There is a deep soft soil under the immersed tube foundation of the Hong Kong-Zhuhai-Macau Bridge (HZMB) island-tunnel joint part. In order to make the foundation stiffness smooth transition at the position，the sand compaction pile(SCP) method was adopted for its no pollution and speedy construction compared with some other treatment methods such as offshore cement deep mixing(CDM) or gravel compaction pile(GCP). This goal will be achieved by controlling the SCP area replacement rate. In this paper，the design basis and the specific design parameters are given and verified by the in situ loading test. Better settlement data was obtained by the application of liquid pressure settlement sensor at the loading process. The three - point method，the hyperbol-ic method and the Asaoka method are employed to predict the ultimate settlement of the foundation. The result predicted by the three method were discussed with the calculation results proposed by Aboshi. It was showed that the in-situ load verification method is directly effective. It can be used as an auxiliary method for the analysis of important engineering foundations. The results obtained by these prediction methods are basic equivalent whereas the results obtained by the hyperbolic method are slightly larger than the other two method. It should be selected a larger time in-thermal as much as possible to get the preferable results when the three-point method was adopted. For the high displacement rate compacted sand piles，the results calculated by the empirical formula proposed by Aboshi are significantly larger than the test results whereas they are very closed to the results calculated by the same formula with the low area replace ratio. The study is expected to provide some reference meaning for the SCP design and in situ test techniques.