Excavation near existing foundation.

This "1 m away" means that some kind of pile wall could be made in order to shore up the existing building. Other option could be to separate the bordering area into sections, excavate them and work one by one, or in groups, forming "dashed line". This depends on whether the plant installation allows such a manner of progressing.

Will you please explain how to do the "PILE WALL" !
Thanks a lot.

make a secant pile of diameter 400mms known as straws in egypt

Secant piles are constructed so that there is an intersection of one pile with another. The usual practice is to construct alternative piles along the line of the wall leaving a clear space of a little under the diameter of the required intermediate piles. The exact spacing is determined by the construction tolerances which can be achieved. These initially placed piles do not have to be constructed to the same depth as the intermediate piles which follow, depending on the way in which the wall has been designed and reinforced.
Concrete is added and before it has fully set the intermediate holes are drilled along a parallel, but slightly offset, line so that the holes cut into the first piles. The intermediate piles are placed through a heavy casing whose cutting edge is toothed and enables the casing to cut into the concrete of the initial piles on either side. Subsequent concreting results in a continuous wall. The concrete chosen will often have a slow rate of setting in order to ease the problem of cutting one pile into another

Typical applications for secant walls include:

• Groundwater barriers
• Retaining walls
• Foundations