1. State of Stress at the depth of planned Laguna Caverns in Pyhäsalmi Matti Hakala, Espoo, 25+26.8.2014 1

2. Rock mass is pre-loaded by in situ stress In situ stress is the driving force behind displacements and stress damages of rock Excavations concentrate in situ stresses in tangential direction and release those in radial direction i.e., produce secondary stresses Stress damages are defined by secondary stress – rock mass strength ratio 2 Matti Hakala, Espoo, 25+26.8.2014

3. 3 Matti Hakala, Espoo, 25+26.8.2014 In Finland E-W to NW-SE trending horizontal compression dominates Caused by plate techtonics; Mid-Atlantic ridge push and collission in Alps Horizontal stress is higher than weight of overburden

4. 4 Matti Hakala, Espoo, 25+26.8.2014 Estimation of in situ stress for Laguna rock mechanics studies is based on two LVDT-cell in situ stress measurements at 1430 level in 2013 (Laguna site investigation project) – moderate/poor reliability six in situ stress measurements on levels 1325, 1350 and 1375 with CSIRO-HI cell in year 2000 (by Pyhäsalmi Mine) – poor reliability, reanalyzed; only two measurement at 1375 level are usable five in situ stress measurements on level 1125 with CSIRO-HI cell in year 1999 (by Pyhäsalmi Mine) – good reliability Measurement is challanging because of high stress - rock strength ratio

5. Overcoring - total stress release - equal displacement magnitude but opposite sign Pilot drilling - stresses concentrated around pilot hole - inward displacements 5 Matti Hakala, Espoo, 25+26.8.2014 In situ stress measurement with CSIRO-HI cell – old measurements at 1125 and 1375

6. 6 Matti Hakala, Espoo, 25+26.8.2014 2013 LVDT-cell measurements locations at 1430 Level

7. 7 Matti Hakala, Espoo, 25+26.8.2014 Drilling 126 mm pilot hole to bypass excavation damaged zone LVDT-cell measurement

8. 8 Matti Hakala, Espoo, 25+26.8.2014 Overcoring to by pass EDZ - raise bore or TBM: 0 cm - drill and blast: 25-50cm Pilot / installation hole - Ø 126 mm - min free length 35 cm Overcoring - Ø ≥ 200 mm min 5 cm Min OC length 35 cm EDZ LVDT-probe In situ stress measurement with LVDT

9. 9 Matti Hakala, Espoo, 25+26.8.2014 Even 200 mm solid core was sliced by discing & folitation -> overcoring impossible -> double or single sidecoring

10. 10 Matti Hakala, Espoo, 25+26.8.2014 LVDT-cell measurement with double sidecoring Pilot1 st side coring 2 nd side coring Isocontours and vectors for total displacement

11. 11 Matti Hakala, Espoo, 25+26.8.2014 Prof-1: right wall and roof Prof-2: left wall and roof Prof-1: 4double sidecorings 1single sidecoring 3rejected pilot holes Summary of LVDT-cell measurements done Prof-2: 3double sidecorings 3single sidecoring 3rejected pilot holes

12. 12 Matti Hakala, Espoo, 25+26.8.2014 Definition of elastic parameters for inverse solution of in situ stress

13. 13 Matti Hakala, Espoo, 25+26.8.2014 LVDT-cell measurement results UnConstrained Slope Constrained

14. 14 Matti Hakala, Espoo, 25+26.8.2014 LVDT-cell measurement – Effect of mining sigma1 Y2000  72 MPa sigma1 2013  65 MPa In situ trend Magnitude underestimated max -7 MPa trend; max ±10° plunge; max 15° down towards orebody sigma1 Y2000  72 MPa sigma1 Y2013  65 MPa

15. 15 Matti Hakala, Espoo, 25+26.8.2014 Mean values and 95% upper confidence limits : Suggested in situ stress for Laguna rock mechanics studies Mean (MPa) Upper (MPa) Trend Major horizontal stress, MPa5472280°-311° Minor horizontal stress, MPa3944 Vertical stress, MPa3943 -mean and upper values are connected but the trend of major horizontal stress in NOT -values are valid for depth level 1430 -based on reported in situ stress measurements above 1100 level the depth trends in Finland are 4.9 MPa/100m for maximum horizontal stress and 2.8 MPa/100m for minor horizontal stress and vertical stress.

16. 16 Matti Hakala, Espoo, 25+26.8.2014 Suggested in situ stress for Laguna rock mechanics studies Big black open signals for suggested mean and variation

17. Thank You 17 Matti Hakala, Espoo, 25+26.8.2014