Special projects such as mining, tunneling, undersea tunnels, or those undertaking projects around hostile borders deserve special attention. These large and complex projects that are executed under extraordinary environmental conditions at times also require the customisation of equipment.Prabhukumar LT, Assistant General Manager of L&T ECC, who has been associated with L&T for the past 14 years and the project head for Rs 2,000 crore Rishikesh Karanprayag railway tunnel package 2, spoke on the challenging situations and how innovation is helping in bringing about optimal solutions during the CONSTRUCTION TECHNOLOGY SUMMIT, held virtually on July 22-23, 2021.Challenge: Geological conditionsTunnels are important elements of any infrastructure project – hydro power, water supply and sewerage system, etc. Tunneling for infrastructure projects is becoming more and more mechanised by use of tunnel boring machines (TBMs) and other methods. However, the drill and blast method is more flexible as it is easier to adapt to varying profile requirements as compared to a TBM, which gives a circular cross section, especially for railway tunnels, resulting in a lot of over excavation in relation to the actual cross section needed.Major tunnelling method used by L&T is the drill and blast method. “The goal of modern tunnelling technologies is to convert the unpredictable to predictable,” said Prabhukumar LT.On the challenges faced in tunnelling, he said “Many projects are coming up near the Himalayan mountains. The Himalayan range are young mountains with highly varying geology, coupled with diversified problems such as difficult terrain conditions, thrust zones, shear zones, folded rock sequence, in-situ stresses, rock cover, ingress of water, geothermal gradient, etc., which makes them highly unpredictable. Major challenges faced by us are the geology and predicting things ahead. Due to unpredictable geology, safety is compromised during project work, which leads to extended project completion and cost over run.”Said Prabhukumar LT, “During survey, the major challenge we face is during the pictorial output of profile geometry in real time at tunnel face. It was difficult to spot undercut/over break, and spot analysis of over break quantity. We also face problems like real time shotcrete layer thickness measurement and analyse the data to control overspray or underspray of shotcrete.He added, “We implemented robotic survey profilers with Amberg and Trimble tunnel software. Using this, the real time analysis—excavation profile (undercut, overbreak) and shotcrete profile (underspray/overspray)—were easily available at site. Even 3D project can be prepared for the entire tunnel line, and it provides high accuracy and reduces cycle time.”Automated drill jumbosThe underground jumbo drill rigs are used for blast hole drilling in underground mining and tunneling. “Earlier the challenge was completely dependent on the operator skill – whether they are doing at the right angle. We implemented fully- and semi-automated drill jumbos. It increases pull accuracy by 90%, and reduces undercut and overbreak. The operator gets training on the machine using a simulator before using it real time. It also provides realtime round report generation and data transfer,” said Prabhukumar LT.With automated drill jumbos, the data can be transferred from the office itself as it is WiFi-enabled. It gives efficiency of the drill, machine parameters, pull out analysis, round report analysis and drill tool life analysis.Usage of bulk explosives“Earlier we were using package blasting, now we use bulk explosives (ammonium nitrate emulsion and sodium nitrate mixed at nozzle tip), which is inserted inside the drill holes with high pressure to fill the blast holes completely,” he said. “These explosives are very safe compared to package blasting. Package explosives were time consuming, and the process involved was manual. Also there was inconsistency of pull and higher undercut and over breaks. The loading of bulk explosives is done by automated equipment, and has higher accuracy of pull and optimisation in cycle time is reduced by a minimum of 30-45 minutes per round.”Shotcrete machinesSaid Prabhukumar LT, “We used to use manual shotcrete machines and the quality of the spray depended on the operator. We now use automatic robotic shotcrete machines with job analysis software, which provides real time reports – capturing time, quantity, accelerator dosage, spraying time. Here the operator skill can also be evaluated.”“We are planning to implement thermal scanners, where it scans the surface and tells you immediately where the shotcrete is oversrpead or underspread. It gives real time data to the operator, and proper thickness and finishing,” he added.Deformation monitoring“We are monitoring all the deformations through MPBX (multipoint borehole extensometer), bi-reflex targets and load cells. These technologies give exact deformations in the surfaces and loads coming on the poles. It gives proper deformations in realtime and in millimeters (mm) – 5 mm, 10 mm and 15 mm. MPBX is designed to monitor changes in the distance between downhole anchors, each set at a specified depth in the borehole, and a measurement head at the surface. Rods extend upward from the anchors to the head, where measurements are made with a depth micrometer or displacement transducers,” said Prabhukumar LT.Geological predictions“For predicting geology, we use two types of technologies – probe hole drilling and tunnel seismic prediction (TSP) system,” he said. The probe hole report captures geological conditions 18 m ahead, while the TSP system can capture geological conditions like water pockets available up to 150 m ahead. This helps get a safe working platform and can predict the geologies ahead. With this, one can take corrective/preventive actions before taking up the work.The probe hole drilling and TSP system helps in prediction of face ahead and preplanning the works, detection of hazardous fault zones and cavities, exploration of water bearing formations and detecting changes in rock mechanical properties. The probe hole drilling machine can indicate rock fracture indicator, rock strength, drill parameters, round reports, and additional reports like water ingress and rock quality.Digitalisation“We have implemented a video analytics system for vehicle and manpower tracking. This tracks vehicle and manpower movement, automatic attendance capturing, cycle time monitoring, and ensures safety of men and machinery,” said Prabhukumar LT.He added, “We also have rear view cameras on dumpers, telehandlers, and CCTV at all locations for better safety during continuous reverse operation inside the tunnel, and continuous monitoring.” The tunnel communication system and IOT provides remote data transfer between drill jumbos and the main office, and provides Internet connectivity inside the tunnel for communication. The IOT installed in vehicles is used to monitor real time fuel consumption. Even drones surveys are used for open works. It saves a lot of time and is effective.He adds, “With this, we are going to give a safe working environment. We can take precautions before taking on something challenging since it gives a better idea of geological challenges ahead. There are a lot of savings on the cycle time. It gives 5 to 25% savings. The life of the project increases and it reduces 5-8% cost.”Prabhukumar LT concludes, “Predicting the unpredictable is the essence of extreme project management in underground works.”