ABSTRACT

Measurements of rock stress changes induced by rock excavation were presented to be one of the main works involved in the structure safety monitoring during the rock excavation of the permanent shiplock in TGP. Three different kinds of monitoring instruments were accepted as the basic methods available for monitoring changes of rock stresses. They are YOKE gauges imported from Australia, Piezoelectrical stress gauges and Piezomagnetic stress gauges. Some of these instruments had being working in field for more than two and half years. This paper presents the performance of these instruments used in situ for monitoring changes of rock stresses in TGP, and the problems related to the long term monitoring works are discussed.

INTRODUCTION

For the purpose of navigation across the dam of the Three Gorges Project (TGP) on the Yangtze River, China, a permanent shiplock would be built through the mountain area in the left bank of the dam site. The shiplock was schemed out as a double-way and 5-step continuous ship locks. The total length of the double way and 5 step continuous shiplock Was 6442 m, including the upstream and downstream approaching channels. The length of shiplock itself Was 1607 m. The effective dimensions of each lock chamber were 280 m × 34 m × 5 m. All of these would be built through the mountain area by deep excavation to form high and steep rock slopes of85 to 120 m high, and the maximum reaches 170 m. The rock excavations of the permanent shiplocks began in 1994, and ended in October 1999.

To evaluate the stability of the high rock slopes, Some numerical analysis models, such as FEM and FLAC etc, had been used to simulate their excavations. Informed by the numerical analysis results, the stress state in rock mass prior to or during rock excavation would play a very important role for deformation properties of the artificial rock slopes.

Prior to the excavation of the navigation engineering, eight holes of absolute stress measurements in the shiplock area had been carried out by the Over Coring Stress Relief Method and the Hydraulic Fracturing Testing Method. On the basis of the stress measurements, the initial rock stress state had been analyzed by 3-D finite element regression analysis.

For the purpose of engineering and scientific research works, measurements of rock stress changes induced by rock excavation were considered to be one of the main works involved in the structure safety monitoring during the navigation construction period.

Two different ways were employed to be necessary methods for measurements of rock stress changing: absolute stress measurements in different excavation stages and stress change monitoring with measurement sensors installed in the rock mass. Excepted for the absolute rock stress measurements in different stages which were normal methods similar to the initial rock stress measurements, three different kinds of monitoring instruments had been accepted as the basic methods available for monitoring changes of rock stresses. They were YOKE gauges imported from Australia, Piezoelectrical stress gauges and Piezomagnetic stress gauges.

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