ENGINEERING GEOLOGY AND ROCK ENGINEERING ASPECTS OF OPERATION AND CLOSURE OF KBS-3

Transcription

1 ENGINEERING GEOLOGY AND ROCK ENGINEERING ASPECTS OF OPERATION AND CLOSURE OF KBS-3 DAVID SAIANG Principal Consultant SRK Consulting Sweden NEIL MARSHALL Corporate Consultant SRK Consulting UK 1 of XX

2 SRK s REVIEW APPROACH FAMILIARISATION: with the Forsmark Project with the purpose and goals of the project with the significance of the project with the concepts of the KBS-3 repository with reference design parameters and production criteria 2 of XX APPROACHED OBJECTIVELY: By having in mind the purpose and functions of each component of KBS-3 repository Sensitivity of each component with respect to the safety of the repository Consequence of impairing the functions of each component What were the significant factors and how were they addressed? RELEVANCY Focused only on the aspects of Engineering Geology and Rock Engineering during operation and closure.

3 FAMILIARISATION KBS-3 CONCEPT 1 Spent nuclear fuel stored in copper canisters and surrounded by compacted bentonite blocks 2 Access tunnels backfilled by a mixture of bentonite and crushed granite or by Friedland clay 3 of XX

4 KBS-3 4 of XX

5 5 of XX REPOSITORY LAYOUT AT FORSMARK

6 6 of XX MAIN PHASES OF WORK AT FORSMARK

7 OPERATIONS AND CLOSURE SRK Consulting was tasked to review sections of safety reports on the OPERATIONS and CLOSURE of the KBS-3 Repository 7 of XX

8 UG EXCAVATION DESIGN STEPS The basis for the design of underground excavation is the geological information gathered from site investigation. SKB has prepared a site descriptive model (SDM) for Forsmark. The geological information are than translated to guidelines and design parameters, by applying rockmass characterisation and classification techniques The underground excavation is then designed based on these guideliness. In general there are no rules! The choice of the method to carry out the excavation depends the rock mass characteristics. 8 of XX

9 ROCK MASS AS NATURAL BARRIER The rockmass is the main natural barrier in the KBS-3 concept Thus, the knowledge of the rockmass characteristics before and after the excavation as well as during the excavation is critical Any excavation of the rock certainly affects the properties of the rock mass immediately around the excavation, creating what is generally referred to as the Excavation Damaged Zone (EDZ) The rock mass will also be disturbed by installation of rock support during the excavation and operation period. 9 of XX

10 FUNDAMENTALS OF ROCK ENGINEERING After Palmström & Stille, 2007 INTERACTION BETWEEN ROCK AND SUPPORT SYSTEM 10 of XX

11 EXCAVATION PROCESS CHART EXCAVATION (I) Excavation method - Drill & Blast - Mechanical (tunnel boring) (ii) Excavation geometry (iii) Safety PHYSICAL CONSEQUENCES - Development of new cracks (excavation and stress induced) - Opening of pre-exsiting cracks (mainly stress induced) INHERENT AND MECHANICAL CONSEQUENCES Reduction in rock strength Indicators: - Reduction in stiffness and general change in rock mechanical properties - Reduction in seismic wave velocity Increase in hydraulic parameters Indicators: - Increase in void ratio - Increase in permeability constant INPUT PARAMETERS - Purpose of the excavation - Rock mass and hydrogelogical conditions - Insitu stress conditions ASSESSMENT (MAINLY QUALITATIVE) - Structural mapping - Core logging - Borehole image processing - Microscopic examination - Displacement measurements ASSESSMENT (MAINLY QUANTITATIVE) - Seismic and sonic wave velocity measurements using geophysical methods - Variation in mechanical properties derived from velocity measurements - Direct stiffness measurements using for example the Goodman jack - Hydraulic conductivity tests - Saturation tests on samples

12 REFERENCE METHOD OF EXCAVATION AT FORSMARK DRILL & BLAST FOR DRIFTS, RAMPS, TUNNELS CORING FOR DEPOSITION HOLES 12 of XX

13 EXCAVATION IMPLICATIONS ON THE SAFETY OF REPOSITORY Rockmass conditions Hydrogeological conditions In-situ stresses EXCAVATION (I) Excavation method Drill and Blast Mechanical (II) Excavation geometry (III) Safety and Support Purpose of the excavation SITE DESCRIPTION MODEL (SDM) PREMISE/REQUIREMENTS

14 PHYSICAL CONSEQUENCES DRILL AND BLAST (reference excavation technique, except deposition holes will be cored) Natural cracks Natural cracks Half-casts or Half-casts half-pipes PHYSICAL CONSEQUENCES New cracks (excavation and stress induced) Opening of pre-existing cracks Irregular tunnel profile Impact on the reference tunnel geometry Stress-induced cracks Blast-induced Stress-induced cracks cracks Blast-induced cracks Half-pipes or half-casts Undamaged rock mass Undamaged rock EDZ Damaged BIDZrock 14 of XX

15 PHYSICAL CONSEQUENCES Impact of drill and blast on reference tunnel geometry Backfilling the disposal tunnels becomes a challenge because of irregular tunnel surface 15 of XX

16 MECHANICAL AND HYDRAULIC CONSEQUENCES (OF EDZ) MECHANICAL AND HYDRAULIC CONSEQUENCES Reduction in rock mechanical properties Indicators: Reduction stiffness Reduction in strength Reduction in seismic wave velocities Increase in hydraulic conductivity Increase in void ratio Increase in permeability constant Undamaged rock rock mass EDZ BIDZ Damaged rock Pre-existing fractures outside the vicinity of the EDZ is also affected 16 of XX Damaged zone

17 BEHAVIOUR OF EDZ ROCK MODULUS DEVIATORIC STRESS TRANSMISSIVITY Distance from excavation boundary EFFECTS: The rock within the EDZ may deform due to low stiffness, thus may impact the functionality of the backfill. High transmissivity may permit circulation of water through the EDZ 17 of XX

18 EXCAVATION PROCESS CHART EXCAVATION (I) Excavation method - Drill & Blast - Mechanical (tunnel boring) (ii) Excavation geometry (iii) Safety PHYSICAL CONSEQUENCES - Development of new cracks (excavation and stress induced) - Opening of pre-exsiting cracks (mainly stress induced) INHERENT AND MECHANICAL CONSEQUENCES Reduction in rock strength Indicators: - Reduction in stiffness and general change in rock mechanical properties - Reduction in seismic wave velocity Increase in hydraulic parameters Indicators: - Increase in void ratio - Increase in permeability constant INPUT PARAMETERS - Purpose of the excavation - Rock mass and hydrogelogical conditions - Insitu stress conditions ASSESSMENT (MAINLY QUALITATIVE) - Structural mapping - Core logging - Borehole image processing - Microscopic examination - Displacement measurements ASSESSMENT (MAINLY QUANTITATIVE) - Seismic and sonic wave velocity measurements using geophysical methods - Variation in mechanical properties derived from velocity measurements - Direct stiffness measurements using for example the Goodman jack - Hydraulic conductivity tests - Saturation tests on samples

19 LIKELY ROCK MECHANICAL PARAMETERS THAT MAY IMPAIR THE FUNCTION DISPOSAL HOLES 1 SPALLING 19 of XX After Andersson, 2007

20 LIKELY ROCK MECHANICAL PARAMETERS THAT MAY IMPAIR THE FUNCTION DISPOSAL HOLES 2 DEFORMATION ZONES OR STRUCTURES INTERSECTING THE DISPOSAL HOLES 20 of XX Disposal holes impaired by the structures are rejected using the Extend Full Perimeter Criterion (EFPC)

21 GROUND SUPPORT In order to assist in the design of the ground support system, SKB has domained the rock mass into different ground types (GT) according to the Q- values: GT 1: Q > 100 GT2: Q = GT3: Q = GT4: Q = of XX

22 GROUND BEHAVIOUR The main ground behaviour (GB) identified for the forsmark area are: GB1: Gravity driven fallout of rock blocks GB2: Stress induced gravity assisted failures GB3: Fractures by water pressure GB 1: has been identified as the main instability in Forsmark. 22 of XX

23 SEALING AND CLOSURE SEALING IS THE BACKFILLING AND PLUGGING OF DEPOSITION HOLES (REVERSIBLE PROCESS) CLOSURE IS THE BACKFILLING AND PLUGGING OF ACCESS, SHAFTS, RAMPS TO THE DISPOSAL SITE TO MAKE IT INACCESSIBLE (IRREVERSIBLE) 23 of XX

24 SEALING AND CLOSURE 24 of XX

25 25 of XX REPOSITORY EXCAVATION AND CANISTER DEPOSITION SEQUENCE DURING OPERATION PHASE

26 26 of XX TRIAL EXCAVATION AND DEPOSITION SEQUENCING

27 SEALING SEALING OF DEPOSITION HOLES & TUNNELS WITH REFERENCE SEALING MATERIALS WHICH ARE SPEFICALLY DEFINED FOR LOW PH AND LOW HYDRAULIC CONDUCTIVITY 27 of XX

28 CLOSURE CLOSURE OF ACCESS DRIFTS, RAMPS, SHAFTS, WITH REFERENCE BACKFILL MATERIALS AND CLAY Specifications of backfill materials vary for top sealing and bottom sealing 28 of XX

29 PLUG PERMENTANTLY SEALS OFF A DEPOSITION TUNNELFROM THE MAIN TUNNEL PLUG ANCHORED IN A ROCK AROUND THE TUNNEL 29 of XX

30 BACKFILL BLOCKS AND PELLETS MANUFACTURED FROM SPECIFIED BENTONITE CLAY (WITH LOW PH AND LOW HYDRAULIC CONDUCTIVITY) 30 of XX

31 BACKFILLING DEPOSITION HOLES 31 of XX

32 MATTERS ARISING It is not entirely clear whether the backfill will purely perform a closure function only or it will also perform some support functions. The interaction between backfill and the surrounding rock could play an important role in defining function of the backfill. Frequent of use of the words such as can be, may be gives an impression that the ideas are still suggestions. Standard reference coordinate system for modeling exercise, perhaps with respect to the orientation of the deposition tunnels Backfilling process is rather tedious with the profiles created by drill and blast. Is there any series for alternatives? Backfilling report (R-08-59, Chapter 8) have raised a number of important issues, which need attention and incorporation into design. No indication of reliability engineering. This branch of engineering takes into account uncertanties in design. ca. in the safety reports means approximately in English. Needs to corrected for non-english readers. 32 of XX

33 CONFIDENCE Learning from others Continuous research and development Monitoring during operation and closure stages Update design as new information becomes available Unlike in mining and some civil engineering projects the site is specifically selected after assessing its suitability. 33 of XX

34 UNCERTAINITIES Rockmass and hydrological parameters have a 3-dimensional and spatial characteristics. Majority of the measurement techniques we use today are 2-dimensional. In that respect there will remain the uncertainty over the accuracy of the measured parameter. The rockmass and hydrological properties we seek to define are generally tensor quantities. Nevertheless, we try to relate them with vector quantities. For example, the mathematics of relating velocity, a vector quantity, to rockmass modulus, a tensor quantity, must be more complicated then what we have today. There is no experience to rely upon for the performance of an engineered system, such as for a repository, over long periods (1000 years or more). However, extensive research and development will give us some confidence over its long term performance. 34 of XX

35 OVERALL REMARK SKB leadership in research and development to ensure the safety of the repositories have clearly led to some of the well driven objective driven work and safety reports with well defined scopes. Such work have also been recognized by international rock mechanics community, in for example, awarding two candidates, Daniel Ask and Christer Andersson, the Rocha Medal by ISRM within the last 5 years for their work in geological engineering with SKB s repository research facilities 35 of XX

36 36 of XX THANK YOU

37 Backfill in disposal tunnel The concept of backfilling of a KBS-3V deposition tunnel is the transport of dissolved matter is by difussion and not by waterflow, which requires that the hydraulic conductivity of the backfill does not exceed e-10m/s The density of backfill is 1,950 kg/m 3. The back should exert an effective pressure of at least 100 kpa on the rock, in order to provide support to the rock to spalling To resist compression caused by upward expansion of the buffer Three methods of backfiling have been stated Block manual method, tedious and will cause unacceptable delays REFERENCE METHOD Robot method is rational but may be difficult to apply PROPOSED FOR FURTHER EVALUATION Module method Superior - PROPOSED Disposition will be 1 canister per day, which means backfilling will be at a rate of 6. of XX 37 to 8 m per day (canister is spaced 6 to 8 m apart) Any interruptions with the procedure will cause problems, especially in areas where water inflow is significant.