Chalk fill platform for house construction: a case study

Abstract

This paper presents the assessment of short- and long-term settlements and bearing capacity of a 13 m high chalk fill platform for a housing development in a former chalk quarry in Medway Gate, Kent, UK. A roped-access inspection followed by an intrusive site investigation provided evidence that the quality of in situ chalk improved with depth. It was also indicated that there was sufficient structured chalk on site for the platform construction. End-product specification with the stipulation of dry density and moisture content limits was used for the required chalk compaction. Trial compactions were carried out to confirm roller suitability and the thickness of each compacted layer. Nuclear density tests supplemented by sand replacement and laboratory tests provided a quick means of monitoring dry density and moisture content during construction. In situ plate bearing tests confirmed that compacted chalk with a dry density above 1·55 Mg/m3 could generally provide a bearing capacity greater than 150 kN/m2 as required in the contract. Post-construction settlement monitoring results indicated both immediate and creep settlements in the compacted chalk, and confirmed the time required for creep settlement to complete: hence the suitable timing for house construction.