CIVIL APPLICATIONS Case Study: Dean and Dyball
Location:Gunwharf Keys, Portsmouth
Objective:Construction of a Piling Mat
Area:550m squared x 0.9 meters in depth = 4950m cubed
Traditional method
To remove from site 10,000 tonnes of spoil and transport it to landfill. 4000 tonnes of spoil could be taken to a local landfill site, however, it was discovered that 6000 tonnes was contaminated with mixed metals and therefore classed as ‘Hazardous waste’. There nearest Hazardous landfill site was located in Swindon, which is approximately 90 miles away. To backfill the excavation to construct the piling mat approximately 10,000 tonnes of Type1 MOT stone was needed. For engineering performance a CBR of 30% was to be achieved.
Cost
Disposal of contaminated spoil at £100 a tonne x 6000 tonnes = £600,000
Disposal of uncontaminated spoil at £10 a tonne x 4000 tonnes = £40,000
Type1 MOT stone at £15 a tonne x 10,000 = £150,000
TOTAL = £790,000
SMR method
To mix SMR into the existing spoil. SMR works by: drying out the existing spoil (so it is in a compactable state) and by bonding together the particles in the spoil. Compaction is needed after the spoil has been treated with SMR. It was decided that 1.5 bags of SMR were needed per cubic metre. Therefore 7425 bags of SMR were needed (186 tonnes). All spoil would remain on site as it would all be re-used. Again a CBR of 30% was needed.
Cost
186 tonnes of SMR at £284 a tonne: £52,824
Other costs (labour, plant, fuel): £20,000
TOTAL: £72,824
In addition when tested an average CBR of 500% was achieved.
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Mixing the SMR was carried out using a 30 tonne, 360 degree excavator. One bag of SMR was used per bucket load. |
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The curling action of the bucket was all that was needed to mix the SMR into the excavated spoil. |
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The SMR treated spoil was compacted using a Bomag 140 Roller. |
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By using SMR it resulted in savings of approximately £750,000 when compared with traditional methods. |
The SMR Benefits
- 999 LORRY MOVEMENTS SAVED
- £750,000 COST SAVING
- AN AVERAGE CBR OF 500% ACHIEVED
- CONTAMINANTS LOCKED IN ON-SITE
- 10,000 TONNES DIVERTED FROM LANDFILL
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