全充填岩溶地区冲孔灌注桩施工技术

Discussion on construction technology for punched(bored)cast-in-situ piles in fully filled karst area

针对全充填岩溶地区冲孔灌注桩施工中存在的沉渣过厚、孔内坍塌与漏浆、卡钻、偏孔、和断桩等问题,基于全充填岩溶地区的特点,探讨了问题产生的原因、解决方案与预防措施,通过某工程桩基施工表明:依据地层特性选择相应的泥浆浓度与二次清孔落到实处是解决孔底沉渣过厚的有效措施;回填片石与黏土或钢护筒护壁能有效解决孔内坍塌与漏浆;将卡钻处的石块挤进孔壁或击碎,必要时可利用高压水枪冲击卡点处处理卡钻;可用回填与孔底岩石强度相同的块石或混凝土,再重新冲击钻进,必要时可采用爆破进行钻孔纠偏;导管的气密性与初次灌注的混凝土量是影响断桩的两个重要因素。

In view of the problems existing in the construction of the bored cast-in-situ piles in the fully filled karst area, such as too thick sediments, hole collapse and slurry leakage, sticking, borehole deviation and broken pile etc. , based on the characteristics of fully filled karst area, the causes of the problems, the solutions and preventive measures were discussed. The pile foundation construction of a project shows the followings ： Selecting appropriate slurry concentration according to the ground strata characteristics and conducting secondary hole cleaning are the effective measures for solving the problem of thick sediment at the hole bottom; Backfilling rubbles and clays or using steel- cased protection walls can effectively solve the hole collapse and slurry leakage; Squeezing or crushing the stones into the hole wall at the sticking point and using water cannons to hit the sticking point when necessary to solve the sticking problem; In view of the problem of hole deviation, backfill the rubbles or concrete with the same strength as hole bottom rock strength, re-drill the hole again and adopt blasting for correction when necessary; The air tightness of ducts and the concrete volume poured firstly are two important factors influencing the pile breaking.