Retaining wall and Geogrid questions

[gad3319]

We are building a retaining wall using V-Interlock blocks (from World block, formerly design pro) 2'x2'x4' (3 blocks/6' high. On recent inspection the inspector said we needed specifications provided proving how high the wall could be before reinforcement is needed. (geogrid) I have been on line for days and called a number of places and NO ONE will give me an answer. Any help as to where I could look/find this answer would be greatly appreciated. Thanks for your time.

 

[fattdad]

There should be a design calculation (or design drawings that provide this detail. The answer would depend on the toe slope, the top slope, the soil strength, the type of soil in the reinforced zone, the surcharge at the top of the wall and stuff like that.

f-d

¡papá gordo ain’t no madre flaca!

 

[concretemasonry]

V-Interlock would be the place to start for design and documentation.

All of the licensed smaller retaining wall units companies have ream on ream of of test reports, certifications and design information (much is available on CD). It is needed for the walls that have built up to 45' high domestically and internationally.

V-Interlock is much smaller organization, so they would not have the large amount of information as the licensors of the block-sized units, but they should have something.

Dick

 

[GeoPaveTraffic]

As fattdad pointed out there really is no one answer as to how the wall can be built with reinforcement. Some wall designers like to think there are is, but there really isn't. You should have a design for the wall by a local engineer familure with the conditions and the product being used. That design would indicate how the wall should be constructed. Without that design, you and the block manufacturer are really just guessing.

 

[concretemasonry]

With the right product, the individual block producer relies on the engineering testing and certifications for the real tough design of projects. This part of the engineering field is not like stacking up "Mafia" blocks or come-back concrete slugs.

I know of engineers working for licensors that travel internationally and domestically to conduct testing, code work and certifications. Several major licensors are engineering firms that have had a history of working for years in the industry before acquiring a block licensing company.

 

[JML4TCM]

It is a gravity wall system, so a stability analysis should tell you if the resisting force of the weight of the blocks is sufficient to resist the driving forces of the lateral earth pressure of the soil behind the wall plus any loads, ie structrue, traffic, construction, other.

That being said NCMA Design Manual for segmental retaining walls says to use geogrid reinforcement for any wall higher than 4 feet. This is more applicable for the smaller dry cast blocks but there is no standard for the big blocks. The cost of the geogrid will be minor compaired to the other component of the wall.

 

[concretemasonry]

NCMA has nothing to do with the massive larger blocks and only is for the smaller blocks made on automated equipment with controlled curing.

V-Interlock should have the information you need regarding the installation and application of geogrid, if needed.

The attachment of the reinforcement is critical if you want to develop the benefits of the geogrid. There should be some pull-out test available for you.

It sounds like you have an inspector accustomed to the common use of geogrid in higher walls where they are and engineered wall and not just a low gravity wall. There should be some contract documents and resposibility of the EOR to provide information on the products specified and supplied.

If there are no requirements, you are accepting additional liability by making any construction suggestions if you do not have any information on the design and use of the product.

I don't know about V-Interlock, but the arbitrary and casual use of a big chunk of concrete is unfortunately all to common. There are more much more commonly used products that have total research, testing, details and support.

Dick

 

[concretemasonry]

I did a quick search for "V Interlock" ans found the site that has no real information on the product or its use. It appears it is just another forming system designed to get rid of or use up returned concrete since they talk about making 2 block per day.

There was no technical or design information available at the site I found.

Dick

 

[palmahouse]

I am fairly confident that concretemasonry is incorrect about NCMAs application to large block wall design. Use of NCMA's SRWall software is the standard of practice for large segmental block retaining wall design here in Northern California (and likely elsewhere). NCMA just rolled out the latest version - I think it is a $200 or so download off their website.

The only disadvantage to the NCMA design procedure is that, you need data regarding the geogrid/block interface strength (and/or the block to block strength for gravity walls). This data comes from fullscale laboratory testing for each block size, manufacturer, and lock mechanism, in combination with various geogrid manufacturers and modesl. NCMA has a database (and, you may need to buy the data on top of everyting!). I have had to use a "best fit" and conservative assumptions in the past when there was no data available.

 

[concretemasonry]

palmahouse -

You may be correct about the application of the large units being able to be used with the NCMA program since they are the major force in the industry domestically and internationally, but you should be able to justify the assumptions for the products used.

The large blocks are typically supplied by producers that do not have testing or background in retaining wall design or they have been absent from submitting information or testing on the unit/geo-grid connection reliability.

Since the smaller units represent a huge part of the international market, the licensors of the units have engineering staffs and regularly participate in technical code and standards committees.

When I said "reams on reams of test reports", I was referring to real wall tests including walls tested under actual conditions and moisture conditions to insure a proper connection between the wall veneer (the block) and the geo-grid back into the soil. There is very serious question about the reliability and failure mode of the block/geo-grid interface under all conditions (moisture soil contamination the can reduce the friction) and the presence of sand.

I have no connection with the NCMA, but have a good professional relationship with the professional employees, their attention to proper testing since the also do testing for various other private and government groups because of the staff and facilities. I have seen many large installations (one was several miles long in Spain that had walls from ground to 30 meters high) globally and always have admired the engineering the designers exhibited.

Dick