Soil Values

Allowable Soil Bearing:

The maximum allowable soil bearing pressure for static conditions. Using the spin buttons you can vary the value in increments. Usual values for this vary from 1,000 psf to 4,000 psf or more.

Lateral Pressure Method:

Here you can choose between E.F.P. or Coulomb formula. EFP refers to "Equivalent Fluid Pressure," where you can enter a lateral soil pressure in psf per foot of depth. "Coulomb" instructs RetainPro to use the Coulomb method to calculate active and passive soil pressures using an entered angle of internal friction for the soil. When Coulomb is chosen, the Ka*Density value for active pressure is computed.

When the EFP Method is selected:

Active Soil Pressure - Heel Side:

Enter the equivalent fluid pressure (EFP) for the soil being retained that acts to overturn and slide the wall toward the toe side. This pressure acts on the stem for stem section calculations, and on the total footing+wall+slope height for overturning, sliding, and soil pressure calculations.

Commonly used values, assuming an angle of internal friction of 34°, are 30 pcf for a level backfill; 35 pcf for a 4:1 slope; 38 pcf for a 3:1 slope; 43 pcf for a 2:1 slope; and 55 pcf for a 1.5:1 slope. These values are usually provided by the geotechnical engineer.

When the EFP method is used the value entered is the horizontal component of the active earth pressure, commonly called the lateral earth pressure. Because active pressure is always due to an active soil wedge there are horizontal and vertical components. Using the specified horizontal component and the soil density, the program iterates for a value of an effective soil friction angle (“Phi”, the angle of internal friction) using the Coulomb equation. Once Phi is known, the program can calculate a vertical component of the active pressure and provide options to have this vertical component applied at the plane of retained earth, which is always considered to be at the rear of the heel. The user can choose to apply this force for overturning resistance, sliding resistance, and/or for soil pressure calculations, by checking the boxes in the category named "Use of vertical component of active lateral soil pressure".

Passive Pressure:

This is the resistance of the soil in front of the wall and footing to being pushed against to resist sliding. Its value is in psf per foot of depth (pcf). This value is usually obtained from the geotechnical engineer. Its value usually varies from 100 pcf to about 350 pcf.

Soil Density (heel side):

Enter the soil density for all earth (or water if applicable) above the heel of the footing. This weight is used to calculate overturning resistance forces and soil pressures using the weight of the soil block over the projecting heel of the footing. When surcharges are applied over the soil, the surcharges are transformed to equivalent uniform lateral loads acting on the wall by the ratio force = (Surcharge/ Density)*Lateral Load. Input this value in lbs. per cubic foot. Usual values are 110 pcf to 120 pcf. More if saturated soil. Water is usually assumed to be 64 pcf.

Soil Density (toe side):

Enter the soil density on the toe side, which may be different than the heel side. When surcharges are applied over the soil on the toe side, the surcharge is transformed to equivalent uniform lateral loads acting on the wall by the ratio force = (Surcharge/ Density)*Lateral Load. Input this value in lbs. per cubic foot. Usual values are 110 pcf to 120 pcf.

When the Coulomb Method is selected:

Soil Friction Angle:

This value is entered in degrees and is the angle of internal friction of the soil. This value is usually provided by a geotechnical engineer from soils tests, but can also be found in reference books or building codes for various typical soil classifications. This value is used along with Soil Density within the standard Coulomb equations to determine "Ka" and "Kp" multipliers of density to give active and passive soil pressure values.

Active Pressure (or At-Rest Pressure for Restrained Walls):

This value will be computed using the Coulomb formulas. This represents the lateral earth pressure acting to slide and overturn the wall toward the toe side. The result will be presented in units of psf/ft. This pressure acts on the stem for stem section calculations, and on the total footing+wall+slope height for overturning, sliding, and soil pressure calculations.

When the retained soil is sloped, a vertical component of the lateral earth pressure over the heel can be applied vertically downward in the plane of the back of the footing. You can choose to apply this force for overturning resistance, sliding resistance, and/or for soil pressure calculations, by checking the boxes on the Options tab.

Passive Soil Pressure:

This value will also be computed using the Coulomb formulas. This is the resistance of the soil in front of the wall to being pushed against to resist sliding. Its value is in psf per foot of depth (pcf). Common values usually vary from 100 pcf to about 350 pcf.

Soil Density (heel side):

Enter the soil density for all earth (or water if applicable) above the heel of the footing. This weight is used to calculate overturning resistance forces and soil pressures using the weight of the soil block over the projecting heel of the footing. When surcharges are applied over the soil, the surcharges are transformed to equivalent uniform lateral loads acting on the wall by the ratio force = (Surcharge/ Density)*Lateral Load. Input this value in lbs. per cubic foot. Usual values are 110 pcf to 120 pcf. More if saturated soil. Water is usually assumed to be 64 pcf.

Soil Density (toe side):

Enter the soil density on the toe side, which may be different than the heel side. When surcharges are applied over the soil on the toe side, the surcharge is transformed to equivalent uniform lateral loads acting on the wall by the ratio force = (Surcharge/ Density)*Lateral Load. Input this value in lbs. per cubic foot. Usual values are 110 pcf to 120 pcf.