Longcross Studios Drainage & Services, Chertsey

OVERVIEW:

Lawson Group was awarded the title of principal contractor for this prestigious project located near Chertsey, approximately 25 miles west of London. It involved the removal of specific buildings, and a drainage and services package within the site. Set in over 200 acres, the area first started life as a Ministry of Defence site. In its MoD days, the site was run as the Military Vehicles and Engineering Establishment (MVEE), which was a British defence research unit. During the 1960s, the famous ceramic Chobham armour, along with other armoured vehicle designs, was conceived here. In 2006 the site was taken over by Longcross Film Studios.

Over the years, numerous buildings, office blocks and workshops ranging in size from 2,000 sq. ft to 13,000 sq. ft were built on the site, all of which have recently been used by various leading production companies. Many blockbuster films such as Thor 2, Fast and Furious 6 and Skyfall have been made at Longcross Studios. This first phase of Longcross studios was approx. 50 acres in size and was referred to as C1 and C2.

CHALLENGE

Care would need to be taken as works would continue around live services such as water, electricity, telecoms, and gas. Being an ex-MOD site, there could be a risk of unexploded ordnance (UXOs) buried in the ground. Licensed asbestos was identified in multiple buildings, so this would need removing subject to a Plan of Works for each unit.

Evidence of bats had been found in an ecology report, meaning that the wellbeing of this protected species would need to be a considered factor before any demolition works could commence. The entire demolition process would need to take place over an 18-week programme. Japanese Knotweed was also identified in some localised areas of the site and this would need to be carefully removed. Moving of current drainage, BT internet, gas, electric and water services would be required. Social distancing rules would need implementing and enforcing to keep all staff safe. Extensive welfare services for demolition operatives would be required. Thorough cleaning and hygiene practices would need to be laid down, as well as the implementing of other special measures in line with government COVID-19 directives.

Some businesses within the Longcross Studios site would continue to operate whilst the demolition works took place. This meant meticulous planning and excellent communication channels with business owners would be required.

SOLUTION

Drainage and services movement.

This part of the project involved the re-siting of drainage, water, electric, gas and BT Internet services to an agreed easement area that tracked round the boundary of the site. At the same time isolating all the services within the site and making them safe. This occurred simultaneously with the demolition programme. Specialists were brought in to use their CCTV equipment to view and identify any collapsed underground pipework. They also provided the specialist jetting services that were needed at certain areas around the site. Lawson Group also worked closely with another specialist drainage and services laying subcontractor. They dealt with installing of the new service and drainage lines including specially licensed work on the roundabout outside the main entrance to Longcross studios.

Before work could continue behind the first building (#100/101), soil contaminated with knotweed needed dealing with first. Eighty-tonnes of material were dug out and carefully removed by Lawson Group. This contaminated topsoil was laid out up to 300 millimetres thick on 1,200-gauge polythene sheeting. This material was left on poly sheeting for a three-year quarantine period (possibly five years) – depending on evidence of regrowth or only when the inspectors were happy that all the spores and plants had disappeared.

The mains water started near this building so this is where the digging began. Water to the entire site was isolated and a new trench was dug leading up to building #100/101. This was completed at a rate of around 300 metres per day.

The trench was dug to a depth of 950cm for the water mains. The pipe was laid on a bed of sand which was 50mm deep and 150mm sand placed on top. The drainage line ran parallel to the water pipe trench at this point.

Behind building #100/101, a new drainage trench was also dug out up to a depth of 4.5 metres up a hill and proved one of the more challenging aspects of the drainage laying. This was because of the hill’s gradient and so many trees creating an obstacle at this point. To rectify this, a tree surgeon was subcontracted to carefully cut a corridor in amongst the trees for Lawson Group to gain access to the back of building #100/101; and to enable the laying of new drains and services.

At the top of this hill was another major challenge. According to the drawings, the drains were supposed to lead down from Chamber SW-1. However, this and another drainage line running behind building #114 did not exist anymore. Further CCTV investigations showed that they had either been previously removed or had collapsed. Because of this, Lawson Group instructed the specialist drain subcontractor to install a new drainage line from manhole 3248 down to SW-1 and to then connect into the new network.

Behind building #108 is where a connection was made between the new water mains and the older original water mains at 90 degrees.

It was while operatives were hand digging behind buildings #108 / #62, that they came across unexploded ordnance. The object was an M26 grenade which was complete apart from the missing pin and handle mechanism from the top. The immediate area was evacuated, and the police and bomb squad were called in. The grenade was deemed safe and not a threat; and therefore, was carefully removed from site by the bomb disposal technicians. Works could then recommence.

A T junction was also located here, that ran to the left of building #124 on the western elevation. This was then connected further on up to another water main. Where required, other services were laid alongside but slightly higher up in the trench. HV lines were also laid to a newly installed substation behind building #124. Again, Lawson Group sought the services of a highly specialised subcontractor for this work. To the rear of building #124 was yet another challenge to the laying of new services. The area was covered with a multitude of crisscrossing older services within the grounds.

From the newly installed substation, ran a Low Voltage line across the front of building #124 and into another substation alongside this building. These lines where then connected onto the new power line and looped around that parcel of land. After this had been completed, then the original line was no longer needed and therefore disconnected.

Another challenge was encountered near building #124 regarding the laying of water and drainage services. The original agreed plan was to dig 4.5 metres deep alongside this building. However, this proved impractical due to the very close proximity of a substation, and it was suspected that footings and pilings were here that Lawson Group were not aware of. Rather than go in-between the substation and the building #124, it was agreed with the client to go around the back of the substation.

Digging then started next to building #124 and it was found that taking the new route was the correct decision. However, once digging started, it became clear that there was a ‘spiders-web’ of services that had to be avoided or negotiated. These included: 2 x high voltage cables; low voltage cables; street lighting cables; gas line; and numerous communication cables. Some of these were on the drawings but many others were not. In addition to this, this small section of land had the highest concentration of buried obstacles such as: buried water chambers; concrete chambers; different types of water mains; having to dig down 4.5 metres. This resulted in the team having to hand dig everything here. This made this section the most challenging and time-consuming of the entire project. Special machinery was used in order to manipulate the pipework.

Foul drainage and storm drains were located outside buildings #62/63 and the trench digging here was down to 5 metres deep. Some of the units in the vicinity of these works were still occupied and being used by engineering companies. This meant that access to their units was restricted whilst the work was going on. A mechanic was also in the vicinity – his vehicular access was cut off for seven days whilst works were commencing. This is where strong planning and communication channels came in to play; minimising any disruption to these businesses and ensuring they could carry on working. At the front of building #60, three other trenches were dug to four and a half metres deep to join up to manhole covers. Also, in the same area of building #63, Lawson Group was instructed to remove all the trees and shrubbery.

To the rear of building #60 was found another challenge to the drainage and services laying works. There was a known high-voltage cable here, but it was found to be running through the centre of two concrete stanchions buried in the ground, instead of underneath them. This meant hand digging was required in this area. The water and drainage were run through this section, with the foul and storm drains running down a bank and to the rear of unit #41 where the hardstanding was removed in order to dig the trench.

Behind building #41, the pipework for foul and storm drains was split off. Another storm drain was placed alongside building #26. Then the trench was dug alongside the buildings #41 and #42 where it ended. The trench was dug to around 3.5 metres deep in this area.

RESULT

All the drainage and main services on site were successfully moved, with the old services being isolated. This left the site ready for the next stage of development by the client.

To find out more on how Lawson Group can help with your next demolition or asbestos removal project, call 01793 782000, email enquiries@lawsongroup.co.uk.