Job Description

IN-SITU LIME CONDITIONING AND LIME/CEMENT STABILISATION FOR CAPPING

Client: Highways Agency
Main Contractor: Skanska Construction UK Limited
Quantity Embankment Fill: 48,886m³
Capping Layer: 21, 326m²

 

Project Overview

The A66 trunk road runs through the village of Temple Sowerby in Cumbria, which has been desperately waiting 24 years for a bypass. The main contractor, Skanska, appointed Beach Soil Stabilisation as specialist stabilisation contractor.

 

Scope of Works

The 5 kilometre route takes it through an SSSI and European SAC; which specifically related to the flood plane of The River Eden. Therefore, to minimise the possible effect of lime and cement dust contaminating the Eden, extreme care had to be taken when carrying out stabilisation in this area.

The stabilisation was twofold. First of all, conditioning (improvement) of the ‘host’ soils took place in the Main Line, Connector and Slip Road Embankments. This was because the host had an MCV below 75 and tests had determined 7.5 to be minimum allowable.

The ‘host’ soils were in the main of sandy, gravelly clay, there were also areas of Penrith Sand. The sandy, gravelly, clay soils were treated/improving using Singleton Birch Burnt Fine Lime 2. Then, the host was dug by adding 2% Quicklime. MCV tests were carried out continuously prior to lime addition. As well as during the mixing process and just before the layers were trimmed and compacted Nuclear Density Tests were carried out after compaction on each improved layer to ensure 95% MDD was achieved.

The specification for the Capping Layer was achieved by adding 3% cement to the lime improved ‘host’. Also the majority of the Capping was constructed to 300mm, with some minor adjustments in depth to meet the design specification. Then water was added during the mixing process at an average rate of 1%.

Appendix 1.5 had some testing carried out. Insitu CBR tests were also carried out at 24 hour, moulds were made up and 7 day soaked CBR tests carried out in the Laboratory. The results were well in excess of the Capping specification. Areas with Penrith Sand as the ‘host’ were treated using cement only at the same percentage rate of 3%.