Trough width parameter ī derived from 24 stabilized troughs are
shown in Fig. 16 to represent the relationship between ī and z.
Round points indicate that there is no confined water around the settlement
trough whereas square points indicate that there is confined
water. It can be concluded that when the revised tunnel depth z tends
to be deeper, the trough width parameter, namely, the radius of the
risk scope, tends to be wider. Moreover, confined water seems to centralize
the safety risk scope around its location by decreasing the
trough width parameter. Consequently, the confined water is considered
as an unfavorable geological condition in Wuhan Metro Project.
However, this finding was not considered in former research works.
Furthermore, the proposed trough width parameter (i.e. ī) cannot
comprehensively reflect the degree of safety risk as it can only represent
the influenced scope of the ground. Because the settlement
trough could still be very shallow sometimes when ī tends to be a larger
value, the degree of safety risk tends to be minor. Consequently, a
more comprehensive parameter should be introduced to represent
both the depth and width of the settlement trough.