Comparison of measured Gaussian distribution and PIM-predicted surface settlements. V is the volume of transparent soil and the volume of sand. V _L is the volume loss. V _Lti is the volume loss at time t _i in the subsidence process. The ground volume loss rate at time t_i is V _Lti: ‰ = V _Lti/V × 1000 (i = 1, 2, 3, …, 7). The surface settlements at (a) t ₀ and t ₁; (b) t ₂ and t ₃; (c) t ₄ and t ₅ (d) t ₆ and t ₇