Applying Artificial Pillar to Replace the Coal Pillar Protecting Roadway to Increase Production Efficiency and Sustainable Development in the Vietnamese Coal Industry

Vietnam's domestic coal production is growing fast and is expected to reach 68.9 million tonsin 2030, nearly 1.5 times higher than today. Open-pit mines will gradually reduce production and close,and underground mining coal output will increase progressively year by year and take a leading role.Besides the investment in new mines to achieve these goals, it is necessary to maximize the coal reserveexploited annually of existing underground mine projects, which its coal reserve in pillars protectingroadways currently accounts for 12−15%. The further exploitation of this coal reserve will decrease thecosts of preparation of underground mines and granting mining rights and depreciation of infrastructureassets. Moreover, it will help reduce the loss of non-renewable resources and contributing to thesustainable development of Vietnam’s coal industry.

Comparison of Coal Reserve Estimation Methods, Case Study PT. Bukit Asam Area, South Sumatra, Indonesia

The calculation of coal reserves is influenced by the dimensions or size of the coal deposit. There are several types of coal reserve calculation methods, and the use of these methods is adjusted to existing geological conditions. Each method will produce a different amount of coal reserves, although the location is the same. Besides, the amount of coal mining that can be produced is primarily determined by the mine design, especially the optimal slope as a basis for mining pits in the coal extraction. This research aims to estimate coal reserves based on existing pit designs using a variety of methods. Data on coal thickness and topography are used as the basis for reserves estimation. Coal reserve estimation is conducted in several methods: nearest neighbor point (NNP), inverse distance weighted (IDW), and kriging using Surfer 13 software. The results of the reserves estimation indicate that kriging is the best method by providing the smallest error value with an RMSE value of 0.67 and coal reserves of 27,801,543 tons.

Research on the Deformation and Control Technology of Surrounding Rock in Entry Retaining along the Gob Side

This paper studies and introduces the successful case of gob-side entry retaining technology and the typical mining pressure law in Luan mining area, which is the main mining coal seam in Qinshui coalfield. Qinshui coalfield has an estimated coal reserve of 300 billion tons, accounting for 9.58% of the total national coal reserve in China, especially anthracite, chemical coal, and coking coal. The methods of field investigation, theoretical analysis, physical experiment, and industrial test are adopted. Through the field investigation, theoretical analysis, physical experiments, and industrial test, the following conclusions have been drawn in this study: (1) A thorough engineering geological investigation was conducted on the entry retaining along the gob side on noncoal pillar mining working face, which covers multiple periods of mining process including the roadway excavation period, primary mining period, primary mining stability period, and secondary mining influence period. A series of analysis and tests were conducted such as core sampling, rock mechanics property testing, borehole detection, and flexible formwork support evaluation, which laid a foundation for identifying the mining pressure law of gob-side entry retaining by using noncoal pillar mining. (2) The mining pressure law was studied through the collection of the field measurements taken from the entry retaining along the gob side on noncoal pillar mining working face. The keys to achieve the roadway surrounding rock stability through noncoal pillar mining are obtained. According to the study, the stability control of retained roadway surrounding rock mainly depends on the stability of top coal, coal side, and shoulder angle coal. (3) In this study, a roadway reinforcement scheme is proposed to improve the surrounding rock control technology for gob-side entry retaining by noncoal pillar mining, whose effectiveness has been verified by a series of industrial test. Therefore, the wide adoption of the noncoal pillar mining method in Number #3 coal mine can significantly relieve the predicament of coal pressing under a large number of buildings in Luan mining area, which provides insightful guidance to the coal-free pillar mining in the whole Luan mining area.

GEOLOGICAL MAPPING AND PROVENANCE ANALYSIS: AS THE KEY TO IDENTIFY DISTRIBUTION OF MUD DIAPIR AND ITS IMPLICATION ON COAL RESERVES IN PT. ARUTMIN INDONESIA SITE SENAKIN

ABSTRAK Identifikasi keberadaan diapir merupakan hal esensial dalam pertambangan batubara mengingat sifatnya yang seperti intrusi dapat mengurangi cadangan batubara. Seperti yang teramati pada area pertambangan PT Arutmin Indonesia. Kehadiran mud diapir pada PIT HG telah terbukti mengurangi cadangan batubara, dengan luas area terdampak 0,7 Ha. Selain itu, beberapa diapir diperkirakan belum terpetakan karena terletak di bawah permukaan dan belum tersentuh oleh pengeboran eksplorasi PT Arutmin Indonesia, sehingga tanda-tanda permukaan seperti singkapan batuan dan struktur geologi maupun provenance diapir dapat menjadi petunjuk yang penting. Oleh sebab itu, tujuan penelitian ini adalah untuk mengetahui pola distribusi dan korelasi antara keberadaan diapir dengan struktur geologi, stratigrafi, dan provenance teridentifikasi yang kemudian dapat digunakan untuk memperkirakan persebaran diapir lainnya. Analisis dilakukan pada data primer hasil pemetaan geologi lapangan sebagai representasi struktur geologi maupun stratigrafi makro sebagai identifikator provenance. Hasil pemetaan lapangan seluas 60 km2 menunjukkan daerah penelitian terdiri dari tiga satuan batuan, yaitu satuan batupasir-batulempung termasuk lima singkapan diapir di dalamnya, satuan batulempung, dan satuan intrusi andesit. Satuan batupasir-batulempung memiliki kesetaraan dengan Formasi Tanjung yang merupakan formasi batuan sedimen tertua di daerah penelitian. Struktur geologi yang berkembang pada daerah penelitian adalah sesar geser menganan serta sesar geser mengiri yang berperan besar sebagai pengontrol keterdapatan diapir. Analisis stratigrafi menunjukkan provenance mud diapir berasal dari satuan batupasir-batulempung, Formasi Tanjung. Berdasarkan hasil analisis di atas, persebaran mud diapir berkorelasi dengan persebaran struktur geologi terutama sesar geser dan persebaran satuan batupasir-batulempung. Karena hal tersebut, maka pada area Tambang Senakin terdapat potensi keberadaan mud diapir yang tidak tersingkap di permukaan dan dapat menyebabkan hilangnya cadangan batubara termodelkan yang jauh lebih besar dari yang telah terbukti saat ini. Sebagai langkah preventif untuk mengetahui keberadaan diapir yang belum teridentifikasi, maka penulis membuat peta potensi keterdapatan diapir pada area penelitian di PT. Arutmin Indonesia Tambang Senakin. Untuk mendapatkan hasil yang lebih baik, penulis menyarankan pihak pelaksana tambang untuk melakukan analisis geolistrik pada titik yang telah direkomendasikan penulis. Kata kunci: mud diapir, Formasi Tanjung, analisis stratigrafi, pemetaan geologi lapangan, cadangan batubara ABSTRACT Identifying diapir occurrence is essential in coal mining activities knowing it behaves like an intrusion that can lead to a reduction in coal reserve. As we can observe in PT Arutmin Indonesia mining field. The presence of mud diapir on PIT HG has been proved to cut down its coal reserve, with the total area affected is 0,7 Ha. Since not all of the mud diapirs are exposed to the surface, we suspected that some of them are still yet to be found by PT Arutmin Indonesia’s exploration. Hence, diapir provenance and surface hints such as outcrop and geological structure can be a crucial indication. Therefore, this study objectives are to identify distribution and correlation between diapir occurrence and geological structures, stratigraphy, and its identified provenance that can be used to estimate other diapirs. This study began with geological mapping to identify the geological structure and its stratigraphy. Stratigraphic analysis is carried out as provenance identifier. Geological mapping in 60 km2 area concluded that the area have three lithological units, sandstone-claystone unit including five diapir outcrops, claystone unit, and andesite intrusion unit. Sandstone-claystone unit is equivalent to Tanjung Formation which is the oldest sedimentary rocks formation in the area. Dextral strike slip and sinistral strike slip faults which are found in the area considered to have a significant effect on diapirs occurrence. Further stratigraphic analysis shows that the the mud diapir’s provenance is from Tanjung Formation. Based on these analyses, we conclude that mud diapir occurrence has a good correlation to geological structures especially the strike slip faults and sandstone-claystone unit distribution. Consequently, Senakin Mine Field has a chance of losing its potential coal reserve much bigger than previously estimated due to unidentified mud diapirs occurrence below the surface. We will provide a mud diapir occurence potential map as a preventive measure in identifying unknown diapirs. We also suggest doing subsurface resistivity analysis for further detailed and better results. Keywords: mud diapir, Tanjung formation, stratigraphic analysis, geological mapping, coal reserve

PERKEMBANGAN TEKNOLOGI BATUBARA BERSIH BERWAWASAN LINGKUNGAN

Coal has a very important role to meet energy demand in Indonesia, however, it is also the dirtiest fuel among the fossil fuels. As coal utilization continues to increase, pollutants and greenhouse gases emissions from the coal utilization also increase, that would lead to environmental problems. Therefore, development of clean coal technologies for reducing those emissions from coal utilization needs to be considered. The technologies areintended to reduce the policy conflict between continuing coal utilization and protecting environment potential by improving the effectiveness of control technologies and reducing their costs. In addition, the technologies have higher efficiency that would impact on conserving fuels that lead to reducing costs and extension of coal reserve availability.