THE INFLUENCE OF SOIL CRYOSTRUCTURE ON THE CREEP AND LONG TERM STRENGTH PROPERTIES OF FROZEN SOILS A THESIS Presented to the Faculty of the University of Alaska Fairbanks in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY By Matthew Thomas Bray, M.S. Fairbanks, Alaska December 2008 UMI Number: 3351785 INFORMATION TO USERS The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleed-through, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion. ® UMI UMI Microform 3351785 Copyright 2009 by ProQuest LLC. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. ProQuest LLC 789 E. Eisenhower Parkway PO Box 1346 Ann Arbor, Ml 48106-1346 The Influence of Soil Cryostructure on the Creep and Long Term Strength Properties of Frozen Soils by Matthew Thomas Bray RECOMMENDED: Committee Chair A c partmerk^ofCivil & Environmental Engineering APPROVED: Dean o f the Graduate School Date Abstract The time dependent mechanical properties of ice-rich frozen soils were studied in relation to their cryostructure. The CRREL permafrost tunnel was the primary source of the studied ice-rich soils. Mapping of the permafrost geology of the main adit of the CRREL permafrost tunnel was performed and reinterpreted in the context of a cryofacial approach. The cryofacial approach in based on the concept that cryostructure is dependent on how a soil was deposited and subsequently frozen. Three main soil cryostructures were determined to represent the main aspects of the permafrost geology. Soils with micro-lenticular cryostructure represent the original ice-rich syngenetic permafrost formed during the Pleistocene. Reworked sediment due to fluvial- thermal erosion resulted in soils with massive cryostructure and soils with reticulate-chaotic cryostructure. Ice bodies within the tunnel include syngenetic wedge ice and secondary thermokarst cave ice deposits. A testing program for determining the time dependent mechanical properties, including the creep and long term strength characteristics of permafrost in relation to soil cryostructure, was performed. Undisturbed frozen soils include silty soil containing micro-lenticular, reticulate- chaotic, and massive cryostructure. Remolded silt from the tunnel was used to create artificial samples with massive cryostructure for comparison to the undisturbed frozen soils. In addition to frozen silt, undisturbed ice facies were tested. These included syngenetic wedge ice, Matanuska basal glacial ice, and Matanuska glacial ice. Testing methods include uniaxial constant stress creep (CSC) tests and uniaxial relaxation tests. It was shown that soil cryostructure and ice facies influences the creep and long term strength properties of frozen soils. It was shown that remolded soils provide non-conservative creep and long term strength estimates when extrapolated to undisturbed frozen soils. Minimum strain rate flow laws show that at low stresses, undisturbed soils creep at a faster rate than remolded soils. At high stresses, frozen soils creep at a faster rate than ice. It was also shown that the unfrozen water content influences the mechanical properties of frozen soils and that the unfrozen water content is influenced by soil cryostructure. Through cryostructure, the permafrost geology is related to the time dependent mechanical properties of frozen soils. iv Table of Contents Page Signature Page ............................................................................................................................... i Title Page ................................................................................................................................ ii Abstract .............. .................................................................................................................................iii Table of Contents ............................................................................................................................iv List of Figures ................................................................................................................................ vii List of Tables ................................................................................................................................ xiv Acknowledgments ...........................................................................................................................xvi Preface xvii Chapter 1: Introduction ..................................................................................................................1 Chapter 2: Literature Review ........................................................................................................4 2.1 Background on Cryostructure ...................................................................................4 2.2 Effects of Cryostructure on Deformation Behavior ..............................................5 2.2.1 Influence of Cryostructure on Rapid Loading .....................................6 2.2.2 Influence of Cryostructure on Long Term Loading ............................ 8 2.3 Background for Creep Determination .....................................................................15 2.4 Creep of Ice ................................................................................................................18 2.5 Literature on Undisturbed Permafrost ................................................................... 20 2.6 Literature on Fairbanks Silt .................................................................................... 22 2.6.1 Creep of Remolded Fairbanks Silt ....................................................... 22 2.6.2 Creep of Undisturbed Fairbanks Silt .................................................... 25 2.7 Summary ....................................................................................................................31 Chapter 3: Permafrost Geology of Soil for Studies .................................................................... 33 3.1 Introduction .................................................................................................................34 3.2 Background .............................................................................................................. 37 3.3 Mapping methods .....................................................................................................39 3.4 Cryogenic Micro-Morphology ................................................................................ 40 3.5 Cryostructures and Their Associated Micro-Morphology ..................................40 3.6 Discussion .................................................................................................................42 3.7 Conclusions .............................................................................................................. 45 Chapter 4: Soils and Cryostructures ..........................................................................................46 4.1 Grain Size Distribution .............................................................................................46 4.2 Soil Cryostructure .................................................................................................... 47 4.2.1 Micro-lenticular Cryostructure ..............................................................49 V Page 4.2.2 Undisturbed Massive Cryostructure .................................................... 52 4.2.3 Remolded Massive Cryostructure ....................................................... 52 4.2.4 Reticulate-Chaotic Cryostructure ........................................................ 58 4.2.5 Wedge Ice ............................................................................................... 61 4.2.6 Matanuska Basal Glacial Ice and Glacial Ice .................................... 64 4.3 Water Content and Frozen Bulk Density .............................................................64 4.4 Unfrozen Water Content .........................................................................................68 4.5 Summary ................................................................................................................... 81 Chapter 5: Testing Equipment and Procedures .......................................................................83 5.1 Field Sampling of Soils ..........................................................................................83 5.2 CSC Testing ............................................................................................................ 84 5.2.1 Uniaxial Compression Creep (CSC) Testing Equipment ................ 84 5.2.2 CSC Temperature Control ................................................................... 85 5.2.3 CSC Testing Procedure ........................................................................87 5.3 Relaxation Tests ...................................................................................................... 89 5.3.1 Relaxation Test Testing Equipment ....................................................89 5.3.2 Relaxation Test Temperature Control .................................................90