| With the west exploitation and rapid development of basic construction, many high fill projects came forth. Outstanding characteristics of high fill projects are there are great fill height and large foundation deformation and self-deformation under fill load. Therefore, settlement deformation after-construction is usually controlled strictly in order to cater to superstructure. Settlement deformation control about high fill becomes one of the most important problems for design. For high fill soaked, wetting deformation is brought about under self-weight or exterior load because of water's lubrication to soil grains. Wetting deformation is testified by large vertical and horizontal displacement for upriver dam shell as first water storage. Following wetting deformation is also brought by reduplicative fluctuation of water level. Thus, wetting settlement and displacement can not neglected when the ground of high fill is soaked.Foundation treatment is usually implemented to meet superstructure's deformation demand. Composite foundation can improve foundation bearing capacity, ameliorate foundation deformation and reduce settlement and differential settlement. But, composite foundation theory is developing and do not mature at present. Design measurement employed roots mainly in experience. Deep theory research is necessary for composite foundation.The wastewater treatment plant of new town in Wushan county is situated within the second channel beside the Yangtze River. There are inclement terrain, landforms and very complicated hydrogeological condition here. The treatment plant's foundations are the high fill which maximal height reaches 60m. The high fill under 175m height locates the range of fluctuation of Three Gorges Reservoir water level. Wetting deformation must be considered with infiltration of water. The wastewater poll and oxidation ditch are built on top of the high fill. The criterions which settlement is 10cm and differential settlement is 2cm on post-construction are strictly demanded in order to cater to superstructure. Rigid pile composite foundations were used to control differential settlement under foundation of the No.1 oxidation ditch.This paper takes the high fill engineering under complicated conditions as object.Wetting deformation of the high fill and settlement of composite foundation are analyzed by numerical computation. Control of deformation about the high fill is researched systematically. The main points are as follows:1. Mechanism, factors and preventing measures of wetting deformation are analyzed systematically. It is pointed out that mineral grains of soil, water and gas in porous medias have great influence on soil characters in this paper. Structure of soil made up of big grains is changed easily from looseness to denseness under soak or load. Wetting deformation for big grain soil is more distinct than of soil made up of exiguous grains. Content of capillary water and gravitational water is changed very easily during wetting. Interaction of water and gas in soil makes water supplant gas and dissolve gas under pressure. At last, volume of gas is diminished. All together these factors make volume diversification of soil before and after soak.Degree of wetting deformation lies on these factors, such as soil humidity, gas content, pressure, soil density and particle size distribution, etc. In order to decrease influence of wetting deformation, some measures which include improving embankment density, embanking soil on the high water content side, pre-soak may be applied.2. Moisture potential of soil, character and calculating formula of typical retention curve in soil, function model about coefficient of permeability and matric suction or volumetric moisture content are described based on theory of unsaturated flow here. At the same time, this paper gives saturated-unsaturated flow equation, solution-determining conditions and finite element equations.Unsaturated zone's seepage flow is analyzed under rainfall-infiltration condition for an example of earth dam usin...
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