As learnt in field engineering, tripod gantry with blocks and tackles to hoist a pulley system was erected. Reeving was done by threading the winch drum cable of a dozer. A larger semi-elliptical bucket was fabricated for removing earth. Such expedients can at best be of interim help. The dozer cable had limited length and worse, the wire-rope started fraying with strands coming apart. In fact, it was ill-suited for the task as the bucket used to swing wildly due to the wire-rope lacking non-twist construction. Soon the digging came to a standstill.
Anticipating the requirement for a proper hoisting arrangement, a team had already been sent to Calcutta to identify and procure a suitable haulage system. After considerable effort, a winder assembly manufactured by a local industrialist was identified. Orders were placed for immediate delivery and operators sent for training. With the imminent arrival of the ground-mounted winder assembly, the head-frames (also called winding tower, poppet head or pit head) were quickly constructed with bailey bridge equipment to house the sheave wheel.
While awaiting arrival of the winders, the time was duly utilised to cast shaft collars (also called the ‘bank’ or ‘deck’) with heavy reinforced concrete in three tiers/levels for required stability. In addition, troops familiarised themselves with the ‘drill and blast method’. A bevy of generators and aircompressors were requisitioned. Captain SB Pendse ingeniously established reliable grids to ensure uninterrupted supply of electricity and compressed air.
As regards the geology and the rock formation of the sites. After having cleared the sand over-burden, we encountered conglomerate consisting of gravel, sandstone and silt stone. Digging was tough as the drill used to get stalled in the bores. We also encountered shale, a fine-grained clastic sedimentary rock. It is a mudstone that is fissile and laminated. Instability of the shaft walls became a matter of concern. Loose or unstable portions often fell down due to the vibrations caused by the drill.
During Pokhran-I, within one month of commencing digging, loose shale strata had fallen on the digging party, killing one and injuring four persons. Criticality of shaft stability was well understood by us. At deeper depths, a cave-in could bury the working party alive. Initially, we tried to anchor wire mesh with rock-bolts on the walls to trap falling stones. It proved to be of little use. Blasts used to loosen rocks along the natural cracks on the walls, uprooting the mesh.
Choice of shaft lining depends on the nature of rock strata. In some shafts, lining is done with precast concrete segments and shotcrete. Concrete is highly reliable but is normally used for shafts that are permanent or long-lasting. It is an expensive and time-consuming option. In our case, the shafts were required urgently and for one-off use only. We were at our wit’s end. After much deliberations, we hit upon a unique system of having prefabricated steel jackets in the form of segments of a circle. These could be easily lowered into the shafts and bolted together to form a circular steel liner. Provision had been made to drive rock bolts through them for proper anchoring. Jackets also lent themselves to grouting to block water ingress.
Time for each ‘drill and blast’ cycle varied with the rock formation encountered for drilling and the depth of the shaft. As we went deeper the turnaround time of the haulage bucket increased significantly and removal of rubble took much longer. A standard cycle consisted of the following steps:-
Misfire used to be the most dreaded nightmare. A single defective detonator could fail the entire circuit and the charges would remain unfired. In that case, one had to wait for two hours before entering the shaft, lest a stray spark set the explosive off. Thereafter, the senior-most officer at the site had to go down to the base of the shaft to remove all the charges. By then the shaft used to be flooded with water. It was a highly risky task. The water used to be murky and the officer had to go underwater to locate all the charges by touch. The whole ring main circuit had to be dismantled and all detonators brought over-ground for replacement. Every such misfire invariably put our progress back by a day.
At each shaft, the work was carried out round the clock in shifts. Daily progress report was being submitted to the authorities. After every 10 feet of depth, we had to pause to stabilise the shaft walls with steel jackets and rock-bolts.
We encountered water seepage at 60 feet depth. Although the quantity of inflow was limited, it still posed problems in digging. It had to be collected in a sump and pumped out at intervals. Only electricity driven submersible pumps possess high pump-head. However, they cannot be used in the shafts due to the risk of electrocution of the working party. During Pokhran-I (January 1974), ingress of water had stalled the progress on the shaft within three months of commencing digging. The problem could not be solved even by the scientists. In the end, the incomplete shaft had to be abandoned. As there was no time for attempting a fresh shaft, a dry abandoned well was prepared for the test in May 1974.
We were totally at a loss. To learn about the methodology to pump out water, Col Dhingra and the two shaft commanders (Major S Jagannathan and I) made a quick visit to Khetri copper mines and Zawar zinc mines. There, for the first time, we saw the air operated double diaphragm (AODD) pumps and immediately realised their indispensability. Steps were initiated to procure them. Their receipt helped us go full steam ahead. There was no stopping us thereafter. With the maximum head of AODD pumps being limited, we evolved a system of pumping out water by stages. As we went down, additional stages were erected.
The scientists in army uniforms used to visit us periodically to study the progress and specify additional facilities for tests. They expressed the requirement of niches/alcoves at various depths of the shafts for placing monitoring instruments. Cabling network was also indicated. A tall observation tower was constructed at a distance with crib-piers.
On reaching the stipulated depth, we were asked to make a side chamber of a large bedroom size. As a powerful nuclear device is always placed under natural rock strata to contain blast effect, thermal radiation and radioactive fallout, such a requirement was already anticipated by us. We knew that our shafts would finally be L-shaped. The side chambers were duly completed without much difficulty and completion report submitted.
Soon, we received mock-ups of the nuclear devices. They were lowered and placed in the side chambers to ascertain suitability of the hoisting mechanism. The scientists had demanded that the chambers should be ‘without a drop of water’. We had to harness considerable ingenuity to achieve that. To demonstrate the dryness of the chamber, we laid a carpet on the chamber’s floor and gave tea to the scientists from a thermos flask. The scientists were keyed up and ecstatic. One of them poignantly commented, “Oh my God. This is the most memorable cup of tea – over 600 feet underground”.
The Disappointment: the tests that were not to be
General KV Krishna Rao, Chief of the Army Staff, also visited the shafts. He could not believe