Minimal 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 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 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 "Minimal dimensioning pressure" in the analysis.

To determine the minimal dimensioning pressure the program employs for layers of cohesive soils as the minimal value of the coefficient of active earth pressure an alternate coefficient K_a = 0,2. Therefore it is ensured that the value of the computed active earth pressure will not drop below 20% of the vertical pressure (K_a ≥ 0,2) – see figure. Application of the minimal dimensioning pressure assumes for example the possibility of increasing the lateral pressure due to filling of joint behind the sheeting structure with rain water. If the option of minimal dimensioning pressure is not selected the program simply assumes tension cutoff (K_a ≥ 0,0).   

Minimal dimensioning pressure