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tension and displacement cracking

Earthworks & sub-surface drainage

Sadleir supervised this landslip stabilisation scheme at Blaina, in South-East Wales, for consulting engineers Ward Jackson Associates.

Disturbed ground in the steep slopes of the glacial valley had been further weakened by surcharge from earlier ironworks and colliery spoil tips, since largely removed, but leaving a continuing ground movement to threaten the residential properties in the valley floor.

old mine entry exposed by adjacent subsidence

The weakness was exacerbated by an adverse ground-water régime, itself complicated by a combination of natural geological faulting and abandoned mineworkings at higher levels. Local rates of movement had reached several metres per month. Substantial parts of previous drainage schemes had been totally destroyed by ground movements.

a carefully-monitored pilot excavation commences

The remedial scheme — designed and managed by Blaenau Gwent County Borough Council's Engineer, specialist ground engineering consultants Ward Jackson Associates — entailed the re-profiling of a large area of the valley side, …

forming a toe drain beneath an advancing slip

…in combination with extensive ground drainage.

groundwater response monitoring: drain efflux vs. antecedent rainfall

Proceeding necessarily with caution on unstable and disturbed ground, and working typically on 1 in 2 gradients, safe and efficient execution of the works owed much to the considerable skill of the machine operators assigned to the project by main Contractor Walters UK Ltd.

Throughout the earthworks operations, the Engineer maintained regular monitoring of surface and sub-surface movements, rainfall, piezometric pressures and drainage flow rates.

drilling to intercept deep groundwater flows

Extensive rock-filled buttress and toe drains were complemented by rotary-bored horizontal relief drains, penetrating up to 90m into water-bearing strata.

nearing completion — prior to re-seeding

New surface collector channels were installed with flexible revetments.

Bailey bridge lift

The ¼–million tonne earth-moving operation required a temporary ‘Bailey’ bridge, spanning between reinforced-earth abutments, by which the fleet of 25t 6wd dump trucks could carry excavated material across a busy A‑class road to the disposal area.

drapeau: United Kingdom: Union Flag

UK projects: landslip stabilisation at Blaina