M Fatehi Marji - Assistant professor, Yazd University, Yazd, Iran
M.A Manouchehrian - MSC student, Sahand University of Technology, Tabriz, Iran,

Prior to excavation, any point in rock mass is subjected to stress, which has to beconsidered in the overall distribution after the excavation work is completed. Overthe past three decades, empirical, analytical and field studies have shown that theratio of average horizontal stress to vertical stress plays a dominant role inengineering structure design. Nationally, this ratio is referred to as the coefficient oflateral stress KO, which is a dimensionless positive quantity. In this paper the effectof different values of horizontal stress to vertical stress ratio (KO) on the variation ofstress and displacement in underground constructions has been investigated by usingTWOFS algorithm which is based on BEM. The results show deformations andstress distributions are as a function of KO and excavation shape

Horizontals stress to vertical stress ratio (k), stress distribution, horseshoe shaped tunnel, Boundary element method, TWOFS