43 Palmstrom on Case Histories (1)

8/3/2019 43 Palmstrom on Case Histories (1)

http://slidepdf.com/reader/full/43-palmstrom-on-case-histories-1 1/8

Design and Constructionof Underground Structures,New Delhi,23 - 25 February 1995

CASEHISTORIESINDESIGNUNDERGROUND

ANDCONSTRUCTIONOFSTRUCTURES

byArildPalmström,NorwegianGeotechnicallnstitute,Norway

Introduction

A case historyrerated to rock design and constructionis the documentation of ground condi-

tions and experience gained from the constructionof the structureand its behaviour during

usage. Aisodocumeniationof test results as wellas results fromback analysis are topics

included in such case histories'

In the report "Definitionof the most promising lines of research " presented by ISRM(1971)'correlationbetween the mechanical propertiesof rocks and geological and petrographicdata'

was among the highest priorityresearch subjects defined. In the same Iepoftit was also stated

that: ,,Atpresent timemost geologic ond prírographicdescriptionsof specimens or bodies ofrockare qualitative,whereãs rock mechånics determinationof mechanical properties of rock

are quantitative.Because many engineering decisions are based' on a combinationof geologic and rock mech-

anics data, it is importanlthat a more systematic means of combiningand correlatingthis

informationshould be develoPed'There is a need forbetter documentationand correlationof geological and petrographic data,

and corresponding mechanical propertydataobtaine- '

fromboth laboratoryspecimens and/or

rock masses, together withoperating e'xperience in the same rockmass, or the subsequent

performance {structurein}herockmass created by excavation'"

Thus, already early in the developmentof rock mechanics the importanceof establishing

general methods and systems for improved characterizationof rock masses together witha

common language for ihose "ngug"din engineering and constructionin rockwas clearly

expressed. ttris iequest has to some extent, been met by some of the classificationsystems'

but fewof them aå of a general character as they are mainlydirected towards a specific

engineering functionor design.

As there is no standard or specified standard how to workout case histories' the way theyhave been presented varies.hhispartlydepends on the pulpose they shall serve whichcan be:

-forinternal use for a specific excavationonly, as a documentationfor later use;

-foracertainpurposeorprojectofscientificcharacter;or-in connectionwiìhstandãrd procedures, requirementsor regulationconnected to the

project, whichmay involvecompilationof worksor data foundduring planning, follow-up

and/or construction.

Thus, case histories generally consist of experience gained duringconstructionof measufe-

ment, and include grãund ciaracterization,geometriðdimensions,the type of works carried



Types and applicationsof case histories

In many papers presented at conferences case histories are presented for example as "Con-structionexperience from the excavations works at a certain site" where contractors give anoverviewof his executionof the worksand what challenges he had to cope with.Such cases(see Fig. 1) wouldbe significantlyimproved if they had been worked outin cooperationwithengineering geologists who couldcontribute withinformationof the ground conditions.

On the 104 km new stretch throughthe Sierra Morenamountaineousregionbetween Brazatortas and Cordoba, there are no less than 15 tunnelsbetween 300 m and2,5 km long totalling15 km.

Rock qualityin the Sierra Morena is problematic.The mountains are

composed of an old quartzite formationwhich has weathered and erodedheavily throughthe ages. Nevertheless, all the tunnels have been de-signed as double track tubes ofup to 100 m2 in excavated cross-sectionand finishedto a'75 m2 internalcross-section.

They are excavated in the main by drill+ blast on a top heading and benchprogram andsupported principallyby Dramixsteel fibre reinforcedshotcrete, steel sets and rock bolts according to the NATMconcept'

Support comprised a 5 - 15 cm layer ofimmediate DramixzP30/.50 steelfibre reinforcedshotcrete. The dry shotcretingmethod is the one usedmostlyin Spain.

The final liningconsists of a 30 cm thickunreinforced in situ concretelayer.

Fig.1 Example of a case historyused in the book onshotcrete issued by Bekaert (1994)

Other cases are dealing withthe ground conditionsand the works made to solve stabilityproblems as is shown in the next section.

Designs in rock constructionare very often based on earlier experience gained fror.n 1) con-structions of similarprojects or 2) in similarrock conditions.The accumulated use of thisvast amountof experience is applied among others in the classificationsystems. Other applica-

tions are the use of old constructionexperience in new projects.

qé

nNdb¡-o.!l



The most valuable use of case histories is, perhaps, the sharing and exchange of experienceamong researchers.

To sum up, case historiesare mainlyused for:- Documentationof features and conditions to be applied in possible later renovation/re-

pairs/maintenance duringthe project's life.Such case historiesare generallynotavailable and thereforeof limitedinterest to others.

- Advancingthe state of the art in rock mechanics and rock engineering, for example as:> furtherdevelopment of classificationsystems;> development or improvementof engineering methods/calculations; and> improvinganalyticalmethods in rock mechanics.

- Communication/exchangeof geo data and experience.- The use of earlier experience in new constructionsfor assessment of the geological and

ground conditions.

Examples

In some text books,mainlyolder issues (Stini,1950, Müller,1963) the author has givenexamples, as shown in Fig. 2, of cases to illustratehow ground conditionsmay influenceonthe tunnelexcavationand stability.

I.s'st{t\r

I

Fig. 2 Two examples of cases presented by Stini1950).

One of the most usefulcollectionsof case histories has been presented by Cecilin his Ph.Dthesis (Cecil,l9l0)where he presented a documentationof the ground conditionsand rocksupport for 9l tunnels and caverns in Scandinavia. Figs, 4-5 give twoexamples of his work.These cases were in fact an importantsource of data for the development of the Q methodand this was stronglyacknowledged by the Barton et al. (1974):"Itis not usual to acknow-Iedge the contributionof publications.However, the fieldworkperformed by Cecil(1970) hasproved such a valuable source of informationfordeveloping this method that his contribtúionmust be speciallyacknowledged."



Cecil developed the followingguidelines forhis mapping of the ground conditions:

INFORM,A.TIONFORMATFORCASE LEGENDFOR TIME'STABILIIY-SUPPORTHISTORIES CLASSIFTCATION

1. project,location A st¿ble at blasting, no anticipatedfalls,no

2. Type of tu¡u¡elor room supportB, W = widthof opening,meters B minor lallsor overbreak at blasting, support

4. H = height of opening,meters not conside¡ed necessary forpreventionof5, .q, = area of opening,square meters loosening6. Nature of instability(rooffall,wallsli¡out, C stabte at blastilg,support ûranticipationof

overbreak, etc.); (stabilityclassification, looseningsee leçnd below) D stable at blasting, unsupported,gradual

7. L = length of conditionunder consideration, deteriorationald subsequent supportmeters E fallsat blasting, support in a.nticipation of

I, Geologicfeatures responsible for condition, progressive looseningrocktvpe F fallsat blasti::g, no support immediatelyafter

9. support or remedialmeasure blasbing, progressive loosening, support10. D = depth of overburden (soiland rock), applied to prevent furtherloosening

meters G fallsat blasting, support shortlyafter blasting

11. RQD, location, method; RQDI¡;RQD" to prevent or stop progressive loosening12. V = seismic velocity,m/sec3* H support shorgy after blasting, failureof13. SVR = seismic velocityratio support thereafter, additionalsupportL4. Regionaltectonics or major struchrral geologr

features15. Grounilwater condition16. Otåe¡ notes

*V"lo""given in parentheses have been t¿ken fromprojected groundsurface dat¿,

Fig.3 The list of informationand documentation applied by Cecil (1915)

A frequent documentationof ground conditionsand tunnel support is made in the formoftunnelmapping schemes like the example presented in Fig. 6.

Frg.7 shows example of a case historyshowing constructionexperience of some large under-ground caverns. Such cases formNGI'sdata bank used as documentation in the Q-system.

Where to search for case histories?

An importanttask when using case histories is to findout or detect where the data of interestare located. A search on the topic 'case histories' whichwas pedormed in a geotechnical database on the headings/titlesof published papers gave 90 references. When 'rock'was includedin the search only13 references were found.Similarly,in second search using the same key-words in another data base 120 and 9 references were found.Thus, general data bases may notgive much help in findingcase histories.Today, the best source is probably in proceedingsfromconferences and in the reference list given in conference articles.

A data bank or a special group in the geomechanics abstract wouldhelp to increase the inter-est to publish and use the valuable informationstored in many case histories.

I



Case 39

t.2.

5.6.

7.8.

r0.11.L2.13.L4.

15.

RendaL Hydroelectric, central-Nonayheadrace tunnelw=8nH= 6m

e = 43n2najor roof falls, progressive fomation of dome- andvault-shaped crownr falls from face(see skeÈch)t (G)L = 5Onshear zone in @artzitei "sugar cube', rock structure

càst concrete alch lmediately after muckingD = 200mROD= 2qÉ al1 directions, estimated

najor regional nornal faultj.ng is responsible forhorst-graben topography in area5-10 lit,/mln waÈer inflows

Case 52

1-5. sane as Case 476. stable section, mlnoroverbreak,no fallsi (À)7. L = 5Om

8. very cLoselyJoLnted E9!e!9IPÞ9SS4S¡3yE!9!9(seephoto)? sinilar to rock in case 5l' but contal-nsnoslickensides, structure is very tight

9. no structural supPort required¡ llght shotcrete orgunlte lor protectlonagains! snalLPieces of falLingrock

10. D = ?onLl. ROD= ø all dtrectÍons,neasured

14. sile as Case 4715. inslgnlflcant tnflowsf6. IocaÈlonabout 200m fron case 51

J

cast-in-placeconcrete lining

Fig. 4 - 5 Two examples from the case histories presented by Cecil (1970)



Fig. 6 Example of tunnel mapping (fromBartonet al.' 1980)

Project:NORZINKWASTECAVERNS,Odda, Norway

Cavern geometry: Span = 17.5 m Height= 23.5 m Length=211 - 225 m (each cavern)Cavern usage: Caverns for disposalof waste products fromzinc productionCavern depth below surface:

Verticaioverburden 2OO - 450 m. (Behindthe caverns nearby mountainsrise up to 1500 mabovethe caverns)Descriptionsof the ground cond¡t¡ons:

precambrian medium to coarse grained gneiss withoccasional veins of pegmatite, amphiboliteandgranite. Uniaxialcompressive strength of rock is 145 MPa, point load index16 MPa, E-modulus25 GPa and a Poisson's rationof 0.1'Generally3 jointsets occur. The main set is along the the steep dipping foliation'Another sethasnear vedical dip and strikes normal to the foliation.Mostjoints are rough and planar.Onlyminor fracturezones occur in the area.ln situstress measuremehts o, = 6.7 MPa, 6z = 1'7 MPa, oa = 0'6 MPa'

Excavationmethod:Drilland blast. Excavationby 7 - 11 m high top heading, and two benches 6 - 8 m

Stability:

ruo ÁtaOifityproblems

duringexcavation,but rock burst sounds have been heard in the inner part of

caverns.Rock mass quality:Average Q = 13 - 25 (good)

(RQD=80-100,Jn=6-9, Jr=1.5, Ja=1, Jw=1, SRF=1)Rock support (incavern 1 - 6):

Spot bolting(125 - 1600 bolts in roof and walls give a bolt spacing of 3 - 11 m) and occasionalshotcrete.

Completion date: 6 caverns had been excavated in 1993, 9 more are planned.References:

Rohde, J. (1993):Storage of industrialwaste in rock cavernsat Norzink,Odda. Publ. No 9 issued bythe Nonruegian Soil and Rock EngineeringAssociation.

Fig.7Example of a case historyapplied as documentation in the

Qsystem.



The need fora 'language' to be used in case histories fordocumentationof the groundconditions

Generally, observations and measurements of geological and geotechnical data have beenmade by individuals,based on their personal experience rather than on any collectivebasis.Therefore,a commondeficiencyof both geologicand geotechnical literaturehas been the lackof an adequate and generally accepted means to transmit the rock mass conditionsand stabil-

ityexperience in an overallassessment of the nature of rock masses to those who have nothad an opportunityto observe them. ISRM(1911) finds it importantthat a more systematicmeans of combiningand correlatingthis informationshould be developed. A 'language' com-mon to rock mechanics specialists and experts fromrelated fields should, according to ISRM(1980),be available. This need was, in fact, already presented by Matula(1969).

In this connection Deere et al. (1969) mention that a better language willhelp in accumulationof experience associated withvarious classificationsystems when the description of the para-meters are quantitativeand can be 'translated' fromone system to another.

The qualityof the documentationof ground conditionsis paramount in most cases. Ideally,itshould containboth the verbal descriptionof the compositionand structure of the rock massas wellas the numericalvalues of importantparameters (see Fig. 8), based on welldefinedratings. 'When such informationis availablethe case histories present a significantlybettersource for developments in design of rock constructions.

NW.r'

o2

Fig. 8 The main features whichinfluence the underground conditions(fromBarton,1990).

As a conclusionthe followingfeatures may stronglyimprovethe documentation of groundconditionand the exchange of geo-data:

- The inclusionin the case historyof a welldefined rock mass characterization.- A listof definitionsof common rock mass features and terms to anive at more concise

descriptionswhichmay be used to 'translate' qualitativedescriptions into quantitativenumbers.

- Guidelines/definitionsof appropriate methods to improvethe qualityof observations usedto determine inputdata applied in rock mass characterizations.

1

,ffi¡(tt,ryt



References

Barton N., LienR. and LundeJ. (1914):Engineering classificationof rockmasses for thedesign of rock support. Rock Mechanics,No 6, I974,pp. 189-236'

Barton N., Löset F., LienR. and Lunde J. (1980):Applicationof the Q-system in designdecisions concerning dimensions and appropriate support forunderground installations.

Proc. Int. Conf. onSub-surface Space, Rockstore,Stockholm,Vol. 2, pp.553 - 561.

Barton N. (1990): Scale effects or sampling bias? Proc. Int. 'Workshop Scale Effects in RockMasses, Balkema Publ., Rotterdam,pp. 31-55.

Cecil O.S. (1970): Correlationsof rock bolt - shotcrete support and rockqualityparameters inScandinavian tunnels. Ph.D thesis Univ.of Illinois1970, /Alsoin Proc. Swedish Geotech.Institute,No 27, 19'75,215 pp.)

Deere D.U.,Peck R.8., Monsees J.E. and SchmidtB. (1969): Design of tunnel linersandsupport system. Officeof high speed ground transportation,U,S. Department of transportation.PB 183799.

InternationalSociety forRock Mechanics(ISRM),Commissionon "Definitionof the mostpromising lines of research" (1.97I):Finalreport. Int.Soc. Rock Mech.,secretary, Lisbon.

InternationalSociety for Rock Mechanics(ISRM),Commissionon classificationof rocks androck masses (1980): Basic geotechnical descriptionof rock masses. Int. J. Rock Mech. Min.Sci. &Geomech. Abstr.,Vol. 18, pp. 85-110.

MatulaM.(1969):Engineeringgeologic investigationsof rock heterogeneity.11th US Symp.

on Rock Mech.pp 25-42.MüllerL. (1963):Rockconstruction(inGerman). FerdinandEnke, Verlag, Stuttgart,Vol. 1,

624 pp.

Stini I. (1950): Geology in tunnel construction(in German).Springerpublishers,Vienna,366 pp.

Vandewalle M.(1994):Tunnellingthe world.N.V. Bekaert S. 4., Zwevegem. Belgium,229 pp.

43 Palmstrom on Case Histories (1)

Documents

Transcript of 43 Palmstrom on Case Histories (1)