Status quo and critical review of PPV safe limits for subsurface construction blasting close to low-rise buildings

Abstract

Subsurface construction blasting may result sever man-made ground vibrations.Waves generated due to detonating a charge in a solid medium like rock generate particle movement and travel at different wave velocities. As such, ground-borne vibrations have effects on nearby buildings that range from disturbing the occupants to causing severe threshold "cosmetic" or structural damage. The said ground vibrations are usually monitored to assess their impact on nearby structures. Currently, codes of practice adopt safe limit criteria which are mainly based on field observations where the structural damage is correlated to the soil Peak Particle Velocity (PPV) produced on the ground surface close to the structure. For example, the criteria limit the PPV of the ground vibration to 51 mm/s at the nearest "non-owned" structure to the blasting site. On the contrary, it is not the soil PPV that matter but it is the structural response to the ground vibration which causes the damage: All the blast-vibration complaints are actually due to the structure vibration not the ground vibration. In this paper, some of the currently adopted safe limit criteria of ground vibration generated by subsurface construction blasting are reviewed. Two real case studies have been performed on low rise buildings (houses) located nearby an excavation performed by blasting in rock. The PPV and the vibration frequency due to excavation by blasting measured close to these low-rise buildings satisfied the existing safe limit criteria for subsurface blasting ground vibration. Despite this fact, both buildings suffered threshold cracks and one of them even had structural cracks. Thus, it is argued that the current safe limit criteria ignore a very important factor which is the structural response to the ground vibration. It is also argued that ground vibrations with low level frequencies affected the structural response of the two houses may have caused resonance andwall rattling.These, in turn, caused threshold, and even structural, cracks beside the severe disturbance to the residents. So, as an urgent modification, it is recommended that the PPV for low level frequency vibrations (4-30 Hz) should be multiplied by a magnification factor before comparing them to the current safe limits of the codes of practice. This would simulate the resonance or wall rattling which may occur to low rise buildings subjected to ground-born vibrations with low level frequencies. © 2013 Taylor & Francis Group, London, UK.