Based on the uniform design

the influence of pile cap

cushion

pile spacing and pile length on bearing capacity of settlement reducing pile foundation has been researched through six lab model tests with 3×4 pile group. Earth pressure

axial force of pile shaft

and tunnel settlement are measured under the different load of immersed tunnel. Owing to the application of the uniform design

the test data can be analyzed with the mathematical statistics methods such as correlation and regression analysis

and the significant degree and influence effect of the four influence factors on the settlement are estimated. Different from the traditional single factor optimization

this approach makes it possible to study the comprehensive influence of the pile foundation on the tunnel settlement under the multi-factor and multi-level conditions. The result shows that the influence of pile length

pile spacing and pile cap on tunnel settlement varies with the increase of the external load

and that the cushion and the pile cap interacts with each other

having a joint effect on the tunnel settlement. Finally

with the back analysis based on the fitting results

one optimum combination is obtained among 432 combination forms and verified in the successive test

which provides a new effective and practical way for the optimum design.