Horizontal Drilling Heaving

[Sojisub]

A contractor on my project was using horizontal drilling to pull a fusible pvc 20 ft deep in the ground. As they were pulling, drilling fluid came through the existing joints along an old trench. And supposedly, the ground heaved 1". My question is it possible for the ground to heave when the pipe was pull so deep in the ground? Since the pavement heaved 1", are there possible damage to the pavement. There are no new cracks. The pavement is about 6" AC and 12" CTB.

 

[bimr]

Using the frac-out occurs during the drilling operation. A frac-out occurs when the down hole mud pressure exceeds the overburden pressure (i.e. shallow or loose sections of the bore), or the fluid finds a preferential seepage pathway (such as fault lines and fractures, infrastructure or loose material)

Direction drilling requires judgment and accurate geotechnical data. Assumptions are required regarding contractor practices, mud properties, pilot and reamed diameters. When assumptions regarding geotechnical conditions and drilling practices are invalid, results are likewise unsatisfactory.

The Contractor should be monitoring the drilling fluid pressure and the route of the drilling for frac-outs. Doesn't seem possible that a 20 ft deep drilling will result in frac-outs.

You have to include frac-out contingency plan in the Contract documents. Otherwise, you are dealing with change orders.

Why are you installing an electrical conduit 20 ft deep?

Link

 

[Sojisub]

This is a sewer line and it is 20 ft deep to avoid existing storm drains. Does the heave seem possible considering the bore is 20 ft deep?

 

[bimr]

It depends on the underground conditions. You mentioned that there are storm drains which will indicate that the ground has been disturbed already and maybe is not compacted.

Is this a forcemain or gravity sewer? What is the diameter?

 

[Sojisub]

This is a 6" force main.

 

[geotechguy1]

What are the ground conditions and does the driller have a record of the pressure in the bore

 

[cvg]

has the 1 inch heave been confirmed with survey? "pavement damage" includes a hump in the road, probably not very serious. any concrete curbs, gutters or sidewalks might crack

how large was the reamer?