Report from June 1992
Permafrost research in Canada is undertaken within various agencies and organizations. Most work is carried out, however, in universities, consulting engineering companies and government laboratories (see Frozen Ground No. 10 for a review of permafrost research at the Geological Survey of Canada). This report comprises a short note about research on pipelines in permafrost being undertaken at Carleton University, Ottawa, and a review of permafrost engineering work done at one of Canada's major consulting engineering companies, EBA Engineering Consultants Ltd., of Edmonton.
Chilled Pipelines and Frozen Soils:
The Geotechnical Science Laboratories of Carleton University, Ottawa, cooperate with the French institutions, Laboratoire Central des Ponts et Chausses and Centre National de la Recherche Scientifique, in operating a large controlled-environment laboratory in Caen, France. The experiments study the effects of natural gas pipelines in northern terrain. The passage of a buried chilled gas pipeline across the boundary between permafrost and unfrozen, frost-susceptible ground is simulated. Frost heave of the ground surface, stresses in the ground and soil displacement are being monitored. Data from the first phase of the experiment are presently being analyzed. High stresses develop within the frozen soil and the deformation of the pipe is characterized by a sharp inflection at the interface between the permafrost body and the adjacent soil. Sophisticated instrumentation has given much information on the thermodynamics of freezing soil. For further information contact Peter Williams or Michael Smith, Geotechnical Science Laboratory, Carleton University, Ottawa.
Consulting Engineers' Contribution to Permafrost R and D:
Consulting engineers have made substantial contributions to the advancement of permafrost engineering and science in North America over the past 20 years. The research is "demand-driven," with projects usually requiring unique engineering solutions within a set time frame and a fixed budget. Consultants also fund their own internal research inexpectation that the product will provide a competitive edge. Internal R and D is often directed at sampling and testing tools or computer programs for improved analyses or possible sale.
Exploration for oil and gas in the western Canadian Arctic, in the early 1970s, provided unique opportunities for consultants to cany out industry-funded research. An immediate need was created to develop a methodology for permafrost terrain analysis, improve predictive capabilities for design and for innovative construction techniques. The following briefly describes applied research camed out at EBA Engineering Consultants Ltd. and how it has helped to close the technology gap between fundamental research and design and construction practice.
One of the most significant contributions of the consulting industry has been the development of a number of computer programs to perform ground thermal analyses. EBA developed a finite element program that models transient heat conduction in the ground for the purpose of predicting thaw or freezing. The program can accommodate phase change over a range of temperatures which can be used to model the variation of unfrozen water content with temperature. The boundary conditions can be applied through a number of options such as meteorological data applied at the ground surface, constant heat transfer at an interface or constant temperature applied at a boundary. The program can also simulate a change of the freezing domain geometry due to thaw subsidence. It is commonly used to simulate the thermal behavior of buried pipelines, utilidor systems, heat pipe foundations, and frozen backfill for mines in permafrost. Many years of experience has established geothermal predictions as a design tool for most northern projects. It is also being used by terrain scientists to model geomorphic processes.
One of the construction methods for artificial islands used for drilling platforms in the Alaskan Beaufort Sea has been the use of frozen granular material excavated from pits and quames. EBA camed out a testing program to evaluate the engineering properties of frozen granular fill dumped through seawater at its freezing point. A number of special tests were designed to evaluate the material properties including: compacted and non-compacted densities of frozen and thawed soils; thaw strain and consolidation behavior; thermal conductivity; angle of repose; sedimentation characteristics; shear strengths for frozen and thawed soils; and the in-place density of the mass of frozen lumps placed under water at sub-zero temperatures. A number of conclusions were drawn from the laboratory results. The two most significant are: 1) the lump sizes and gradation influence the density of the fill, and 2) the strength of a subsea structure formed from frozen lumps can exceed the strength of a similar structure built from thawed fill material.
A number of studies of subsidence caused by production of hydrocarbons through permafrost have been undertaken at EBA. The theoretical analysis considered three different aspects. First- the transient thermal changes due to the temperature boundary condition on the well casing; second-prediction of the deformation of the soil due to thaw; and third-the development of stresses and strains on the well casing. A special testing program was camed out by EBA on samples from a deep core drilled to provide data throughout the subsea permafrost horizon. The testing program was developed to assess thaw strains and consolidation properties under high stress conditions in a temperature-controlled odometer. The specially designed apparatus could measure stresses, changes in pore pressure and volumetric strains both in the vertical and radial directions upon thaw.
Another phase of the testing program established a correlation between geophysical and physical properties of the deep subsea permafrost. This component was carried out as contract research for the Geological Survey of Canada. The program was developed to measure seismic S and P wave velocities on undisturbed samples at in-situ stresses and temperatures and to correlate the lab-oratory results with downhole measurements.
EBA recently carried out a comparative study of two different frost heave testing procedures to select the best method for production testing for a proposed natural gas pipeline across Alaska. The two methods selected were the quick freezing insulated warm end test and the ramped temperature test. A number of improvements were made to standard equipment to achieve the desired precision during testing. The test was carried out in a water-cooled environmental enclosure instead of in a cold room. An in-line feedback temperature control system coupled with moderators and multiple heaters were provided to produce temperature stability of +O. 1°C at both end plates. The test cell was designed as a solid barrel inserted into an insulated jacket and a temperature gradient control was developed to promote one-dimensional frost front advancement during testing. The test method was developed and overview provided by a committee of experts assembled by the client.
A recent research program at EBA was a study of the mechanical behavior of saline permafrost. This study was carried out under contract for the Geological Survey of Canada with theobjective of further developing the understanding of strength and time-dependent de-formation properties of frozen saline soils. The study investigated the influence of soil type, salinity concentration, confining stress and strain rates on the mechanical behavior of three different frozen soils.
Research camed out within the consulting industry allows firms to develop expertise that makes them more competitive, improving opportunities for international marketing of services. It complements and builds on the more fundamental research camed out at universities. Firms currently operating in the Canadian and Alaskan arctic regions have developed unique skills for dealing with design and construction on permafrost terrain. The skills related to planning and executing field programs, project management, analyses and design methods will be needed for development of other circumpolar regions.
Prepared by Elizabeth Hivon and Don Hayley
EBA Engineering Consultants, Ltd., Edmonton
Report from December 1992
During the winter of 1991-92, Canada had issued a formal invitation to the IPA to hold the VII International Conference on Permafrost in 1998 in Yellowknife, NWT, Canada. The invitation was issued by the National Research Council of Canada, after discussions with the Geological Survey of Canada, the Canadian Geotechnical Society, and the Science Institute of the Northwest Territories, each of which has agreed to support the organization of the conference (see IPA Council discussion, p. 6).
The Canadian National Committee for the International Permafrost Association (CNC/IPA) held its annual meeting in Toronto on 28 October 1992, directly following the Canadian Geotechnical Conference. Two new members of thecommittee were welcomed: Michel Allard, Centre d'études Nordiques, Université Laval, Quebec; and J.F. (Derick) Nixon, Nixon Geotech
At the meeting, the Committee received reports from the meeting of the Council of the IPA, the Cold Regions Division of the Canadian Geotechnical Society, the Permafrost Committee of the Science Institute of the Northwest Territories, and the Canadian Polar Commission. Brief progress reports were presented on IPA activities, particularly the Multilingual Glossary project of the Terminology Working Group, and the Circumarctic Permafrost Map project. Communications issues, both internationally and within Canada, were also discussed. The next meeting of the CNC/IPA will be held in association with the 46th Canadian Geotechnical Conference, in Saskatoon, Saskatchewan, 27-29 September 1993.
The 45th Annual Meeting of the Canadian Geotechnical Society was held in Toronto, 26-28 October 1992 The Cold Regions Division sponsored a session on Permafrost Engineering, in which eight papers were presented dealing with:
- The distribution of landslides in the Mackenzie Valley
- The engineering geology of Richards Island, Mackenzie Delta
- The strength and time-dependent deformation of frozen saline soils
- Pile load testing of grouted piles in the western Arctic
- The prediction of creep settlements of foundations in permafrost on the basis of in situ tests
- Investigation of permafrost in the foundations of dikes at the Gull Generating Station in northern Manitoba
- The occurrence of permafrost in bedrock and its consequences
- Geotechnical investigations of permafrost in Ungava (northern Quebec) using ground-probing radar.
In addition, J.M. Konrad, Laval University, Quebec, gave the Geotechnical Colloquium on the topic of "Frost Heave and Engineering Structures." Several other papers on frost-related topics were also presented in other sessions.
The 46th Canadian Geotechnical Conference will include a session on "Research Needs in Cold Regions Geotechnology." The conference will also include regular sessions for submitted papers. Abstracts of 500 words or less should be submitted by 4 January 1993. Further information can be obtained from Dennis Pufahl, Dept. of Civil Engineering, University of Saskatchewan, Saskatoon, Saskatchewan S7N OWO.
The 1993- Roger J.E. Brown Award, which was established in 1986 to honor the memory of the renowned Canadian permafrost scientist, was awarded jointly to Pavel Kurfurst and Scott Dallimore of the Geological Society of Canada. for their paper "Engineering Geology of Nearshore Areas off Richards Island, NWT: A Comparison of Stable and Actively Eroding Coastlines," in the Canadian Geotechnical Journal (vol. 28, no. 2, p. 179-188) and also in recognition of their many years of involvement in studies of the geotechnical properties of permafrost materials in the shore zone of the Beaufort Sea.
Prepared by J.A. Heginbottom