Minimum Dimensioning Pressure
When determining the magnitude and distribution of earth pressures it is very difficult to qualify proportions of individual effects. This situation leads to uncertainty in the determination of earth pressure loading diagram. In reality, we have to use in the design the most adverse distribution in favor of the safety of the structure. For example, in case of braced structures in cohesive soils when using reasonable values of strength parameters of soil along the entire structure we may encounter tensile stresses in the upper part of the structure - see figure. Such tensile stresses, however, cannot be exerted on the sheeting structure (consequence of the separation of soil due to technology of construction, isolation and drainage layer). In favor of the safe design of sheeting structure particularly in subsurface regions, where tensile stresses are developed during computation of the active earth pressure, the program offers the possibility to call the option "Minimum dimensioning pressure" in the analysis.
To determine the minimum dimensioning pressure the program employs for layers of cohesive soils as the minimal value of the coefficient of active earth pressure an alternate coefficient Ka = 0.2. Therefore it is ensured that the value of the computed active earth pressure will not drop below 20% of the vertical pressure (Ka ≥ 0.2) - see figure. Application of the minimum dimensioning pressure assumes, for example, the possibility of increasing the lateral pressure due to filling of joint behind the sheeting structure with rainwater. If the option of minimum dimensioning pressure is not selected the program simply assumes tension cutoff (Ka ≥ 0.0).
Minimum dimensioning pressure