Development of miniature dynamic triaxial apparatus for microct scanning and its experimental verification
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摘要: 土体的微观结构对其宏观力学性质有着很大的影响,为了能更深入研究土体在循环荷载作用下的微观结构演化与其宏观力学特性之间的联系,研制了一种适用于工业显微CT(computerized tomography)扫描的微型动三轴仪。该仪器主要由控制采集箱系统、主机系统、气水转换器组成。其具有体积较小、试样小型化(直径×高=10 mm×20 mm)、便于操作、兼容性强等优点,可在无需改装已有CT设备前提下对试样进行旋转扫描。以丰浦砂干砂样为材料,采用微型和常规动三轴仪进行了不同围压(50,100,200,300 kPa)和循环荷载作用下的不固结不排水试验,并对测得的初始动弹性模量E0,动剪切模量Gd,阻尼比
λ 进行了对比分析。结果表明:微型动三轴仪测得的初始动弹性模量E0,动剪切模量Gd,阻尼比λ与常规动三轴仪测得的结果基本相近。试验结果误差较小,验证了该仪器的可靠性。Abstract: The microstructure of soil has a great influence on the macroscopic mechanical properties. Therefore, to study the relationship between the macroscopic mechanical properties and the microstructure evolution of soil under the cyclic loading, a miniature dynamic triaxial apparatus is developed, which is suitable for industrial micro CT (computerized tomography) scanning. The apparatus is mainly composed of the acquisition control system, loading device system, and air-liquid converter. It has the advantages of small volume, miniaturization of the specimen (diameter × height=10 mm×20 mm), convenient to operate, strong compatibility, and the specimen can be rotating-scanned without refitting the existing CT equipment. By using the miniature dynamic triaxial apparatus and conventional dynamic triaxial apparatus, a series of unconsolidated-undrained triaxial tests on Toyoura sand under cyclic loading and different confining pressures (50, 100, 200 and 300 kPa) are carried out, and the initial dynamic elastic modulus (E0), dynamic shear modulus (Gd) and damping ratio (λ ) are comparatively analyzed. The results show that the experimental curves of the initial dynamic elastic modulus (E0), dynamic shear modulus (Gd) and damping ratio (λ ) exhibit a similar evolution. The difference of experimental data is small, thus, the reliability of the miniature dynamic triaxial apparatus is verified. -
感谢张家港晟泰克智能仪器有限公司对微型动三轴仪的加工制作,及负责人蒋敏华,软件研发部门黄兴、邵斌斌,机械设计制作部门盛文佳、李志宏等对工作的协助和配合。感谢天津大学沈振义、庞红星、尹福顺和张仕伟硕士在论文修改中提出的宝贵意见。
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表 1 日本丰浦砂物理性能参数
Table 1 Physical parameters of Toyoura sand
试样 土粒相对密度Gs 平均粒径D50/mm 不均匀系数Cu 最大孔隙比emax 最小孔隙比emin 丰浦砂 2.65 0.2 1.32 0.977 0.597 表 2 试验方案
Table 2 Experimental schemes
序号 试验仪器 试样 干密度ρd/(g·cm-3) 频率f/Hz 围压 σ3 /kPa1 微型 丰浦砂 1.483 0.2 50,100,200,300 2 常规 丰浦砂 1.483 0.2 50,100,200,300 表 3 动剪切模量与动剪应变
Table 3 Dynamic shear modulus and dynamic shear strains
微型动三轴仪 常规三轴仪 相对误差/% 动剪应变γd/% 动剪切模量Gd/kPa 动剪应变γd/% 动剪切模量Gd/kPa 0.012 508 0.012 534.4 4.9 0.031 408 0.031 387.2 5.4 0.062 264.8 0.062 286.4 7.5 0.12 217.6 0.12 230 5.4 0.25 170 0.25 177.49 4.2 0.5 133.8 0.5 140.69 4.9 2 69.43 2 70.31 1.3 表 4 初始动弹性模量
Table 4 Initial dynamic elastic moduli
围压 初始动弹性模量E0/MPa 相对误差/% 微型动三轴仪 常规三轴仪 50 1.43 1.37 4.2 100 2.50 2.38 4.8 200 14.29 13.70 4.1 300 17.86 17.83 0.2 表 5 不同围压条件下阻尼比
Table 5 Damping ratios under different confining pressures
围压 阻尼比 λ 相对误差/% 微型动三轴仪 常规动三轴仪 50 0.2366 0.2349 0.6 100 0.2429 0.2527 3.8 200 0.2572 0.2745 6.3 300 0.2717 0.2831 4.0 -
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