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IS 13216 (1991): Code of practice for geologicalexploration for reservoir sites [WRD 5: GelogicalInvestigation and Subsurface Exploration]

IS 13216 : 1991

~T!1flf ~ 3fernr~ ar;~ur ~ ~ urn m~Indian Standard

CODE OF PRACTICE FOR GEOLOGICALEXPLORATION FOR RESERVOIR SITES

@) BIS 1991

BUREAU OF INDIAN STANDARDSMANAK BRAVAN, 9 BAHADUR SHAH ZAFAR MARG

NEW DELHI 110002

Octob" 1991 Price Group 2

AMENI)MENT NO.1 OCf()IIER 1992-'1'0

IS 13216: 1991 CODE OF PRACfICE FORGEOLOGICAL EXPLORA1"ION I;OR RESERVOIRS

SI'I'ES

(Foreword, line 10 ) - Substitute '8 degree or for 'modicum'.( Page 2, clause 4.1.1, line 4 ) - Substitute 'major dislocations' for 'jaor

dislocations' .

( Page 3, clause 4.2.4, line 12) - Substitute 'angle of internal friction 00' for'angle ofintemal friction (0)'.

(Page 3, clause 4.2.5 ) - Substitute 'IS 6065 ( Part 1 ) : 1985' for 'IS 606S :1985'.

( Pag« 4, clause 4.3.3, lines 5 and 7 ) - Substitute'5 metre' for'S metres'.

(Pa~~ 4, clause 4.J.7,/inc to ) - Substitute 'SOO cubic nlelre'for '500 cubicmetres' .

( Page 4, clause 4.3.7, line 11 ) - Substitute '60 metre' for '60 metres'.

(RVD5 )Htprography Unit, 81S. New Delhi. India

AMENDMENT NO. 2 AUGUST 1998TO

IS 13216: 1991 CODE OF PRACfICE FORGEOLOGICAL EXPLORATION FOR

RESERVOIR SITES( Page 1, clause Z.l ) - Insert 'SP 36 (Part 1) : 1987 Compendium of

Indian Standards on soil engineering: Part 1 Laboratory testing of soils for civilengineering purposes' at the end.

( Page3, clause 4.2.3 ) -Insert tbe following at tbe end of the clause:

'For conducting laboratory tests, reference should be made to SP 36 (Part 1).'

(Page 3, clause 4.1.4, line 13) - Substitute '+' for '0'.( Page 4. clause 4.3.4, line 7 ) - Substitute 'angle of internal friction' for

'angle of friction'.

( Page 4, clause 4.3.4 ) - Insert the following at the end of tbe clause:

'For conducting laboratory tests, reference should be made to SP 36 (Part 1).'

(RVD05 )

RtproeraphyUnit, 81S,New Delhi, India

Geological Investigation and Subsurface Exploration Sectional Committee, RVD S

FOREWORD

This Indian Standard was adopted by the Bureau of Indian Standards, after the draft finalizedby the Geological Investigation and Subsurface Exploration Sectional Committee had beenapproved by the River Valley Division Council.

Keeping in view the thrust towards hydroelectric power generation and the enhancement ofirrigation capacity as well as control of flood situations, in our country today, a number ofprojects are under way for the construction of dams. While identifying a suitable site for theproposed dam, it is of paramount importance that the proposed reservoir site be thoroughlyinvestigated and explored. The basis of planning for such explorations is to have a rapideconomical and dependable preinvestment evaluation of sub-surface conditions. It is alsonecessary that a modicum of uniformity be followed while carrying out subsurface explorationsso that the frame of reference of the investigation covers all requisite respects.This standard lays down guidelines defining the requirements to be fulfilled while carrying outsubsurface explorations for reservoir site by defining the data requirements, the investigationsneeded and the areas to be investigated as well as the various stages of investigation fromthe reconnaissance stage to the post construction stage.

IS 13216 : 1991-

Indian Standard

CODE OF PRACTICE FOR .GEOLOGICALEXPLORATION FOR RESERVOIR SITES

1 SCOPE

1.1 This code lays down the guidelines for sur-face and sub-surface geological exploration forreservoir sites.

2 REFERENCES

2.1 The Indian Standards listed below arenecessary adjuncts to this standard:

IS No. Title

4453 : 1980 Code of practice for explora-tion by pits, trenches, driftsand shafts (fiutrnuwn)

5497 : 1983 Guide for topographic surveysfor river valley projects (firstrevision)

5529 Code of practice for In situ(Part 1) : 1985 permeability tests: Part 1 Test

In overburden ( first r"ision )5529 Code of practice for In situ( Part 2 ) : 1985 ~ermeability tests: Part 2 Test

In bed rock (first revision )

6065 Recommendations for the pre-( Part 1 ) : 1985 paration of geological and geo-

technical maps for river valleyprojects : Part 1 Scales ( fir,'revision)

6935 : 1973 Method Cor determination ofwater level in a bore hole

3 DATA REQUIRED

3.1 Reservoir projects in river valleys aremeant to hold water, therefore, the followingaspects of the reservoirs have to be properlyinvestigated ( a ) water tightness of the basins( b ) stability of the reservoir rim, (c) avail-ability of construction material in the reservoirarea. (d) silting, (e) direct and indirectsubmergence of economic mineral wealth, and( f) seismotechtonics. These investigations arecarried out by surface and sub-surface explora-tion of proposed basin during the reconnais-sance, preliminary investigation, detailedinvestiaation, construction and post-construc-tion atales of the project.

1

., INVltSTlGATIONS

4.1 RecODDaI.....ee

4.1.1 In the reconnaissance stage, the objectiveof investigation is to bring out the overallgeological features of the reservoir and theadjacent area to enable the designers, cons-truction enginers and geologists to pinpointthe geotechnical and ecological problemswhich have to be tackled. The scale of geolo-gical mapping for this stage of work need notbe very large and the available geological mapson 1 : 50,000 or 1 : 250,000 scale may be madeuse of. It is advantageous to carry out photo-geological interpretation of aerial photographsof the area, if available. If a geological mapof the area is not available, a traverse geolo-gical map should be prepared at this stagepreferably using the aerial photos as base mapson which the engineering evaluation of thevarious geotechnical features exposed in thearea should be depicted.

4.1.2 A topographical index map on 1 : SO 000scale should be used at this stage to delineatethe areas which would require detailed study,subsequently.

4.1.3 To prevent an undesirable amount ofleakage from the reservoir, the likely zones ofsuch leakage, such as major dislocationsand pervious or cavernous formations runningacross the divide of the reservoir should beidentified at this stage of investigation forfurther detailed investigations.

4.1.4 Major unstable zones, particularly in thevicinity of the dam in tight gorges, should beidentified at this stage for carrying outdetailed investigations for the stability of thereservoir rim.

4.1.5 Ths locations Cor suitable constructionmaterial available in the reservoir area shouldbe pin pointed at this stage so that afterdetailed surveys such materials can be exploitedfor proper utilisation during the constructionstage prior to impounding of reservoir.

4.1.6 The rate of silting of the reservoir is vitalfor planning the height of the dam and workingout the economic life of the project. Since therate of sUtinl, in addition to other factors, is

IS 13116: 1"1

dependent on the type of terrain in the catch-ment area of the reservoir, the major geologicalformations and the ecological set up shouldbe recognized at this stage to enable a moreaccurate estimation of the rate of silting of thereservoir. Por example, it should be possibleto estimate at this stage that forty percent ofthe catchment of a storage dam project iscovered by Quaternary sediment and that thisis a condition which is likely to a yield a highsilt rate or that ninety percent of the catch-ment of another storage dam project is compo-sed of igneous and metamorphic rocks andis likely to yield a relatively low sedimentrate. This information will also be useful inexamining whether or not tributaries flowingfor long distances through soft or unconsolid-ated formations, prior to forming the proposedreservoir, can be avoided and if not, whatremedial measures can be taken to control thesilt load brought by these tributaries.

4.1.7 The impounding of a reservoir may sub-merge economic/strategic mineral depositsoccurring within the reservoir area or theresultant rise in the water table around thereservoir may cause flooding, increased seepagein quarries and mines located in the area andwater logging in other areas. It is, therefore,necessary that the economic mineral deposits,which are likely to be adversely affected by thereservoir area are identified at this stage of theinvestigation. Por example, if an undergroundworking is located close to a proposed storagereservoir area, it should be identified for regu-lar systematic geohydrological studies sub.sequently. These studies would establishwhether the impoundment of the water in thereservoir had adversely affected the under-ground working or not. References should alsobe made to various agencies dealing with theeconomic minerals likely to be affected by theimpoundment in the reservoir for proper eva-luation of the problem and suitable necessaryaction.

4.1.8 A dam and its reservoir are affectedby the environment in which they are locatedand in turn they also change the environment.Impoundment of a reservoir sometimes resultsin an increase of seismic activity at, or near thereservoir. The seismic activity may lead tomicrotremors and in some cases lead to earth-quakes of high magnitude. It is, therefore,necessary to undertake the regional seismo-techtonic study of the project area. The faultshaving active seismic status should be delinea-ted at this stage. Simultaneous action to planand install a network of seismological observa-tories encompassing the reservoir area shouldalso be taken.

4.2 Pre1lmJ...ry layeltl••tloB

4.1.1 The object of preliminary investigationof the reservoir area is to collect furtherdetails of the surface and subsurface geologicalconditions, with reference to the likely prob-lems identified during the reconnaissance stageof investigation by means of surface mappingsupplemented by photogeological interprets..tion of aerial photographs, hydrogeologicalinvestigations,. geophysical investigations.preliminary subsurface exploration and byconducting geo-seismologlcal studies. of thearea.

On the basis of studies carried out durin,the reconnaissance stage it should be possibleto estimate the extent of exploration that maybe required during the preliminary stage ofinvestigation including the total number ofholes required to be drilled and the totalnumber and depth of pits, trenches and driftsas also the extent of geophysical surveys whichmay be necessary. Por exploration by pits.trenches, drifts and shafts guidelines laid downin IS 4453 : 1980 should be-followed.

4.1.2 The potential zones of leakage from thereservoir and the lateral extent of variousfeatures, such as extent of aeolian sand depo-sits, glacial till, land slides, jaor dislocationsor pervious and cavernous formations runningacross the divide, should be delineated on ascale of 1 : .ooסס5

The geohydrological conditions of thereservoir rim should be established by surfaceand sub-surface investigation as well as inven-tory, as a free ground water divide risingabove the proposed level of the reservoir is afavourable condition against leakage fromthe reservoir. The level of water in a bore.hole should be determined as liven inIS 693S : 1973.

4.2.3 The extension of various features atdepth, wherever necessary, is investiaated bygeophysical exploration and by means of pitstrenches, drifts and drill holes. For example'the resistivity survey should be able t~identify water saturated zones. The natureof the material is investigated by means oflaboratory and in litu tests, to determinepermeability an:d assess the quantum ofleakage which may take place through thesezones on impoundment of the reservoir.Moreover, permeability of rocks/overburdenin the reservoir, area is determined from watertable fluctuations and pumping tests ih wells.For determining in litu permeability in OVOr.-burden and rock, reference should be made toIS 5529 (Part I) : ~98S and IS; 5529

2

( Part II) : 1985 respectively. The informationabout permeability would enable the designersto estimate the treatment cost for controllingleakage/seepage from the reservior and todecide whether it would be desirable tochange the location of height of the dam toavoid these zones.

4.2.4 Major unstable zones along the reservoiridentified during the reconnaissance stage andwhich are of consequence to the storagescheme should be investigated in detail at thisItage by means of surface and sub-surfaceexploration. The areas should be geologicallymapped in detail on a scale of 1 : 2 000. Thesuspect planes/zones of failure should beidentified and explored by means of drifts,trenches and pits. Disturbed and undisturbedsamples of the plastic material should betested for cohesion (c) and angle of internalfriction (0) as well as for other relevant pro-perties. The stability of slopes should alsobe evaluated considering the reservoirs ope-rational conditions. These studies shouldprovide the designers with an idea of themagnitude of the problems. that may beencountered, so that they may be able to takeremedial to stabilize zones or to abandon thesite altogether, if the situation demands.

4.2.5 The topographic survey of the reservoirarea shall be carried out as per IS 5497 : 1983and the scale of mapping shall be as perIS 606S : 1985.

~.2.6 During the reconnaissance stage it shouldhave been possible to identify those reachesof the main river and tributories which, due totheir geological and ecological set up, arelikely to yield abnormally high silt loads. Asystematic network of silt observationstations should be set up to provide accuratedate for planning remedial measures such ascheck dams afforestation, etc.

4.%.7 The areas having potential economicmineral wealth and which are likely to beadversely affected by the impoundment of thereservoir should be explored by means- ofsurface and sub-surface investigation toestablish their importance both in terms oftheir value as well as strategic importance.This information would be necessary for arriv-ing at a decision regarding the submergence,or otherwise, of the mineral deposit. Thenature and amount of the existing seepage, ifany, in the existing mines and quarries in theadjacent areas of the reservoir should berecorded and monitored regularly. This datais necessary, to ascertain whether or not therehas been any change in the quantum of seepage

IS 13116 : 1'91

In the mines and quarries due to the impound.ment of water in the reservoir, directly orindirectly.

4.2.8 Large scale geological mapping andterrace matching across the faults with seismi-cally active status, delineated during thereconnaissance stage, should be carried outon a scale of 1 : 2000 and the trend, andbehaviour of the fault plane should be investi-gated in detail by means of surface studies andsub-surface exploration by pits, trenches anddrifts etc. A network of geodetic survey pointsshould be established on either side of thesuspected faults to study micromovementsalong these suspected faults, if any, both priorto and after impoundment of the reservoir.Micro earthquake studies should be carriedout using portable 3-station or 4-stationnetworks in areas with proven seismicallyactive fault features.

4.2.9 The data from the seismologicalobservatories available till now should beevaluated so that shift or addition in thenetwork of the observatories, if necessarycould be considered. '

4.3 Detailed In,estigation Stage (Pre-construc-tion stale)

4.3.1 On the basis of the studies carried outduring the preliminary stage it should bepossible to estimate the quantum of explora-tion which may be required during the detailedstage of investigation including the totalnumber of holes required to be drilled and thetotal number and depth of pits, trenches anddrifts as also the extent of geophysical surveywhich may be necessary.

4.3.2 Detailed surface and sub-surface investi-gation of all features connected with thereservoir should be carried out to provideinformation on leakage of water through theperiphery and/or basin of the reservoir area.Based on these investigations and analysis ofdata it should be possible to decide as towhether the reservoir area in question would

.hold water without undue leakage. If, not, thedam site may have to be abandoned in favourof suitable alternative site.

4.3.3 The zones, which on preliminary investi-gation are found to be potential zones ofleakage/seepage from the reservoir, and whichdue to other considerations cannot be avoidedare geologically mapped on a scale of 1 : 2 000and investigated in detail at this stage bymeansof a close spaced sub-surface explorationprogramme. The purpose of this stage ofinvestigation is to provide the designers

3

IS 1321' : 1"1

sufficient data to enable them to plan theprogramme of remedial treatment. The sub-surface explorations are carried out by meansof pits and trenches, if the depth to beexplored is shallow, say up to 5 metres, and bydrill holes and drifts, if the depth to beexplored is greater than 5 metres.

4.3.4 The unstable zones around the reservoirrim, specially those close to the dam sites intight gorges, should be explored in detail bymeans of drifts, pits and trenches so that thelikely planes of failures are located withprecision. The physical properties includingangle of friction and cohesion of representativesamples of the material along which movementis anticipated should be determined. The aboveinformation would enable the designers towork out details for preventive measures, forexample, it may be possible to unload the topof the slide area or to load the toe of the slidewith well drained material. within economiclimits.

4.3.5 Sub-surface explorations by drill holes,drifts, pits and trenches should be carried outat possible locations of check dams and at thelocations of other preventive structures pro-posed to restrict the flow of silt into thereservoir. These studies would enable thedesigners to assess the feasibility of suchproposals.

4.3.6 Detailed plans, regarding the economicmineral deposits within the zones of influenceof the reservoir should be finalized during thisstage by the concerned agencies. The seepageinvestigations in the quarries and mines withinthe zone of inftuence of the reservoir shouldbe continued.

4.3.7 The seismotectonic studies should befurther intensified and continued for severalyears even after the impoundment of thereservoir, or till it is established for certainthat the impoundment of the reservoir willnot have any effect on the seismic stage of thearea.

Moreover, detailed seismotechtonic investi-gations should be carried out for reservoirs ofcapacity more than Soo cubic metres and damsof height greater than 60 metres.

4.4 CoDltrac dOD Stql'

4.4.1 It is likely that major discontinuities ofpervious formations/zones etc located at theperiphery or in the reservoir basin may extendupto the dam alignment. In such casesthe dispositions of features established duringthe investigation stage, by sub-surface explora-tion, can be confirmed during foundationexcavation and can be studied more preciselyvisually. Moreover, those weak featureswhich were missed during the various stagesof investigation may get exposed duringexcavation of the foundation. The implicationof such features on the competency or stabilityof the reservoir rim needs to be studied andremedial measures taken accordingly.

The compilation and evaluation of variousgeological reports and drawings preparedduring various stages of investigations shouldbe done. The compilation should also containdetails of remedial measures taken for thetreatment of weak features present in thereservoir basin, rim and foundation of thedam, having relation to the stability of thereservoir rims, storage of the reservoir andseismic aspects etc.

4.5 Post-construction Stage

4.5.1 The object of post-construction geolo-gical investigations is to monitor the criticalproblems encountered during all the stages ofinvestigation of the project and the effective-ness of treatment provided to those weakfeatures. Por example, it would be necessaryto monitor the critical areas which aresusceptible to landslides or to keep a watchon the areas where special treatment, such asthat against leakge, has been provided so thatnecessary action, if warranted, can be takenin time. Monitoring of the seepage in minesand quarries within the zones of the influenceof reservoir, precision geodetic repeat surveysacross fault planes or in slide prone areas andevaluation of microseismic and seismic datafrom the network of seismological observa-tories has to be continued for a sufficiently longtime till adequate reassurance in the matterhas been achieved.

4

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