Pokhran II: the challenge of sinking shafts

Pokhran II: the challenge of sinking shafts

Major General Mrinal Suman

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

Hoisting Bucket with Winder Assembly in the Background

(Photo courtesy Nikita Dhingra)

Pokhran II took place in May 1998 under Operation Shakti. A total of five tests with weapon grade plutonium were conducted – three on 11 May and two on 13 May. 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 TV 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 PV 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.

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.

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 carries ducts for the pumping of fresh air, dewatering pipes and electrical fittings. All mining manuals term shaft sinking to be the most dangerous and hazardous task of all mining operations. 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 the task. The regiment was under the command of the late Lt Col KC Dhingra (later rose to the rank of Major General). Col Dhingra was an extremely intelligent officer with 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.

Head Frame Tower under Camouflage Nets

(Photo courtesy Dhingra)

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 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 a number of times over the next two days to get a feel of its extent and zeroed 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 the water would pose minimal impediment to the shaft sinking operations. Hence, site selection was a highly critical step. But, how to go about it? We had no knowledge.

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 advice as to where the water could be found. 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. It is believed that the flow of underground water induces some vital currents above the surface and a person with induction attributes can sense them through the movement of a freshly plucked twig. We watched in disbelief while the water diviner announced that none of the sites held abundant 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 application of a more exact and scientific method.

After much persuasion, Col Dhingra agreed to seek help of a local hydrogeology agency that specialised in water prospecting for wells. The agency was told the same story i.e.  the army was looking for a camp site with a water source. 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 inputs (whatever be their worth), 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. However, 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 in Feb 1981 end 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, 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 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 air-compressors 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, sand stone 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:-

·         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 explosive 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 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.

Commanding Officer Lt Col KC Dhingra, Task Force Commanders Maj Mrinal Suman and Maj S Jagannathan

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 bed room size. As a powerful nuclear device is always placed under natural rock strata to contain blast effect, thermal radiation and radio-active fallout, such a requirement was already anticipated by us. We knew that our shafts would finally be L-shaped. The side chambers was 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 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.

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 a 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. Various regiments continued with the maintenance till 1998 when they were finally put to nuclear tests. We learnt of the tests with immense pride but somewhere down in our hearts there was a tinge of disappointment. We were not destined to be a part of the historical event. 

  

Sinking the 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 the 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 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. As India has declared self-imposed moratorium on nuclear tests, need for deep shafts will never arise again. In other words, the feat of 113 Engineer Regiment will remain unequalled. As General Krishna Rao had stated, 113 Engineer Regiment contributed to the history of India: a unique distinction indeed. The regiment has deservingly earned the appellation “Shaft Sinkers to Nuclear India”.