Once inserted into the well, the bore is grouted up with a bentonite clay slurry and the grout pipe
is removed for reuse on the next well.
Once the push is completed, (the casing and grout pipe
completely installed from the entrance shaft to the exit shaft) the grout is pumped through the pipe.
By using the 30-inch and eight-inch fusible PVC, while this allowed for a smaller bore than HDPE, it also reduced the internal space and provided for only two, three-inch thermal grout pipes from either side of the bore.
On the first bore, it was necessary to utilize all three grout pipes (two from the primary side; one from the far side) because of delays in delivery.
Six-meter-long [phi]70 mm grout pipes
were drilled from the ground surface toward the tunnel crown.
The highest pumping pressure recorded was 110 psi, at 20 to 25 cubic yards per hour using several four-inch diameter HDPE grout pipes
spaced in the bore.
'This was accomplished with little hazard to personnel by driving sleeve port grout pipes
, instead of drilling them in, and controlling overflow water from the trenches during operation,' says Berry.