浸水环境下重载铁路改良土路基动力特性研究

浸水入渗与重载列车动载耦合作用下路基的动力响应程度更突出，对行车安全及路基长期稳定提出更严要求。为揭示重载列车动载作用下干燥与浸水路基的动力特性，依托浩吉（浩勒报吉－吉安）重载铁路工程背景，开展循环加载400万的现场激振试验，利用激振设备和配重块组合模拟了轴重25～30 t、速度120 km/h列车动载作用。试验结果表明：路基干燥与浸水状态下，动应力与加速度沿路基深度变化趋势吻合，传至基床底层底面衰减量可达80%；浸水入渗与列车动载的加剧作用更多体现在基床表层与底层的衔接处，相同荷载条件下，衔接处浸水路基的动应力最大可提高28%；相较而言，加速度受浸水环境影响的敏感性远低于动应力；对比可知，沿路基深度范围内动应力水平远小于同位置填料的临界动应力，试验结束路基面累积变形小于5 mm，且呈收敛趋势，说明无论从动强度还是动变形角度来评估，水泥掺量3%～5%改良膨胀土用作基床底层及以下路堤填料时均能满足稳定需求。该研究成果能够对重载铁路改良膨胀土路基的精细化建设养修提供理论参考。

Study on dynamic characteristics of cement-stabilized expansive soil subgrade of heavy-haul railway under immersed environment

The dynamic characteristics of subgrade is aggravated under the interaction of immersed infiltration and dynamic loads of trains, which affects the safety of train operation and long-term stability. Based on the engineering background of cement-stabilized expansive soil subgrade of Hao-Ji heavy-haul railway(Haolebaoji-Ji'an), field excitation tests of subgrade with four million cycles were carried out under dry and immersed conditions to investigate the dynamic characteristics. Large-scale excitation equipment, combined with dead weights, were used to simulate the dynamic behavior of heavy-haul trains with 25-30 t axle load. The test results show that the variations of dynamic stress and acceleration along the depth of subgrade are consistent, and decay rate is 80% at the base of subgrade. The influence of immersed infiltration and dynamic load of train is more significant at the interface of between the subgrade bottom and fill. Under the same loading conditions, the dynamic stress at the interface under the immersed condition is 28% larger than for the dry condition. The acceleration is much less sensitive to the immersed environment than the dynamic stress. At the same time, the dynamic stress level along subgrade depth is much lower than the critical dynamic stress of fill in the same location. The cumulative deformation of subgrade surface under cyclic loading of 4 million times is less than 5 mm and remains stable, which indicates that the improved expansive soil with 3%-5% cement content can be used as the subgrade bottom and fill to meet the dynamic stability requirements of subgrade. The research results can provide theoretical reference for high-quality construction and aintenance of expansive soil roadbed improved by heavy-haul railway.