不良地质条件下旋挖桩施工风险管控与效果分析

Risk Management and Effectiveness Analysis to Construction of Rotary Bored Piles under Adverse Geological Conditions

分析在淤泥层、深厚饱和砾砂层、强风化岩夹层及孤石等不良地质条件下旋挖钻进大口径灌注桩所面临的孔壁坍塌、涌砂、孔底沉渣严重、入岩界面判定困难、钢筋笼制作安装定位及混凝土灌注量偏差大等施工安全与质量风险。设计了基桩施工前做好超前施工勘察钻孔方案。结合岩土工程勘察资料、旋挖桩工艺性试验桩结果,提出了采用无套管静泥浆反压护壁、泥浆反循环洗孔、泥沙分离等工艺手段,做到了钻孔壁稳定、入岩界面判断正确、嵌岩深度及孔底沉渣合格。分析施工后基坑开挖成桩效果及基桩检测数据,各项检测指标均符合设计和规范要求,验证了旋挖桩施工工艺的安全可行性。该工艺大幅度降低了工程成本,提高了基桩施工效率,缩短了工期,为类似不良地质条件下大口径旋挖桩施工开提供了参考。

This paper intends to analyze construction safety and quality issues reported from construction of bored cast-in-situ piles by using large-diameter rotary drilling rig under adverse geological conditions such as silt layer, thick layer of sandy gravel, intercalary strata mainly consist of strong-weathered rock, boulder, etc.These issues include the collapse of the hole wall, sand inrush, severe sediment problems at the bottom of the hole, difficulties of identifying the interface of entering rock, making and installation of reinforcement cage, and large deviation of the quantity of concreting.It is necessary, as the paper proposed, to have a forward plan of exploration and hole drilling before the construction of foundation piles.Moreover, with the data of geotechnical exploration and testing results of technological test piles, some crucial techniques, such as grouting static mud to hold the hole wall without casing pipe, flushing holes by mud in reverse circulation and separation of mud and sand are suggested, which achieves the stability of the hole wall, the identification of interface of entering rock, the standard of rock-socketed depth and sediment at the bottom of the hole.After analyzing results of pile-forming and testing data of foundation piles, all indexes meet the requirements of design and technical specification, demonstrating the safety and feasibility of construction techniques of rotary bored piles.Such techniques extremely minimize engineering costs and time-consuming, raises efficiency of construction of foundation piles, shortens the construction period, which opens up a new technological approach for the construction of large-diameter rotary piles under similar unfavorable geological conditions.