Resilient and accumulative plastic deformation characteristics of subgrade lateritic soil under different loading modes and moisture content
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摘要: 为研究湿热多雨地区在役红黏土路基在不同动载条件及湿化作用下的回弹和累积塑性变形规律, 开展了不同含水率、加载方式、动应力幅值和围压的动三轴试验, 分析了单级、间歇、多级加载以及湿化幅度、应力水平对红黏土试样回弹应变、动回弹模量和累积塑性应变的影响。分析结果表明: 单级加载条件下回弹应变随加载次数的增加呈先快后慢的非线性衰减特征, 而累积塑性应变先快速增加后趋于稳定; 动应力幅值对红黏土回弹应变和累积塑性应变的影响随着含水率的增加而增大, 随着围压的增大而减小; 当含水率从最优含水率(OMC)提高到OMC+4.5%时, 回弹应变和累积塑性应变分别增加了2.99倍和59%, 当围压从30 kPa提高到90 kPa时, 回弹应变和累积塑性应变分别降低了52%和38%;基于结构元理论建立了考虑临界动应力不确定性的模糊多元回归模型, 模型可以较好地反映临界动应力与含水率、围压之间的关系; 在相同应力水平下, 多级加载方式下的累积塑性应变均低于单级加载, 第1级低应力水平加载作用使第2、3、4级加载后的累积塑性应变大幅降低; 当动偏应力低于30 kPa时, 单级加载和间歇加载的回弹和累积塑性应变差异较小, 当动偏应力高于90 kPa时, 单级加载作用下的塑性应变显著高于间歇加载。研究结果可为红黏土地区路基韧性设计和长期服役性能评价提供借鉴。Abstract: To investigate the resilient and accumulative plastic deformation laws of in-service lateritic soil subgrades in humid and rainy areas under different dynamic load conditions and wetting effects, dynamic triaxial tests were conducted under different moisture content, loading modes, dynamic stress amplitudes, and confining pressures. The influences of the single-stage, intermittent, and multi-stage loading, wetting amplitude, and stress level on the resilient strain, dynamic resilient modulus, and accumulative plastic strain of lateritic soil samples were analyzed. The analysis results indicate that under single-stage loading conditions, the resilient strain exhibits a characteristic of nonlinear decay which is fast first and then slow with the increase of loading times, while the accumulative plastic strain shows a rapid increase first and then tends to stabilize. The effect of dynamic stress amplitude on the resilient strain and accumulative plastic strain of lateritic soil increases with the increase of moisture content and decreases with the increase of confining pressure. When the moisture content increases from the optimum moisture content (OMC) to OMC+4.5%, the resilient strain and accumulative plastic strain increase by 2.99 times and 59%, respectively. When the confining pressure increases from 30 to 90 kPa, the resilient strain and accumulative plastic strain decrease by 52% and 38%, respectively. A fuzzy multiple regression model considering the uncertainty of critical dynamic stress was established based on the structural element theory, which can well reflect the relationships of critical dynamic stress with moisture content and confining pressure. The accumulative plastic strain under multi-stage loading is lower than that under single-stage loading at the same stress level. The low-stress-level loading in the first stage significantly reduces the accumulative plastic strain after the second, third, and fourth stages of loading. When the dynamic deviatoric stress is below 30 kPa, the differences in resilient and accumulative plastic strain between single-stage loading and intermittent loading are small. When the dynamic deviatoric stress is higher than 90 kPa, the plastic strain under single-stage loading is significantly higher than that under intermittent loading. The research results can provide a reference for the toughness design and long-term service performance evaluation of subgrades in lateritic soil areas.
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表 1 红黏土的基本物理性质
Table 1. Basic physical properties of lateritic soil
液限/% 塑限/% 塑性指数 最优含水率/% 55.3 33.4 21.9 18.8 最大干密度/ (g·cm-3) 粒径小于0.075 mm颗粒质量分数/% 粒径小于0.005 mm颗粒质量分数/% 1.65 85.55 33.37 表 2 单级加载试验工况
Table 2. Test conditions of single-stage loading
含水率/% 动应力/kPa 围压/kPa 频率/Hz 振次 18.8 30、50、70、90、300、320 30 1 1.0×104 20.3 30、50、70、90、250、260 21.8 30、50、70、90、230、240 23.3 30、50、70、90、200、220 18.8 30、50、70、90、330、340 50 20.3 30、50、70、90、280、290 21.8 30、50、70、90、250、260 23.3 30、50、70、90、220、240 18.8 30、50、70、90、360、380 70 20.3 30、50、70、90、300、320 21.8 30、50、70、90、270、290 23.3 30、50、70、90、240、260 18.8 30、50、70、90、380、400 90 20.3 30、50、70、90、340、360 21.8 30、50、70、90、300、320 23.3 30、50、70、90、260、280 表 3 间歇加载试验工况
Table 3. Test conditions of intermittent loading
含水率/% 围压/ kPa 动应力/ kPa 频率/ Hz 间歇时长 振次 18.8、20.3、21.8、23.3 30 30、50、70、90 1 每加载2 000 s间歇900 s 1.0×104 表 4 多级加载试验工况
Table 4. Test conditions of multi-stage loading
含水率/% 围压/kPa 动应力/kPa 频率/Hz 振次 18.8、20.3、21.8、23.3 30 30→50→ 70→90 1 每级1.0×104次,总计4.0×104次 表 5 临界动应力模糊数据的范围
Table 5. Range of fuzzy data for critical dynamic stress
含水率/% 不同围压(kPa)下临界动应力模糊数据范围/kPa 30 50 70 90 18.8 [300, 320) [320, 340) [340, 360) [360, 380) 20.3 [250, 260) [260, 280) [280, 300) [300, 320) 21.8 [230, 240) [240, 260) [260, 280) [280, 300) 23.3 [200, 220) [220, 240) [240, 260) [260, 280) -
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