An experimental study of the dynamic characteristics of cement soils subjected to staged cyclic loading
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摘要:
随着车辆载重的变化，其荷载幅值也会随之变化。然而，已有的研究大多关注恒定动荷载下水泥土动力特性，对分级循环荷载作用下水泥土的动态特性研究较少。利用GDS动三轴仪，开展一系列水泥土动三轴试验，探讨分级荷载条件下静偏应力和围压等因素对水泥土动力特性的影响。试验结果表明：水泥土的轴向塑性应变随着围压和静偏应力比的增加而增加。水泥土轴向应变在0.1%～0.5%范围，其应变发展属于稳定型，分级加卸载对应变发展过程影响较大，对最终应变影响较小。建立了考虑水泥土加卸载条件、围压和静偏应力比的塑性应变的经验模型，分级卸载的相关系数大于0.95，而分级加载的相关系数在0.8～0.9之间。分级卸载时，第一级荷载对应变发展起主导作用，而分级加载时，最大动应力比无法主导前几级荷载较小时的应变发展。在分级加卸载条件下，水泥土的骨干曲线表现为2种模式：上升型和下降型，可将其简化为多段直线，利用建立的累积塑性应变计算方法，提出了确定多段直线分界点的方法，并验证了其可行性。
Abstract:With the change in vehicle loading, the load amplitude will also change. However, most of the existing studies focused on the dynamic characteristics of cement soil under the constant dynamic loading, and the dynamic characteristics of cement soil under staged cyclic loading were seldom examined. Using the GDS dynamic triaxial apparatus, a series of dynamic triaxial tests of cement soil are carried out to investigate the influence of static deviator stress and confining stress on the dynamic characteristics of cement soil. The results show that the axial plastic strain of cement soil increases with the increasing confining stress and static deviator stress ratio. The axial strain of cement soil is in the range of 0.1%～0.5%, and its strain development belongs to a stable type. The staged loading and unloading have a great influence on the development process of the plastic strain of the cement soil, but have little influence on the ultimate strains. The empirical model of plastic strain considering loading and unloading conditions, confining stress and static deviator stress ratio is established. The correlation coefficient of staged unloading is greater than 0.95, while that of staged loading is between 0.8 and 0.9. The results show that the first stage load plays a leading role in the strain development, while the maximum dynamic stress ratio cannot dominate the strain development when the first stage load is small. Under the condition of staged loading and unloading, the backbone curve of the cement soil shows two modes: ascending type and descending type, which can be simplified as a multi-segment straight line. Based on the established cumulative plastic strain calculation method, a method to determine the dividing point of the multi segment straight line is proposed, and its feasibility is also verified. The research results lay a foundation for systematic analyses of the dynamic mechanical properties of cement soil under traffic loading.
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Key words:
- staged cyclic loading /
- dynamic triaxial tests /
- cement soil /
- plastic strain /
- backbone curve /
- empirical model
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表 1 水泥土动三轴试验方案
Table 1. Dynamic triaxial test scheme of cement soil
试验编号 围压/kPa 加载方式 静偏应力比 D1 40 分级加载 0.00 D2 60 分级加载 0.00 D3 80 分级加载 0.00 D4 40 分级卸载 0.00 D5 60 分级卸载 0.00 D6 80 分级卸载 0.00 D7 80 分级加载 0.15 D8 80 分级加载 0.20 D9 80 分级加载 0.25 D10 80 分级卸载 0.15 D11 80 分级卸载 0.20 D12 80 分级卸载 0.25 
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表 2 不同围压下累积应变
Table 2. Cumulative strain under different confining stresses
/% 加载方式 围压/kPa 动应力比 0.25 0.30 0.35 0.40 0.45 0.45 0.40 0.35 0.30 0.25 加载 40 0.174 0.192 0.207 0.216 0.228 卸载 40 0.203 0.218 0.225 0.229 0.232 加载 60 0.224 0.241 0.253 0.261 0.267 卸载 60 0.246 0.255 0.260 0.266 0.270 加载 80 0.275 0.289 0.307 0.326 0.336 卸载 80 91.200 0.326 0.332 0.336 0.340
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表 3 不同静偏应力下累积应变
Table 3. Cumulative strains under different static deviator stresses
/% 加载方式 静偏应力比 动应力比 0.25 0.30 0.35 0.40 0.45 0.45 0.40 0.35 0.30 0.25 加载 0.00 0.275 0.289 0.307 0.326 0.336 卸载 0.00 0.310 0.326 0.332 0.336 0.340 加载 0.15 0.315 0.329 0.345 0.357 0.379 卸载 0.15 0.348 0.364 0.374 0.379 0.383 加载 0.20 0.347 0.356 0.367 0.391 0.400 卸载 0.20 0.385 0.397 0.402 0.403 0.404 加载 0.25 0.361 0.378 0.399 0.419 0.444 卸载 0.25 0.409 0.427 0.432 0.434 0.443
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表 4 水泥土累积塑性应变拟合参数
Table 4. Fitting parameters of the cumulative plastic strain modes of cement soil
编号 a1 a2 a3 a4 D1 2.49 N/A 0.41 0.093 D2 2.49 N/A 0.64 0.089 D3 2.49 N/A 0 0.091 D4 2.21 N/A 0.35 0.070 D5 2.21 N/A 0.27 0.068 D6 2.21 N/A 0 0.074 D7 2.49 3.16 0 0.055 D8 2.49 2.70 0 0.057 D9 2.49 1.67 0 0.080 D10 2.21 1.57 0 0.057 D11 2.21 1.48 0 0.032 D12 2.21 0.68 0 0.038
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