Hydro-fracturing test in sandstone rock mass: A case study from Himalayas

DOI

10.2991/rare-16.2016.15How to use a DOI?

Keywords

In-situ stress; hydro fracturing; sand stone; alignment of powerhouse; Rock mass

Abstract

Rock mass are naturally occurring construction materials which are subjected to in-situ stresses. In-situ stresses occur due to the weight of overburden and tectonic stresses. Prior knowledge of in-situ stresses is important before aligning the longitudinal structures in rock mass such as tunnels and powerhouse. During excavation in rock mass, in-situ stresses get redistributed around the openings and sometimes may cause instability of the opening. Therefore, proper design of support system and alignment of the cavity requires determination of in -situ stresses. In the present paper, a case study of hydro-fracturing test conducted by the authors at powerhouse site of Thana-Plaun hydroelectric project situated in Himachal Pradesh is discussed. The power house cavern will house 3 nos. of main generating units of 50.33 MW each and 2 nos. of environmental units of 20 MW each (Total capacity 191 MW). The rock type encountered in the area is represented by fresh, hard and compact sandstone with subordinate siltstone and claystone bands having gradations contacts and dipping towards upstream. The average bedding dip value is of the order of 570 in N0750 direction. In addition, five joint sets have been deciphered in the area. A total of 14 tests, 5 in vertical drill holes and 9 in two horizontal drill holes have been conducted. These tests were conducted in three orthogonal boreholes of 30 m depth in the exploratory drift at powerhouse site. The results of these tests have been used to determine the in-situ horizontal and vertical stresses along with their orientation for the purpose of alignment of powerhouse. Average Orientation of maximum horizontal Stress was found to be N 780 E. Maximum horizontal stress and minimum horizontal stress were found to be 5.49 MPa and 3.07 MPa, respectively. Measured vertical stress was found to be 3.45 MPa, whereas, estimated vertical stress based on overburden depth is 3.32 MPa. Further, it is found that lateral earth pressure coefficient at state of rest (K0) i.e. ratio of horizontal stress to vertical stress for rock mass varies from 0.89 to 1.59 in the two horizontal directions

Copyright

© 2016, the Authors. Published by Atlantis Press.

Open Access

This is an open access article distributed under the CC BY-NC license (http://creativecommons.org/licenses/by-nc/4.0/).

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TY  - CONF
AU  - G.V. Ramana
AU  - Pathak Shashank
AU  - K.K. Mishra
AU  - Dev Hari
PY  - 2016/11
DA  - 2016/11
TI  - Hydro-fracturing test in sandstone rock mass: A case study from Himalayas
BT  - Proceedings of the conference on Recent Advances in Rock Engineering (RARE 2016)
PB  - Atlantis Press
SP  - 91
EP  - 96
SN  - 2352-5401
UR  - https://doi.org/10.2991/rare-16.2016.15
DO  - 10.2991/rare-16.2016.15
ID  - Ramana2016/11
ER  -