Dismantling by controlled blasting technique of blast furnace foundation for rehabilitation

摘要

A Blast Furnace foundation constructed in a steel manufacturing plant has a top circular shaft pedestal on an octagonal raft. Due to the envisaged expansion of steel production capacity from 0.6 MT to 1.0 MT, there is an additional load on the furnace and hence, it was felt necessary to check the existing blast furnace foundation for the additional loads. Also, the top circular shaft pedestal has developed a number of cracks on the concrete surface during its service life. Hence, the foundation was checked for the additional load and found that only the top circular shaft over the existing octagonal raft need reconstruction. Dismantling of existing top circular shaft pedestal and reconstruction would require a long time. However, to complete the job in a shortest duration, an experimental study was organized for controlled blasting of the existing top circular shaft pedestal. The study was planned for controlled blasting of circular shaft on a blast furnace foundation model and to evaluate the concrete integrity of octagonal raft by Non Destructive lest (NDT) techniques prior and after blasting. This paper deals with the construction of the blast furnace foundation model, formulation methodology for controlled Masting of the top circular shaft pedestal and NDT evaluation of octagonal raft. Ultrasonic test data is presented to assess the concrete homogeneity and integrity. Rebound hammer test results to determine the surface hardness are also presented along with core sampling and testing procedures carried out to determine the actual strength of concrete used in the foundation. A methodology is illustrated for controlled blasting of the model foundation with the details of spacing, depth, number of holes, the quantum of blasting charge, time delay etc., and the controlled blasting was successfully carried out on the model. Transient dynamic response parameters, namely pressure, acceleration and strain were measured on the model and the values were recorded during blasting to check these parameters with their tolerable limits. After blasting, the condition of the concrete in the octagonal raft was assessed by NDT tests which were compared with the values before blasting. The data obtained from this study such as NDT, dynamic pressures, dynamic strains and accelerations indicate that the integrity of the concrete in the octagonal raft portion was not significantly disturbed with the controlled blasting technique suggested. Based on this detailed experimental study, the actual controlled blasting design was formulated to dismantle the prototype blast furnace foundation and this design got successfully executed at the real site.