Constructing a Retaining Wall on Sliding Soils

The old retaining wall (which failed) was constructed on soils that were sliding downhill!  The rock was too deep to put the new retaining wall on the bedrock, so we drilled piers down to the bedrock to stop the hill from sliding and to support the new retaining wall.

This video shows you how to prevent a retaining wall failure when there are sliding soils!


Link to Photos of this project
Joseph Kowalski, P.E.
Current State PE Registrations

Tiered or Merged Retaining Walls?

When one retaining wall is constructed above another retaining wall, the two walls together are called a Tiered Wall System.  Tiered walls look like this:

When dealing with tiered walls, a retaining wall contractor will ask:
  1. How far apart are the walls?
  2. How high are the walls?
  3. Are they really two separate, independent walls?
  4. Do the two tiers of wall join and become one (merged) wall?                      
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Retaining Wall Design Contracts

Obviously, retaining wall design involves contracts.  These contracts between the Engineer and the Client are important.  Does the contract benefit both parties?  Is using contracts a win-win? 

Contracts are important to:

1.    Memorialize everyone's understanding of each party's roles and responsibilities;

2.    Reach a mutual understanding of the project requirements;

3.    Establish the rules to which the parties will adhere; and,

4.    To identify and allocate risk fairly.

 A good contract fairly allocates reasonable risk to both parties, based on the benefits of the project to each party.

Here's an example of fair allocation of reasonable risk:  when the contract includes a Limitation of Liability for the Engineer.  Why, you might ask, am I limiting the Engineer's liability and how is that fair?

Well, here's how it is fair:  The Engineer doesn't demand an Unlimited Fee.  With an unlimited fee comes unlimited liability.  With a limited fee there is limited liability.

Sounds fair to me.  What do you think?

Retaining Walls: What is Global Stability?

Global Stability is the stability of the hillside ABOVE and BELOW a retaining wall.  By it's very existence, a retaining wall changes the shape of a hillside.  These changes should be addressed by the Engineer and Contractor to determine if the hillside is stable.  Take a look at these sketches, photos and video:




Gslope Slope Stability Software

A complete retaining wall design analyzes wall stability and Global Stability.  One of our recommended software programs for global stability is Gslope!

GSLOPE allows geotechnical engineers to carry out limit equilibrium slope stability analysis of existing natural slopes, unreinforced man-made slopes, or slopes with soil reinforcement. The program uses Bishop’s Modified method and Janbu’s Simplified method. GSLOPE allows either method to be applied to circular, composite, and non-circular surfaces.