软土地区旧桩拔除技术和新建桩基础调整方案及施工措施

结合天津南开区某地块定向经济适用房项目，介绍其在基础施工中遇到旧预制方桩时，采用全套管高压喷气、射水振动沉管施工工艺清孔拔桩，并对该工艺进行分析得出:该拔桩施工工艺适用于软土地区旧桩拔除项目；并针对旧桩孔无法回填压实、部分新建桩基础与拔除旧桩孔距离较近等原因导致钻孔倾斜、串孔等问题，提出远离旧桩位置或调整至旧桩桩心位置等方法调整桩位，并采用加大桩径、增设承台等调整方案承担因调整桩位而产生的上部偏心荷载；采用拌和白灰、分层压实、回填静置等措施提高回填土的密实度，采用保证垂直度和调节泥浆配合比等措施，以改善不良施工条件，得出适当增加混凝土充盈系数保证成桩质量等施工经验，为后续类似工程提供借鉴。

Old Pile Extraction Technology in Soft Soil Area and Adjustment Plan and Construction Measures of New Pile Foundation

Combined with an affordable housing project in Nankai District, Tianjin City, this paper introduced a new method to remove the prefabricated piles in foundation constructing. High-pressure air injection concrete was used, as well as water jetting and vibrating. Moreover, analysis results of the process indicated that it is suitable to the old pile drawing projects in the soft soil areas. To the low-pressure compaction degree of the old pile holes, and sloping hole or cross-hole issues may occur due to short distance between new piles and old pile holes. For these issues, we proposed adjusting pile position from the old pile position or adjusting to the old pile core position, and adopt adjustment schemes such as increasing pile diameter and re-design the cushion cap to bear the eccentric load caused by adjusting pile position. In order to improve the construction condition, measures such as mixing white ash, stratified compaction and backfilling static placement were adopted to improve the compactness of backfill soil, and measures such as ensuring the perpendicularity and adjusting the mud mix ratio were adopted to obtain the construction experience of increasing concrete filling coefficient to ensure the quality of pile, and provide references for the similar projects.