The main factors affecting reinforcement result,such as broken stone cushion,an area ratio of column to soil and change of column rigidity are studied.

To have a further study of the new type soft subgrade reinforcing system of geocell reinforced gravel mattress and gravel pile composite foundation of its mechanism of load capacity and settlement development,three comparative model tests were designed and carried out under the direction of similarity theory and similarity criterions deduced through dimension analysis method.

Corresponding calculation method and construction technique of gravel cushion for soft soil foundation treatment are briefly introduced.

Several methods are used are to test the physicomechanical indices of the gravel cushion.

Numerical tests on the mechanism of the cushion in composite foundation;

According to the results of in-situ tests,the failure mechanism of composite foundation is mainly decided by the interaction between soil and cushion in the state of thick cushion or under embankments;and the practical bearing capacity of a pile in composite foundation is not brought into full play.

A cushion is installed under a pile cap, then the load is redistributed between the pile and soil.

According to the laboratory and in situ tests, this paper discusses into the roles Of the mattress of compositefoundtion with cement, fly-ask, gravel pile (CFGP), the bearing ratio of CFGP to soil under the vertical loads, and thedeformation behaviour of the compsite foundation.