The M61 is a busy motorway linking the M60 to the south of Bolton and the M6 just south of Preston. A ground improvement solution was required due to washout of abutment fill material caused by a fractured drainage pipe / valve. An area measuring 1.5 x 1.5m within the northbound hard shoulder had already settled by up to as much as 100mm. This section had to be closed off to general traffic for fear of total failure.
Geobear were contacted mid 2018 following an intrusive ground investigation that indicated the presence of extensive voiding from 1m down to 9m in places within the abutment adjacent to the bridge joint.
Geobear were tasked with providing a cost effective, long term solution that wouldn’t disrupt the daily flow of traffic. Work was therefore carried out at night between the hours of 10pm – 4am under full road closure. Due to the quick curing time of geopolymer the road could be reopened to traffic at 5am. Geobear employed two teams of technicians to halve the programme duration and thereby minimise disruption to late night traffic and also to halve the traffic management costs. Programme duration was 9 night shifts, project cost £171k.
We treated the hard shoulder, Lane 1, 2 & 3 of the northbound carriageway, the central reservation and Lane 3 of southbound carriageway. The Treatment area measured 27m x 3m approx with treatment depths from 9m to 1m below ground level.
Our ground improvement technique uses an injected geopolymer material, that expands in the affected areas filling voids and binding with existing fill. The compressive strength of our material enables a stronger foundation which can withstand the required loads placed upon it.
The alternative methods available would require the permanent closure of the motorway, both north and southbound carriageways north of junction 9 with a full excavation to depth and reconstruct. The effect of full excavation could have the potential to destabilise the bridge meaning that the railway line would have also needed closing during these works.
Our solution was selected due to the speed of remediation and the non-disruptive nature of the solution. The methodology we employ has a reduced environmental impact in terms of material usage and Co2 emissions, which all amounted to an extremely cost effective solution.