北京地铁14号线暗挖隧道下穿某大型桥梁桥区群桩，对桥梁的沉降控制要求非常严格，安全风险很大。砂卵石地层地铁暗挖隧道穿越桥桩时，分别对“采用”和“不采用”复合锚杆桩2种情况，对整个实施过程中的监测数据进行对比和分析，得出在砂卵石地层下，复合锚杆桩虽然能对桥桩起保护作用，但施工本身也会导致桥梁沉降，因此，应根据砂卵石地层情况决定是否采用复合锚杆桩，以免造成不必要的浪费。

A mined tunnel of Line 14 of Beijing Metro runs underneath the group piles of a large scale bridge. The group piles of the bridge are located in sandy cobble ground and there is strict requirement on the settlement of the bridge. Therefore, there are great risks in the construction of the mined tunnel. Most of the group piles are consolidated by composite bolt piles, while 2 group piles are not consolidated by composite bolt piles. Analysis is made on these two cases and conclusion is drawn that in sandy cobble ground, although the composite bolt piles can protect the bridge piles, the installation of the composite bolt piles can induce settlement to the bridge. It is proposed that whether composite bolt piles should be installed or not shall be determined according to the conditions of the sandy cobble ground so as to avoid unnecessary waste.