Self Drilling Hollow Bars to Stabilize a Stone Retaining Wall

[crcivil]

I've submitted a proposal to stabilize a gravity stone retaining wall 13' tall, 450 yd long, 25" width on the top, batterd towards the backfill, and with a width of 8' at the bottom. The foundation rests on soft clay soil, and the backfill material for the wall consists of coarse gravel (ballast) partially saturated.

There is a row of concrete small apartments resting on this backfill all along and just a few feet away from the wall. This wall exhibits horizontal cracks and tilting (3-4" from vertical) in some sections and I have proposed the owner to restrain it by means of two rows of 9 m and 7.50 m long soil nails employing 38 mm hollow bars with a 3 1/2" drill bit for a simultaneous drill and grout operations.

How should I go about drilling a 3.5"-4.0" borehole through a 8-feet width stone wall with a top hammer track drill without disturbing the structure before I start drilling and grouting through the coarse gravel backfill?

Best regards

 

[Ron]

Coring would be better than percussion drilling

 

[crcivil]

What are your thoughts about the proposed solution to stabilize the retaining wall?

 

[crcivil]

Thank you Ron, that's what I thought too but I'm not sure about the kind of rig I should use to go through such a depth

 

[oldestguy]

I had a job fixing a stone wall around a prison that has been built by inmates years ago. It was only a wall, but not retaining anything. The wall was built as weak as possible I suppose in hopes of allowing a prison escape break out some day. However, it was falling apart, tipping and supported masonry structures some 20 feet high. It was repaired by injecting a cement grout, due to it being porous allowing that injection. Just passing this on as a possible option.

 

[crcivil]

Thank you oldestguy, it is well appreciated.

 

[Ron]

crcivil....most commercial concrete coring firms have the capability to core through depths that you've described. They will return incremental cores, but I take it you're not interested in the core, just the hole.

 

[crcivil]

How about the rock samples taken for a mining project? I think they can employ track drills for that job, but what kind of bit to be used with the top hammer for my purpose? I will also ask for an estimate from a concrete coring company as you've suggested Ron. Regards.

 

[crcivil]

DTH drilling using a Stenwick rig with a carbide button drill, would that damage the wall? Boreholes every 1.80 m, 4" diameter, 2.40 m long, through a stone wall.

 

[crcivil]

Carbide button bit I meant

 

[Nuccio]

If the stone is loose with a lot of seams you will have a problem drilling without a temp. casing. A DTH drill with a casing would be your best bet in my opinion.