Brief Description of Main Contract Works (Client Brief):

‘To undertake remedial works to the culverts which includes applying sprayed concrete lining to the culvert, removal of debris and Himalayan balsam. All preparation works (traffic management, gas monitoring, and preparations works) will be completed to the required specification. All loose and delaminated stonework to be removed from the watercourse, steel to be fixed to the defective areas using resin and L bars. Concrete is to be applied using the dry spray process (Gunite) in one continuous build up. The final surface would be an ‘as sprayed’ finish to the nominal depth of 15mm, unless otherwise directed by the overseeing Client, and cured using either a sprayed degradable membrane or light weight plastic sheeting. Protection to the watercourse is the main requirement, and all protection is to meet EA standards and inspections’.

One of the main issue for our company personnel, and the installation of the sprayed concrete lining to the culvert, was the potential for the presence of dangerous levels of gas, and by default, low oxygen levels. The list of potential hazards and risk identified for this phase of works was extensive as highlighted in the planning meetings pre-contract start, and included fluvial flood risk / instability of existing structure / collapse /damage and loss of habitat, to name just a few.

GSSL crews are trained in confined space working to City & Guilds Level 2 with BA standard, and are well versed in restricted access and confined space working environments. Gas monitoring and escape procedures for working within the culvert were the highest priority at planning stage and throughout the works to final completion. Air extraction units were sited at strategic positions within the culvert during the works to mitigate against this potential hazard, together with water fluming contingencies in case of flood conditions during the works programme.

The watercourse was obstructed for virtually the entire length, and over twenty cubic metres of material (dislodged stone coursework, brick work, trees, vegetation and general waste material that had been washed down the course of the river and blocked the flow) had to be removed from the culvert invert to skips for recycling or disposal at licensed waste sites, before the remedial works could even begin.

All exposed cavities created by flooding and erosion of the culvert lining were reinstated with steel reinforcing mesh and fast setting sprayed concrete, together with an overlay of minimum 15mm to the vertical walls of the culvert walls down to invert level. It was calculated, at planning stage, that the additional sprayed concrete lining, and subsequent reduction of the culvert diameter would not significantly affect the flow rates of the watercourse and compromise the culvert structure or performance.