Rock excavation in urban areas, either for surface or underground workings, is always a matter of concern due to the various environmental impacts generated by those operations. Among the harmful impacts to be controlled, ground vibrations are usually the most important ones, because of their damaging effects on surrounding structures, which require detailed and careful site investigations. Under these circumstances, baseline vibration surveys are required for urban areas in order to characterize the dynamic behaviour of nearby structures in the pre-existing situation, particularly induced vibrations caused by heavy traffic. A methodology for developing dynamic baseline studies is described and several application examples are presented, involving construction sites at Lisbon and Oporto.
The need for Environmental Impact Studies (EIS) is nowadays essential in most domains of engineering activities, as a pre-requisite for the implementation of Sustainable Development (SD) principles. Contemporary society requires that all potentially disturbing actions on the environment are carefully analysed in advance, so that responsible authorities can approve or license those projects, in order to comply with laws created under the SD philosophy. Abundant legislation exists everywhere, by means of which all concerned organizations may be informed about the rules to be followed, the steps of process licensing and related time constraints. According to each specific field of activity, there are detailed regulations to comply with and checklists to obey in order to produce the necessary EIS. For the heavy construction industry (involving both civil and mining workings) there are several important chapters that must be presented in those reports, such as (Kiely, 1997):
Review of existing documentation on the concerned area, regarding matters of topography, geology, land use, social and political aspects;
Development of an Environmental Baseline Survey (ESS) to characterize the preexisting natural conditions at the site, so that further project induced impacts may be compared and evaluated.
Description of proposed project activities, with emphasis on their expected effects on the region's relevant environmental items, such as air pollution, surface and underground water quality, impacts on fauna, flora and existing patrimony, as well as on the populations affected. Quantification of their relative importance, by means of Environmental Impact Matrices or similar classification methods is recommended for these topics.
Characterization of mitigation procedures to be followed during (and after) project implementation in order to keep all impacts below the Theresold Limit Values (TLV) established in the corresponding laws.
Description of practical techniques aimed to assure that TLVs are not exceeded.
Instrumentation and monitoring techniques to be installed so that anomalous environmental parameters may be detected and adequately corrected.
Presentation of a non-technical summary report of the EIS. Attention is now devoted to the second one of the documents indicated above.
An EBS may be defined as a study conducted to establish the existing environmental conditions at a site, before any engineering work takes place there, allowing predictions to be made concerning the likely environmental effects of that work.