The Job
As part of distribution improvements, National Grid’s contractor bored 830LF through rock using HDD. The bore was 30″, with a 16″ HDPE casing, carrying three, 4″ HDPE conduits.
As part of the installation, the NY Thruway Authority required the casing to be back-grouted, and the casing pipe’s annular space grout filled.
The Challenge
The proposed back-grout had to be pumpable 830LF at very low pressure, dense enough to displace the 10PPG drilling mud and provide sufficient strength to meet Thruway requirements. The proposed annular space grout had to be pumpable 830LF at very low pressure, light enough to not apply excessive pressure on the conduit pipes, and also provide sufficient strength to meet Thruway requirements.
The Solution
CJGeo proposed two different grout mixes to meet the project requirements. 85lb/cuft casing background for the displacement of the 10PPG (75lb/cuft) drilling mud, and 25lb/cuft annular space grout within the casing.
CJGeo’s crew mobilized to the site, and successfully performed the back-grouting and annular space grouting in a single day.
