汉源大渡河大桥巨厚砂层大直径灌注桩施工技术

Construction of large diameter bored piles in massive sand formation for a Dadu River Bridge

摘要:

汉源大树大渡河大桥2号桥墩12根钻孔灌注桩，钻孔直径2500 mm，钻孔深度为63~75 m不等，桩径大，桩孔深，属于河水位以下的巨厚砂层桩基，具有一定的施工难度。2号墩基岩上覆覆盖层存在多层砂土及卵石夹土（质土），且砂层巨厚，在11.5~49.4 m之间除厚5.5 m的卵石夹土外均为砂土，对桩基成孔施工极为不利。采用冲击钻进成孔，泥浆净化除渣系统，通过对钻头直径的控制、内护筒的使用、灌注时导管埋深的控制等措施，确保了工程的顺利完工。相关技术措施可为其他类似工程提供借鉴。

Abstract:

The 12 bored piles for the 2^# pier of the Dashu Dadu River Bridge in Hanyuan county have a diameter of 2500mm and a depth of 63~75m， posing some construction difficulty due to large diameter and great depth and drilling in massive sandy gravel formation below the river water level. There are multiple layers of sand and pebble soil overlying the bedrock at the 2^# pier， and the sand layer is very thick. Sandy soil prevails between 11.5~49.4m except for a layer of 5.5m thick gravel cobble with soil inclusion， which is very disadvantageous to drilling of pile boreholes. Percussion drilling was used to sink the holes with the mud purification device to remove cuttings； meanwhile， some technical measures were adopted to ensure successful completion of the works， such as control of the bit diameter， use of the inner casing， control of the tremie pipe buried depth during concreting. The relevant technical measures can provide reference for other similar projects.