Tunneling & Direct Pipe
NorthStar develops fluid programs for direct-pipe, large diameter tunneling and micro-tunneling projects. These programs provide contractors with accurate fluid volume and additive amount estimates. Estimates are based on a detailed geological analysis of the proposed bore path and surrounding geology. Each EDFP is tailored to meet the specific challenges of each project. Each program contains a breakdown of the proposed slurry and lubrication fluid systems. These breakdowns contain fluid properties, recommended additive concentrations and alternative fluid formulations. A geotechnical walkthrough of the bore is also provided to help crews prepare for and troubleshoot possible problem zones.
Slurry fluid systems can be designed for a large range of varied geologies. Slurry fluids can be designed to provide inhibition, stabilization and fluid loss control. Inhibitive slurries aim to reduce occurrences of cutter clogging and formation swelling while traversing reactive formations. This results in reduced downtime and increased advancement rates. Stabilizing fluids are designed to creates a low-permeability filter cake in order to mitigate fluid migration into the formation. The addition of a filter cake on the cutting face subsequently increases bore stability, holding the formation in place and reducing the risk of sloughing or hole collapse.
Annular Lubricating Fluids
Annular fluid systems are designed to enhance bore stability and reduce jacking forces. The annular space between the formation and the machine is filled with this fluid to help reduce the coefficient of friction and reduce the required jacking forces. This allows the machine or pipe to slide more easily along the bore. Similarly, to slurry fluids, lubricating fluids also create a filter cake on the bore wall. The filter cake is meant to stop groundwater ingress into the annular space and to stop lubricating fluid from leaving. In porous formations the annular fluid further increases the bore stability being able to form a grout-like consistency which holds the formation in place.