In cases that the permission for excavation cannot be issued due to the factors such as; no consent from neighbors due to legal reasons or facing high align underground water within the project, the safest method to implement is top down.
There is no limit for the depth of excavating, but deep excavation can be very dangerous and must be done base on accurate calculation and monitoring. In fact excavation without inhibition is only possible to the same depth of neighbor’s foundation and violating the depth even for couple of centimeters requires implementing different inhibition methods.
Not implementing proper soil restraint can cause financial damages as well as human casualties due to the fact that in case of incident all the adjacent buildings would fall into the foundation hole. There are many sites in Iran that had to deal with this carelessness for months, for not having a proper health and safety strategy in place and they also had to deal with the legal side of the problem all that causes long delays in the project. However bracing base on the methods of nailing, anchorage and soldier plie or the mixture of them are temporary, and they are not very effective until the buffer walls are installed.
Comparing Top-Down with other traditional methods of excavating