Abstract

The in-situ stress field is one of the primary parameters influencing the performance of underground structures particularly in the Himalayas where there is strong influence of topography and geology on in-situ stresses. It is always advisable to measure the in-situ stresses, in whatever best way possible. Hydrofracturing is one of the methods by which in-situ stress can be measured. This paper briefly describes details of the concept of Hydrofracturing in arriving at the in-situ stresses of the rock mass at Pancheswar Project. The data obtained from the tests has been analysed, interpreted and the results are presented in this paper.

Kurzfassung

Das Spannungsfeld an Ort und Stelle ist einer der wichtigsten Parameter, die das Verhalten der Untergrund-Struktur beeinflussen, insbesondere in den Himalayas, wo die Topografie und die Geologie einen grossen Einfluss auf die oertlichen Spannungen ausueben. Es empfiehlt sich stets die Spannungen an Ort und Stelle so gut wie moeglich zu erfassen. Die Hydrofraktur bzw hydrografisches Zerstueckeln ist eine der Methoden, die bei den Messungen der oertlichen Spannungen verwendet werden koennen. Diese Abhandlung beschreibt kurz Einzelheiten ueber das Konzept von Hydrofraktur bei der Bestimmung der Spannungen an Ort und Stelle von der Felsmasse bezueglich des Projekts Pancheshwar. Die gewonnenen Daten aus den Messungen wurden analysieret und ausgewertet. Die Ergebnisse werden dabei vorgelegt.

Sommaire

Le champ de contraintes in-situ est un des paramèters principaux influencant l'execution des structures souterraines particulierèment en Himalaya où les forces in-situ sont fortement influencees par les caracteristiques topographiques et geologiques de la region. La fracturation hydraulique est une technique qui permet de mesurer des forces in-situ des massifs rocheux. Cet article decrit brièvement le mecanisme de fracturation hydraulique et presente les resultats de mesure des forces in-situ des roches au site du projet hydroelectrique de Pancheswar.

Introduction

The Pancheshwar multipurpose project is located in bordering state of Uttaranchal in India and Nepal, which envisages the harnessing of the water resources by the construction of 288 m. high earth and rock fill dam across the river Mahakali. The project is being investigated jointly by the Government of India and the Government of Nepal.

To measure in-situ stresses for the design of the underground powerhouse Central Soil and Materials Research Station (CSMRS) conducted Hydrofracturing test in 3 Nx size boreholes in the left bank and 1 Nx size borehole in the right bank of Pancheshwar Multipurpose project using Surface Hydrofracturing Equipment manufactured by Strata Tek Pty Ltd, Australia.

In-Situ Stress Measurement

The importance of in-situ stress measurements for underground structures has been well established in the recent times by many researchers throughout the world (Amadei and Stephanson, 1992; Enever and Walton, 1987). The other major requirement of in-situ stress measurement is as input for the numerical methods such as Finite Element Method and Discrete Element Method which are increasingly being used these days due to the availability of fast digital computers.

The natural stress pattern of Himalayas has not been well established so far and there is strong influence of topography and geology on in-situ stresses.

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