Abstract：A 3-story brick concrete structural building was added to 7-story in Xi¢an City，Shaanxi Province；and the new-added part is a frame structure. Because two different structural systems are not separated completely and the designer adopted unsuitable ground treatment method，the building became leaning seriously when the major structure was completed. The inclination ratio and settlement rate of building are up to 18.6‰ and 9.15 mm per day，respectively；and the building is bound to collapse. The scheme of rectifying deviation by jack-up and by preloading underpinning pile was employed after investigation for sake of safety. Based on this case，the following aspects are investigated：the formula to determine the numbers of underpinning piles for rectifying leaning building is presented；scheme choice of rectifying deviation，designing method，construction procedure of preloading underpinning pile，jacking monitoring and controlling are introduced in derail；difficult factors and corresponding problems during jacking construction are provided. After 3-day jack-up construction，the inclination ratio of building is steady at 0.53‰ and settlement rate is less than 0.007 7 mm per day and tends to be stable. After five years regular service，it can be concluded that preloading underpinning pile is feasible to reinforce or rectify similar structures and project in loess region.
