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Author: Admin | 2025-04-28
Practice, and the mean and variance can be approximated by using the three time estimates. Additionally, the easy input requirements relatively boost the prevalence of the PERT-beta distribution, rather than others.2.2 Discussion and Modification of PERT/CPM for using in Underground Mining Operations2.2.1 Discussion of PERT/CPM for using in Underground Mining Operations.After the debut of CPM and PERT for more than five decades, there have been new techniques developed based on PERT/CPM, which are however more sophisticated for mining operators and require complex user input. The PERT/CPM are particularly appropriate tools to be used in the scheduling for discrete events, e.g. serial operations in underground mining (including scaling operation, shotcreting operation, bolting operation, drilling operation, explosive charging operation). Nonetheless, some drawbacks in both techniques have restricted their applications in underground mining operations. First, the PERT/CPM do not give a method to find the predefined sequence. It is normally complicated to determine the sequence of many mining operations for many working faces. There has been a study for solving this problem [10]. Next, the time estimates are subjective, based on the personal knowledge and abilities. This cannot guarantee the objectiveness of the input and take advantage of the data recorded in mining management system. Moreover, it is required to estimate the duration for every operation. There can be hundreds of operations to be carried out in large-scale underground mine, and the operations can vary considerably. It is almost impossible and inefficient to estimate all the durations manually. Additionally, the PERT analysis assumes the mean tm and variance v are normally distributed, because it is rather difficult to calculate the cumulative probability function of the PERT-beta distribution. The probability of the completion time of the entire mining process can be obtained by summing the means and variances on the critical path, and then the probability of the completion time can be obtained according to the standard normal distribution table [11]. This assumption relies on the central limit theorem, which requires sufficient amount of operations. In underground mining operations, it is quite doubtful whether there are sufficient operations on the critical path. Therefore it cannot warrantee the assumed normal distribution, and the probability of the complete time is questionable. Furthermore, the CPM neglects the existence of different probabilities of the mining operations’ completion time. For example, it calculates the critical path simply using the deterministic values of the completion time of different activities, though there are different probabilities behind these deterministic values. This can lead to a wrong critical path. In view of the above disadvantages, a new method should be customized for using in underground mining, based on the PERT/CPM and combining other theories.2.2.2 Modification based on PERT/CPM for using in Underground Mining
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