Seminar - Derek Avalle - Ground Improvement using Impact Rolling

Wednesday, September 7, 2005, 1.10 - 1.50 pm
Civil Engineering Lecture Theatre 3

Abstract

Impact rolling, utilising a non-circular towed compaction module to improve ground characteristics, has been used for many decades over a wide variety of applications in various parts of the world. Although the methods and principles of rolling dynamic compaction are well established, verification methods vary widely. The background to the technology is presented, and its use over a wide range of ground conditions outlined.

A case study is highlighted for an industrial property in Sydney. The geology comprises Botany Sands, which are uniformly graded, poorly cemented, fine to medium grained quartz sands. Former structural footings and underground tanks had disturbed the ground to a depth of 1-2m over parts of the site. Ground conditions were initially investigated with trial pits, boreholes and Standard Penetration Tests.

Ground improvement with the “square” impact roller was selected in order to produce a denser more uniform sub-grade for the proposed site re-development, suited to the construction of light industrial structures supported on shallow footings, with ground-bearing floor slabs and conventional pavements. The more costly and time-consuming alternatives would have been piled foundations and, possibly, suspended floor slabs, or the necessity to backfill excavations with engineered fill and re-work existing fill.

Immediately prior to and after impact rolling, sonic piezo-cone tests were carried out. Dynamic cone penetrometer tests were utilised by the supervising geotechnical engineers to monitor the effects of the impact roller, and surface settlements were also measured. Ground vibrations and the response on adjacent structures were monitored.

The depth of ground improvement is seen to reach at least 3m below the surface. The Improvement Index for Densification (Id), which is related to the specific energy of penetration computed from the cone penetrometer tip resistance before and after impact rolling, is used to quantify the degree of ground improvement.

Finally, the range of issues that are driving impact roller research are outlined.