Didcot Power Station A
During the Winter of 2018, Clowes Developments (UK) Limited employed us to carry out the enabling package at Didcot Power Station A, Oxfordshire.
Historically used as a ministry of Defence (MOD) depot, the site later became a 2,000 MWe sub-critical coal and gas-fired power station.  It had recently ceased operation following the EU’s Large Combustion Plant Directive.  
Technical challenges
Working on a decommissioned power station site had its challenges.
The site team developed an innovative grid overlay system for use with Google Earth to assist them.

This helped in referencing the percentage of work completed on-site in conjunction with standard GPS survey equipment.

The grid overlay system also assisted all site staff to reference their individual parcels of work on-site when explaining issues, as they all have the grid overlaid on Google Earth. When they use the Google Earth map location tool, it shows precisely which work grid they are in. 

Power Station A, spanned 35 hectares in scale, and was bound to the North and East by the remainder of the Didcot Power Station B site and to the South by Milton Road. Beyond this was the Great Western Mainline and the A4130. To the west, a recently-constructed steel-framed warehouse.

The majority of the site was covered with a 300mm reinforced concrete slab with several large flooded voids present and multiple stockpiles in the southeast and southwest. These notably included a 70,500m3 pulverised fuel ash by-product generated during the power station’s coal and oil manufacturing period.  

The bedrock geology of the site consisted of gault formation, Upper Greensand to the southern boundary and superficial alluvium deposits across the central and northern parts.

Enabling works, earth and land re-profiling, civils and infrastructure all took place under stage one works with stage two involving earthworks, land re-profiling and civil works.  
With the first stage of the multi-phased project completedwe moved onto the second stage, consisting of the earthworks, land re-profiling and civil works.
Stage 2

Works to the site began with the clearance of approximately 55,000m2 of topsoil, trees and associated vegetation. In-situ and ex-situ bioremediation works occurred along with the cut and fill, compaction and chemical and geotechnical testing of approximately 120,500m3 of material.  

19,000m3 of grouting was carried out to various underground obstructions utilising an 80:1 PFA/OPC mix. The demolition of an above-ground reinforced concrete treatment lagoon also allowed the placement of a capping layer across the site to act as a working platform for a piling rig. 

Stage 3

Stage three at Didcot Power Station involved the design and construction of a 960m watercourse including break-out and diversion of an existing. The watercourse spanned fifteen metres in width and up to three and half metres in depth with connection being made from an existing 1500 box culvert which carried the existing watercourse from Milton road to the south. The profiled excavation resulted in over 50,000m3 of volume of reworked natural clay. 

Summary of service 
Enabling works
Land re-profiling
Groundwater treatment and disposal
Demolition of underground structures
Civil works