ROSS HIGH SCHOOL

CONSOLIDATION OF OLD MINEWORKINGS

Method of Working - Drilling and Grouting
Client - Ballast Wiltshire
Consultants - David R. Murray and Associates

In 2002/2003 DCE were appointed as specialist drilling and grouting contractors to treat themineworking beneath the existing footprint and proposed extensions on Ross High school as part of an extensive renovation and new build project.

Following site investigation drilling, significant mineworkings were recorded within The Great Seam at shallow depth beneath the school and proposed areas of extension. Intact coal of up to 2.5 metres was recorded together with voids and broken strata up to 4.0 metres thick due to roof collapse above the workings.

A treatment grid consisting of approximately 1500 boreholes located at 3.50 metre centres into which grout consisting of Ordinary Portland cement and pulverised fuel ash in the ratio of 1:10 was injected, to prevent future settlement of the building.

In order to meet the clients programme requirements works were undertaken during school time, and as such Health and Safety issues to include the protection and wellbeing of approximately 800 pupils was of prime importance.

The drilling rigs utilised included Casagrande C6 and Hymac/Krupp rigs employing both rotary and rotary percussive drilling techniques with air as the primary flushing medium. The versatility of these rigs to drill angle boreholes was critical in progressing the works on a broad front. Inaccessible boreholes within internal quadrangles were completed by mini rigs, which accessed the internal garden areas via the school corridors.

The contract was completed safely with no reportable accidents on budget and to programme, and called upon the experience and skills of the DCE team in providing a successful conclusion to the project.