Feature/norsand updates

[jgiven100]

Describe the PR

NorSand formulation is updated to be aligned with Jefferies and Been (2019) as described previously here -> https://github.com/cb-geo/mpm/issues/714 . Internal formulation changes include updates to the yield function. There are no proposed changes for user-facing components of the NorSand model.

Test cases are updated for the new formulation.

In addition to the NorSand updates, this PR contains a small refactoring of the material utility function dp_dsigma(...). As mentioned in the above issue, passing a vector of the current stress state should not be required. Thus, passing this vector is removed.

Validation

A simple FEM code is availabe from the publishers (found here). Updates to the CB-Geo implementation of NorSand are compared to the FEM code for a suite of triaxial compression tests. These tests include:

* Undrained TX,  psi_0 = -0.05
* Undrained TX,  psi_0 = +0.05
* Undrained TX,  psi_0 =  0.00
* Drained TX,    psi_0 = -0.05
* Drained TX,    psi_0 = +0.05
* Drained TX,    psi_0 =  0.00

Below is an example of the validation for the undrained, dense sample.

* solid black == FEM code
* dashed red == updated CB-Geo MPM code
* dashed purple == previous CB-Geo MPM code

The other 5 validation plots are are posted [here]().

Remaining work

Documentation will be updated prior to merging in develop.

Following this NorSand improvement, anisotropic elastic stiffness will be considered.

Edit:

Here is the mpm-doc PR -> https://github.com/cb-geo/mpm-doc/pull/62

[jgiven100]

@ezrayst I would appreciate if you took some time to look at the proposed updates!

[codecov[bot]]

Codecov Report

Merging #717 (b4f70fe) into develop (86ba10e) will decrease coverage by 0.01%. The diff coverage is 97.06%.

@@             Coverage Diff             @@
##           develop     #717      +/-   ##
===========================================
- Coverage    96.78%   96.77%   -0.01%     
===========================================
  Files          130      130              
  Lines        25899    25920      +21     
===========================================
+ Hits         25065    25083      +18     
- Misses         834      837       +3     

Impacted Files	Coverage Δ
include/materials/modified_cam_clay.tcc	89.10% <ø> (ø)
include/materials/norsand.h	100.00% <ø> (ø)
include/materials/norsand.tcc	97.67% <96.00%> (-1.13%)	:arrow_down:
include/materials/material_utility.tcc	100.00% <100.00%> (ø)
include/materials/mohr_coulomb.tcc	99.29% <100.00%> (ø)
tests/materials/material_utility_test.cc	100.00% <100.00%> (ø)
tests/materials/norsand_test.cc	100.00% <100.00%> (ø)

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