The following possible risks or problems are identified with the activities involved with pile execution.
Survey – Out of Positioning of the Pile
The pile position shall be cross-checked by the Engineer, Contractor and Sub Contractor before the installation of pile. If any out of position of the pile (more than the allowable tolerance) has been noticed after the concreting of the pile, it shall be brought to the notice of the Engineer through N.C.R.
Drilling – Loss of Drilling Tools in Bore Holes
During the drilling operation there are remote chances for the loss of drilling tools in the bore holes due to the high torque applied to cut the soil / rock. In order to avoid the same periodic checking shall be carried out on drilling tools. If any drilling tool has been lost in the bore hole then the issue to be brought to the notice of Engineer immediately and all the activities around that pile shall be stopped. A Method Statement for the extraction of drilling tools will be submitted to the Engineer for approval and further action.
BENTONITE DRILLING – COLLAPSE OF BORE HOLE
The collapse of borehole may happen if the drilling is carried out through the unstable strata and poor quality bentonite slurry has been used for the drillings. This can be avoided by checking the bentonite slurry properties during drilling operations. In the case of collapse of borehole & rapid loss of drilling fluid, the bore hole will be back filled without delay using drilled material from the heap, near the bore hole.
The Engineer’s approval will be obtained before resuming boring in that location.
WATER DRILLING – COLLAPSE OF BORE HOLE
The collapse of borehole may happen if the drilling is carried out through the unstable strata. The soil investigation report for the particular site shall be checked for the prevailing strata before starting drilling operation. A trial bore hole to be drilled within the site but away from any pile location. The borehole to be monitored for minimum 12.0 hours. If collapse or excessive sedimentation is noticed the borehole will be back filled without delay using drilled material from the heap, near the borehole. Engineer’s permission shall be sought for drilling the piles with bentonite slurry support system.
Reinforcement – Loss of Reinforcement Segment During Installation
During the installation of piling reinforcement cage support beams and jacks shall be provided to hang the reinforcement segment in the bore hole in addition to the safety sling from the service crane. The coupler connection between the reinforcement segments shall be double verified by the Foreman before removing the support system for the bottom segment. Any loss of reinforcement segment shall be notified immediately to the Engineer.
Concreting – Clogging of Tremmie Pipe
The tremmie pipe is made up of segments of 15.0 m for diameter 150 mm and approx. 2.0 m length for diameter 250 mm. The connection between the pipes to be checked before lowering to the bore hole. Rubber ‘O’ ring and tremmie grease shall be provided to make the joints watertight. The concrete shall be checked for the workability before permitting to the site.
Low slump concrete will clog in the tremmie pipe. The tremmie pipe shall be removed immediately from the bore hole on clogging of pipe and Engineer’s instruction shall be followed for the further action.
Bursting of Bentonite Hoses / Lines
The bentonite slurry will be delivered to the pile bore by using a combination of flexible hoses and steel pipes, connected with couplers.
As far as possible, hoses and pipes shall be placed below surface respectively shall be covered by a rigid protection, such as casing etc to avoid damage due to site traffic. In case a hose / pipe bursts it shall be replaced immediately by a proper one and the spilled bentonite shall be removed in order to clean the area.