personally it is the bored piles with cappingbeam and lagging wall.
the main reason for this collapse may be the shortage of bending moment resistance of the wall. the surrounding building is the critical origin of the large lateral force.
from the photo it can be seen that the site soil is not so bad.
measures may be : soil nailing between the piles to increase the wholly stability of the wall;
increase the embedment (if the collapse came from overturning of the wall); prop up the wall with berms or inclined wall; or tie back from the back of the wall;
meanwhile, monitoring should be carried out very carefully.