ABSTRACT

ABSTRACT: This paper describes the present condition of mining-induced damages in Japan and the characteristics of them. The change of mining operation and environmental condition has caused various significant impacts on the ground environment: subsidence, cave-in, springing out of ground water etc. The characteristics and the influences of these phenomena are discussed by investigation of the actual conditions and by fundamental studies. Some counter measures are also introduced.

1 INTRODUCTION

Japan has ten underground coal mines in operation and approximately a thousand mines either inactive or abandoned. All active mines are operating under the sea, forests or waste lands. The reasons for this is not so much due to the shortage of coal reserves but rather for preventing damages in the land. Due to huge mining damages in the past and for prevention of damages in the future, the Japanese government and mining companies have been devoting themselves to fulfilling rehabilitation plans and have spent much effort towards preventing and minimizing future damage. However, remnant damages are estimated at about 590 billion yen (4.9 billion dollars); this may depend on social and political situations to a certain extent.

Most of the damages are due to extraction of coal seams, that is usual surface subsidence. Discharging of mine water or used water, accumulation of abandoned stones and mineral tailing, or discharging of mining smoke have also cause damages in some districts. However, changes in mining operations, accompanied by mining under worse conditions or mine closure, have caused new complicated environmental impacts, namely: subsidence due to mining and dewatering in areas of thick alluvium, cave-in due to cavities remaining at shallow depths, and springing out of ground water at abandoned mines. These damages were first brought to public attention at the end of the 1940's, though they had occurred before, and have brought a severe social problem. In addition, some types of damage will continue for a long period. This paper describes the characteristics of subsidence related environmental problems and some preventive measures against them from a geotechnical point of view.

2 HISTORICAL VIEW AND PRESENT CONDITION OF MINING DAMAGE

Underground coal mining has been practiced in Japan, particularly in Kyushu, the southernmost of the four main Japanese islands, for approximately 500 years. This condition constituted a potential mining damage. Within Kyushu, the Miike and Chikuho coal fields were discovered in the 15 century, and the Takashima coal field was developed in the 18 century, where coal was produced primarily for domestic use. In the latter part of the 19 century, coal industries had an important role as a major energy supplier for the overall Japanese economy, and production of coal increased at an accelerated rate. Up until the middle of the 19 century, mining damage was neither physically severe nor a socially serious matter, because of primitive method of mining and small scale production. However, after the introduction of mechanized methods of mining for large scale underground production, near the end of the 19 century, tangible damage like as land subsidence began to emerged.

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