Active pile foundation underpinning structure and constructing method thereof

The present invention provides one kind of active pile foundation underpin structure, which includes a new underpin pile with pile cap and an underpin beam slab, and has a lifting jack on the pile cap for pre-lifting and unloading the underpin beam slab so as to transfer the load from the pile to be underpinned to the newly constructed underpin structure and realize force conversion. The present invention also provides the construction process of the active pile foundation underpin structure. The present invention makes it possible to control actively the deformation of the upper building to be underpinned, and is suitable for pile foundation underpin with great axial force.