FRACOD Modeling of Rock Fracturing and Permeability Change in Excavation Damaged Zones

Transcription

1 The 12 th Intenational Coneence o Intenational Association o Compute Methods and Advances in Geomechanics (IACMAG) 1-6 Octobe, 28 Goa, India FRACOD Modeling o Rock Factuing and Pemeability Change in Excavation Damaged Zones O. Stephansson GeoFoschungsZentum-Potsdam, D Potsdam, Gemany B. Shen CSIRO Exploation and Mining, Qld 469, Bisbane, Austalia M. Rinne FRACOM Ltd., Faasbacken 14, FIN-24 Kykslätt, Finland K. Amemiya and R. Yamashi Hazama Cop., Tokyo, Japan S. Togui Radioactive Waste Management Funding and Reseach Cente, Tokyo, Japan Keywods: ock actue mechanics, excavation damage zone, EDZ, pemeability, validation ABSTRACT: Chaacteization o Excavation Damaged Zone (EDZ) aound an undegound excavation is a majo eseach topic o deep geological disposal o medium to high level adioactive waste. Rock actuing due to excavation and themal loading and its esultant ock mass pemeability change in the EDZ ae impotant aspects in the EDZ chaacteisation. A new unction to pedict ock mass pemeability change in actued ocks has been developed and added into the existing actue mechanics code FRACOD. The new unctions in FRACOD has been applied to pedict the extent o EDZ and pemeability change in the vicinity o the TSX tunnel o URL (Canada), the ZEDEX tunnel o the Äspö Had Rock Laboatoy (Sweden) and the deposition tunnels in cystalline and sedimentay ocks (Japan). The pedicted the EDZ and its pemeability ae consistent with the measuement data o the TSX tunnel. In the validation test against the ZEDEX tunnel esults, a boad ageement between the FRACOD pediction and measuements has been achieved. The esults om both tests indicate that FRACOD with the new unction is capable o ealistically pedicting the EDZ and pemeability change. Following the validation tests FRACOD is applied to studying the EDZ o conceptual deposition tunnels o adioactive waste in Japan. 1 Intoduction Wheneve ock is excavated, the zone aound the excavation is alteed. Two dieent types o alteation zones ae possible: a) an excavation damaged zone and b) an excavation distubed zone. The excavation damaged zone (EDZ) is deined as the pat o the ock mass adjacent to an opening whee ievesible deomation and actue popagation and/o new actues ae developed. The excavation distubed zone (EdZ) is deined as the zone beyond the EDZ whee stess edistibution occus but the deomations ae mainly elastic and evesible with mino changes in pemeability. A eview o EDZ and EdZ in dieent ock types ae pesented by Tsang et al. (25). In the pesent pape the EDZ is consideed. In pincipal thee ae ou actos aecting the chaacteistics and extent o the EDZ: 1) excavation method; 2) the in-situ stess and its oientation; 3) stength and deomability o the ock mass; and 4) hydaulic pessue in the goundwate suounding the opening. When an undegound opening is excavated the vigin stess in the ock mass will be changed and a stess concentation and eduction will appea at the peiphey o the opening which might lead to ock all and spalling. The excavation method used will cause an additional EDZ. Dilling and blasting geneally causes geate damages than tunnel boing machines. The ZEDEX expeiment in the Äspö Had Rock Laboatoy compaed the extent o EDZ in tunnelling caused by tunnel boing machine and dilling and blasting (Emsley et al., 1997). The EDZ caused by the tunnel boing machine is much less than that caused by dilling and blasting method. Cetain ock eatues, such as poosity, micostuctues and hydaulic conductivity in the EDZ aound deposition tunnels aect the long-tem saety aspects. Theeoe, it is o the utmost impotance to minimize the extent o EDZ and to undestand its evolution with time. The EDZ can be educed by oienting the excavations and tunnels 148

2 so that the longest axes o the openings coincide with the oientation o the maximum pincipal stess, optimizing the geomety o the openings to avoid stess concentations, and avoiding aeas with low ock stength. A ock actue mechanics code FRACOD has been used in this study. FRACOD was designed to simulate actue initiation, popagation and coalescence in had ocks (Shen and Stephansson, 1993; Shen, 22), and it has been used in a numbe o eseach pojects o the Swedish nuclea waste deposition, including the Äspö Pilla Stability Expeiment (APSE) (Rinne et al., 22, 23). It has also been used in modelling boehole beakouts (Shen et al., 22). The code has the capacity o pedicting actue initiation, popagation and coalescence o pe-existing joints and newly omed actues in the vicinity o excavations. It also pedicts the locations and elative magnitude o Acoustic Emission (AE) o micoseismicity. This contibution concens the latest development o FRACOD, in which the theoetical omulations and the numeical pocedues o a new pemeability unction ae descibed togethe with the ollowing validations and applications: Validation tests o FRACOD against AECL s URL pemeability measuement esults in the TSX tunnel o URL, Canada. Validation tests against the ZEDEX measuement esults in the Dill & Blast Tunnel and the TBM Tunnel o the Äspö Had Rock Laboatoy, Sweden. Application o FRACOD to pedict EDZ pemeability o the Japanese deposition tunnel in cystalline actued ock. 2 Hydaulic conductivity in actued ock mass A actued ock mass consists o the intact ock and ock actues. Fluid low in a actued ock mass occus in both the actues and though the poous intact ock, although oten the actue low is dominant. The hydaulic conductivity o a actued ock mass is a combination o that o the actues and the intact ock. Depending on the distibution o the actues, the equivalent ock mass conductivity may o may not be easily obtained. 2.1 Rock mass with a single actue Let us examine a simple case as shown in Figue 1, whee a ock mass contains a though-going actue. L Q Q (a) Poous ock Joint Q Q w Figue 1. An idealised hydaulic model o a actued ock mass. Fo a 2D poblem, the total low volume in the intact ock and the actues with apetue a can be witten as: Factue: Intact ock: Q Q 3 a dp 12μ dl Fo the whole actued ock mass, the total low volume is: o Q Q = Q = (1) dp dl = wk (2) + Q ( + K ) w K 3 a = w + K 12μw dp dp = wk dl dl dp dl = (4) (3) 149

3 Whee K is total conductivity o ock mass, K is conductivity o actue, K is conductivity o intact ock, w is width o ock mass element. In Equation (4), the actue conductivity is expessed as K 3 a 12μ w = (5) and the total ock mass conductivity is expessed as: K = K + K (6) Note that the actue conductivity in the equivalent om o the poous ock conductivity is expessed as a unction o the actue apetue (a) and the width o ock mass element (w). In a ock mass which contains a set o actues, the width o ock mass element (w) is actually the actue spacing. 2.2 Rock mass with seveal actues In a ock mass with sub-paallel actues, the luid pessue loss in each actue is the same, wheeas the total low volume o all actues is the sum o that o each individual actue. I thee ae n paallel actues with a dip angle θ to the hoizontal diection, the total ock mass conductivity can be calculated by: 3 ai cosθ i i= 1, n K = + K 12μw (7) In a ock mass with a seial o n connected actues the total ock mass conductivity is govened by a summation o the contibution om each individual actue as ollows: Li cosθ i K i= 1, n L / K + K = whee L i is the length o a actue segment, and i= 1, n K i ( i) ( i) 3 ai = 12μw Fo a ock mass with andomly-distibuted actues, it is vey diicult to obtain an analytical expession o the oveall pemeability. An appoximation method is used in this study to estimate the oveall ock mass conductivity. We conside two exteme cases. The ist is that all the actues ae linked end-to-end in a seial patten. The oveall hydaulic conductivity o all the actues in this patten is given by ist tem o the ight hand side in Equation (8). The oveall actue conductivity o a set o actues connected in a seial patten. It is oten dominated by the least conductive actues, hence epesents the lowe end o the possible conductivity values. The second case is that all actues ae ovelapped in a paallel patten. Then, the oveall hydaulic conductivity o all the actues in this patten is given by the ist tem in Equation (7). It is the oveall actue conductivity o a set o actues ovelapped in a paallel patten. It is oten dominated by the maximum conductivity o all the actues, hence epesents the highe end o the possible conductivity values. We then estimate the actual actue oveall conductivity by using the mathematical mean value o its highe- and lowe-end values as ollows: 1 ( i) 2 L cos ik θi i= 1, n K = (9) ( i) / Li K i= 1, n Using Equation (9), the actue system is simpliied to be a single equivalent actue with a conductivity The eective length o the equivalent actue is estimated by L = L i i= 1, n (8) K. cosθ i (1) The eective length L may be longe o shote than the ock mass element L. I it is shote than L, the equivalent actue is contained in the ock mass. The conductivity o the ock mass system is then estimated by: 15

4 K L / L ( L L ) / L ( K + K ) ( K ) = (11) In Equation (11), i the equivalent length L is zeo (i.e. no actues), the esultant ock mass conductivity is the intact ock conductivity K only. I L equals to L, the esultant ock mass conductivity will be K + K. I the equivalent actue length L is geate than L, it will be teated as one (o moe) though-going actue with length o L and a contained actue with a length o L = L -L. Then the conductivity o ock mass is estimated by: K L L ' ' L / L ( L L )/ L ( K + K ) ( K ) = intege K + (12) 3 Pedicting conductivity using FRACOD FRACOD simulates ock mass ailue using explicit actuing pocess such as actue initiation, popagation and coalescence. The nomal and shea displacements o the existing and new actues ae pedicted and ecoded duing the ailue pocess. It pedicts the actue apetue change using the nomal displacement o the actues. Each actue is discetised into a numbe o Displacement Discontinuity (DD) elements in a FRACOD model. Each element has a constant actue apetue calculated based on its nomal displacement. The conductivity o each actue element is calculated in FRACOD by 3 a g K = (m/s) (13) ρ 12 μ w whee µ is the dynamic viscosity (o wate at oom tempeatue, µ = 1-3 Pa s); w is the width o the actue zone in metes, o gidpoint spacing used o estimation; ρ is the wate density (kg/m 3 ); and g is the acceleation o gavity (m/s 2 ). Factue θ y x Excavation θ Gid point Window Figue 2. Gid points and windows used o conductivity estimation. In FRACOD models, a numbe o gid points ae speciied in the solid, and the stesses and displacements ae calculated at each gid point. These gid points ae also used to estimate the ock mass conductivity. As shown in Figue 2, we speciied a squae window aound each gid point o conductivity calculation. Only the actue elements within the deined window ae consideed. Fo a ock mass with explicit actues, the hydaulic conductivity is diection dependent. Theeoe, o each gid point we need to conside at least two othogonal diections (i.e. x and y). Fo poblems with cicula excavations, we also conside the adial and tangential diections, see Figue

5 The ock mass conductivity in the x-diection (K) x can be estimated using the equations (9)-(12) and θ i in these Equations is the angle o each actue element to the x-axis. The ock mass conductivity in the y-diection (K) y is calculated by eplacing cosθ i with sinθ i in the same equations. Seveal tests have been peomed using the new hydaulic conductivity unction in FRACOD. A simple model with a single actue located in a.25 m wide ock plate and subjected to uniaxial tension was selected. The theoetical maximum apetue at the cente o the plate is m and the conductivity is m/s. The numeically pedicted conductivity using FRACOD is m/s which is in ai ageement with the analytical solution. 4 Validation tests against AECL S URL pemeability measuements 4.1 Pemeability measuements in EDZs Seveal lage-scale undegound expeiments have been conducted at AECL s Undegound Reseach Laboatoy (URL) in Canada to addess geomechanical issues elated to the disposal o nuclea uel waste. As pat o these expeiments, hydaulic chaacteisation o EDZ was investigated in Room 425 o Tunnel Sealing Expeiment (TSX). The tunnel was excavated using contolled dill and blast technique. In-situ hydaulic expeiments including pulse tests wee conducted aound Room 425 at depth o 425m. The tests wee peomed using SEPPI pobe in eight shot (3-4m in length) adial boehole dilled aound Room 425. Typical vaiations o the in-situ pemeability in the oo and sidewalls o the tunnel ae povided by Souley et al (21). The ock in the AECL s URL is pedominantly Lac du Bonnet ganite. Its mechanical popeties have been extensively studied and well documented. The ock mass is basically intact, containing no o vey ew actues. The in-situ stesses in the AECL s URL ae well undestood. This site is an ideal site o the validation tests because o its simple geology and well undestood ock popeties and in-situ stesses. Room 425 has an elliptical coss section. It is about 4.4m along longe axis and 3.5m along the shote axis. The tunnel is aligned to the maximum hoizontal stess σ 1, and its coss section is in the σ 2 - σ 3 plane. 4.2 Mechanical input paametes used in the validation study Rock mechanical paametes used o the validation study ae mostly om the open liteatue o the AECL s URL, including Souley et al (21), Hajiabdomajid et al (22) and Matino & Chandle (24). Some special input paametes needed o FRACOD modelling ae not eadily available om the liteatue. They had to be assumed based on the past expeience. Whee possible, sensitivity studies ae conducted to quantiy the eect o the assumed paametes. The input paametes o the AECL s URL validation study ae listed in Table FRACOD models and modelling esults The numeical models include the elliptical opening o Room 425. The model s x- and y- axes ae otated to align with the intemediate and mino pinciple stesses. Fou basic numeical models ae used, which have dieent blast damaged zone sizes. The blast damage is simulated by intoducing andomly distibuted shot actues within a speciied distance om the excavation bounday. Model 1: No blast induced actues in ocks Model 2: Random blast induced actues within.2m into ocks Model 3: Random blast induced actues within.4m into ocks Model 4: Random blast induced actues within.6m into ocks 4.4 EDZs With o without the blast induced actues, all ou models pedict actue initiations in the oo and loo o the elliptical caven. The pedicted EDZ and pemeability o Model 4 ae shown in Figues 3. The zones o actue initiation ae appoximately -.7m deep into the ock. The newly initiated actues ae not pedicted to popagate unde the stess conditions applied. Theeoe, no extensive spalling o beakout has been pedicted to occu. This agees with the obsevation at Room 425 that the excavation was geneally stable. In the sidewalls o the elliptical caven, no stess induced actue initiations ae pedicted because the stesses ae eleased athe than inceased om excavation. Any damage in these zones is likely to be caused by the excavation pocess athe than stess concentation. 152

6 4.5 Hydaulic conductivity in EDZs The EDZs and the hydaulic conductivities in the oo and sidewalls o the elliptical caven using the ou models wee simulated. In each model, two hydaulic conductivity values ae povided: one in the x-diection (subhoizontal), the othe in y-diection (sub-vetical). A geometical mean value o the two values is also calculated. In the caven oo, the pedicted hydaulic conductivities o all ou models ageed easonably well with the measuement esults, Figue 4. The pedicted EDZ is about m-.7m om the excavation bounday. In the EDZ, the modeled hydaulic conductivity is mostly in the ange o 1x1-12 to 1x1-9 m/s, matching well with the measuement esults. Table 1. Input paametes o the AECL s URL validation study. Input paamete Value Souce Rock type: Lac du Bonnet ganite Hajiabdolmajid (22) ; Souley et al. (21) Intact compessive stength (σ c) Intact tensile stength (σ t) Rock mass stength (σ cm) 224 MPa 1 MPa 128 MPa Hajiabdolmajid (22) Intenal iction angle (φ) 48 Intact ock cohesion (c) 43 MPa Based on σc and φ Young s modulus (E) 6 GPa Poisson s atio (ν).2 Hajiabdolmajid (22) Factue toughness: K Ic.96 MPa m1/2 Souley et al. (21) Factue toughness: K IIc 2 MPa m1/2 Assumed In-situ stess σ 1 In-situ stess σ 2 In-situ stess σ 3-55 MPa -48 MPa MPa Souley et al. (21) Factue initiation level (σ ci):.3σc o 67 MPa Emsley et al. (1997) Factue nomal stiness (K n) 138 GPa/m Assumed Factue shea stiness (K s) 399 GPa/m Factue iction angle (φ) 48 Fom intact ock stength Factue cohesion (c) 43 MPa Factue dilation angle (φ d) 5 Assumed In-situ hydaulic conductivity (K in-situ) 1-14 m/s Souley et al. (21) Factue initial apetue (e initial) Factue esidual apetue (e esidual) m m Assumed In the sidewalls, Model 4 (with blast induced cacks within.6m into ock) poduces the best esults compaed to the measuement esults, Figue 4. The modeled EDZ is about.7m and the hydaulic conductivity is about 1x1-13 to 1x1-12 m/s, both ae in geneal ageement with the measuements. Othe models with no o smalle blast damage zones have pedicted EDZs in the sidewalls smalle than the measuements, depending puely on the assumed extents o the blast damage. The stesses (tensile o compession) in these zones ae not high enough to cause actue initiation. 153

7 Pemeability tests - URL validation (Model 4) Max. Hydo-Conductivity: E-9 Elastic actue Open actue Slipping actue Factue with W ate 3.5 Facom Ltd 3. Date: 13/9/26 13:29: E E-1 1E E E E E E E E E-14 Figue 3. Pedicted EDZ and pemeability K x in Model 4. Roo Side wall Hydaulic conductivity (m/s) E-8 E-9 E-1 E-11 E-12 E-13 Measuements: Hydaulic conductivity (m/s) Model 4: hoiz. conduc. (m/s) Model 4: vetical. conduc. (m/s) Model 4: mean value (m/s) H yd au lic co n d u c tivity (m /s) E-8 E-9 E-1 E-11 E-12 E-13 ` Measuements: Hydaulic conductivity (m/s) Model 4: hoiz. conduc. (m/s) Model 4: vetical. conduc. (m/s) Model 4: mean value (m/s) E Distance into wall (m) (a) Roo E Distance into wall (m) (b) Side walls Figue 4. Model 4: measued and simulated hydaulic conductivity; x-diection (let), y-diection (ight). Oveall, the FRACOD modelling esults agee well with the pemeability measuement data at Room 425, paticulaly in the caven oo and loo. The numeical esults also indicate that blast damage dominates the EDZs at sidewalls but has little eect on the EDZs in the oo and loo whee damage is caused by stess concentation. At AECL s URL, a Blast Damage Assessment Tunnel was excavated and investigated (Matino and Chandle, 24). It was ound that the blast damage can extend up to m into the walls. Theeoe, the assumption o blast damage zone o.4m-.6m in Models 3 and 4 is consideed to be easonable. 154

8 5 Validation tests against ZEDEX EDZ measuements 5.1 Investigation o EDZs at ZEDEX site ZEDEX (Zone o Excavation Distubance Expeiments) was one o the ist undegound expeiments conducted to study the damage and distubance om excavation by blasting and tunnel boing. It was conducted at ÄSPÖ Had Rock Laboatoy in Sweden at a depth o 42m. Two paallel expeimental tunnels wee excavated, one by dill & blast (D&B) and the othe by TBM. The D&B tunnel is a semi-cicula excavation with a lat loo. The TBM tunnel is a cicula opening. Both tunnels have a diamete o 5m. The tunnels wee diven in the diection o appox. 45 om the hoizontal pincipal stesses. 5m 25m 5m (a) D&B Tunnel (b) TBM Tunnel Figue 5. ZEDEX tunnels geomety. Compehensive tests wee conducted to chaacteise the EDZs aound the two tunnels (Emsley et al., 1997), which include in-situ stess measuements, AE monitoing, displacement monitoing, in-situ and laboatoy pemeability tests, and seismic mapping. The esults om ZEDEX indicate that the EDZ in the TBM tunnel is in the ange o -.35m depending upon the method o measuements. In the D&B tunnel, the EDZ is in the ange o -m, and the deepest EDZ was measued in the loo. Hydaulic conductivity was measued both in-situ using Pulse Tests and in laboatoy using the oiented coes om dill holes. The in-situ hydaulic conductivity is in the ange o m/s, is highly iegula and possibly aected by the pe-existing actues. The laboatoy measuements indicate that, in the TBM tunnel walls the hydaulic conductivity all within a naow ange om m/s, wheeas in the D&B tunnel, it anges om In both tunnels, an obvious incease o hydaulic conductivity was measued within.2m-.6m into the tunnel walls. The ZEDEX expeiments ae a complicated case o the code validation tests, pimaily due to the ollowing easons: (a) the geology is complex and actues ae well developed at the ZEDEX site, (b) the in-situ stesses ae not ully undestood. Uncetainties exist in the measued and extapolated stesses at the ZEDEX site, and (c) the EDZs ae vey limited, making it diicult to study the stess-induced actues. Theeoe, this study o the ZEDEX expeiment is moe qualitative than quantitative. 5.2 Input paametes Rock mechanical paametes used o the validation study at the ZEDEX site ae mainly based on: SKB technical epot by Emsley et al. (1997), Chyssanthakis et al. (23), Rinne et al. (23). The input paametes o the ZEDEX validation study ae listed in Table

9 Table 2. Input paametes o the ZEDEX validation study. Input paamete Value Souce Rock type: Äspö Dioite Emsley et al. (1997) Intact compessive stength (σc) 165 MPa Rinne et al. (23) Intact tensile stength (σt) 14.8 MPa Intenal iction angle (φ) 49 Intact ock cohesion (c) 31 MPa Young s modulus (E) 68 GPa Poisson s atio (ν).24 Factue toughness: KIc 4 MPa m1/2 Rinne et al. (23) Factue toughness: KIIc 6.35 MPa m1/2 In-situ stesses: σh (317.5 N) -2.7 MPa Chyssanthakis et al. (22) σv -1.4 MPa σh -9.6 MPa Factue initiation level (σci):.3σc and.12σc Emsley et al. (1997) Factue nomal stiness (Kn) 138 GPa/m Assumed Factue shea stiness (Ks) 399 GPa/m Factue iction angle (φ) 49 Fom intact ock stength Factue cohesion (c) 31 MPa Factue dilation angle (φd) 5 Assumed In-situ hydaulic conductivity (Kin-situ) 1-13 m/s Emsley et al. (1997) Factue initial apetue (einitial) m Assumed Factue esidual apetue (eesidual) m Two actue initiation levels (.3σ c and.12σ c ) ae used in this study. The ist is based on the pevious laboatoy tests and the AECL esults, wheeas the second is based the AE monitoing at ZEDEX expeiments (Emsley et al., 1997). It has been agued by Emsley et al. (1997) whethe the measued AEs at ZEDEX epesent the actue initiation because it is signiicantly lowe than the nomal level. It could be also possible that the actual in-situ stesses ae highe than measued, esulting in a highe actue initiation level than.12σ c. Results om actue initiation stess.12σ c ae pesented in this contibution. 5.3 FRACOD models and modelling esults The D&B tunnel and the TBM tunnel ae simulated sepaately using two models, each assumed to be in an ininite ock mass. The ollowing ou cases wee studied: Case D&B1 D&B tunnel without blast induced actues Case D&B2 D&B tunnel with blast induced actues Case TBM1 TBM tunnel without blast induced actues Case TBM2 TBM tunnel with blast induced actues. The modelling esults o tunnels with actue initiation level.12σ c ae shown in Figue 6. The pedicted EDZ is pedominately in the oo and loo o the tunnels whee stess concentation occus due to the highe hoizontal stess than the vetical stess. Fo the D&B tunnel, the EDZ extends up to 1.3m into the loo and.8m into the oo, but vey limited distance into the sidewalls. Fo the TBM tunnel, the EDZ extends about.7m into both the oo and loo, and insigniicant distance into the sidewalls. The pedicted hydaulic conductivity in the EDZ anges om the backgound value o m/s to a maximum value o about m/s. The maximum value agees well with the measued hydaulic conductivity in the vetical boeholes o the D&B tunnel which is about m/s (o m 2 in the epot by Emsley et al., 1997). Howeve, the pedicted hydaulic conductivity does not agee with the vey low values measued in the oo and loo o the TBM tunnel. The FRACOD models also pedict a maximum convegence o 2.6mm in the D&B tunnel and 2.8mm in the TBM tunnel. The measued maximum convegence at two locations o the TBM tunnel is 3.6mm and 1.3mm espectively. Thei aveage value o mm agees well with the FRACOD model pedictions. Oveall, the pedicted EDZs in the ZEDEX tunnels ae in a boad ageement with the measuements, taking into account the uncetainties in the in-situ stesses and the local actue initiation levels. 156

10 Pemeability validation tests - ZEDEX Blast Tunnel Max. Hydo-Conductivity: E Elastic actue 4.5 Open actue 4. Slipping actue 4. Factue with Wate Facom Ltd 5. Pemeability validation tests - ZEDEX TBM tunnel Max. Hydo-Conductivity: 3.864E Elastic actue 4.5 Open actue 4. Slipping actue 4. Factue with Wate Facom Ltd 3. Date: 27/9/26 18:33: E-8 3. Date: 27/9/26 18:39: E E E-9 1E-9 1E-9 3.2E-1 3.2E E E E E E E E E E E E E (a) D&B Tunnel 1E (c) TBM Tunnel 1E-13 Figue 6. Pedicted EDZ and hydaulic conductivity o D&B tunnel (let) and TBM tunnel (ight) o the ZEDEX expeiment at Äspö Had Rock Laboatoy. 6 FRACOD pediction o EDZ pemeability o deposition tunnels in Japan FRACOD is applied to pedict the EDZ and the pemeability change aound a deposition tunnel o the Japanese concept o adioactive waste disposal in had ocks. The epositoy consists o paallel deposition tunnels with a diamete o 2.26m. The distance between tunnels is 6 times the tunnel diamete. Input paametes used in the FRACOD models o cystalline ock at depth o 1m ae shown in Table 3. The existence o pe-existing actues has some eect on the EDZ (Figue 7). The pe-existing actues within m om the tunnel wall ae patially activated and expeiencing shea slipping. The slipping actues howeve, ae not pedicted to popagate, and the tunnel emains stable. The maximum hydaulic conductivity in the EDZ is about which occus at the pe-existing actues nea the tunnel. 7 Conclusions A systematic study is conducted in this poject to investigate the easibility o using FRACOD to pedict the EDZ and pemeability change o nuclea waste disposal. This study includes: Detailed omulations to estimate the hydaulic conductivity o an explicitly actued ock mass. The calculated hydaulic conductivity allows inlow calculations to be made once the hydaulic bounday conditions ae known. The theoetical omulations have been implemented into FRACOD, and the new code vesion can now pedict the ock mass hydaulic conductivity duing ock actue initiation, popagation and coalescence. Validation tests o FRACOD have been conducted against AECL s URL pemeability measuement esults in the TSX tunnel. The FRACOD model pedicts the EDZ and its pemeability that ae consistent with the measuement data, paticulaly in the oo/loo egion o the TSX tunnel whee stess concentations exist. In the sidewalls whee stess elease occus, the model has to include the blast-induced actues to poduce esults easonably close to the measuements. Validation tests have been caied out against the ZEDEX measuement esults in the Dill & Blast Tunnel and the TBM Tunnel at Äspö Had Rock Laboatoy, Sweden. An oveall ageement between the FRACOD pediction and measuements has been achieved. The uncetainties in insitu stess data and the actues at the ZEDEX site, howeve, made it diicult o a detailed compaison between the numeical esults and measuements. The validation tests against both the AECL URL measuements and the ZEDEX measuements indicate that FRACOD is capable o ealistically pedicting the EDZ and pemeability change. In addition, the tests also povide us conidence on the input paametes used in the FRACOD models. 157

11 Tunnel at 1m depth - HAZAMA pemeability ptoject Max. Hydo-Conductivity: E-9 Elastic actue Open actue Slipping actue Factue with Wate Facom Ltd 2. Date: 28/9/26 6:25: E E E E E-9 1E E E E-9 8E E E E E-9 Figue 7. FRACOD simulation o EDZ and hydaulic conductivity in a tunnel o actued had ocks at a depth o 1 m o the Japanese adioactive waste pogam. Table 3. Input paametes o the tunnel at cystalline ock at depth o 1m. Stephansson et al. (23) Input paamete Value Souce Rock type: Cystalline ock Yamayama (pesonal communication) Intact compessive stength (σ c) 115 MPa Intact tensile stength (σ t) 8 MPa Intenal iction angle (φ) 45 Intact ock cohesion (c) 24 MPa Young s modulus (E) 37 GPa Poisson s atio (ν).25 Factue toughness: K Ic 1.73 MPa m 1/2 Factue toughness: K IIc 3.7 MPa m 1/2 In-situ stesses: σ H MPa Yamayama (pesonal communication) MPa σ v Factue initiation level (σ ci):.3σ c Emsley et al. (1997) Factue nomal stiness (K n) 138 GPa/m Stephansson et al. (23) Factue shea stiness (K s) 399 GPa/m Factue iction angle (φ) 45 Fom intact ock stength Factue cohesion (c) 24 MPa Factue dilation angle (φ d) 2 Stephansson et al. (23) In-situ hydaulic conductivity (K in-situ) 1-9 m/s Amemiya (pes. communication) Factue initial apetue (e initial) m Assumed Factue esidual apetue (e esidual) m Following the validations tests, FRACOD is applied to study the EDZ o the conceptual deposition tunnels o adioactive waste in Japan. When the tunnels ae excavated at depth o 1m in a cystalline actued ock, the 158

12 pedicted EDZ is limited within.25m into the tunnel walls and the hydaulic conductivity in the EDZ is less than m/s. The limited EDZ ae contibuted by the nealy hydostatic stess condition and high ock stength. 8 Acknowledgements The development o the pemeability unction in FRACOD and the validation tests wee kindly suppoted by the Hazama Copoation, Japan. 9 Reeences Chyssanthakis P., Tunbidge L., Chistiansson R. 23. Numeical modelling in 3D o the TBM/ZEDEX tunnels at Äspö, Had Rock Laboatoy and compaison with in-situ measuements. Poceedings o Undegound Constuction Coneence, London. Emsley S., Olsson O., Stenbeg L. Alheid H-J., Falls S Zedex A study o damage and distubance om tunnel excavation by blasting and tunnel boing. SKB Technical Repot Hajiabdolmajid V., Kaise P.K., Matin C.D. 22. Modelling bittle ailue o ock. Int J Rock Mech & Min Sci. 39, Matino, J.B., Chandle N.A. 24. Excavation-induced damage studies at the Undegound Reseach Laboatoy. Int J Rock Mech & Min Sci. 41, Rinne M., Shen B., Lee H-S. 23. Äspö Had Rock Laboatoy. Äspö Pilla Stability Expeiment. Modelling o actue stability by FRACOD. Peliminay esults. SKB IPR-3-5, Svensk Känbänslehanteing AB, Stockholm. Rinne M, Shen B, Lee H-S, Jing L 23. Themo-mechanical simulations o pilla spalling in SKB APSE test by FRACOD. GeoPoc23, Intenational Wokshop Octobe, Stockholm. Shen B. 22. FRACOD Vesion 1.1, Use s manual. FRACOM Ltd. Shen B. 24. Development o FRACOD o Multiple Region Poblems. FRACOM Ltd Repot (24) Pepaed o Hazama Copoation. Shen B., Stephansson, Modiication o the G-citeion o cack popagation subjected to compession. Int. J. o Engineeing Factue Mechanics 47(2), Shen B., Stephansson, O. and Rinne, M., 22. Simulation o boehole beakouts using FRACOD 2D, Oil & Gas Science and Technology Rev. IFP, 57(5), Shen B., Rinne M., Stephansson O. 26. Development o FRACOD o pemeability modelling in MIU Poject. FRACOM Repot, Pepaed o Hazama Copoation. Souley M., Homand F., Pepa S., Hoxha R. 21. Damage-induced pemeability changes in ganite: a case example at the URL in Canada. Int J Rock Mech & Min Sci. 38, Stephansson O., Shen B., Rinne M., et al. 23. Mechanical evaluation and analysis o eseach shats and galleies in MIU Poject, Japan. The 1 st UE Koyoto Symposium. Pape No. UE3-K9, Mach, Kyoto, Japan. Tsang C-F., Benie, F., Davies, C. 25. Geohydomechanical pocesses in the Excavation Damaged Zone in cystalline ock, ock salt and induated and plastic clays in the context o adioactive waste disposal. Int. J. Rock Mech. Min. Sci. 42,