The extended building to Tongji University Library is composed of two cantilever beam structure towers with height of 50 m and 11 floor. In order not to affect the normal serviceability of the original library the large and deep compensated box foundation is adopted and a diaphragm wall close against box is employed as an anti-permeability veneering structure. Practice in this extension project has shown that compensated foundation is one kind of the best foundations for tall buildings in the areas with dense buildings in Shanghai. This paper studies in detail the distribution of contact pressure beneath box foundation. It has been found such composite foundation structure can improve the distribution of contact pressure, then reduce the moment and settlement of foundation. Based on the measured values of contact pressure the friction between box foundation and diaphragm wall can be predicted
