Retaining Walls-Fence Posts and Floods

VIDEOS, Fence Systems
By Doug Blackburn
Sep 17, 2008 - 4:15:49 PM

Today we’re at a Walgreen’s store in Loveland, Ohio and we’re going to talk about three things for a specific retaining wall that we designed in about the year 2000. The first thing we’re gonna talk about is how not to install a fence on a retaining wall.  The second thing we’re gonna talk about is one really good way to attach guardrail to a structure near a fence. And the third thing we’re gonna talk about are some techniques to protect a wall in the event a wall is expected to be inundated with water from a creek.

You will notice at this site that there’s a fence located approximately 1 foot behind the wall.  Before this fence was moved to behind the wall, they unfortunately attached the fence to the wall.  This is a very poor way to do it.  Let me show you why.  (Panning in to show caps) These caps are not able to take the load of a retaining wall.  Even if you put non-shrink grout, the movement of the fence causes these blocks to crack.  This happened all the way along this wall in the area where the fence was attached to the wall.  Let’s go take a look at the guardrail now.

We’re here at the Walgreen’s taking a look at the guardrail now.  There are a number of ways to secure a guardrail near a retaining wall.  In this case, the contractor elected to pour a relatively thick concrete sidewalk just behind the retaining wall and attach the guardrail to the concrete sidewalk.  This provides a very stable base so the guardrail won’t affect the wall in case a car hits it. 

The third thing we’re talking about here at the Walgreen’s retaining wall regards designing and constructing a retaining wall so that it is safe under flood conditions.  This particular retaining wall went through a flood in the year 2001.  Water was above the retaining wall (the top of the retaining wall) because of this big creek.  This first thing we did is we used all angular gravel within the geogrid reinforced zone.  The second thing that we did was extended the length of the geogrids to account for the water pressure and the rapid draw down.  The third thing we did is we buried a significant portion of the wall.  You will see that this retaining wall is approximately 10 feet showing.  There’s another 8 feet buried into the ground.  The bottom of this retaining wall is equal to about the bottom of the creek.  So there’s a significant amount of wall buried, all drainage gravel, which allows the water to come back out after the flood and the extended geogrids.  Today we talked about three things:  1. How not to attach a fence to a wall.  2.  How to attach guardrail near a wall.  3.  And some ways to improve a wall’s stability in the event of flood.