Abstract:

Based on the following two reasons, applying static bolt-pile for construction of basement in existing buildings is practicable. (1) The gravity of the existing building can be used as reaction-force to drive piles; (2) As the temporary underpinning components, the driven piles can be used to support the existing building, thus the soils under the building can be excavated. In clay, when all piles are driven to the design elevation and the excess pore pressure is dissipated, the soil under pile caps can be excavated. In sandy soil, settlements of the existing building can be controlled by controlling the speed of driving piles and excavating soil, thus driving piles and excavating soil can be constructed at the same time. After the soils around the pile is excavated, stability analysis of the pile is done according to a high–caps pile model with a major unsupported length. Resistance in driving pile process is determined by using the dynamic penetration results of soil. The number of the static bolt-piles is calculated synthetically by the loads of service and construction processes and the results of pile stability analysis. According to punching shear bearing capacity before interface slip of new-to-old concrete, the pile cap design has sufficient safety. Punching shear strength is held by some slanting concrete columns; while the tensile force is created in bottom of the pile cap. The differential settlements of piles cause structure additional internal forces which influence safety of the existing building. Calculating the differential settlements by layer-wise summation method should consider factors as following: additional stress increase induced by gravity of piles and concentrated loads on the top of piles, as well as additional stress decrease because of excavating soils.

Key words: static bolt-pile, existing building, basement, underpinning