预应力锚索锚固效应动态模型试验

为了解既有列车振动荷载对锚索预应力损失、地表沉降及桩体水平位移的影响，以京石高铁石家庄六线隧道明挖深大基坑桩、锚围护结构为工程背景，根据相似关系，试验确定了土体-桩锚系统模型试验材料；针对列车振动荷载特点，开展了基坑开挖完成后连续振动162 d（相似关系）的模型试验，分析了振动频率分别为8.282，13.801，20.704 Hz时锚索预应力的损失规律、地表沉降、桩体水平位移以及锚索预应力随锚固深度变化的特点。试验结果表明：随着振动频率（列车行车速度）的增加，锚索预应力损失率、最终地表沉降值和桩体水平位移均大幅增加； 8.282 Hz频率（行车速度120 km·h^-1） 下振动28 d，锚索预应力平均损失率为2%；13.801 Hz频率 （行车速度200 km·h^-1） 下振动53 d，锚索预应力平均损失率为8%；20.704 Hz频率（行车速度300 km·h^-1）下振动53 d，锚索预应力平均损失率高达23%；锚固段锚索应力沿锚索锚固深度呈喇叭状开口递减趋势，接近锚固段底部时，其应力几乎为0。通过动态模型试验，掌握了列车振动荷载作用下锚索预应力随时间的损失规律，对临近铁路深大基坑锚索设计与施工具有理论指导意义。

Dynamic Model Test on Anchoring Effect of Prestressed Anchor Cables

In order to determine the influence of train vibration load on the prestress loss of anchor cables and the subsidence and horizontal displacement of the pile-taking the deep foundation pit pile-anchor retaining structure in the open-cut section of the Shijiazhuang six line-tunnel as engineering background-the materials of the soil-pile anchor system were determined in model tests based on the similarity relation. According to the vibration characteristics of the train load, model test with continuous vibration for 162 days (similarity) after foundation excavation was carried out. The law of prestress loss in anchor cables, the subsidence and horizontal displacement of the pile under different vibration frequencies, and the effect of anchor depth on prestress loss were analyzed when vibration frequencies were 8.282, 13.801, 20.704 Hz. Test results reveal that the prestress loss of anchor cables and the subsidence and horizontal displacement of the pile greatly increased with the increase of vibration frequency. The average loss rate of prestressed anchor cable is 2% when driving for 28 days (prototype) continuously at the speed of 120 km·h^-1. The average loss rate increases to 8% and 23% when driving for 53 days (prototype) continuously at the speed of 200 km·h^-1 and 300 km·h^-1, respectively. The prestress loss of anchor cables in the anchorage section decreased along the anchorage depth of the anchor cables; the prestress is almost zero at the bottom of the anchorage section. The dynamic model test result reveals the effect of traveling speed on the prestress of anchor cables and the subsidence and horizontal displacement of the pile. The prestress loss of anchor cables under the train load is known according to the dynamic model test, which can reference for the design and construction of anchor cables in deep and large foundation pits near railways.