Natalie Bennett Frost wedging and fracture propagation in hard rock slopes in cold regions Master’s thesis in Cold Climate Engineering Supervisor: Charlie Li, Thomas Ingeman-Nielsen June 2020 Master’s thesis NTNU Faculty of Engineering Department of Geoscience and Petroleum Norwegian University of Science and Technology Abstract In cold regions, the presence of moisture combined with freezing temperatures leads to a phys- ical weathering process in rocks known as frost weathering. Frost weathering is driven by the volumetric expansion of ice and ice segregation (Matsuoka and Murton, 2008). This study fo- cuses on the former and how it affects the stability of hard rock slopes in cold regions through fracture propagation, frost wedging, and freeze thaw cycles. The study of fracture propagation assesses this process in two different types of hard rock: Iddefjord Granite and Fauske Marble. The tests are organized into the three following sub cate- gories including 1. basic fracture propagation (Test A), 2. fracture propagation from intervaled infilling of water (Test B), and 3. fracture propagation with a free surface involved (Test C). The results show that significant ice buildup is required to induce fracture propagation from a mechanically made tip (Test A). The interval infilling method (Test B) did not see any fracture propagation throughout the four cycles. Both the basic fracture propagation (Test A) and free surface fracture propagation (Test C) tests exhibited full fracture propagation throughout the samples. Additionally, these results showed that the number of cycles required to fully propa- gate the fracture through the sample is dependent on both the rock type and the distance to the free surface. The effects of frost wedging are assessed through laboratory work, field investigation, numerical modelling, and analytical approach. A frost wedging test (Test D) was performed in the lab- oratory on two marble samples with wedges created within those samples. The samples were geometrically designed to represent a basic planar failure. One block was created to be a stable wedge, and the other an unstable wedge. The results of the laboratory investigation show that the effects of frost wedging on these samples are independent of the slope of the sliding plane. The field investigation was conducted near Soknedal, Norway, and assessed areas that could potentially have reduced stability due to frost wedging that occurs during months with sub zero temperatures. The analytical approach shows that the uplift from ice formation in joints leads to small horizontal displacements over time. The results of the assessment of frost wedging show that the presence of ice within the joints of a rock mass can lead to slow movements within the rock mass, thereby decreasing the overall stability of the rock mass. Freeze thaw cycles have been shown to cause damage in the form of physical weathering, and hence, decrease the strength of high porosity rocks. The damage to low porosity rocks is typically less extensive due to their lack of pore space (Matsuoka and Murton, 2008). An analysis of the effects of six freeze thaw cycles is conduced on low porosity Iddefjord Granite core. UCS tests are conducted on the core samples which have been subjected to the freeze thaw cycles and on a control group of core that was never frozen. The results showed no difference in strength from that of the control group. This study shows that some of the effects of frost weathering, specifically fracture propagation and frost wedging, lead to a decrease in the stability of hard rock slopes in cold regions. i Acknowledgement This masters thesis was written at the Department of Petroleum and Geosciences at the Nor- wegian University of Science and Technology in conjunction with the Department of Civil Engineering at the Technical University of Denmark. It fulfills the requirements for the Land Track with specialization in Rock Mechanics of the joint masters degree in Cold Climate Engi- neering at the Norwegian University of Science and Technology and the Technical University of Denmark. I would like to thank my primary supervisor, Charlie Li, for always showing excitement in my work and all of the time you have taken to provide assistance and guidance during this process. My supervisor at DTU, Thomas Ingeman-Nielsen, thank you for your guidance and further inspiring my love for working in the Arctic during your course in Greenland. Thank you to Gunnar Vistnes for all your help in the rock mechanics lab. Thank you for preparing all of my samples, assisting with testing, and for completing my UCS testing. Knut Høyland, thank you for all your help during my time in Norway. Thank you for taking the time to discuss ice mechanics with me and for allowing me to work in Ice Lab during my thesis. Thank you to Sønke Maus for lending me the thermistors for testing and helping teach me how to use them. Thank you to Chungxin Lyu for always helping me around the lab and for your words of encouragement. Thank you to my fellow classmates in the cold climate engineering program. We have been on quite the adventure together over the past two years. I feel so grateful to have had you to lean on during the difficult times and celebrate with during the good times. I will forever cherish the times we had in Denmark, Greenland, and Norway. A big thank you to my loving and supporting parents. Thank you for welcoming me back home when a global pandemic was declared in March, and for putting up with my makeshift office that has taken over our living room for the past three months. While I am sad to have not finished my thesis in Norway as planned, I feel lucky to have been able to soak up some extra family time before I transition into a career. Mom and Dad, I would not be where I am today without you. Thank you for all the sacrifices you have made so I could have so many incredible opportunities. Lastly, I would like to thank my loving boyfriend Jeff for all his love and support over the past two years. ii Table of Contents Abstract i Acknowledgement ii Table of Contents vi List of Tables x List of Figures xv Abbreviations xvi 1 Introduction 1 1.1 Cold Regions ................................... 2 1.2 Hard Rock ..................................... 2 1.3 Purpose of Study ................................. 3 1.4 Outline of Sections ................................ 3 2 Background Information 5 2.1 Slope Stability ................................... 5 2.1.1 Factor of Safety .............................. 6 2.1.2 Failure Modes .............................. 6 2.1.2.1 Planar ............................. 7 2.1.2.2 Wedge ............................. 7 2.1.3 Fracture Mechanics ............................ 8 2.2 Frozen Ground .................................. 8 2.2.1 Freezing Process ............................. 9 2.3 Freezing in Soil .................................. 9 2.3.1 Ice Wedging ............................... 10 2.3.2 Solifluction ................................ 10 2.4 Freezing in Rock ................................. 11 2.4.1 Ice Segregation (Microgelivation) .................... 11 2.4.2 Ice Wedging (Macrogelivation) ..................... 11 2.4.2.1 Spatial and Temporal Relationship .............. 11 2.4.2.2 Rock Mass Properties ..................... 12 iii 2.5 Climate Change Impacts ............................. 12 3 Ice Driven Fracture of Intact Rock 13 3.1 Introduction .................................... 13 3.2 Methods ...................................... 13 3.2.1 Test A - Fracture Propagation ...................... 14 3.2.2 Test B - Interval Infilling - Fracture Propagation ............. 15 3.2.3 Test C - Free Surface - Fracture Propagation ............... 16 3.2.4 Temperature Monitoring ......................... 16 3.2.5 Procedure ................................. 17 3.3 Results ....................................... 18 3.3.1 Test A - Fracture Propagation ...................... 18 3.3.1.1 Test A.1 - Granite Block with 9 cm Fracture ......... 18 3.3.1.2 Test A.2 - Marble Block with 9 cm Fracture ......... 26 3.3.1.3 Test A.3 - Granite Block with 6 cm Fracture ......... 28 3.3.2 Test B - Interval Infilling - Fracture Propagation ............. 39 3.3.2.1 Test B.1 - Granite Block with 6 cm Fracture ......... 39 3.3.3 Test C - Free Surface - Fracture Propagation ............... 47 3.3.3.1 Test C.1 - Fracture 1 ...................... 48 3.3.3.2 Test C.2 - Fracture 2 ...................... 52 4 Ice Driven Displacement of Blocks 59 4.1 Introduction .................................... 59 4.2 Field Investigation ................................ 59 4.2.1 Background Information ......................... 60 4.2.2 Structural Mapping ............................ 61 4.2.2.1 Location 4 ........................... 62 4.2.2.2 Location 7 ........................... 63 4.2.2.3 Location 10 .......................... 64 4.2.3 Photographic Assessment ........................ 65 4.2.4 Ice Covered Rock Cut .......................... 65 4.3 Numerical Modelling ............................... 66 4.3.1 Location 4 ................................ 67 4.3.1.1 Initial Conditions ....................... 67 4.3.1.2 Water Pressure Conditions ................... 68 4.3.2 Location 7 ................................ 68 4.3.2.1 Initial Conditions ....................... 69 4.3.2.2 Water Pressure Conditions ................... 69 4.3.3 Location 10 ................................ 70 4.3.3.1 Initial Conditions ....................... 70 4.3.3.2 Water Pressure Conditions ................... 71 4.4 Analytical Approach