1、TECHNICAL GUIDEInfrastructure in permafrost: A guideline for climate change adaptationPLUS 4011-10Published in June 2010 by Canadian Standards AssociationA not-for-profit private sector organization5060 Spectrum Way, Suite 100, Mississauga, Ontario, Canada L4W 5N61-800-463-6727 416-747-4044TECHNICAL
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16、rastructure in permafrost: A guideline for climate change adaptationACKNOWLEDGEMENTSDevelopment of this Guideline would not have been possible without the generous support of a number of organizations and the significant volunteer efforts of a sizeable group of people. Support for the development th
17、is Guideline was provided by Infrastructure Canada and Indian and Northern Affairs Canada.Members of the Permafrost Working Group (Appendix 1) were the main parties involved in developing, refining, and endorsing the Guideline. Certain members made especially significant contributions in this regard
18、, serving as lead authors for one or more chapters of the Guideline, or providing their editorial advice. The Lead Authors and Principal Editor of the Guideline are noted in Appendix 1, as are the Co-Chairs of the Working Group, Dr. Chris Burn and Ms. Sara Brown, P. Eng.Dr. Neil Comer of Environment
19、 Canadas Adaptation and Impacts Research Section produced original analysis for Chapter 5 of this Guideline. Sharon Fernandez coordinated the scientific contributions of Environment Canada throughout the development of the Guideline.More than 60 people (Appendix 4) provided input on a preliminary ve
20、rsion of this Guideline at three outreach sessions, in Whitehorse, YT, Iqaluit, NU, and Inuvik, NT. Canadian Standards AssociationiiEXECUTIVE SUMMARYIntroduction to the GuidelineInfrastructure in the North commonly depends on permafrost for its foundation material. Such infrastructure should be desi
21、gned with full consideration for the potential of climate change, particularly increases in air temperature, to cause permafrost warming and/or thawing and create significantly different foundation environments in the future.This Guideline is for decision makers with a role in planning, purchasing,
22、developing, or operating community infrastructure in permafrost regions. It will assist people who are not experts in permafrost and/or climate change, by providing: (i) a better understanding of critical permafrost- and climate change-related issues; (ii) a means for locating key information source
23、s on these topics; and, (iii) the ability to ask “the right questions” of those they hire to ensure appropriate planning, assessment, design, and construction of community infrastructure projects. The Guideline provides contextual material and guidance on the following:1. Permafrost as an environmen
24、tal variable, and its response to climate and other environmental change (Chapters 2 and 3);2. Foundation types for community infrastructure in permafrost (Chapter 4);3. Trends in climate and permafrost conditions across northern Canada (Chapters 5 and 6); and4. A process for ensuring that climate c
25、hange is incorporated into (a) the siting, and (b) the design of foundation systems in permafrost terrain (Chapter 7).This Guideline is focused on new infrastructure projects rather than on maintenance of existing structures. It addresses how to estimate and account for the effects of future climate
26、 on permafrost and on foundations at sites where permafrost may be a factor. Most information in this Guideline is of relevance to the majority of community infrastructure types.Introduction to permafrostPermafrost is ground (soil or rock) that remains below 0C for two or more consecutive years. Per
27、mafrost is fundamentally a product of climate, so it is found at high altitude as well as high latitude. While the majority of permafrost in Canada is found in the territories, there is also considerable permafrost in the mountains of Alberta and British Columbia, and in the northern portions of the
28、 provinces from Alberta eastwards to Newfoundland and Labrador. iiiTECHNICAL GUIDEInfrastructure in permafrost: A guideline for climate change adaptationThe ice content of permafrost is, together with temperature, a key determinant of permafrosts strength and behaviour as a foundation material. The
29、ice content commonly varies with soil type and other local conditions. Fine-grained soils such as fine sands, silts and, clays are particularly susceptible to the development of ground ice in permafrost, especially in the uppermost few metres at a site. Many northern communities are located close to
30、 the ocean, rivers, or lakes at sites with silt and clay-rich marine and floodplain soils containing significant amounts of ground ice.An increase in temperature at the surface of the ground, whether due to a disturbance of the ground or to a change in climate, will lead to gradual and generalized i
31、ncreases in temperature throughout the permafrost. Permafrost at temperatures very close to 0 C will respond more slowly to the effects of surface warming than permafrost below about 4 C, since in the “warm” permafrost a significant amount of the energy that is introduced by surface warming is absor
32、bed by melting of ice rather than in raising the ground temperature.Changes to the characteristics and occurrence of permafrost due to construction activities and climate changeClimate is the principal factor controlling the formation and persistence of permafrost. There are general relations betwee
33、n air and ground temperatures, permafrost thicknesses, and summer thaw depths, but local factors are important in determining specific permafrost conditions at a site. A change in air temperatures and other climate variables will result in a change of ground temperature, but this will vary depending
34、 on site conditions, so the design, construction, and management of infrastructure foundations must always recognize the importance of site-specific conditions. During site preparation and infrastructure construction, activities such as vegetation clearance, surface grading, and removal or compressi
35、on of the organic layer will occur, usually raising ground temperatures. Where the structure is a building, the most significant impact on permafrost normally occurs immediately beneath the building, as heat generated through its use is conducted downwards into the foundation.For construction design
36、, a main difference between unfrozen soils and permafrost is the strength presented by pore ice which binds the soil particles together in permafrost. However, frozen soils weaken as they warm, and, when they thaw, lose all strength conferred by their ice content. The long-term strength of frozen gr
37、ound depends on the soil or rock of which the ground is composed, and the amount of ice in the ground. Ground ice may deform (or bend) under sustained loads over time, a process known as “creep”. The potential for creep increases rapidly as ice approaches its melting point.Where ground is covered by
38、 sediments, the upper parts of permafrost commonly contain “excess” ice ice content greater than the pore space of the thawed soil. Soils with excess ice undergo considerable transformation when they thaw. Initially, the excess water content reduces the strength of the soil. As excess water from tha
39、wing permafrost drains, the soil settles and the ground subsides. Spatial variation in excess ice Canadian Standards Associationivcontents and soil drainage can result in differential thaw settlement. This is a design factor for larger structures which may cover patches of different materials, as di
40、fferential settlement may lead to deformation of the structure.Northern infrastructure foundationsConventional foundation design primarily considers two related factors: bearing capacity and settlement. Settlement is both the total and any differential settlement beneath a structure, resulting from
41、one or several of the support elements. Foundation design in permafrost imposes several challenges for control of differential settlement and the resulting deformation of structures. First, the bearing capacity of permafrost is largely a function of the amount and temperature of ground ice. As the a
42、mount of ground ice commonly varies across the area of a construction site, bearing capacity may differ across a foundation, causing different portions of the structure to experience settlement at different rates. Second, since ice-rich soils consolidate and discharge excess water as they thaw, vari
43、ably distributed ground ice can result in the settlement of portions of the ground, causing distortion in the structure above. Third, if the “active layer” of ground above the permafrost that thaws and freezes each year deepens, foundation systems that rely on piles may experience accentuated frost
44、heaving. Less of the piles surface will be frozen year-round to the surrounding soil, while more will be exposed to the lifting force exerted through soil expansion when the water in the active layer re-freezes in the autumn and winter. It is important that long-lasting community infrastructure in p
45、ermafrost regions accommodate the potential instability of the ground. Foundations that rely directly on frozen ground must be designed to ensure the ground does not thaw following construction, and all foundations must accommodate changes that are anticipated throughout the service life of the stru
46、cture.Three principal foundation types are commonly used in permafrost terrain:Surface pads: The construction of a surface pad to preserve the temperature of the underlying permafrost is common in northern Canada. One of the primary advantages of using surface footings on a granular pad with a cold
47、crawl space below is the ability to compensate for any differential settlement through jacking or shimming. Unheated structures may be built directly on a pad, but only if they are well ventilated, have insulation inserted between the structure and the pad, and remain unheated throughout their servi
48、ce life.Deep foundations: There are two fundamental pile types in use in the Canadian North: adfreeze piles and rock-socketed piles. Their designs and applications are fundamentally different. Adfreeze piles are commonly installed where permafrost soils extend to substantial depths without encounter
49、ing bedrock. These piles rely on the bond with the surrounding ground for their load-bearing capacity. The ground can be ice-rich but should be below 3 C, and colder still if the soil is saline. Rock-socketed piles are used vTECHNICAL GUIDEInfrastructure in permafrost: A guideline for climate change adaptationwhere bedrock occurs within a practical depth below the surface. These piles are designed to transfer the full load of a structure to the underlying bedrock.Foundations with heat exchangers: Foundations enhanced with heat exchangers are now widespread in Canadas
