Passive Earth Force

Question

How can I get from PLAXIS the mobilized earth passive pressure in orden to calculate the earth resistance ratio? 
 I appreciate your help. 
 Best regards, 
 Ram&oacute;n Salazar

Dennis Waterman · Answer

Dear Ramon, 
 There are 2 possibilities: 
 1) If you have an interface along the structural element from which you want to know the earth pressure, just check the interface stresses - in particular sigma_N. 
 2) Draw a cross section along the structural element and check the normal forces in the cross section. 
 The first method is more accurate, but of course it requires the presence of an interface. 
 
 With kind regards, 
 Dennis Waterman

Dennis Waterman · Answer

Dear Ram&oacute;n, 
 In an interface there is the possibility to check the maximum shear stress (t_max) and the relative shear stress (t_rel) which is the actual shear stress as percentage of the maximum shear stress. In a cross section this is possible too, and additionally it's possible to see for instance the deviatoric stress (sig1 - sig3)/2. Note that the maximum shear stress is based on the assumption that the mean effective stress doesn't change (hence the Mohr Circle doesn't move along the normal stress axis). This assumption may be correct for the Mohr-Coulomb model, but mostly likely not for the advanced models. In principle the maximum shear stress is not known until it's reached - we only make an conditional assumption that especially for advanced models in particularly undrained conditions may not be correct. 
 With kind regards, 
 Dennis Waterman