احسان حقيقي

Elastic bearings are usually installed under buildings during construction in order to isolate buildings from generally ruinous subway-induced vibrations. Despite various investigations on isolators' performance, the effectiveness of under foundation resilient mat as a simpler and less costly countermeasure (compared to elastic bearings) has been only studied and used at the source (i.e. machine foundation & railway track). In this regard, the present study is devoted to developing the knowledge of isolation of new buildings with the aid of an elastic layer under the foundation and also existing buildings by soft grout injection method under the foundation. To this end, a finite/infinite element model of a building and its surrounding soil media was developed. It includes an elastic soil media, a railway embankment, a resilient mat, and the building. The model results were validated using analytical and numerical solutions reported in the literature. The performance of resilient mat was examined by an extensive parametric analysis on the soil type, bedding modulus of resilient mat, and dominant excitation frequency. The results obtained indicated that although the shock mat can substantially reduce the building vibrations, its performance is significantly influenced by its underneath soil media. The softer the soil, the lower the shock mat efficiency. Also, as the train excitation frequency increases, better performance of shock-mats is observed. Although the performance of the under the foundation resilient mat in controlling annoying ground vibrations was shown using the numerical mode, there is a palpable lack of empirical evidence in this regard. To fill this gap, a laboratory model in the 1-g condition was developed. It includes a soil container, soil, building, and resilient mat with harmonic and impulsive excitations. Through various dynamic tests, it was shown that the best vibration suppression occurs when the isolation frequency is smaller than the natural frequency of the floor. Higher excitation frequencies also improve isolation effectiveness. It was found that the resilient mats are most effective when the excitation frequencies are close to the natural frequencies of the floor owing to the preventive impacts of isolators on the incidence of resonance in the floor. Finally, the effect of a soft V-shaped grouted layer on vibration mitigation on the ground was eva‎luated via a parametric analysis that determined the impacts of soil type, grout specifications, and train speed. The obtained results clearly indicated that a softer isolator (i.e., the grouted layer) in combination with stiffer soil provides the best configuration for attenuating the subway-induced vibrations. Furthermore, the injection angle and train speed were shown to have minimal impacts on the isolator performance.

ارتعاشات زميني , جداسازي پايه , لايه ارتجاعي , گروت نرم , روش اجزا محدود , مدل‌سازي فيزيكي

Ground-borne vibration , base isolation , Elastic layer , Soft grouting , finite element method , Physical modeling

Ehsan Haghighi

Dr. Mir Mohammad Sadeghi