This post is an extension of a previous post https://howtoengineer.com/retaining-wall-lateral-earth-pressure/

The spreadsheet will use the nomeclature found in NCMA’s Design Manual for Segmental Retaining Walls and Coulomb Theory.

See here:
Lateral Earth Pressure – Soil Basic 1 Geometry Sketch

Also here is a ‘fun’ spreadsheet where you can enter values in green columns. There are a bunch of graphs to show you how ka (the horizontal earth pressure coefficient will change with different values for backslope, effective friction angle, wall batter, and friction between wall and soil.

Earth pressure spreadsheet: Lateral Earth Pressure – Coulomb

Attached are a couple of TEDDS calcs that show the analysis of active and passive pressures based on Coulomb Theory. I am working on incorporating a berm distance into the passive equations and will probably present this in a seperate post. Using Coulomb equations for Toe slopes and backslopes should be used with caution and these conditions may warrant a Global (or slope) Stability Analysis!

Soil Evaluation NAVDAC DM – 7.2

Soil Evaluation – NCMA

Equivalent Slope

Another note: When there is a toe slope that passive pressure will be reduced a good reference for this condition is CALTRAN Trenching and Shoring Manual 2011 and NAVDAC DM 7.2 page 7.2-65 Figure 4 .

The post Lateral Earth Pressure II appeared first on How To Engineer.

Just like any other engineering problem it is wise to start with a free body diagram. This will help you get a feel for the loads and what we need to do to resist them. Then next thing is to have an understanding of what assumptions are being made in the analysis. For reference I will use earth retention system and retaining wall interchangeably for most of following articles.

There are many types of earth retention systems but here are some of the basics:

Soldier Pile wall which may also use soil anchors, deadman or whalers.

Soldier Pile and Lagging

Sheet Pile wall which may also use soil anchors, deadman or whalers.

Sheet Piling

Concrete cantilever retaining walls which may be used in some foundations as well.

Concrete Retaining wall

Segmental Retaining Walls which may be made up of large concrete units or reinforced with geogrid.

Tiered Segmental Retaining Walls

These are just some of the basics but the principles of almost all systems are very similar. No matter what system is chosen the retaining wall must be designed to resist soil pressure, hydro-static pressure, surcharges and any other externally applied loads (typical hand rails, guardrails or fences).  Typically there are there areas of stability that should be checked – external, internal and global (or slope stability). External stability typically refers to sliding, overturning and bearing failures of the wall acting as a rigid body. Internal stability is a check of the components which make up the wall to ensure the wall is acting as a rigid body. Overall or global stability is an evaluation of the entire excavation or slope of soil which the wall is bearing on and retaining. This analysis is most commonly preformed by the geotchnical engineer but should be clearly stated on the plans as to whether or not this failure state has been evaluated.

We will now move on to address the lateral earth pressure do to soil and hydrostatic load.

The post General Earth Retention Design appeared first on How To Engineer.

Offset surcharges have provided me with some of my largest learning hurdles as a young engineer. We will spend some time discussing different design options when faced with an offset surcharge. We will not spend much time on uniform surcharges as these are relatively straight forward. They are also covered extensively in texts and most importantly there is a a general consensus on how to evaluate the resulting lateral pressure. We will also provide some spreadsheets and written examples. We will also try a few video tutorials as well.

Upcoming Topics:

1. We will first cover the basics of a uniform surcharge. Generally Fq=Ka*q*H.
2. Elastic Methods – Point Load, Line Load, Strip Load, Area Load, with spreadsheet.
3. Other approximate methods
4. What is appropriate and when

The post Retaining Wall Offset Surcharges appeared first on How To Engineer.