Depending on the existing capacity of the equipment, the geological conditions of the construction, the designing regulations on piling depth and maximum allowed depth, the Contractor can choose suitable pile method. Principles for selecting hammer as follows:
- Enough capacity to put the pile down to designing depth with the maximum allowed depth as specified in designed document, through the thick soil layer even the hard cladding layer;
- Causing the dynamic press not over the allowed press of pile to limit the risk of cracking pile
- Total of hammering times or total time of pile leading is not over the limiting value in the design to prevent the risk of tired pile;
- The maximum allowed depth of pile is not too tiny can caused to damage of hammer head.
It is general practice to use steam hammer, air harmer, water pressure hammer or diesel hammer. Diesel hammer of closed type ram shall be of standard capacity and device measuring its output capacity shall be attached to the hammer.
The slots between the side face and the cushion of the pile is not over 1 cm each. A suitable pile cushion of adequate thickness, preferably greater than 10 cm, shall be provided between the cap and pile top. The pile cushioning material shall be replaced before the thickness of hammer cushion is compressed by 50% of the original thickness
On all pile driving equipments, except for the gravity hammer type equipment hammer cushioning materials of adequate thickness shall be attached to prevent damage to hammer or pile and to secure free and uniform movement of hammer.
- Materials for hammer cushion shall be durable to maintain long lasting uniform function of cushioning. But, wood, wire rope or asbestos hammer cushions shall not be used.
- Steel plate for hammering shall be placed on hammer cushion to secure uniform compression of cushioning material.
- Hammer cushion shall be inspected before and after execution of pile driving and every 100 hours.
- The hammer cushioning material shall be replaced before the thickness of hammer cushion is reduced by greater than 25%
- Piles shall be supported in alignment and position with leads while being driven
- Leads shall be designed and constructed to afford freedom of movement of the hammer and to permit proper placing of batter piles.
- Leads shall preferably be of sufficient length to be firmly supported on the ground space.
- The driving of piling with followers shall be done only under written permission from the Engineer.
- When followers are used, and if deemed necessary by the Engineer, one pile from each group of 10 (ten) shall be a long pile driven with a follower, and shall be used as a test pile to determine the average load capacity of the group.
Selecting the piling equipment need to satisfy the following requirements:
- The capacity of equipment is not less than 1.4 time of the biggest pressing force as regulated in the design
- The pressing force of the equipment must ensure right effect on the pile coax central vertical when driving pile from top and regular distributing on the side face of pile when embedding, not caused horizontal force on the pile.
- The equipment must obtain the inspection certificate for dead-time on the pressure gauge and oil valves together with the calibration adjustment issued by the authorize organization
- Piling equipment must ensure for safety running condition and safety labor when operating.
Selecting reaction system for piling work depending much on the features of the Site, characteristics of the construction, geology as well as capacity of piling equipment. It is possible to create the reaction system by tightly twisting anchorage underground or arranging load by heavy items on the ground in pre-piling or the anchorages available in the construction foundation in order to use the construction weight as the reaction system in the post-piling method. In all cases, the total weight of the reactions system should not be less than 1.1 times of the biggest pressing force as specified in the design.