上软下硬地层基坑钢管吊脚桩支护技术

Deep Excavation Supporting System Using Concrete Filled Point Bearing Steel Pipe Pile in Quaternary Soils over Bedrock

山东半岛东南部广泛分布片麻岩和花岗岩,基岩埋藏较浅甚至出露,基坑工程自上而下一般分布有第四系松散沉积物、强风化岩层、中~微风化岩层,具有"上土下岩"的特殊结构。依托实际工程,提出一种钢管吊脚桩支护结构型式,即上部土层为钢管混凝土桩+锚索支护结构,下部岩层为微型钢管桩+岩石锚杆支护结构的组合支护形式,此方案解决了坚硬岩层灌注桩成桩困难的问题,施工工效高,工程造价相对较低,通过单元计算和现场监测数据分析,该方案可满足基坑的变形要求,保证了基坑的稳定及邻近建筑物的安全。

Gneiss and granite bedrock are widely distributed in the southeast of Shandong Peninsula, and the bedrock is shallow deposited or even exposed. A typical soil/rock profiles that is frequently encountered in the deep excavation projects consists of the following special strata that is locally called "soil overlying bedrock", namely, from top down: Quaternary unconsolidated deposits;strongly weathered bedrock and moderately to slightly weathered bedrock. This paper presents a case history of deep excavation supporting structure that is consisting of anchored concrete filled, point bearing steel pipe pile in the upper soil layer and rock socketed micropile with rock anchors in the lower bedrock layer. This supporting structure has the advantages of cost effective and high efficiency. Compared with drilled and cast-in-pace concrete piles, this supporting structure can be easily installed in the bedrock layer. Based on the analysis and construction monitoring results, the supporting system could meet the deformation requirements of the deep excavation and the safety of the adjacent structures and utilities were warranted.