Two methods of stress measurements have been executed on the surface and underground to construct an oil storage cavern using hydro-fracturing and overcoring method. The first measurement has been performed to make a design of the caverns before excavating and the second to confirm the stress state during excavation. Six measurements have been carried out in the hydro-fracturing test at the depths between -17.8 and 54.5m from the sea level and a single measurement in the overcoring test in a single borehole at the depth of -21m from the sea level. The ratios of the maximum horizontal to vertical stress measured using hydro-fracturing and overcoring method are 2.95 and 3.1, respectively. Also, the orientations of the maximum horizontal stress are N53E and N58E. These measurements show that both methods give almost same results and significant horizontal stresses are acting on this cavern.

Deux methodes de mesure de contrainte ont etè executees sur la surface de terrain et sous la terre pour construire une cavite de stockage de petrole en utilisant l'hydro-fracturing et l'overcoring. La première mesure a etè faite pour le plan des cavites avant l'excavation et le seconde pour confirmer l'etat de contrainte durant l'excavation. Six measures ont etè faites dans le teste de l'hydro-fracturing à la profondeur entre -17.8 et 54.5m depuis l'elèvation maritime. Une seule mesure a etè faite dans le teste de l'overcoring dans une seule trou de songdage à la profondeur de -21m. Le ratios de la maximale contrainte horizontale à la contrainte verticale mesure par les deux methodes sont 2.95 et 3.1, respectivement. Les orientations de la maximale contrainte horizontale sont N53E et N58E. Ce montre que les deux methodes donnent presque m me resultats et la contrainte importante est activee sur ces cavites.

Zwei Druckmessungen wurden durchgefuehrt auf der Erdoberflache und im Innern von Ölspeicher- kavernen unter vergleichender Anwendung des Hydrofraktionierungs- und des Kernbohrungsver- fahrens. Die erste Messung wurde durchgefuehrt um einen Plan der Kavernen vor der Herstellung zu erstellen und die zweite um die Druckverhaltnisse wahrend der Bohrung zu ueberpruefen. Sechs Messugnen wurden mit der Hydrofraktionierungsmethode bei einer Tiefe von 17,8m und 54,5m unter dem Meeresspiegel und eine einzige Messung mit der Kernbohrungsmethode in einem Bohr-loch bei einer Tiefe von 21m unter dem Meeresspiegel vorgenommen. Das Verhaltnis von maxi- malem horizontalem zu vertikalem Druck bei der Hydrofraktions- und der Kernbohrungsmedthode ist 2,95 bzw. 3,1. Die Bezugspunkte des maximalen horizontalen Drucks in beiden Verfahren sind N53E und N58E.


It is essential to measure virgin stresses for the purpose of stability analysis of underground caverns in numerical way. Hydro-fracturing and overcoring methods are largely used for stress measurement in Korea. As the stress state depends closely on the geological structure, different stress values might be obtained according to measuring points even in a small area. To avoid this, several tests should be carried out in different points but few measurements could be made in a project because of the expenses. Another way to obtain a representative data is to measure and compare the stresses using two different methods. Cai et al.(1997) presented a case study of in-situ stress measurement by hydro-fracturing and overcoring tests for the design of an underground mine.

In this study two methods, hydro-fracturing and overcoring, have been adopted to obtain reliable data of virgin stresses for the proper design of an underground oil storage cavern. Hydro-fracturing test has been performed before excavating the cavern (Choi et al., 1999) and overcoring test during the excavation. This paper reports the comparison of the results obtained by two methods.

Measuring Site

In-situ stress measurements have been made to construct a large underground facility for the oil storage.

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