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CASE STUDY

Keeping Network Rail on track

Temporary haul road at the Holmes Chapel TWEMLOW viaduct

 

The background

Twemlow viaduct in Holmes Chapel was completely refurbished as part of Network Rail’s on-going railway upgrade plan. This included the removal of water stains on the walls, repairs to brickwork and the installation of new waterproofing and drainage.

The challenge

Works to the top of the Grade II listed viaduct, which included the railway line, needed to be carried out during an 11 day closure during February 2016, in order to cause the least amount of disruption to the public. This meant that work could be carried out in one continuous block.

The result

The railway track was removed and pre-cast concrete units were laid along with waterproofing and a brand new drainage system which will protect the brickwork for another 125 years.

Refurbishment of the brickwork, which included repairing cracks using crack-stitching, re-casing and pointing works, was carried out up to November 2016.

UPDATE – EXTERNAL DECOMMISSIONING ANALYSIS

The site was decommissioned in Winter 2016, since additional testing and analysis has been undertaken to confirm the successful restoration of site soils. This has been carefully undertaken over the three years since decommissioning to ensure an appropriate window of study.

SITE SOILS PRIOR TO CONSTRUCTION

The soil type at the Holmes Chapel scheme consisted of a red/brown sandy clay silt material. This is typical of the material type found in existing boreholes in the area.

The site was used as grazing/pastureland prior to construction and was returned to the DEFRA indices for pH and Nutrient appropriate to this land use and the original soils.

ADDITIONAL TESTING

Additional testing has also been undertaken to ensure that an Iron Pan Layer has not been created and that there are no cementitious materials still present in the soil. To verify that either of the above has not occurred the following testing and information has been undertaken:

1. Dynamic Cone Penetrometer testing to ensure that the density of the soil has not increased underneath the former GEOBIND® enhanced layer due to the compaction required to install the structures. Increased density can lead to drainage and permeability issues at the site. 

2. pH and Nutrient testing to ensure that cementitious elements are not present in the soil which could affect pH and nutrient status. pH testing and Nutrient analysis (Phosphorus, Potassium and Magnesium) has been undertaken and related to the relevant DEFRA Index. 

VISUAL SUMMARY

The visual evidence taken after the Decommissioning process demonstrates that full re-growth has occurred in the previously GEOBIND® enhanced areas. These areas now appear to be denser in terms of grass growth than in the previous years before the decommissioning process was undertaken.

This is also backed up by the signed Landowner acceptance letter and during the site visit conducted by Balfour Beatty in March when he addressed the visiting party.

AGRICULTURAL CONSULTANT COMMENTS

The site was analysed by external agricultural specialists, Reading Agricultural Consultants who commented the following:

In my capacity as Soils and Agricultural Consultant to the DJV supporting the HS2 Enabling Works North Contract, I have been asked to offer my professional comments and observations on the Geobind soil enhancement process, particularly in respect of the quality of the reinstated agricultural soils after the ‘reversal’ of the Geobind process.

As part of this assessment, I visited a site in October 2019 to examine a reinstated temporary works compound and access road at the Twemlow Viaduct near Holmes Chapel. These had been constructed by Geobind some two years earlier to support works undertaken for Network Rail on the Twemlow Viaduct. I attended site with representatives of Geobind, Laing O’Rourke Murphy JV and the landowner.

The siting of the temporary compound and access road was no longer discernible on the ground, and there was no difference in the quality of the grass sward between the land that had been subject to the temporary works and neighbouring undisturbed land in the same field. Similarly, there was no discernible distinction between the arable land that has been subject to the access road and neighbouring land. There were no signs of compaction or impeded drainage on the land.

I dug soil pits to examine the depths, textures and structures of the topsoil and subsoil within the former compound area. The restored soil profiles comprised 300mm of friable sandy loam topsoil which was not compacted and contained many roots which penetrated into the subsoil. The subsoil comprised a loamy sand to a depth of 600mm and showed no signs of compaction. Importantly, there was no compaction at the interface of the topsoil and upper subsoil, which is a common deficiency of reinstated agricultural land. The upper subsoil lay over a lower subsoil of sand from a depth of 600mm.

From my inspection, I concluded that the impact of the installation and subsequent reversal of the Geobind temporary works system had no detrimental effects on the topsoil and subsoil and their inherent structure and density, causing me no concerns for the use of such a process on the HS2 Enabling Works Contract North.”

Director

Reading Agricultural Consultants

  • Reduction of wagon movements 96% 96%
  • Reduction in imported aggregate 88% 88%
  • Reduction in waste to landfill 100% 100%
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