钻孔灌注桩承载力异常现象分析

列举了上海及周边地区 6个工程共计 19根钻孔灌注桩的静载试验情况 ,其中大部分桩的极限承载力出现异常现象。同一工程场地同一几何尺寸的桩 ,单桩极限承载力相差可达 10 0 %以上。分析表明 :施工机具、成孔时间、护壁清孔方式、桩身结构完整性、地下障碍物及重复加载方式均对单桩承载力有重要影响。如果施工工艺不合理 ,会导致单桩极限承载力偏低很多 ;超载预压后 ,粉土、砂土地基中的钻孔桩承载力会增加 ,在软粘土地基中则会减小 ;与旧基础相连 ,将使桩的承载力偏大不少。

Analysis of abnormal phenomena in ultimate bearing capacity of bored pile

Static loading test results of nineteen bored piles in six projects in Shanghai region are introduced.Ultimate bearing capacities of most of these piles are unusual.The ultimate bearing capacity of one pile can be twice of another at the same site and with the same dimension. Abnormal phenomena in ultimate bearing capacity of bored piles is mainly attributed to construction factor,such as construction equipment,drilling time,bore retaining and cleaning,and pile integrity.The ultimate bearing capacity of bored piles can be greatly decreased if construction process is unreasonable and can be obviously increased in silty or sandy soils but reduced in cohesive soils after surcharge pre loading in the first static loading test.It can also be enhanced a great lot if piles are connected with old spread foundations.