Stable Feature Behind MSE Wall / Narrow Wall
This will be one of several posts regarding MSE walls with complex geometry. The main references for this post and the posts to follow will be the research conducted by The Federal Highway Administration (FHWA) and mainly the publications listed below. The methods presented are simplified / preliminary methods. Ultimately a limit equilibrium analysis should be run. However this is beyond the scope… for now.
FHWA-NHI-10-024 Design and Construction of MSE walls and Reinforced Soil Slopes
FHWA-NHI-00-043 MSE Walls and Reinforced Soils Slopes Design and Construction Guidelines (Now superseded by publication above)
FHWA-CFL/TD-06-001 Shored MSE Wall Systems (SMSE) Design Guidelines
All of which can be found here on FHWA website.
I am posting my notes that correlate to the spreadsheet for now and a brief overview. We will elaborate more on the procedure in the near future.
The stable feature prevents external lateral earth pressures from exerting force on the reinforced soil mass. Therefore traditional sliding and overturning are not generally a design concern. For the trial wedge we define the geomtry and solve for the forces in the horizontal and vertical directions. We have two unknowns and two equations of equilibrium which we solve using matrix algebra (in excel) to determine the active force on the wall.
Required checks are as follows:
- Pullout of geogrid
- Reinforced soil and stable feature interface failure plane stability
- Global / Slope stability
Calculation assumes that the stable features extends up or very near the top grade surface. The wall face, top grade and stable feature slopes may all be adjusted. Currently the failure angle must be ‘manually’ adjusted to find the maximum active pressure acting on the back of the wall facing units.
As always please use with caution and check for errors!