Site investigation must focus on near surface material to ensure working platforms are designed properly, says Abed Haimoni.
Work on construction sites often starts with the installation of a working platform to allow construction plant to operate effectively and safely.
In many cases, working platforms are built without design or proper evaluation of the pressure induced by plant or the bearing capacity of the platform.
Therefore, and perhaps not surprisingly, platform failures have taken place.Although complete toppling of plant is rare, when it occurs it can lead to fatalities.
This state could not be allowed to continue.Proper design, evaluation and risk assessment of working platforms will not only lead to safer platforms but can also lead to efficiency and economy.Motivated by its concern with the inadequacies of many piling platforms, the Federation of Piling Specialists has initiated a research programme at the BRE to develop a simple procedure for the design of platforms to allow all contractors, large and small, to be able to provide a properly evaluated platform.
The initiative was supported by the Health and Safety Executive and many organisations that are concerned with this issue.The work at the BRE has culminated in a document that discusses all matters related to the construction of a working platform including design, installation, maintenance and repair.
The document has passed the approval stage and should be published in the near future.
However, this timely initiative cannot deliver the intended benefits without improvements in site investigation (SI) practice.Unfortunately, most site investigations aim at establishing the soil bearing capacity at depth while the working platform relies on the near-surface material.
These materials not only suffer from lack of testing, they often consist of variable soil and require much more frequent testing to allow adequate characterisation of the soil to produce the parameters needed for the design.
Moreover, behaviour of these soils is likely to be weather dependent, hence they require more care and sophistication so that misleading results are not obtained.
Historical use of the site can have great effects on the performance of a working platform.Buried structures and obstructions, cavities and loosely backfilled excavations can lead to plant failure and need to be identified and reported.
With this initiative and the expected publication of the BRE report there is an opportunity to improve SI practice to complete the loop and reap the full benefits.
Specifiers need to stipulate adequate and appropriate soils sampling and testing and contractors should improve and develop test methods to obtain appropriate parameters for the design of a working platform.
It is important to provide soil parameters that cover the whole working area, rather than the current practice of boreholes and trial pits.The SI report needs to discuss and report on all matters affecting the platform including past use, areas of weakness, weather and weather-dependent parameters.
The information obtained should be conveyed in full to the platform designer, who in turn should report on the assumptions and limitation of the design.He should convey these to the contractor to allow him to check the exposed soil against the design assumption.
The loop can then be completed by proper operation of construction plant and proper maintenance and repair of the working platform.Only by completing the whole loop can it be certain that the piling contractor is moving on firm tracks.
Abed Haimoni is chairman of the technical committee of the Federation of Piling Specialists and chief engineer at Keller Ground Engineering.
The editor welcomes readers'comments on issues raised in Talking Point, or any articles in GE.Please write to Max Soudain, Ground Engineering, Emap Construct,151 Rosebery Avenue, London EC1R 4GB, or email max. soudain@emap. com