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  • Client:
    North Yorkshire County Council
  • Duration:
    10 Days
  • Shift Type:
  • Year:
  • location:
    North Yorkshire, UK
  • AREA:
    Bacel Hardfoam

Project Goal:

North Yorkshire County Council had a problem where an abandoned shaft which had been used as a landfill site had opened up and the old rubbish mound was progressively collapsing into the hole presenting grave danger to walkers and animals (some of which had been lost own the shaft).

The Council appointed Jacobs Engineers to find a solution for filling or closing up the collapsed vertical air shaft 20 metres deep x 8 metres diameter at this old landfill site at Great Ayton.

Access was the main problem facing a filling solution. The shaft was 3 km from the nearest road and at the top of a large hill over soft compressible soil topped landfill material mostly surrounded by fully cultivated fields with no access road capable of taking tipper trucks. On one side access was closer but there was a vertical grade of 1 in 1 from the foot of the hill running up to the top of the shaft. Vehicle access was out of the question.

DWG Resins were approached to fill the shaft using medium density Bacel hardfoam. Bacel foaming and pumping equipment is able to be demounted from the truck and still be used at remote locations without need for external power or water. The pumping equipment and materials were transported to the remote location by rough terrain multifunction forklift / telehandler. All materials were mixed off site and transported by “moffett mounty” truck to the access point in IBC’s and these were then transported up to the top of the shaft by the tracked telehandler and a small track mounted transporter.

BACEL pumping equipment only requires compressed air as the only means of power and so the compressor was taken up the hill also and located a short hose length from the shaft. The BACEL pumping equipment was designed for working in petrochemical situations and so the foaming is a “cold” electricity free process which reduces health & safety issues in wet, dangerous, or gaseous discharge situations.

The BACEL foam is produced in-situ from 2 base liquids stored and transported to site in 1000 liter IBCs from which large volumes of foam can be created (approx. 16 m³ from each IBC dependant on density required). This makes BACEL an ideal solution where access and logistics are a problem compared to foam cement “ready mix” trucks which carry only 6-8 m³ per delivery.

The work was carried out in 3 phases using expert mountaineering personnel provided by Dave Griffith’s Zenith Leisure to assist DWG Resins foamers with access. The shaft edges were continuously collapsing and no one was allowed next to the opening unless fully roped and tethered with safety harness.

Project description:

Phase 1 – Filling the lower portion of the shaft (-20m up to -12m) EPS (lightweight polystyrene) blocks were dropped into the base of the shaft to sit on the water present at the bottom. Then a 63mm BACEL filling pipe was lowered 20 metres down into the shaft and the BACEL foam was pumped directly on top of the EPS. The BACEL was allowed to spread and fill all voids within the surrounding landfill materials bonding them together in 1.5 meter high lifts which allowed 3 metres vertical fill per day.

This filling continued over 4 days by which time 290m³ had brought the top of the BACEL foam level with a rock layer which would be the foundation for a concrete cap at that level (still minus 12 metres) Steel wire mesh fencing panels were placed across the foam between lifts and also when wrapped in geotextile at the entrances to 2 horizontal shafts running left and right into the rock layers. This way it was possible to block off the horizontal shafts to minimize the m³ of foam pumped whilst bring up the top of the foam level with the rock head.

Phase 2 – Placing a concrete cap at rock head level at -12m After one week of cure time, it was possible for rescue men to be lowered into the shaft and stand on the BACEL foam, but there was still high danger of further sidewall collapses so this was avoided as a work method. Therefore the concrete cap at rock head level was placed by using a local concrete pumping company to pump up the steep side of the hill that had the close truck access. This way a 400 mm thick lightweight slab was pumped from the mouth of the shaft top directly down onto and over some geotextile which had been spread out over the top of the BACEL foam.

Phase 3 – Filling from -11.5m to - Grd level. Again the BACEL foam was pumped from above down into the shaft via 63mm filling hoses to avoid man access down the shaft. This time the BACEL was pumped onto the concrete slab in daily lifts of up to 2-3 metres until the required height was achieved. Then a 500mm layer of heavy density BACEL was foamed as a cap, and this was covered with geotextile. After a 3 week cure time, 500mm of local soil (scraped from the surrounding area) will be placed onto the geotextile to finish the filling process. This phase had a total of 750m³ of foam pumped in 6 days.