Figure 5. Several stress-strain relationships describing the mechanical behavior of an undisturbed sample from Section 149-897D-3R-2, 73-103 cm. The yield stress is well-shown by the minimum in constrained modulus (M), where M = _v'/_v. The yield stress (shown by arrows) is estimated from all relationships as 1.2 ± 0.1 MPa, and K_o is constant and well defined at 0.57 ± 0.01.