Rock mechanics-achievements and current problems Mehanika stijena-dostignuća i aktualni problemi
Prof. em. Ivan Vrkljan
Faculty of Civil Engineering University of Rijeka President of Croatian Geotechnical Society ISRM Vice President at Large (2011-2015)
Content
Foundation of the ISRM Some of actual rock mechanics and rock engineering problems - Rock behaviour characterisation - In situ stress and residual stress in intact rock - What is the Strength of a Rock Mass? Rock mechanics position in Eurocode 7 Polemics in rock mechanics community Expectations of rock mechanics and ISRM Conclusions Foundation of the ISRM Circumstances in which the rock mechanics has been recognized
Geology Engineering geology Rock mechanics
Malpasset, 1958 450 people were killed Circumstances in which the rock mechanics has been recognized
For rock mechanics recognition, next circumstances are specially important:
Critical mass of knowledge about the behavior of rock masses have been reached. Technologies of excavation and stabilization have begun to significantly affect on the rock engineering and rock mechanics.
The hardline of experts in the field of soil mechanics that rock mechanics should be developed within the soil mechanics. Circumstances in which the rock mechanics has been recognized
Bjerrum, Terzaghi i Casagrande, august, 1957. (ISSMFE officers) Circumstances in which the rock mechanics has been recognized
The early 1960s were very important in the development of rock engineering world-wide.
1910-1964: 60 slides were recorded in cuts along the Panama canal.
These slides were predominantly controlled by structural discontinuities.
1936: Karl Terzaghi on the first international conference on Soil Mechanics and Foundation Engineering in 1936 : ‘The catastrophic slopes of the deepest cut of the Panama Canal showed that we were overstepping the limits of our ability to predict the consequences of our actions ....’ Circumstances in which the rock mechanics has been recognized
Panama Canal Foundation of the ISRM
Müller officially registered the ISRM with the name „Internationale Gesellschaft für Felsmechanik“ Correspondence between Bjeruma, as Vice ISSMFE President, shows that Müller registered Society only when Terzaghi gave his consent.
Terzaghi was Müller’s professor and he wanted that new Society to be born with his agreement.
Müller and ISMFE leadership wished that two Societies have a close collaboration. Foundation of the ISRM
ISRM Constitutional Meeting, Salzburg, 25 May 1962. Voting.
Foundation of the ISRM
ISRM Constitutional Meeting, Salzburg, 25 May 1962. Head table with Müller and Pacher
Foundation of the ISRM
Prof. Josef Stini Prof. L. Müller Prof. Karl von Terzaghi Engineering geol. Rock mechanics Soli mechanics (1993-1958) (1908-1988) (1883-1963) It is truly remarkable that the founders of the disciplines of Engineering geology, Soil mechanics and Rock mechanics - each now represented by International Society were all from Austria. ISRM 50-years anniversary celebrations
The celebrations of the 50th anniversary of the ISRM
started in October 2011 in Beijing, had a peak during the Eurock2012 in Stockholm, and finish in October 2012 during the 61st Geomechanics Colloquy in Salzburg, the same city where it was formed in 1962. ISRM 50-years anniversary celebrations
A number of activities took place during this year of celebrations, among which the publication of the
ISRM 50th Anniversary Commemorative Book 1962-2012 ISRM 50-years anniversary celebrations
Salzburg, 2012. Dr Franz Pacher, the only living member of the ISRM founders
Leopold Müller Award
Prof. Leopold Müller The award is made once every four years in recognition of distinguished contributions to the profession of rock mechanics and rock engineering Leopold Müller Award Recipients of the Müller Award
Evert Hoek Neville Cook Herbert Einstein Charles Fairhurst CANADA, 1991 USA, 1995 USA 1999 USA, 2003
Ted Brown Nick Barton John A. Hudson AUSTRALIA, 2007 UN KINGDOM , 2011 UN KINGDOM , 2014 ISRM achievements of the past 50 years ISRM Suggested Methods
• More than 50 Suggested methods have been published • 18 ISRM commission and 3 Joint Technical Committee are active
John Franklin
John Hudson ISRM achievements of the past 50 years
ISRM Suggested Methods
SUGGESTED METHODS are NOT standards They are explanations of recommended procedures to follow in the various aspects of rock characterisation, testing and monitoring.
However, the SMs can be used as standards on a particular project if required, but they are intended more as guidance. ISRM achievements of the past 50 years
ISRM Suggested Methods
ISRM Suggested Methods are presented with standardized formats, each of which has the following contents:
(1) Introduction and history of the suggested method, (2) Scope, (3) Apparatus, (4) Procedure, (5) Calculations, (6) Reporting, (7) Final credits, (8) Acknowledgments, and (9) References. ISRM achievements of the past 50 years
ISRM Suggested Methods
Yellow Book 1981 edited by E.T. Brown
Rock characterization, testing & monitoring
The first collection of the Suggested Methods of the ISRM was edited by Professor Ted Brown and published by Pergamon Press in 1981. ISRM achievements of the past 50 years
ISRM Suggested Methods
Blue Book Editors: R. Ulusay and J.A. Hudson.
The Complete ISRM Suggested Methods for Rock Characterization, Testing and Monitoring: 1974-2006
40 methods
Free for ISRM members! ISRM achievements of the past 50 years
ISRM Suggested Methods
Orange Book
Editor, R. Ulusay SMs 2007 – 2014.
21 separate new and upgraded ISRM Sms ISRM achievements of the past 50 years
Online lecture
The ISRM Online Lecture series was launched in 2013.
Every three months, experts in different fields of rock mechanics were invited to give a lecture on a specific topic.
ISRM achievements of the past 50 years ISRM achievements of the past 50 years ISRM achievements of the past 50 years ISRM achievements of the past 50 years ISRM achievements of the past 50 years ISRM achievements of the past 50 years ISRM achievements of the past 50 years ISRM achievements of the past 50 years ISRM achievements of the past 50 years
ISRM ISRM President 2015-2019.
Dr. Eda Freitas de Quadros, Brazil
First woman as president of ISRM or ISSMGE in 75 years FedIGS
The aim of FedIGS
The aim of FedIGS is enhance cooperation between international geo-engineering societies. FedIGS
The three founding sister societies are 1. ISSMGE (International Society for Soil Mechanics and Geotechnical Engineering), 2. IAEG (International Association for Engineering Geology) and 3. ISRM (International Society for Rock Mechanics). More recently 4. IGS (The International Geosynthetics Society) joined the group and others are being invited to join. FedIGS
The current position of the FedIGS
FedIGS operates at low level of activity without secretarial assistance and with only 3 JTC’s. (Joint Technical Committee)
JTC1 - Natural Slopes and Landslides JTC2 - Representation of Geo-Engineering Data JTC3 - Education and Training FedIGS
The historic meeting of the Presidents of the sister Societies in Lisbon where it was decideed in principle FedIGS (2007) Some of actual rock mechanics and rock engineering problems Actual problems
We are faced with several problems:
We have a wide range applications to the rock mechanics and the design in rock engineering. We deal with natural material. Different behaviour of same rock in different conditions. Actual problems
Wide range of applications
• Foundation, • Slope, • Tunnel, • Mine (underground and open pit), • Geothermal energy, • Petroleum engineering, • Waste disposal. Actual problems
Rock mass is natural material
• Discontinuous • nhomogeneous I acronim: DIANE • Anisotropic • Not Elastic • Pre loaded
Rock is unlike many other artificial materials, like concrete or steel, or soil, mainly due to discontinuous character. Actual problems Rock mechanics and structural geology
We deal with deformed and fractured rock It is important to understand the sequence of fracturing Modeling and design techniques require structural geology information to be explicitly included in computer model Actual problems
Rock mechanics and structural geology subject of interest
Past FUTURE Structural Geology Interpretation of natural processes that Prediction of natural geohazards, such have created the rock structures we as volcanic eruptions, earthquakes, see today landslips Rock Mechanics Interpretation of past engineering Prediction of the rock mass response practice: past successes, and past to engineering perturbations failures
Hudson 2012, Beijing Actual problems
Natural fracture Artificial fracture
Rock slabbing and spalling
Actual problems
Different behavior of the same rock around shallow and deep tunnels
Garvity induced failure Failure controlled by rock mass structure
Stress induced failure causing slabbing and spalling, sqeezing Actual problems
Gravity induced behavior – discontinuity controlled blocks Mechanism: gravity induced failing, sliding or rotating of blocks into the excavation, along discontinuities with potential for local shear failure. Important parameters:
• number, orientation and distance of discontinuities or degree of fracturing, • waviness, • roughness persistence, • tension and shear strength in general, • strength and deformability of the rock material, • water pressure, • primary stress conditions. Actual problems
Stress induced behavior
Mechanism: the loading of the rock mass due to secondary stresses around the excavation exceeds the rock mass strength.
Important parameters: deformation and strength parameters of intact rock, discontinuities and rock mass.
Goricki Actual problems Stress induced behavior
σ3=O
Squeezing Spalling, slabbing Shear failure mode High uniaxial stress Actual problems
Different behavior of the same rocks in the vicinity of the excavation
3 1- Uniaxial stress 2- Traiaxial stress 2 1 3- Tensile stress Actual problems
Deformability and strength in function of the lateral pressure
Confining pressure
σax increasing
σ3≠0 Ductile σ1
σ3 σ Brittle 3
σ3≠0 σ3 σ3
σ3≠0 σ1
σ3= 0 Traiaxial test
Axial strain εax Rock behaviour characterisation
“True” rock behaviour – a primary geomechanics challenge Rock behaviour characterisation Site characterisation approach for standard geo-engineering projects
Geological data collection Rock mass behaviour ? Laboratory and in situ testing Rock mass behaviour ? Rock mass characterization and classification (Q, RMR, GSI, joint properties, in situ stress, water, …)
Selection of excavation and support alternatives
Rock mass behaviour ?
Numerical methods Empirical methods
Rock mass behaviour ? Gravity-driven Stress-driven failure failure Peter Kaiser, Canada Excavation and support design
Kaiser and Kim, 2008. Rock behaviour characterisation
Rock behaviour models Site characterization Kaiser: From shallow to deep tunnelling, costly mistakes Geological can be made because the rock behaviour may model change and the rock may behave in an unexpected manner.
Rock may behave differently when unconfined (near an excavation) or when confined (in the core Rock mass of a pillar). model
Hence, it is not sufficient to just provide a ? geological and a rock mass model; it is necessary to translate the knowledge gained from Rock geological to rock mass and then to rock behaviour behaviour models. model Rock behaviour characterisation Distinction by failure mode
Kaiser: Distinction by failure or behaviour mode is often ignored or even misrepresented by the chosen numerical model.
Almost exclusively, the most commonly recognised behaviour modes are related to shear failure; either along block boundaries or through the rock mass.
The effects of tensile failure or spalling are rarely anticipated and correctly modelled, and thus not properly described.
Distinction by failure or behaviour mode is very importnt! Rock behaviour characterisation
σax Before failure After failure Failure criterion 0,5 σ ' σ ' = σ ' +σ 3 + 1 3 ci mi 1 σ ci τ
(σ1)
τ = σ tanφ + c
axial strain εax (σ3) σ
Simultaneously mobilisation of Failure envelopes are smooth forms cohesion nad friction (linear and nelienaran) c+ σtanΦ Is this approach correct? Observations show that it IS NOT! Rock behaviour characterisation Bi-linear failure envelope of over-consolidated clays
Transition from a cohesive to a 12% ε q' ax frictional yield mode (Schmertman i 7,5% ε ax Osterberg, 1960.) 4% εax
1,5% εax
0,75% εax
the frictional strength component dominates at large strains and high confinement.
the cohesive strength component dominates at low strains and at low confinement (p’)
p' tensile Axial splitting Tension type failure
σ1/ σc characterisation Rock behaviour strength Intact rock Spalling failure In situ strength shear
Deamage threshold type failure (shear failure) Triaxial state
much beter much S the behavior of rock of behavior the -
σ shaped failure failure shaped 3 Kaiser, 2008. / σ c mass mass
describes describes criteria
in situ
Rock behaviour characterisation
Failure criterion of limestone
Triaxial tests H-B criterion
Faculty of civil engineering Rijeka Rock behaviour characterisation
Spalling limit σ1 σ1/ σ3~10 GSI=100 Intact rock
ACS GSI=50 UCS
0,1 UCS σ3 tensile type failure shear type failure Rock behaviour characterisation
τ = σ tanφ + c Mohr-Coulomb
a σ ' σ ' = σ ' +σ 3 + Hoek & Brown 1 3 ci mb s σ ci τ Cohesion + friction σ
τ Cohesion than friction
σ Rock behaviour characterisation
Kaiser: In more general terms, the fundamental shear strength equation with strain-independent parameters
τ = c +σ ' tanφ is not applicable over the entire confinement range for brittle rocks and thus may be misleading when applied to rock mechanics problems.
Kaiser P.K., 2010, How highly stressed brittle rock failure impacts tunnel design, Eurock-2010-Laussane, Switzerland, p.p. 27-38. Rock behaviour characterisation
Barton was interviewed by Vrkljan during Barton's stay in Croatia from 1 to 6 June 2011.
“Conventional continuum modelling with ‘c plus σ’ tan φ’ (linear or non-linear) does not describe rock mass baviour good enough. So all the ‘colour’ in consultants and students appendices showing ‘plastic zones’ are actually better omitted, until a general improvement of method is adopted ‘c than σ’ tan φ’ (degrade cohesion and mobilize friction at different strains)”. In situ stress and residual Stresses in the Intact Rock In-situ Rock Stress
World Stress Map, 2008 (Tectonic scale and regional stresses)
In engineering practice, we have little benefit from this map because we operate in a small area (site scale). In-situ Rock Stress
Scale effect on the in-situ stress
Tectonic scale and regional stresses Site scale Excavation scale Borehole/measurement scale Microscopic scale In-situ Rock Stress Engineering effect- The Influence of a free face excavation surfaces Geological effect- rock fracture will change the orientation and size of the principal stress
σ1 Fracture σ3
σ1 Rock mass σ3
Principal stresses are locally parallel and Principal stresses are parallel and perpendicular to the fracture surface. perpendicular to the free surface. In-situ Rock Stress
The Influence of a free face
3
3
2 2 1 1 In-situ Rock Stress
The Influence of a free face
Hermosillo, Mexico In-situ Rock Stress
The Influence of a free face
Cracks in concrete Residual stresses
Carrara marble quarries in Italy Residual stresses
Finlandia City Hall, Helsinki (2001). The new marble panels clearly bowed in less than 1 year after the old marble panels had been replaced.
Almost all of the old panels were bowing concave, however the new panels bow convex! Hudson, 2009 In both cases the marble type was a Carrara marble. Residual stresses
ZAGREB - Croatia Carrara marble Residual stresses
ZAGREB - Croatia Carrara marble What is the Strength of a Rock Mass? What is the strength of a rock mass?
Müller and Pacher, were interviewed the same day when ISRM has been founded on a Salzburg radio station.
In the interview, the reporter asks:
“Do we know the strength of rock?”
Müller replied:
“For rock (specimens) tested in the laboratory, yes”.
What is the strength of a rock mass?
Müller: For a rock mass, no. This is what we need to determine.
This is why we need an International Society for Rock Mechanics.”
What is the strength of a rock mass?
Müller’s central question “What is the strength of a rock mass?”
How far we have come in answering the question? What is the strength of a rock mass?
What is the Strength of a Rock Mass? Progress in answering Müller’s (implicit) question
Vienna-Leopold-Müller Lecture, 2010.
Charles Fairhurst What is the strength of a rock mass?
How to solve problem of discontinuous character of rock mass and scale effects?
Large in-situ test (Plate load teste, large flat Jack test, test chambre)
Back analysis based on observations
Numerical analysis What is the strength of a rock mass?
The Synthetic Rock Model (SRM)
Discontinuum analysis has been introduced to rock mechanics in 1971.
Peter Cundall, then a student of Prof E. Hoek at Imperial College, London presented the paper:
“A Computer Model for Simulating Progressive Large Scale Movements in Blocky Rock Systems”
Cundall and his colleaguse have cotinued to develop the “discrete element method” for modelling of jointed rock to the present time.
What is the strength of a rock mass? Synthetic Rock Model (SRM) The rock mass is assumed to be composed of two principal components:
intact rock a system of joints
σax
εax Constitutive behavior of the intact rock should be determined from standard laboratory tests in which the ‘complete stress-strain response’ is observed. What is the strength of a rock mass?
Synthetic Rock Model (SRM) The intact rock is represented in the model by an assembly of circular discs or spheres bonded at the contacts.
The joints are introduced into the intact rock model through the Smooth Joint Model (SJM) which allows slip and opening on joint planes.
Intact Rock Fracture Representation Rock mass Representation (PFC) Particle Flow Codes (DFN) Discrete Fracture Network What is the strength of a rock mass?
Comparison of the discontinuum (SRM) and continuum (FLAC) analyses (Fairhurst, 2010)
Synthetic Rock Model (SRM) 40,225 discontinuities 330,000 particles 38,656 blocks
In the FLAC continuum analysis discontinuous slip along joints This comparison is encouraging. The expectations from SRM are great. What is the strength of a rock mass?
Fairhurst about Synthetic Rock Model (SRM)
Computer methods now allow us to consider virtually many of the rock mechanics questions that have been raised over the last 50 years.
Advances in computer power and disconinuum modelling provide a more rational framework for rock rengineering than current empirical rules.
The critical next step to advance rock machanics and rock engineering is to obtain field-scale data to verifay and improve numerical predictions. Urgent attention should be given to developing cost-effective ways to obtaing such data. What is the strength of a rock mass?
Empirical approach
Many empirical rules have been develeoped due to complex mechanical behaviour of the rock mass.
An important limitation of empirical rules is that they should not be used outside the boundaries within which these laws were developed. That is not always respected.
When the better theoretical framework becoming available, we will have to check these rules.
Until then, empirically approach will play an important role in rock mechanics and rock engineering. What is the strength of a rock mass?
Empirical approach
Bieniawski: RMR-Rock Mass Rating
Barton: Q system; Shear strength of discontinuities Hoek & Brown: Rock mass failure criteria; GSI What is the strength of a rock mass?
Empirical methods still find wide- Empirical approach spread use today
Hoek-Brown failure criteria
The foundations of the Millau viaduct in France (François Schlosser ) What is the strength of a rock mass?
Empirical approach Empirical methods still find wide- spread use today
Q system, Barton
Olympic games 1994 The worlds largest cavern hall for public use Height : 25 m Length: 91 m Width: 62 m
Rock mechanics position in Eurocode 7 Eurocode 7
2010 The Eurocode 7 or EC7, EN-1997-1:2004 (CEN, 2004), became the Reference Design Code (RDC) for geotechnical design – including rock engineering design – within the European Union (EU).
2018-2020 The next version of EC7 will be written between now and 2018, and will then be published in 2018 for adoption in 2020. Eurocode 7
Impact of Eurocode 7 worldwide
EC7 has been also adopted by a number of other countries beyond the EU.
On this way it is becoming a key design standard for geotechnical engineering worldwide. Eurocode 7 1980 Agreement between the Commission of the European Communities (CEC) and the International Society for Soil Mechanics and Foundation Engineering (ISSMFE).
1981 ISSMFE established an ad hoc committee for this task.
1987 ISSMFE produced a ‘draft model for Eurocode 7.
1990 Work was transferred to CEN (Comité Européen de Normalisation / European Committee for Standardisation), and in particular CEN’s
Technical Committee TC250. Harrison et al, 2015. Eurocode 7
EC7 development has been undertaken from the point of view of foundations and retaining structures on and in soils.
In EC7 development, ISRM and IAEG have not been formally involved.
It is now widely recognised that EC7 is in many ways inappropriate – and in some circumstances inapplicable – to rock engineering. ISRM Commission on Evolution of Eurocode 7 http://www.isrm.net/gca/?id=1143 Eurocode 7
Maintenance work programme 2011-2020
Maintenance period was aimed at improving the applicability and ease-of-use of the EC7.
Maintenance period started in 2011 and will conclude in 2020 with the publication of a revised version of EC7.
Eurocode 7
The Eurocode maintenance work programme
http://eurocodes.jrc.ec.europ a.eu/images/MaintenanceWP .gif
Eurocode 7
2011 CEN/TC250/SC7 established 14 Evolution Groups (EGs) to identify how EC7 could be improved.
Andrew Bond John Harrison (chairman TC250/SC7) (Secretary of EG 13) Eurocode 7
EG Title Members (Convenor/Secretary) 0 Management and oversight Andrew Bond (Chairman SC7) 1 Anchors Eric Farrell (Ireland) 2 Maintenance and ease-of-use Bernd Schuppener (Germany) 3 Model solutions Trevor Orr (Ireland) 4 Numerical methods Andrew Lees (Cyprus) 5 Reinforced soil Martin Vanicek (Czech Republic) 6 Seismic design Giuseppe Scarpelli (Italy) 7 Pile design Christian Moormann (Germany) 8 Harmonization Andrew Bond (Chairman SC7) 9 Water pressures Norbert Vogt (Germany) 10 Calculation models Christos Vrettos (Germany) 11 Characterization Lovisa Moritz (Sweden)) 12 (Tunnelling) To be decided 13 Rock mechanics John Harrison (UK/Canada) 14 Ground improvement Paolo Croce (Italy) Eurocode 7
Rock mechanics EG 13 tasks
identify deficiencies in EC7 with regard to rock engineering design and construction practice; bring these deficiencies to the attention of CEN/TC250/SC7 and the other Evolution Groups; inform the rock mechanics community of the maintenance cycle, in order to ensure that CEN/TC250/SC7 obtains as much practical feedback on the use of EC7 as possible. Harrison et al, 2015. Eurocode 7
Evaluation Group 13 (EG) activity
Preliminary Workshop at the Eurock 2012 conference in Stockholm, Sweden, Workshop on the “Applicability and application of Eurocode 7 to rock engineering design” at the Eurock 2014 conference in Vigo, Spain. Eurocode 7
Andrew Bond (chairman TC50/SC7) Evaluation of Eurocode 7 Delft workshop, 30 Nov-1 Dec 2011
SC7's highest priorities for development in next revision of EN 1997 1. Harmonization (Simplify/reduce number of Design Approach; Revise/harmonize NDPs following review of countries' National Annexes) 2. Incorporate recent research results and technical studies (Add/improve guidance on ground water pressures; numerical models; selection of characteristic parameters; use of EN 1997 with EN 1998for seismic design) 3. Sustainability (Remove conservatisms from connection with structural Eurocodes; provide better treatment of consequence/ reliability clases) 4. New part of Eurocode 7 (Reinforced soil, rock mechanics, tunnelling) 5. Simplification of rules (Revise EN 1997-2 to remove material readily found elsewhere; revise/remove text duplicated scross ENs 1997-1 and 2. Eurocode 7
ISRM activities related to EC7
2014 ISRM Commission on the Evolution of Eurocode 7 has been established.
The inaugural meeting of the Commission was held in Vigo, Spain during the EUROCK 2014.
http://www.isrm.net/gca/?id=1143
Eurocode 7
Tunnelling in EC7
Geotechnical category 2
Tunnels in hard, non-fractured rock and not subjected to special water tightness or other requirements.
Is there are non-fractured rock?
Schubert: In EC 7 tunnels in general belong to the category 3 structures, requiring detailed investigation and analysis. Eurocode 7
Limit State Design (LSD)
EC7 requires designs to adhere to the principles of Limit State Design.
However, it is not clear that current rock engineering design practice can satisfy this requirement.
Harrison et al, 2015. Eurocode 7
Rock mass characterization
EC7 does not give details on rock mass characterization and on how the rock discontinuities should be considered in order to quantify the degree of fracturing and anisotropy.
Ferrero, A.M., Sofianos, A., Alejano, L.R., 2014, Critical review of Eurocode-7 regarding rock mass characterization. Eurock 2014 Workshop, 26th May, Vigo, Spain, pp. Eurocode 7
Prescriptive measures Rock mass classification systems
Empirical prescriptive measures is allowed in EC7 “ in design situations where calculation models are not available or are not necessary”. 1. Which type of geotechnical structures? 2. Does design by prescriptive measures (classification systems) can be apply only to EC7 category 1 or also to geotechnical category 2?
Lamas et al, 2014. Schubert calls for reducing the use of these techniques Polemics in rock mechanics community Polemics in rock mechanics community NATM New Austrian Tunnelling Method
Neue Österreichiche Tunnelbaumethode (Neue Österreichiche Tunnelbauweise)
1944 Rabcewicz, idea 1948 Rabcewicz, patent 1956 Venezuela, first use 1963 Birthday of NATM
L. Rabcewicz, L. Müller and F. Pacher ("fathers" of the NATM). Polemics in rock mechanics community
Kovári NATM
Prof. Kovári and Prof. Likar, Ljubljana, 2000
At the Rabcewicz-Geomechanical Colloquium held in Salzburg in 1993, on the occasion on the thirtieth anniversary of the birth of the NATM, professor K. Kovári criticized the NATM concept. Polemics in rock mechanics community
Prof. Kalman Kovári, (ETH Zürich), 1993. Lecture given at the Rabcewicz-Geomechanical Colloquium in Salzburg, Octobre 14, 1993
NATM rests not on an established theoretical foundation, but rather on two fundamental misconceptions (fundamental error).
1. The rock mass (ground) becomes part of the support structure. 2. NATM theory can optimize the design of the tunnel lining following the so-called Fenner-Pacher ground reaction curve. Polemics in rock mechanics community
According to Prof. Gudehus, the polemic between Prof. Kovári and Austrian experts was exceeded only by the well know polemic between Terzaghi and Fillunger, which ended quite tragically.
The University blamed Fillunger, who then committed suicide by opening the gas jets in the bathroom, with his wife Margarete Gregoritsch 08.03.1937. Terzaghi Fillunger
It seems that the remaining scientific and professional community observed these events without too much interest. Polemics in rock mechanics community
The rock mass (ground) becomes part of the support structure
Kovári: NATM alone allows the ground to act as a structurally supporting component
“The New Swimming Technique is based on the concept that by activation of uplift the water becomes a supporting medium”.
Kovári: NATM ignores the achievements of those to whom credit is due for recognizing and clearly formulating this fundamental law of tunnelling: Ritter (1879), Engesser (1882), Wiesmann (1912), Maillart (1923), Mohr (1956).
Polemics in rock mechanics community
Kovári: According to the official definition of the New Austrian Tunnelling Method, the concept of tunnelling is replaced by the concept of the NATM.
TUNNELLING METHOD 1
TUNNELLING METHOD 2
NATM
………………………..
TUNNELLING METHOD X Polemics in rock mechanics community
Correct NATM definition according to Kovári
TUNNELLING METHOD 1
TUNNELLING METHOD 2
TUNNELLING NATM
………………………..
TUNNELLING METHOD X Polemics in rock mechanics community
Kovári: Conclusions regarding the NATM edifice of thought
A critical discussion of the NATM within its own framework of ideas is not possible.
Its terms are so ambiguous that they defy close examination.
If one considers the NATM as a whole, however, not only is it not free from criticism, it is simply groundless. Polemics in rock mechanics community
Does the NATM really exist ?
Austrian experts Kovári, (ETH Zürich), 1993
YES NO Polemics in rock mechanics community
ITA-Austria 2012
50 Anniversary of NATM
http://www.austrian- tunnelling.at/download/NATM_Buch.pdf Austrian Tunnelling Association Polemics in rock mechanics community
Name?
NATM Sequential Excavation technique
Conventional tunneling method
Polemics in rock mechanics community Polemics about classification systems Palmstrøm Barton (Q) Barton (Q) and Bieniawski (RMR) Hoek (GSI) Schubert Barton (Q); Bieniawski (RMR); Hoek (GSI)
Palmstrøm Barton Bieniawski Hoek Schubert Polemics in rock mechanics community
Palmstrøm Barton
Palmstrøm: Potential users of the Q-system should carefully study the limitations of this system as well as other classification systems they may want to apply, before taking them into use. Many of the comments given on the limitations apply also to other classification systems having similar input parameters as Q. A solution often used in works on rock engineering is to link Q values to other classification systems - or opposite - applying correlation equations. This is a procedure we strongly do not recommend.
Polemics in rock mechanics community
Barton (Q) Hoek (GSI)
Barton was interviewed by Vrkljan during Barton's stay in Croatia, June 1 to 6, 2011.
“Of more concern to me these days is the absurdity of the algebraic equations linked to GSI (which is only RMR (minus 5?) anyway. I do not believe, nor ever will believe, that one can look at a picture and ‘classify’ a rock mass. The childrens-method of diagram recognition is entirely innapriopriate to the challenges of describing the anisotropic water-bearing medium that we call rock masses”. Polemics in rock mechanics community
Barton (Q) Hoek (GSI)
Barton: It is time to question this wide-spread method, and the absurdly complex algebra ‘links’ to parameters, that are not actually empirically based. Polemics in rock mechanics community
Schubert Barton; Bieniawski
Are classification systems outdated? ISRM-EUROCK-2013, Wrocław , Poland.
Some Remarks On Current Rock Engineering Design Practices ISRM-EUROCK-2012, Stockholm, Sweden. Polemics in rock mechanics community
Classification systems
Schubert: Selection of parameters, weighting and rating is experience under specific conditions. Classification parameters are universally applied to all rock mass types.
Could this experience be used in other conditions? Polemics in rock mechanics community
Classification systems and tunnel design
Schubert: Some classification systems are extended to tunnel design tools by including additional parameters. This approach does not consider different behavioural modes of the ground and its interaction with excavation and support.
Tunnel designs based on such systems necessarily are inaccurate and sometimes even entirely wrong!
Polemics in rock mechanics community
Classification systems and tunnel design
Schubert: Risk oriented design approaches are becoming more common.
The call for engineering approaches to tunnel design and construction continuously spreads.
With the current state of the art in engineering and legal as well as insurance issues in mind, abandoning empirical methods, such as classification system should be abandoned as quickly as possible.
Expectations of rock mechanics and ISRM Expectations of rock mechanics and ISRM in the next 50 years Rock engineering
Mining Underground structures will be • Open pit deeper than 1000 m bigger, deeper and will be built in • Underground excavations at depths difficult geotechnical conditions greater than 3000 m • Oil drilling deeper than 10000 m Expectations of rock mechanics and ISRM in the next 50 years Rock mass characteriztion
DUSEL - Deep Underground Science and Engineering Laboratory URL - Underground research laboratory
Underground laboratories will play a major role in field validation of theoretical development
Mon Terry, Švicarska Expectations of rock mechanics and ISRM in the next 50 years
MODELLING We have great expectations from the: Coupled Models
DECOVALEX Development of Coupled Models and Their Validation Against Experiments Project Chair: J.A. Hudson and Discontinuum modeling DEM - Discrete Element Method SRM - Synthetic Rock Mass Model Expectations of rock mechanics and ISRM in the next 50 years
MONITORING Monitoring of the in situ behavior of the rock mass is extremely important: New techniques will accelerate the collection of quality data.
Randa in the Matter valley – Switzerland
May 1991, rockslides of approximately 30 million cubic meters of debris Conclusions Conclusions
Since ISRM foundation, significant advances have been made in a number of relevant areas or rock mechanics and rock engineering. “True” rock behaviour is still a primary geomechanics challenge. Close interaction with engineering geology is essential for optimum advance. Developing better methods of characterising the geometry and mechanical properties of the fractures should be the main goal of structural geology. Geophysical methods promises although are still not as successful as in medicine. Conclusions
We need more integration of subjects (e.g., fully- coupled numerical modelling that captures all the required variables, parameters and mechanisms). Underground laboratories will play a major role in field validation of theoretical development. Neural network ‘intelligent’ computer programs should be used more often. More integration of science and engineering is necessary. We need more international co-operation. Thank you! References
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