A STUDY ON DYNAMIC CHARACTERISTICS OF SANDSHALE ELUVIAL LATERITE AT KUNMING CHANGSHUI INTERNATIONAL AIRPORT
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摘要: 昆明长水国际机场残积红土既是区域内重要的土地资源，更是各类工程建设的建筑地基，由于裂化特性，在现代气候条件下，红土出现了严重的开裂变形，其工程性质不断恶化。文章针对昆明长水国际机场砂页岩残积红土开展了一系列固结不排水动三轴试验分析研究。变形试验结果表明：砂页岩残积红土在某一次循环动应力中存在屈服应变；在相同的应变水平下，动弹性模量随着固结围压的增大而增大；同时砂页岩残积红土的阻尼比在动应变小幅度的增加时会发生骤降，并随着动应变的增加逐渐趋平。同时通过动强度试验得出砂页岩残积红土破坏动强度随着固结围压的增大而增大，并得到砂页岩残积红土在固结比Kc=1时的动抗剪强度指标，即cd=25.182 kPa，φd=12.985°，将其与固结不排水的静三轴试验下得出的抗剪强度指标进行了对比与分析。红土在动力作用下的剪切破坏实质是其土体中的弱结合水大量丧失，导致其颗粒之间的粘结力降低，从而内部单元体产生了相对位移。该研究成果对红土系统深入研究及工程实践应用具有重大的指导意义。Abstract: The eluvial laterite of Kunming Changshui International Airport is not only an important land resources in the region, but also the construction foundation for a variety of engineering construction. Due to the cracking characteristics, the laterite is seriously cracked and deformed under the modern climatic conditions, and its engineering properties are deteriorating. A series of consolidated undrained dynamic triaxial tests were carried out on sandshale eluvial laterite at Kunming Changshui International Airport. The results of deformation tests show that the eluvial laterite of sandshale has yield strain in a cyclic dynamic stress; the dynamic elastic modulus would increase with the growing of the consolidation confining pressure at the same strain level; moreover, the damping ratio of the eluvial laterite in sandshale would decrease sharply when the dynamic strain increases slightly, and level off gradually with the growing of dynamic strain afterwards. The dynamic strength tests show that he dynamic failure strength of the eluvial laterite in sandshale would increase with the growing of consolidation confining pressure, and the dynamic shear strength index of the eluvial laterite in sandshale at consolidation ratio Kc=1 could is obtained (that is cd=25.182 kPa and φd=12.985°), which was compared and analyzed with the shear strength index obtained under the consolidated undrained static triaxial test. In fact, the shear failure of laterite under dynamic action is due to the loss of a large amount of weakly bound water in its soil, which leads to the reduction of the cohesive force between its particles, resulting in the relative displacement of the internal units. Combined with the features of the earthquake in Kunming, the obtained research results on the dynamic characteristics of the eluvial laterite in sandshale have great guiding significance for the in-depth study of the laterite system and engineering practice.
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图 1 试样不同围压下动应力-动应变曲线(固结比Kc=1)
Figure 1. The dynamic stress-dynamic strain curves of the samples under different confining pressure
图 2 红土试样在不同围压下1/Ed-εd关系曲线
Figure 2. 1/Ed-εd relation curves of the eluvial laterite samples under different confining pressure
图 3 红土试样在100 kPa围压下Ed-εd关系曲线
Figure 3. Ed-εd relation curves of the eluvial laterite samples under confining pressure of 100 kPa
图 4 试样参数a与围压σc的拟合直线
Figure 4. The fitting straight line of the sample parameter a and the confining pressure σc
图 5 试样参数b与围压σc的拟合直线
Figure 5. The fitting straight line of the sample parameter b and the confining pressure σc
图 6 红土试样不同围压下阻尼比-动应变的关系散点图
Figure 6. The relation scatter diagram of the damping ratio-dynamic strain of the laterite samples under different confining pressure
图 8 昆明长水国际机场砂页岩残积红土动抗剪强度包络线(Kc=1)
Figure 8. The dynamic shear strength envelope curves of the eluvial laterite in sandshale at Kunming Changshui International Airport when Kc=1
表 1 昆明长水国际机场砂页岩残积红土的基本物理力学性质指标
Table 1. The basic physical mechanical property indexes of the eluvial laterite in sandshale at Kunming Changshui Airport
基本试验指标 界限含水率 抗剪强度指标 粒度成分特征值 密度ρ/(g/cm3) 含水率ω/% 土粒比重Gs 孔隙比e 液限ωL/% 塑限ωp/% 塑性指数Ip/% 液性指数IL 粘聚力c/kPa 内摩擦角φ/(°) 粉粒 黏胶粒 胶粒 0.075~0.005 0.005~0.002 < 0.002 1.42 41 2.83 1.81 69 38 31 0.1 72.708 11.875 83 5 4 
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表 2 昆明长水国际机场砂页岩残积红土固结不排水动三轴试验方案
Table 2. Dynamic triaxial test scheme for the eluvial laterite in sandshale without drainage at Kunming Changshui Airport
试验类型 变形试验 强度试验 组数 一 二 三 四 五 六 七 八 九 试样编号 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 施加的固结围压/kPa 100 200 300 100 200 300 施加的动应力/kPa 分级施加(50~300) 110 115 125 160 180 200 220 240 260 设定的振动次数/次 每级振动7次 振动300次
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表 3 不同固结围压下参数a和b的值
Table 3. The values of parameter a and b in equation (1)
参数 围压/kPa 100 200 300 a 0.01477 0.00764 0.00427 b 0.03678 0.03457 0.0312
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