1. When there is only settlement joint between the foundation of new and old buildings, it is generally low-rise office buildings and residential buildings. If the geology is uniform, the bearing capacity of the bearing layer is FA ≥ 80 ~ 100 kPa, and the foundation settlement is very small, it is only necessary to strengthen the rigidity of the adjacent outermost room, and the foundation does not need to be reinforced. If the geology of multi-storey office and residential buildings is uniform, and the characteristic value of bearing capacity of bearing stratum is FA ≥ 120 ~ 180 kPa, and the foundation settlement is very small, it is only necessary to strengthen the stiffness of the adjacent outermost bay building, and the foundation need not be treated. Otherwise, foundation treatment should be carried out or the distance between old and new buildings should be adjusted. It is suggested that cantilever foundation or lime-soil compaction pile be used for reinforcement.
2. Pile foundation is suitable for soft foundation treatment, but pile group effect and checking calculation of soft cushion under pile foundation should be considered.
3. Cantilever pile foundation: When the geological conditions or old building conditions do not meet the above requirements of 1 and the distance between two floors is not allowed, cantilever foundation should be adopted to solve the problem, including strip foundation and cantilever beam cantilever, raft foundation and cantilever beam cantilever. Either way, the requirements of deformation and strength must be met first, and the net reaction force of foundation must meet the requirements of PMAX ≤1.2fa.
4. Local treatment method for foundation strength failing to meet the above requirements: If the original design is a strip foundation, the foundation can be partially expanded into a whole foundation to meet the requirements of the upper load on the foundation, or the foundation can be reinforced under the local foundation, and treated according to the Technical Code for Building Foundation Treatment (JGJ 79-9 1) to make it close to the net reaction requirements of the original foundation; If the original design is a raft foundation, the foundation treatment meeting the bearing capacity requirements can be adopted under the local foundation. No matter which treatment method is chosen, it should meet the requirements of PMAX ≤1.2fa.