If you could go back and do some sampling, I suggest using thin wall tubes (or Shelby tubes). Such samples would be considered undisturbed. Although, I'll agree with you, there will always be some disturbance. Also, if you go back for sampling, try to do insitu vane testing. Shear strength...
Estimates of shear strength values on disturbed samples are nearly impossible to obtain. But if going back and obtain undisturbed samples, or perhaps in-situ testing are not possible, then there are a few things you could attempt with your dessicated samples and get, at best, a range of shear...
