Grouting pressure in Tutorial 6 of Plaxis 2D

Question

Dear Sirs, 
 
 In tutorial 6, settlement due to tunnel construction, grouting pressure is included by pref of -230kPa. May I ask how this value of -230kPa was calculated?

Stefanos Papavasileiou · Answer

Dear Nadeem, 
 The value used in the tutorial example is taking into consideration the fact that one should prevent having the following situations: 
 
 Crown should not collapse or blow out 
 
 The sides should not blow out horizontally

Concerning these, you can calculate the value based on the vertical and horizontal stresses around your tunnel and make sure to apply about the same value as grout pressure. 
 Note that the exact value depends on the deformation pattern and settlement requirements at the soil surface, so then one can increase/decrease the grout pressure.