REMEDIATION AND MONITORING OF A BURNING COAL REFUSE BANK AFFECTING THE SOUTHSEA LOOPROAD AT BRYMBO, NORTH-WALES

Southsea Looproad at Brymbo suffers large and varied settlements where the highway crosses a smouldering coal refuse bank. A sudden surge in combustion activity during 1991 resulted in considerable subsidence w ithin the carriageway and posed recurring and persistent difficulties for road safety and highway maintenance. Initial investigations involv ed subsurface temperature measurements to delimit the hot spots and pr ovide a basis for the design of remedial works. The aim of remediation was to extinguish the migrating fire in the outer loop area and to co ntrol the burning throughout the remaining areas. The principal strand of the remediation strategy involved excavating the burning coal refu se, cooling, mixing with pulverized fuel ash and compacting. Supplemen tary containment measures included limestone-filled cut-off trenches, cementitious grout curtains and impervious clay blankets. The works ac hieved the design objectives, however, small pockets of smouldering ma terial remained within the inner loop. Subsequent monitoring of the si te disclosed two markedly different patterns of temperature response o n each side of the road. On the outer rim of the looproad temperature trends were steadily downwards in accordance with expectations and ind eed reached ambient temperature within about one year. However, on the inside of the looproad seasonal surges in temperature have been recor ded during winter months every year since the completion of the remedi al works in 1993. The explanation for this unusual pattern of combusti on activity is thought to be related to climatic effects and particula rly the combined influence of rainfall, atmospheric pressure, air temp erature and wind strength and direction. The relative contribution of these factors remains uncertain. Temperature monitoring continues in o rder to identify the eventual end of combustion activity and determine the appropriate time to complete reinstatement of the carriageway. (C ) 1998 Elsevier Science B.V. All rights reserved.