Core Drill Handrail/Chain Link Fence on Modular Blocks

[jaggars]

I have couple of issues to get some better suggestions
A)wrt to specifying core drilling of handrail/chainlink fence on top modular blocks of Segmental Retaining Walls i have got quite a few complains from the site that the blocks seems to crack i looking for suggestion what is the best method to use for coredrilling of handrails and how much deep it should go typically i specify 450mm deep coredrill with non shrink grout and put a geogrid about 4.0ft long (in between top 3 units) just to compensate for 50lb/ft linear load as per our codes.

B) Is there any way to check where we should put filter fabric behind the wall to seperate infill soil and retained soil zones.

 

[concretemasonry]

Drlling and grouting a post in the wall seems to make a section of the wall rigid, which is contrary to the concept of the system. This could lead to long term problems as the wall movement goes through seasonal weather cycles.

Have you considered placing the posts immediately behind the block, which are really a facing unit on the block/soil mass? I have seen this application often, but was usually on walls in the 15 to 30 foot high range.

If the units used are one of the national systems (Allan Block, Anchor Wall Systems, Keystone or Verslok), their staff engineers may be able to provide details based on their domestic and international experience through the years. Each type of unit is different, but many of the design concepts are the same. I have seen details on their sites for similar applications.

Your application is also similar to a common situation on lower walls near and around swimming pools and some highway/municipal applications.

Dick

 

[civilperson]

Another method of pole connection is to use welded base plates with 4 Hilti embeded bolts. 2 5/8" embed to 5 1/2" embed will give bolts tension values of the magnitude required.

 

[PEinc]

Be careful attaching fence or railing posts to loosely stacked SRW blocks. I would use posts embedded behind the wall. I've seen recommendations that the posts be 3' behind the top of wall.

 

[concretemasonry]

PEinc is right on.

The block are dry stacked, relying on the weight and usually a lip for stability and shear resistance.

Applying a moment(lever arm x 50#) by attaching a post results in a very unstable situation. To resist the lateral load on a railing you need depth into the soil.

Dick

 

[jaggars]

I agree with small had place srw units coredrilling is not a option since the shear wt of the units would be able to take the load of 50lb/ft. But there are some big dry units manufactured by Unilock they do specify hadrail to coredrill these blocks are ranging from 600lbs to 1800lbs.
Also, i am looking for some good guideline wrt to when to use filter fabric and when not to use filter fabric to seperate the well graded granular (infill zone) with retained zone.

 

[DarthSoilsGuy]

check this link out

http://www.advancedhardscape.com/anchorwalls/anchorwalls.html

haven't used it yet, but considering it.

 

[jaggars]

Thanks i would put this option to my client but still i would like to get thoughts on coredrilling as an option.

 

[concretemasonry]

jaggers -

You will have to go quite deep to develop enough moment capacity in the top portion of a dry stacked wall. - That is why posts are usually put in the backfill behind the wall and not into the "veneer" that protects the front and ties the grid in place.

The effectiveness of any grout in the lower units would be questionable.

Dick

 

[MSEMan]

Putting posts in the blocks is an absolutely nuts idea. Back to basics - the connection between blocks is a shear connection and has extremely limited moment capacity. The forces acting on the post impose a shear and a moment. The moment tends to open the blocks at the rear face which in turn leads to a a separation of the blocks a reduction in normal force acting on the grid and pullout failure. Put a grade beam at the back of the wall sink your posts in that and be done with it.

 

[oldestguy]

Consider placing a concrete slab on top, something like a sidewalk. Then use any standard method to attach fence to that slab.

 

[OnceOverEasy]

As mentioned previously, there is a product being distributed throughout the U.S. called Sleeve-It that is the answer to all of these comments. It is a pre-engineered, economical foundation system designed specifically for fence posts at the top of segmental retaining walls. Installed by the wall contractor, it is economical and is being used in many states. Go to:

http://www.advancedhardscape.com/