列车荷载作用下风积沙包芯路基动力响应试验研究

Experimental research on dynamic response of aeolian sand cored subgrade under train load

我国沙漠铁路沿线优良填料极其匮乏而风积沙资源相对丰富,但风积沙存在级配不良、结构松散等缺陷,不宜直接用作基床填料。风积沙包芯路基兼顾经济环保与力学性能,就地取用沿线风积沙填筑基床底层,取用卵石土对其包边封层。通过对风积沙包芯路基开展现场实车动测,获得路基动响应与振动能量的空间分布特征以及随轴重和车速的变化规律。研究结果表明:路基动应力沿深度的衰减主要集中于路基面以下0~0.6 m和1.5~2 m范围内,加速度沿边坡的衰减主要在距轨道中心5 m范围内。动应力和加速度幅值均随轴重和车速的提高明显增大,衰减速率随轴重的增加而降低。动应力频谱服从倍频规律和幅值调制效应,0~2 Hz的低频振动对动应力起控制作用。加速度振级集中分布于12.5~31.5 Hz中心频段内,0~10 Hz的低频段振级沿边坡衰减剧烈,10~40 Hz高频段振级的衰减相对较小。振动总能量沿路堤边坡耗散近80%,总能量在各频带上的聚集量:频带2>频带1>频带3>频带4。各频带能量均随轴重和车速的增加而增大,增长幅度随频带的提高逐级递减。研究成果可以为沙漠铁路路基工程的后续建管标准与运维实践提供参考。

Coarse-grained soil fillers are extremely scarce along railways in the desert areas in China.However,there is abundant aeolian sand.Because aeolian sand has defects including being bad-graded and having open grains,it is not suitable to direct use as subgrade fillers.The aeolian sand-cored subgrade takes into account the economic,environmental protection and mechanical properties,it uses aeolian sand along the railway to fill the bottom layer of subgrade,and uses pebble soil to wrap the subgrade slope.By conducting dynamic tests on the novel subgrade,the spatial distribution characteristics of dynamic response and vibration energy of the subgrade and their changes with the train axle load and train speed were obtained.Results are shown as follows.(1)Attenuation of the dynamic stress on the subgrade with the depth is mainly concentrated in ranges of 0~0.6 m and 1.5~2 m below the subgrade surface.Attenuation of the acceleration along the slope is mainly observed in the range 5 m from the track center.The dynamic stress and acceleration amplitude both grow obviously with the increase in the axle load and train speed,while the attenuation rate reduces with the growing axle load.(2)The amplitude spectrum of dynamic stress follows the octave characteristic and the amplitude modulation effect,and the low-frequency vibration at 0~2 Hz exerts a control effect on the dynamic stress.The vibration acceleration level(VAL)is concentrated in the central frequency band of 12.5~31.5 Hz.The VAL in the low-frequency range of 0~10 Hz attenuates violently along the slope,while the VAL in the high-frequency range of 10~40 Hz attenuates slightly.(3)Almost 80%of the total vibration energy is dissipated along the subgrade slope.According to the aggregation quantity of total vibration energy in each frequency band,the frequency bands are listed in a descending order as frequency bands 2,1,3,and 4.The energy in each frequency band always grows with the increases in the axle load and train speed while the growth rate decreases progressively with the increase of frequency from frequency band 1 to frequency band 4.