Least Squares Finite Element Approach in Assessing Excavation Damaged Zone and Excavation Disturbed Zone

During the construction of underground structures, the redistribution of in situ stresses cause damage to material around the structure. The damage can be categorized via three types of zones; namely the Excavation disturbed Zone (EdZ), the Excavation Damaged Zone (EDZ) and the Highly Damaged Zone (HDZ). In this study, a numerical approach is presented for assessment of EdZ and EDZ. The computational process is based on least squares finite element method. The suggested approach allows one to calculate nonlinear distribution of induced stresses in EDZ and EdZ, along with the thickness of EDZ, for a circular tunnel subjected to hydrostatic stress condition in a homogeneous and isotropic medium. Comparison of the results obtained from suggested methodology with published results shows the differences to be insignificant. The maximum relative error for EDZ thickness value and the radial stress at EDZ-EdZ interface were found to be 1.2% and 1.4% respectively. The results also demonstrate that values of EDZ thickness and induced stresses at EDZ-EdZ interface are related to the nonlinear rock mass quality and in situ stresses.

Keywords:

Excavation Disturbed Zone , Excavation Damaged Zone , Tunnel , Least squares , Finite Element Method , Stress