Gatwick Airport originally opened in 1930 as the Surrey Aero Club, a small flyers club and was used exclusively by flying enthusiasts. In 1958, Gatwick Airport was officially opened by Her Majesty The Queen as a public airport and the world’s first airport with a direct railway link. In 1974 Gatwick in Surrey became part of West Sussex as the result of county boundary changes. Today, Gatwick is the world’s most efficient single-runway airport and the UK’s second largest.
Between 2008 and 2014, £1.2 billion was invested in Gatwick, £440k of which was directed towards the redevelopment of the surface water drainage channel infrastructure at Car Park J.
Historically, the drainage channel running adjacent to the Car Park was an open, muddy ditch. This had served the area well for many years, but with an increase in passenger traffic and number of flights, the drainage infrastructure required significant improvement.
The project to bulk excavate and refine this major drainage channel would allow the upgraded culvert to operate more effectively in managing surface water from the runway and the surrounding areas. Unleaded kerosene (used in plane fuel) and other hydrocarbons from the nearby road surfaces would be more efficiently managed in order to reduce the amount of contaminated water reaching the River Mole.
Enviromesh were initially approached by Land and Water Limited to review the proposed designs for the culvert scheme. The revised design drawings submitted by Enviromesh showed that savings could be made in materials and labour. Traditionally, Mass Gravity Gabion Retaining Walls and Gabion Mesh Mattresses are the go-to solutions for the civil engineering sector in these types of applications.
On this occasion, Enviromesh were involved in the scheme at the early stages, which offered the client a significant advantage in terms of forward planning as well as identifying where cost savings could be made. Enviromesh were on site to advise on design, materials and installation throughout the project, meaning key issues could be addressed both before and during the works.
A major challenge for the construction team was dealing with excess water (caused by the inclement December weather; the main watercourse and a network of drainage systems flowing into the culvert). Pumps were installed along the length of the culvert to help alleviate this issue.
GABION RETAINING WALLS
One of the singular health and safety concerns related to the culverts’ sloped banks which were cut at a steep angle, due to space constraints. The concern here was the increased potential for the sides to collapse (being unstable and unsupported). Exposure to the harsh December weather compounded this particular issue.
The cut slopes of the culvert were excavated progressively to address both the unstable and easily erodible nature of the surrounding soil. Work on building the retaining walls began soon after and continued in short six-metre sections. Therefore helping the team focus on a smaller, more manageable area at any one time. The retaining walls were specified as 3mm wire throughout with heavier gauge 4mm facing panels and filled with Kent Ragstone (Class 6G).
Hexagonal Woven Mesh Mattresses were specified for the base of the culvert primarily because they would help mitigate erosion issues. Their inherent flexibility would also suit the uneven ground. In this case, using mattresses in combination greatly improved the integrity of the foundation, and using lacing wire to joint adjacent mattresses, resulted in a stronger, more effective continuous structure.