The need for this study was highlighted by a National Audit Office (NAO) report (see IRRD 826681) published in 1989. This report presents the results of a study which included the examination of past performance of a number of projects in order to try to find correlations between the SI work and the additional costs arising from geotechnical causes during construction. This historical study was set in the context of present day SI practice by means of a review of the development of the SI industry and DOT procedures. Lack of available records from schemes gave rise to some difficulty, but it is possible to conclude that there is no evidence for a direct causal link between expenditure on SI and cost increases incurred on highway schemes. Instead, a number of areas are revealed where problems had been encountered in construction; most commonly these related to earthworks - the suitability of materials and the groundwater regime. The report presents recommendations for improvements to SI (site investigation) practice. The compilation of a database of information on current and all future schemes is also recommended.

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