Estimation of vertical bearing capacity of piles using the results CPT and SPT tests

Piles as a structural element commonly are employed to overcome the problems like low bearing capacity of subsoil layers, high values of overturning moments, considerable subsidence and etc. However since the very early stage of geotechnical engineering profession, estimation of the bearing capacity of piles had been a challenge for engineers. Using the results of penetrometer tests like Standard Penetration Test (SPT) and Cone Penetration Test (CPT) to estimate the bearing capacity of piles had been the subject of considerable number of researches and several approaches have been proposed. This paper embraces the results of a statistical analysis to compare the results of several direct CPT and SPT methods which commonly are used to estimate the vertical bearing capacity of piles. For this purpose a data bank of full scale pile load tests was compiled. Each case includes the result of CPT and SPT test in the closest possible location to the executed pile. A discussion on the spiral failure zone around the pile's toe which is formed during loading also has been presented.