Given the soil structure there, the sole option is foundation on piles. In consultation with the engineer, we decided to explore the possibility of both foundations with pre-cast concrete piles and and an in-situ, soil displacing vibrated-pile system. After further investigation, advice and engineering the choice was made to go for vibrated-pile foundations.
According to the information provided, there were no other existing foundations present in the vicinity of the new pile foundations The vibrations caused by the pile driving could possibly cause disruption and other interference in the surrounding area. Given the presence of existing buildings, it was recommended to monitor vibrations while the piling work was in progress.
The vibrated-pile foundations need to be installed by a reputable company that is specialised in this sort of work. Insertion of the steel tube should preferably be done with an adjustable piling rig.
Where the pile-insertion levels differ, individual piles have to be made ‘from the bottom up’, in order to make it easier to monitor the piling work.
In order to obtain sufficient insight into how the bearing capacity is built up and the transitions in the depths in the penetration tests, it is necessary to count the number of blows through the foundation sand stratum, from the top of the positive skin friction depth. Once the base level has been reached each pile must be checked to make sure that no water has been able to get into the tube. The reinforcement cage must be sufficiently strong and stiff, enabling transportation and positioning, without permanent deformation. The tube must be filled with fresh concrete up to a level above ground.
In particular, where the reinforcement cage lengths are relatively long, a decrease in concrete pressure at the bottom of the tube must be factored in. As the tube is being removed, there must be sufficient concrete pouring pressure in the foundation sand stratum to satisfy the principles of load-bearing capacity in soil mechanics. While the tube is being removed it is important to check that the cage remains intact. Adding concrete is permitted solely as long as the bottom of the tube is still in the foundation sand stratum. It is important that the removal speed is matched to the concrete pouring speed, so as to limit the risk of necking. It is not permitted to pour to a level under the work level.
When making new piles and manoeuvring the piling rig, the concrete level of piles in the vicinity that are still curing must be properly monitored.
