ABSTRACT:

A study of the effect of water-saturation for instantaneous freezing on the dynamic properties of granite rock obtained from Mandai, Singapore was carried out. 3 states of water-saturation were selected, i.e. bone-dry samples with 0% saturation, air-dry samples with 60% saturation and 100% saturated samples. Water-saturation treatment was done prior to the instantaneous freezing, which is achieved by submerging samples in liquid nitrogen. Physical properties of the granite such as density, wave velocity and Young?s Modulus were observed to be decrease at bone-dry and saturated state. This trend is also observed for the peak failure stress of the granite. A more brittle and explosive failure mode, with samples fractured into smaller fragments, is also observed with the increase of water-saturation. A decrease in strain rate is obtained from the same strike velocity with the increase of water-saturation. The effect of high strain rate has shown that with the increase of strain rate, there is an increase in peak failure stress.

1. INTRODUCTION

The multiple-utilization of land has been a growing trend in recent years, owning to the global increasing need for land-space. Of many types of multiple-utilization, underground cavern remains as one of the more popular choices. Granite is one of the most ideal materials for the selection of underground cavern as it is chemically and mechanically stable. Underground cavern has a wide variety of usage such as storage of nuclear fuel waste, liquefied gases, transportation network, recreational facilities, etc. This study focus on usage of these underground caverns for storage of liquefied gases. Gases are stored at liquefied state so as to increase the amount (volume) of storage. Liquefied gases are known for their low sub-zero temperature, with liquid nitrogen going to as low as -196°C. The commonly stored gases, LPG and LNG are highly explosive and volatile. Thus, the dynamic compressive strength at low temperature was looked into. In most studies, dynamic compressive strength was done on rock cores. These rock cores are "core and store" prior to the testing with some cores stored up to as long as a few years. The water-saturation of these core changes over the years. Water-saturation is an essential parameter when assessing the effect of low temperature, as water expands after 4°C. This expand in volume will cause further cracking besides the micro-crack that occurs due to differential shrinking. In order to simulate and assess the dynamic properties of the granite that has been exposed to instantaneous freezing, the response of the material to high strain rate is required. Many studies have been done previously regarding the static compressive strength granite at low temperature and water-saturation. Yet little study was done in the field of dynamic compressive strength of granite exposed at low temperature and water-saturation. This paper investigates the effect of water-saturation for instantaneous freezing on the dynamic properties of granite.

2. SAMPLE PREPARATION

Samples were prepared to the thickness of 30 mm from rock core with core diameter of 50.5 mm. To ensure that there is no inherit fissure in the samples taken from the rock core, a selection of the rock core needs to be done.

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