Dynamic Characteristics of Silt Considering Time Intermittent Effect
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摘要: 列车荷载是揭示路基真实动力响应特性的前提，以往的动三轴试验将列车荷载视为连续动荷载，忽略了追踪列车间隔时间对路基土体动力特性的影响. 利用室内动三轴仪对粉土开展了连续加载和间歇加载（连续加载与间歇交替循环）的动三轴试验，分析了两种加载方式下粉土超孔隙水压力、回弹模量、累积塑性应变等的发展规律. 研究结果表明：持续动荷载作用下累积的超孔隙水压力在间歇阶段会发生消散，轴向应变在间歇阶段得到一定程度恢复，进而提高了试样抵抗变形的能力；室内动三轴试验忽略间歇效应将高估列车动荷载作用下试样超孔压和塑性应变的累积量及发生破坏的可能性；间歇加载下试样的永久变形行为可依据安定理论划分为塑性安定、塑性蠕变和增量破坏.Abstract: Train dynamic load is the premise to reveal the real dynamic response characteristics of subgrade. The train load is regarded as a continuous dynamic load in previous cyclic triaxial tests without considering the time intermittent effect. Dynamic triaxial tests of silt under continuous loading and intermittent loading (continuous loading and intermittent alternating circulation) were carried out by using indoor dynamic triaxial apparatus, and the development laws of excess pore water pressure, modulus of resilience and accumulated plastic strain of silt under two loading modes were analyzed. The accumulated excess pore water pressure under continuous dynamic load will dissipate in the intermittent stage, and the axial strain will be restored to a certain extent in the intermittent stage, thus improving the ability of the sample to resist deformation. Ignoring intermittent effect in indoor dynamic triaxial tests will overestimate the cumulative amount of excess pore pressure and plastic strain and the possibility of failure. The permanent deformation behavior of specimens under intermittent loading can be divided into plastic stability, plastic creep, and incremental failure according to stability theory.
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图 2 DDS-70微机控制动三轴仪
Figure 2. DDS-70 microcomputer controlled dynamic triaxial apparatus
图 4 连续加载轴向应变时程曲线
Figure 4. Time history curves of axial strain under continuous loading
图 5 连续加载条件下超孔压时程曲线
Figure 5. Time-history curves of overpressure under continuous loading
图 6 间歇加载下轴向应变时程曲线
Figure 6. Time history curves of axial strain under intermittent loading
图 7 间歇加载条件下超孔压时程曲线
Figure 7. Time history curves of excess pore water pressure under intermittent loading
图 9 回弹模量Mr随振次的变化曲线
Figure 9. Variation curves of rebound modulus Mr with vibration frequency
图 10 累积塑性应变随振次的变化
Figure 10. Variation of cumulative plastic strain with vibration frequency
图 11 间歇加载下应变随时间的关系
Figure 11. Relationship between strain and time under intermittent loading
图 12 加载阶段累积的塑性应变与间歇阶段的回弹应变情况
Figure 12. Cumulative plastic strain in loading stage and rebound strain in intermittent stage
图 13 间歇加载方式下累积塑性应变随循环振次关系曲线
Figure 13. Relationship curves between cumulative plastic strain and cyclic vibration times under intermittent loading
图 14 不同动力行为临界应力的估算公式
Figure 14. Estimation formula of critical stress for different dynamic behaviors
表 1 低液限粉土的基本物理参数
Table 1. Basic physical parameters of silt with low liquid limit
颗粒密度/（g•cm−3） 最大干
密度/（g•cm−3）最优
含水率/%饱和
含水率/%塑限/% 塑性
指数渗透系数k/（cm•s−1） 2.71 1.96 11.80 19.75 18.2 7.8 1.238 × 10−7 
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表 2 动三轴试验方案
Table 2. Test scheme of dynamic triaxial
kPa 试验序列 试验类型 σ3 σd 1 连续加载 60 30，60 2 30 30，60，90 3 分阶段循环加载 60 30，60，90，120 4 90 30，60，90，120，150
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