Assessment of Soil cohesion of Soils on Tunnel Excavation

Excess pore pressure under seismic loadings has always been a main concern in geotechnical engineering practices. Undergoing the phenomenon in a soil can cause the effective stress and hence the shear strength of the soil to decrease considerably and large deformations happen in the area. Generally, increasing the pore pressure occurs under the undrained condition. If it can be formed the drain conditions, its consequences decreases seriously. The damages caused by Excess pore pressure are divided in to two groups, surface damages and underground structures damages. Generally, first case is visible after the seismic loadings about which wide researches have been carried out. But in the second group, the lack of these occurrences and investigation problems cause the underground structures damages to be assessed less. There are several reports on devastations caused by excess pore pressure in the surrounding soil of the underground structures. As stresses and deformations of the tunnel lining increase, the surrounding soil of the tunnel is liquefied and large deformations are observed in the area. And if increasing the pore pressure occurs in the surrounding soil of the tunnel, improvement of the surrounding area of the tunnel, the stresses and deformations should be controlled to be set on the allowable limit. Therefore, evaluation of excess pore pressure effects on the tunnel lining can be regarded as an important issue. This paper is designed to focus on the topic.