The trimming eliminates the polluted/dirty concrete and a minimum of sound concrete above the cut-off level, over the full cross section of a pile (Standard EN 1536: Execution of special geotechnical works: bored piles). Trimming shall be carried out without damaging the concrete, reinforcement and instrumentation of the pile.
The FPS (Federation of Piling Specialists) has prepared an excellent document about breaking down of piles, which includes the most relevant technologies for pile trimming. The following videos show some of them.
Trimming can be performed with mechanical equipment, but care must be taken in order to avoid cracks in the pile. It might be necessary to restrict the type and size of the concrete breaker.
It is also common to use specific hydraulic pile breakers, which result in time savings and a more accurate cut-off profile. This system might not be appropiate for some of the larger pile diameters.
The Elliot method is an integrated passive system which consists of installing the piles with isolation foam securely fixed to the reinforcement cage along the pile length that has to be trimmed. Holes are drilled in the exposed pile and a concrete splitter is used to induce a crack at the cut-off level. A lifting eye installed at the top of the pile enables the removal of the trimmed section. This system is commonly used in large diameter piles.
Recent developments in pile breaking are in the form of integrated active systems, like inducing a horizontal crack by introducing chemicals into the pile through carefully positioned delivery ducts to expansion chambers positioned at cut-off level.
Special devices have also been developed to trim concrete precast piles.
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