Understanding 2008 Kresten Lecture

As described in Week 5's blog, 2008 Kresten Lecture by Hoek et al was one of the discussion point during last week. According to our Professor Daniele Peila, this is the best paper (on Tunnel design) ever written [dot]! That was instigating enough to make us extra curious to read this paper ;)

This paper is available at Hoek's corner. This paper presents two detailed case studies which could serve as guidelines for Tunnel designers. This paper uses the derivation of equation for capacity curves presented in Carranza-Torres et al (2009) - discussed in Week 6 blog post. This post highlights the critical features addressed in this paper:

• While using 2D numerical model, it should be noted that analysis section near the excavation face is a 3D problem however it can be simulated in 2D environment by means of deformation control process. This process consists of three steps:

• Step 1: Calculate deformation for different Inclusion modulus (in steps) and prepare characteristic curve as shown in Figure 7 of the paper. In addition, for deep tunnels (as in case study 2 of this paper), we also need to determine maximum plastic radius (unsupported condition), using a plane strain analysis.
• Step 2: Prepare Longitudinal deformation profile for the tunnel (this can be done based on Appendix 1 of the paper, my spreadsheet on support interaction curve could be used as a starting point. This could also be done using commercially available software RocSupport by RocScience). Axis symmetric continuum model could also be used for this purpose.
• Step 3: Based on the distance of installation of support (and Longitudinal deformation profile), determine the deformation already realized in the tunnel. This value can further used to determine the corresponding inclusion modulus required for 2D simulation.

• Another important issue addressed in this paper is about choosing shotcrete properties. Authors suggest to use support capacity curves (based on Carranza-Torres et al 2009), instead of Concrete codes for their design and presents the shotcrete strength development curve developed by Melbye and Garshol (2000).
• Contribution of shotcrete in long term load carrying capacity is dicussed in the paper and recommendations from ITA Guidelines for Design of Tunnels (1988) is cited for the conditions under which shotcrete's strength could be used for final lining design.
• Authors have suggested to use Elastic capacity curves proposed by  Carranza-Torres et al (2009) even for final lining design and have justified by comparing with the results from structural program Response 2000 (based on modified compression field theory -Vecchio and Collins, 1986).
• Convergence confinement analysis is explained for a yielding support system using the second case study.

Appendix 1 and Appendix 2 are essential excerpts from the papers by Vlachopoulos et. al (2009) and  Carranza-Torres (2009).

References:

[1] Hoek, Evert, et al. "The 2008 Kersten Lecture Integration of geotechnical and structural design in tunneling." 56th Annual Geotechnical Engineering Conference. 2008 (available for educational purpose at: Hoek's Corner)

[2] Vlachopoulos, N., and M. S. Diederichs. "Improved longitudinal displacement profiles for convergence confinement analysis of deep tunnels." Rock mechanics and rock engineering 42.2 (2009): 131-146.

[3] Carranza-Torres, C., and M. Diederichs. "Mechanical analysis of circular liners with particular reference to composite supports. For example, liners consisting of shotcrete and steel sets." Tunnelling and Underground Space Technology 24.5 (2009): 506-532.

Week 5 Tunnelling & TBM Course: Support System

Week 5 (17th Feb '14 to 21st Feb '14) of 2nd Level specializing course in Tunnelling and TBM covered the concepts of Tunnel supports (overview and key design concepts) which included:

• General overview of Supports (Temporary and Permanent)
• Recent developments in support system types (Rock bolting, Shotcrete, Steel sets/ Lattice girder, wire mesh etc)
• Water proofing of Tunnel using Conventional Tunnelling and TBM

Design Aspects Covered:

• Method 1: Closed form solution - Define the loads (independent of the behaviour of system), Idealize geometry, apply the loads (with partial safety factor) to obtain the results (like Terzhaghi - 1946 method).
• Method 2: Convergence Confinement Method. Partial safety factors on the loads are not applied. Factor of safety are however applied on the final response for the design. 
• Method 3: Limit Equilibrium Method

Other Aspects Covered:

• Brief on 2008 Kresten Lecture (more details here)
• Reinforced rock mass - Equivalent Parameters (Spreadsheet to calculate, to be updated)
• Bedded Beam Spring Model
• Use of commercially available software - "RocSupport" to understand convergence confinement (a part of the functionality is reproduced in this spreadsheet here)
• Equivalent model for Steel Set - Shotcrete system

To help with our understanding and completeness, we also had lectures by invited speakers from Sandvik (Mr. Hanno Bertignoll) and Atlas Copco (Mr. Stefano Airoldi).

Mr. Peinsitt give us a lecture on the drilling tools and road header used in Tunnelling. Mr. Peinsitt gave us a comprehensive overlook on the applications of road header for excavation of tunnel and explained innovative methods to combine road header excavations with D&B excavation and TBM excavation with practical examples.  The lecture was followed by a practical exercise to assess the suitability of a roadheader for a particular problem.

Mr. Hanno Bertignoll  (Sandvik)'s Lecture on Roadheader and Drilling Tools

Mr. Airoldi gave us an overview of types of rock bolts available in the market and the suitability of different types of bolts for different objectives. We also had an opportunity to see the samples of different types of rock bolts and prototypes of drilling bits. Some of the photos are included below.

Mr. Airoldi (Minova / Atlas Copco)'s Lecture on Rock Anchor and their application

Self Drilling Anchors (SDA) made of Fiber glass and Steel

Split Sets

Swellex Anchor (Initial and Inflated position)

Prototype of Symmetrix Drilling Bit (Assembled and Individual parts)

References:

[1] E.Hoek et. al, "Support of Underground Excavations in Hard Rock", A.A. Balikema Publishers, The Netherlands

[2] Chapter 5 - Dimitrios Kolymbas, "Tunnelling and Tunnel Mechanics - A Rational Approach to Tunnelling", Springer Publishers

[3] Chapter 11 - Brady, B.H.G. and Brown, E.T. 1985. Rock mechanics for underground mining. London: Allen and Unwin, USA

[4] Chapter 9 - E.Hoek et al, "Underground Excavations in Rock", E & FN Spon Publishers, London

[5] Chapter 12 - B. Singh et. al "Tunnelling in Weak Rocks", 2006, Elsevier Publishers, London

[6] Hoek, Evert, et al. "The 2008 Kersten Lecture Integration of geotechnical and structural design in tunneling." 56th Annual Geotechnical Engineering Conference. 2008 (available here)

[7] Hanna, T.H. (1982). "Foundations in Tension GroundAnchors" Vol. 6 of Series on Rock and Soil Mechanics. Trans Tech and McGraw-Hill, USA

[8] Method of calculating grouted tie rods and micropiles (in French) : Bustamante, M; Doix, B Bull Liaison Lab Ponts ChaussesN140, Nov–Dec 1985, P75–92 (DOI: http://dx.doi.org/10.1016/0148-9062(86)90866-1)

[9] Grasso, P., A. Mahtab, and S. Pelizza. "Reinforcing a rock zone for stabilizing a tunnel in complex formations." Int. Congr. on Progress and Innovation in Tunnelling, Toronto 2 (1989): 663-70.

[10] Galler R., Doucet C., Gschwandtner G.G., "Roofex® bolt and its application in tunnelling by dealing with high stress ground conditions" Workshop "Berechnungsverfahren in der Geotechnik - Versagensmechanismen und Parameterentwicklung", Austrian Society for Geomechanics, Salzburg, Austria

[11] Carranza-Torres, C. and Diederichs, M.S. "Mechanical analysis of a circular liner with particular reference to composite supports –e.g., liners consisting of shotcrete and steel sets", Tunneling and Underground Space Technology, Feb 2009

Week 4 Tunnelling & TBM Course: Drill & Blast

Week 4 (10th Feb '14 to 14th Feb '14) of 2nd Level specializing course in Tunnelling and TBM was mostly dedicated to Drill & Blast methods. The cycle of operation in Tunnelling during Drill and Blast (Viz, Blasting scheme preparation, Drilling, Charging, Blasting, Scaling and Mucking) was discussed one by one. 

D and B Cycle [1]

A brief idea about the evolution of explosives from Black powder --> Nitroglycerin based explosives (1st generation) --> TNT based explosives (2nd generation) --> Emulsion based explosives (3rd generation) was discussed. Different applications of the above explosives for specific conditions are studied.

• Nitroglycerin based explosives (1st generation) include: Dynamex, Gurit (used for contour blasting), Primex, 
• TNT based explosives (2nd generation) include: Watergel explosives, ANFO
• Emulsion based explosives (3rd generation) include: Emulite, 

Details of Initiation device / Detonators was discussed with emphasis on the NONEL detonator. Electric detonators are divided into:

• Instantaneous detonators - Used for stone and boulder blasting, presplitting etc.
• Milli-second detonators (less than 100 ms) - Used for bench and trench blasting
• Half-second detonators (500ms) - Are used when longer delays are required to prepare space for the movement of blasted rock mass.

NONEL is similar to electric detonators but it is immune to any electric hazard. It is based on shock wave instead of an electric pulse hence, fuse wires and legwires are replaced by plastic tubes (~3mm dia).

Two main schemes of Cut Types were discussed in detail:

• Parallel holes cut: Used for narrow tunnels but can be used for large tunnels also. Consumes more explosives for the initial cut 
• Inclined holes cut: Used in large excavation cross section

Different building codes are studied for the allowable vibration level and the methods adopted to control the vibrations were discussed.

Guidelines for Allowable Vibration - Swedish Standard [3]

The lectures were followed by an exercise on the design of the Blasting round for both the cut types mentioned above and the design of charging volume  for vibration control based on a practical example (more details later).

References:
[1] Heiniö, Matti. Rock excavation handbook for civil engineering. Sandvik, Tamrock, 1999.
[2] Olofsson, Stig O. Applied explosives technology for construction and mining. Applex, 1990.
[3] Persson, Per-Anders, Roger Holmberg, and Jaimin Lee. Rock blasting and explosives engineering. CRC press, 1993.
[4*] Johansen, John, and C. F. Mathiesen. Modern trends in tunnelling and blast design. CRC Press, 2000.

Rock Mass Quality for Tunnel Boring Machine (Q TBM)

[Update: This post is by Mr. Ramadoss Muthukuar, details here. He will also be contributing to this blog hereafter]


Rock Mass Quality for Tunnel Boring Machine (Q TBM)

I came across an article which is quite unique and interesting to study about Rock Mass Quality, so far wrt Rock Mass classification i have studied various quantitative approaches from RQD to GSI and these shall be applicable for both conventional and mechanized Tunneling methods.

But Sir Barton et al  approach for TBM is quite impressive, he modified his Rock Mass Quality (Q) of Conventional Tunnelling with Machine Rock parameter like Cutter life index,Quartz content in rock mass & average cutter load finally  arrived the  (Q TBM).By using this Rock mass quality index the penetration rate(PR) ,advance rate (AR) and necessary support requirements shall be designed.Even by advancing/varying the Penetration Rate (PR), advance rate (AR) and with other rock parameters the Rock Mass quality shall be back analyzed. 

I found this Rock Mass Quality (Q TBM) for Tunnel Boring Machines is logically represented and it will much helpful in designing the supporting system,tentatively to predict the time for boring tunnels with TBM and also to design the cutter head according to the requirement.

Link for download is shared in this blog:- 
http://tunnellingnatm.blogspot.com/2014/02/rock-mass-quality-for-tbm.html

"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

Terzaghi's Rock Load Theory

[Update: This post is by Mr. Ramadoss Muthukuar, details here. He will also be contributing to this blog hereafter]

Karl von Terzaghi (October 2, 1883 – October 25, 1963) was an Czech civil engineer and geologist known as the "father of soil mechanics".

 

In 1900, Terzaghi entered the Technical University in Graz to study mechanical engineering, where he also developed an interest in theoretical mechanics. He was nearly expelled at one point but ended up graduating with honors in 1904.Terzaghi translated and greatly expanded a popular English geology field manual into German. He returned to the university for one year and combined the study of geology with courses on subjects such as highway and railway engineering. Shortly thereafter he published his first academic paper on the geology of terraces in southern Styria.

The Rock load classification method is one of the first methodologies for rock mass classification for engineering. Karl von Terzaghi developed the methodology for tunnels supported by steel sets in the 1940s. By many regarded as obsolete as ideas about rock and rock mass mechanical behavior have since further developed and the methodology is not suitable for modern tunneling methods using shotcrete and rock bolts.

But still the Rock load theory have been in use for shallow tunnel design of tunnel width smaller than 6m.Later the rock load theory was modified by Deere et al to arrive an Quantitative approach to design the support system.

{update} Terzaghi's Rock load theory is covered in the book referred below 

 “Tunnelling in Weak Rocks” by Bhawani Singh and. R.K. Goel.

Week 3 Tunnelling & TBM Course: Rock Mechanics and Charecterization

Week 3 (3rd Feb '14 to 7th Feb '14) of 2nd Level specializing course in Tunnelling and TBM was both eventful and special. We had a special lecture by the ITA-AITES president (more about that here) and also we had a nice party at one of our classmates place (photo here). 

The focus of this week's lecture was on Rock Mechanics (by Professor Monica Barbera) and Rock Mass Characterization (by Dr. Russo). Prof. Barbera introduced us to characterization of discontinuities, Stereographic representation, lab and field testing of rock samples. However, most part of her lecture was focussed on Non linear generalised Hoek & Brown criterion and analytical development of it.

As further reading, following papers are studies to understand the rock classification systems and the correlations between them:

[1] Barton, N. (2002). Some new Q-value correlations to assist in site characterisation and tunnel design. Int. J. Rock Mech. Min. Sci. Vol. 39.

[2] Palmström A. (2000) Recent developments in rock support estimates by the RMi. Journal of Rock Mechanics and Tunnelling Technology, Vol. 6, No. 1 May 2000, pp. 1 – 19

[3] Palmström A. (2005) Measurements of and correlations between block size and rock quality designation (RQD). Tunnelling and Underground Space Technology, 20, 362–377

[4] Palmström A. (2009) Combining the RMR, Q, and RMi classification systems. Tunnelling and Underground Space Technology, 24, 491-492

[5] Russo, G. (2009) A new rational method for calculating the GSI. Tunnel. Tunnelling and Underground Space Technology, 24: 103-111.

International Tunnelling Association (ITA) President's Lecture on Risk Management

Today (7th February, 2014) we had a special lecture by Mr. Søren Degn Eskesen (President of International Tunnelling Association and Chief Project Manager of COWI). To welcome the ITA president, we also had with us, Prof. Daniele Peila (Technical Director of ITACET Foundation and the coordinator for this specializing course), Mr. Piergiorgio Grasso (Vice President of ITACET and Director of Geodata Engineering), Prof. Marco Gilli (Rector of Politecnico di Torino) and Prof. Monica Barbera (Professor of Rock Mechanics, Politecnico di Torino).

Mr. Eskensen gave us a lecture on Guidelines for Tunnelling Risk Management, prepared by ITA Working Group No. 2, and published in Tunnelling and Underground Space Technology 19 (2004) 217-237, Elsevier Publications (for more details about on the topic, please refer to the paper in ITA website, available here) and PAT - Plan for Advancement of Tunnel (briefed in my blog post). We studied the risk management procedure with a case study on Copenhagen Metro project.

Mr. Søren Degn Eskesen (ITA President) with the Tunnelling and TBM (9th Edition)

-Senthil Nath G T

Rock Mass Classification Lecture by Dr. Giordano Russo

On 6th Feb, 2014 we had a guest lecture by Dr. Giordano Russo on Rock Mass Classification. Dr. Russo is a Geomechanical expert working with Geodata Spa. He has a wealth of knowledge on Geomechanical characterization, Probabilistic approach of Tunnel design and Rock mass classification. Dr. Russo is the person who proposed "multiple graph" approach to determine the support class for the tunnels. He briefed us about different Rock classification methods and an overview of "multiple graph" approach. 

Dr. Russo's Lecture on Rock Mass Classification

Update: More on "multiple graph"approach here.

Book Review: NATM - The Austrian Practice of Conventional Tunnelling

NATM book by Austrian Society of Geomechanics,
ISBN: 978-3-200-01989-8

NATM - The Austrian Practice of Conventional Tunnelling is the book released by the Working Group "Conventional Tunnelling" of The Austrian Society of Geomechanics in the year 2010. I had a chance to go through this book and want to share my impression through this blog post.

As described by Professor Robert Galler, during the release of this book, this book contains all the topics concerning NATM with the necessary references. Although the topics are not covered in-depth, this book acts as a primer to all the disciplines of engineers/stakeholders to start understanding about conventional tunnelling / NATM.

First four chapters covers the general definitions, applicability of the method and explains the typical stages in design phase. Chapter 3 on "Application of NATM" briefly explains the construction sequence clearly with the help of illustrations and site photographs. I found it very useful in relating with site conditions and visualization of the construction sequences. For the soft ground conditions, three examples of Tunnels (Road tunnel with shallow overburden, Metro tunnel in urban area with shallow over burden and Railway tunnel with shallow overburden) are explained with typical excavation sequence & tunnel cross sections.

Chapter 5, 6 and 8 covers the details about Geotechnical investigation, geotechnical design and geotechnical monitoring along with flowchart for design process at different stages of project.

The remaining chapters gives a general overview about safety management, contracts and risk management. Since the target audience for this book is varied (which includes engineers, geologists, owners, decision makers, etc.) specific topics like Rock mechanics, rock classifications, numerical modelling, design of supports etc, are not discussed in this book. Very good book to start understanding about Tunnelling and allied aspects.

-Senthil Nath G T

Site Investigation in Tunnelling

[Update: This post is by Mr. Ramadoss Muthukuar, details here. He will also be contributing to this blog hereafter]

Each tunnel project is unique! 

A week back I was checking out my collections to study about the Site investigation  I came across  a chapter  "Investigation and description of the ground" from an ebook "Tunnelling and tunnel mechanics—a rational approach to tunnelling" by Dimitrios Kolymbas, Springer Publications, Germany. I found this material is providing necessary guidelines and use of site investigations for planning and design of tunnels.It also provides an overall approach or perspective rather than cookbook solutions. I feel that  inflexible rules or cookbook solutions often work for some situations in design of civil works but not in all geotechnical investigations.

Find below the download link:
https://drive.google.com/file/d/0B2sXZENzNEsLMVhSVXE1bUYtQnc/edit?usp=sharing 

A Souvenir with Prof.Wulf Schubert & colleagues in Salzburg, Austria

[Update: This post is by Mr. Ramadoss Muthukuar, details here. He will also be contributing to this blog hereafter]

We are group of 13 professionals from around the world  in NATM ENGINEER 2013,

"THERE IS A LIGHT AT THE END OF EVERY TUNNEL".

University Course "NATM Engineer" and MEng in Tunnelling

[Update: This post is by Mr. Ramadoss Muthukuar, details here. He will also be contributing to this blog hereafter]

    I am in the third batch of NATM Engineer programme ,i would say that TU Graz & Montan University is the place where you will  learn the art of tunnelling in purely professional way.Since the brochure for NATM Engineer 2015,has not been released yet.I thought the last year brochure might give  an idea to all who are interested to participate.

For further detail check in at  http://www.natm.at/

University Course "NATM Engineer" and MEng in Tunnelling                                                

  The course is jointly organized by the Graz University of Technology and the University of Leoben.
Courses are held in Graz and Leoben in Austria.The degree holders shall be enabled to accomplish tunnelling projects on their own in the face of geotechnical, structural, organizational, contractual and economic needs according to the latest state of the art.The Course addresses civil engineers, geotechnical engineers and engineering geologists who do have a distinctive technical education and aim at a specialization in conventional tunnelling.Future fields of work may be planning, design and consulting of underground projects for engineering offices, or construction management for contractors and owners.

New Contributor: Ramadoss Muthukumar

We have a new contributor to this blog. Mr. Ramadoss Muthukumar is a Civil Engineer with around 7 years of work experience and currently pursuing the NATM Engineer course in TU Graz, Austria. This is a specialized course in New Austrian Tunnelling Method (he will post more details about the course). As he is also doing a specialized course in tunnelling, I have invited him to contribute to this blog.

Mr. Ramadoss is at present working for Seychelles Land Transport Agency in Seychelles and will share his experiences related to the NATM course in Austria and project experiences related to Geotechnical Engineering and Tunnelling in this blog.

Thank you Ramadoss.

-Senthil Nath G T

Week 2 Tunnelling & TBM Course: Geological and Geotechnical Aspects of Tunnelling

Week 2 (27th Jan '14 to 31st Jan '14) of 2nd Level specializing course in Tunnelling and TBM was completely dedicated to Geological and Geotechnical aspects of Tunnelling. We had expert lectures from Geodata: Mr. Luca Soldo (blog post here) and from National Research council of Italy: Mr. Corrado Fidelibus. Mr. Fidelibus gave us an overview of Soil Mechanics and presentations related to Natural and Induced stress states because of Tunnelling. The lectures also covered the investigation methods,  lab tests, instrumentation and interpretation of Geophysical tests.

Geological studies were explained with a case study on Gotthard Base Tunnel by explaining the geological and geotechnical explorations carried out to detect Piora fault.

Mr. Fidelibus discussed the procedure and the precaution to be taken in calculating the Natural stress states while using in a numerical model. An example of prediction of induced stress state using a FEM program was demonstrated. Key concepts of stress measurements methods were discussed with emphasis on stress relief methods, Hydrofracturing method and flat jack method along with other available methods. Carrara marble project case study was used to demonstrate the use of stress measurement methods.

In addition to the above lectures, following literatures are studied for case studies and to understand the prevailing guidelines:

• "Some new Q-value correlations to assist in site characterisation and tunnel design", N. Barton, International Journal of Rock Mechanics & Mining Sciences 39 (2002) 185–216
• "ISRM Suggested Methods for land geophysics in rock engineering", T. Takahashi, International Journal of Rock Mechanics & Mining Sciences 41 (2004) 885–914

More about the above papers later.

-Senthil Nath G T