Money Over Matter | The Challenge of Sinking Shafts

A first-hand account of 113 Engineer Regiment’s indomitable spirit, determination and ingenuity in digging two 600 feet deep shafts in 1981-82 which made Pokhran II possible in 1998

Maj. Gen. Mrinal Suman (retd)Maj. Gen. Mrinal Suman (retd)

Pokhran II took place in May 1998 under Operation Shakti. A total of five tests with weapon-grade plutonium were conducted — three on May 11 and two on May 13. The tests included a 45 kt fusion bomb (also called hydrogen or thermonuclear bomb), a 15 kt fission bomb (atomic bomb) and three experimental sub-atomic devices of 0.5, 0.3 and 0.2 kt respectively.

Dr K. Santhanam of the Defence Research and Development Organisation (DRDO) was the director for the test site preparations. In an interview to Times Now television channel in April 2008, he revealed that India had dug two deep shafts at Pokhran in 1981-82. The fission and fusion bombs were placed in these shafts. For sub-atomic tests, use was made of three abandoned dry wells in the near vicinity. These wells had earlier been dug by the villagers and deserted as no water had been struck.

The Indira Gandhi government had decided to carry out tests in 1982-83 and the army was asked to sink the shafts. 113 Engineer Regiment completed the task ahead of schedule, but the tests were shelved due to external pressures. More than a decade later, Prime Minister P.V. Narasimha Rao asked the scientists to go ahead with the tests in 1994-95. Unfortunately, the US satellites detected the preparations. Once again, India was forced to abort the tests.

Hoisting bucket with winder assembly in the background at the shaft site; ©Photo Courtesy NIKITA DHINGRA

A word about shaft sinking will be in order here. To approach underground mineral seams, a vertical opening (shaft) is provided from the surface to the mining zone. These shafts are used to carry men, material and equipment to the mining zone; as also, to haul the extracted ore to the surface. Being the lifelines of all underground mines, shafts are sunk with exacting technical specifications. All mining manuals term shaft sinking to be the most dangerous and hazardous assignment of all mining operations. It is considered to be the most unforgiving task where even a minor slip-up results in casualties.




Essentially, a shaft contains a head-frame (tower) to house the hoist; a shaft collar of reinforced concrete to provide foundation support to the head frame and to accommodate mechanism for men, materials and services to enter and exit the shaft; and shaft barrel that continues from the collar to the planned depth. The shaft also houses exhaust ducts (for extracting stale air at working face), pipes for compressed air for the operation of pneumatic tools, dewatering pipes and circuits for 24-volt electrical fittings. It requires domain expertise and specialised equipment. There are a handful of shaft sinking companies in the world, normally called ‘sinkers’. All mining companies outsource shaft sinking operations to them.

113 Engineer Regiment, located at Jodhpur, was asked to undertake this onerous task. The regiment was under the command of the late Lt Col K.C. Dhingra (later rose to the rank of Major General). Col Dhingra was an extremely intelligent officer with a phenomenal memory and exceptional capacity for sustained hard work. The regiment was acutely aware of the criticality of the task and the trust that had been reposed in its capability to deliver. It was determined not to let the nation down. I was a Major in the regiment and had the privilege of being involved from the beginning to the culmination of the task.

It was an unprecedented assignment. To sink a shaft hundreds of feet deep with no experience and no equipment was a huge challenge — more so as none of the officers had ever visited a mine or seen a shaft; nor had anyone studied mining engineering which is a specialised course. Although site preparations for Pokhran-I were also carried out by the army engineers, the task was of an entirely different genre and did not entail sinking of subterranean shafts ab initio. Pokhran-I was conducted at a much shallower depth, using an abandoned dry well.
Site Selection

It was the month of January 1981. After an exercise in the desert, Col Dhingra asked me to accompany him for an operational reconnaissance. While driving to the Pokhran ranges he told me that the regiment had been tasked to sink a deep shaft of more than 500 feet. Repeatedly stressing the need for secrecy of the mission, he gave out other broad parameters. With maps in our hands, we traversed the ranges many times over the next two days to get a feel of its extent and zeroed in on to a nine square km area that satisfied our security and secrecy concerns. It was well away from the highways and the villages. The aim was to identify a location where water would pose minimal impediment to the shaft sinking operations. Hence, site selection was a highly critical step and warranted deliberate treatment.

(Left to right) Commanding Officer Lt Col K.C. Dhingra; Task Force Commander Maj. Mrinal Suman; Task Force Commander Maj. S. Jagannathan

Within a week, I was back in the Pokhran area with a team of officers and men for detailed ground reconnaissance. After much scouting and ground survey, we selected four tentative sites that lay in the inter-dunal low-lying areas with least sand overburden. We also approached the nearby villagers to draw benefit from their local knowledge. We told them that the army wanted to establish a permanent camp and was looking for reliable water sources. We showed them the four sites and asked them to help us in identifying likely water sources. We, of course, intended to eliminate those sites.

One evening, without informing us, the local headman brought a water diviner from Pokhran town and started appraising the sites. It was a full moon night. Water divining is an esoteric ancient method in which the locals have immense faith. We watched in disbelief while the water diviner announced that none of the sites held ample water. For us, it was just a gratuitous input of little consequence as the technique lacked scientific authentication.

We approached Central Arid Zone Research Institute (CAZRI) at Jodhpur for help in identifying water sources. They explained to us that the availability of perched aquifers (an underground layer of water-bearing permeable rock, rock fractures or unconsolidated materials) and underground streams depended on the geology and geomorphology of the area. CAZRI readily gave us geologic and topographic maps of the area. We studied them in detail, trying to relate them to the four sites selected by us. However, we were still not confident and sought the application of a more exact and scientific method.

We also sought the help of a local hydrogeology agency that specialised in water prospecting for wells. However, the agency could carry out core drilling for geologic sampling up to 150 feet only. Once again, the core logging declared all the sites ‘unfit for sinking well’, meaning thereby that water was not available in exploitable quantity. Even the seismic survey gave the same report. Though encouraging, the reports were not a clincher as we had to go down to more than 500 feet.

After studying all the available inputs, we selected two sites. In consultation with the higher authorities, it was decided to attempt digging at more than one site to cater for unforeseen hold-ups. All the same, as the work progressed, the authorities decided to go ahead with both the shafts.

 

Sinking of the Shafts

Two task forces were constituted, and the work started at both the sites by the end of February 1981 without much fanfare. A small ceremony was held to invoke blessings of Ramdevra, the ruling deity of the desert whom the locals consider to be an incarnation of Lord Krishna. Thereafter, the diameter of the shaft was marked on the ground with pegs and the digging commenced with picks and shovels. For a few days, hauling of the dug earth was done manually with mortar pans. Thereafter, the unit crane was deployed with a modified coal-tar drum. Soon the crane rope reached its limit. To prevent caving in, revetment of the walls was done with flattened CGI sheets and iron pickets.

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 Kolkata 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 the 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’. It was an intensely equipment-assisted task. A bevvy of generators and air-compressors were requisitioned. Reliable grids were established to ensure uninterrupted supply of electricity and compressed air. With ongoing 24/7 operation, a very high serviceability state of the equipment was essential. Immense credit goes to the technical support team for providing excellent repair and spare back-up.

After having cleared the sand over-burden, we encountered a conglomerate consisting of gravel, sandstone and siltstone. Digging was tough as the drill would get stalled in the bores. We also encountered shale, a fine-grained clastic sedimentary rock. Instability of the shaft walls became a matter of concern. Loose or unstable portions often fell due to the vibrations caused by the drills.

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 the wire mesh with rock-bolts on the walls to trap falling stones. This proved to be of little use. Blasts were 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 permanent shafts, lining is done with precast concrete segments and shotcrete. 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 deliberation, 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 and the depth. 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:

  • Clearing of the floor of the shaft and construction of a sump in a corner to collect and pump out water.
  • Drilling of multiple slanting holes of varying depth to create free face with delayed detonators for optimum blast effect.
  • Filling of the holes with explosives and connecting all detonators through a ring main circuit for firing.
  • Removal of drills, pumps and other construction equipment out of the shaft.
  • Firing of the charges.
  • Removal of the blasted rock (rubble) to obtain the floor face for the next cycle of drilling.

Misfire of the charges 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. A 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 could not 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 of pumping 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 imported air-operated-double-diaphragm (AODD) pumps and immediately realised their indispensability. Steps were initiated to have them developed/ manufactured indigenously. 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 the size of a large bedroom. 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 the 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.

 

The Tests That Were Not to be

Chief of the Army Staff General K.V. Krishna Rao also visited the shafts. He could not believe that the army engineers had completed the task without any external help. After visiting both the shafts, he told Col Dhingra, “I knew it was a tough assignment but can appreciate its magnitude only after this visit. You have amazed me. You must be a very proud commanding officer. Do you realise that your unit is writing the history of India?” Col Dhingra conveyed the Chief’s words to both the shaft commanders.

To demonstrate the dryness of the chamber to the visiting defence minister R. Venkataraman, we laid a carpet on the chamber’s floor and offered tea to him from a thermos flask. He was pleasantly surprised and poignantly commented, “Oh my God. This is the most memorable cup of tea, over 600 feet underground”.

Visits by the scientists became more frequent. Things were moving fast. The atmosphere was charged with excitement. Trial with mock-ups was seen by us as an affirmative sign. We were upbeat and thought that the tests were imminent – it was a question of ‘any day’. However, it was not to be. We waited for days and weeks without the much-awaited bang. With great disappointment, we learnt that the government had decided not to go ahead with the tests. It was ruled that the shafts be maintained and dewatered regularly with submersible pumps, awaiting another opportune moment for the tests.

Our regiment had been in the desert for over three years. We were asked to hand over the maintenance of the completed shafts to another regiment. We left Pokhran with a heavy heart but a great deal of satisfaction. We did have a few close shaves but did not suffer a single injury due to strict adherence to well-evolved drills and procedures. Most importantly, utmost secrecy was maintained by all ranks. Even within the regiment, information was shared purely on ‘need to know’ basis.

The regiment was awarded six Vishisht Seva Medals (including two jawans) and numerous Chief’s commendations. But that was of little consolation. We were not destined to be a part of the historical event. Various regiments continued with the maintenance till 1998 when ‘our shafts’ were finally put to nuclear tests. We learnt of the explosions with immense pride but somewhere down in our hearts there was a tinge of disappointment — wish it had happened during our tenure!

Sinking shafts of over 600 feet depth, lining the walls and preparing side chambers in such a compressed time frame had been a monumental achievement. The world over, the average rate of sinking shafts with ‘drill and blast’ method is pegged at 3 feet per week by professional companies possessing decades of experience, consummate expertise and latest equipment. We, the soldiers of 113 Engineer Regiment, had no experience, no knowledge and no equipment. We did struggle initially but our perseverance helped us overcome all challenges. It was a race against time, but we did not let the country down. It was an unparalleled feat by all standards.

According to the information available in public domain, no country in the world has ever asked its army engineers to dig deep shafts for the nuclear tests. Now that India has declared a self-imposed moratorium on nuclear tests, need for deep shafts would never arise again. In other words, the achievement of 113 Engineer Regiment will remain unequalled. Finally, as General Krishna Rao had stated, 113 Engineer Regiment did contribute to the history of India: a unique distinction indeed.

 

600 Feet Underground

600 Feet UndergroundWe sank shafts that were over 600 feet deep. The height of Qutub Minar is 240 feet. In other words, the depth of the shafts was two and a half times the height of Qutub Minar.

The shafts were vertical in alignment. Looking up from such depths, against the darkness of the shaft walls, one saw a bright disc of sky with dazzling brilliance. It used to be an awe-inspiring spectacle. The night sky presented a sight of celestial blues. Memories of those experiences are still fresh.

Working at such depths is highly challenging. With water flowing along the walls, it is humid and hot. Normally, after 100 feet depth, temperature rises by one degree in every thirty feet. In the absence of fresh air, ventilation ducts were installed for circulating fresh air from top. Simultaneous operation of multiple rock drills produced unbearable din with clouds of dust hanging in the air. Every soldier had to have ear plugs and wear protective eye goggles.

As water was being pumped out in stages, failure of any pump in the chain used to result in tons of water falling on the working party. In case it happened while the drilled-holes were being loaded with explosives, the problems used to get compounded, causing considerable anxiety and delay. Due to a complete lack of any other source of light, everyone had to wear miners’ lamps on the helmet. One had to master the art of working with these lamps for long hours, having to turn one’s head frequently to focus the beam.

All soldiers had to be repeatedly cautioned about the lethality of the falling objects. To drive home the point, they were shown that even a bolt falling from a height of 600 feet could split open a protective helmet due to its potential energy. Every single implement and tool had to be strung and tied to prevent accidental fall from hand.

 

Managing Water Woes

AODD-PumpIt is a common misconception that deserts are devoid of subterranean water. It is just that the water’s quality, quantity and availability (at deep depths) do not lend itself to economic exploitability. Only electricity driven submersible pumps can pump out water from deep wells, but they cannot be used in under-construction shafts due to the risk of electrocution of the working party.

On encountering significant quantity of water, we visited mines and learnt that pneumatic pumps were the only answer. An Air Operated Double Diaphragm (AODD) pump is a type of positive displacement pump that uses compressed air as a power source, using reciprocating elastomeric diaphragms and check valves to pump fluid.

These pumps were not available in India and import would have taken long as also compromised secrecy. Adopting the proverbial ‘jugaad’ method, we visited scrap markets near a few mines to procure discarded, non-functional and scrapped AODD pumps. These were dismantled, the working principle analysed, and various parts identified. A local workshop was roped in to cast the components as per our drawings. After a few failures, we did manage to assemble a reasonably efficient pump. However, the problem of obtaining elastomeric diaphragms persisted until we located a small entrepreneur in Thane who agreed to develop it for us. Once we had AODD pumps in sufficient quantity, there was no looking back.

AODD pump proved to be our saviour. Most appropriately, a scale model has been prominently displayed in our regiment.

 

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