FINITE ELEMENT ANALYSIS OF HALF TUNNEL

Abstract

Half tunnels,which are primarily transportation tunnels with one wall on the hill side and a nonexistent wall on the valley side due to excavation at the toe,are superior to conventional full tunnels because they involve cheaper excavation and less time besides saving of ventilation costs etc. For design and construction of half tunnels,the knowledge of stresses developed due to excavation is essential. A pre knowledge of the stress distribution,zone of stress concentration and associated deformations to assess the stability and to perform effective support system. In this present study,to obtain the stress distribution,deformation and zone on stress concentration two dimensional Finite Element Analysis of half tunnel for various span and slope angles has been done. It has been observed that in half tunnels the deformation are negligible and the stresses all around are compressive expect near the crown of half tunnel where tensile vertical(normal) stress concentration is formed. The magnitude of which increases for steeper slopes but that can be permitted if no discontinuity is present in that zone. Therefore,it may be concluded that construction of half tunnels in hard and steep slopes is safe provided the detailed study of discontinuities confirm their stability. Also at the time of construction if any loose blocks are met with, they should be spot-bolted