Use of Rock Mass Rating (Rmr) Values for Support Designs of Tunnels Excavated in Soft Rocks Without Squeezing Problem

Abstract

Effect of the rock material strength on the RMR value and tunnel support designs was investigated within this study including site works, analytical and numerical analyses. It was found that rock material strength effect is quite limited in the RMR method to determine an accurate rock mass class to design tunnel support. Since the limitation, rock mass classes are evaluated to be usually misleading and supports designed in accordance with the RMR value are insufficient for tunnels excavated in rock masses with low strength values of rock materials. Totally, five different tunnels in Turkey have been supported using a new strength adjustment factor calculated in consideration of the in-situ stress and the uniaxial compressive strength values of rock materials. As confirmed by the field applications, analytical and numerical analyses, a newly modified RMR value (RMRus) was suggested to be used in tunnel support design works.

An Investigation of Foam Concrete Usability as a Cavity Filler Material in Mining

“…Excessively low modulus of elasticity values can cause unwanted convergences in case of using low density polymeric foams. High stiffness values can make proper limitations in the rock mass deformations, prevention of progressive loosening and dead load occurrences in underground openings [17][18][19]. Because the FC filler material has significantly higher modulus of elasticity values, they are more advantageous than light polymeric foams in terms of having a proper stiffness for controlling convergences in the rock masses.…”

Case studies on Q-slope method use for slope stability analyses

“…The Q-slope method and that kind of empirical methods are usable for the rock masses which are able to be homogenized. In case of various structural controlled failure mechanisms like toppling or a planar slide at the major weakness plane, rock mass cannot be homogenized and the homogenization approach should not be trusted because of having lacks of details [22][23][24][25]. As noted before, the SRF slope value is taken as the biggest one of the strength reduction factors of SRF a , SRF b, and SRF c .…”