(a) Minor weighting behaviour , with weightings on a 10 - 15m cycle (b) Moderate to major weighting behaviour (15m - 25m cycle ) (c) Serious weighting behaviour (25m - 40m + cycle ) Part B i. Identify key factors which are likely to influence caveability . (3 Marks ) ii. What is defined as the secondary fragmentation ? List the major factors impacting the secondary fragmentation . Identify and describe main modes of secondary fragmentation . (3 Marks ) Question 3 (23 Marks ) Part A In underground coal mining using longwall methods , the design of chain pillars is a critical factor for the success of the operation - both in terms of safety and production . Chain pillar design involves number of different geotechnical considerations Identify and discuss the full range of geotechnical considerations , which affect chain pillar design , including the risk factors to be considered , the design approaches available and the overall methodology for addressing the multiple issues . Provide examples of the typical parameters involved in these considerations and how they can impact on both safety and production . (6 Marks ) Part B You are designing a system of underground coal mine pillars in a production panel in a bord and pillar mine . The panel consists of 9 headings. The pillars are square pillars , with centre to centre spacing of 28m . Roadway widths are 5.5m . Mining height is 3.6m and the mining depth is 320m . i. Calculate the average vertical pillar stress acting on each of these pillars (state and justify any assumptions you have made ). (5 Marks )