Effect of shrinkage characteristics of bentonite with different sand mixing rates and dry densities
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摘要:
膨润土具有明显胀缩性, 收缩引起膨润土的强度变化并伴随着裂隙的产生, 对工程结构安全有非常重要的影响, 研究膨润土的收缩性对工程安全具有重要意义。通过对膨润土开展恒温干燥收缩试验, 结合数字图像技术, 从干密度和掺砂率2个方面研究其对土体干燥收缩过程中水分蒸发、各向收缩应变和裂隙的影响。土体的干燥收缩过程可以分为减速阶段和残余阶段, 高干密度和高掺砂率土样在干燥收缩过程中失水更少、各向收缩应变更小、裂隙更少。通过扫描电镜试验观察得到高干密度和高掺砂率的土体在微观结构上更加均匀、密实, 孔隙明显减少。针对土样收缩特征模型的选取发现T&D模型数据拟合效果较好。试验表明提高掺砂率和干密度是减小膨润土收缩性的有效手段。
Abstract:Objective Bentonite is a special soil with obvious expansion and shrinkage, and its strength change caused by shrinkage, accompanied by the formation of fissure has significant impact on the safety of engineering structures.Thereby, investigation on the shrinkage of bentonite is of great importance to engineering safety.
Methods By carrying out the drying shrinkage test under constant temperature, combined with digital image technology, the effects of dry density and sand mixing rate on water evaporation, anisotropic strain and fissure during the drying shrinkage process of soil were studied.
Results The results showed that the drying shrinkage process of the soil can be divided into deceleration stage and residual stages. During shrinkage process, the higher the dry density and sand content ratio in soil sample, the less the water loss, the smaller the strain in each direction and the fewer the fissure created. The soil microstructure observed by scanning electron microscopy showed that the higher the dry density and sand content ratio, the more uniform and dense the soil microstructure, and the less the pores in soil. According to the selection of the soil sample shrinkage characteristic model, the T&D model has a better data fitting effect.
Conclusion Experimental results evidence that increasing the sand addition rate and dry density is an effective means to reduce the shrinkage of bentonite.
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Key words:
- bentonite /
- sand mixing rate /
- dry density /
- dry shrinkage /
- fissure
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图 2 不同掺砂率土样含水率曲线(a)和蒸发速率曲线(b)
1.5-T.初始干密度为1.5 g/cm3,未掺砂土样;1.5-10T.初始干密度为1.5 g/cm3,掺砂率为10%土样;1.5-20T.初始干密度为1.5 g/cm3,掺砂率为20%土样;1.5-30T.初始干密度为1.5 g/cm3,掺砂率为30%土样;1.5-50T.初始干密度为1.5 g/cm3,掺砂率为50%土样,下同
Figure 2. Moisture content curve (a) and evaporation rate curve (b) for soil samples with different sand content ratios
表 1 膨润土主要化学成分
Table 1. Main chemical components of bentonite
成分 SiO2 Al2O3 Fe2O3 MgO CaO Na2O K2O MnO TiO2 P2O5 wB/% 61.52 16.62 4.73 5.45 2.73 0.13 0.11 0.03 0.30 0.03 表 2 膨润土基本物理性质
Table 2. Basic physical properties of bentonite
密度/(g·cm-3) 液限/% 塑限/% 比表面积/(m2·g-1) 自由膨胀率/% 线缩率/% 缩限/% 体缩率/% 2.75 155.08 49.54 468.2 155.0 2.22 24.0 27.0 表 3 干密度1.5 g/cm3模型拟合参数
Table 3. Fitting parameters for soil sample with dry density of 1.5 g/cm3
掺砂率/% k0 k1 k2 k3 相关系数R2 0 0.710 95 -0.766 96 2.128 19 -0.976 89 0.997 57 10 0.615 34 -0.471 21 1.712 42 -0.771 90 0.999 30 20 0.658 48 -0.889 31 2.486 71 -1.349 52 0.999 45 30 0.735 41 -1.512 43 3.772 39 -1.949 72 0.999 41 50 0.564 69 -0.798 85 2.221 90 -0.947 26 0.998 14 注:k0, k1, k2, k3均为模型参数 -
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