Experimental Study on Dynamic Strength of Subgrade Loess under Continuous and Intermittent Loads
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摘要:
列车在运行过程中产生的周期性动应力对路基填料的动强度构成了显著挑战，现有研究多采用连续加载方式模拟列车荷载，未能充分反映列车荷载的间歇性，为探究连续、间歇加载下黄土路基的动强度差异性，采用GDS 动三轴仪设计一系列连续和间歇加载的固结不排水试验，探讨围压和动应力幅值对土体动强度的影响，并对比分析不同加载方式对路基黄土动强度及其强度参数的作用效果. 试验结果表明：黄土路基的动强度随着围压的增大而增大，但增长幅度却逐渐减小；动粘聚力（
c d）和动摩擦角（$ {\varphi _{\text{d}}} $）随破坏次数（lgN f）的增大而减小，整体呈线性关系；相对于连续加载，间歇加载作用下土体的c d和$ {\varphi _{\text{d}}} $有明显提升，c d提高了2.18%～5.09%，$ {\varphi _{\text{d}}} $提高了4.03%～13.78%；通过引入静三轴抗剪强度对动强度进行归一化处理，提出以静强度为变量的黄土路基动强度经验公式，为评估路基在动力作用下的稳定性提供了重要依据.Abstract:The cyclic dynamic stress generated during train operation presents a significant challenge to the dynamic strength of subgrade fill materials. Existing research has mostly simulated train loads using continuous loading methods, which fails to fully reflect the intermittency of these loads. To investigate the differences in dynamic strength of loess subgrade under continuous and intermittent loading, a series of consolidated undrained tests under continuous and intermittent loading conditions were conducted using a GDS dynamic triaxial apparatus. The influences of confining pressure and dynamic stress amplitude on the dynamic strength of the soil were examined. The effects of different loading methods on the dynamic strength and strength parameters of the subgrade loess were compared. The experimental results indicate that the dynamic strength of the loess subgrade increases with higher confining pressure, but the growth rate diminishes gradually. Both dynamic cohesion (
c d) and dynamic friction angle ($ {\varphi _{\text{d}}} $) decrease with the increase in the failure cycles (lgN f), showing an overall linear relationship. Under intermittent loading, the soil exhibits a marked increase inc d and$ {\varphi _{\text{d}}} $compared to continuous loading, withc d increasing by 2.18%–5.09% and $ {\varphi _{\text{d}}} $ by 4.03%–13.78%. By normalizing the dynamic strength using the static triaxial shear strength, an empirical formula for the dynamic strength of the loess subgrade based on static strength is proposed, which provides a critical basis for assessing the stability of the subgrade under dynamic loads.-
Key words:
- subgrade loess /
- continuous loading /
- intermittent loading /
- dynamic strength /
- static strength
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图 7 不同围压下土体动强度曲线
Figure 7. Dynamic strength curves of soil under different confining pressures
图 9 不同Nf及加载方式对应动强度的应力强度指标
Figure 9. Stress strength indexes corresponding to dynamic strength for different Nf
图 10 动黏聚力与动内摩擦角随破坏次数的变化关系
Figure 10. Relationship between dynamic cohesion and dynamic internal friction angle with number of damage
表 1 土的物理参数指标
Table 1. Indicators of physical parameters of soil
Gs wopt/% ${\rho _{d\max }}$/（g•cm−3） WL/% WP/% IP 2.72 19.1 1.85 37.4 21.2 16.2 
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表 2 试验方案
Table 2. Experimental program
${\sigma _3}$/kPa ${q_{\text{f}}}$/kPa CCSR ${\sigma _{\text{d}}}$/kPa 加载方式 30 440.51 0.7、0.75、0.8、0.85、0.9 308.35、330.38、352.40、374.43、396.459 连续加载（加载到 10000 次或应变达到10%时结束）60 564.73 0.6、0.65、0.7、0.75、0.8 338.83、367.07、395.31、423.54、451.78 90 632.16 0.55、0.6、0.65、0.7、0.75、 347.68、379.29、410.90、442.51、474.12 30 440.51 0.8、0.85、0.9、0.93、0.95 352.40、374.43、396.45、409.67、418.48 间歇加载（每一阶段振动200次，停振600 s，加载到 10000 次或应变达到10%结束）60 564.73 0.7、0.75、0.8、0.85、0.9 395.31、423.54、451.78、480.02、508.25 90 632.16 0.6、0.7、0.75、0.8、0.85 379.29、442.51、474.12、505.72、537.33
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表 3 动强度值及拟合参数表
Table 3. Dynamic strength values and fitting parameters
加载方式 ${\sigma _3}$/kPa ${\sigma _{{\text{d,}} 100}}$/kPa A d R2 连续加载 30 344.49 436.6573 0.035 0.9795 60 418.08 546.5850 0.048 0.9825 90 456.29 602.2356 0.047 0.9897 间歇加载 30 368.28 440.5294 0.0512 0.9888 60 451.42 563.4870 0.0581 0.9981 90 493.03 624.9116 0.0602 0.9671
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表 4 不同破坏次数对应的抗剪强度指标
Table 4. Shear strength indexes corresponding to different numbers of damage
加载方式 Nf/次 $ {c_{\text{d}}} $/kPa $ {\varphi _{\text{d}}} $/（°） 连续加载 20 88.48 27.53 100 84.04 24.83 500 79.82 22.08 2000 76.36 19.66 间歇加载 20 90.41 28.64 100 86.72 26.48 500 83.18 24.29 2000 80.25 22.37
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