on behalf of DEEP Underground Engineering GmbH

Transcription

1 Rock mechanical investigations on the strength and creep behaviour of core samples from Larne - Carnduff location (Ireland) Final Report - Status:.. on behalf of DEEP Underground Engineering GmbH Clausthal, June Chair for Waste Disposal Technologies and Geomechanics Erzstraße 37 Clausthal-Zellerfeld - Tel.: 33/ 7 Telefax: 33/ 73 uwe.duesterloh@t-online.de

2 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff

3 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff Rock mechanical investigations on the strength and creep behaviour of core samples from Larne - Carnduff location (Ireland) Final Report - Status:.. on behalf of DEEP Underground Engineering GmbH Clausthal, June () (Prof. Dr.-Ing. habil. K.-H. Lux) Univ. Prof. Dr.-Ing. habil. K.-H. Lux / Chair for Waste Disposal Technologies and Geomechanics Erzstraße 37 Clausthal-Zellerfeld Tel.: 933/7 Telefax: 933/ 73 uwe.duesterloh@tu-clausthal.de 3

4 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff Contents page Motive and background to the test programme... Specimen preparation and physical parameters... 3 Short-term tests under uniaxial compression Test procedure and method Test evaluation Measurement results of uniaxial pressure tests... 7 Short-term tests under triaxial compression.... Test procedure and method.... Test evaluation....3 Measurement results of the triaxial compression tests.... Indirect tensile tests Test procedure and method Test evaluation Measurement results Direct shear tests Test procedure and method Test evaluation Measurement results Creep tests under uniaxial compression Test procedure and method Test evaluation Measurement results... 3 Creep tests under triaxial compression Test procedure and method Test evaluation....3 Measurement results... 9 Triaxial extension tests with cyclic loading Test procedure and method Test evaluation Measurement results of the triaxial extension tests with cyclic loading... Compilation of the measurement results and derivation of material parameters Lubby material model Parameters for stationary creep... 7

5 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff.3 Transient creep parameters.... Failure and dilation strength.... Failure strain.... Deformation energy....7 Shear strength mudstone.... Thermal expansion coefficient... Appendices... 9 Appendix : Appendix : Specimen details Measurement records and photographic records of specimens before and after testing

6 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff Motive and background to the test programme The Chair for Waste Disposal Technologies and Geomechanics was engaged to conduct uniaxial and triaxial short-term as well as uniaxial and triaxial long-term tests to evaluate the strength and creep properties of salt from the Larne location. The core material used for the laboratory tests was taken from exploration well Carnduff shown in Fig... core boxes selected for rock mechanical testing box depth 3 / 39 / 37 7,m -,m ,9m - 7,m 33 / 3 / 3 /3 7,9m - 73,9m 39 / 39 77,7m - 7,m / 3 7,m - 7,m 9 / 7,m - 77,m / 73,m - 7,m 3 79,m - 79,9m 3,3m - 3,m 39 /,m -,m 7,9m - 9,m 3 33,9m - 3,m 37,m - 39,m 7 9,7m -,m 7,m - 7,m,9m -,7m / 7 93,7m - 97,3m 9 9,m - 9,3m 9 / 9 99,7m - 9,m 99 97,m - 99,m Figure.: Details of samples for rock mechanical testing (Well Carnduff )

7 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff The test programme comprised the tests reffering to the priliminary planning shown in Table.: TC-tests (Triaxial Compression), UC-tests (Uniaxial Compression), BT-tests (Brasilian Test), 3 UCc-tests (Uniaxial Compression creep) with a total of 9 load steps, 7 TCc-tests (Triaxial Compression creep) with a total of load steps, TCccyclic-tests (Triaxial Compression creep cyclic) with a total of load steps of d in each case, d duration). No. depth (m) testing 3 (MPa) (MPa) T ( C) h (mm) d (mm) technique, - 3, UC RT,, 79, - 7, UC RT,, 3 73, - 7, UC RT,, 37, - 39, UC RT 9,9, 9, - 93, UC RT,, 79, - 79,9 UC RT,, 7 99,9-7, BT RT, 79,9 7,9-7, BT RT, 79,9 9 7, - 7, BT RT,, 9, - 93, BT RT,, 79, - 7, TC 9 3 9,9 79,9 73, - 7, TC 7 3, 79,9 3 7, - 77, TC,, 7, - 77, TC 3,, 73, - 7, TC,, 73, - 7, TC 3,, 7 79, - 79,9 TC, 79,9, -, TC 9,, 9 33,9-3, TC,, 33,9-3, TC 3 3,, 7

8 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff 37, - 39, TC 7, 79,9,9 -,7 TC 9,, 3 9, - 97,3 TC 3 3, 79,9 9, - 93, TC 3 3,, 7,9-7, TC 3 3,, 73, - 7, TCc // 3/3/3 3// , - 79,9 TCc // // 3//7 - -, -, TCc // 9/9/9 3// , - 39, TCc // 3//9 3/3/ , - 7, TEczykl. ///.. 3 9,9, 3, -, TEczykl. /// ,9, 3 9,7 -, TEczykl. ///.. 3,, 33 7,9-9, TEczykl. ///.. 7 3,, 3 73, - 7, TCc // 3/3/3 3//7,, 3 79, - 79,9 TCc // // 3//7,, 3, -, TCc // 9/9/9 3//7,, 37 37, - 39, TCc // 3//9 3/3/3,, 3 9, - 97,3 TCc // 3//9 3/3/3,, 39 9,7 -, UCc 3//7 9,9, 37, - 39, UCc 3//7 9,9, 33,9-3, UCc 3//7,, Tab..: Rock mechanical test programme summary (priliminary planning) Because during inspection of core material weak mudstone layers were observed particulary in a depth level of 7m - 7m as well as in a depth level of m - m the test programme had to be expanded and modified to get information about the mechanical behaviour of the weak mudstone layers. To keep the offered costs for the lab tests on the one hand and to analyze the material properties of the weak mudstone on the other hand, preliminary planed tests no. to 9 (see Table.) were substituted by tests no. to (see Table.). Due to the bad quality of the core material available from the depth levels with weak mudstone preparation of pecimens with typically used dimensions was not possible. The weak

9 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff mudstone in gerenal is characterized by disintegration into small pieces of few centimeter in length partially combined with solution of the sample surface. Therefore direct shear tests and brasilian tests were performed to generate a first impression about the mechanical strength properties of the weak mudstone. A tabular comparison of the enlarged test programme is given in Table.. No. depth (m) testing technique 3 (MPa) (MPa) T ( C) h (mm) d (mm) 7, - 7,7 BT RT,, 3 7,7-7,77 BT RT, 79,9, -, BT RT,, 7,77-7,99 ST /7/9 RT, 79,9, -, ST // RT 9,9, 7, -, ST // RT 3,, loosened material taken from box compacted by MPa ST // RT 3, 9, 9 7, - 7, ST /7/9 RT 3, 79,9 7, - 7, ST // RT 3, 79,9 7, - 7, ST // RT 3, 79,9 9, - 93, TC 3,, Carnduff # Pressure vessel storage 3, -, TC 3,,,7 -, TC 3 3,,, -,9 TC 9 3,,, -,9 TC 3,, 7 9, - 9,3 TC 3 3,, 9, - 9, TC 9 3,, Tab..: Additional rock mechanical test programme The specimens were produced and prepared as described in Section. Sections 3 to 9 describe the tests and test procedures, the test methods and the test evaluations, and summarise the test results in tables. Sections present the test results overall. 9

10 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff Specimen preparation and physical parameters Confining specimens with plan-parallel end faces were produced on the lathe shown in Figure. from the cores selected for the rock mechanical lab tests. Preparation of the outer surface of the specimens took place if possible refering to sample quality. If material quality was too bad, preparation of outer surface was disclaimed. By performing UC, TC, TCc tests respectively the length l of the specimens is usually twice the specimen diameter d (l /d =). In case of conducting indirect tensile tests (Brasilian tests) a length/diameter ratio of l /d = was used. Direct shear tests have been performed at samples of l /d,. The specimens were photographed before and after the rock mechanical tests to document the nature and fabric of the material forming the specimens. Specimen photographs are attached in Appendix and the CD accompanying the report. Figure.: Lathe of the Chair for Waste Disposal Technologies and Geomechanics for producing standard specimens After photographic documentation, the specimens were placed in the dilational wave analyser built by Geotron-Elektronik, where they underwent axial analysis, Fig...

11 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff Figure.: Dilational wave analyser of the Chair for Waste Disposal Technologies and Geomechanics The measured ultrasonic wave velocities of the P or longitudinal waves (vp) and the S or transverse waves (vs) were entered into Eqs. (.) and (.) to calculate the dynamic elasticity modulus E dyn and the dynamic Poisson s number dyn : E dyn vs 3vp vs vp vs (.) vp vs dyn (.) vp vs where E dyn dynamic elasticity modulus (kpa) dyn dynamic Poisson s number (-) rock density(t/m 3 ) vp longitudinal wave velocity (m/s) vs transverse wave velocity (m/s) The dimensions were measured half way up the height of the specimen and along the central axis of the confining specimen using a slide calliper gauge. The diameters and the lengths, as well as the rock densities calculated from the weight and volumes of the specimens are summarised in Appendix. The rock densities were calculated from Eq. (.3):

12 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff m g (.3) d h rock density (N/m 3 ) m specimen mass (kg) d h diameter of unstressed specimen (m) height of unstressed specimen (m) g gravity (m/s ) After conducting the tests, the specimens were dried in a drying cabinet (as shown in Fig..) at a temperature of C, until constant weight had been achieved (until the mass diminishes by less then / within hours, cf. DIN ). The moisture content is calculated from Eq. (.) by taking the mass difference before and after drying: mh md w m (.) d w moisture content (%) m d m h mass of dried sample (g) mass of wet sample (g) The measured moisture contents are shown in a table in Appendix. Figure.: Drying cabinet of the Chair for Waste Disposal Technologies and Geomechanics

13 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff Additionally to the determination of the moisture content the length of the samples were measured at a temperature similar to room temperature (T = C, before drying) and at a temperature of T = C (after drying). The length measurements were used to calculate the thermal expansion coefficient coresponding to Eg. (.). ( l l ) / l th (.) T th thermal expansion coefficient, K - l sample length at C, mm l sample length at C T temperature difference between length measurement l and l, K A compilation of the thermal expansion coefficients determined by the test programme is given in chapter 7. 3 Short-term tests under uniaxial compression 3. Test procedure and method The short-term tests under uniaxial compression (UC = Uniaxial Compression) were carried out in the hydraulically-controlled kn test bench shown in Fig. 3.. After positioning between the pressure plates of the test bench, the specimens are subjected to a constant strain rate of =. %/min =.33. s reaching the initial specified axial compression of. %. The next phase of the test involves a stress-controlled stress release and stress buildup cycle to determine the deformation modulus. The axial stress is then increased under constant strain rate until the failure load is reached. The stress-dependent axial compression is recorded with an inductive displacement transducer positioned between the upper and lower pressure plates. The axial pressure acting on the specimen was calculated by converting the hydraulic pressure measured in the test cylinder by the absolute pressure transducer. The test temperature corresponded to room temperature (RT C). 3

14 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff Figure 3.: kn test bench of the Chair for Waste Disposal Technologies and Geomechanics 3. Test evaluation During the short-term tests under uniaxial compression, the data recorded by the inductive displacement transducer and the absolute pressure transducer were sampled and electronically saved every. seconds. The axial strain ε of the specimen was calculated from this data (Eq. 3.). By limiting the evaluation to small deformations (ε %), the strains can be calculated as a technical strain ε t in accordance with the standard definition of strain. Technical strain is the quotient of the vertical change in specimen length Δl and the original length l : l % (3.) l t where ε t technical strain (%) l length of the unstressed specimen (mm) Δl measured axial deformation of the specimen (mm)

15 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff In the case of larger specimen deformations (ε > %), technical strain ε t is replaced by natural or true (logarithmic) strain ε ln calculated from the integral of the quotient of the instantaneous (infinitesimal) change in specimen length dl and the instantaneous (current) length l: l dl l ln % ln % ln t % (3.) l l l where ε ln true (logarithmic) strain (%) l current length of the (stressed) specimen = l Δl (mm) l length of the unstressed specimen (mm) The axial pressure which is applied is calculated from the measured hydraulic pressure in the test cylinder making allowance for the cross-sectional area ratios between the piston of the hydraulic cylinder and the specimen pursuant to Eq. (3.3): P A K P PK A (3.3) P where P P P K axial pressure on the specimen (MPa) axial pressure in the hydraulic cylinder (MPa) A K cross-sectional area of the piston (hydraulic cylinder) (mm ) A P cross-sectional area of the specimen (mm ) The documentation for the short-term tests under uniaxial compression, including the axial stress, the axial compression and the axial strain over the whole of the test period is recorded in Appendix, alongside the associated stress-strain diagram. Whilst the diagram of the measured axial stress against test time records compliance with the constant stress rate defined by the test procedure, the depiction of the readings in the stress-strain diagram shows the derived operating characteristics of the specimens reflecting the material properties. The evaluation involves plotting the uncorrected stress-strain curve with σ u pursuant to Eq. (3.), and the corrected stress-strain curve. For the uncorrected stress: F d u where A (3.) A

16 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff The corrected stress is determined using a linear or logarithmic correction of the crosssectional area A of the specimen changing in accordance with compression Δl as defined in Eqs. (3.) or (3.): F A uc where A A F ucln where A where σ uc σ uc-ln F t A ln (3.) A (3.) linear-corrected vertical logarithmically-corrected vertical vertical force (MN) A cross-sectional area of the tested specimen (m ) A cross-sectional area of the untested specimen (m ) l length of the unstressed specimen (m) ε t technical strain (-) ε ln true (logarithmic) strain (-) The stress-strain diagram is used to derive the failure strength D (= highest value of vertical stress or deviator stress) and the failure strain ε ln-fracture. The short-term strength β uc-ln is defined as the stress state in accordance with Fig. 3. at which local destruction takes place in the specimen during the test leading to a significant decrease in stress. The compression corresponding to this stress level is called the failure compression - ln-failure.

17 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff 3 3 uc-ln ln-failure,,, 3 3, siguc-ln Eentl. Figure 3.: Determining short-term failure strength and failure compression in UC tests and determination of the deformation modulus Eentl. 3.3 Measurement results of uniaxial pressure tests The failure strengths and failure strains determined from the uniaxial pressure tests are shown in Table 3.. sample depth no. (m) 3 material uc-ln - ln-failure (MPa) (MPa) (%) ( C), - 3, muddy salt,,3 79, - 7, muddy salt,9, 3 73, - 7, muddy salt 9,, 37, - 739, muddy salt,, 9, - 93, mudstone 3,,7 79, - 79,9 muddy salt,7,93 T Tab. 3.: Mechanical strength parameters from uniaxial compression tests 7

18 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff Short-term tests under triaxial compression. Test procedure and method The short-term tests under triaxial compression (TC = Triaxial Compression) were conducted on the hydraulically-controlled kn test benches shown in Figure.. Figure. shows the principle behind the triaxial cells. () Axial piston () Cover plate (3) Cell sleeve () Base plate Figure.: Schematic diagram of a triaxial cell The construction of the triaxial cell is therefore characterised by four modules: axial piston, cover plate, cell sleeve and base plate. The cover plate and the cell sleeve are screwed together until friction-locked to form a cell cylinder. The base plate and the cell cylinder are connected by a reversible threaded connection and are screwed together after the specimen has been positioned on the base plate or lower pressure plate. The triaxial cell is then filled with the confining pressure medium (hydraulic oil) via the inlet pipe in the base plate. When the triaxial cell has been completely filled (confining pressure medium forced out of the vent hole at the end of the cell) the inlet pipe and the vent hole are closed and the triaxial cell is positioned in the load frame using the moving slide table. The load frame and the triaxial cells are designed for the tests to be conducted using the Kármán principle, i.e. the lateral fluid pressure acting on the confining surface of the specimen (confining pressure) σ = σ3 and the axial pressure σ can be regulated independently of one another. Confining pressures of up to,3 = 7 MPa can be generated in the triaxial test apparatus used here. Test data are recorded during the short-term tests under triaxial compression using three inductive displacement transducers mutually offset by. These record the axial specimen compression. There are also two absolute pressure transducers to record the axial and radial stress on the specimen.

19 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff Figure.: kn test benches of the Chair for Waste Disposal Technologies and Geomechanics Before being positioned in the triaxial cell, the specimens are covered with an impermeable 3 mm thick flexible rubber sleeve to prevent the pressure medium penetrating the specimen during the test. After the specimen has been positioned in the triaxial cell, it undergoes an approx. -hour recompaction and tempering phase under an isotropic stress of MPa (depth of samples 7m - 9m) and a temperature similar to the testing temperature. At the end of the recompaction phase, the axial pressure and the confining pressure are uniformly lowered to atmospheric pressure. This is then followed by the actual controlled test under which the specimen is subjected to uniform isotropic stress till it reaches the specified confining pressure. The test temperature during the test corresponds to the operating temperature of the hydraulic fluid in the hydraulic cycle (specified temperature; C, 3 C, C respectively). Starting from the isotropic stress state, the specimen was subjected to an axial stress at constant confining pressure = 3 under a constant strain rate of =. %/min =.7. s until reaching the initial specified axial compression of. %. The next phase of the test involves main- 9

20 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff taining constant confining load during a stress-controlled stress release and stress build-up cycle to determine the deformation modulus. The axial stress is then increased under constant compression rate until the failure load is reached. The axial compression is recorded during the test by three inductive displacement transducers mutually offset by. The axial pressure acting on the specimen is determined by converting the hydraulic pressure measured in the test cylinder by an absolute pressure transducer. The specimens are removed from the apparatus after the test and photographed again for the record. The photographs of the specimens are shown in Appendix and in the CD attached to this report.. Test evaluation During the short-term tests under triaxial compression, the data recorded by three inductive displacement transducers and the absolute pressure transducer were sampled and electronically saved every. seconds. The axial strain ε of the specimen was calculated from this data (Eq..). By limiting the evaluation to small deformations (ε %), the strains can be calculated as a technical strain ε t in accordance with the standard definition of strain. Technical strain is the quotient of the vertical change in specimen length Δl and the original length l : l l l3 3 l t % % (.) l l where ε t technical strain (%) l, l, l 3 axial deformation measured by the three inductive displacement transducers (mm) l Δl length of the unstressed specimen (mm) measured axial deformation of the specimen (mm) In the case of larger specimen deformations (ε > %), technical strain ε t is replaced by natural or true (logarithmic) strain ε ln calculated from the integral of the quotient of the instantaneous (infinitesimal) change in specimen length dl and the instantaneous (current) length l:

21 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff l dl l ln % ln % ln t % (.) l l l where ε ln true (logarithmic) strain (%) l current length of the (stressed) specimen = l Δl (mm) l length of the unstressed specimen (mm) The axial pressure which is applied is calculated from the measured hydraulic pressure in the test cylinder making allowance for the cross-sectional area ratios between the piston of the hydraulic cylinder and the specimen pursuant to Eq. (.3): P A K P PK A (.3) P where P P P K axial pressure on the specimen (MPa) axial pressure in the hydraulic cylinder (MPa) A K cross-sectional area of the piston (hydraulic cylinder) (mm ) A P cross-sectional area of the specimen (mm ) The documentation for the short-term tests under triaxial compression including the axial stress, the confining stress, the v. Mises stress, the axial compression, and the axial strain over the whole of the test period, is recorded in Appendix, alongside the associated stress-strain diagram. Whilst the diagram of the measured axial compression against test time records compliance with the constant strain rate defined by the test procedure, the depiction of the readings in the stress-strain diagram shows the derived operating characteristics of the specimens reflecting the material properties. The evaluation involves plotting the uncorrected stress-strain curve with σ u pursuant to Eq. (.), and the corrected stress-strain curve. For the uncorrected stress: F d u where A (.) A The corrected stress is determined using a linear or logarithmic correction of the crosssectional area A of the specimen changing in accordance with compression Δl as defined in Eqs. (.) or (.):

22 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff F A uc where A A F ucln where A where σ uc σ uc-ln F t A ln (.) A (.) linear-corrected vertical logarithmically-corrected vertical vertical force (MN) A cross-sectional area of the tested specimen (m ) A cross-sectional area of the unstressed specimen (m ) l length of the unstressed specimen (m) ε t technical strain (-) ε ln true (logarithmic) strain (-) The stress-strain diagram is used to derive the failure strength D (= highest value of vertical stress or deviator stress) and the failure strain ε ln-fracture. The short-term strength β uc-ln is defined as the stress state in accordance with Fig..3 at which local destruction takes place in the specimen during the test leading to a significant decrease in stress. The compression corresponding to this stress level is called the failure compression - failure. Figure.3 also shows the determination of the Youngs modulus as the gradient of the lines through the inflection points of the pressure decrease and pressure increase curves. A tabular compilation of the determined Youngs modulus is shown in appendix.

23 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff 7 -ln 3 ln-failure strain (%) sigu siguc siguc-ln sig3 Eentl. Figure.3: Determination of the short-term failure strength and failure compression in TC tests and determination of the deformation modulus Eentl. In addition to the standard recording of axial pressure, confining pressure, axial deformation and temperature, other parameters recorded during the tests were the volume change of the specimen and the change in ultrasonic velocity. The volume change is determined as shown in Figure. from the inductive readings of axial specimen deformation l and the volumetric change in the oil volume in the triaxial cell. The oil volume ±V displaced from the triaxial cell during the test is fed into a twin-chamber cylinder. A mm movement of the piston in the measuring cylinder corresponds to a constructionally defined volume of. ml. Given a measurement accuracy of / mm of the piston of the twin-chamber cylinder, the system outlined here can record changes in volume of the order of. % in the specimen volume. 3

24 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff l M ultrasonic transducer V Figure.: Sketch of the dilation measurement The dilation strength dil-vol is determined on the basis of the volume change characterises. As shown in Figure., the axial stress which is corresponding to a minimum volumetric specimen deformation is identified as dilation strength dil-vol (primarily dilation deformation after exceeding min vol ). Appendix contains a diagram in each case reflecting Figure. to document the dilation strength under triaxial compression determined on the basis of the volume strain.,,, dilatancy (-),3,, dil-vol 3 -, epsvol siguc sig3 Figure.: Determination of dilation strength on the basis of volume strain

25 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff Ultrasonic probes are integrated within the cover and base pressure plates to determine the dilation strength more precisely, see Figure.. The continuous transmission of the samples during the test to record the ultrasonic velocity enables the dilation strength to be determined independently of the volume measurement on the basis of the stress level observed. This is done by detecting a reduction in ultrasonic travel times as a result of the development of physical damage (microfissures). Figure. is a typical example of the determination of dilation strength on the basis of ultrasonic travel times. Fig.. clearly shows that the relationship between the current ultrasonic travel time v p and the ultrasonic travel time at the start of the test v p rises initially (contraction test phase, compression of the specimen) and then ultimately decreases during continued exposure of the specimen to stress as a result of the formation of microfissures. Dilation strength dil-vp is defined as the axial stress at which the ratio v p /v p reaches a maximum. Appendix contains a diagram in each case reflecting Figure. to document the dilation strength under triaxial compression determined on the basis of the ultrasonic travel times., vp/vp (-),9,9,9 dil-vp 3 axial,9,9 vp/vp siguc Figure.: Determination of dilation strength on the basis of ultrasonic travel times

26 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff Within the material model Lux/Wolters the volume change vol as well as the the ultrasonic velocity v define the intensity of damage D (Eq..7). v v p p v v s D s D (.7) vol v v p p vol vol v v s s where v s, v p ultrsonic wave velocity of p-/s-waves at the beginning of the tests, m/s v s, v p current ultrsonic wave velocity of p-/s-waves, m/s D damage, - vol volume change, - (dilatancy - / contraction +) Appendix contains a diagram in each case reflecting to Figure.7 to document the damage induced inside the specimens during the triaxial compression tests. Fig..7 clearly shows that the damage at the start of the test becomes negative because of the increasing ultrasonic wave velocity and the decreasing specimen volume. After a minimum value has been reached, a continous increasing of damage follows depending on the rate of volume change and ultrasonic velocity change. A further mechanical parameter to characterise the stress-strain behaviour is the so called deformation energy in the failure point. Therefore appendix contains a diagram in each case reflecting Figure.. The deformation energy shown in Fig.. is calculated by Eq. (.): bruch W d d v v (.) where v-ln logarithmically corrected v. Mises stress respectively equivalent stress, MPa v-ln logarithmicall v. Mises strain, - W d deformation energy, MPa

27 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff,,, D (-),, D failure 3 -, D siguc sig3 Figure.7: Determination of damage for the failure point - TC-tests 7 deformation energy W d (MPa) 3 w d-failure 3 Wd siguc sig3 Figure.: Determination of deformation energy for the failure point - TC-tests 7

28 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff.3 Measurement results of the triaxial compression tests Table. shows the failure strengths, dilation strengths, failure strains and deformation energies determined by the triaxial compression tests. sample depth no. (m) 3 material uc-ln - ln-failure dil-vol dil-vp W d (MPa) (MPa) (%) (MPa) (MPa) (MPa) 79, - 7, 9 muddy salt,77, 37,,,9 73, - 7, 7 muddy salt 9, 3, 3,3,,7 3 7, - 77, muddy salt 3,3 7, 3, 9,,7 7, - 77, 3 muddy salt,3,39,7,9,7 73, - 7, muddy salt 7,9,9,9 -, 73, - 7, 3 muddy salt 3,33 3,,9,9,9 7 79, - 79,9 muddy salt 3,,, 7, 3,, -, 9 muddy salt 9,33,9 3, 7,, 9 33,9-3, muddy salt 33,7,3,7,,7 33,9-3, 3 muddy salt 3,,99 3, 3,7 3, 37, - 39, 7 muddy salt 9, 7,33,3 33,,97,9 -,7 9 muddy salt,7 3,,3,33 7, 3 9, - 97,3 3 muddy salt 7,,,, 3,9 9, - 93, 3 mudstone,,77 3, 3,, 7,9-7, 3 mudstone,99,,9,9, 9, - 93, mudstone 9,9,9,9,7,37 3, -, mudstone 9,9,, -,,7 -, 3 mudstone, 3,7 - -,, -,9 9 mudstone,3,,9 -,9, -,9 mudstone,9 7,7,7 -,9 7 9, - 9,3 3 mudstone 7,, 7, -, 9, - 9, 9 mudstone,,,3,3,7 Tab..: Mechanical strength parameters from triaxial compression tests

29 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff. Indirect tensile tests. Test procedure and method The tensile tests were carried out on the hydraulically-controlled kn test bench shown in (Fig..). As documented in the letter of instruction no. (research group no. 9 testing technique of rock mass DGGT (Deutsche Gesellschaft für Geotechnik / german association of geotechnique) the application of the slat burden was done by two circular steal plates positioned between the top and the bottom piston of the loading frame as shown in Fig... The leverage shown in Fig.. is used to adjust the circular steal plates over the top and the bottom of the samples. The determining of the (brasilian) tensile strength is based upon the elasticity theorie. Thereafter the tensile strength is computed approximately by Eq. (.): F F F SZ, l r l d 3 l d (.) where tensile strength (MPa) SZ F r d l axial load (N) specimen radius (mm) specimen diameter (mm) specimen length (mm) SZ F F F, l r l d 3 l d drill holes to conduct connecting rods Bild.: kn test bench for determining the brasilian tensile strength 9

30 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff After positioning between the pressure plates of the test apparatus, the specimens are subjected to a constant pressure rate of =. MPa/min until failure load is reached. The stress-dependent axial force is recorded with an inductive displacement transducer positioned between the upper and lower pressure plates. The axial pressure acting on the specimens was calculated by converting the hydraulic pressure measured in the test cylinder by the absolute pressure transducer. The test temperature corresponded to room temperature (RT C).. Test evaluation The computer-supported regulation of the tensile test bench is conducted by automatically sampling the transducers every. seconds followed by a set-actual comparison of the specified stress rate. The registered measurement data are electronically saved during the test and kept for the record and for subsequent evaluation of the results. The tensile stress-strain diagram based on these readings as exemplarily shown in Fig.. are attached to this report in Appendix to document the tensile tests. The stress-strain diagram is used to derive the tensile failure strength SZ (stress value by first occurrence of a crack). 3, brasilian tensile,, SZ,,,,,,3,3,, Figure.: Determining tensile strength by brasilian tests 3

31 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff.3 Measurement results The tensile strengths determined from the brasilian tests are shown in Table.. sample no. depth (m) SZ (MPa) (MPa/min) material 7 99,9-7,,3, mudstone 7,9-7,,7, muddy salt 9 7, - 7,,3, muddy salt 9, - 93,,, mudstone 7, - 7,7,, mudstone 3 7,7-7,,3, mudstone, -,,, mudstone Tab..: Results of tensile tests. Direct shear tests. Test procedure and method The shear tests were carried out on a hydraulically-controlled kn rock frame shear apparatus constructed by Wille Geotechnik (Fig..). Figure.: kn rock frame shear apparatus 3

32 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff The axial force and the shear force can be regulated independently via the computersupported controls. Load cells record the axial and shear forces exerted during the test, and a displacement transducer measures the amount of shear displacement. The specimen is placed in the shear box and then subjected to an axial load corresponding to the level of the specified axial stress. The shear test was then started using a preset deformation speed of. mm/min. After reaching failure strength a preset shear displacement of mm governed by the test apparatus were realized to observe the postfailure strength. Thereafter shearing was continued after the normal stress had been increased to a second respectively third load level to determine the postfailure strength depending on the load level of axial stress. The shear displacement was preset to mm in each case for the second and third load level. The test was ended and the specimen removed after reaching the end of the third load level. The specimen was again photographed after removing it from the shear box. The photographs of the specimens after the test and the measurement data records are attached in Appendix and documented in the CD accompanying the report.. Test evaluation The computer-supported regulation of the frame shear apparatus is conducted by automatically sampling the transducers every seconds followed by a set-actual comparison of the specified deformation rate and the specified normal stress. The registered measurement data are electronically saved during the test and kept for the record and for subsequent evaluation of the results. The shear displacement/shear time diagram and the shear stress / shear displacement diagrams based on these readings are attached to this report in Appendix to document the shear tests. Whilst the diagram of the measured shear displacement over the test time documents compliance with the shear speeds preset by the test method, the presentation of the measurement data in the shear stress/ shear displacement diagram reflect the operating characteristics of the specimen. The normal stress and shear stress are calculated from Eqs. (.) and (.) from the quotients of the normal force F n and shear force F s recorded during the test and the effective shear plane A in each case: F n n A (.) F s (.) A 3

33 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff n F n F s normal stress, MPa shear stress, MPa normal force, N shear force, N A effective shear plane, mm The effective shear plane A does not remain constant throughout the test. It becomes smaller as the shear displacement increases. As Fig.. shows, when shearing off takes place, the two halves of the specimen are moved against one another. r s A d s r (d-s)/ s/ d Figure.: Diagram of effective shear plane A against shear displacement s The geometric relationships outlined in Fig.. are used to calculate the effective shear plane A as follows: A d s d s A ar cos( ) d s (.3) where: s ar cos (.) d r radius of specimen [cm] A area of a segment of a circle [cm ] s shear displacement [cm] α angle [rad] A diagram of the effective shear plane against shear displacement are shown in Fig

34 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff 7 effective shear plane A, mm 3 s d s A arccos( ) ( ( d d s ) ) / shear deformation s, mm Figure.3: Effective shear plane against shear displacement.3 Measurement results The shear stress/shear displacement diagram in Fig.. shows the failure strength and the residual shear strength for each test. shear 3,,, failure shear strength f residual shear strength r shearing distance (mm) mean normal shear stress mean normal Figure.: Definition of failure strength and residual shear strength 3

35 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff As shown in Fig.., the failure shear strength br is defined as the stress state at which local destruction of the rock fabric occurs during the test along the apparatus-defined shear plane, leading to a significant decline in shear force. Once the shear fracture surfaces have been created, an almost constant shear stress can be observed as the shear displacement increases. This characterises the frictional properties of the rock along the fracture or slip plane and is defined as the residual shear strength. The shear strengths determined during the direct shear tests are shown in Table.. sample no. depth (m) n (MPa) (mm/min) prefailure (MPa) postfailure (MPa) material 7,77-7,99 7 9, -, 7, -, loosened material taken from box compacted by MPa 9 7, - 7, 7 9 7, - 7, 7, - 7,,,,9,,, 3, -,7,,,9,,,3, -,9,3,,7,,,9,,,,,3,,3,,,9,9,, mudstone mudstone mudstone mudstone mudstone mudstone mudstone Tab..: Results of rock-mechanical shear tests 3

36 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff 7 Creep tests under uniaxial compression 7. Test procedure and method A servo-hydraulically-controlled creep tester of type RRP built by Carl Schenk AG was used for the creep tests under uniaxial compression (UCc). The creep tester is designed to carry out tests simultaneously on three confining specimens under axial loads of up to kn and temperatures of up to C (Fig. 7.). All of the creep testers are connected to a kva-ups to ensure there are no interruptions during any possible power cuts upper bearing displacement tranducer handwheel for control valve upper piston 7 fitting for displacement transducer bottom piston 3 temperature leverage 3 control valve Pressure h b plate 9 spacer hydraulic cylinder sample load cell bottom bearing Figure 7.: Creep tester of the Chair for Waste Disposal Technologies and Geomechanics Data is collected during uniaxial creep tests by a computer-controlled system incorporating: - Three inductive transducers whose average was used as the measured value to register the axial specimen compression (three inductive transducers per specimen 9 inductive transducers per creep tester), - A load cell which determines the load on the specimen immediately between the specimen and the pressure plate at the head of the apparatus ( load cell per specimen 3 load cells per creep tester), - An absolute pressure transducer to continuously monitor and control the hydraulic pressure ( absolute pressure transducer per creep tester), 3

37 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff - A Pt transducer with post-connected temperature control for the continuous regulation and monitoring of the temperature specified for the tests ( temperature transducer per creep tester). Multipoint measuring equipment sampled the analogue signals from the displacement, load, pressure and temperature transducers in the creep tester at preset intervals to continuously record the test readings. These readings were then saved in a computer after AD conversion. The confining specimens had a length of l = mm and a diameter of d = mm. After placing the specimens in the creep tester, tempering at 3 C took place for approx. hours to heat up the tempering chambers and the specimens to the preset temperature. The axial load was then applied at a loading rate of MPa/min. The load was readjusted pursuant to Eq. (7.) to adjust the axial load to the increasing cross-sectional area of the specimen resulting from the axial compression: F A uc where A A t (7.) where σ uc F linear-corrected vertical vertical force (MN) A cross-sectional area of the loaded specimen (m ) A cross-sectional area of the unstressed specimen (m ) ε t technical strain (-) 7. Test evaluation During the uniaxial creep tests, the measurement transducers of each creep tester (9 inductive displacement transducers, 3 load cells, absolute pressure transducer, Pt transducer) were sampled at intervals of minutes, and the readings determined in this way were then saved electronically. Evaluating the uniaxial creep tests involves converting the measured changes in length into creep strains in accordance with Eq. (7.) and plotting them against test time in a strain vs time diagram: 37

38 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff l l l3 3 l % % (7.) t l l where ε t technical strain (%) l, l, l 3 axial deformation measured with three inductive displacement transducers (mm) l Δl length of unstressed specimen (mm) measured axial deformation of the specimen (mm) The dependence of creep rate on time was also determined from Eq. (7.3) to form the basis for the theoretical description of the creep behaviour. This was plotted in a simple logarithmic creep rate vs time diagram: t t (7.3) t where t creep rate (/d) creep strain (here: = ln ) (-) t time interval (d) A compilation of the operating characteristics of the creep tests derived from these readings is attached in the form of strain vs time diagrams as well as a plot of creep rate vs test time, is attached in Appendix of this report. 7.3 Measurement results The results determined from the creep tests under uniaxial compression are shown in Table 7.. The table shows the stationary creep rate s (which is the main feature of the specific time-dependent deformation behaviour of each of the specimens) estimated as the average of the readings and taken from the shape of the meaurement curves over specific time periods. sample depth,3 v T testing s no. (m) MPa MPa MPa C time /d d 39 9,7 -,,,,, 3 3 3,E-,3E- 3

39 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff 37, - 39, 33,9-3,,, 7 3,E-,, 3 3,E-,, 3,E-,, 7 3,E-,, 3 3,E-,, 3,E-,, 7 3,3E- Tab. 7.: Table showing the test results of the uniaxial creep tests Creep tests under triaxial compression. Test procedure and method The creep tests under triaxial compression (TCc) were conducted in the longterm pressure balances shown in Figure. using specimens with a diameter of d mm and a length of l mm. The axial load of the creep states applied gravimetrically using the lever mechanism was max. KN. The triaxial cells are designed to withstand a constant confining pressure of max. MPa. The readings during the triaxial creep tests were recorded as follows: - Three inductive transducers whose average value was taken as the measurement value for registering the axial compression of the specimen, - A load cell which determines the axial stress on the specimen immediately between the triaxial cell and the stationary head plate of the load frame, - An absolute pressure transducer to continuously measure and monitor the confining pressure, - A Pt transducer to control the specified temperature. To protect the specimen from the penetration of the pressure medium, it was placed in a rubber sleeve before being positioned in the triaxial cell. Once the specimen had been placed in the triaxial cell, an isotropic stress level corresponding to the specified confining pressure was established by alternately increasing the axial load and the confining pressure. The triaxial cells were then wrapped in heating sleeves and heated up to the specified temperature of 3 C C (= 9K) by an automatic temperature regulation system. After waiting for hours under isotropic stress conditions and at a constant temperature, the test proper was begun. The 39

40 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff deviatoric increase in load was achieved by adding weights at a loading speed of approx. MPa/h. longterm balance lever arm autoclave load cell 7 hydraulic fluid 3 piston pressure plate displacement transducer 9 piston (bottom) sample weights Figure.: Longterm balances of the Chair for Waste Disposal Technologies and Geomechanics To keep the axial stress constant throughout the test, the axial load was regularly recalculated depending on the deformation-related changes to the specimen cross-section, and then regulated by adding weights at defined time intervals pursuant to Eq. (.): F uc where A A A (.) t where σ uc F linear-corrected vertical vertical force (MN) A cross-sectional area of the loaded specimen (m ) A cross-sectional area of the unstressed specimen (m ) ε t technical strain (-)

41 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff. Test evaluation The transducers sampled the creep state every minutes during the creep tests and the recorded values were electronically saved. A diagram analogous to Fig.. was prepared from these readings to document the stresses generated in each test. These diagrams are included in Appendix of this report time (d) siguc sig3 Figure.: Stress vs time diagram TCc test The characteristic curves of the creep tests based on the measurement data, and shown in the strain vs time diagrams and the creep rate vs time diagrams, all resemble the examples shown in Figure.3. The characteristic curves for the TCc tests reported in this laboratory report are attached in Appendix.

42 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff,,,,, time (d) Figure.3: Strain and strain rate against test time TCc test.3 Measurement results Table. shows the results of the creep tests under triaxial compression. In addition to the reference stress v, the table also shows the stationary creep rate s estimated as the average of the measured values derived from the change in the data curves over a specific time. sample depth,3 v T testing s no. (m) MPa MPa MPa C time /d d 3 73, - 7, ,E-,E ,E- 3 79, - 79, ,3E-,9E ,E- 3, -, ,E-,E ,7E-

43 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff 37 37, - 39, ,E-,E ,E- 3 9, - 97, ,E-,E ,9E- Tab..: Table listing the test results from the triaxial creep tests 9 Triaxial extension tests with cyclic loading 9. Test procedure and method The extension tests with cyclic loading were conducted on the hydraulically-regulated triaxial test benches shown in Figure 9.. The autoclaves shown in Fig. 9. can generate confining pressures of up to 3 MPa. Maximum axial force is KN. The axial pressure and confining pressure can be regulated independently of one another. The axial deformation, axial pressure, confining pressure, temperature, volume change and ultrasonic travel times were measured and collected during the test by a computer-controlled system analogous to that described in Section. The description is therefore not repeated here. The test procedure and method are basically identical to that of longterm balances. Any differences in the test procedure and method are associated with the hydraulic generation of the axial pressure compared to the gravimetric pressure generation in the longterm balances, and the computer-controlled regulation of the confining pressure compared to the maintenance of a constant confining pressure in the longterm balances using membrane storages. 3

44 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff Figure 9.: Frameless triaxial test apparatus of the Chair for Waste Disposal Technologies and Geomechanics After the specimen has been positioned in the triaxial cell, it initially undergoes an approx. -hour recompaction and tempering phase under an isotropic stress of MPa and a temperature of 3 C. At the end of the recompaction phase, the axial pressure and the confining pressure were lowered uniformly to / 3 = MPa/ MPa respectively / 3 = 7 MPa/7 MPa, and subsequently the confining pressure was raised to 3 = MPa respectively 3 = MPa. This forms the initial stress state. This was then held constant for a period of t = d. The confining stress was then decreased to 3 = MPa respectively 3 = MPa at a constant stress rate of 3 =MPa/min and again held constant at 3 = MPa respectively 3 = MPa for a period of t = d. The axial stress remained unchanged and was kept at a constant = MPa respectively = 7 MPa throughout the test phase. The loading cycle described above was repeated several times to reveal whether and to what extent the transient and stationary creep rate is repeated by loading and unloading. 9. Test evaluation The tests are evaluated based on plots against time of the measured axial and radial stresses, axial deformations, volume changes (dilation) and the ultrasonic travel times. Figs. 9. and 9. show examples of the change in dilation and ultrasonic travel time against test time.

45 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff Figure 9. clearly shows that the plotted ultrasonic travel times did not reduce over the test period of d and that no time-dependent damage was therefore observed. The changes in volume recorded during the experiment and shown in Fig. 9. reveal a constant volume of the specimen during cycling. No dilational weakening was therefore observed over time.,,3,,99 vp/vp (-), time (d),9 sig sig3 vp/vp Figure 9.: Ultrasonic travel time against time under cyclic TE loading

46 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff,, -, dilatancy (-) -, time (d) -, sig sig3 epsvol Figure 9.: Dilation against time under cyclic TE loading 9.3 Measurement results of the triaxial extension tests with cyclic loading Table 9. lists the results determined during the triaxial extension tests with cyclic loading. sample no. depth (m) 3 (MPa) 3 (MPa/h) (MPa) quantity of cycles testing time (d) damage (yes / no) 3 73, - 7, / / v p -no / vol -yes? 3, -, / 7 7/7 v p -no / vol -no 3 9,7 -, / / v p -no / vol -no 33 7,9-9, / 7 7/7 v p -no / vol -no Tab. 9.: Mechanical strength results of the triaxial extension tests with cyclic loading

47 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff Compilation of the measurement results and derivation of material parameters. Lubby material model The mathematical-mechanical plot of creep behaviour using the Lubby material model is achieved using a bipartite approach where the creep deformation observed in the lab tests is divided into transient and stationary creep deformation. The total creep rate v and the sum of the transient creep rate with Eq. (.): tr and the stationary creep rate st are calculated in accordance v, t v tr st k v (.) k v M where G k G *, T M expm v *, T MT expl T *, T M expm v expl T * Gk expk v * k expk v M M M k, T v viscous creep rate (d - ) M,T Maxwell viscosity coefficient (MPa. d) M Maxwell viscosity coefficient (MPa. d) G k Kelvin shear modulus (MPa) k Kelvin viscosity modulus (MPa v v. Mises stress respectively equivalent T temperature (K) k, k, m, l material parameters. Parameters for stationary creep The Maxwell viscosity coefficient M the stationary creep rate st : is defined as the quotient of the equivalent stress v and v M, T (.) st The smaller the Maxwell viscosity coefficient, the higher the resulting stationary creep rate for each defined equivalent stress. This parameter describes the time-dependent rigidity of 7

48 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff viscous material in an analogous way to the time-independent rigidity defined by Hooke s material model. M is determined for each single test (each load stage) on the basis of the creep rate readings determined during the stationary creep phase. Fig.. shows an example of the derivation of the Maxwell viscosity coefficient by execution a two-load-level creep tests. The dependence of the stationary creep rate on stress comes about, as shown in Fig.., when the Maxwell viscosity coefficient determined at the different equivalent stresses, is plotted against the equivalent stress. (Note: The testing temperature must be equal at each test to guarantee that there is no dependency between the Maxwell viscosity coefficient and the temperature!) A semi-logarithmic plot in accordance with the exponential formulation function M *, T M expm v (.3a) * reveals a linear correlation between M and v where m is the gradient and M is the inter- * cept. Logarithmising from Eq. (.3a) allows m and M to be calculated.,9,,7,,,,3,, st,3%,%, d t 3d d 9MPa M, T, MPad, d st,%,3%, d t d d MPa M, T,9 MPa d, d 3 time (d) Figure.: Determination of the Maxwell viscosity coefficient M from test values

49 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff,E+7 * M =,. maxwell viskosity coefficient (MPa d),e+,e+,e+ ln y * M, T M expm * M, T ln M m b m x : logarithmize :linear equation gradient determination respectively stress exponent : y ln( M, T ) ln() ln(9) 3,3,9 m,37 x v 9 9 * axis intercept determination respectively.parameters M : * y y m x x ln() ln(9),37 (9 ) ln M,3 * * exp(ln( )) 9 M M v m = -,37,E+3 equivalent * Figure.: Example of the determination of M and m from test values The dependence of the stationary creep rate on temperature comes about, when the Maxwell viscosity coefficient at the different temperatures, is plotted against the temperature. (Note: The equivalent stress must be equal at each test to guarantee that there is no dependency between the Maxwell viscosity coefficient and the equivalent stress!) A semi-logarithmic plot in accordance with the exponential formulation function M * const, T MT expl T (.3b) * reveals a linear correlation between M and where l is the gradient and MT is the intercept. * Logarithmising from Eq. (.3b) allows l and MT to be calculated. The stationary creep rates derived for each of the tests using the approach described above are shown in Table.. 9

50 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff s no. material T ( C) 3 (MPa) (MPa) ( / d) M (MPa d) 3 muddy salt muddy salt muddy salt muddy salt muddy salt muddy salt 3 7 muddy salt 3 7 muddy salt ,,,,,,,,, 3,E-,E-,E-,3E-,9E- 9,E-,E-,E-,7E-,E-,E-,E-,E-,E-,9E-,E-,3E-,E-,E-,E-,E-,E-,E-,3E-,E+,E+,3E+7,33E+7,7E+7 3,E+ 3,3E+7,7E+,E+,E+,3E+,7E+,33E+,E+,3E+ 3,E+7,E+7,7E+,E+7,9E+7,E+,E+7,E+7 7,9E+ Tab.. Specimen-related parameters for stationary creep The location-specific parameters derived from the separate measurements are drawn in Figure.3a to Figure.3f.

51 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff stress dependency of creep behaviour,e+ maxwell viscosity coefficient (MPa. d),e+,e+,e+ 3 3 equivalent Labor-Larne-T = 3 C Regression * Fig..3a: Determination of M and m from creep tests conducted at T = 3 C stress dependency of creep behaviour,e+ maxwell viscosity coefficient (MPa. d),e+,e+,e+ 3 3 equivalent Labor-Larne-T = C Regression * Fig..3b: Determination of M and m from creep tests conducted at T = C

52 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff stress dependency of creep behaviour,e+ maxwell viscosity coefficient (MPa. d),e+,e+,e+ 3 3 equivalent Labor-Larne-T = 7 C Regression * Fig..3c: Determination of M and m from creep tests conducted at T = 7 C temperature dependency of creep behaviour,e+ maxwell viscosity coefficient (MPa. d),e+,e+,e+,e+ 3 3 T (K) Labor-Larne-equivalent stress = MPa Regression Fig..3d: * Determination of MT and l from creep tests conducted at v = MPa

53 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff temperature dependency of creep behaviour,e+ maxwell viscosity coefficient (MPa. d),e+,e+,e+,e+ 3 3 T (K) Labor-Larne-equivalent stress = MPa Regression Fig..3e: * Determination of MT and l from creep tests conducted at v = MPa temperature dependency of creep behaviour,e+ maxwell viscosity coefficient (MPa. d),e+,e+,e+,e+,e+ 3 3 T (K) Labor-Larne-equivalent stress = MPa Regression Fig..3f: * Determination of MT and l from creep tests conducted at v = MPa 3

54 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff The stationary creep rate can be calculated (Eq. (.)) as a function of the equivalent stress from the previously determined material parameters for stationary creep, and compared with the laboratory tests. Fig.. shows this comparison for the tests described in this laboratory report. Fig.. also shows the parameters for stationary creep rate as a function of the v. Mises stress derived from the averages from each of the tests: st v (.) * m expm v,e+,e-,e- stationary creep rate (/d),e-3,e-,e-,e-,e-7 Regression - 3 C Carnduff# -3 C Carnduff# - C Carnduff# - 7 C Regression - C Regression - 7 C,E-,E-9 equivalent Figure.: Calculated and measured stationary creep rates Carnduff.3 Transient creep parameters The parameters the Lubby material model. The Kelvin shear modulus G k is defined as the quotient of the v. Mises stress v and the transient creep strain for t = : * * G k, k, k and k must be determined to characterise the transient creep with

55 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff v G k (.) tr where v v. Mises stress respectively equivalent tr transient creep strain for t = The smaller the Kelvin shear modulus, the higher the transient creep strain resulting from a defined equivalent stress. G k is determined from the strain derived from the readings in a way shown as an example in Figure.. by using a two-load-level creep tests. Figure. shows that the transient proportion of creep strain is obtained when the stationary portion and the elastic portion are subtracted from the total creep strain.,9,,7,,, tr v st v,, E v MPa Gk MPa tr,7 3, 3,7,3,, tr v st v,3, E v 9MPa Gk MPa tr, 3 9, 3 time (d) Figure.: Determination of G k from the test values tr is calculated for the first loading stage in accordance with Eq. (.): tr v st t (.) el where v total creep strain in the first loading stage, (-)

56 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff el elastic strain as a result of deviatoric load, (-) st t stationary creep rate within the first load stage, (/d) duration of the first load stage, (d) tr is calculated in an analogous way for the subsequent load stage from Eq. (.), by also taking into consideration the stationary creep strain during the first load stage (Fig..). The creep parameters (.7): G k * Gk k v * G k and k are derived from the exponential formulation function Eq. exp (.7) by plotting the Kelvin shear moduli semi-logarithmically against equivalent stress. Analogous to the determination of the stationary creep parameters, this gives rise to a linear correlation between G k and v where k is the gradient and * G k the intersect. k and mathematically by logarithmising Eq. (.7) as shown in Figure.. * G k are determined,e+ kelvin shear modulus (MPa),E+3 * G k =3 MPa * Gk Gk expk v * lng k lng k k v y b m x :linear equation gradient determination respectively stress exponent k : y ng k ln() ln() 7, 7, k,37 x v 9 9 * axis intercept b determination respectively parameter Gk : * y y m x x ln() ln(),37 (9 ) ln Gk 7,9 * * G exp(ln( G )) 3MPa k k : logarithmize k = -,37,E+ equivalent Figure. Determining parameters k and * G k from test values

57 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff Table. compiles the parameters derived for each single test using the approaches described above. tr no. material 3 (MPa) (MPa) (-) G k (MPa) 3 rock salt 3 3,E-3,E+3 3,E-3,E+3 3,E-3,E+3 3 rock salt 3,E-3 3,E+3 3,3E-3,7E+3,E-3,9E+3 3 rock salt 9,9E-3,7E+3 9 9,E-3,E+3 9 9,E-3,7E+3 37 rock salt 3 3,E-3,3E+3,E-3,9E+3 9,E-3,3E+3 3 rock salt 3 3,E-3,3E+3,E-3,E+3 9 7,7E-3,E+3 39 rock salt,,e-3 7,E+3, 9,7E-,E+,,E-,E+ rock salt,,e-3,9e+3,,e-3 7,97E+3,,3E-3 7,7E+3 rock salt,,e-3,e+3,,39e-3,e+3,,9e-3,e+3 Tab.. Specimen-related parameters for transient creep 7

58 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff The location-specific parameters derived from the separate measurements are drawn in Figure.7.,E+,E+ kelvin-shear modulus (MPa),E+3,E+,E+,E+ 3 3 equivalent lab-carnduff# Regression Fig..7: Determination of * G k and k from creep tests The Kelvin viscosity modulus k is dependent on the Kelvin shear modulus, the equivalent stress and the transient creep strain (strain hardening approach). It can be calculated from Eq. (.): k where v Gk t (.) G ln( tr k ) v v. Mises stress, (MPa) tr transient creep strain at time t, (-) G Kelvin shear modulus, (MPa) k k Kelvin viscosity modulus, (MPa d)

59 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff Unlike the Kelvin shear modulus and the equivalent stress which can be directly determined from the creep test results, determining the transient creep strain tr can only be done indirectly by back-calculating in accordance with Eq. (.9). This involves reading the total creep strain measured during a test from the test curve at a specific point in time and reducing it by the amount of stationary creep strain st calculated for this point in time. Calculation of the stationary creep strain at time t involves equation Eq. (.): tr v st (.9) st v t (.) M, T Figure. shows an example of the determination of the Kelvin viscosity modulus from the test values by using a two-load-level creep tests.,9,,7,,,,3,, v t d,7 st t d, d d 7,,,7,7 tr v st 9, MPa d k 33MPa d MPa ln(,7 ) 9MPa v t d,7 st t d, d d,,3,, 3MPa d k 3MPa d 3MPa ln(, ) MPa 3 time (d) tr v st 3,,3 Figure.: Determination of k from test values Exponent k is calculated by plotting the Kelvin viscosity moduli as shown in Figure. against the equivalent stress in a semi-logarithmic plot. In accordance with the exponential formulation function * k k exp( k v ) (.) 9

60 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff * the stress exponent k is derived from the gradient, and the parameter k is derived from the intersect of the compensation lines determined by linear regression through the sets of paired values ln( k ) and v. Figure.9 shows an example of the determination of k and. * k,e+ kelvin viskosity modulus (MPa d),e+3 * k k expk v * ln k ln k k v : logarithmize y b m x :linear equation gradient determination respectively stress exponent k : k y ln( k ) ln(33) ln(3),,9,7 x v 9 9 * axis intercept b respectively parameter k : * y y m x x ln(33) ln(3),7 (9 ) ln k,9 * * exp(ln( )) 39 k k,e+ equivalent * Figure.9: Determination of the parameters k and k from test values The parameters derived for each test on the basis of the approaches described above are compiled in Table.3. v, t no. material 3 (MPa) (MPa) (-) k (MPa d) 3 rock salt 3 3,E-3,7E+ 3 3,E-3,E+ 3,3E-3 9,7E+3 3 rock salt 3 rock salt 9 9 3,7E-3,3E-3,E-3,E-3 9,3E-3,77E+,E+,3E+,7E+3,9E+3

61 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff 9,E-,9E+3 37 rock salt 3 9 3,7E-3,E-3,9E-3,E+,E+,E+ 3 rock salt 3 9 3,7E-3,E-3,93E-3,E+,E+,E+3 39 rock salt,e-3,9e-3,e-3 7,33E+ 3,E+,E+ rock salt,e-3,e+,3e-3,e+,e-3,e+ rock salt,e-3 7,9E+,3E-3 7,3E+,3E-3 7,E+ Tab..3 Specimen-related parameters for transient creep The location-specific parameters derived from the separate measurements are drawn in Figure. are as follows.

62 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff,E+,E+ kelvin-viscosity modulus (MPa),E+,E+3,E+,E+,E+ 3 equivalent lab-carnduff# Regression Figure.: Derivation of location-specific parameters the Larne location * k and k for muddy salt at. Failure and dilation strength Figure. shows a plot of the failure strengths of rock salt dependent on confining stress determined from Larne location core material. The strengths on which the plot is based are documented in Tables 3. and.. In addition to the readings determined in the laboratory, Figure. plots a curve fitting of the measured strength values in accordance with Eq. (.) and Eq. (.3): TC a a7 exp( a 3 ) 3 (.) TC ucln 3 3 (.3) where TC failure strength, (MPa) 3 uc-ln logarithmically-corrected axial stress in the fracture state, (MPa) 3 a confining pressure, (MPa) material parameter, (MPa)

63 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff a 7 a material parameter, (MPa) material parameter, (/MPa) The given curve fitting is a general overview, not a predefinition of the material strength. The scattering of the measured strength values shown in Fig.. is assumed to be induced by the quality of the core material and the content of mudstone. Additional investigations are recommended for clarification. 7,,, TC (MPa), 3,,,,,,,,,,,,, 3 (MPa) muddy salt T= C upper scatter band muddy salt lower scatter band muddy salt muddy salt T=3 C muddy salt T= C mudstone Figure.: Failure strength of muddy salt and mudstone at the Larne location A plot of the dilation strength against minimum stress is shown in Figures.. The strengths on which the plot is based are shown in Table.. In addition to the readings determined in the laboratory, Figures. plots a curve fitting of the measured strength values in accordance with Eq. (.): TC Dil (.) TC ( a exp( a 3 )) 3 where TC 3 3 failure strength, (MPa) TC dilation strength, (MPa) Dil 3 3

64 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff 3 confining pressure, (MPa) a material parameter, (-) a material parameter, (/MPa) 3, 3,, Tc dil (MPa),,,,,,,,,,,,,, 3 (MPa) Carnduff# (-a*exp(-a*sig3))*ßtc-upper scatter band (-a*exp(-a*sig3))*ßtc-lower scatter band Figure.: Dilation strength of muddy salt at the Larne location The given curve fitting is a general overview, not a predefinition of the dilation strength. The scattering of the measured strength values shown in Fig.. is assumed to be induced by the quality of the core material and the content of mudstone. Additional investigations are recommended for clarification.. Failure strain Figure.3 shows a plot of the failure strain (compression) against confining stress determined from specimens of rock salt from the Carnduff borehole. The strain values on which the plot is based are shown in Table 3. and.. The scattering of the measured failure strain values shown in Fig..3 is assumed to be induced by the quality of the core material and the content of mudstone. Additional investigations are recommended for clarification.

65 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff 3, 3,, y =,x +, failure (%),,,,,,,, 3,,,, 7,, 9,, (MPa) muddy salt Carnduff# Linear (muddy salt Carnduff#) Figure.3: Failure strain of muddy salt from the Larne location plotted against confining pressure. Deformation energy Figure. shows a plot of the deformation energy against confining stress determined from specimens of rock salt from the Carnduff borehole. The values on which the plot is based are shown in Table 3. and.. The scattering of the deformation energy shown in Fig.. is assumed to be induced by the quality of the core material and the content of mudstone. Additional investigations are recommended for clarification.

66 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff,,,, W d (MPa),,, y =,x,,,,,,,,,, 3 (MPa) muddy salt Carnduff# Linear (muddy salt Carnduff#) Figure.: Deformation energy of muddy salt from the Larne location plotted against confining pressure.7 Shear strength mudstone Figure. shows a plot of the shear strength against normal stress stress determined from specimens of mudstone from the Carnduff borehole. The values on which the plot is based are shown in Table..

67 Chair for Waste Disposal Technologies and Geomechanics Laboratory Report Larne - Carnduff 3, 3 shear stress, MPa,, y =,9x +, y =,7x +,, mean normal stress, MPa prefailure postfailure postfailure-recompacted Linear (postfailure) Linear (postfailure-recompacted) 7 shear stress, MPa 3 y =,9x +, y =,7x +, mean normal stress, MPa prefailure postfailure postfailure-recompacted comparable location prefailure comparable location postfailure sample--box33 sample--carnduff sample--carnduff sample--carnduff sample-3-carnduff sample--carnduff sample-a-carnduff Linear (postfailure) Linear (postfailure-recompacted) Figure.: Shear strength of mudstone from the Larne location plotted against normal stress 7