I have a situation where there is an RC slab of a retaining wall where the bored pile is required to bore through. The base is located approximately 5m below top of ground level. Is this possible? OR do I have to excavate to the base and remove the base before bore piling?
Anything is possible! The degree of success in attemting to pile through obstructions depends on a number of parameters such as: - the level of competence and ingenuity of the contractor and/or engineer under field conditions - the size and condition of the obstruction - the strength, thickness and reinforcement of the rc slab - the number of piles requiring to be installed through the obstruction - the size/weight of the piling rig and equipment relative to the obstruction - geotechnical conditions including water table and soil/rock strength above obstruction depth - pile diameter - ease of access to the site for alternative equipment.
5m is not deep, it's within the reach of a modest excavator. Excavation and removal of the obstruction is probably the preferred option if this obstruction applies only to a few piles, otherwise it may be worthwhile to invest time in devising an above-ground method for dealing with the obstruction.
Obviously all of the above factors vary from site to site, but the first listed is usually the most telling.
Do you happen to have a big down the hole hammer and compressor lying around on site?