Gravity Wall design that incorporates drainage stone?
Gravity Wall design that incorporates drainage stone?
(OP)
Hell All,
I'm reviewing a set of gravity wall calculations for a segmental block retaining wall. Where the wall height begins to get around two feet, the designer seems to change methodology to incorporate the drainage stone behind the segmental block facing units. When analyzing sliding and overturning, the base width of the wall is equal to the segmental block facing unit depth plus the width of the drainage stone - essentially doubling the width of the wall. The designer also (conservatively?) only uses the unit weight of the segmental block for the entire width of the "modified" wall instead of using the unit weight of the drainage stone (which is heavier).
Has anyone come across this before, and if so, are there any publications that promote its use?
Thank you!
I'm reviewing a set of gravity wall calculations for a segmental block retaining wall. Where the wall height begins to get around two feet, the designer seems to change methodology to incorporate the drainage stone behind the segmental block facing units. When analyzing sliding and overturning, the base width of the wall is equal to the segmental block facing unit depth plus the width of the drainage stone - essentially doubling the width of the wall. The designer also (conservatively?) only uses the unit weight of the segmental block for the entire width of the "modified" wall instead of using the unit weight of the drainage stone (which is heavier).
Has anyone come across this before, and if so, are there any publications that promote its use?
Thank you!





RE: Gravity Wall design that incorporates drainage stone?
You are right about the conservative situation, but it is designed for D0-It-Yourselfers in many situations, so that is necessary. Obviously, there is a weight added to the soil being slightly higher that a more fluid soil not being quite as heavy as backfill that has more defined specifications.
The main reason for the drainage stone is mainly for reduction of the moisture directly behind the soil and the lessening of amount of material that can be washed through the non-sealed joints. This is especially true with the curved walls that are very common in landscaping applications.
Each type of unit has a specification for the unit and the gravity wall properties, especially since the "batter" of different units can vary.
The major 4 products have extensive libraries of tests and designs based on getting engineering requirements globally since all are made and used globally and for different association and government requirements.- Just do not ask for all possible test and designs unless you have a very large truck. The other brands of units are usually copies without all the features and the amount of back-up and support varies wildly.
Dick
Engineer and international traveler interested in construction techniques, problems and proper design.
RE: Gravity Wall design that incorporates drainage stone?
RE: Gravity Wall design that incorporates drainage stone?
RE: Gravity Wall design that incorporates drainage stone?
RE: Gravity Wall design that incorporates drainage stone?
Normally, codes do not require engineering until a wall until it is over 4' or 5' tall, but even then the engineering approach is not realistic, but history and safety have shown this is a rational limit.
Trying to finely engineer a 24" high wall using 8" or 12" wide units defies any engineering logic since to many assumptions are made. Next people, will want to come up with a standard for the coefficient of sliding friction between two rough surfaced units that may or may not have moisture of sand between them.
Segmental retaining walls are not adhered, grouted or placed on concrete footings since they are an engineered flexible wall system
For real engineering concerns for engineered walls (5 to 20'), I have seen instrumented tests of the soil, stresses in the geogrid, interaction of the connections to different type of units and the connection of the grid to the units (friction or pins) performed by several systems groups. - I don't think that engineering applies to 24" high walls, but does begin to apply as wall heights and construction methods change since there is better controls over specifications and materials.
Dick
Engineer and international traveler interested in construction techniques, problems and proper design.
RE: Gravity Wall design that incorporates drainage stone?
I'm not exactly sure where the method you described comes from but I have seen it more than you'd think.
EIT
www.HowToEngineer.com