naa a22 4500 510756816 CHVBK 20180411083125.0 cr unu---uuuuu 180411e20131101xx s 000 0 eng 10.1007/s12594-013-0184-6 doi (NATIONALLICENCE)springer-10.1007/s12594-013-0184-6 Imaging of sand lens at a barrage site in the Indian Himalaya — a case study using cross-hole seismic tomography [Elektronische Daten] [S. Nelliat, P. Jha, P. Mohanty] Drilling at the barrage site of a hydropower project usually gives a reasonable picture of the sub-surface rock mass condition. However, when the overburden (OB) comprising river borne materials is very thick and the basement rock is deep, the drilling results become unreliable. In the present case, the depth to the granitic gneiss basement is 45m from the river level and the height of the proposed diversion barrage is only 24.5 m. For this reason, stripping of the overburden up to the basement is not considered feasible. Cross-borehole seismic tomography (CST) was carried out at the barrage site to investigate the inclusions and structure of the OB material in order to facilitate a foundation design suitable for permeable formation. Three sets of CST surveys were carried out up to a depth of 30 m between the three vertical boreholes that were prepared at the vertices of an equilateral triangle with a separation of 17.8 m. The tomograms precisely imaged the nature and disposition of the different constituents of the overburden material. A lens shaped low velocity layer (LVL) with seismic velocity Vp=2000-2500 ms−1 was mapped at a depth of 14.5m from the surface. Hence, it was recommended to shift the barrage axis by 50 m towards the downstream side of the proposed axis. The outcome of this study proved valuable for the designer who finalised the foundation design. Successful application of CST in OB characterisation has reiterated the need of such studies for barrage site investigations particularly in the Himalayan terrain. Geological Society of India, 2013 Cross-borehole seismic tomography nationallicence Barrage site nationallicence Himalaya nationallicence River borne material nationallicence Seismic imaging nationallicence Nelliat S. National Institute of Rock Mechanics, 563 117, Kolar Gold Fields, India aut Jha P. National Institute of Rock Mechanics, 563 117, Kolar Gold Fields, India aut Mohanty P. Indian School of Mines, 826 004, Dhanbad, India aut Journal of the Geological Society of India Springer India 82/5(2013-11-01), 529-534 0016-7622 82:5<529 2013 82 12594 https://doi.org/10.1007/s12594-013-0184-6 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/s12594-013-0184-6 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Nelliat S. National Institute of Rock Mechanics, 563 117, Kolar Gold Fields, India aut NATIONALLICENCE 700 1- Jha P. National Institute of Rock Mechanics, 563 117, Kolar Gold Fields, India aut NATIONALLICENCE 700 1- Mohanty P. Indian School of Mines, 826 004, Dhanbad, India aut NATIONALLICENCE 773 0- Journal of the Geological Society of India Springer India 82/5(2013-11-01), 529-534 0016-7622 82:5<529 2013 82 12594 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer