Scottish Quartz Dolerites: An Investigation Into the Engineering Properties of Certain Sills and Their Aggregates

The present study sets out to investigate the quartz dolerites of the Midland Valley of Scotland; in particular: 1. Petrographical and geochemical properties. 2. Geotechnical properties of intact rocks and their aggregates. 3. Correlations between their petrography, geochemistry and engineering properties. Petrographical and geochemical studies were carried out on samples obtained from various sites, and the main variations in the rocks are caused by grain size and degree of weathering (or alteration). Variations occur at the same site, particularly in thick sills, where the upper part of the middle zone of the dolerite sheet is coarser in grain size and more prone to alteration. A micropetrographic index (Ip) has been calculated from the ratio of the volume of sound constituents/volume of unsound components (including voids, fractures etc.) which indicates the degree of change from fresh quartz dolerite to altered quartz dolerite extremely well, and this ratio is then used as an index to correlate with engineering tests results. A set of engineering tests was carried out on all the quartz dolerites sampled to evaluate their quality both as intact rock and aggregate. The correlation between Ip and the engineering properties of the quartz dolerites showed that a value of Ip above 5 indicates that the rock material would be suitable as roadstone and concrete aggregate under all conditions The classification of the quartz dolerites examined here is based upon the results of the petrographical, geochemical and engineering examinations which divide the quartz dolerites into three groups. The relatively fine grained and fresher quartz dolerites from Cairneyhill and Hillend quarries are in group 1; the more altered material from Caldercruix, Duntilland, Tam's Loup 1 and Boards are in group 2, and the coarser and most altered material from Tam's Loup 2 and Westcraigs quarries are in group 3. Graphing engineering properties test results against each other, and against different indices suggests that some engineering properties of the quartz dolerites can be predicted from other properties. The usefulness of these relationships lies in the simplicity and rapidity of performing some tests such as the Schmidt hammer test on intact rock and the aggregate impact value test on aggregates. Aggregates from the quartz dolerites are suitable for most roadstone and concrete applications and a satisfactory performance will be achieved from all the quartz dolerite groups. The aggregate impact value is between 7 and 17, the aggregate abrasion value is between 4.7 and 8 and the polished stone value is between 56 and 63. The best results are shown by group 1 whereas group 3 possesses the poorest results, except for PSV where this group showed the best results, due to alteration improving the skid resistant qualities of their aggregates