INTRODUCTION:
The overall success of the river linking is based on the engineering safety of the dams. Channels and structures in the link. As geological conditions that would lead to failure of tunnels, dams. Aqueducts and erosion of channels are of common occurrence a geological study of the linking channels is essential. While comparing the cost of a tunnel with that of an open channel, the cost of protection works required for the tunnels and channels must also be taken into account. Dams required to divert the channels as well as the foundations of the aqueducts will also have to be properly investigated in engineering geological perspective. Sufficient time will usually be available to carry out the necessary geological investigations
And to design and to execute appropriate protective works. But it is important to take cognizance of the problem immediately as it manifests itself and to proceed scientifically to tackle it.
Aqueducts in River Linking Project: While carrying water through different regions,thousands of cross drainage works will have to be 'constructed. Very high and long aqueducts will haveto be designed before construction. Propergeological investigation of the foundations of allsuch structures is very important. The success of thewhole: project is depending on the engineeringsafety of channels, structures and dams in the link.
DAMS IN THE RIVER LINKING PROJECT:Dams are key structures in river linking schemes. In such projects besides the existing old dams, new darns or di version barrages will have to be planned. Besides being a source of wealth, darns can also be a source of accidents, albeit it few in number: an average of less than 1% of dams has suffered accidents over a long period of time. Yet the resulting damage and loss of life mean that all such accidents are unacceptable. A dam prevents the flow of water on surface, but if water is to be stored, it has also to be seen that there is not a flow below the surface either. This means that the foundation rocks must be watertight, and if they are not naturally so, suitable steps have to be taken to prevent loss of water through them. Also, to avoid the disastrous effects of dam failure safety and stability of a dam have to be assured. These will depend among other things on the strength and soundness of foundation rocks, which in turn will depend on the nature and structure of these rocks. An analysis of dam failures of the past has shown that failure to recognize or to treat properly defects in foundation rocks was responsible for a substantial number of them. The safety, stability and effectiveness of a dam therefore will depend largely on the geological conditions at the foundation and these must be known with accuracy and in sufficient detail before the work on a dam is undertaken. Detailed geological investigations have therefore to be carried out for obtaining the necessary information about rocks at the dam site and over the reservoir area
TUNNELS IN RIVER LINKING PROJECT: Tunnel is a very essential component now-a-days in a dam project. The modernized methods andexperience in tunneling techniques-enables an engineer to opt 'for the tunnels. However engineering geology plays very important role for a successful tunnel. Proper knowledge of thestrata and investigation by proper geologist is therefore very important. Collapse of a bottlenecktunnel may prove a total project economically unsafe.
GEOLOGY OF MAHARASHTRA: About 85% of Maharashtra is covered by igneous volcanic rocks- Deccan trap basalts. In rest of
The portions older rocks belonging to Archaen, Dharwar, Cuddapah, Vindhyan and Gondwana series of Indian Geology occur. The Deccan Traps mainly consist of basalts, but as there is considerable variation in the characteristics of basalts, and as rocks. Derived from them by modifications taking place in the volcanic process also occur. It is proposed to describe here some case histories of dams, at which we have carried out geological work, in an attempt depict the varying geological conditions in the Deccan Trap rocks that effect tunneling operations.
THE DECCAN TRAP ROCKS: As the suitability or otherwise of geological conditions for tunneling will depend on thecharacteristic of rocks met with along the alignment, an acquaintance with the various rock typesoccurring commonly in the Deccan Traps and their engineering behaviors is necessary.
Compact and Amygdaloidal Basalts: In the Deccan Trap basalts two main types occur: The compact nonvascular basalts without gascavities filled with secondary minerals such as zeolites. And chlorophaeite which give themspotted appearance. Both compact and amygdaloidal basalts often contain small slender laths asphenocrysts giving polyphyritic varieties.
Chlorophaeitic Basalts: Chlorophaeitic basalts in which a major portion of groundmass glass has been converted intochlorophaeite are common. When large amounts of chlorophaeite are present the rocks becomedark black.
Hydrothermal Alteration: Magmatic gases that produce cavities sometimes chemically alter the basalts, and this action iscalled hydrothermal alteration. The normal grey or bluish color of basalts is turned into shadesof green. Pink. Red. Purple or brown by hydrothermal alteration. Most commonly hydrothermalalteration brings about only such color changes in basalts without affecting their physicalproperties but more intense hydrothermal alteration at times weakens rocks.
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