14 May, 2007 (FIDSNS)
In 1986 a team of Indian Army officers visited some countries in Europe to carry out a study on modernization of ammunition depots with a view to construct cost effective store houses for ammunition. The team had recommended Igloo pattern of ammunition store houses, on trial basis, at some Ammunition Depots.
Defence Research and Development Organisation (DRDO) was tasked to develop Igloo type store houses. Since conventional reinforced concrete cement (RCC) used for magazines/bunkers is known to have limited ductility and concrete confinement capabilities, these properties are especially required for structures subjected to blast and impact loading environment.
DRDO directed the efforts to prove these properties of RCC. The structural properties of RCC could be improved by modifying the concrete matrix and by suitably detailing the reinforcements. Two new construction techniques, namely Steel Fibre Reinforced Concrete (SFRC) and Laced Reinforced Concrete (LRC) were trial evaluated vis-a-vis RCC for their shock mitigation efficiency and for use in the design of blast resistant structures and blast containment structures.
The SFRC technique involves mixing of steel fibres in concrete matrix which increases the energy absorption capability of concrete. It also increases ductility of the structure, arrests the formation and propagation of cracks, and also improves the spall resistance by 30 per cent compared to conventional RCC.
On the other hand, LRC consists of continuous bent shear lacings along with longitudinal reinforcements on both faces of a structural element. The LRC enhances the ductility and provides better concrete confinement. Moreover, LRC technique is cost-effective
compared to RCC for same level of protection: the reinforcement requirements can be lesser by 30 to 40 per cent for LRC.
The conventional storage magazines require large safety distances between the two adjacent storage magazines. Due to paucity of land there was a need to develop compact layout of storage magazines without compromising on safety aspects. When a large quantity of explosive is required to be stored in the limited space, the total quantity of explosive is distributed in a number of storage magazines constructed according to a planned layout in such a manner that if accident occurs in one of the magazines, its destructive effects remained confined to that unit only. In other words, at a time only one unit is at risk. This unit risk principle has been established by DRDO for an IGLOO explosive storage magazine of 5 ton capacity.
Terminal Ballistics Research Laboratory ( TBRL) along with Centre for Fire, Explosive & Environment Safety (CFEES), both are units of DRDO was tasked for design, testing & evaluation of LRC based Explosive storage building (IGLOO).
A site at Field Firing Range (FFR), Babina with an area of 4 km X 4 km was earmarked by army. 122mm rocket grad warhead was selected for 15 ton explosive trial to validate the design of IGLOO up to 75 ton NEC. The objectives were:
a) To assess effect of blast loading and structural behavior under blast on full scale IGLOO type explosive buildings with higher capacity of NEC.
b) To study the effect of variation in structural response of IGLOOs to blast stimuli with increase in volume to estimate minimum required separation distance between two IGLOOs.
c) To assess effect of blast in donor IGLOO on ammunition stored in acceptor IGLOO.
On the ammunition side, the detonatibility trials were conducted at TBRL. The trails showed that a Torpey filled shell is equivalent to one TNT and 782 number of 122mm rocket grad warhead (6.4 kg each) were required. The sympathetic detonation has been established and stoking pattern was finalized.
Once the ammunition was created, a simulated accidental explosion was conducted to study the efficacy of the LRC. The safe distance between two IGLOO structures of W kg capacity was established as 0.7 W1/3 m which is just outside the crater radius. This distance for a conventional magazine may vary from 2.4W1/3 to 3.6 W1/3.
It was also found that the soil bearing capacity at these stations was not suitable for construction of store houses on the Igloo pattern and the initial cost of construction of Igloo type store houses was higher than the cost of conventional construction. But the Igloo type store house was considered economical in the long run because of its longer life. Therefore, Indian Army decided to construct a mix of both Igloo and conventional type of store houses, keeping in view the operational requirements, availability and suitability of land and cost justification.
TBRL has now undertaken design and development of IGLOO of enhanced capacity of 136 Ton NEC.