Compensation grouting is an active technique used to counteract relaxation of the ground caused by tunnel excavations.
how it works:
Compensation grouting is a method in which precise and typically small quantities of grout are injected between the tunnel roof and the structures exposed to danger with low grout pressure and flow rate. It can be carried out via either using subvertical or subhorizontal drilling.
why you need it:
Compensation grouting is used most often when the construction of a tunnel causes movements of a sensitive structure. After tunneling is completed, a final grout phase is typically performed to deal with any post-tunneling settlement, particularly in clayey soils.