开挖顺序对PBA地铁车站竖向土压力分布影响

Influence of Excavation Sequence on the Vertical Soil Pressure on PBA Subway Station

以北京地铁六号线PBA工法东四站为工程背景,分析了开挖顺序对小导洞和车站拱顶的竖向土压力分布的影响.结果表明:边导洞外侧拱脚竖向土压力约为内侧拱脚处的1.27倍,拱顶存在明显偏压现象,上下层边导洞外拱脚处竖向土压力分别约为土体自重应力1.1倍和1.2倍.中导洞竖向土压力受同层导洞开挖顺序影响,后施工的导洞其竖向土压力更大.拱顶竖向土压力主要受扣拱顺序影响,采用“先边后中”施工方案时,拱顶竖向土压力波动范围较大,边跨跨中竖向土压力最小约为自重应力0.77倍,拱与导洞相接部位竖向土压力最大约为自重应力1.05倍.

By taking the Dongsi PBA station of Beijing Metro Line 6 as an example,the influence of the excavation sequence on the distribution of the vertical earth pressure on the pilots and the station arches was analyzed respectively.The results show that soil pressure on the station arches is bias,and the vertical earth pressure at the arch feet of the outer side pilots is 1.27 times than that at the inner side pilots.The vertical earth pressure at the outer arch feet of the upper and lower side pilots is about 1.1 times and 1.2 times of the gravity stress respectively.The vertical earth pressure on the central pilots is affected by the excavation sequence of the pilots in the same level,and is larger on the later constructed pilots.The vertical earth pressure on the station arch is mainly affected by the construction sequence of the arches.In the“first edge and then middle pilot”construction plan,the vertical earth pressure on the crown arches of the station fluctuates as such that the vertical earth pressure on the side span can be as low as 0.77 times the gravity stress,while the vertical earth pressure at the junction of the arch and the central pilot can be as high as 1.05 times the gravity stress.