Typical test on saturated transparent soil – test 7 with phreatic surface at d_w = 0 – time series of images with PIV vectors showing unstable air entry coincidental with shear bands developing during plastic collapse: (a) 0·0 s; (b) 0·2 s; (c) 0·4 s; (d) 0·6 s; (e) 0·8 s; (f) 1·0 s; (g) 1·2 s; (h) 1·4 s; (i) 1·6 s; (j) 1·8 s; (k) 2·0 s; (l) 2·2 s