"Multiple Graph" Approach for Excavation Behaviour in Tunnelling

Multiple Graphs for Determination of Ground Behaviour [2]

Last week (6th February 2014), Dr. Giodano Russo gave us a lecture on Rock Mass Classification. Additional topic of discussion during the lecture was "Multiple graph" approach for preliminary estimate of excavation behaviour. This blog post summarizes Dr. Russo's research papers on this particular topic.

Multiple graph approach was first published by Dr. Russo in 2008 as a simplified method for preliminary assessment of excavations in rock. Later Dr. Russo and Geodata used this approach in many projects including the Chenani Nashri Tunnel - The longest road tunnel in India [3]. And recently this approach is being updated by Dr. Russo [2].

The multiple graph is composed of 4 individual graphs placed in four quartdents of a cartesian axis. Two adjoining graphs share the overlapping axis. The author considers bottom right as the first quadrant and moves clockwise. First quadrant is used to determine GSI based on joint conditions. GSI determined in first quadrant is used to determine Rock mass strength in second quadrant. Rock mass strength is used to determine "Competency of Rock" in third quadrant which is in turn used in fourth quadrant to estimate the ground behaviour.

I find this method very useful for preliminary forecast of excavation behaviour in tunnelling and thus the tunnel design can consequently focus on the detected potential problems. Moreover, "multiple graphs" gives us a clear picture of all the influencing factors of excavation behaviour (Joint conditions, Intact rock strength, In-situ stress etc) in one glance which is very useful for a designer.

References:

[1] G. Russo, 2008. "A simplified rational approach for the preliminary assessment of the excavation behaviour in rock tunnelling ". Tunnels et Ouvrages Souterraines n. 207 (May - June)

[2] G. Russo, 2013/2014. "An update of the ‘‘multiple graph’’ approach for the preliminary assessment of the excavation behaviour in rock tunnelling" Tunnel. Underg. Space Technol. (Article in press)

[3] M. Palomba, G. Russo, F. Amadini, G. Carrieri and A.R. Jain, 2013. "Chenani-Nashri Tunnel, the longest road tunnel in India: a challenging case for design-optimization during construction ". World Tunnel Congress 2013 Geneva