China
Africa
Explore chapters and articles related to this topic
The evolution of pillar mining at the Polaris Mine
Published in John E. Udd, A.J. Keen, Mining in the Arctic, 2020
Recoveries in the Keel pillars averaged about 80% at the start of pillar mining while ground conditions were still favorable. Recoveries declined to 60% to 70% for the last five pillars mined before CRF was introduced. With each pillar containing 400,000 t to 850,000 t of reserves, low pillar recoveries became a concern. Many problems were encountered while mining the early pillars, including massive hangingwall failures, frozen fill failures, and deteriorating ground conditions in pillar drifts. Pillar stages left open for too long caused large cracks to form in the adjacent pillar stage. Wedge failures into the open void occur if the void is not filled quickly. Figure 5 shows a section through 208 pillar in the Keel Zone illustrating the consequences of these problems. Large post pillars were left in 208 pillar, not just to contain the dry fill, but also to support the hangingwall. A massive hangingwall failure in Stage 3 resulted in large loss of drilled and broken reserves. Steel sets were installed in 850-208 pillar access, after 8 m cables, rebar, screen, and straps failed in an effort to keep the drift open for drilling.
Pillar design issues in coal mines
Published in Xia-Ting Feng, Rock Mechanics and Engineering, 2017
Many researchers have devoted a part of their studies to prevention of pillar squeezes, massive pillar collapses and pillar bumps (Khair & Peng, 1985; Campoli et al., 1989; Maleki, 1992; Mucho et al., 1993; Chase et al., 1994; Zipf, 1996; Mark et al., 1997; Zipf & Mark, 1997; Zipf, 1999; Maleki et al., 1999; Chen et al., 1999; Zingano et al., 2004; Iannacchione & Tadolini, 2008; Esterhuizen et al., 2010; Poeck et al., 2015; etc.). The occurrence of pillar failure in underground coal mines entails detrimental effects on miners in the form of injury, disability or fatality as well as mining company due to downtimes, interruptions in the mining operations, equipment breakdowns, and etc. Proper pillar design is the key to prevention of pillar failure and reduction of related accidents. Coal mine pillar design has been the subject of sustained and intensive researches in the major coal producing countries of the world. Pillar design and stability are two of the most complicated and extensive problems in mining related to rock mechanics and ground control subjects. The main aim of this chapter is to describe the pillar design issues in coal mines. This chapter is organized as follows: panel pillars issues are explained in section 2. In section 3, the design procedures of chain pillars are described. In section 4, design formulas for barrier pillars are presented. The design considerations of web pillars are explained in Section 5 and finally, the yield pillar design issues are presented in Section 6.
Pillar design issues in coal mines
Published in Xia-Ting Feng, Rock Mechanics and Engineering, 2017
Many researchers have devoted a part of their studies to prevention of pillar squeezes, massive pillar collapses and pillar bumps (Khair & Peng, 1985; Campoli et al., 1989; Maleki, 1992; Mucho et al., 1993; Chase et al., 1994; Zipf, 1996; Mark et al., 1997; Zipf & Mark, 1997; Zipf, 1999; Maleki et al., 1999; Chen et al., 1999; Zingano et al., 2004; Iannacchione & Tadolini, 2008; Esterhuizen et al., 2010; Poeck et al., 2015; etc.). The occurrence of pillar failure in underground coal mines entails detrimental effects on miners in the form of injury, disability or fatality as well as mining company due to downtimes, interruptions in the mining operations, equipment breakdowns, and etc. Proper pillar design is the key to prevention of pillar failure and reduction of related accidents. Coal mine pillar design has been the subject of sustained and intensive researches in the major coal producing countries of the world. Pillar design and stability are two of the most complicated and extensive problems in mining related to rock mechanics and ground control subjects. The main aim of this chapter is to describe the pillar design issues in coal mines. This chapter is organized as follows: panel pillars issues are explained in section 2. In section 3, the design procedures of chain pillars are described. In section 4, design formulas for barrier pillars are presented. The design considerations of web pillars are explained in Section 5 and finally, the yield pillar design issues are presented in Section 6.
Diagnostics of pillars in St. Mary’s Church (Gdańsk, Poland) using the GPR method
Published in International Journal of Architectural Heritage, 2019
Jacek Lachowicz, Magdalena Rucka
The rebuilding of the roof and vaults began in 1947. During reconstruction work, five pillars began to crack and tilted from the vertical (Bogdanowicz 1990). All damaged pillars were strengthened using a technique of jacketing (c.f. Júlio, Branco, and Silva 2003). In Figure 2, the reinforced pillars are indicated. As the first example, pillar S.1 was repaired in 1948 with the use of prefabricated elements (Figure 3a). Molds were prepared, and 500 pieces of concrete cover with heights of 20 cm were fabricated. The pillar was then covered with the prefabricated elements over 3 months at a height of 18 m. One year later, cracks appeared on pillar S.4 during vault reconstruction. Damage started to propagate rapidly, and a horizontal crack emerged. In this situation, immediate reinforcement of the pillar was necessary, and monolithic reinforced concrete was used. The reinforcement of a cracked area was completed in 24 hr. The concreting was conducted in few stages, each with a section height of approximately 110–140 cm (Figure 3b). The remaining three pillars (S.2, S.3, and S.5) were also reinforced using monolithic concrete.
Numerical study of stability of coal pillars under the influence of line of extraction
Published in Geomatics, Natural Hazards and Risk, 2022
Lingampally Sai Vinay, Ram Madhab Bhattacharjee, Nilabjendu Ghosh, Gnananandh Budi, Jagapthal Vinod Kumar, Shankar Kumar
However, a range of geological, geotechnical, and operational factors are associated with strata behaviour, increasing pillar failure proneness and strata control issues. Coal pillars need to be designed to initiate regular caving and avoid other strata control issues. Overlying strata plays a crucial role in the caving mechanism. Caving is generally delayed in the case of strong and massive roof strata. It takes place after a large overhang. This increases stress acting over surrounding pillars and affects the dynamic loading of supports, leading to sudden and violent failure of pillars.