Verma, Chandrani Prasad and Kumbhakar , Subodh and Sangode , Anand and Somkuwar, Prarthana (2025) Review of Design Approaches and Failure Behaviour of Transition Crown Pillar. Indian Geotechnical Journal.

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Abstract

Opencast mining is highly productive till pit limit is reached and thereafter underground mining is the only option to recover deposits at greater depth. During this transition from open pit to underground mining, barrier pillar is left in between to isolate the two workings and is often termed as Crown Pillar. Determination of its optimum size is crucial for safety as well as to prevent too much ore being locked-up. There are a few analytical and empirical approaches available but are limited in their application. In this paper, a review of available design methodologies and its application to Indian geomining data is presented. Bakhtavar approach is found to provide realistic estimation of crown thickness especially for orebody having ultimate pit at shallow depth. Scaled span approach suggests quite higher thickness. While other analytical approaches suggests inappropriate thickness mainly due to lack of consideration of rock mass characteristics. Numerical modelling outperforms in site specific study. A review of transition crown failure case studies is also discussed to visualise likely instability issues. Pot-hole formation along with water seepage, large scale slope instability and movement along fault planes or cracks have been reported as major causes of crown failure. Most of the cases have followed caving method of mining and slope wall movement is observed in each case. Very limited data is available on failure pattern specific to transition cases. Hence, already published failure pattern of surface crown is also discussed and reviewed, to visualise any likely similarity in transition crown failure modes. Numerical modelling of few Indian cases suggests caving, unravelling and hangwall side slope failure as dominant failure mode. Pot-hole formation is also likely in case of soft ore. Based on detailed review and statistical analysis, a number of different critical parameters are identified. Apart from pit geometry other parameters like in situ stress, geological structures, depth of working and method of working are also found to have a greater influence on crown pillar design. But all of them cannot be quantified. This review will serve as input to development of design methodology in near future.

Item Type:	Article
Uncontrolled Keywords:	Transition crown pillar Design approaches Data analysis Failure mechanism
Subjects:	Bord and Pillar Mining
Divisions:	UNSPECIFIED
Depositing User:	Mr. B. R. Panduranga
Date Deposited:	28 Apr 2026 10:28
Last Modified:	28 Apr 2026 10:28
URI:	https://cimfr.csircentral.net/id/eprint/2986

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