Mega Sleeve

Stages of works:

• Collaboration with National Gas Services, Mott MacDonald & Carr Civils to design G19 for grouting process with full approval & appraisal 
• Various pre site meetings with relevant stakeholders 
• Site set-up 
• Plate testing carried out at 3 locations along the sleeve trajectory to test ground stability to 50 kPa load to ensure no risk of sleeve movement following insertion of additional mass in the sleeve 
• GPS location of both sleeve ends & at change of diameter in sleeve 
• Trial holes carried out with machine assistance 
• 3nr battered excavations with assistance of 21t excavator to expose full circumference of sleeve with 700mm clearance below 
• Q10 material scrapings & wall thickness tests carried out 
• Grit blasting & recoating of full circumference of sleeve 
• Camera survey & pressure testing of sleeve by use nitrogen to confirm that the sleeve held pressure in preparation for grouting 
• Thrust block pour carried out to ensure the integrity of sleeve end seal (16,356 litres / 3.5 tonnes of grout) – 28 days allowed for curing prior to completing main works – remaining annulus space filled with Nitrogen during 28 day interim period 
• Drilling & tapping of Nitrogen sleeve to install 2” connection point for venting during grouting process 
• Main grout pour carried out to fill remaining annulus (155,208 litres / 33.437 tonnes of grout) – new innovative pump & colloidal mixer designed specifically for this project with use of a 50 tonne silo to self-feed grout powder into mixer 
• Mud balance & timed marsh funnel testing carried out periodically to ensure optimum viscosity & to monitor weight of grout mixture during the process