Philip Jenkins, retired geotechnical engineer, and John Davidson, Dundee University. This paper was first published in GE’s September 2015 edition.
Stony cohesive fill derived from glacial till can be utilised to construct stable and durable embankments; in addition such fill can provide an adequate load-bearing platform for structures. Stony cohesive fills are generally classified as Class 2C Fill as defined by the MCHW Table 6/2 (Grading requirements for acceptable earthworks material).
Since glacial till is generally over-consolidated, the in situ moisture content is usually close to or less than the optimum moisture content derived from a compaction test. However, the upper layer of many glacial tills has been subjected to weathering and consequent water ingress which has resulted in an increase in moisture content. Inclement weather during the earthworks phase can result in a significant increase in moisture content which may render the fill material unsuitable for engineering purposes.
Relationship testing using routine laboratory tests can be used to assess the suitability and predict the performance of fill material at moisture contents in excess of optimum moisture content.