Awarded as the best online publication by CIDC
The steep dipping and variable nature of karst surfaces poses problems for installation of driven piles. Very often, the consequences of hard driving piles over steeply-inclined karst are slipping and buckling of piles. To tackle these problems, the following two options are mostly adopted:
There are two kinds of holes present in the steel plate connected to H-piles in the pile cap. The first kind of holes is designed to be filled with welding for better connection with H-piles. The second kind of holes is present to facilitate concreting works of the pile caps.
For pile driving in certain soils like dense silt and weathered rock, the occurrence of false set phenomenon is not uncommon. During the driving process, negative pore water pressure is developed and the driven piles appear to have sufficient capacity during pile driving as the built-up of negative pore water pressure leads to an apparent temporary increase in driving resistance and strength.
For basement construction, if piles are driven from the centre to the perimeter, there is a tendency of soils to move outwards. Such lateral movement of soil may cause damage to nearby structures and utilities.
In a certain region of H-piles subjected to ground water table fluctuation, painting is sometimes applied on the surface of H-piles because the rise and fall of water table contribute to the corrosion of H-piles.
When piles are driven through an upper layer of granular soils, thick (10mm) bitumen layer would be scrapped off during the driving process. A thin coat of 1mm to 2 mm thick is not likely to flow in storage and to peel off during pie driving.
The change in pore water pressure varies in different soils. In loose sands and sandy silts, the pore water pressure increases during pile driving owing to soil densification. The increase in pore water pressure reduces the soil strength. However, after piling operation ceases for a certain period of time, upon dissipation of pore water pressure the soils would result in increased strength by soil “set-up”.
Hammer efficiency refers to the ratio of kinetic energy of the hammer to the rated energy (or potential energy). In essence, it is undoubtedly that certain energy losses are induced by the hammer itself prior to the actual impact on the driven piles. For instance, these losses may include the misalignment of the hammer, energy losses due to guiding friction, inaccurate dropping height etc
A follower is an extension between the pile head and the hammer that transfers the blow to the pile in which the pile head cannot be reached by the hammer or is under water .For construction of driven piles, the piling frame and hammer are normally erected on existing ground level but not at the base of pile caps.
