ISRM-9CONGRESS-1999-269_Determination' of Rock Mass Modulus Using the Plate Loading Method

8/12/2019 ISRM-9CONGRESS-1999-269_Determination' of Rock Mass Modulus Using the Plate Loading Method

1/5

D eterm ina t ion ' o f rock m ass m odu lus us ing the p la te load ing m e thod~ " . .

Ut il is a t i on d 'un es s a i de p l aq ue pou r la de t e r m i na t ion de l a de f o r m ao l l lt e d ' une r o c he/ r . B es t i m m un g de r V e r f o r m ung s m od u l s v on G eb i rge m i tt e l s L as t p l a t tenv e r s uc he

J .T .G E O R G E , R . E . F IN L E Y .& M . R I G G IN S , S a n d i a N a t io n a l L a b o r a to r ie s , A lb u q u e r qu e , N . M e x . , U S A, ' ,

. I

.1

.'

,,

ABSTRACT: A suite of plate loading tests has recently been conducted by Sandia National Laboratories at the Exploratory Studies

Facility at Yucca Mountain, Nevada. Fielding of these in situ tests as well as other approaches undertaken for the determination of

rock mass modulus are described. The various methodologies are evaluated and their data compared. Calculation by existing empirical

methods and numerical modeling are compared to each other as well as to field data., 1

RESUM~: Une succession de tests de plaques sous haute pression a ete conduite recemment par les Sandia National Laboratories aleur site des etudes exploratoires a Yucca Mountain, au Nevada. Cet article decrit les methodes de recherches sur le terrain ainsi que

celles dues a d'autres approches utili sees pour determiner le module des masses rocheuses. Les differentes methodologies sontevaluees et leurs donnees comparees, Les calculsqui resultent de differentes methodes empiriques et d'analyses numeriques sontcompares les uns aux autres ainsi qu'aux donnees rassemblees sur le terrain:' I

.;, i .~ \ ,1 f .;

d . , I, i

ZUSAMMENFASSUNG: Eine Versuchsreihe von "plate loading" Tests wurde kUrzlich von den Sandia National Labs in der

Exploratory Studies Facility am Yucca Mountain in Nevada durchgefilhrt. Beschrieben wird der Verlauf dieser in situ Tests als auch

anderer Ansatze zur Bestimmung des Gesteinsmassenmoduls,' Die verschiedenen Methoden werden evaluiert und ihre Daten

verglichen, Berechnung durch existierende empirische Methoden und numerische Modellierung werden sowohl miteinander als auch

mit den experimentellen Daten verglichen. . .

INTRODUcnON

The welded tuff s of Yucca Mountain, Nevada are being

considered by the United States Department of Energy (DOE) as

potential host media for the storage of high level waste (HLW).'

As part of the site characterization efforts for the Yucca

Mountain Project (YMP), a mechanically excavated Exploratory

Studies Facility (ESP) was completed in 1997. A Thermal

Testing Facility (TTF), subsequently constructed off the main

drift of the ESF, included the Single Heater Test (SHT) block

and the Drift Scale Test (DST). The DST is being constructed in

a 50-m long, 5-m diameter Heated Drift (HD). To determine

potential changes in the rock mass modulus resulting from

thermally induced closure of the fractures, a plate loading niche

was constructed near the DST such that one' side of the niche

would be near ambient temperature and the other side was heated

to ~ 100C (Fig: 1).' Determination - of rock mass l modulus, a

parameter of significance to the Yucca Mountain geomechanics

program, is calculated using data gathered from the PlateLoading Test (pLT). It will be used in numerical analysis of drift

stability, ground support interactions, and drift and repository

behavior. Rock mass modulus may also be used in the coupling

of the various thermal-mechanical-hydrological-chemical (T-M-

H-C) models used for the proposed repository. _ '! "

The PLT, conducted as part of the long-term DST, consisted

of multiple elements, each unique though closely related. The

elements included rock mass quality mapping, Goodman jack

tests, and pre- and post-test elastic numerical predictions of the

stresses and displacements within the rock mass using the actual

flat jack pressurization cycles.

'. , 'The successful conduct of these comparati ve testing

techniques has allowed Sandia National Laboratories (SNL) to

undertake a comprehensive evaluation of the mechanicalbehavior of the Yucca Mountain welded tuffs, including

determination of rock mass modulus, as well as providing data

against which analytical models can be compared.-

1.1 . Background' . '.

SNL's experience u;ing1

1arge-scale (up to 0.80 m2) flat jacks

dates back to the mid-1980s, during which time jack fabrication,

instrumentation, and monitoring techniques were developed andrefined through pressurized slot testing conducted within the G-

Tunnel facility on the Nevada Test Site (Zimmerman & Finley1987, Hansen et al. 1990). In addition," pressurized slot

experiments using the large-scale flat jacks for determination of

rock mass modulus were conducted by SNL on behalf of the

United States Defense Nuclear Agency in 1994 at the Fort Knox

Military Reservation (Finley 1994)..~. J

!

PLT_

, DrlIIsc:..

TOIl Region

" , I t

i \ ('

u...,U (;, J.\

lr!l

. ]"

Cenl_ CS2&+27

Figure 1. Plan view of the ESF Thermal Test Facility.' t' " Ii.,('. ' -

1367


2/5

consistent enough to suggest that the rock mass .in the region

surrounding the PLT Niche could be reasonably described by the

~ rock mass quality estimates from the HD., r. ,-...1The United States Bureau of Reclarnation performed full

periphery fracture mapping along the complete length of theConnecting Drift and the HD. This represents the HD-side ofeach of the blocks of rock that were loaded by the PLT. In

'contrast, SNL performed line surveys 'for rock mass quality ofthe left rib of the HD and the Connecting Drift. Each of thesesurveys provided values of rock mass quality parameters Q and

RMR, which can be used to estimate the rock mass deformationmodulus. What is most striking in comparing the surveys are thedifferences in estimated rock mass quality values for the samesections of rock with RMR values varying from 52 to 79 and Qvalues varying from 2.1 to 11, although the reader should becautioned that the Q system is logarithmic and such differencescan be expected from one region to the next.

1.2 Modulus Determination Approa,ches.. .! Also, the rock mass quality survey was performed as a line

Rock mass or deformation modulus can be estimated via several survey, and the fracture mapping was performed as a fullmethods that include both direct in situ testing and empirical periphery survey. Therefore, features apparent to one may not betechniques that incorporate properties of the rock mass including seen in the other. ' ; -fracture and intact rock characteristics (e.g., Goodman et al. A summary of these surveys for each side of the PLT Niche1968, Hustrulid &Schrauf 1979, Rocha 1964, Pratt et al., 1977" can be given by averaging the rock mass quality estimates forBrown 1981, .Zimmerman & Finley 1987, Hansen et al. 1990, sections describing the hot and ambient sides of the rockGoodman 1980). These techniques include large-scale in situ surrounding the PLT Niche. Such a simplified ,approach yields.

tests such as plate loading tests, rock mass block tests, ,I the average RMR values of 64.7 and 66.8, and average Q valuespressurized gallery tests, flat jack tests in slots, borehole tests of 4.03 and 7.7 for the hot and ambient sides respectively. (1 " .such as the borehole jack (Goodman jack) and dilatometers, The rock mass quality values can be related to estimates ofgeophysical techniques such as cross-hole ultrasonics, and, the deformation modulus for each, side of the P~T usingestimations from rock quality field surveys. They 'also include . empirical equations developed by other. researchers: As aanalysis techniques to better interpret the in situ data from the .!'preliminary estimate, the' empirical equations developed byGoodman jack and plate loading tests (e.g., Heuze & Amadei 1 Barton (1983) Serafim & Periera (1983) and Bieniawski (1978)1985, Boyle 1992). Additionally, a limited number of laboratory i'are used below to estimate the rock mass deformation modulusrock joint compliance studies have been conducted by SNL for on each side of the PLT.the YMP. Table 1 lists each empirical method and the predicted rock

Each of these techniques has merit but also inherent mass deformation modulus for each side of the PLT Niche. "limitations. Although the Goodman jac~ tests proved relativelyeasy' to conduct, the physical size limitations of the equipmentcould not load an adequately large volume of rock, resulting in

local heterogeneities strongly influencing the results. ",,, .Large-scale techniques such as block tests, slot pressurization

tests, pillar tests, and radial jacking tests offered scaleadvantages by testing at a more reasonable rock mass scale.However, the test preparation, geometry, and conduct' provedsignificantly more complex and costly than plate loading testsand were not considered for the YMP thermal testing program.

The empirical techniques for estimating rock massdeformation (Barton 1983, Nicholson & Bieniawski 1986,Serafim & Periera 1983, Bieniawski 1978) have been somewhat

beneficial. However, because they tend to rely on analyticalcombinations of related parameters, these methods wouldnecessarily have to be verified through direct measurements,such as plate loading, before they could be universally applied

throughoufthe YMP facility.Because the aforementioned tests, techniques, and studieshave been presented elsewhere, and a detailed discussion of alltechniques is beyond the scope of this paper, only specificmethods used in the conduct of the PLT experiment will be

present~ for c?mpleteness.,

Having previously identified and described plate loading tests '

in the Site Characterization Plan (US D6E 1988) as the primary

deformation modulus test to be conducted in. the YMP

underground testing facility, SNL' championed Incorporation ofthe PLT into the DST during excavation in 1997. The envisionedPLTs were to be based on standard testing techniques consistingof the construction of a reaction frame and the application ofstatic horizontal loads on the surface of the rock near the DSTexcavation (Brown 1981, ASTM 1980, ASTM 1994a, ASTM1994b). DST excavation geometry allowed for the design of a

plate loading niche whereby the application of static horizontalloads could be applied to both ambient and thermally perturbedrock masses concurrently. Pressures in the loading system anddisplacements in the surrounding rock masses would then bemeasured and recorded on a real-time basis.

,I'

1.3 Rock Mass Quality Estimates

Rock mass quality estimates of the HD drift wall were performedshortly after construction of the HD. These estimates included

both the NGI "Q" system and the CSIRO "RMR" system.Two separate sets of estimates were performed, one by the

United States Bureau of Reclamation and one by SNL. Theseseparate surveys targeted different parts of the HD, although norock mass quality estimates have yet been performed within thePLT Niche itself' or on core retrieved from the PLTinstrumentation boreholes. Nevertheless, -the reported data are

Table 1. Comparative empirical methods.

Parameter - Ambient Side

A verage Rock Mass Q=7.7 (RMR=66.8)Quality .: " "

E (GPa) from Bieniawski, 33.6 GPa

,1978

E (GPa ) from Se ra fim & 26.3 GPa

Periera, 1983

E (GPa) from Barton, 1983 22.2 GPa

- E = Modulus of Elasticity

Heated Side

Q--4.03 (RMR=64.7)-

29.4GPa

23.3 GPa '.

IS.1 GPa

. ljf,~, j r ;

These, empirical results suggest that the heated side of thePLT Niche should have a slightly lower rock mass modulus,although the range of estimates differs by as much as about afactor of two, with the Barton (1983) method providing the

lowest estimates for both sides of the PLT Niche: ) ",I

Il,

1.4 Goodman jack Tests r.r I . ir 1 I",. J ,_J 'f ill' . :' 1\ J , : j"

Goodman jack tests were performed at a single depth in each ofthe PLT instrumentation _boreholes prior to, installation of thePLT multiple point borehole extensometer (MPBX)instrumentation. These tests were conducted six months into theDST heating phase, on 12 May 1998, at a depth of 1.2 m fromthe collar of borehole #187 and 2.6 m from the collar of borehole#188. Borehole #187 is drilled approximately 3 m into the rightrib on the ambient SIdeof the PLT,.and borehole #188 is drilledapproximately 3 m into the left rib on the hot side of the P~T.The rock in p te vicinity of the PLT created difficulty in settingthe jack; therefore only the single location in each borehole was,tested. For YMP applications, the jack is typically pressurized to

34.5 MPa (5,000 psi) to 55.2 MPa (8,000 psi) and back to zero'with linear variable displacement transformer (LVDT) readings,recorded during both loading and unloading.

", ,.,',

1368


3/5

The results of the Goodman jack testing in the PLT

instrumentation boreholes are a calculated rock mass modulus of

3.31 GPa for. the ambient side of the PLT Niche at a depth of1.2 m in borehole #187 and 5.9 GPa at a depth of 2.66 m in

borehole #188. These values suggest that the hot side modulus isabout twice as high as the ambient side modulus. TheseGoodman jack estimates for rock mass deformation modulus areconsistent in magnitude with values obtained from the SHT

block. It is important to note that the Goodman jack loads therock along an orientation that is perpendicular to the direction of

loading for the PLT.

1.5 Pre-Test Analysis

Pre-test analyses of the expected rock response as a result of thePLT were performed. Two methods of analysis were used. Thefirst was a hand calculation involving a plate load source on asemi-infinite elastic half-space using the equation for a squareloaded area on a homogeneous, elastic half-space. A singleelastic modulus of 5 GPa was used in the solution to predict theexpected displacements of the PLT-loaded rock surfaces and theleft rib of the Data Collection System (DCS) alcove. The secondmethod involved a finite element elastic solution. Two elasticmoduli were used in the analyses, 5 GPa and 36.8 GPa. Thesetwo moduli represent what were considered the likely bounds

between a relatively fractured yielding rock (5 GPa) and anintact rock (36.8 GPa). The two moduli give essentially the samestress distribution but yield significantly different displacementfields.

The hand solution using the 'equations mentioned aboveshows the plate displacement to be on the order of 6 mm with auniform surface load on the plates of 47 MPa. At the DCS alcovewall, the displacement is on the order of 1 mm, and the normalstress adjacent to the DCS alcove wall is on the order of 1 MPa.

Stress and displacement using the finite element code showthat the normal stress fields are identical for the two elasticmoduli. This is to be expected, as the elastic stresses areindependent of modulus. The second item of interest is that thenormal displacement at the DeS alcove wall is on the order of

2 mm for the 5 GPa case and negligible 0.1 mm) for the 36.8GPa case. A third item of interest is that the plate displacement ison the order of 9 mm for the 5 GPa case and about 1.2 mm forthe 36.8 GPa case.

Based on the above elastic analysis of the PLT, the expecteddisplacements at the HD and DCS walls would be expected to bebounded by the 1.2 mm and 9 mm displacement predictions.Similarly, the normal and transverse stresses adjacent to thesame regions should be on the order of 1 to 2 MPa. The indirecttensile strength of the rock has been reported to be between 4 to16 MPa (Hardin, in press). The results from the PLT are quitelinear for the range of flat jack pressures achieved, This suggeststhat linear elastic analyses are adequate for predicting the rockmass response for the PLT, !

2 PLATE WADING TEST CONFIGURAnON

The PLT was designed based on the standard test described inthe International Society for Rock Mechanics (lSRM) testingmanual (Brown 1981), ASTM standards D4394 and D4395(1994a, b), rock mechanics testing literature, and previoustesting experience with high-pressure flat jacks in G-Tunnel(Zimmerman & Finley 1987, Hansen et al. 1990).

,The PLT conducted as part of the DST differs somewhat fromthe recommended standard techniques, although the differencesare not considered significant and are justified based on the PLTconfiguration .within the context of the larger DST. The

differences are noted throughout this paper..The, experiment niche was mined using drill, and blasttechniques in the construction phase of the DST during 1997.The PLT was designed to mechanically load the rock in a

horizontal orientation using large square-shaped flat jacks that

press against both ribs of the PLT Niche with a steel reaction

frame constructed between the ribs. This flat jack design is basedon flat jacks originally fabricated and tested by SNL for G-Tunnel rock mass strength and deformability testing (Hansen etal. 1990). The G-Tunnel tests achieved flat jack pressures inexcess of 30 MPa (4400 psi), and the surrounding rock failedduring the test without failure of the flat jack.

Because the flat jacks produce forces of roughly 454,000 kg(1,000,000 lb) per each 6.9 MPa (1000 psi) increment in

pressure, it was not possible to pressure-test the jacks prior toconducting the PLT. The jacks were radiographed and heliumleak-tested by the fabricator prior to installation in the PLT.

": I

2.1 Reaction Frame Design

Design of the PLT reaction frame was predicated on materialshaving compressive strengths in excess of 55.2 MPa (8,000 psi:maximum jack pressure design) and havin~ a minimum Modulusof Elasticity (E) of 30 GPa (4.3512 x 10 psi). In addition, theexcavated rock surfaces of the PLT Niche were required to beprepared in accordance with ASTM 4394-84 (1994a). Numerousmethods, including hydraulic jacks and pipe columns, cast-in-place high-strength concrete, and structural steel (lor H beamconstruction) were considered for the' reaction frame.( Theinstalled configuration consisted of 0.91-m (36-in.) square, mildsteel plates stacked horizontally across the diameter of the PLTNiche near the springline (Fig. 2).

This reaction frame design allowed the flat jacks to providerelatively uniform pressure to a single (each side) 2.5-cm (l-in.)thick bearing platen. Each platen bears on a nominal 1O.1-cm(4-in.) thick grout pad cast directly on the hand-smoothed rocksurfaces to provide a uniform bearing surface for PLT testing.Availability of materials, ease of installation, and constructionschedule time constraints also influenced this design choice. Thisconfiguration provided not only, simplicity, but also thenecessary mass upon which the anticipated large loading forcescould react. Although the joints between the stacked platesallowed some compliance' during low-pressure cycles, the

compliance was reduced by adding additional aluminum shims-during initial depressurization cycles prior to actually conductingthe PLT. Upon completion of this low-pressure pre-loading, thereaction frame was considered stiff enough to allow generalloading ofthe PLT. , .

2.2 Pressurization System \ \

The heart of the pressurization system used for the PLT was apneumatically driven 103 MPa (15,000 psi) maximum dischargepressure pump, which featured a large air piston joined to asmaller diameter plunger. The pressure ratio was the differenceof these two areas and was the method of determining maximumoutput pressure. The pump was designed to stop automatically

.rFlat JackBleed Port

",.

SNL Flat Jack

.j'.

Borehole ',88

, MPBX1.(elevated temperatura)'"

~ fii

1,'; 'r I

Plate loading Reaction Frame, '_'

Figure 2. View of reaction frame and flat jack setup used in !he PLT.

1369


4/5

when the output pressure forces and the air drive forces were

equal. The pump would then restart with a slight drop in the

outlet pressure or an increase in the air drive pressure. Thepressurization fluid used was potable water. Water was usedinstead of the standard fluid (hydraulic oil) so as to limit thepotential impact of system leaks on the surrounding rock. '

3 PLATE LOADING TEST INSTRUMENTATION i'I",1

The PLT instrumentation included displacement sensors in thePLT boreholes and on the data collection system (DCS) side ofthe PLT pillar between the PLT Niche and the DeS alcove:Pressure transducers were used to monitor the flat jack systempressure. Borehole anchor locations were selected in competentrock in each borehole based on borehole video logs of each hole.The resulting' displacement measurements along with themeasured flat jack pressures were used to calculate the rock massdeformation modulus. i' ,I .. Another set of displacement measurements across the. OCS

alcove was intended to monitor the stability of the west rib of thePLT Niche pillar as the flat jacks were pressurized.r'Ihis wasconsidered prudent, as the operational range of the flat jacks wasexpected to exceed 30 MPa (4400 psi) which would impart more

than 1,816,000 kg (4,000,000 lb) of force on the rock. No cross-drift (PLT Niche) displacements were made as suggested by theISRM testing manual (Brown 1981). . ~'l

An additional test setup deviation from the ISRM-suggestedmethod was in the depth and number of the MPBX anchorsrelative to the size of the loaded area. (Although the ISRMsuggests that the bottom anchor be placed approximately six flat

jack (loading platen) diameters away from the loaded surfaceonly, the close proximity to the. nearest direct Iheat sourceallowed borehole depths of only 3 m. Because Ithe boreholedepths were shortened from the recommended ISRM depth, thenumber of anchors was also reduced. . ~.! I' 1 , I

The final deviation from the ISRM-suggested method was inthe loading itself. The ISRM method suggests the load be cycled

in multiple increments, with each incremental cycle duration of(up to) three daysBecause of safety issues related to extremelyhigh loading pressures, it was decided to conduct each test in themost expedient manner possible. Maximum pressure incrementswere established at 9.5 MPa (1400 psi) with cycle durations heldto the minimum time required for displacement stabilization.

3.1 PLT Data Acquisition System

The data acquisition system for the PLT consisted of a 16-bitanalog to digital (AID) converter with I in 1216 resolutioninstalled in a laptop computer with a PCMCIA port. The virtualdata acquisition instrument "PL DATA LOGGER" was createdusing LabView graphical programming language. ('J

;'," ": ':J ~ ~ I .'~~

3.2 Plate Loading Tests through June 1998

Two plate loading tests were conducted on 28 May 1998 and9 June 1998 using the double acting flat jack and reaction framesystem previously described. Both tests terminated as a result offlat jack failures resulting in a loss of pressure. For the 28 May1998 test, the maximum flat jack pressure achieved was about8.8 MPa (1280 psi). The 9 June 1998 test achieved maximumflat jack pressure of about 16.5 MPa (2400 psi) prior to failure ofone of the flat jacks. ~ .

The PLT results are presented in terms of pressure/dis-placement plots in Figures 3 and 4. : It must be noted that thepressure data required for such plots and subsequent analyses isthe pressure directly applied to.the rock mass and not necessarily

the pressure measured in the flat jacks or loading systems. In thecase of the YMP PLT, the bearing pressure is estimated from themeasured flat jack pressure, the estimated dimensions of the flat

jack at that pressure, and the bearing platen dimensions. Because

14

" - " l " - " - ' - ~ - - . _ ' j - : _ . ' . . . . . . . . . _ --...t-.......- ....:-.."7~ ,,. . . . . . .1 . . . . . . .

,",

o

0.0 0,1 0.2 0.3 0,4 0.5 0.6 0.7 0.6 0.9 1.0

Displacement (mn)

Figure 3.' Bearing pressure versus displacement for ambient side.

1

14

r ,. . f.I'

-t:

0.1 0.2.0.3 ,0.4 0.5 I 0.6 0.7 0.6.0.9 1.0

" D is pl ac em en t (n vn )

Figure 4. Bearing pressure versus displacement for heated side.

J' t ",Il" .. I

the flat jacks are flexible, they deform under their internalpressure, and as they extend from the initial thickness of 9.5 mmthe effective loading area decreases. The assumed decrease in

loading area was calculated as follows: . r','f . I .' I )< ~, ,~ f. Bearing Pressure = Flat Jack Pressure x (78 cmi/(91.4 cm)~.

= 0.728 x Flat Jack Pressure I(

) ,.)'

4 POST-TEST ANALYSIS .. 'I ~ I. . .t \

Post-test analysis involved modeling the rock mass with anelastic 3D finite element vmecbanlcs code (JAC3D). Theequilibrium stress state was used as the initial condition for thePLT analysis. 'Two loading histories (steps) were modeled. Thefirst was the test performed on 28 May 1998 with a plate bearing

pressure of 6.4 MPa. The second was the test performed on 9June 1998 with a plate bearing pressure of 11.9 MPa.'. t' ,

The rock mass moduli on the ambient and heated side of thePLT Niche were taken to be 12 GPa and 30 GPa, respectively.The normal displacements at each MPBX anchor location for thetwo bearing pressures were calculated and compared to theobserved displacements. The results are given in Tables 2 and 3.. Tables 2 and 3 show' that the predicted and observed

displacements compared favorably. For each case (except one)the elastic r solution slightly', underpredicts the observeddisplacements with an average difference on the order of 18%.This difference may be attributed to displacements associatedwith initial fracture closing and plate seating prior to mobilizingthe strength of the rock mass, Note also from Tables 2 and 3 that

both the measured and predicted displacements on the ambientside of the drift are approximately. 2.5 times greater than the

displacements on the heated side of the drift.:' "/.1"J > This can be attributed, in part, to the closing of fractures as a

result of heating and thus a higher mobilized rock strength on theheated side of the PLT Niche. In addition, factors such as-rock'

1370


5/5

Table 2. Nonna! displacements on ambient side of PLT Niche.

Anchor Depth (m) BearingPressure6.4 MPa

Observed JAC3D

(mm) (mm)

0.41 0.300.48 0.370.51 0.44

BearingPressure11.9MPa

Observed JAC3D(rnrn) (mm)

0.67 0.560.84 0.680.95 0.82

0.861.54

3.21

Table 3. Normal displacements on heated side of PLT Niche.

Anchor Depth (m) BearingPressure6.4 MPa

Observed Calculated

(mm) (mm)0.17 0.12

0.22 0.160.19 0.19

BearingPressure11.9MPa

Observed Calculated(mm) (mm)

0.29 0.230.36 0.290.37 0.35

0.871.31

2.70

inhomogeneity, drift geometry, and mining methods could also

have contributed to the difference in the rock mass strength.

5 CONCLUSIONS

This paper presents results from a unique PLT conducted to

support coupled thermal-mechanical evaluations of the DST for

the YMP. The uniqueness lies in the measurement of rock mass

stiffness for both ambient temperature and thermally perturbed

rock masses for the double acting system. This paper presents

only the ambient measurements prior to significant heating of the

rock mass, although the test is planned to be conducted

periodically as the rock mass heats from the DST.

A number of techniques were used to estimate rock mass

modulus and are discussed in this paper. These techniques

include estimation of rock mass modulus from rock mass quality

surveys, estimation from borehole jacking tests, and estimation

using the plate loading technique. The results from the PLTyield

rock mass moduli of 11.4 GPa and 29.5 GPa for the ambient and

heated sides of the PLT Niche, respectively. Conversely, the

borehole jacking test results yield rock mass modulus estimates

from 3.3 GPa to 5.9 GPa for the same rock mass. The rock mass

quality estimates yield rock mass modulus estimates within therange determined from the PLT; however, the values determined

from surveys of the ambient versus heated sides of the niche do

not show the 2: 1 rock mass modulus ratio observed in the PLT.

Results of numerical modeling of the PL T as well as thermal

output from the DST suggest that the PLT rock mass modulus

values better represent the actual response of the rock mass

surrounding the PLT Niche than the other techniques discussed.

The PLT results suggest that the heated side of the PLT Niche,

even early in the DST heating phase, has caused the fractures in

the vicinity of the niche to close, thus presenting a stiffer rock

mass for the PLT. Alternatively, the rock mass quality estimates

from the rock mass surrounding the PLT Niche may be more

heterogeneous than previously thought, with the heated side

actually having a higher rock mass quality than initiallyestimated. Additional evaluation of the rock mass quality will

determine the extent to which this applies to the PLT results.

The PLT results provide important information regarding the

rock mass mechanical properties for the Yucca Mountain Project

design and performance assessment programs. The estimations

regarding the coupling of the thermal and mechanical response

are critical inputs for estimates of rock mass stability, rock

mass/ground support interactions, and the coupling of the

thermal-mechanical and thermal-hydrologic processes necessary

for performance assessments. Future PLT testing can further aid

in understanding the complex T-M-H coupling necessary for

determining the overall performance of the proposed Yucca

Mountain repository.

REFERENCES

ASlM (American Society for Testing and Materials). 1980. TestingTechniques for Rock Mechanics, ASlM STP 402. Philadelphia, PA:

American Society for Testing and Materials. TIC Catalog Number:

209879.ASlM (American Society for Testing and Materials). 1994a. Standard Test

Method for Determiningthe In Situ Modulus of Deformation of Rock

Mass Usingthe RigidPlate Loading Method (R 1994),ASlM 04394-84.Philadelphia,PA:ASlM. TIC Catalog Number: 238037.

ASlM (American Society for Testing and Materials). 1994b. Standard TestMethod for Detennining the In Situ Modulus of Deformation of RockMass Using theFlexiblePlateLoadingMethod (R 1994),ASlM 04395-84.Philadelphia,PA: ASlM. TIC Catalog Number: 238038.

Barton, N. 1983. Applicationof Q-System and index tests to estimate shearstrength and deformability of rock masses. Proceedings: International

Symposium on Engineering Geology and Underground Construction, ll:ll.51-ll.70. lisbon, Portugal: Sociedad Portuguesa de Geotecnia and

LaboratorioNacionalde EngenhariaCivil.TIC Catalog Number: 240444.Bieniawski, ZT. 1978. Determining rock mass deformability: Experience

fromcase histories.Inte rna tion al Jou rna l of Roc k Mec han ics and Min ingSciences and Geomechanics Abstracts. 15(5): 237-247. Oxford; NY:

Pergamon.TIC Catalog Number:218740.Boyle, W,J. 1992. Interpretation of Plate Load Test data. Imemational

Jou rna l of Roc k Mec han ics and Min ing Sci enc es and Geo mec han icsAbs trac ts. 29( 2): 133-141. Oxford; NY: Pergamon. TIC Catalog

Number:238852.Brown, E.T. Editor. 1981.Rock Characterinuion Testing & Monitoring:

ISR M Sug ges ted Me tho ds. Oxford;NY: Pergamon.TIC Catalog Number:

9663.CRWMS M&O. 1997.Ambient Characterization of the Drift-Scale Test

Blo ck. BADDOOOOO-OI717-5705-

ISRM-9CONGRESS-1999-269_Determination' of Rock Mass Modulus Using the Plate Loading Method

Documents

Transcript of ISRM-9CONGRESS-1999-269_Determination' of Rock Mass Modulus Using the Plate Loading Method