RITE OF PASSAGE
The tunnelling industry is not new to India, with some of the best tunnels having been constructed during the pre-independence period using the traditional drill and blast technique, and still going strong. However, the fact remains that there was an abundance of time and workforce available at a low-cost during that period, making such masterpieces possible. This is not the case today. Tunnelling has evolved a great deal over this time, and today, with the latest technologies and Tunnel Boring Machines (TBMs) available, the tunnel development process in India has received a shot in the arm.
According to reports, more than 1,600 tunnels have been either completed or are under development since the past few years. Some examples of wonderful feats in this domain include the Chenani-Nashri tunnel – touted as India’s longest road tunnel – and under-water tunnels, which help to create a robust transport network. Amit Uplenchwar, CEO, HCC E&C, acknowledges that there are abundant prospects for more such projects, saying, “With India’s strategic infrastructure development plans on their way to implementation, there is great scope for tunnelling in India,
especially for developing urban infrastructure, underground rail and road networks, transportation in mountainous regions and so on.”
The Indian tunnelling industry is undergoing a tremendous transformation. While domestic players have always been active in delivering the requirements of Indian consumers, the fast expanding Indian market has now attracted global players to India. Another welcome change in the industry structure is around domestic players seeking tie ups and forging business alliances with global players to take advantage of the latest technologies and seeking partnerships for capital-intensive equipment supply. Given the requirement for tunnels in urban India to bring in metro rail
networks and underground water supply systems through congested areas, there is a growing interest amongst project managers for new designs and techniques for tunneling.
On their part, OEMs and vendors have been responding to this need by bringing in new standards of design as well as introducing new classes of materials to improve the quality of tunneling in Indian conditions.
THE RIGHT TECHNIQUE
Of course, determining the most suitable tunnelling technique largely depends upon geological studies and further geotechnical analysis. Such studies include important parameters like rock quality that needs to be excavated, stress test of the land (tectonics) and groundwater conditions. Apart from the age-old drill and blast technique of tunnelling, most use mechanised
techniques for hilly and difficult underground or underwater areas. In such cases, tunnel boring machines (TBMs) are the most commonly employed mechanised solution. Daljeet Singh, director (works), DMRC, explains the process adopted. He says, “Indian infrastructure companies undertake station construction, while tunnelling work is done by their foreigner JV agencies. Their scope of work is clearly defined in the JV agreement, based on a specific construction methodology, and keeping in view the available land for the construction of shafts for lowering or retrieval of TBMs, list of utilities, and geotechnical investigation report.” He cautions that, “Any change of methodology has a huge financial implication and the cash flow of an individual JV partner and contractor is bound to fail, and the project will be delayed. My advice to contractors is to finalise the construction methodology of a project after procuring a detailed geotechnical investigation, utilities, building conditions survey and available land.”
It is acknowledged that even though tunneling is only a part of any mega infrastructure project, it is one that could run into a delay because of unknown issues with regard to geological parameters. Therefore, to avoid any delays impacting overall schedules, utmost attention is required to be afforded to the tunneling segment. Dr VK Gahlot, urban transport engineer, public works department, Government of Rajasthan, suggests, “Tunneling being specialised work needs special attention during the whole process, thus resulting in early completion of projects. The progress of tunneling work depends on the geology of the earth strata. In fact, sometimes, despite smooth progress, work may be delayed by many weeks due to the hard rock that lies in the path of a boring machine.”
Sahadeva Singh, director, project and planning, MEGA Ltd, also emphasises on contractor alignment, when he states, “The tunneling requires detailed domain knowledge on geotechnical parameters of the ground to be mined, and the structural condition of physical assets that exist in the influence zone of tunneling. Other key inputs come from the experience of the contractor to effectively co-ordinate the data with the structural design team and tunnel manufacturers in order to finalize the selection & design of the TBM or other mining equipment and the tunnel lining design of precast segments/in situ lining.” In recent times, public authorities, and also private ones in a few cases, have taken up projects of replacing age-old water supply systems to cities and towns. In such cases, a technique of micro tunneling – also called the trenchless technique – has become popular for implementation, particularly in congested areas.
TBMS RULE THE ROOST
With a boom in infrastructure projects in India, tunneling requirements are on the rise for projects involving railways, highways, metro networks, water supply networks as well as sewage systems in congested urban areas. Apart from the cost considerations, the speed of completion for these projects is the most critical business requirement for developers and project managers. In this context, TBMs provide the ideal choice to deliver on this key requisite. Considering the known advantages such as speed of project completion, controlled debris management and efficient traffic management in congested areas, TBMs are the most preferred technique in many of these projects.
ANY CHANGE OF METHODOLOGY HAS A HUGE FINANCIAL IMPLICATION AND THE CASH FLOW IS BOUND TO FAIL- DALJEET SINGH
Recounting the challenges involved in tunnelling and how TBMs support in overcoming these, Uplenchwar of HCC points out, “Boring a tunnel through a densely populated city too poses different sets of challenges. A typical challenge in an urban area is tunneling without disturbing the traffic and structures above ground. In the case of the Delhi Metro Rail project, the tunnel alignment passed beneath thickly populated residential areas that included schools, temples, hospitals and old heritage structures. Prior to the tunneling work, a structural survey was carried out in a 30m influence zone on either side of the alignment. To check the impact of tunneling on the buildings above, various monitoring instruments such as inclinometers, magnetic extensometers, piezometers, rod extensometers, precise level markers, bi-reflex targets and crack meters, were installed at regular intervals. This ensured that ground movements adhered to the design limits during and after the tunneling work. Choosing the right TBMs & equipment and ensuring engineering precision hold the key to successful implementation of a project.”
In the context of Indian conditions, he goes on to add, “Tunnelling methods in India are evolving from non-mechanised to mechanised. Given the Indian soil conditions, drilling with TBMs is the most preferred way of tunnelling. Wherever a TBM cannot be implemented, tunnelling is mostly done by the New Austrian Tunnelling Method (NATM). Key equipment like computerized hydraulic drill rig, high-precision surveying equipment, robotic arm shotcrete machine, telehandler with rib catcher etc. are used in this technique.”
CHALLENGES AND VENDOR SUPPORT
MANY TUNNELLING CONTRACTORS RELY ON EXTERNAL EXPERTS TO GUIDE THEM DURING THE DESIGN AND EXECUTION PHASE- SAHADEVA SINGH
Yet, despite the latest techniques, equipment and systems supporting land surveys and geotechnical analyses, tunneling activities remain risky and with some inherent challenges. The major issues that adversely affect the growth of tunneling demand are inadequate attention given while contracting, non-availability of skilled manpower, and lack of well-defined safety standards, apart from understanding and addressing geological challenges. In addition, having unclear clauses between the contractor and tunnelling agencies often results in avoidable
disputes at a later date. Many of these result in rework, thus adding to costs and delays.
As Sahadeva Singh puts it, “Many tunneling contractors rely, to a large extent, on external experts to guide them during the design and execution phase, regarding the design, specifications, equipment’s specification and method of construction. The contractors are primarily liable for quality, safety, structural soundness and completeness of project as per contract. The liability of experts in the form of detailed design consultants and/or project management consultants remains limited, and that introduces risks for the client. In tunneling activities, paying attention to safety goes a long way, not just in getting the job done most efficiently, but also protecting the needs of future users of the tunnel. Unfortunately, there are no standard safety guidelines only for tunneling, which can cause delays and even loss of property and life. The assistance provided by advanced instruments and machines helps in addressing some of these issues.
Gahlot says, “Monitoring triggers and impact sensors are being installed by vendors, during the tunneling work, so that no damage is caused to the existing buildings and safety during boring is ensured.”
Given the long-term use of tunnels by many, ongoing maintenance of tunnels is an equally big challenge. There is a huge requirement to understand the degradation to tunnel structures after a gap of time. In such cases, one has to go through techniques like 3D measurement, imaging and realization technology. Faro, a global company with its presence in India, specialists in this arena. Faro has a laser scanner (Focus) to capture a comprehensive set of geometric measurement results. The images of tunnel walls generated are accurate to the millimetre level. In fact, accuracy is at levels better than 5mm, and users can directly extract geometric measurements from the images. Oftentimes, it is through these images that tunnel defects are detected, or ancillary facilities are studied. These scanners are also useful to take 3D measurements from a distance in cases where areas are dangerous or inaccessible.In such cases, the scanners help in projects that involve measurement of depositions and changes in shapes of urban structures; as well as interference simulation projects.
MONITORING TRIGGERS AND IMPACT SENSORS ARE BEING INSTALLED, SO THAT NO DAMAGE IS CAUSED TO THE EXISTING BUILDINGS- DR VK GAHLOT
This data indicates to the team exactly how much reinforcement is required to maintain the tunnel’s structural stability, which is a major concern for a high-traffic passageway. To sum up, India would immensely benefit if tunneling technologies remain relevant to local conditions and are developed while keeping in consideration local knowledge of data. Given the number of infrastructure projects on the anvil, this is truly the need of the hour, if India is to benefit from employing advanced tunneling technologies to fast track these projects.