Underpinning method used to build new foundation from top to bottom.

[LYS]

I am working on a four story residential project with a bottom of the basement elevation -9 ft below finished grade. Its a 25x100 lot, having two existing buildings on each side of the lot. One building is right along the property line, and will be underpinned to adjust for deeper new foundation. The existing building on the other side is 3'away from our property line. Since that 3' is not part of our lot, and the neighbor is not allowing us to excavate it, we cant underpin it. I proposed solder piles and laggings to shore the earth at the locations where we are not along adjacent building.

To save money on solder piles and laggings to excavate the site, the client is insisting on building the foundations from top to bottom using underpinning. The plan is to first built the top 4' of foundation wall and install the floor beams, then continue down with the excavation using the method of underpinning. Basically, once the first four feet of top of the foundation wall is set with the steel beams, the contractor is planning to underpin the wall further down, until the required depth is reached, and then build footing also using underpinning method.

Had anyone actually seen this method in practice? One of the main concerns is the lateral soil pressure on the sections of underpinning, as well as the cold joints between underpinning sections. Not sure if its possible to build a basement wall using this method. Any help/ideas/comments appreciated!

Thanks