Drilled Pier bored through geogrid

[JAE]

I have a building addition that is anticipated to be constructed near an existing modular block/geogrid retaining wall.

The wall is about 10 feet high and there are supposedly horizontal geogrids extending from the earth side of the wall back about 10 feet or so.

I need to establish buildng columns just behind the wall and want to use deep drilled piers to support it - the column/piers would be located about 5 to 8 feet behind the wall.

Can one drill a pier through existing in-place geogrid successfully? Does it just tear the geogrid in the discrete locations or would we run the risk of snagging the geogrid and ripping it from the wall?

The piers are about 30 feet apart so the damage to the geogrid would be very localized.

 

[Brad805]

I forsee three problems. First, I can't imagine drilling through the grid is going to work very well at all. The grid will hold up suprisingly well and will get tangled in the drilling equipment and as they turn the bit I suspect they could do a lot of damage to the grid. I am sure you could drive a pile through it, but that might not be an option. The second concern I have is are you going to cause any damage to the retaining wall design? The third question is will your new structure impose any surcharge loads to the existing retaining wall? If so, you need a new retaining wall design so none of the above matters.

Brad

 

[Nuccio]

I have seen fence guys try to auger geogrid ti install fence and the auger grabs the geodrid and actully pulls the the SRW outof aligment at the top of the wall. If you know where the geogrid is usally every 3 courses maybee you can run a core barrel at that elvation and then clean up with an auger.

 

[JAE]

Brad805 p thanks for the reply - no problem on the wall as the building loads will go only to the piers to the deeper strata.

Nuccio - does a core barrel (not sure what that is) work for a 30" or 36" diameter drilled pier?

 

[Nuccio]

A core barrel is just a round casing like tool with cutting tools on the end. You can have it made any size you want. Most suppliers will get it the size you need and you can spec the kind of cutting teeth on the end. Maybe it can be made with a saw tooth pattern on the end to try to cut geogris instead of grab it an tear it. How many do you have to install and how deep.

 

[msucog]

better get the wall designer to sign off that they're ok this work won't impact their design or you just bought that wall. depending on your location, the wall designer likely already disclaimed liability 14 ways anyways but going forward without a letter in hand bumps you up to the prime candidate to be sued when it falls someday.

i agree with above comments, it'll likely jerk the grid and wrap around the auger. driven would work better. i'd try to offset behind the grid or in front of wall if punching the grid isn't allowed.