Abstract：Owing to the complexity of soil core character，the calculation of bearing capacity of tubular pile isn¢t mature and the operation mechanism of single pile bearing capacity is not clear yet. A test study example is introduced and the Q-S curve is gotten from the test. From two aspects of soil core height and its mechanical characteristics，the influence on load bearing character of large-diameter tubular pile using cast-in-situ concrete is studied. According to whether the top soil core bears load or not，the tubular pile structure is classified into two types to analyse the mechanism of inside friction. The reason for the occurance of inside friction is that the relative displacement or the trend of it exists between the soil core and pile. By assuming that the inside friction changes in minus exponential function，the method for load distribution between inside wall of pile and the top soil core is established. The result indicates that the core contributes much to enhance pile bearing capacity and to decrease pile settlement. At last，the calculation formula of vertical bearing capacity of tubular pile is established，which is proved to be practicable in projects.
