Through ascertaining the rule which is employed to obtain the value limits of clayey surrounding rock classification indices

value limits of liquid index

natural density and plastic index in design phase are made certain based on analyzing existing research results

a long sequence test data of clayey surrounding rock and test data. The research results show that it is reasonable to ascertain the value limits according to the different conditions of classification indices as intensity ratio changing. While the depth of the tunnel is constant

consistent result

which can be received through statistic analysis and testing

is that intensity ratio decreases with liquid index increasing. If the value of liquid index is larger

the influence of natural density increasing on intensity ratio is inapparent. The value limits of liquid indices are 0

0.25

0.5; and 1.6g/cm3

2.0g/cm3 for natural density; 18 for plastic index

respectively.