Spalling occurs in many different types of projects in rock masses in Scandinavia, including projects in the mining, infrastructure, and storage sectors. Spalling can be problematic for these projects as it may change the profiles of the excavations and transmissivity of the surrounding rock mass. However, numerical modelling of spalling is complex. Typically, continuum models are used with strain softening constitutive models, but they are only a proxy for spalling. They are unable to capture the mechanisms underlying spalling, and they therefore work best as back analysis.

This project studies the suitability of a new modelling technique to represent spalling in Scandinavia. The technique is called “Bonded Block Modelling” (BBM) and represents the rock mass as a conglomerate of blocks. Rock mass damage is represented by breakage of the contacts between blocks. The focus of this study is to give advice to practitioners who wish to use BBM in the future, through a literature review and an application of BBM to laboratory tests and in situ spalling of an actual case from LKAB’s Malmberget Mine. The report concludes with a discussion, recommendations, and suggestions for future work to provide practitioners and researchers alike a path forward.

The project group included Jonny Sjöberg and Jessa Vatcher (both with Itasca Consultants AB). The reference group included Axel Bolin (Trafikverket), Diego Mas Ivars (SKB), Beatrice Lindström (formerly Trafikverket), Marie von Matérn (WSP), Thomas Wettainen (LKAB), and Per Tengborg (Rock Engineering Research Foundation – BeFo).

It is our hope that this report is one of many steps towards the common use of BBM techniques. This project was financed by BeFo, Rock Engineering Research Foundation, and Itasca Consultants AB contributed in-kind. 

Stockholm, 2021
Per Tengborg