Horizontal directional drilling at Varuna Beach

A large pipe slowly arises from the ground amidst cheers for a job well-done. The pipe went into the ground at ‘Guna’s school’, the Kuilapalayam Trust School extension uphill at Bommaiyarpalayam. From there it travelled 400 metres horizontally underground at a depth of 7 metres – first beneath a narrow local road, then below the national highway known as the East Coast Road, then underneath a cemetery, before finally emerging at ‘Varuna Beach’.

“It’s fantastic!” says Toby, who has been overseeing the project on behalf of Varuna. “The underground drilling didn’t disturb anybody!”

The decision to go for underground drilling was made after months of research and deliberations on how to pump desalinated water from Varuna Beach, the location of the future Auroville desalination plant, up to the centre of Auroville, 5.5 kilometres away. The main problem was crossing the East Coast Road, a two-lane National Highway which will soon be widened to four-lane. The Tamil Nadu Highways Department would not give permission to dig up the road and suggested to lay the pipe in an existing water duct. This solution was far from ideal, not only because it would involve a great number of perpendicular bends, but also because the pipe would be too exposed. Moreover, when the road would be widened, a new duct would have to be installed and the pipe would need to be temporarily removed.

Varuna proposed horizontal directional underground drilling to the Highways Department. “We supplied technical and legal reports and examples where it had been successfully done.”

After crossing the ECR, how to reach Auroville? “We considered four possible routes,” says Toby. “One was going along the road up to Kuilapalayam; the second going through a canyon and then through Auromodèle community; the third going along the Utility road; and the fourth, crossing a cemetery and going along a narrow local road which leads to Guna’s school.

“The first option was discarded as there is not sufficient space along the sides of the road to dig in the pipes. The second option implied that the pipeline would have to cross many privately-owned lands, which could become a problem in future. The third option would entail demolishing houses at the crossing of the ECR and the Utility Road. This left the fourth option, but here too there were problems,” says Toby.

“The villagers, understandably, objected to digging a trench through the cemetery. And the village road was too narrow to allow for a 3.5 metre deep trench to be dug next to it. People or cattle might fall in the trench; and during the monsoon, part of the road might slide into it. There was only one possibility: to go for a one-stretch seven metre deep underground drilling, starting at the Varuna Beach all the way up to Guna’s school.”

For Krita, the Bangalore-based engineering company that specialises in underground drilling, the Varuna job was nothing special. “We use the term HDD, Horizontal Directional Drilling,” explains director Lalit Nahata. “HDD is a steerable trenchless method of installing underground pipes for gas, water, sewage and telecommunication cable conduits. The method causes no ecological damage, and has the big advantage that you do not need to disturb any surface or traffic, as compared to open trenching.”

The Krita equipment – nine immense trucks loaded with the drilling rig, ancillary machinery and bentonite clay – arrived at the end of September at Varuna Beach. The process started with a pilot bore hole being drilled. A viscous fluid, a mixture of water and bentonite clay, was continuously pumped to the drill head to cool it, to facilitate the removal of sand and to stabilize and lubricate the bore hole. Once the drill head had reached the destination, it was pulled back and replaced by a larger drill head known as ‘the reamer’. The reamer went back into the bore and increased its diameter to the width required for the passage of the pipes. In the process, more viscous fluid was pumped into the bore.

How did Krita know where the drill head was going? “We used the so-called ‘walk-over locating system’,” says Lalit. “A transmitter fixed behind the bore head registers angle, rotation, direction and temperature data. This information is encoded into an electro-magnetic signal and transmitted through the ground to the surface where someone holds a receiver which decodes the signal and sends steering directions to the bore machine operator, who is steering the drill from his cabin on the beach.”

The 12 metre long, 400 mm diameter HDPE (High Density Polyethylene) pipes, which had arrived at Varuna Beach a year ago, had meanwhile been moved to Guna’s school and had been fused together into stretches of various lengths, up to 120 metres. After the reamer emerged from the ground, it was replaced by the ‘pulling head’. An HDPE pipe-stretch was connected to it and then both were slowly pulled backwards into the enlarged bore. A second stretch of pre-fused pipes was then butt-welded to the first, and so on, until the entire length of 407 metres was installed. [Butt fusion welding is a process where the ends of two pipes are pressed together after having been heated up to the welding temperature by a heating plate, eds.] Then followed the second pipeline – also a 400 mm diameter HDPE pipe, which was laid next to the first. “We have decided to install two pipelines, because a job like this, you only do once,” says Toby. “The purpose of the second one has not yet been exactly defined – it may serve when we need more capacity in future, or when other ideas come up – there are many possibilities.” The process was completed on November16th.

From Guna’s school the pipelines go to the Utility Road in a stretch of land Varuna recently purchased, which connects the school to the Utility Road. UPI Polymers, the company that supplied the pipes and which does the butt-welding, dug a 3.5 metre deep trench, laid the pipelines and connected them to the underground pipes.

What is the risk that the pipes will leak in future? “Zero,” says Mr. Bhushanam, the Director of UPI. “The walls of the pipes are 3.6 centimetres thick; each butt-weld has been separately checked; and the entire length has been tested at 21 bar, 1.3 times the maximum pipe pressure of 16 bar, far higher than the operating pressure of 13 bar. As we anticipated, no leak was detected. That’s why we have given a guarantee on the pipes for 50 years and on the butt-welding for 25 years.” The guarantee includes replacement of defective pipes and fittings and the cost of civil works involved.

The first, and perhaps the most difficult stretch of the pipeline between the beach and Auroville has now been installed. Also the permission requests are proceeding as hoped for. “The Collector of our district, who is the first authority to approve the desalination project, was positive and in our meeting lauded the Environmental Impact Assessment study done by the firm of Larsen Toubro Randøll. She commended the project as ‘well-thought of, an example for the people with a negligible environmental impact’. We are now pursuing the other permissions required,” says Toby.

Auroville’s Water Group and the Town Development Council too are positive about the developments as there are increasing signs of ground water shortage. “Last year’s enormous monsoon has recharged the aquifers, but we may have a deficient monsoon this year and over-pumping of the aquifers is ongoing. The salinisation of bore wells along the beach is slowly happening – not like a bombshell, but the groundwater’s mineral content is increasing. This is a sign of worse things to come,” says Toby.

It keeps him awake at nights, he says, and complains that Auroville is too passive. “We have only three sources of water: groundwater, harvested rainwater and desalinated water. The groundwater resources are slowly getting depleted; desalinated water may become a reality in say 5 years; but we are not sufficiently looking at the other possible source, and that worries me.” Toby feels that each house should have a big sump to catch rainwater runoff, and that larger rainwater harvesting tanks should become mandatory for all new developments in Auroville. “Varuna is progressing slowly but steadily. I hope Auroville will find the money to do the same in this field.”