, 0.5%, 0.8% and 1.0% by weight of the dry soil mass. The plasticity, compaction, swelling, compressibility, hydraulic conductivity, strength and durability characteristics of the treated and un-treated expansive soil are examined. Results show that the plasticity index of the treated soil mass initially increases but beyond 0.5% biopolymer addition it decreases sharply. The optimum moisture content and maximum dry density of treated soil, found out from light and heavy compaction tests, do not follow any definite trend. It is also found that increasing XG content increases compressibility slightly but, it reduces swelling pressure, differential free swelling value and hydraulic conductivity remarkably. On the other hand, time-dependent compressive strength and resistance to mass loss increases with increasing XG content. Microscopic examination confirms the formation of gel-like linkage, which brings about the modifications in the treated expansive soil. 相似文献
17.
Despite the increasing understanding of bentonite behaviour, there is still missing evidence on how different hydro-mechanical loadings, including sequences of hydration and compression, affect the fabric and the volume change behaviour of the material. It is generally assumed that the interplay between the behaviour of clay assemblages and the overall fabric of the material is the reason of having final states that are dependent on the stress path followed. Here the results of an experimental campaign aiming to study these factors are reported and discussed. Free swelling and swelling pressure tests were performed, both followed by compression to a relatively high stress. The experimental program involved various samples that were dismantled at intermediate states in order to perform microstructural observations by means of mercury intrusion porosimetry and electronic scanning microscopy. It was observed that while the void ratio at a given stress level depends on the stress path, subsequent compression led to a unique virgin compression line. The data obtained at the microscale gave further insight for an interpretation of the volume change behaviour observed at the macroscale, showing that at high stress the material tends to recover the same fabric regardless of the path to saturation. 相似文献
18.
Based on a standard compaction test and a standard sieve analysis test on five tested materials, the effects of the particle size distribution on the compaction behavior and particle crushing of a crushed mudstone particle mixture were investigated. Testing results indicate that the value of the maximum dry density ranges from 2.09 to 2.17 g/cm 3, the optimum moisture content from 7.40 to 11.66 %, and the average relative breakage from 0.065 to 0.285, respectively. Based on the tested data, the variations of the maximum dry density, optimum moisture content and average relative breakage, with the median particle diameter and gravel content of the tested mixtures, were analyzed, respectively. 相似文献
19.
Compacted clay soils are used as barriers in geoenvironmental engineering applications and are likely to be exposed to salinization and desalinization cycles during life of the facility. Changes in pore fluid composition from salinization and desalinization cycles induce osmotic suction gradients between soil–water and reservoir (example, landfill/brine pond) solution. Dissipation of osmotic suction gradients may induce osmotic swelling and consolidation strains. This paper examines the osmotic swelling and consolidation behaviour of compacted clays exposed to salinization and desalinization cycles at consolidation pressure of 200 kPa in oedometer assemblies. During salinization cycle, sodium ions of reservoir fluid replaced the divalent exchangeable cations. The osmotic swelling strain developed during first desalinization cycle was 29-fold higher than matric suction induced swelling strain of the compacted specimen. Further, the diffusion controlled osmotic swelling strain was 100-fold slower than matric suction-driven swelling process. After establishment of ion-exchange equilibrium, saturated saline specimens develop reversible osmotic swelling strains on exposure to desalinization cycles. Likewise the saturated desalinated specimen develops reversible osmotic consolidation strains on exposure to cycles of salinization. Variations in compaction dry density has a bearing on the osmotic swelling and consolidation strains, while, compaction water content had no bearing on the osmotic volumetric strains. 相似文献
20.
依托浙北1 000 kV变电站新建工程,对28个基槽回填土试样的压实系数试验结果进行研究。试验所用指标主要为干密度、最大干密度、40 mm颗粒含量等,基于主成分分析法的基本原理,找出对该工程回填土试样试验结果产生较大影响的因素。结果表明,40 mm颗粒含量对于压实系数的准确测定存在影响,而在普通压实系数测定过程中往往忽略这一因素,因此,有必要根据40 mm颗粒含量对试样的压实系数进行校正。通过引入校正度这一概念,反映出随着40 mm颗粒含量的增加,实测结果对理论曲线的离散度增大,试验结果的精度逐渐降低。 相似文献
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