Abstract: In-situ loading test is the most reliable method for determining bearing capacity of composite foundation. Many construction projects show that, when loading tests haven’t reached a high degree of loading, the characteristic value of subgrade bearing capacity is unable to be determined by ultimate load. In this case, the method suggested by technical code for ground treatment of buildings should be employed to determine the characteristic value of composite foundation being capacity, but sometimes this characteristic value determined by the code is too small, which will lead to the results that the engineer adopted smaller bearing capacity characteristic value of composite foundation than normal in the design, and the design results are too conservative. From this it will bring out the technology investment and the cost of engineering economy increase. disadvantages of the method determined bearing capacity characteristic value of composite foundation by in-situ loading test are analysed by comparing a group of in-situ load test data of the plain concrete pile composite foundation with a group of in-situ loading test data of natural foundation in the same site and the same condition; and the reasons for defects are discussed. This paper complements the method for determining the bearing capacity of composite foundation by the load test proposed by technical code for ground treatment of buildings, and in order to promote the application of composite foundation technique and in situ loading test.

Key words: in-situ loading test, composite foundation, plain concrete pile composite foundation, foundation bearing capacity