Response of Strata and Buildings to Blast Induced Vibrations in the Presence and Absence of a Tunnel

Blast induced vibrations form an inevitable and major part of modern day construction. The changes that happen to the strata or buildings surrounding the blast are evident in a fraction of a second. Effect of damage is more pronounced in the absence/presence of the tunnel. The vibration produced due to blast may be induced due to a deep underground explosion, a surface explosion or even an in-tunnel explosion. In this study the above three situations are numerically modeled by a Distinct Element software 3DEC (3.0). Soil properties are varied representing soft and stiff strata. Further, three velocity time histories of 2, 45 and 85 Hz are used as an input in the model and are applied at three different boundaries of the model. Results of the analysis reveal that the response of building in softer strata and lower frequencies led to greater magnification of velocities and displacements compared to response of buildings in stiff strata. Presence of the tunnel led to reduction of peak velocity (PV’s) and displacements at the building top due to damping effect. PV’s at the top floor were greater than the PV’s at the bottom floor and there was an upliftment of the soil mass at the ground level. However, the upliftment in the presence of the building was lower than the upliftment in the absence of the building. Stress in the tunnel lining increased in the presence of the building, however percentage reduction of stress depends on the number of building stories.