Case Studies

LIPPITS HILL - Metropolitan Police Air Support Unit 

  • Client: Metropolitan Police Air Support Unit 
  • Main Contractor: Walker Construction Ltd
  • Main Sub Contractor: Tom Blackwell Ltd
  • Qualitity Stabilised: 6500m3
  • Sub Contract Value: £135,000

Lippits Hill is home to the Metropolitan Police Air support Unit the 'Sky Cops', as featured on the BBC programme of the same name. The two Eurocopter EC145 choppers patrol the air over Lodon, providing assistance to the ground patrols.

Each time they take off, the helicopter pilot has to perform a number of checks to ensure that the aircraft is fully operational.  These checks have to be done whilst hovering above the relatively small take off pad.

Beach was called in to assist with the construction of a brand new 'runway' that the pilots could land safely on in the event of an emergency.  The material on site was silty sandy clay but, whilst it had resonable strenghs, an elevated sulphate spike in one of the trial holes meant Engineers, Scott Wilson, trialled the material with Quicklime and GGBS (Ground Granulated Blas Furnace Slag).  The results proved poitive and a mix design of 3% Quicklime and 3% GGBS agreed. 

In order for the full depth of the runway to be treated.  Beach suggested to the Client that the entire formation be dug and placed in 3 separate treatment areas adjacent to the new runway.  This enabled us to increase production outoputs as the earthworks plant were able to pick up the treated material and place it in the areas that had been bench cut, without having to avoid stabilisation plant and visa versa!

Working for Tom Blackwell Contractors of Essex, Beach successfully carried out the stabilisation of 6500m3 of material, exceeding the Clients expectations.  Testing was carried out in accordance with SHW Series 800 Earthworks, Class 9G.  

LANCASTER FLOOD ALLEVIATION SCHEME - EARTH BUND SECTION  

  • Client: Environment Agency
  • Main Contractor: Mowlem
  • Main Sub Contractor: Beach Soil Stabilisation Ltd
  • Quantity Stabilsed: 75,500m3
  • Sub Contract Value: £1.25 million

In March 2006 we commenced the excavation and filling of earth bund section of this Environment Agency Scheme together with Mowlem Civil Engineering (now Carillion).  The EA had secured a large borrow pit area and had tested the soils for suitability for use as construction fill in the bund.  They found that the moisture content of the grey clay was slightly too high and had to be reduced before use.  We also tested the material by excavating trial pits and then carried out laboratory tests, which told us that we needed to mix in 2% of lime.  This would reduce the moisture content to within the optimum limits.

The first section of bund was completed by excavating the clay and spreading it out in layers on the bund area.  Our wheeled spreader and Wirtgen mixer were able to travel over the material and carry out a normal 'mix in place' operation.  However, as we excavated deeper into the burrow pit, the material changed from firm clay to very soft clay.  In addition the north end of the pit changed into running silt with water pouring into excavations.

A major re-think had to be carried out and while the Environment Agency pursued an imported clay option, we carried out more tests on the materials.We found by increasing the amount of lime, we could still change the material so that it could be used as embankment fill.  We then devised a method of extracting the soft clay and silt by using long reach excavators and we would then load the dumptrucks, which would be fitted with tailboards.  We specially purchased a tracked dumper and converted it into a lime spreader so that it could traverse the softest of material.

In the meantime, the EA found out the problems associated with importing good quality clay.  Firstly, there were none available, secondly, the access track leading to the site would not take the amount of heavy transport required to complete the works and finally the cost would greatly exceed their budget.

They therefore instructed us to try out our suggestion and were amazed that it worked perfectly.  The bank completed in time before winter rains and the material that was trimmed off the sides of the batters was used in the final topping up of the bund's crest to allow for any settlement that might occur over the lifetime of the flood defence.

A66 TEMPLE SOWERBY-BY-PASS 

 

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

  • Client: Highways Agency
  • Main Contractor: Skanska Construction UK Limited
  • Soil Stabilisation: Beach Soil Stabilistation Ltd
  • Quantity Embankment Fill: 48,886m3
  • Capping Layer: 21,326m2
  • Contract Duration: April 2006 - October 2006

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.

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

The stabilisation was twofold - firstly, conditioning (improvement) of the 'host' soils took place in the Main Line, Connector and Slip Road Embankments, as 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.  The 'host' was dug in the cut, placed and treated in the desposition areas in 300mm layers.  An MCV of 8-12 was the target value and this was achieved by adding 2% Quicklime.  MCV tests were carried out continuously prior to lime addition, 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'.  The majority of the Capping was constructed to 300mm, with some minor adjustments in depth to meet the design specification.  Water was added during the mixing process at an average rate of 1%.

Testing was carried out to Appendix 1.5.  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%.