Notes for Guidance on the Extraction of Temporary Casings and Temporary Piles
The extraction of temporary casings and temporary works piles has long been common practice within civil engineering and the piling industry in particular. Temporary casings are regularly used in the construction of bored piles to both provide a guide for the auger and to support otherwise unstable soils. Perhaps the most common temporary works piles are sheet piles although ‘H’ piles and steel tubes are often used for temporary support being extracted on completion of the works, particularly in marine applications. The details of the extraction method, in particular for the removal of temporary casings used in the construction of traditional bored piles, has largely been selected on the basis of the judgement of experienced personnel and, in most cases, has been successfully concluded. However, if this judgement is incorrectly made the results can be catastrophic. For example, where a crane is being used the sudden failure of a hoist rope will in turn trigger a sudden release of load on the boom which may cause it to fail dramatically as it whips back hard against the stops and back over the cab (Figure 1). This may result in personal injury, or worse, significant damage to both equipment and the works under construction or even third party structures. At the end of the day a failure of the selected method will inevitably lead to delay and increased cost.
Since its formation in 1963 The Federation of Piling Specialists has always had as one of its main drivers the improvement of the Safety of both its members’ operations and the Piling Industry as a whole. In general terms the F.P.S. has been most successful in this regard largely due to the work of the Safety and Training Committee. This committee, which meets on a quarterly basis, is open to the safety representatives of all member companies and is a forum where these representatives can meet to exchange experiences for the benefit of all concerned.
Reports of accidents and incidents, including RIDDOR reports with the names of individuals and companies removed, are sent to the FPS secretariat so that statistics identifying type of accident, cause, injury etc can be prepared and presented to the committee for analysis by the meeting. Specific accidents/incidents can then be reviewed to identify ways in which safety within the piling industry can be improved. The piling industry is extremely competitive in all respects however FPS members do not compete on safety but aim to share experiences for the benefit of all.
This particular document considers the removal of temporary casings and temporary piles which is a common requirement of the industry and is an operation which may generate significant forces which are difficult to quantify. The extraction process may require the use of rigs, cranes, purpose built extractors, jacking systems or other means but whatever the system employed an assessment needs to be made of the specific operation being undertaken. The variables which contribute to the force required to extract a particular element are many, varied and difficult to calculate and are not only limited to the soils applying friction to the outside of the casing or pile. To date, in most cases, assessments have been made on the basis of experience, however, following recent occurrences within the industry, the Safety and Training Committee, together with the H.S.E., identified that a more rigorous procedure was required and that a set of guidelines which outlined the various factors which need to be considered would be a useful tool, hence this document.
It is noted that this document does not cover the extraction of augers during the construction of Continuous Flight Auger or other piles, for which the rig manufacturer’s recommendations should be followed, nor does it cover the extraction of pokers during vibro compaction operations which should be assessed by the vibro specialist. Operations undertaken utilising mini-rigs (i.e. small drilling rigs in which the mast is directly supported by the ground) are also excluded from this document.
As with a number of previous documents produced by the FPS, this document has been produced in association with the HSE and the FPS thank them for their valuable input.
The document is commended to all those within the industry who may have reason to extract a pile or casing as part of their works, whether or not they are a member of the FPS, so that the industry can be more comfortable in the knowledge that this operation is being undertaken in a safe manner.
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