Technical factors influencing decisions to recommend underpinning of low-rise buildings on shrinkable clay

Wilkin, D 1993, Technical factors influencing decisions to recommend underpinning of low-rise buildings on shrinkable clay , MPhil thesis, University of Salford.

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Abstract

Foundations to buildings which fail, are frequently underpinned and since 1971 when house insurers began to offer cover for damage due to "subsidence", the underpinning industry has grown to enjoy a multi-million pound turnover. Much of England southeast of a line from the Humber to Exeter, has a sub-soil of clay. Although it has been known for more than a century that this material shrinks when dry, failures on clay to dwelling houses have lately become a subject of interest to householders, building professionals and insurance companies in particular. This study concentrates on the technical factors taken into account when professionals investigate a failure to a lowrise building on shrinkable clay; from the preliminary hypothesis that underpinning is done too often. A body of technical literature exists and is brought under survey so as to isolate those main factors which in the amalgamated view of the leading authors are central to a well-based decision to carry out,or to refrain from, underpinning. Consulting engineers in Essex were surveyed hi order to discover volume and quality data about their subsidence work on a firm-by-firm basis: also to conduct case studies of actual-practice examples in relation to the regime of main factors identified by the leading authors. The regime was applied to 282 cases of failed buildings in the light of a response by 63% of the sample from the exploratory questionnaire, to the effect that in their opinion underpinning was indeed carried out too often. The preliminary hypothesis appeared to be correct. From analysis of the case-data it appears that in actual practice the fields of investigation of causes identified by the authorities were respected by the respondents who were able to supply a full body of data. The strongest correlation in respondents' data as an indicator of the actual decision to underpin or not however was the initial level of damage. Damage is an effect and a tendency was found in decisions towards the exclusion of analysis of data emerging from the investigation of cause. In short, the quantity and not the quality of damage appears to bear much the stronger relation to a decision to underpin.

Item Type: Thesis (MPhil)
Schools: Schools > School of the Built Environment
Depositing User: Institutional Repository
Date Deposited: 02 Jul 2021 13:36
Last Modified: 02 Jul 2021 13:36
URI: http://usir.salford.ac.uk/id/eprint/61090

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