# Retaining structures – Pressure Distribution

**FUNDAMENTALS OF ENGINEERING**hide

For the Civil FE exam, under knowledge area number** 12. Geotechnical Engineering**, the NCEES FE exam specifications tell us we have to understand how to analyze the stability of retaining structures – **E. Stability of retaining structures (e.g., active/passive/at-rest pressure)**.

Before we can do this, we must have a complete understanding of how the pressure is disturbed along the active side of a retaining wall considering:

- Active Rankine coefficient
- Total stress
- Pore water pressure
- Effective stress
- Water table location
- Surcharge load

With a clear understanding of how the active pressure is distributed both qualitatively and quantitively, we can determine the active pressure force per unit length of wall **P _{A}**.

To prepare for your FE exam, use the pressure distribution diagrams shown below to help you determine that crucial pressure force we will always need when conducting a stability analysis.

### Active Pressure Distribution (Dry Soil)

The location from the bottom of the pressure force (P_{A1}) can be found by using the table on **page. 111 in FE Handbook 10.1**. This is the y-distance centroid for a triangle shape.

### Active Pressure Distribution (Partially Submerged Soil)

The locations from the bottom of the pressure forces (P_{A1} and P_{A2}) can be found by using the table on **page. 111 in FE Handbook 10.1**. This is the y-distance centroid for a triangle shape and a trapezoidal shape.

### Active Pressure Distribution (Completely Submerged Soil)

### Active Pressure Distribution (Partially Submerged soil with Surcharge Load)

The location from the bottom of the pressure force (P_{A}) can be found by using the table on **page. 111 in FE Handbook 10.1**. This is the y-distance centroid for a trapezoidal shape.

### Pressure Distribution (Bearing Pressure)

Since the stem of the retaining wall is located off center with respect to the centroid of the wall, eccentricity is said to exist where a bending moment in produced. In this case, the pressure developed is not uniform and can be evaluated as a combined loading case.

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