Hello everybody
Assume a reconstitute cemented granular soil subjected to direct shear testing under usual testing requirements, The plot of shear stress versus shear strain shows two local strain softening before peak strength but the general trend is strain hardening the question is what is the reason for numerous softening, I attached an example of aforementioned plot
Thanks.
Local softening may occur due to the inhomogeneity of the mixture of soil and binder, as there are in the sample locally weaker zone
Thank you so much dear Mirjana you are absolutely right specially when we are using two or more additives in the mixture , I did change the mixing methods to produce more homogeneous sample and the results were much better in inclinations toward peak failure, so I have another question is there any standard regarding the tolerance of this softenings or inhomogeneity of the sample?
Best Regards
Concentrated stresses have two sources:
Non homogeneous specimen properties were mentioned already. Whereas equipment induced distortion is not as easy to notice. Conventional triaxial apparatus and a shear box, both induce tremendously non-linear stress states within the specimen.
Dear
I agree with Vukicevic, and besides the non homogeneity of the mixture, the stress relaxation will also causes the local softening.
Hello Dear Mr Sarsam
Thank you for your reply, Can you elucidate the influence of stress relaxation? Is it possible to happen for a brittle cemented soils with a rigid body?
Dear
stress relaxation usually happens to both ductile and rigid materials, for ductile material like steel, it is termed as yielding, while for rigid material like concrete, it is called the strain due to stress relaxation
I think, from a structural point of view, when a local failure happen (such as small crack or sliding in a small area of the sample) a local strain softening will notice due to the stress relaxation. After that, the new geometry of the sample can carry more loads, so strain hardening will continue.
Hello Dear Mohannad Husain
I am not familiar with the term "stress relaxation" in strain hardening behavior Can you introduce me some paper or a book regarding this matter in soils or rocks, I'd appreciate it
Thanks
Dear Bobak Jamhiri
Please notice Fig. (19) and the author describe.
https://tidsskrift.dk/index.php/geografisktidsskrift/article/viewFile/7355/13887
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