[HM] Initial total stress input
With the changes in this MR, the initial stress can be input as total stress. An optional attribute named total
is added to the initial_stress
tag to indicate whether the input initial stress is total stress or effective stress.
A benchmark is prepared to verify the implementation. The benchmark uses a [0,1 \text{m}]^3
cubic domain. The initial pore pressure is 10^6
Pa. the initial total stresses are \sigma_{xx}=\sigma_{yy}=0.8\cdot 10^6
Pa, \sigma_{zz}=2\cdot 10^6
Pa. The boundary conditions are given as
Boundary  H  M 

top 
p = 10^6 Pa 
\tau_z = 2\cdot 10^6 Pa 
bottom 
p=10^6 Pa 
u_z=0 
others    u_n=0 
With the Biot' constant being 0.8, the output effective stresses are expected as \sigma_{xx}=\sigma_{yy}=0
Pa, \sigma_{zz}=1.2\cdot 10^6
Pa.
TODO: The same implementation for THM, RM, TRM, and TH2M.

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