Assessment of Rock Pressure for Tunnels in the Himalayan Region — A Case History

Since early sixties numerous tunnels had been planned and constructed for hydro-electric power generation in the Himalayan Region of India. The mountain chain is of very recent origin geologically and is believed to be still active tectonically. The geology is complex and tunneling under such circumstances had been a real challenge. It was a tough task to predict the geotechnical behaviour of the tunneling media. Beginning with the classical approach of Terzaghi (1925-46) many rock pressure estimation theories had been evolved for prediction and estimation of rock pressure for designing competent and stable tunnel supports. The author has made an attempt to project real field data, which is rare to find, during a period of over thirty years of his association with the construction of numerous tunnels driven through diverse rock formations. Various theories in vogue for rock pressure assessment yielded different results. An attempt had also been made to reason out the differences. The rock pressure assessment is still a dark area, shaded darker when dealing with weak and very weak rock formations. It is believed that earthquakes affect the surface structures most but the sub surface structures are less affected. Some earthquakes occurring in India support this notion

Oyster mushroom waste as manure in fish culture: a preliminary study

In an attempt to recycle the waste substrates of the oyster-mushroom crop, tanks were stocked with seed of Indian major carp Cirrhinus mrigala at the rate of 600,000/ha and waste substrate was applied at weekly interval at 0, 50, 100, 150, 200 and 250 g/tank. Oyster mushroom waste not only provided highly nutritive colonised detritus to the fish as direct feed, but also produced rich plankton in the tank. In waste treated tanks, production was better than in the control in 150, 200 and 250 g/tank treatment suggesting the possibility of fish-oyster mushroom integration

Rock Mass Behaviour Assessment for Large Cavern in Rock

A large power house cavern (22m x 50m x 250m) is proposed to be excavated for installing a 1000 MW hydroelectric power plant for Tehri Dam Project. The gorge chosen for the dam is very narrow and the topography is rugged and inhospitable. This dampened the process of preconstruction investigations. A number of tunnels were constructed for various project structures in the vicinity of the cavern. This provided an excellent opportunity to study the rock mass behaviour. Tunnel closure and rock loads were monitored with the help of instruments. Deformation moduli were also determined for different rock grades with the help of various techniques. A voluminous data had been obtained. This data had been analyzed thoroughly and values of various parameters had been suggested for the final design of underground cavern and the supporting structures

Geomechanical Studies for a Himalayan Tunnel in Jointed Dolomites: A Case History

Reported case history of Himalayan tunnel reveals that Barton\u27s and Bieniawski\u27s classification systems provide better assessment of the rock mass behavior. The design and shear strength parameters derived from these classifications provided a preliminary design of the tunnel, which has been critically evaluated with the design, adopted at site. Based on the structural feature and ground water conditions, a number of tunnelling conditions have been predicted. The studies indicated the loosening rock pressures would be occuring at site with an estimated range of 0. 25 kg/cm2 to 3. 58 kg/cm2. Problems of roof collapse, flowing ground condition and cavity formation may occur during the excavation. Multiple drift excavation method is suggested for extremely poor conditions

Experiences of the Support Designs in the Two Large Underground Openings in India

Support requirements for two caverns arc worked out by empirical and the numerical approaches. The adequacy of the shotcrete-rock bolt support system is monitored by measuring the deformations of caverns walls and roof. The measurements are compared with the results obtained from the numerical approach. Brief geology, the supports, and the results of performance monitoring are presented in the paper

Preparation and characterisation of TIG-alloyed hybrid composite coatings for high-temperature tribological applications

There is an increasing interest in the tribology community for developing high-performance composite coatings to meet severe tribological conditions in advanced mechanical systems which require high operating temperature and long life. In the present work, powder preplacement and tungsten inert gas (TIG) torch melting techniques have been employed to generate titanium carbide (TiC)-based composite coatings containing hexagonal boron nitride (hBN) or Ni–P coated hBN (Ni–P-hBN) lubricant additive. The effects of preplaced powder composition on the cross-sectional microstructures and surface hardnesses of the developed coatings were analysed. Furthermore, the friction and wear behaviours of the composite coatings at 600°C were evaluated using a Ducom ball-on-disc wear test rig. The results indicate that the TIG-melted surface containing TiC and Ni–P-hBN powder mixtures exhibits optimum properties combining good control of microstructures and uniformly distributed hardness as well as excellent tribological properties due to the enhanced wettability action of Ni–P encapsulated hBN particles

Squeezing Problems in Indian Tunnels

Case histories of three Indian tunnels indicate that squeezing conditions are created due to plastic flow of rock masses under the influence of high cover pressures. These examples emphasize that a tunnel experiencing squeezing conditions must be allowed to deform to optimize support costs and avoid delays. Allowance for desirable tunnel deformations must, therefore, be made while planning the size of excavation. Field data has shown that a flexible support system of compressible backfill and steel ribs may be used as an alternative to shotcrete support which is unpractical in Indian tunnels excavated largely by conventional methods. Instrumentation indicates that large broken zones are associated with late stabilization and that the coefficient of volumetric expansion of failed rock masses is significantly lower than believed so far. Comparison of measured rock pressures with those estimated from available methods shows that the elasto-plastic theory may provide reliable predictions provided that the strength parameters of rock masses are known precisely