Empirical correlations for prediction of tunnel deformation in squeezing ground condition

Abstract

The Himalaya has undergone various tectonic activities which resulted in variant geology in the region. Complex geology and weak geological structures along with ingress of water give rise to a high degree of fragility and instability in the whole mountain system. Moreover, the high mountainous topography causes high overburden pressure and stresses in the underground structures causing squeezing and other stability problems.There are several parameters which do affect the squeezing behavior of rock. Parameters like rock mass strength, in-situ stresses, overburden pressure, support stiffness, joint orientation and water play a significant role in influencing the squeezing behavior of rock.In this paper three dimensionally correct empirical correlations have been developed using regression analysis for prediction of tunnel deformation. In the study, data collected from 75 numbers of squeezing tunnel sections from Himalayan region have been included. Rock mass quality index (Q), rock mass number (N), ratio of horizontal stress (σh) to vertical stress (σv) that is K0, joint factor (Jf), support stiffness (K), vertical stress (σv), tunnel radius (a) and observed deformation (Uobs) are the governing parameters considered for developing the correlations.The developed correlations with regression coefficient of 0.87, 0.79 and 0.78 have been compared with existing correlations with main parameters as joint factor (Jf), rock mass quality index (Q) and rock mass number (N). In addition comparisons with existing correlations have been done on the basis of coefficient of accordance and linearity. The proposed correlations are definitely an improvement over the reported ones.