Geosynthetics in India’s Tunnel Construction Boom: Zojila, Bullet Train and Beyond

India is building tunnels at a pace it has never managed before. From the high Himalaya to the creek beds under Mumbai, tunnels are being driven for highways, high-speed rail and metros, through terrain that used to force roads to climb, wind and close for months at a time. In almost all of them, geosynthetics (membranes, fabrics and drainage composites) keep the water out. This article explains how geosynthetics are used in tunnel construction in India, from the Zojila tunnel to the undersea section of the bullet train, and why the choice of material matters.

India’s Tunnel Boom: An Overview

Hundreds of tunnels are now in service or under construction across India’s highway, railway and metro networks. Tunnels turn a dangerous, weather-bound mountain crossing into a straight, all-weather route, and they let high-speed rail hold its alignment through hills and cities. The Zojila tunnel in Ladakh, the Atal Tunnel near Manali (already in service), the long tunnels of the Rishikesh-Karnaprayag railway, metro tunnels under most major cities and the tunnels of the Mumbai-Ahmedabad High Speed Rail are all part of this wave.

Whatever their purpose, all these tunnels have to deal with water. Groundwater seeps under pressure through fractured rock and saturated soil, and if it is not controlled it corrodes reinforcement, cracks linings, freezes in winter, damages track and systems, and shortens the life of a structure designed to serve for a hundred years or more. Geosynthetics are the main means of controlling it.

Why Water Is the Enemy of Every Tunnel

A tunnel is held open against the pressure of the ground and the water in it. In fractured Himalayan rock, in soft alluvium under a city and below the seabed of a coastal crossing, water is always trying to get in. It corrodes steel reinforcement and attacks the concrete lining chemically. It builds up pressure behind the lining that can crack it. In cold, high-altitude tunnels like Zojila, seepage freezes, expands and spalls the concrete, and forms ice on the carriageway. In rail and metro tunnels, dripping water damages track, signalling and power systems. A leaking tunnel is expensive to maintain and may never perform as designed.

So in modern tunnelling the waterproofing is designed and installed as a core system, with the same care as the lining, and it is made almost entirely of geosynthetics.

How Tunnel Waterproofing Works: The Geosynthetic Sandwich

Most of India’s drill-and-blast and conventional tunnels are built by the New Austrian Tunnelling Method (NATM): a sprayed concrete primary lining stabilises the excavation, and a permanent inner lining is cast later. The waterproofing system sits between the two linings, as a sandwich of geosynthetic layers with separate jobs.

First, against the rough sprayed concrete, comes a protection and drainage layer of non-woven geotextile, often called the cushion fleece. The waterproofing geomembrane, the impermeable sheet that keeps the water out, is fixed over it. Drainage geocomposites and perforated pipes collect the water that reaches the membrane and carry it to the tunnel’s side drains, so pressure does not build up. Finally the inner concrete lining is cast against the membrane. Together these layers form a continuous, drained, watertight barrier around the tunnel. In India and internationally the work is guided by IRC:SP:91 (guidelines for road tunnels), International Tunnelling Association (ITA) recommendations, and material standards such as EN 13491 for geosynthetic barriers used in tunnels and underground structures.

The Tunnel Waterproofing Geomembrane

The main element of the system is the tunnel waterproofing geomembrane: a flexible thermoplastic sheet, usually plasticised PVC or a flexible polyolefin (FPO), welded into a continuous skin around the tunnel. Unlike a rigid coating, it moves with the structure, bridges small cracks and, in undrained designs, resists the water pressure of the surrounding ground.

Two features set tunnel membranes apart. The first is the signal layer: a thin, brightly coloured layer under the surface, so any scratch, weld fault or installation damage shows up against the contrasting colour and can be repaired before concreting. The second is compartmentalisation: the waterproofing is divided into sealed sections with waterstops, so if a leak develops in service it is confined to one compartment and can be repaired by injection without removing the lining. The membrane is welded by hot-wedge and extrusion methods and every seam is tested, by air pressure for double-track wedge welds or by vacuum box for extrusion welds, as on a critical containment liner. Material performance is checked against standards such as EN 13491.

The NATM Tunnel Geotextile

The NATM tunnel geotextile is what lets the membrane survive. It is a heavy nonwoven fleece, needle-punched from polypropylene or polyester, typically from several hundred to over a thousand grams per square metre, installed against the sprayed concrete before the membrane. It has two jobs.

First, it protects. Sprayed concrete is rough, sharp and uneven, and without a cushion the membrane would be punctured as soon as it was pressed against it or the inner lining was poured. The fleece takes up those irregularities and shields the membrane during construction and in service. Second, it drains. The fleece is permeable, so water reaching the back of the membrane flows through the fabric down to the collector drains instead of ponding and building pressure. The geotextile is fixed to the primary lining with plastic discs (rondels), and the membrane is then welded to the discs, so no fixing pierces it. Because the fleece does both jobs, every NATM waterproofing system includes one, and its quality directly affects how long the tunnel stays dry.

Geocomposites for Water Management

Drainage geocomposites handle the wider water management. A drainage geocomposite combines a three-dimensional drainage core with a geotextile filter bonded to one or both faces, forming a thin channel with high in-plane flow capacity. In tunnels they are used behind linings, at construction joints and in the invert to collect seepage and route it to the drainage system. Being thin and prefabricated, they replace granular drainage layers that would take up too much space inside a tunnel, and they are quicker to install.

Case Study: The Zojila Tunnel

The Zojila tunnel shows what is at stake. Its 14.15-kilometre main tunnel, a bi-directional road tunnel on the Srinagar-Leh highway, will be one of the longest and highest road tunnels in Asia. It runs beneath the Zojila pass to give Ladakh its first all-weather road link to the rest of the country; the pass is closed by snow for months each year. By 2025 about eighty percent of the excavation was complete, a breakthrough was reported in June 2026, and opening is targeted for 2028.

Zojila is a hard waterproofing problem. It lies at high altitude in fractured Himalayan rock, with plenty of groundwater and winter temperatures far below freezing. Water that seeps in and freezes would spall the lining and form ice inside the tunnel, a serious hazard at that altitude. Tunnels like this rely on a strong protection fleece, a durable signal-layer membrane and an efficient drainage system to keep snowmelt and groundwater out of the structure and carry it away before it can freeze. For a tunnel that must stay open through a Ladakhi winter, the waterproofing system decides whether it works as an all-weather route.

Case Study: The Bullet Train Tunnels

At the other end of the country are the tunnels of the Mumbai-Ahmedabad High Speed Rail, India’s first bullet train. The corridor includes a 21-kilometre tunnel between Bandra-Kurla Complex and Shilphata, with India’s first undersea rail tunnel, a stretch of about seven kilometres under Thane Creek. The demands here are different. A high-speed rail tunnel must be kept dry, because water on the track slab or in the signalling and power systems cannot be tolerated at bullet-train speeds, and the undersea section is under constant hydrostatic pressure.

Holding back that water for the life of the line falls to the waterproofing system: membranes, heavy protection geotextiles and drainage geocomposites forming a continuous watertight envelope that resists sustained water pressure and protects the systems inside. As India builds more high-speed rail and urban metro lines, demand for this kind of waterproofing will keep rising.

Product Specifications at a Glance

The table below summarises the main geosynthetic products used in tunnel waterproofing and water management, with representative properties and the standards that govern them.

The right grade for a given tunnel depends on water pressure, ground conditions, temperature and design life, so match the product to the tunnel rather than picking from a catalogue.

Why Ocean Non Wovens for Tunnel Projects

Tunnel sites are remote and technically demanding, so the supplier has to deliver consistent material on schedule. Ocean Non Wovens is an Indian manufacturer and supplier of geomembranes, non-woven and woven geotextiles, geocomposites, geocells and geobags, producing materials tested to Indian and international specifications.

Ocean Non Wovens supplies tunnel waterproofing and drainage, underground and metro works, slope and portal protection, as well as highways, expressways, water resources, defence infrastructure, railways and industrial projects across India. For tunnel contractors and engineers, that means one source for protection geotextiles, drainage geocomposites and geomembranes, with technical support to specify the right product for the ground and water conditions. If your project involves tunnel waterproofing, protection fleece, drainage geocomposites or underground water management, talk to Ocean Non Wovens.