you can use from different apparatus for measurement maximum soil shear strain or strength. for example direct shear box, in situ torsional apparatus. . .

I attached some paper that can use, please find them.

Good luck.

@Smaeil Momivand: I am developing a numerical computer code using matlab for the analysis of equivalent linear ! should i determine a time history of shear strain or use from a earthquake shear strain time history?

thank you

I assume you would want to use some soil parameters. For which soils are you going to implement your code? If you want a generic code, you can always use constitutive relationships to determine the shear modulus of the soil. But then you will need to determine where failure occurs for your soil. This depends on how you describe the soil behavior (ie. linear elastic, bilinear elastic perfectly plastic and so on).

I hope this helps.

From direct shear test,  unconfined test ,  triaxial test, in situ van tests 

Torsional shear Test