InformationPublished on February 15 2015
A. ABOUT THE ROCKMASS SITE
The rockmass.net web site has existed since year 2000. Two earlier versions have been presented: version 1 in 2000 to 2008 and version 2 in 2008 – 2011. Version 3 was launched in March 2011.
An update of the site was presented on November 2013 with many new issues, among others:
- Several papers on investigation
- Some updates of spreadsheets
- More paper references and additional definitions
- Some new papers and updates of files.
A new update (this version) came in February 2015 with:
- Approx. 200 more references
- Additional files on investigation
- More papers
- Updated spreadsheet for RMR, Q and RMi calculation
- Updated sheet for geo observations
Update January 2018:
- Additional paper references
- Some new papers
- Update of the excel spreadsheet for calculation of RMR-Q-RMi
Update April 2020:
- Additional paper references, now 2171 references
- Finally some comments on Eurocode 7 (EC7), mainly on rock design
- Some few additional papers
- Some text adjustments
The main objectives of the RockMass website are:
- To inform on geological, rock mechanics and rock engineering aspects.
- To pinpoint possibilities, limitations and difficulties in the use of geological data, possible difficulties and errors in measurements, in collection and in the use of rock engineering and design tools.
- To give advice / give recommendations / communication to achieve proper and best use of engineering geology and rock mechanics in rock engineering and design.
Thus this web page gives you information on how field observations can be performed and used in practical rock engineering. The Rock Mass index (RMi) system has been developed as a tool in this field.
The rockmass.net website has also information on other items related to engineering geology, rock mechanics, and to rock engineering and design.
It is hoped that content of the rockmass.net page can be of interest and a help to people education as well as practicing in planning, rock design and rock engineering.
B. INFORMATION ON THE HANDBOOK IN ENGINEERING GEOLOGY
The handbook in Engineering Geology and Rock Engineering of 250 pages was launched in 2000. It is issued by the Norwegian Rock Mechanics Group (http://www.bergmekanikk.no), affiliated ISRM and IAEG and the Norwegian Tunnelling Society (NFF).
C. INFORMATION ON THE TEXTBOOK ON ROCK ENGINEERING
The first edition of the textbook on Rock Engineering was launched in 2010, the second edition of 444 pages in December 2014. The layout of the book and at the same time the process in rock engineering is illustrated here.
The book (and ebook) can be ordered from the following link https://www.icebookshop.com/Products/Rock-Engineering,-2nd-edition.aspx
DiscussionPublished on February 15 2015
A. DISCUSSIONS on the use of CLASSIFICATION SYSTEMS
After publishing the paper The deformation modulus of rock masses – comparison between in-situ tests and indirect estimates in 2001, see the comment by Dr Nick Barton and the reply by the authors
B. COMMENTS on the paper "Norwegian tunnel builder are the world’s best – a myth?
(from the web site [url=http://www.tunnel.no]http://www.tunnel.no[/url] of NFF, (Norwegian Tunnelling Association))
During the NFF Fall Conference on 27 November 2014, Arild Palmström, PhD, MSc, RockMass AS presented points of view on the Norwegian tunnellers. Some of us assuming that the level of competence is high (even extremely high) whereas others, and the author, have a more factual view. His presentation underscores some facts rocking the bases for exaggerated self-esteem. In the following you will find a selection from his paper.
Arild Palmström is well known in the Norwegian geo-engineering sector, he is author of numerous papers, author or co-author of books on rock mechanics, and has wide experience from projects worldwide. In his thesis (Doctor Scientiarum Oslo University 1995), an important part concerns methods for collecting and using geological parameters with focus on block size, rock material and the quality description of the rockmass defined in the index RMi.
Some Norwegians within the underground construction environment boast of our tunnellers (not limited to the crew at tunnel face), claiming that these obtain weekly advance higher than competitors abroad. Frequently one will hear that the Underground Olympic Hall in Gjövik (some 100 km north of Oslo) is the largest underground opening for public use, the Lärdal Tunnel is the longest road tunnel, or that one will find the deepest subsea road tunnel on the west coast of the country, and repeatedly that the largest number of underground power house complexes will be found in our country. The Greek word hybris (arrogance) fits well, maybe mixed with ignorance one may say.
Smooth tunnelling in line with the planned progress and economy is not always the case. Sometimes one will meet unexpected difficulties, for some rather few projects the problems turn out to be serious. Such incidents, mistakes or lessons learned, are frequently presented by papers for domestic conferences, workshops or similar events.
The whole paper that was presented on [url=http://www.tunnel.no]http://www.tunnel.no[/url] can be found here
Some Rock Engineering ToolsPublished on February 15 2015
Tools for rock engineering have been presented and discussed in many papers and textbooks, e.g. Hoek and Brown (1980) and Bieniawski (1984, 1989), in addition to modern building codes such as the Eurocode 7.
The stability of an underground opening depends on the behaviour of the ground surrounding it. The various types of ground behaviour require different assessments or calculation methods (rock engineering tools) for a proper design that can be relied on to cover the actual case. Therefore, it is necessary to understand the actual type of behaviour, as a pre-requisite for estimates of rock support and other evaluations.
The classical approach is to base the design either on the subjective experience called engineering judgement, or some existing empirical design rule (e.g. classification system (/articles/classification/classification systems.html)), or some kind of calculation. For many rock mechanical applications, however, an observational approach is preferable.
A. On the NATM - New Austrian Tunnelling Method (In German NÖT - Neue Österreichische Tunnelbauweise)
The NATM was first presented by Rabcewicz at the XIII Geomechanics Colloquium in Salzburg, Austria in 1962. This was based on earlier developments in the concept of tunnelling.
1948 Introduction of the dual-lining (initial and permanent) support system by Rabcewicz.
1954-55 Shotcrete and rockbolts were introduced as rock support.
1962 The NATM was presented by Rabcewicz at the XIII Geomechanics Colloquium in Salzburg.
1964 English form of the term NATM first appeared in literature.
The NATM is a strategy or a concept for tunnelling that is based on safe techniques in soft rocks in which the stand-up-time is limited from squeezing. The rock support of the tunnel is immediate (initial) shotcrete followed by systematic rock bolting with application of permanent shotcrete lining, forming a load-bearing support ring, given as:
- Flexible initial support by shotcrete and rock bolts to preserve the load-carrying capacity of the surrounding rock masses,
- Monitoring the deformation/displacements of the tunnel, strengthening of initial support if needed
- Design of permanent support by shotcrete when the displacements have been reduced to a predefined level
The collapse of the Heathrow Express Rail Link Station tunnels with NATM design in 1994 and downfalls or collapses of some other projects applying the NATM, forced the NATM to be put under close examination. Since then the use of NATM has been more balanced.
The uses and problems with the NATM can be summarized here
The NATM has been described in numerous publications, especially during the 1970s, 1980s and first part of 1990s. One of these can be found here.
Some references on NATM can be found here.
B. Observational method
The principles of the Observational method are that the presumptions and results found in the planning phase are verified through monitoring, measurements and observation during construction.
The observation method was first introduced by Karl Terzaghi in the late 1940s and first used in soil engineering. It has later been described by Raph B. Peck, by Herbert H. Einstein and presented by K. Kovari and P. Lunardi on the EngGeo2000 conference in Melbourne, Australia 2000.
The method is integrated as a part of the NATM through the systematic assessment and monitoring in the construction phase.
The Observational method form an important part of the Eurocode 7 of Geotechnical engineering.
Joints and JointingPublished on February 15 2015
The figure below shows the main features occurring in rock masses, which are divided into two main groups: Detailed jointing and Weakness zones.
Joint features, like joints characteristics and the degree of jointing are important parameters applied as input to classification systems, as described in the tag 'Classification systems'.
The main characteristics of joints include:
- joint plane planarity or waviness,
- joint surface smoothness, and
- condition (alteration) of the joint wall (whether it is weathered/altered or has coating or the joint has some sort of filling
- joint size (length) and continuity
These are indicated in the figure below:
You can find more on the joint features in the tag 'Field Observations'
There is a great variety of joints, from small cracks to long shears or seams, as seen below:
Joint characteristics are used as input parameters to many classification systems, see the tag 'Classification systems'.
You will find examples and applications of joint characteristics in several papers presented in other locations on this web page and also in the Rock Engineering book.
Jointing here means the assemblage of joints. It can be measured and characterized in different ways, manly from:
- field observations at terrain surface or in the underground excavation (tunnel, cavern, shaft)
- drill core logging
- seismic or sound velocities
The main jointing features are:
1. Degree of jointing.
This property can be measured as rock quality designation (RQD), volumetric joint count (Jv), block volume Vb), and joint spacing (S), as shortly presented in the paper Block sizes and block size measurements
The volumetric joint count (Jv) is a measurement of the degree of jointing. It is given as the number of joints in a volume of rockmass (of 1m3 size) The following papers deal with the Jv, which was first presented (in Norwegian) by Palmstrom in 1974, later presented in 1982, 1985, 1986, and 1996.
The paper Application of seismic refraction survey in assessment of jointing shows how the seismic velocities can be used to estimate the Jv.
The paper Measurements of and correlations between block size and rock quality designation (RQD) shows the difficulties in establishing a good comparison between RQD and Vb (block size).
2. Orientation of joints and joint sets.
This has special interest when the joint set is unfavourably orientated parallel or at a small angle to a tunnel or cavern. This feature is used as input to the RMR system and the RMi rock support method.
3. Pattern of joints, which is used as input in the Q-system and the RMi support method.
Joint pattern is the occurrence of joint sets in an area. It is manifested in the shape of the rock blocks as shoen in the figure below:.
The Q and the RMi classification systems use a simplified jointing pattern given as 'number of joint sets' as an input parameter. See also the paper on 'Observation of jointing features'.
A more comprehensive description of various measurements and observations is given in the paper Measurement and characterization of rock mass jointing.
More can be found in the Rock Engineering book.
Classification SystemsPublished on February 15 2015
Classification systems are probably among the most frequently tools used in the design of underground excavations in rock. The primary object of all rock mass classification systems is to quantify different engineering properties of, or related to, the rock mass based on past experience. Their main core is the assessment of the rock mass quality that, preferably, can be used as an indicator for rock engineering. From a set of parameters of the rock, rockmass, groundwater and stresses, the quality of a rockmass with respect to strength, deformability and stability can be estimated.
Another important task is that they serve as a kind of checklist.
Three different types of output can be distinguished from the rock mass classification systems:
- Characterisation of the rock mass expressed as overall rock mass quality, incorporating the combined effects of different geological parameters and their relative importance for the overall condition of a rock mass. This enables the comparison of rock mass conditions throughout the site and delineation of regions of the rock mass from 'very good' to 'very poor', thus providing a map of rock mass quality boundaries.
- Empirical design with guidelines for tunnel support compatible with rock mass quality and the method of excavation. Traditionally, this is often seen as the major benefit from the use of rock mass classification systems.
- Estimates of rock mass properties. Rock mass characterisation expressed as an overall rock mass quality has been found useful for estimating the in situ modulus of rock mass deformability and the rock mass strength to be used in different types of design calculations.
- The accuracy of these existing empirical design methods is not established.
- Contractual problems are often created when unforeseen geological conditions have been encountered, and where the system has not been applicable. Typical conditions that are not covered sufficiently are swelling, squeezing, ravelling, flowing, and popping ground.
In the early stages of a project, the existing quantitative rock mass classification systems (empirical design methods) can be applied as a useful tool to establish a preliminary design. At least two systems should be applied (Bieniawski, 1984, 1989). Classification systems are, however, unreliable for rock support determinations during construction, as local geometric and geological features may override the rock mass quality defined by the classification system. Restrictions on their use here are also pointed out by Bieniawski (1997).
Several classification systems have been developed over time. Some have been developed specifically for a project. Some comments on classification systems are presented here and some references are presented here.
To view a paper on the ability and use of classification systems, see the paper 'Classification as a tool in rock engineering'.
2. The RMR classification system
The RMR (or Geomechanics) system was launched by Bieniawski in 1973. It was a further development of the RSR system by Wickham, Tiedemann and Skinner (1972). Later, the system has been revised/updated by Bieniawski in 1974, 1975, 1976 and 1989. A short description of the RMR is shown here.
Numerous papers have been presented and published on the RMR system and the system is currently being used by many practitioners. The input parameters to RMR and the RMR support table are shown here.
In applying this classification system, the rock masses are divided into a number of structural regions. The boundaries of the structural regions usually coincide with major structural features (Bieniawski 1984, 1989). Bieniawski strongly emphasises that a great deal of judgement is needed in the application of rock mass classification to support design.
The RMR value has also been used to estimate rock mass properties. Bieniawski (1984, 1989) and Serafim and Pereira (1983) have given a relationship between the RMR and the rockmass deformation modulus (Em). The RMR value is also used as one way to estimate the m and s factors in the Hoek Brown failure criterion (Wood, 1991; Hoek, 1994; Hoek and Brown, 1997) as well as the GSI value to evaluate the rock mass strength properties.
The RMR-values can be estimated using a computer spreadsheet together with Q-values and RMi-values.
3. The Q classification system
The Q system was launched in 1974 by Nick Barton, Reidar Lien and Johny Lunde of the Norwegian Geotechnical Institute (NGI). The Q-system is as an empirical design method for rock support. Together with the ratio between the span or height of the opening and an excavation support ratio (ESR), the Q value defines the rock support. This is described here.
Over the years, some developments have been introduced by:
- a new design of the support diagram (Grimstad and Barton, 1988), see list of published paper here.
- adjustments of the input parameter SRF (Grimstad and Barton, 1993), inclusion of the rock strength (Barton, 1995), inclusion of shotcrete ribs as a support element (Barton and Grimstad, 2004).
- updated support diagram by NGI, presented on the internet.
A paper presenting Q and NATM systems gives some information on the two systems.
Grimstad and Barton (1993) have also presented an equation to use the Q value to estimate the rock mass deformation modulus (for values of Q > 1). The Q value is also used as one method to estimate the m and s factors in the Hoek Brown failure criterion (Hoek, 1983; Hoek and Brown, 1988).
In 1999 the originator of the Q system has increased the limitation of the original Q to also incorporate excavation by TBM (tunnel boring machines) introducing QTBM (Barton, 1999) and to also use Q-values for estimates of the effect of grouting (Barton et al, 2001), estimate Q-values from sound velocities in the ground (found from refraction seismic measurements).
Some comments on the limitations of the use of classification systems are presented in the paper 'Use and misuse of classification systems with special reference to the Q system'. This paper was first presented at the annual Norwegian conference on Rock and Soil excavation in 2002. A summary in English of this paper can be read here.
The Q-values can be estimated using a computer spreadsheet together with RMR-values and RMi-values. See also Section 6 below.
4. The RMi classification system
The rock mass index, RMi, is a volumetric parameter indicating the approximate uniaxial compressive strength of a rock mass. The system was first presented by Palmström (1995) in his PhD. and has been further developed and presented in several different papers, see the tag 'Why RMi?'
The application of RMi is two-fold:
- RMi gives an approximate value for the compressive strength of the rockmass (MPa)
- RMi is used as input to other calculations or estimates of rock properties, like rock support, TBM progress assessment, deformation modulus of rockmass.
RMi makes use of the uniaxial compressive strength of intact rock (UCS) and the reducing effect of the joints penetrating the rock (JP) has. This is expressed as RMi = UCS x JP
A short introduction to the RMi system is shown here and a more detailed description here where also the input parameters to RMi are shown. RMi requires more calculation than the RMR and the Q system, but spreadsheets can be used from which RMi-values can be found together with RMR-values and Q-values from the same input observations, see also Section 6 below.
Based on RMi combined with the geometrical features of the underground opening and rock stresses, the rock support can be estimated using support charts or from the excel spreadsheet. RMi can also be applied as input to other rock engineering methods, such as numerical modelling, the Hoek-Brown failure criterion for rock masses. The paper 'Deformation modulus of rock masses' shows how RMi can be used.
The system applies best to massive and jointed rock masses where the joints in the various sets have similar properties. It may also be used as a first check for support in faults and weakness zones, but its limitations here are pointed out by Palmström (1995).
For special ground conditions like swelling, squeezing, ravelling, the rock support should be evaluated separately for each and every case. Other features to be separately assessed are connected to project specific requirements such as the life-time of the project.
There is more to be found on RMi in the tag 'Ph.D. Thesis on RMi'.
5. Other classification/characterization systems
Several other classification systems have been developed over time. Some have been developed specifically for a project.
The first one to present a practical classification system for use in rock engineering was Dr. Karl Terzaghi when he in 1946 wrote the famous article Introduction to tunnel geology (Terzaghi, 1946) as a chapter in the book 'Rock Tunneling with steel supports' by Robert V. Proctor and Thomas L. White after visits to several tunnelling projects in America and in Europe. Many of these projects experienced tunnel excavation and stability problems.
In the 1940s, the rock support was often performed by steel arches, on which the support evaluation in the Terzaghi system was developed. Today, the Terzaghi classification system has lost much of its interest. However, the engineering geological part of the book is very interesting and pinpointing important geological features with respect to tunnel construction.
The NATM (New Austrian Tunnelling Method) is a sequence of tunnel planning, design and follow-up, and hence not an ordinary classification system.
6. Combination of RMR, Q and RMi classification systems
In two papers Comparing the RMR, Q and RMi classification systems, a Comparison on the RMR, Q and RMi systems is presented in Part-1 and Part-2. Shorter versions are presented in the papers 'Combining the RMR, Q and RMi classification systems' and in a Technical note.
An overview of the input parameters used in the RMR, Q, and RMi systems are presented here.
A computer spreadsheet has been worked out where the RMR, Q and RMi values are calculated independently by combining the input parameters as described in the papers mentioned above.
See also references on classification systems.
ClassificationsPublished on February 15 2015
The geologic classification of the rock material is based on origin, mineralogical composition, mineral size and petrologic characteristics. The condition, i.e. classes of the various features to be used in rock engineering should be easily observed or measured in the field and/or laboratory.
The rockmass contains several features, each of them with properties. They all play a role in its strength and modulus of deformation. Many of these features are applied as input to classification systems. A collection of classifications is presented below:
- Rock properties
- Joint and jointing characteristics
- Other rockmass properties or features
- A summary of classifications
Classification should provide a common basis of communication, and to identify a rock mass into one of the groups having well defined characteristics and also yield basic input data for engineering design.
The terminology used should be widely accepted by engineers and geologists. Only the most significant properties of the rock should be considered, which will influence the engineering properties and behaviour.
The paper "Classification systems and use og geological data" presented at the Iranian conference "Tunnelling and Climate", gives an overview of the geological parameters applied in classification systems and how these can be combined to calculate the values (rockmass quality) in different classification systems. The latter is also shown in the spreadsheet file here.
Estimations with RMiPublished on February 15 2015
A. Estimate of rockmass properties
1. Estimates of rockmass strength. As shown in papers on RMi, the RMi-value approximately gives the uniaxial compressive strength of a rockmass. The RMi-value can be found from:
- calculations as given, for instance in the tag 'Papers on RMi', or
- a graphical method to calculate the RMi-value, or
- the computer spreadsheet RMi Calculation, or
- the computer spreadsheet Combining the RMR, Q and RMi systems
2. Estimate of deformation modulus as described in the paper The deformation modulus – comparisons between in situ tests and indirect estimates.
3. Estimate of input parameters to Hoek-Brown failure criterion for rockmasses as described in the Ph.D. thesis on RMi.
B. Estimate of rock support
The RMi is used in rock support as described in several papers, see the tag 'Papers on RMi', especially the paper Recent developments in rock support estimates by the RMi.
The estimate of rock support can be found by application of the computer spreadsheet on Rock support
Why RMi?Published on February 15 2015
Construction materials commonly used in civil engineering are mostly characterized by their strength properties. In rock engineering, however, no strength characterization of the rock mass is in common use. Most engineering is carried out using various descriptions, classifications and unspecified experience.
Hoek and Brown (1980), Bieniawski (1984), Nieto (1983) and several other authors have, therefore, indicated the need for a strength characterization of rock masses. The RMi system has been developed to meet this need.
The development of the RMi system
The concept of RMi was first presented at the Norwegian National annual conference on Rock mechanics (Bergmekanikkdagen) in 1986. This was partly a continuation of the ideas of the volumetric joint count (Jv), which had been presented in several papers since 1975.
The practical development of RMi was performed from 1991 to 1995 in a PhD. thesis named RMi – a rock mass characterization system for rock engineering purposes, at Oslo University, Norway.
Since 1995 the RMi has been applied in several projects; several papers on have been published. Some developments and improvements of the RMi rock support method were presented in 2000, in the latest published paper on the RMi rock support method Recent developments in rock support estimates by the RMi, with some simplifications. In addition, a few minor errors have been corrected since the RMi system was published in 1995.
Description of the RMi system
The Rock Mass index (RMi) combines numerical values of relevant parameters in the rock mass to express the RMi value. Most of these parameters, including the rock material and the joints intersecting it, can be found from common observations or measurements in the field.
The RMi-value is an approximate measure of the uniaxial strength of the rockmass. It can be used in several calculation methods in rock engineering and rock mechanics, such as for rock support estimates in underground excavations, input parameters to the Hoek-Brown failure criterion for rock masses, and for estimating penetration rate of TBMs (tunnel boring machines). In addition, RMi can be useful in estimation of some input data used in numerical modelling.
The Ph.D. thesis on RMi gives the whole development and background on this characterization/classification system and how it can be applied in rock engineering.
Geological UncertaintiesPublished on February 15 2015
Due to the complex character of geological materials there is always an element of uncertainty in geological investigation and testing. In this connection the following terminology is often used:
- Uncertainty or lack of absolute sureness. In geology it means that observations, measurements, calculations and evaluations are not reliable. As a consequence, the use of geological data often may involve some form of guesswork.
- Error is defined as the difference between computed or estimated result and the true value.
- A bias is the difference between the estimated value and the true value based on statistically random sampling. For example, joints sub-parallel to an outcrop have less chance of being sampled than joints perpendicular to an outcrop. This is a bias in sampling for orientation.
Geotechnical design problems often originate from a lack of knowledge, which contributes to uncertainties and difficulties in determining in advance the actual geology and the behaviour of a geotechnical structure. A lack of knowledge of the design conditions becomes evident in the execution phase, something that also was acknowledged by Terzaghi and Peck (1948) when they formulated the observational method. This procedure has been accepted and formalized in the new Eurocode 7 for geotechnical problems.
In principle the uncertainties in data are depending on the extent of investigations. However, in tunnelling it may be impossible to carry out any detailed investigate in advance. The most optimal solution may then be to carry out investigations during the excavation and apply the results to adjust the design if necessary.
Some comments on uncertainties can be seen here.
The paper Rock engineering and tunnelling - A Nordic approach includes description on geological uncertainty.
Collapses of tunnels
Slides, cave-ins, flowing ground which sometimes occur in tunnels are some of the unexpected problems during tunnel excavations. Some comments on this are shown in the paper Collection of geo-data – limitations and uncertainties.
Unexpected events are often caused by geological features because of lack of information from field investigations and collection:
- Although extensive field investigation and good quality descriptions will enable the engineering geologist to predict the behaviour of a tunnel more accurately, it cannot eliminate the risk of encountering unexpected features.
- A good quality characterisation of the rock mass will, however, in all cases except for wrong or incorrect interpretations, improve the quality of the geological input data for evaluation and analyses, and hence lead to better design.
- The methods, effort and costs of collecting geo-data should always be balanced against the probable uncertainties and errors.
There are generally great difficulties to perform investigation from the terrain surface for a tunnel hundreds of metres below surface. As long as the tunnel construction is found feasible, some of the investigations may be performed later from the tunnel face during tunnel excavation.
Some of the impact from uncertainty can be reduced by flexibility in tunnelling contracts by a risk-sharing system has obvious advantages.
More on geological uncertainties is presented in the Rock Engineering book
Weakness Zones and FaultsPublished on February 15 2015
Weakness zones and faults are among the most important features in rock excavation. See the definitions for right understanding of these terms.
Weakness zones and faults are described in the Ph.D. thesis, Appendix 2.
See also the paper 'The significance of weakness zones in rock tunnelling'.
Weakness zones including fault zones have been responsible for many problems and collapses in rock tunnelling as described in the tab 'Geological uncertainties'.
More on weakness and fault zones is presented in the Rock Engineering book.
Rock PropertiesPublished on February 14 2015
Several textbook describe formation, development and composition of rocks as well as rock properties, among others Lama and Vutukuri (1976), see Publication references.
Some information on rocks can be found in the following:
- Geological classifications of igneous, sedimentary and metamorphic rocks
- A schematic overview of rock development is presented here.
- Classification of mineral sizes.
- Some rock strength and mi values.
- Some rock rock strength and deformability values.
(mi is the factor used in the Hoek-Brown criterion for rockmasses)
Take also a look at the rock classification of Prof. Richard Goodman worked out for technical use.
A special feature in the occurrence of rocks is weathering. Various classifications of weathering as well as some definitions and comment are given here.
See also Classification.
Geological InformationPublished on February 14 2015
The geological setting is generally a prerequisite for a good understanding of the ground conditions in the project area. Often a general geological map exists in scale between 1: 50,000 and 1:100,000. For large projects, a separate or additional geological mapping is often conducted. A wrongly geological base may cause wrong interpretations as e.g.as described in the paper by Winter et al, 1994 and hence strongly influence on the construction of the project.
You will find a geological timescale here and here (/files/geo_timescale.pdf) and in website
(note that Tertiary has been changed into Paleogene and Neogene)
More on geological times can be found on International Commission on Stratigraphy
Field ObservationsPublished on February 13 2015
Geo-observation means observation and mapping of rockmass and ground parameters that are influencing on the behaviour of rock excavations, such as cuttings, tunnels, caverns and shafts.
In fact, geo-observations are often the most important contributor for:
- the planning and design of rock excavations;
- the engineering geological map;
- stability and support evaluations, as well as
- numerical modelling.
A precondition for good characterizations is that the geological conditions are understood /or documented so the engineering geological observations can be placed or viewed in a broader context. Especially important when the rocks are faulted. Field characterization of rocks, joint features and jointing features includes:
When the geo-observations are performed in the rock excavation (where the information is used for engineering and design), the results can be used directly in evaluations and rock engineering.
However, when the geo-observations are made on the terrain surface, often far off the underground rock excavation in question. Some sort of extrapolation is needed to make a probable assessment of the underground conditions. This is explained in the paper 'Geo-registrations, Rockmass conditions and Ground quality', which also introduces a geo-registrations form. This form can be combined with the Excel spreadsheet geo-calculations where the rockmass and ground quality are calculated. An example of the use of the Geo-registrations form and the spreadsheet Geo-conditions is shown here.
The ability to observe exposed rocks in the terrain surface varies with the sites, from entire cover by loose materials and/or vegetation or water to 100% exposed rocks. Different types of investigations can be performed depending on this and whether the rocks are weathered at the terrain surface. Some information on field investigations is given here.
As shown here the RMR, Q and RMi systems use partly the same input parameters. Common registrations of these parameters can be easily made when the field registration scheme described above is used.
Examples with comments of some rockmass observations can be studied here
Observations with the Q-system
As the Q-system is often used for documentation of field observations, there are a few important issues to be aware of:
1. Observations at terrain surface:
The Q-value found is site specific, i.e. it specifies the ground conditions at the actual location. This is important regarding the two input parameters stresses and groundwater. When mapping in the terrain surface, the stresses are low/zero and there is no groundwater pressure or inflow (the observation area may even be above the groundwater table). What Q input values should be used for these parameters to characterize the Q-value in the observation point? The 'geo-observation' paper discusses this problem. See some more comments here.
2. Observations in the tunnel or cavern:
The Q- value indicates the ground quality (i.e. stability) at a specific location. The area to be supported is often one or two blast rounds long (a blast round varies mostly between 3m and 5m). Thus the area for assessment of roof stability will be approx. tunnel span × blast round. For a tunnel with 10m span, the area is 30 – 50m2 (or the double if 2 blast rounds are evaluated). This is important when the number of joint sets is assessed because the joint sets are those found within the 30 – 50m2 only. This is further discussed in the 'geo-observation' paper.
Observations with RMi
The RMi value is an approximate measure of the compressive strength of a rockmass. It may be crudely found from input shown in the figure below, which can be downloaded here. Other methods for calculation of the RMi value and the support are given in 'Why RMi?'.
On Investigation MethodsPublished on February 13 2015
The main aim to perform investigations for a rock excavation is to provide sufficient information and a basis to carry out the planning of and to evaluate the consequences for the rock excavation in question. This means to characterize the ground qualities with respect to the actual construction works and find the distribution of the qualities along the actual excavation.
There should be good reasons for selecting the type(s), amount and locations of the investigations to be performed, for providing data and relevant, useful information on the ground conditions to be applied in the further evaluations and calculations.
The geological conditions of the sites may vary within wide limits. Each site has its own characteristics, and there are no “standard investigation procedures or methods”, which in all cases will be the only right one. Therefore, the investigations have to be tailored for each site.
Most investigations are performed
- during planning (before construction),
- during excavation, or
- during operation for maintenance purposes
There are numerous methods to perform investigations for an underground excavation project. A list of various types performed in the field and/or in the laboratory is given here
Additional information on collection of geological and rockmass information is presented in 'Geo-observations'. More can be found in the Rock Engineering book, especially in Chapter 3 from which a couple of tables are presented.
The investigation should be planned in a way that all investigation results can be utilized in the evaluations and assessments made during rock engineering, calculations and design.
Thus, it is of little use to map the orientation of joints and work out a joint rosette when joint orientation (with regard to the tunnel) is not used in the evaluations/assessments made, such as in the Q system, which has no input parameter on joint orientation.
The results from different investigation methods can be combined for the derived result to be further used in the rock quality assessments, see the Rock Engineering book where examples are shown on:
- how core drillings and seismic measurements can be combined
- core drilling and engineering geological observations can be combined
- geological setting with information on rock properties
Comments on Eurocode 7Published on January 30 2015
On Eurocode 7 (EC7)
The standard for geotechnical design was given the name Eurocode 7: Geotechnical Design Part 1: General Rules (EC7). Approved in 2004, it has been given the status of national standard in all European countries from 2010.
The EC7 includes both soil mechanics and rock mechanics. The two subjects have great similarities, but also significant differences, especially related to ground investigations and methods for verifying the design. The ongoing revision of the Eurocode looks into the possibilities to facilitate separate issue of rock mechanics problems like slopes, cuttings and underground
- appropriate choice of design method,
- suitable materials and construction methods,
- appropriate design, and
- control procedures for design, construction relevant to the particular project.
Here, you find abstracts of three papers dealing with Eurocode 7:
- Practical use of the concept of Geotechnical Categories in rock engineering,
- On the Need for a Risk‑Based Framework in Eurocode 7 to Facilitate Design of Underground Openings in Rock,
- Principles of Risk‑Based Rock Engineering Design
See also the paper on Prescriptive measures in Eurocode 7.
Field Observation SchemesPublished on January 30 2015
The methods for the collection of geological data have not changed very much over the past 20 years. Due to the high cost of sub-surface exploration, the main investigation is often restricted to field observations. The geo-registrations are mainly based on observation and mapping performed on:
- Outcrops or open cuts
- Underground excavations (tunnels, caverns, shafts) during and after construction, or in adits made prior to construction
- Drill core logging
For the field mapping a hammer, compass with clinometer, camera and a notebook are the basic equipment for the engineering geologist. In addition to this, maps, air photos, pocket stereoscope, knife, hydrochloride acid (for identifying potential calcite) etc., are indispensable tools. Also, GPS-instrument and altimeter may be useful. Good photo documentation is often a good investment.
The Geo-observation scheme contains characterization of all the items in Table 1, similar as used in the classification systems. An example of registrations made is shown here. (See also the example on using the Observation scheme As described in the paper 'Geo-registrations, Rockmass Conditions and Ground Quality' the scheme is adapted to an Excel spreadsheet where the rockmass and the ground quality can be calculated.
Sampling is an important part of the field work. A logical first step is to take small hand specimens to get an overview of the distribution of the different rocks and the variations within each type. Later, a programme for the sampling of larger specimens for mechanical testing (often 15 - 20 kg or more) can be worked out. Great care must be taken to collect representative specimens. To avoid taking weathered samples, some blasting is often necessary. This may, however, induce new cracks in the specimens.
Strike and dip measurement
The orientation of joint planes and other planar geological features are described by their strike and dip. A geologist's compass is needed to make the necessary readings. The strike of a plane is the trace of the intersection of that plane and a horizontal surface, and is measured with the compass held horizontally against the plane. The dip is describing the plane's inclination to the horizontal, and is measured with the compass held in the vertical plane. Also dip direction is used by many geologists. The relationship between the three terms is illustrated in Figure 1.
Figure 1: Definition of strike and dip.
There are many ways to note the results of strike and dip measurements. The best method is always the one that the respective engineering geologist is most familiar with. If no particular preference exists, it is recommended to measure the strike angle in a clock-wise direction as indicated in Figure 8.3. To make the dip designation unambiguous, it is important to indicate also the direction towards which the plane dips. It is also important to indicate whether a 360o or 400g compass is used.
For the situation in Figure 8.3, the recommended designation of strike and dip thus will be:
strike/dip = N130oE/60oNE or N130o/60oNE
The dip direction and dip are:
dip direction/dip = N40oE/60o
(generally dip direction is found from: strike + 90o or -90o; in this case 130o - 90o = 40o).
The orientation of weakness zones is often best evaluated and calculated from studies of air photos and maps. It is, however, advantageous, and often necessary, with additional observations in the field. A problem in the field is often to find representative planes on which the zone orientation measurements can be made, since close to a tectonic weakness zone there are always joints and fissures of different directions.
Observations and mapping of tunnel conditions
For the owner it is useful to have detailed information of the ground conditions of the project. Many tunnels are difficult to inspect after they have been put in operation. As shotcrete often is applied shortly after the blast, the rockmass conditions must be observed and mapped before the rock surface and the rock conditions are covered and hidden. Tunnel geo-maps should contain all geological elements that influenced on the stability and conditions of the tunnel, such as rock type and character, jointing, faults, water leakage and areas with rock burst problems, in addition to information about support work.
Tunnel mapping may be carried out in various ways, and there are several alternatives for presentation of the results. For additional documentation, the observations may be supplemented by photos.
When the project is completed and all investigations carried out, a final report should be made containing all experience gained during the planning and construction period. Maps and drawings should, as earlier described, be included in this report.
AboutPublished on March 12 2011
A. About the RockMass.net site
Constructions in rock, such as tunnels, caverns and shafts generally involve so large volumes that the properties of the rock mass cannot be measured in the laboratory, and seldom in the field. Therefore, the rock mass properties have to be determined mainly from observations in the field.
This web page gives you information on how field observations can be performed and used in practical rock engineering. The Rock Mass index (RMi) system has been developed as a tool in this field. Some parts of the RMi system are also described in the Handbook on Engineering geology and rock mechanics, issued by the Norwegian Rock Group affiliated ISRM and IAEG. Also the textbook Rock Engineering, now in a Second edition contains useful information on classification systems, including the RMi system.
The rockmass.net website has also information on other items related to engineering geology, rock engineering and design, as well as to rock mechanics for information and help to those involved in applied geology in rock constructions.
B. Information on the RockMass company
The RockMass consulting company works in the fields of engineering geology and rock engineering with vast Scandinavian and international experience.
C. Information on the author of the rockmass.net site
Dr. Arild Palmström, the author of this web site, has a M.Sc. from the Norwegian Technical University of Norway in 1967 and Ph.D. from the Oslo University, Norway in1995. He has more than 40 years of experience in applied geology, rock engineering and design.
ContactPublished on March 12 2011
Mobile: +47 918 29 909
Information on errors, comments, or suggestions for content or layout etc. may be sent to:
Some Useful InformationPublished on March 12 2011
- Technical units used in rock engineering.
- English – metric units
- Definitions of rock engineering and engineering geological expressions and terms.
- A list of ISRM (International Society for Rock Mechanics) Suggested methods for laboratory testing, field measurements, etc.
The book on Rock Engineering, second edition gives useful information in the planning, design and construction of rock excavations. You may also take a look at the contents of the book-second edition and its layout and structure.
- On Norwegian constructions in rock, rock engineering and design of constructions in rock: www.tunnel.no
- Norway’s largest consulting company with vast experience in engineering geology, rock engineering and geotechnical engineering: http://www.norconsult.com.
- Norwegian Geotechnical Institute (NGI) http://www.NGI.no
- Information on tunnel constructions in Norway longest tunnels: http://www.lotsberg.net/
- The acrobat reader program of pdf files: www.adobe.com/products/acrobat/readermain.html
- The journal Tunnels and Underground Space Technology (TUST), the official journal for ITA (International Tunnelling Association): www.elsevier.com/locate/tust
- The International Society for Rock Mechanics (ISRM): www.isrm.net
- The International Association for Engineering Geology and Environment (IAEG): www.iaeg.info
- Hoek’s corner www.rocscience.com/education/hoeks_corner on rock engineering items
On Norwegian Rock ConstructionsPublished on March 12 2011
Norway is a mountainous country with 5 mill. inhabitants. Located between 58o and 71o north, it has an area of 324 000 km². Rock construction has played an important role in this country during the last 100 years; first for hydropower development, then for transport and water supply and later for oil development.
Over the years, more than 5000km of tunnels have been excavated, probably the world record compared with the country’s size and population. Click here to see a short history of Norwegian tunneling
The frequent use of the underground for various purposes has generated some Norwegian specialties in rock constructions, such as:
- unlined pressure shafts and pressure tunnels (for hydropower);
- air cushion surge chambers in rock (for hydropower);
- lake taps by piercing to the lake bottom with the tunnel (for utilizing a larger volume in the reservoir lake for hydropower);
- subsea tunnels (i.e., tunnels passing beneath lake or sea bottom);
- storage caverns in rock;
- effective sealing of water inflows by grouting.
Subsea tunnels are tunnels which pass under the sea, rivers, and lakes. Lake taps are tunnels, which make a hole-through (piercing) to the sea or lake bottom.
Some information on these items and on Norwegian rock construction activities can be found in:
- The list of some road tunnels in Norway up to 2002. (See also http://www.lotsberg.net)
- The annual volumes of underground excavations in Norway
- The list of some underground hydropower stations, large water tunnels and unlined surge chambers
- The paper on subsea tunnels and lake taps
- The table showing some of the unlined pressure water tunnels and shafts
- The paper on the Norwegian development and experience with unlined pressure tunnels and shafts
- The English abstract of the paper in Norwegian: slides in Norwegian tunnels
- The papers on world records in tunnelling progress at Sauda HPP and at Kjosnesfjorden hydropower plant
Obituaries of the following prominent Norwegian engineering geologists, internationally well-known:
- Professor Rolf Selmer-Olsen (1927 - 1989).
- Dr. Olav Torgeir Blindheim (1944 - 2005).
- Professor Dr. Tor Brekke (1934 - 2009)
For more information on these items and on activities in Norwegian rock construction, see www.tunnel.no
The Norwegian Tunnelling Society (NFF) together with the Norwegian Rock Mechanics Group (NBG) and Norwegian Geotechnical Society (NGF) arranges an annual conference on tunnelling, rock engineering/engineering geology and soil mechanics in November called the NFF Fall Conference.
Some Published PapersPublished on March 12 2011
Various papers on rock engineering, design and construction. From time to time, additional papers or summary of papers will be presented. The papers (in pdf-format) cover the following items:
1. Swelling clays in seams and faults:
- Stability problems in tunnels caused by seams and zones with swelling clay and a method to measure the swelling activity and pressure of the swelling material
2. Hydropower planning and construction, and experience : (see also the tag 'Some designs' )
- The engineering geological planning and design of the 110 MW Tjodan power plant with an unlined pressure shaft with 950m head located in gneiss excavated by TBM.
- Seminars on hydropower planning and development, arranged by the Norwegian Export Council in Spain (1989), presented in Spanish and in India (1990)
- The paper "The Design of Unlined Tunnels and Shafts - 100 years of Norwegian experience" gives a state-of-the-art on the application of unlined waterways and recommendation on mainenance.
3. Various items:
- Case histories in the design and construction of underground structures.
- Engineering geology applied in the planning of the Lyse one-lane road tunnel
- The concept study of the Petromine project: 50km long undersea tunnels from the shore to the Troll oilfield for bringing the oil on shore.
- Oslo, the capital city of Norway has numerous tunnels and caverns in rock as shown in two papers describing “The Oslo underground” and “The use of the underground in Oslo”
- A paper on how engineering geology is practised in Norway
- The paper Rock engineering and tunnelling - A Nordic appoach describes the whole sequence from investigation through design to tunnel construction, including water sealing by grouting.
Several papers on Undersea tunnels and on Unlined pressure tunnels are presented under the tag 'Some designs'.
Publication ReferencesPublished on March 12 2011
LISTS on References of published papers
- The file References of published papers in the fields of geology, engineering geology, rock mechanics, rock engineering and rock design now contains more than 2100 different references. The list will be updated from time to time.
- References of papers published by Dr. Palmström.
Papers on RMiPublished on March 12 2011
Palmström A.: RMi – a rock mass characterization system for rock engineering purposes. Ph.D. thesis, Oslo University, Norway, 1995, 400 p.
Palmström A.: Characterizing the strength of rock masses for use in design of underground structures. Int. Conf. on Design and Construction of Underground Structures, New Delhi, 1995.
Palmström A.: Characterizing rock burst and squeezing by the rock mass index. Int. Conf. on Design and Construction of Underground Structures, New Delhi, 1995.
Palmström A.: RMi - a system for characterizing rock mass strength for use in rock engineering. Journal of Rock Mechanics and Tunnelling Technology, Vol. 1, Number 2, 1995, pp. 69-108.
Palmström A.: RMi - a new practical characterization system for use in rock engineering. Conference Svenska Bergmekanikdagen 1996, Stockholm, pp. 39-63.
Palmström A.: The rock mass index (RMi) applied in rock mechanics and rock engineering. Journal of Rock Mechanics and Tunnelling Technology, Vol. 2, Number 1, 1996.
Palmström A.: Characterizing rock masses by the RMi for use in practical rock engineering. Part 1: The development of the rock mass index (RMi). Tunnelling and Underground Space Technology, Vol. 11, No. 2, pp. 175-186, 1996.
Palmström A.: Characterizing rock masses by the RMi for use in practical rock engineering. Part 2: Some practical applications of the rock mass index (RMi). Tunnelling and Underground Space Technology, Vol. 11, No. 3, pp. 287-303, 1996.
Palmström A.: A new method to characterize rock masses for applications in rock engineering. Norwegian annual conference, Bergmekanikkdagen, 1996, Oslo, 27 p.
Palmström A.: Collection and use of geological data in rock engineering. ISRM News, 1997, pp. 21- 25.
Palmström A.: Characterization of rock masses by the RMi for use in practical rock engineering. (in Spanish). Ingeo Tuneles, volume 2, in series Ingenieria de tuneles, Madrid, 1999, pp. 79 – 107.
Palmström A. and Nilsen B.: Engineering Geology and Rock Engineering. Handbook. Norwegian Tunnelling Society, 2000, 250 p. See Useful information under Miscellaneous tag
Hval O.: Comparison between the engineering geological classification systems RMR, Q and RMi – experience from practical applications in the Tåsen and the Svartdal road tunnels (in Norwegian), Cand.scient. thesis, Oslo University, Norway, December 2000, 230 pages. See abstract
Palmström, A.: 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.
Nilsen B., Shrestha G.L., Panthi K.K., Holmøy K.H. and Olsen V.: RMR vs Q vs RMi. Tunnels & Tunnelling, May 2003, pp. 45 – 48.
Ph.D. Thesis on RMiPublished on March 12 2011
RMi - A Rock Mass Characterization System For Rock Engineering Purposes
Ph.D. thesis by Arild Palmström
Table of Contents
Appendix 1: On joints and jointing
Appendix 2: On faults and weakness zones
Appendix 10: Symbols used
Click to see the complete table of contents of the Ph.D. thesis
VariousPublished on March 12 2011
Some DesignsPublished on March 11 2011
Examples on some special rock constructions
A. Unlined water tunnels and shafts with moderate to high pressures
A lined tunnel is a tunnel where the surface is covered (by concrete or concrete and steel). Most often used for concrete lined tunnels. Covers also tunnels with steel pipe imbedded in concrete. The expression ‘lined’ was launched before sprayed concrete (shotcrete) had been introduced as support in tunnels. Today, shotcrete also forms lining when shotcrete is applied on the entire roof and walls.
Unlined tunnels are tunnels without support or with rock bolts, mesh, straps, or when shotcrete has been applied only on the parts of the tunnel surface. Unlined tunnels are appropriate in good and fair rockmass conditions. In parts where local poor rockmass zones occur, concrete or shotcrete lining is used. This is described here
For a typical low-head pressure tunnel, the hydraulic head inside the pressure tunnel might be in the range of 40m to 100m, while high-head pressure tunnels have heads of 300m to more than 1000m.
The following papers deal with unlined pressure tunnels or shafts:
Palmström A.: Norwegian design and construction experience of unlined pressure shafts and tunnels. Int. Conf. on Hydropower, Oslo, 1987, 13 p.
Palmström A.: Unlined high pressure tunnels and shafts. In Norwegian Tunnelling Today, 1988. Tapir Publishers, Trondheim, Norway, pp. 73 – 75.
Aasen O., Odegaard H. and Palmstrom A. (2013): Planning of pressurized headrace tunnel in Albania. In Norwegian Hydropower Tunnelling series, Publ. no. 22, 8p.
Palmström A. and Broch E. (2017): The design of unlined tunnels and shafts - 100 years of Norwegian experience. Presented in the journal Hydropower & Dams.
B. Unlined air cushion surge chambers
An air cushion surge chamber is used for damping surges in the headrace pressure tunnel of and underground hydropower plant. It replaces the conventional, open surge chamber or surge shaft.
Data on some air cushion surge chambers are given here
C. Subsea tunnels and lake taps
Subsea tunnels comprise tunnels, which pass below rivers, lakes or sea bottom. Such tunnels can be road or railway tunnels, or water conveying tunnels.
“Lake tap” or submerged tunnel piercing means hole-through from a tunnel to the sea or lake bottom. Lake taps are used in hydropower where the headrace tunnel may have its intake through the piercing. Data on some lake taps are given here
Papers published on subsea tunnels are found in the following links:
Palmström A.: Geo-investigation and advanced tunnel excavation technique important for the Vardø subsea road tunnel. Int. symp. on Low Cost Road Tunnels, Oslo 1984, 15 p.
Lynneberg T.L., Palmström A., Roska S. and Carstens K.J.: Geology, design, construction and maintenance of Vardö sub-sea road tunnel. Int. conf. on Strait Crossings, Stavanger, Norway, 1986, pp. 623 – 641.
Palmström A.: Sub-sea rock tunnels. Invited paper at the Int. conf. on Strait Crossings, Stavanger, Norway, 1986, pp. 111 – 139.
Holestöl K. and Palmström A.: Subsea tunnelling for oil: The Petromine concept. Tunnelling and Underground Space Technology. Vol. 2, No. 4, 1987, 31.1 - 31.31.
Palmström A.: Subsea tunnels. In Norwegian Tunnelling Today, 1988. Tapir Publishers, Trondheim, Norway, pp. 93 – 96.
Palmström A.: Norwegian experience with subsea tunnels. Int. conf. on Tunnels and Water. Madrid, 1988. A.A. Balkema publishers, Rotterdam. 8 p.
Palmström A.: Introduction to Norwegian subsea tunnelling. Publ. No. 8, issued by the Norwegian Soil and Rock Engineering Association, 1992, pp. 8 – 12.
Palmström A. and Naas R.: Norwegian subsea tunnelling - rock excavation and support techniques. Int. Symp. on Technology of bored tunnels under deep waterways, Copenhagen, 1993, pp. 201 – 225.
Palmström A.: The challenge of subsea tunnelling. Tunnelling and Underground Space Technology, Vol. 9, No. 2, 1994, pp. 145 – 150.
Palmström A. and Naas R.: Under the sea in Norway. World Tunnelling, November 1995, pp. 353 – 360.
Palmström A. and Skogheim A.: New Milestones in subsea blasting at water depth of 55 m. Tunnelling and Underground Space Technology, Vol. 15, No. 1, 1999, pp. 65 – 69.
Nilsen B., Palmström A. and Stille H.: Quality control of a sub-sea tunnel project in complex ground conditions. ITA World Tunnel Congress '99, Oslo, pp. 137 – 145.
Holmöy K., Lien J.E. and Palmström A.: Going sub-sea on the brink of the continental shelf. Tunnels & Tunnelling International, May 1999, pp. 25 - 30.
Palmström A., Stille H. and Nilsen B.: The Fröya tunnel – a sub-sea road tunnel in complex ground conditions. Swedish annual rock Mechanics conference, Svenska Bergmekanikdagen, 2000, pp. 19 – 30.
Nilsen B. and Palmström A.: Stability and water leakage of hard rock subsea tunnels. Conf. on Modern Tunneling Science and Technology, Adachi et al. (eds), 2001, Kyoto, Japan, pp. 497-502.
Palmstrom A. and Huang Z.: Application of Norwegian Subsea Tunnel Experience to Construction of Xiamen Xiang’an Subsea Tunnel. Int. symp. on Construction techniques of subsea tunnels, Nov. 6-8, 2007, Xiamen, China. 12 p.
Nilsen B. and Palmstrom A. (2013): Methodology for predicting and handling challenging rock mass conditions in hard rock subsea tunnels. Intn. conf. on Strait Crossings, Bergen, Norway, 11p.