Storm water injection in Bahrain: pilot studies

Kingdom of Bahrain often suffers from urban flooding problems despite being a desertic country. An attempt has been made in this contribution to study the efficacy of the storm water injection systems not only in tackling urban flooding problems but also in augmenting the depleting ground water resources of the country. Two pilot studies were carried out in a centrally located area, one in a relatively open area and another in a densely populated location. A set of one recharge well and one observation well of about 40 m depth and 30 m apart was drilled in each site. Storm water was injected into the recharge wells after allowing it to pass through a specially designed natural filter system. Ground water levels were monitored at the observation wells on monthly basis and water samples were collected periodically during and after the rainfall events for chemical analysis. Initial results showed that the volume of storm water injected is proportional to the volume of storm water generated in an area. However, in the long run, the injection well having favourable hydrogeological situation and lesser silts in the storm water performed better in terms of total recharge despite having lesser volume of storm water available. Ground water quality for some parameters such as lead and cadmium remained an issue of concern, but could be controlled through construction of stricter filter system. Dilution of the injected storm water with the host ground water too significantly reduced the risks of contamination. The injection well located in the open area performed better than that of the densely populated area despite having lesser volume of storm water available. Site selection of the recharge wells, therefore, plays a vital role in the efficacy of a storm water injection system.     

Analysis of shaking table-structure interaction effects during seismic simulation tests

An analytical model is developed to evaluate performance characteristics of unidirectional seismic simulators (shaking tables). The validity of the model is verified with experimental measurements of the frequency response of the shaking table at the Catholic University of Peru. Interaction effects between shaking table and structure are first studied by analysing the response of a two DOF (degree of freedom) oscillator with mechanical properties representative of the actuator-table-structure system. A single DOF viscoelastic oscillator representing the structural test specimen is then included in the analytical model of the seismic simulator, and the behaviour of the combined system is evaluated, in the frequency domain, in terms of response stability and accuracy of reproduction of the command signal. Numerical simulations of system response under different load conditions are subsequently performed in order to study the influence of shaking table and test structure characteristics on the interaction phenomenon. The results obtained explain some of the performance degradation observed in seismic simulation tests involving very heavy structures and provide guidelines for the design of more reliable shaking table systems.