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Leelasukseree, Cheowchan (Chiang Mai University) | Sangkhaphan, Phutchara (Electricity Generation Authority of Thailand) | Chanwised, Natthawat (Electricity Generation Authority of Thailand) | Pipatpongsa, Thirapong (Kyoto University)
Abstract Mae Moh, Lampang, a small town in northern Thailand, approximately 600 km far from Bangkok, contains a large, open-pit, lignite mine. The mine is managed and operated by the Electricity Generation Authority of Thailand (EGAT) to provide 15 million tonnes of coal per year for its power plants. In 2011, EGAT selected a pit wall 300 m wide (called Area 4.1) to conduct a large-scale experiment to better understand how pit wall displacement responded to undercutting. A monitoring system was installed to measure surface and subsurface movement. During the rainy season in 2016, Area 4.1 experienced a number of remarkable events related to precipitation. The main sequence of slope undercutting to excavate lignite and back filling of Area 4.1 was completed in summer 2017. Area 4.1 was continually monitored and studied during the large-scale experiment, including deploying a ground-based radar system. Inverse velocity technique, using measured movement data from the radar, was applied to predict slope failure and warn site operators. In the 2016 rainy season, Area 4.1 was warned the failure many times, but the undercut slope was visually stable. The undercut slope displayed stick-slip behavior each time the alarm sounded, and the area was appropriately evacuated. The following dry season, Area 4.1 was mined for lignite and backfilled. The mining and backfilling were done as planned in May 2017. The stability of the supported undercut slope Area 4.1 has been satisfied since the following rainy season. 1. Introduction Mae Moh mine is the largest open pit mine in Thailand. It is located in Mae Moh, Lampang, a small town in northern Thailand, approximately 600 km from Bangkok. The mine is managed and operated by the Electricity Generation Authority of Thailand (EGAT) to provide 15 million tonnes of lignite a year for EGAT's 10 coal-fired power plants. Khosravi et al. (2011) used physical models in the laboratory to investigate the behavior of undercut slopes. The study showed that undercut slopes were stable if the undercut span width was narrower than the maximum undercut span width. The maximum undercut span width is greatly affected by the rock strength and the slope angle. In 2011, EGAT then proposed a field experiment in the mine to further study these behaviors (Mavong et al., 2013 and 2014). They selected a northeastern low wall, named Area 4.1, as the experimental site; the area was mined in two stages. In the first stage, Area 4.1 was excavated from its northern end to the center. A weak-plane interface between an underburden Gray claystone and a thin clay seam, called G1, was daylighted as expected on the pit wall approximately 150 meters each stage without backfilling. The backfill supported the potential sliding block along the weak plane. Therefore, the first stage required a series of sequential excavating and backfilling. The first stage was successfully completed in mid-2013, with the weak plane partially daylighted. In 2016, the mine planned the second stage – to mine the remainder of the lignite in Area 4.1, this time starting from the southern end. Fig. 1a. shows the beginning of this second stage. Mining began in February 2017, in the middle of the dry season, at the southern end and proceeded along the working face (red line) in a northwesterly direction. Before mining Area 4.1 in the rainy season of 2016, the area was continually monitored for surface and subsurface movements of the undercut slope, the water pressure in the weak plane, and precipitation. The monitoring data unveiled remarkable movements of the undercut slope in response to precipitation; this paper presents some of this key monitoring data. After the lignite was depleted, the backfilling in the area was started and successfully completed at the end of May 2017 before the rains inaugurated. Fig. 1b. shows the location of the undercut low wall and backfilling (yellow shaded area) after mining was completed in Area 4.1.
Abstract One of unknown rock mass properties in rock mechanics is the elastic modulus. Many researchers have proposed a variety of methods to estimate this rock mass property. One of the method is 3D numerical model calibration to obtain the key mechanical properties of the rock mass. At Mae Moh mine, Lampang, Thailand, engineers initiated a large scale field experiment of a undercut slope in northeast pit wall, named Area 4.1. The complexity of geologic structures, such as beddings and a series of normal faults, causes a number of mining and geotechnical difficulties. Inevitably, lignite exploitation could daylight a weak clay seam, called G1 seam, along the pit wall and possibly activates a massive failure of under-burdened Claystone. The pit wall slope stability must not be jeopardized. The engineers planned and undercut the slope at a particular span width so that the G1 interface would be partly day-lighted. Concurrently, three dimensional numerical models were constructed and analyzed as a preliminary study of the undercut slope. A number of assumptions such as the rock mass's physical properties and strength were added into the preliminary numerical models. So far, Area 4.1 was successfully undercut and stable as planned. During the field experiment, the water pressure and ground displacements were monitored. This slope monitoring data and the numerical analysis results were useful to make a better understanding of the undercut slope behavior at Mae Moh mine. To improve the accuracy of the numerical model analysis, the monitoring data was used for the rock mass elastic modulus determination and the numerical model calibration. After the numerical model calibration, the rock mass elastic modulus was determine and range 103.6–119.7MPa. If the undercut slope's failure and related information are available, it is possibly able to determine the rock mass strength with the same numerical calibration and finally improve the numerical model analysis accuracy.
Abstract: Mae Moh mine is one of the deepest open pit mines in Southeast Asia, currently 300 m below the ground surface. According to its master mine plan, the mine depth will be approximately 500 m by year 2028. It is located in Lampang, 650 km north of Bangkok. Recently, it produced approximately 15 million tons of lignite and over 90 million m3 of waste a year to serve ten lignite-fired power plants, with total capacity of 2,400 MW. The mine and power plants are operated by a prominent Thai state enterprise, Electricity Generating Authority of Thailand (EGAT). To remove such a huge amount of dense Overburden and Interburden claystone, drill and blasting techniques have been utilized. The overburden and interburden are fractured and loosen by blasting suitable for the production and also to reduce fuel consumption and wear rate of excavators as well. There is, however, a major unwanted consequence of the blasting technique which is induced seismic force. The induced seismic force would potentially cause environmental impacts. To increase safety of the working environment and contribute to the social responsibility, the mine has lately replaced the conventional blasting technique with air deck blasting. With less amount of explosive usage, the air deck blasting results in less ground vibration with satisfied mine production. The measured peak particle velocity, related to the induced seismic force and the ground vibration, was reduced by 32-69 %. Surprisingly, the air deck length recommended at 20% of the explosive charge can reduce the induced seismic force while increasing fragmentation and higher productivity.
Leelasukseree, Cheowchan (Chiang Mai University) | Pipatpongsa, Thirapong (Tokyo Institute of Technology) | Khosravi, Mohammad Hossein (Tokyo Institute of Technology) | Mavong, Narongsak (Tokyo Institute of Technology)
ABSTRACT An 80-m high low wall slope at Mae Moh mine, Lampang, Thailand, sits on a low friction interface between an under burden claystone and a thin clay layer called G1. By 2012, the slope must be partially undercut for mining, approximately 1 million tons of lignite. Stability of the sizable slope will be questionable when being undercut and mined. To study the behaviors of the undercut slope lying on an inclined bedding plane, a number of physical models and numerical models are studied. For the physical models, a 1.0 m × 0.45 m × 0.80 m (W×H×D) undercut slope model was constructed by using humid sand, acrylic and an aluminum work frame, low friction Teflon sheet as a smooth interface and sand paper adhered with acrylic plate as side supports. Moist sand physical properties, its strength and all interface frictions were experimentally determined beforehand. Five potentiometers and a camera were installed and employed to monitor and digitally record the crest and the slope face displacements. Stresses in various locations and directions are also measured by installing eight pressure gauges. Concurrently, the numerical model of the undercut slope is created based on the physical model dimensions and the moist sand properties, strength and its interface frictions. 3DEC®, a three dimensional discrete element program, is selected for simulating and studying the behavior of the undercut slope. The behaviors of the undercut slope examined from both physical and numerical models have shown similar tendencies toward measured displacements and stresses during undercutting. Moreover, the buckling failure mode of both slope models is discovered excitedly. The results provide further understandings of the undercut slope behaviors. The better understandings help engineers to design and monitor the undercut slope.
Summary of discussion basins of northern Thailand is composed of a distinct depositional cycle as follows: By means of short synoptic contributions prepared 3. Diatomite, by many specialists, the panel on oil shale occurrence 2. Oil Shale, and and prospects presented much new information on :the general aspects of the occurrence, composition, 1. Lignite. and origin of oil shale; the geology of several im- However, each depositional cycle controlled by portant deposits; and methods of prospecting and lacustrine environment might be absent or repeated in exploration. some intermontane basins. In addition to the 1 1 papers preprinted, two contributions were added to the program, the synopses of which are as follows: Geological studies of the Irati formation Mr. VICENTE T. PADULA stated the oil shales Oil shale deposits in Thailand of Brazil include deposits of Devonian age in the States of Amazonas and Pará; of Cretaceous age in Referring to oil shale deposits in Thailand Mr. C. Maranhão, Ceará Algoas, and Bahia; of Permian age in POOTHAI said that apart from the well known São Paulo, Paraná, Santa Catarina, and Rio Grande do deposits of the Mae Sot oil shale in Tak Province and Sul; of Tertiary age in São Paulo; and of undetermined the Li oil shale in Lamphun Province, oil shale has age in Caerá, Goiás, and Território do Amapá. Of been recently encountered in three drill holes beneath these, the oil shales of the Permian Irati Formation are the diatomite deposit in Lampang basin, KO Kha the most extensive and the most promising for com-District, Lampang Province, northern Thailand. The mercial exploitation, and they have been under study laminated oil shale, 10 meters thick, brown in color, by the Superintêndencia da Industrializacão do Xisto contains fossil leaves, fish scales, insect bones and (SIX) since 1955. Although the Tertiary shales, which probable ostracods. Since the KO Kha diatomite is are of lacustrine origin, are about 35 meters thick, one of five scattered deposits found in the Lampang yield 4 to 13 percent of oil, and contain about 2 billion basin of late Tertiary age, it is suspected that oil shale barrels of oil, their high moisture content (about 35 might be found beneath some of the other diatomite percent) makes them less attractive for exploitation deposits. than the shales of the Irati Formation. Lignite occurs at Mae Moh on the eastern side of the The outcrop of the Irati Formation has the form of a Lampang basin about 30 kilometers east of the KO great "S" that begins in São Paulo Stateandextends Kha District. Oil shale has bken also found in close nearly continuously for 1700 kilometers to the frontier association with lignite at the Li District, about 116 of Brazil and Uruguay. In the States of Paraná and kilometers by highway southwest of the KO Kha