(a1), (a2) TC and TE; (b1), (b2) θ = 0° (b = 0·5) α = 45°; (c1), (c2) HCSS. (a1), (b1) and (c1) show undrained tests stress–strain (q/$p′c$ plotted against ε_q); (a2), (b2) and (c2) show stress path (q/$p′c$ plotted against p′/$p′c$⁠)