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.