Figure 2

The lifting process of a manhole. (a) When \({{h}_{1D}=h}_{2D}+{z}_{2D}\), the overflow process occurs immediately when the head exceeds this critical point in the FSMI method. (b) When \({{h}_{1D}>h}_{2D}+{z}_{2D}\), the overflow process does not occur in the FSMIC method. (c) The critical pressure head is exactly high enough to lift the manhole cover in the FSMIC method. (d) The overflow process occurs in the FSMIC method when the manhole cover is lifted in vertical displacement by the difference between the pressure head and the critical pressure head.