GEOLOGICAL AND ENVIRONMENTAL INVESTIGATIONS OF TUNNEL PROJECTS

Geological and environmental investigation of tunnel projects Purpose of construction of tunnel project Geological impact of construction of tunnel project Environmental impact of construction of tunnel projects Measures to reduce the impact of construction of proposed tunnel projects

Tunnels Tunnel is a nearly horizontal underground passage which is open at both ends. Tunnels are of different types according to their uses like traffic tunnel, hydropower headrace tunnel and public utility tunnels etc. • Tunnels can be driven or holed through a rock or earth mass by method used in mining, including blasting. •  In soft ground tunnels may be excavated by boring machines with the walls being supported by liner plates.

PURPOSE OF TUNNELS Transportation - Reduce distance between two locations , reduce the travelling time (bus, rail) Supply of water for irrigation, industry, agriculture Supply of water for hydropower generation Underground mining Transportation of materials in underground mines Public utility purpose – drainage, gas pipe line, diesel/ petrol/ crude oil pipe line, cables Bunkers for safety . Strategic storage of materials ( HPCL crude oil storage at Visakhapatnam)

Pilot tunnel(subsurface investigation) A small tunnel or shaft excavated in advance of the main drivage in mining and tunnel building to gain information about the ground, create a free face, and thus simplify the blasting operations Geology is the most important factor that determines the nature, form and cost of a tunnel.

Geological profile This profile should show the different type of rocks and soils along the tunnel line, boundaries between them (contacts) and geological defects such as fault. Water tables needed to be located before the alignment of tunnels Tunnelling in hard rocks  is more favourable than into the soft rocks as shale, slate. Tunnelling in soft soil and rock create problem of support as well as squeezing and swelling.

Tunnelling in horizontal bed is more favourable as pressure is distributed in all direction in case of horizontal bed unlike the inclined bed where the pressure concentration is at one side. Location of tunnel in an anticline is not recommended due to the stressed condition of rock in the hinge area. If water bearing strata is encountered in the syncline then the water tends to flow into the tunnel.

How the impact is different from a hazard A proposed tunnel project may have various impacts. All these can be predicted well in advance at the time of preparation of Environmental Impact Assessment (EIA) report. Various Impacts of the tunnel project are Impact on Environment Impact on Economy Impact on Culture Impact on Society.

Geological impact of construction of tunnel projects Any lapse in selection of proper alignment will lead more distance to travel Lapses in identification of fractured/ jointed rocks at roof may leads to collapse of tunnel If tunnel axis below the groundwater table, there will be heavy seepage of water in to tunnel If weak rocks are occurring in the proposed tunnel route, it requires support.

Geological impact of construction of highway projects If faults are not identified before, further displacement of blocks may take place. If folds are not identified properly , the tunnel will not be safe

ENVIRONMENTAL IMPACT OF TUNNEL PROJECT Construction of tunnel projects will also have negative impact on environment Loss of forest land if proposed to pass through forest Problem of dumping of excavated debris

Loss of forest land Loss of Green Cover/tress, shrubs wooden material Loss of tribal culture/ forces migration of tribals to remote areas Loss of forest produce - nuts, leaves , spices, gum, fruits, honey, plant based medicines, fiber, timber, fire wood etc. Impact on climate, rain fall,/ micro climatic changes Loss of carbon absorption capacity Loss of bio diversity Reduction in cleaning capacity of pollutants

Loss of forest land Loss of educational benefits Loss of tourism Loss of aesthetic effect Forest reduces run off and increases infiltration Reduction in infiltration will leads to reduction in availability of groundwater Contributes to floods Loss of ecological benefits In accessible areas in forest will have access to human beings

Loss of forest produce nuts leaves spices gum fruits honey plant based medicines fiber, timber, fire wood etc.

Impact on climate and rain fall Loss of forest cover results in reduction in CO2 absorption capacity in turn capacity to give O2 also comes down Increase in temperature in adjoining areas

Loss of forest land

Loss of wild life Loss of shelter to wild life will lead to migration of wild animals Loss of bio diversity Species may become extinct Livelihood of tribals will get effected

Loss of wildlife

Geological and environmental investigations The purpose of geological and environmental investigation is to identify a suitable site for construction of tunnel projects - tunnel should be safe - cost of construction should be economic - cause less damage to the natural and man made environment - tunnel alignment - least distance between the destinations, less excavation, less lining We need to identify at least two or more routes, evaluate and finally select the route having minimum damage to the environment , safe and economic.

Geological investigations Utilize remote sensing, geological, topographical maps and hydrological maps for alignment of tunnel route We need to look for shortest possible route Avoid the locations where soft rocks are occurring. Soft require lining with concrete for stability, results increase in cost Identify the geological structures – folds, faults and assess stability of rocks by carrying out drilling/ digging shaft along the proposed route

1.main tunnel 2.Service tunnel 3.pilot tunnel 4.connecting gallery

Geological investigations Strong squeezing and high plastic deformation in rocks Spalling and rock burst in hard rocks associated with high in-situ stresses Swelling and creep in argillaceous rocks High water pressure and/or large water inflows

Geological investigations Syncline (the strata slopes upwards)areas are highly unsafe for tunnel when there is water flow in that area Fault areas are unsafe for tunnel Identify the rocks occurring along the proposed route and locations of occurrence of soft rocks. Soft rocks require concrete lining. Identify the position of the proposed tunnel along the proposed route with respect to ground water.

Geological investigations If tunnel passes below the groundwater , it requires lining to prevent seepage. Map the inclination of the rocks. Thin horizontal rocks are unsafe and require concrete lining Excavation is done from both the sides. If any failure/ deviation in route will leads to waste of huge investment

Environmental investigations Detailed investigations are essential to assess the impact of the proposed high projects on natural and man made environment Impact on forestland Wild life Economy Ecological Aesthetic Social Cultural

Measures to reduce the impact of tunnel projects Utilize latest technologies available such as remote sensing geological, topographical maps and hydrological maps to arrive the tunnel alignment Select the route that cause minimum damage Preferably avoid passing the route through forests to the possible extent If required the tunnel to pass through forest , go for compensatory afforestation Prefer the route that requires less lining, less excavation

Measures to reduce the impact of tunnel projects resettlement and compensation in a appreciable manner We need to identify at least two or more routes, evaluate and finally select the route having minimum damage to the environment , safe and economic.