Preparing the ground at Crooks Marsh for underground cables

Injector lorries delivering stone increase safety and reduce vehicle movements

In May 2022, National Grid contractors J Murphy and Sons completed Stage 1 works at Crooks Marsh, adjacent to Seabank substation with the construction of the temporary haul road and site compound. Now the team are preparing the ground to host underground cables.

Once installed, the underground cables mean that six existing pylons can be removed to accommodate the new high voltage line and the building of three cable sealing end pylons. 

Preparation of the ground involves the delivery of 100,000 tonnes of stone to raise the ground levels to safely accommodate the installation of cables. Deliveries to site through Avonmouth began in June, and to date the team have achieved fill depths varying from 1.5 to 4 metres.

The main challenges have been working close to and maintaining the safe clearances needed beneath existing overhead electricity lines. JMS are working closely with supply chain partners and are using specially designed injector lorries to maintain the safety clearances required when operating plant and machinery near electricity lines.

The lorries efficiently release stone from the rear body of truck without tipping. At no point during the delivery of the stone to site is the rear body of the vehicle raised off the ground in this location. A further advantage that the injector lorries carry larger volumes of stone than standard eight-wheel tipper lorries, reducing the overall number of vehicles movements needed to deliver the stone to site.

Janet Sorley, Senior Project Manager for JMS says, “We’re really pleased with our progress at Crooks Marsh to date. I’m particularly proud of the continued efforts of the site team and how well the works are being safely managed.”