Geogrid reinforcing behind rigid concrete retaining walls
Geosynthetics | October 2009
GMA techline answers from Bob Koerner
Subject: Geogrid use behind rigid concrete walls I was wondering if you can provide some information or guidance regarding the use of geogrid reinforcing behind rigid concrete retaining walls. My main questions are: How much can the use of geogrid reduce the lateral earth pressures acting on the retaining wall? How much does the geogrid have to deflect/deform for it to be in tension to support the applied loading? (Joe, New York)
Reply: Nice question and following is my answer. One can construct a wraparound geotextile reinforced wall to the effect that 100% of the lateral load is carried by it and zero goes to the concrete, which now acts as a facing. In fact, this is precisely what the Japanese railroad system does and it has proved excellent under static and seismic conditions. Walls for their bullet train are constructed in this manner. That said, they do require a period of about one year (depending on the type of backfill soil) to allow for compaction and settlement of the wraparound structure before anchoring the concrete facing to it. Regarding your question as to the amount of deformation needed, it depends on the type of backfill soil and its in-situ conditions.
Here in the U.S., we have done similar constructions sometimes with “tilt-up” wall facing panels acting as the permanent facing material for more than 15 years. Go to it!
RSS
Twitter
Facebook
Comments
Comments are the opinion of individual posters and do not reflect the views of Geosynthetics or Industrial Fabrics Association International.
8:45 pm CST
Engineering of a 16′ high reinforced concrete retaining wall
I am a contractor and also a teacher who would like to build a new house. That house will be built into a bank and the rear wall of the home will be basicaly a 16′ high reinforced concrete wall. Could you help me with the design parameters. Wall / footer thickness and reinforcement size,placement and type. 50′ of the rear wall will be supported by the new stucture especially at 10′. There will be a 16′ high by 16′ retaining wall and a 16′ high tapering to 1′high retaining wall 65′ long.
Residential Building code does not provide for such anapplication. My inspector would like those specs approved by a certified engineer.
3:29 pm CST
Re: Engineering of a 16′ high reinforced concrete retaining wall
Note: We received the following response from Robert Koerner.
My answer to the original TechLine question concerned how to eliminate lateral forces on a wall facing under the assumption that there was room behind the wall face to construct some type of geosynthetic system. The one I mentioned was a wrap-around geotextile wall which would handle the forces and the facing need only be attached to the geotextile wrapped soil mass. This is done quite regularly.
Mr. Harpster’s situation is completely different since he does not have any room behind his proposed basement wall. He has a soil slope. What he has to do is excavate incrementally the slope behind the proposed basement wall and simultaneously soil nail and shotcrete the retained soil’s surface. For a 16′ depth he would likely do it in three stages. Now he can build the permanent basement wall using this shotcreted surface as the back of his new basement wall.
The above said, he should not do this work himself. He needs a competent foundation engineer to do the design in a safe and sound manner. The technique I described is one of many ground modification techniques….Bob Koerner
Submit a Comment