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Potential topics for research and development in underground engineering
PLANNING AND DEVELOPMENT
Potential Topics for Research and Development in Underground Engineering The Underground Technology Research Council Subcommittee on Research and Development Needs
A b s t r a c t - - T h e Underground Technology Research Council Subcommittee on Research and Development Needs has conducted a survey to identify R & D needed in the U.S. to improve thepractice of underground engineering. This report summarizes the responses of nearly 50 practitioners of underground engineering to a questionnaire developed by the subcommittee; and presents the 15 highest-ranking topics in order of their priority, as determined by the entire sample.
Introduction he goal ofthe Underground Technology Research Council Subcommittee on Research and Development Needs is to seek opinions and consensus on research and development t h a t can improve the practice ofunderground engineeringinthe U.S., and to publish its findings for the benefit of researchers, practitioners, and funding authorities. To determine current priority topics, the Subcommittee started with a long list of topics and eventually, through discussions and formal evaluations, pared the list down to 20. Some topics were ellmlnated because development had already started on the topic. For example, an early item on the list was a recognition of the need for implementation of trenchless installation of utilities; there is now an association in the U.S. established to promote trenchless construction.
T
The Underground Technology Resarch Council (UTRC) is sponsored by the American Society of Civil Engineers. Members of the WI~C Subcommittee on Research and Development Needs are: Birger Schmidt (Chairman), Ter Brekke, Terence McCuster, Gregg Korbin, Michael Hardy, Francois Henze, George Williamson, John Bischoff, with Joe Sperry as UTRC contact member. Present address for the Subcommittee is c/o Birger Schmidt, Parsons Brinckerhoff, 303 Second Street, Suite 700 North, San Francisco, CA 941071317, U.S.A.
The listof 20 potentialresearch and development topics was submitted for evaluation by nearly 200 practitioners ofunderground works, and 49 answers were recorded. The answers came from a relatively wide spectrum of the industry, as follows: 17 independent consultants, practicing in underground works 10 contractors 9 designers of underground works 6 manufacturers of equipment and materials 4 researchers and professors 3 unclassified. Given this participation, it may be said that the opinions represent the point of view of practitioners rather than an academic viewpoint. The participants were asked to rate the 20 topics in t e r m s of the relative priority level of each topic, considering both the potential beneficial impact of successful research and development and the probability of success within a reasonable time frame. Each topicwas given a priority rating of ~aigh", "medium ~, "low", or "none ~. The Subcommittee then snmmarized the results, using appropriate weights, and was also able to determine trends based on the affiliation and practice of the respondent groups. Below are presented the 15 highestranldng topics in their order of priority, as determlned by the entire sample. The topics are presented in much the same way that they were presented to the participants, with a problem deftnition and a possible implementation
Tunnellingand UndergroundSpaceTechnology,Vol. 6, No. 3, pp. 283-286, 1991. Printed in Great Britain.
P~sumg~Le Soue-Comit$ sur la Recherche et le Ddveloppement de l'Underground Technology Research Council a d~fini les besoine en recherche et ddueloppement aux Etats-Unis pour promouuoir l'application des techniques en souterrain. Ce rapport donne let synth~se des rdponees de quelque 50 spdcialistes des travaux en souterrain au questionnaire mis au point par le sous-comit~, et prfisente, par ordre de prior@d, lee 15 th~mes prineipaux qui ee sont d~gag~s de l'~chantillon.
0886-7798/91 $3.00 + .00 (~ 1991 Pergamon Press pie
strategy. Comments indicate the priority level assigned by the different respondent groups. On the whole, different respondents assigned different priorities in a pattern much as could be expected. People from research and education listed as the three highest-ran kin g topics ~Probing ahead of advancing b m n e l face," ~Definition and scaling of rock mass parameters," a n d ' S h a l t llnln g design." On the other hand, contractors Hsted "Probing ahead of advancing Omnel face" (as did the academics), followed by ~Rapid ground support for TBM t.~mnels in rock, ~ and ~ m p r o v e m e n t of shotcreting practices." "Groundwater inflow into tnnnels ~Was a topic high on the lists of everybody except contractors and the academics. ~ a t e r - a s s i s t e d rock cutting ~ was universally low on the list, except for moderately high interest shown by contractors.
Potential Research and
Development Topics 1. Groundwater Inflow into Tunnels P r o b l e m : Groundwater is probably the cause of more rock (and soil) tunneling difficulties and cost overruns t h a n any other single factor. Really practical and reliable methods to predict inflOW into tnnnela from fractured rock masses have not been developed, and there appears to be little research oriented in this direction. There is a need to define simple parameters defining this problem, to find ways to determine these parameters, and to implement ways to predict the
283
inflow and effects of water, including how inflows diminish with time. Just as the Q- and RMR rock mass classification methods brought some semblance of order to the art of ground support selection, one could hope for similar order in the art of groundwater inflow prediction. I m p l e m e n t a t i o n : This could be the topic of a number of doctoral theses, incorporating both theoretical work and field observations. Rating: This topic was on the top of everyone's list, except contractors and academics, who scored the topic about sixth. Perhaps contractors do not consider water inflow such a big problem; perhaps academics believe the topic too difficult, or not amenable to academic methods?
2. Modern Grouting Techniques for Tunneling Problem: European grout applications often use m u c h higher grout injection pressures than are c o m m o n in the U.S.; different,thixotropic mixes are often used. Fracture grouting (claquage) in lieu of compaction grouting appears useful forimpermeabilization as well as for displacement grouting. Other relatively new grouting techniques include the use of ultrafine cement, and jet grouting. More vigorous use ofthese and other techniques could be helpful to underground in the U.S. Implementation: Through research of case historiesand the basics of the processes to define the relevant parameters; development of theories, guidelines, and specificationsfor design and construction. Rating: Rated second by designers, consultants and unclassified respondents; contractors,manufacturers, and academics rated this topic about fifth. 3. Rapid Ground Support for TBM Tunnels in Rock P r o b l e m : When tunneling with TBM in poor ground, t~ldngtime out to install initial s u p p o r t within the cramped spaces near the TBM head slows down the advance. There is a need to perfect methods ofinitial ground support installation close to the head. An effective method of placing a castin-place concrete lining while the TBM advances, without sacrificing advance rate, is also needed. Implementation: Implementation requires effortsby TBM manufacturers, experienced contractors, and concrete form manufacturers, encouraged by d e m a n d s for r a p i d c o m p l e t i o n specifications. Rating: This topicwas rated number one by contractors,and second to fourth by all others except independent consultants,w h o rated this topic seventh.
4. Long-term Performance of Ground Supports and Lining Systems P r o b l e m : Initial ground support components (bolts, dowels, shotcrete) have increasingly become essential parts of the permanent support system. However, little is known about the longevity of these components under various environmental conditions, considering the effects of corrosion and creep, and other effects. The longevity of these components must be determined during the design phase. Methods of verifying their continued satisfactory performance may also be reqnired. Long-term performance of standard permanent linings also needs documentation. I m p l e m e n t a t i o n : Identification of modes of long-term failure; theoretical assessment of factors of creep, corrosion, and environment on durability and continued functional performance, coupled with field data acquisition from older structures. Assessment of corrosion protection methods. R a t i n g : Rated second to fourth by all except contractors, who rated this topic sixth. As a matter of course, contractors rated long-term performance lower than did others. 5. Determination of Impediments to Innovation and Technology Transfer P r o b l e m : With a few exceptions, European and Japanese underground technology is and has been ahead of U.S. technology, and U.S. engineers and contractors have often been slow to learn. Technologies t h a t are currently available to the U.S. industry are not being used to the extent practicable. There is a need to discover what are the impediments to introduction or transfer of new technology, so they can be overcome. Implementation: Study of economic, sociological, technical, legal, and contracting practice issues that affect innovation and technology transfer. Rating:. Rated second by manufacturers and academics, and relatively high by all others except independent consultants, who rated this topic number 6. (Note: In m a n y cases, the point count for a group of respondents came out even for two or more topics. Hence, the reader will find apparent, but not real, discrepancies in t h e r a t i n g discussions.) 6. Probing Ahead of Advancing Tunnel Face Problem: Probing ahead is often required or desirable for a number of reasons, yet it almost invariably delays production. In addition, probing sometimes fails to define the problems sought. There is a need to develop technology for rapid probing without
284 TUN-~.T.T.~O~-D UNDERGROUNDSPACETECHNOLOGY
delay to the advancing t11nnel,and for recovering the m a x i m u m information from the probing effort. Implementation: Research to define the cirolm.qtances requiring probing ahead, and the benefits of probing; development of practical methods by makers of TBMs, drill tools and instruments. Technology transfer from the geophysical logging industry. R a t i n g : Rated second by manufacturers and academics, third by contractors, and fourth to sixth by all others.
7. Shaft Lining Design P r o b l e m : There are no generally accepted standards, nor even a suitable text book, that adequately deal with the design of shaft linings in the U.S. Standards developed by the German Coal Board are formulated for German coal mining conditions and are not generally applicable in the U.S. The Institute of Shaft Drilling Technology reportedly is developing a guide for the design of drilled-shaft liners, but there is a need for a more general guide. I m p l e m e n t a t i o n : Development of consensus standards by an appropriate professional group; preparation of textbook. Rating: Rated intermediate by most groups, but high by academics.
8. Improvement of Shotcreting Practices Problem: Goodgnidetmes exist for the design and application of ordinary shotcrete for underground support, but not for modern application of fiberreinforced shotcrete and shotcrete with microsilica or other ad mixtures. These have the potential for greater economy and performance. Implementation: Develop and publish guidelines, s t a n d a r d s and specifications for modern shotcrete design, analysis, and application. Publish data on economy, properties and p e r f o r m a n c e of v a r i o u s t y p e s of shotcrete. R a t i n g : Rated second by designers, contractors and manufacturers, but much lower by independent consultants, academics and others. 9. Improvement of Standards for Blasting Excavation P r o b l e m : Poor blasting practices result in excessive use of explosives, rock damage, and overbreak, resulting in excessive ground support and lining requirements. Good blasting remdts in better economy of construction and possibly better long-term performance. The great variety of modern explosives can match any requirement, and modern techniques are available to drill
Volume 6, Number 3, 1991
blast holes with precision (computer control), yet m a n y blasters do not u s e - p e r h a p s do not k n o w - - t h e s e techniques, and do not produce the desired results. I m p l e m e n t a t i o n : Develop standards for quality blasting t h a t can be used and referenced in contract documents; prepare standards for specifications that encourage quality blasting and the use of automated drilling equipment. R a t i n w This topic was given a relativelyhigh rating by designers,consultants, and manufacturers; it was rated m u c h lower by contractors,academics and others.
10. Improvement of Application of Geophysical Tools P r o b l e m : We consider all kinds of geophysical tools, applied from the ground surface, over water, in boreholes, or, for example, used along a tl~nnel wall. Geophysical tools are suitable for certain geologic environments, types ofprejects, and types of problems. They have often been used under circ~m~tances where they are not suited; as a result, they have been discredited and perhaps are not used as often as they should be. Their application is not well understood by most geotechnical and underground engineers. I m p l e m e n t a t i o n : Analysis of successful and unsuccessful applications; preparation of a practical guide to selection and use of geophysical tools, based on realistic expectations. R a t i n g : Given a relatively high rating by all groups except contractors and independent consultants. 11. Definition and Scaling of Rock Mass Parameters P r o b l e m : Definition of rock mass parameters is essential for successful analysis of underground structures. Rock mass parameters are usually assigned on an empirical basis, ignoring the size of the opening relative to discontinuity spacings. Analysis methods cannot succeed without regard to scale effects. Consider also that rock m a s s parameters by definition apply to a certain, large dom-ln of rock; application of rock mass strength by comparison to a calculated stress condition a t a p o i n t is not logically permitted. There is a need to circumvent the need to define rock mass strength parameters that realistically cannot be defined. I m p l e m e n t a t i o n : This is a major problem and involves issues of exploration, testing, analysis, and observations. It requires both theoretical and practically oriented academic research. R a t i n g : Academics, designers, and m-nufacturers rate this topic relatively high (academics near the top), whereas
Volume 6, Number 3, 1991
contractors and consultants rate it very low. Some academics and researchers have indicated a need to separate this topic into several related topics.
12. Effects of Groundwater on TBM Performance Problem: Water inflow at the face o f a TBM tlmne] often has an adverse effect on the advance rate. In order to facilitate better performance prediction, and to build and operate machines under wet conditions, it is desirable to discover and enumerate the ways in which water affects the work of the TBM; to estimate the effect of the water based on rock mass and TBM data; and to find ways to reduce these effects by proper TBM design. I m p l e m e n t a t i o n : Analysis of TBM components, effects of water on cutting, muck handling, wear, corrosion, and breakdowns; case history analyses. A related topic would be the determination of clay stickiness (which results in g~lmmlng up cutters and muck handling equipment), based on clay characteristics and water content. Rating: Rated intermediate by contractors, lower by all others. 13. Swelling and Slaking Rock Behavior P r o b l e m : ~ m n e l s through some clay-shales can result in slaking or swelling and extraordinary lining pressures (and, as a result, stuck shields). Prediction of the magnitude of this type of behavior based on laboratory test data still cannot be done reliably. Once we understand these rock types, perhaps we will learn to deal with then~ I m p l e m e n t a t i o n : Academic research based on case histories, sophisticated laboratory data, and theoretical development. Rating'.. Rated intermediate by everyone except independent consultants, who rated this topic low. 14. Improvements in Shaft Drilling Problem: Large-hole drilling is limited to some extent by the limited effectiveness of standard button-type cutters favored for shaft drilling; by difficulties in flushing cuttings across a large hole radius; and by the limited ability to contrel straightness and verticality, which is especially important for shafts that house hoisting equipment. Withproper flushingtechniques, disc cutters may be more effective than button cutters. I m p l e m e n t a t i o n : Development by equipment manufacturers and cooperatingshai~ drilllng contractors, coupled with academic efforts. Development of tools to measure and correct shaft deviations.
R a t i n ~ Rated intermediate to low by most, and very low by independent consultants.
15. Swelling and Consolidation of Clays around Tunnels P r o b l e m : Case histories have documented long-term consolidation settlements resulting from blnneli_nginclay. Though the problem is mathematically tractable, only the first steps have been taken to develop methods to predict long-term behavior of clays around tun. nels as a function of soil parameters and construction processes. I m p l e m e n t a t i o n : Academic study supported by exper/ments and field observations. Rating:. Rated intermediate by all.
The Runners-Up Listed briefly below are the five topics on the list t h a t did not make it through the final evaluation. Nonetheless, they are not without merit. • Use of|reproved and appropriate ceringtechniques (actually rated fairly high by academics and manufacturers; covered to a large measure by ASTM D 2113). • Stress-controlled rock behavior; rock bursts, popping, spAlling, berehole breakouts, as a function of rock characteristics. • Assessment of building damage resulting from tunneling settlements. • Seepage pressure effects on tunnels in sand; e.g., effect of a small c o h e s i o n on flowing soil conditions in the tunnel. • Water-assisted rock cutting (actually rated fairly high by contractors). Some topics t h a t did not make the top twenty were: • I m p r o v i n g rock discontinuity mapping, using photogrAmmettic techniques and computer graphics and statistics. • Classifying rock mass for the observational approach to tunneling--simpler than the Q and the RMR, useful in the field for day-to-day use (but not a substitute for design use). • Slurry trench stability, especially when the trench is immediately adjacent to existing structures. • Catching cost overruns; determining the common causes ofcest overruns in underground construction. • Effects of joint density on TBM performance. • Extruded concrete liners for tunnels in soils (perhaps their time hasn't arrived yet).
T L u ~ J , ~ a ANDUNDERGROUNDSPACE TECHNOLOGY285
Seismic effects on underground structures--how to prove that they are unimportant.
Additional Topics Respondents were asked to supply their own favorite research and development topics. Below are some of the suggestions: • Gassy ground--M most untreated in civil engineering literature; hard to detect, quantify, handle; transfer ofmlnlngtechnology ;new UTRC Subcommittee suggested. * Bolts, anchors or dowels in yielding rock or soil; how do they act, are they effective? • N o consensus on h o w shotcrete really behaves--in shear, bending or compression, or all three. • Use of geosynthetics in tunnels, including waterproofing liners; need to develop guidelines (other than some developed by manufacturers) for designers, contractors and mAnlLfacturerS. • I m p r o v i n g e a r l y s t r e n g t h of shotcrete.
Fluid transport of TBM muck (other t h a n for slurry shield tnnneling). • Cellular concrete (or grout) backfill, e.g., around steel or concrete pipe placed in tlmnel; there is little unbiased information a v a i l a b l e on m i x e s , p l a c e m e n t m e t h o d s , u s e of bulkheads, interference from inflowing water, quality control, etc. • Case histories on the effectiveness of non-keyed, sloping joints for cast-in-place concrete linings. • TBM gyrescope alignment systenL •
Postscript The Subcommittee thanks all of those who cooperated in the development of this report by answering the questionnaire and through individual discussions. We hope that some people will find inspiration to start or continue work along one or another of the avenues suggested; perhaps this survey will provide someone the backup or justification needed to obtain funding for a favored research topic. By neces-
286 TU~rSELLINOANDUNDER(~ROUNDSPACETECHNOLOGY
sity, the survey employed a limited number of topics believed to be of relatively broad interest; hidden within and on the fringes of these topics are myriad interesting, detailed subtopics. The interested researcher is encouraged to search for and explore these "fringe ~ topics. Details of the analyses carried out on the responses m a y be obtained from Birger Schmldt (415-243-4629). Anyone interested in pursuing one of these topics--for example, through a UTRC Subcommlttcc should call UTRC's Chairman, John W. Critchfield (808235-4118) or UTRC's Technical Committee Coordinator, David Mann (415243-4635). This is the first effort of this nature completed by the UTRC. Depending on the perceived need and the interest generated by this effort, we m a y follow up on this story in a few years to discover whether the suggested topics have, indeed, been subject to development, and whether new topics of pressing interest have popped up. Until then, good hunting; we welcome your calls and letters. []
Volume 6, Number 3, 1991
Potential Topics for Research and Development in Underground Engineering The Underground Technology Research Council Subcommittee on Research and Development Needs
A b s t r a c t - - T h e Underground Technology Research Council Subcommittee on Research and Development Needs has conducted a survey to identify R & D needed in the U.S. to improve thepractice of underground engineering. This report summarizes the responses of nearly 50 practitioners of underground engineering to a questionnaire developed by the subcommittee; and presents the 15 highest-ranking topics in order of their priority, as determined by the entire sample.
Introduction he goal ofthe Underground Technology Research Council Subcommittee on Research and Development Needs is to seek opinions and consensus on research and development t h a t can improve the practice ofunderground engineeringinthe U.S., and to publish its findings for the benefit of researchers, practitioners, and funding authorities. To determine current priority topics, the Subcommittee started with a long list of topics and eventually, through discussions and formal evaluations, pared the list down to 20. Some topics were ellmlnated because development had already started on the topic. For example, an early item on the list was a recognition of the need for implementation of trenchless installation of utilities; there is now an association in the U.S. established to promote trenchless construction.
T
The Underground Technology Resarch Council (UTRC) is sponsored by the American Society of Civil Engineers. Members of the WI~C Subcommittee on Research and Development Needs are: Birger Schmidt (Chairman), Ter Brekke, Terence McCuster, Gregg Korbin, Michael Hardy, Francois Henze, George Williamson, John Bischoff, with Joe Sperry as UTRC contact member. Present address for the Subcommittee is c/o Birger Schmidt, Parsons Brinckerhoff, 303 Second Street, Suite 700 North, San Francisco, CA 941071317, U.S.A.
The listof 20 potentialresearch and development topics was submitted for evaluation by nearly 200 practitioners ofunderground works, and 49 answers were recorded. The answers came from a relatively wide spectrum of the industry, as follows: 17 independent consultants, practicing in underground works 10 contractors 9 designers of underground works 6 manufacturers of equipment and materials 4 researchers and professors 3 unclassified. Given this participation, it may be said that the opinions represent the point of view of practitioners rather than an academic viewpoint. The participants were asked to rate the 20 topics in t e r m s of the relative priority level of each topic, considering both the potential beneficial impact of successful research and development and the probability of success within a reasonable time frame. Each topicwas given a priority rating of ~aigh", "medium ~, "low", or "none ~. The Subcommittee then snmmarized the results, using appropriate weights, and was also able to determine trends based on the affiliation and practice of the respondent groups. Below are presented the 15 highestranldng topics in their order of priority, as determlned by the entire sample. The topics are presented in much the same way that they were presented to the participants, with a problem deftnition and a possible implementation
Tunnellingand UndergroundSpaceTechnology,Vol. 6, No. 3, pp. 283-286, 1991. Printed in Great Britain.
P~sumg~Le Soue-Comit$ sur la Recherche et le Ddveloppement de l'Underground Technology Research Council a d~fini les besoine en recherche et ddueloppement aux Etats-Unis pour promouuoir l'application des techniques en souterrain. Ce rapport donne let synth~se des rdponees de quelque 50 spdcialistes des travaux en souterrain au questionnaire mis au point par le sous-comit~, et prfisente, par ordre de prior@d, lee 15 th~mes prineipaux qui ee sont d~gag~s de l'~chantillon.
0886-7798/91 $3.00 + .00 (~ 1991 Pergamon Press pie
strategy. Comments indicate the priority level assigned by the different respondent groups. On the whole, different respondents assigned different priorities in a pattern much as could be expected. People from research and education listed as the three highest-ran kin g topics ~Probing ahead of advancing b m n e l face," ~Definition and scaling of rock mass parameters," a n d ' S h a l t llnln g design." On the other hand, contractors Hsted "Probing ahead of advancing Omnel face" (as did the academics), followed by ~Rapid ground support for TBM t.~mnels in rock, ~ and ~ m p r o v e m e n t of shotcreting practices." "Groundwater inflow into tnnnels ~Was a topic high on the lists of everybody except contractors and the academics. ~ a t e r - a s s i s t e d rock cutting ~ was universally low on the list, except for moderately high interest shown by contractors.
Potential Research and
Development Topics 1. Groundwater Inflow into Tunnels P r o b l e m : Groundwater is probably the cause of more rock (and soil) tunneling difficulties and cost overruns t h a n any other single factor. Really practical and reliable methods to predict inflOW into tnnnela from fractured rock masses have not been developed, and there appears to be little research oriented in this direction. There is a need to define simple parameters defining this problem, to find ways to determine these parameters, and to implement ways to predict the
283
inflow and effects of water, including how inflows diminish with time. Just as the Q- and RMR rock mass classification methods brought some semblance of order to the art of ground support selection, one could hope for similar order in the art of groundwater inflow prediction. I m p l e m e n t a t i o n : This could be the topic of a number of doctoral theses, incorporating both theoretical work and field observations. Rating: This topic was on the top of everyone's list, except contractors and academics, who scored the topic about sixth. Perhaps contractors do not consider water inflow such a big problem; perhaps academics believe the topic too difficult, or not amenable to academic methods?
2. Modern Grouting Techniques for Tunneling Problem: European grout applications often use m u c h higher grout injection pressures than are c o m m o n in the U.S.; different,thixotropic mixes are often used. Fracture grouting (claquage) in lieu of compaction grouting appears useful forimpermeabilization as well as for displacement grouting. Other relatively new grouting techniques include the use of ultrafine cement, and jet grouting. More vigorous use ofthese and other techniques could be helpful to underground in the U.S. Implementation: Through research of case historiesand the basics of the processes to define the relevant parameters; development of theories, guidelines, and specificationsfor design and construction. Rating: Rated second by designers, consultants and unclassified respondents; contractors,manufacturers, and academics rated this topic about fifth. 3. Rapid Ground Support for TBM Tunnels in Rock P r o b l e m : When tunneling with TBM in poor ground, t~ldngtime out to install initial s u p p o r t within the cramped spaces near the TBM head slows down the advance. There is a need to perfect methods ofinitial ground support installation close to the head. An effective method of placing a castin-place concrete lining while the TBM advances, without sacrificing advance rate, is also needed. Implementation: Implementation requires effortsby TBM manufacturers, experienced contractors, and concrete form manufacturers, encouraged by d e m a n d s for r a p i d c o m p l e t i o n specifications. Rating: This topicwas rated number one by contractors,and second to fourth by all others except independent consultants,w h o rated this topic seventh.
4. Long-term Performance of Ground Supports and Lining Systems P r o b l e m : Initial ground support components (bolts, dowels, shotcrete) have increasingly become essential parts of the permanent support system. However, little is known about the longevity of these components under various environmental conditions, considering the effects of corrosion and creep, and other effects. The longevity of these components must be determined during the design phase. Methods of verifying their continued satisfactory performance may also be reqnired. Long-term performance of standard permanent linings also needs documentation. I m p l e m e n t a t i o n : Identification of modes of long-term failure; theoretical assessment of factors of creep, corrosion, and environment on durability and continued functional performance, coupled with field data acquisition from older structures. Assessment of corrosion protection methods. R a t i n g : Rated second to fourth by all except contractors, who rated this topic sixth. As a matter of course, contractors rated long-term performance lower than did others. 5. Determination of Impediments to Innovation and Technology Transfer P r o b l e m : With a few exceptions, European and Japanese underground technology is and has been ahead of U.S. technology, and U.S. engineers and contractors have often been slow to learn. Technologies t h a t are currently available to the U.S. industry are not being used to the extent practicable. There is a need to discover what are the impediments to introduction or transfer of new technology, so they can be overcome. Implementation: Study of economic, sociological, technical, legal, and contracting practice issues that affect innovation and technology transfer. Rating:. Rated second by manufacturers and academics, and relatively high by all others except independent consultants, who rated this topic number 6. (Note: In m a n y cases, the point count for a group of respondents came out even for two or more topics. Hence, the reader will find apparent, but not real, discrepancies in t h e r a t i n g discussions.) 6. Probing Ahead of Advancing Tunnel Face Problem: Probing ahead is often required or desirable for a number of reasons, yet it almost invariably delays production. In addition, probing sometimes fails to define the problems sought. There is a need to develop technology for rapid probing without
284 TUN-~.T.T.~O~-D UNDERGROUNDSPACETECHNOLOGY
delay to the advancing t11nnel,and for recovering the m a x i m u m information from the probing effort. Implementation: Research to define the cirolm.qtances requiring probing ahead, and the benefits of probing; development of practical methods by makers of TBMs, drill tools and instruments. Technology transfer from the geophysical logging industry. R a t i n g : Rated second by manufacturers and academics, third by contractors, and fourth to sixth by all others.
7. Shaft Lining Design P r o b l e m : There are no generally accepted standards, nor even a suitable text book, that adequately deal with the design of shaft linings in the U.S. Standards developed by the German Coal Board are formulated for German coal mining conditions and are not generally applicable in the U.S. The Institute of Shaft Drilling Technology reportedly is developing a guide for the design of drilled-shaft liners, but there is a need for a more general guide. I m p l e m e n t a t i o n : Development of consensus standards by an appropriate professional group; preparation of textbook. Rating: Rated intermediate by most groups, but high by academics.
8. Improvement of Shotcreting Practices Problem: Goodgnidetmes exist for the design and application of ordinary shotcrete for underground support, but not for modern application of fiberreinforced shotcrete and shotcrete with microsilica or other ad mixtures. These have the potential for greater economy and performance. Implementation: Develop and publish guidelines, s t a n d a r d s and specifications for modern shotcrete design, analysis, and application. Publish data on economy, properties and p e r f o r m a n c e of v a r i o u s t y p e s of shotcrete. R a t i n g : Rated second by designers, contractors and manufacturers, but much lower by independent consultants, academics and others. 9. Improvement of Standards for Blasting Excavation P r o b l e m : Poor blasting practices result in excessive use of explosives, rock damage, and overbreak, resulting in excessive ground support and lining requirements. Good blasting remdts in better economy of construction and possibly better long-term performance. The great variety of modern explosives can match any requirement, and modern techniques are available to drill
Volume 6, Number 3, 1991
blast holes with precision (computer control), yet m a n y blasters do not u s e - p e r h a p s do not k n o w - - t h e s e techniques, and do not produce the desired results. I m p l e m e n t a t i o n : Develop standards for quality blasting t h a t can be used and referenced in contract documents; prepare standards for specifications that encourage quality blasting and the use of automated drilling equipment. R a t i n w This topic was given a relativelyhigh rating by designers,consultants, and manufacturers; it was rated m u c h lower by contractors,academics and others.
10. Improvement of Application of Geophysical Tools P r o b l e m : We consider all kinds of geophysical tools, applied from the ground surface, over water, in boreholes, or, for example, used along a tl~nnel wall. Geophysical tools are suitable for certain geologic environments, types ofprejects, and types of problems. They have often been used under circ~m~tances where they are not suited; as a result, they have been discredited and perhaps are not used as often as they should be. Their application is not well understood by most geotechnical and underground engineers. I m p l e m e n t a t i o n : Analysis of successful and unsuccessful applications; preparation of a practical guide to selection and use of geophysical tools, based on realistic expectations. R a t i n g : Given a relatively high rating by all groups except contractors and independent consultants. 11. Definition and Scaling of Rock Mass Parameters P r o b l e m : Definition of rock mass parameters is essential for successful analysis of underground structures. Rock mass parameters are usually assigned on an empirical basis, ignoring the size of the opening relative to discontinuity spacings. Analysis methods cannot succeed without regard to scale effects. Consider also that rock m a s s parameters by definition apply to a certain, large dom-ln of rock; application of rock mass strength by comparison to a calculated stress condition a t a p o i n t is not logically permitted. There is a need to circumvent the need to define rock mass strength parameters that realistically cannot be defined. I m p l e m e n t a t i o n : This is a major problem and involves issues of exploration, testing, analysis, and observations. It requires both theoretical and practically oriented academic research. R a t i n g : Academics, designers, and m-nufacturers rate this topic relatively high (academics near the top), whereas
Volume 6, Number 3, 1991
contractors and consultants rate it very low. Some academics and researchers have indicated a need to separate this topic into several related topics.
12. Effects of Groundwater on TBM Performance Problem: Water inflow at the face o f a TBM tlmne] often has an adverse effect on the advance rate. In order to facilitate better performance prediction, and to build and operate machines under wet conditions, it is desirable to discover and enumerate the ways in which water affects the work of the TBM; to estimate the effect of the water based on rock mass and TBM data; and to find ways to reduce these effects by proper TBM design. I m p l e m e n t a t i o n : Analysis of TBM components, effects of water on cutting, muck handling, wear, corrosion, and breakdowns; case history analyses. A related topic would be the determination of clay stickiness (which results in g~lmmlng up cutters and muck handling equipment), based on clay characteristics and water content. Rating: Rated intermediate by contractors, lower by all others. 13. Swelling and Slaking Rock Behavior P r o b l e m : ~ m n e l s through some clay-shales can result in slaking or swelling and extraordinary lining pressures (and, as a result, stuck shields). Prediction of the magnitude of this type of behavior based on laboratory test data still cannot be done reliably. Once we understand these rock types, perhaps we will learn to deal with then~ I m p l e m e n t a t i o n : Academic research based on case histories, sophisticated laboratory data, and theoretical development. Rating'.. Rated intermediate by everyone except independent consultants, who rated this topic low. 14. Improvements in Shaft Drilling Problem: Large-hole drilling is limited to some extent by the limited effectiveness of standard button-type cutters favored for shaft drilling; by difficulties in flushing cuttings across a large hole radius; and by the limited ability to contrel straightness and verticality, which is especially important for shafts that house hoisting equipment. Withproper flushingtechniques, disc cutters may be more effective than button cutters. I m p l e m e n t a t i o n : Development by equipment manufacturers and cooperatingshai~ drilllng contractors, coupled with academic efforts. Development of tools to measure and correct shaft deviations.
R a t i n ~ Rated intermediate to low by most, and very low by independent consultants.
15. Swelling and Consolidation of Clays around Tunnels P r o b l e m : Case histories have documented long-term consolidation settlements resulting from blnneli_nginclay. Though the problem is mathematically tractable, only the first steps have been taken to develop methods to predict long-term behavior of clays around tun. nels as a function of soil parameters and construction processes. I m p l e m e n t a t i o n : Academic study supported by exper/ments and field observations. Rating:. Rated intermediate by all.
The Runners-Up Listed briefly below are the five topics on the list t h a t did not make it through the final evaluation. Nonetheless, they are not without merit. • Use of|reproved and appropriate ceringtechniques (actually rated fairly high by academics and manufacturers; covered to a large measure by ASTM D 2113). • Stress-controlled rock behavior; rock bursts, popping, spAlling, berehole breakouts, as a function of rock characteristics. • Assessment of building damage resulting from tunneling settlements. • Seepage pressure effects on tunnels in sand; e.g., effect of a small c o h e s i o n on flowing soil conditions in the tunnel. • Water-assisted rock cutting (actually rated fairly high by contractors). Some topics t h a t did not make the top twenty were: • I m p r o v i n g rock discontinuity mapping, using photogrAmmettic techniques and computer graphics and statistics. • Classifying rock mass for the observational approach to tunneling--simpler than the Q and the RMR, useful in the field for day-to-day use (but not a substitute for design use). • Slurry trench stability, especially when the trench is immediately adjacent to existing structures. • Catching cost overruns; determining the common causes ofcest overruns in underground construction. • Effects of joint density on TBM performance. • Extruded concrete liners for tunnels in soils (perhaps their time hasn't arrived yet).
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Seismic effects on underground structures--how to prove that they are unimportant.
Additional Topics Respondents were asked to supply their own favorite research and development topics. Below are some of the suggestions: • Gassy ground--M most untreated in civil engineering literature; hard to detect, quantify, handle; transfer ofmlnlngtechnology ;new UTRC Subcommittee suggested. * Bolts, anchors or dowels in yielding rock or soil; how do they act, are they effective? • N o consensus on h o w shotcrete really behaves--in shear, bending or compression, or all three. • Use of geosynthetics in tunnels, including waterproofing liners; need to develop guidelines (other than some developed by manufacturers) for designers, contractors and mAnlLfacturerS. • I m p r o v i n g e a r l y s t r e n g t h of shotcrete.
Fluid transport of TBM muck (other t h a n for slurry shield tnnneling). • Cellular concrete (or grout) backfill, e.g., around steel or concrete pipe placed in tlmnel; there is little unbiased information a v a i l a b l e on m i x e s , p l a c e m e n t m e t h o d s , u s e of bulkheads, interference from inflowing water, quality control, etc. • Case histories on the effectiveness of non-keyed, sloping joints for cast-in-place concrete linings. • TBM gyrescope alignment systenL •
Postscript The Subcommittee thanks all of those who cooperated in the development of this report by answering the questionnaire and through individual discussions. We hope that some people will find inspiration to start or continue work along one or another of the avenues suggested; perhaps this survey will provide someone the backup or justification needed to obtain funding for a favored research topic. By neces-
286 TU~rSELLINOANDUNDER(~ROUNDSPACETECHNOLOGY
sity, the survey employed a limited number of topics believed to be of relatively broad interest; hidden within and on the fringes of these topics are myriad interesting, detailed subtopics. The interested researcher is encouraged to search for and explore these "fringe ~ topics. Details of the analyses carried out on the responses m a y be obtained from Birger Schmldt (415-243-4629). Anyone interested in pursuing one of these topics--for example, through a UTRC Subcommlttcc should call UTRC's Chairman, John W. Critchfield (808235-4118) or UTRC's Technical Committee Coordinator, David Mann (415243-4635). This is the first effort of this nature completed by the UTRC. Depending on the perceived need and the interest generated by this effort, we m a y follow up on this story in a few years to discover whether the suggested topics have, indeed, been subject to development, and whether new topics of pressing interest have popped up. Until then, good hunting; we welcome your calls and letters. []
Volume 6, Number 3, 1991