Is the initial stress in General in soil test effective stress or total stress?

Question

Hello 
 I always got smaller q value When using general in soil test than that in experiment. I think there may be the lower initial stress input cause that. So I wander the initial stress input is effective stress or total stress. This is similar with initial unit stress in Triaxial,which can be easily found effective stress. Fig1 shows the clear effective stress, But I can't make sure if the initial stress in General is effective stress or total stress. Any help will be appreciated. 
 
 Fig1. Stress in Triaxial 
 
 Fig2. Stress in General

Vasileios Basas · Answer

Dear Jianshu Liu, 
 The stresses of a General Test compared to a Triaxial test should be identical, provided that the conditions are set up correctly. For example, I have run a "Drained" and "Undrained" analysis on both tests based on the initial stresses you provided. As you can see, the results are identical. 
 
 I think there might be confusion about the cell pressure shown in Fig. 1 of your question. The confining stress &sigma;c (cell pressure) is applied by pressurising the cell fluid surrounding the specimen &ndash; it is equal to the radial stress &sigma;r, or minor principal stress &sigma;3. The deviator stress q is generated by applying an axial strain &epsilon;a to the soil. The deviator stress acts in addition to the confining stress in the axial direction, with these combined stresses equal to the axial stress &sigma;a, or major principal stress &sigma;1. Therefore, when running a General test in isotropic conditions, you need to ensure that the initial stresses (&sigma;xx, &sigma;yy, &sigma;zz) are equal to the cell pressure.