How can I define minimum soil pressures in DeepEX?

In this document we illustrate how we can define minimum earth pressures and lateral earth coefficients in DeepEX – Shoring and tunnel design software.

A. Applying minimum lateral earth pressures and/or lateral earth coefficients for a specific soil type

A.1 Applying minimum soil pressures

The general equation of the active horizontal soil pressures is:

For highly cohesive soils (with great c' or Su values) this equation can result in very low active pressures. If the calculation above becomes negative, then the software will use the value 0.

Fig.: Calculated lateral earth pressures for a highly cohesive soil

To avoid that situation, we can apply the minimum pressure you wish to be applied anyway, disregarding any potential smaller pressures that might have been calculated.

In example for the above scenario, we define for the clay soil a minimum sh' = 0.2 ksf:

Fig.: Applying minimum soil pressures Sh’=0.2ksf to the specific soil type

After the analysis we notice that the minimum requested soil pressures are applied to the whole soil layer.

Fig.: Calculated lateral earth pressures (minimum pressure 0.2ksf requested for the clay soil)

A.2 Applying minimum lateral earth coefficient, Ka

From the Rankine equation:

Similar to the above notes for minimum pressures, a soil with higher friction angle will result having smaller calculated lateral earth coefficient Ka, thus smaller active lateral earth pressures:

Fig.: Calculated lateral earth coefficients Ka and Kp

Fig.: Calculated lateral earth pressures for the default calculated earth coefficients

We can step in this procedure in order to request a minimum Ka to be applied to the soil:

Fig.: Applying a minimum lateral earth coefficient Ka = 0.3 to the specific soil

Fig.: Calculated lateral earth pressures (minimum Ka = 0.3 requested for the clay soil)

A.3 Applying both minimum pressures and minimum lateral earth coefficient

Finally, if we define both a minimum Sh' and a minimum Ka, then the program will use the most critical of the two (the one that results to higher calculated earth pressures):

Fig.: Defining both a minimum earth pressure and a minimum Ka value

Fig.: Calculated lateral earth pressures (requested minimum Sh’=0.5kf and Ka = 0.3)

B. Applying minimum lateral earth pressures and/or lateral earth coefficients for a model (all soil layers)

In the Analysis tab of the program, in the Drive side pressures drop down menu we can select to apply minimum lateral earth coefficients of lateral earth pressures for the selected model. This selection will be applied to all soil layers in the stratigraphy used in our model area.

Fig.: Option to apply minimum pressures and earth coefficients to a model and the corresponding calculated lateral earth pressures.

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