Rudy Sayoga Gautama

Mine ventilation measurements with tracer gas method and evaluations of turbulent diffusion coefficient

Tracer gas measurements have been carried out at the Pongkor underground gold mine, Indonesia, to evaluate mine ventilation flows and to investigate the effective turbulent diffusion coefficients in mine airways. The airflow routes and quantity, and the diffusion coefficient have been obtained by matching the measurements with numerical simulations using the advection-diffusion equation. Two leakages with flow quantity of 26.7 and 36.7 m3/s were detected. Reduction of leakages have been measured with the method after stopping the leakage routes. The turbulent diffusion coefficients for the simple airways have good agreement with the Taylor equation. However, for complex airways in operating mines, the coefficients show higher values (1.5 to 32 times) than that obtained by the Taylor equation and these have been compared with the data measured in the Kushiro coal mine, Japan. It is mainly affected by the ratio of airway length over equivalent diameter and airway frictions, but airflow mixing along the airway also has an effect on the diffusion coefficient.

Development of a new covering strategy in Indonesian coal mines to control acid mine drainage generation: a laboratory-scale result

The waste dump of sulphide-containing rocks is one of the potential acid mine drainage sources, since it contains a huge amount of readily oxidised sulphide mineral, due to its exposure to air and water. The application of the dry cover system is regarded as one of the best practices since it prevents acid mine drainage of the waste rock dump at the surface coal mine. However, the implementation of the dry cover system in field practice has faced several obstacles due to the limited number of cover materials. The nature of geological condition is considered to be a controlled issue, whilst the problem is the mining method and equipment size. This article describes the acid generation mechanism and its control, application of cover system and the problems that are faced in Indonesian coal mines, whilst discussing the preliminary laboratory results of multi-layer cover systems. It finally proposes a new covering strategy in an attempt to overcome the problem.

Application of Coal Ash to Postmine Land for Prevention of Soil Erosion in Coal Mine in Indonesia: Utilization of Fly Ash and Bottom Ash

The increase in the number of coal-fired power plants with the increase in coal production and its consumption has caused the problem of the treatment of a large amount of coal ash in Indonesia. In the past studies, coal ash was applied to postmine land with the aim of improving soil conditions for plant growth; however, heavy rain in the tropical climate may cause soil erosion with the change in soil conditions. This study presents the effects of application of coal ash to postmine land on soil erosion by performing the artificial rainfall test as well as physical testing. The results indicate that the risk of soil erosion can be reduced significantly by applying the coal ash which consists of more than 85% of sand to topsoil in the postmine land at the mixing ratio of over 30%. Additionally, they reveal that not only fine fractions but also microporous structures in coal ash enhance water retention capacity by retaining water in the structure, leading to the prevention of soil erosion. Thus, the risk of soil erosion can be reduced by applying coal ash to topsoil in consideration of soil composition and microporous structure of coal ash.

STUDI KOMPAKSI BATUAN PENUTUP UNTUK PENCEGAHAN TERBENTUKNYA AIR ASAM TAMBANG PADA METODE ENKAPSULASI

Pertambangan batubara sering dikaitkan dengan Air Asam Tambang (AAT) yang dihasilkan oleh penimbunan material overburden yang mengandung mineral sulfida. Sebuah alternatif praktis untuk meminimalkan pembentukan AAT adalah menghindari kontak antara air, udara dan mineral sulfida menggunakan bahan yang tidak permeabel atau mineral lempung yang dipadatkan sebagai bahan penutup. Metode ini dikenal sebagai metode enkapsulasi, dilakukan dengan tujuan untuk mengurangi porositas dan menjadikan batuan bersifat tidak permeabel sehingga mengurangi laju difusi oksigen dan infiltrasi air ke dalam timbunan batuan yang mengandung mineral sulfida. Penelitian ini bertujuan untuk memahami karakteristik pemadatan beberapa jenis batuan overburden batubara yang akan digunakan sebagai material penudung (capping material). Pengujian kompaksi dilakukan delapan buah sampel batuan yang diambil dari tambang batubara Wara Blok I, PT. Adaro Indonesia, di Kalimantan Selatan. Analisis laboratorium, meliputi analisis fisik, batas-batas Atterberg, dan dilakukan uji pemadatan serta uji permeabilitas. Uji pemadatan dilakukan dengan menggunakan uji proctor standar sedangkan uji konduktivitas menggunakan uji tinggi jatuh (falling head test). Hasil uji konduktivitas hidrolik pada delapan sampel menunjukan ada hubungan antara karakteristik fisik tanah yang diperoleh dari hasil uji pemadatan dengan nilai konduktivitas hidrolik. Beberapa peneliti sebelumnya menyatakan bahwa material yang akan dijadikan sebagai material penudung harus memiliki nilai konduktivitas hidrolik sebesar 1x10-9 m/s. Berdasarkan penelitian yang telah dilakukan menunjukkan bahwa sampel yang mendekati nilai konduktivitas hidrolik yang disarankan adalah W112, W122, W123, W123, dan W1DP, sedangkan sampel yang memiliki nilai konduktivitas hidrolik di bawah yang disarankan adalah sampel W121. Kata-Kata Kunci: Air asam tambang, enkapsulasi, pemadatan, konduktivitas hidrolik.

Hydrology Simulation of Ukud River in Lati Coal Mine

Development of mine pit and overburden disposal has caused dynamic changes in the catchment area of Ukud River, one of the rivers that flow through Lati Mining Operation. The maximum discharge of the river reached 13m3/second and the catchment area occupied a total area of 1901.7 hectares. Since the mining operations started, the river discharge fluctuations have changed considerably. In addition, the catchment area that was dominated by overburden disposal area contained sulphide minerals that potentially degrade the water quality of Ukud River due to the formation of acid mine drainage. Hydrological studies are essential to investigate potential environmental impacts of the mining activities. This study was conducted to determine the characteristics of the hydrologic systems in the mining area using semi-distributed models that can be used to simulate the river flow within catchment area.

Geochemical Characterization for Prediction of Acid Rock Drainage Potential in Hydrothermal Deposit

Geochemical characterization is a standard procedure to identify the potential of acid rock drainage generation in a mining project. Using two types of hydrothermal deposit (sediment exhalative and porphyry) as case study, this paper will discuss the importance to understand the genesis of ore body and host rocks in the interpretation of geochemical test results.

Reliability of rainfall intensity prediction method for mine dewatering design in tropical region

Convective rainfall type which is very common in most mines in tropical region is characterized by its high intensity in short duration. For mine dewatering design purposes it is necessary to analyze the extreme rainfall intensity for a certain return period. Extreme value type I probability distribution is the most common used method for storm rainfall analysis. In this paper, the 2-year return period rainfall intensities are calculated for various data series and time periods. The results are compared to the observed rainfall data to see whether the prediction is considerably in line with the actual rainfall.