Noise generation from ground-borne vibrations: beyond noise nuisance to structural damage

Abstract

In view of the limited land available for new development in Malta, 20-year old, two-storey terraced houses are today making way for apartment blocks, typically 5 floors in height, including a number of basement parking levels. This calls for additional civil works beyond simply building the plot, namely involving demolition and excavation below ground level. The new development is sandwiched between two existing terraced houses or similar blocks, thus any excavations are bound to adversely affect neighbouring property to some magnitude. Buildings are constructed in load bearing masonry walls with reinforced concrete slabs having a simple bearing on masonry walls. A soft storey is often introduced to satisfy parking or commercial requirements. This heavy form of construction lacking flexibility is prone to cracking. Studies suggest that blasting, piling, pneumatic machinery and heavy vehicles’ road traffic cause ground-borne vibrations. These typically translate into intolerable noise levels, even if claimed as only temporary. Tolerance limits vanish when nominal superficial cosmetic cracks develop into structural damage to neighbours’ property. These points to the need to assess and regulate the allowable noise and vibration levels in urban areas in order to curtail noise levels, thus preventing unnecessary neighbourhood disturbance, and ultimately structural damage. Through fieldwork on five building sites and empirical studies this paper investigates noise and vibration levels generated from site excavations using standard pneumatic plant. Results already indicate that values obtained are well within established International Standards, however complaints still arise. These stem from cosmetic or serious structural damage to neighbouring property. Currently, in Malta there is no control on the permissible vibration levels or allowable noise levels for such sites. The paper goes on to recommend the allowable limits for noise levels generated from ground-borne vibrations.