Since the settlement of piles of composite ground under embankment is smaller than that of soil between piles

the friction stress on upper part of piles is negative. Therefore the deformation and stress theory for normal composite ground cannot be applied for composite ground under embankment. It is shown by experiments and numerical analyses that there is an equal-settlement zone respectively in the embankment

piles and substratum of composite ground under embankment where the settlement of different position of the same horizontal plane is equal. Therefore

three-equal-settlement-zone model is put forward for composite ground under embankment. Not only are the effects of parameters of ground improvement on composite ground under embankment taken into account by this model

but also the effects of height or thickness

bearing capacity of embankment and substratum are taken into account. The model is proven reasonable and practical by experimental results and numerical analyses.