Handbook for the design of bases and foundations of buildings and other structures on permafrost

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Handbook for the design of bases and foundations of buildings and

other structures on permafrost

CANADA INSTITUTE

FOR SCIENTIFIC AND TECHNICAL

INFORMATION

INSTITUT CANADI EN

DE L'INFORMATION SCIENTIFIQUE

ET TECHNIQUE

NRC / CNR TT· 1865 TECHNICAL TRANSLATION TRADUCTION TECHNIQUE

HANDBOOK FOR THE DESIGN OF BASES AND FOUNDATIONS

OF BUILDINGS AND OTHER STRUCTURES ON PERMAFROST

RESEARCH INSTITUTE OF BASES AND UNDERGROUND STRUCTURES, GOSSTROI, U,S,S,R.

IZDATEL'STVO LITERATURY PO STROITEL'STVU MOSCOW, 1969. 129 PP.

TRANSLATED BY

I

TRADUCTION DE

V. POPPE

THIS IS THE TWO HUNDRED AND TWENTY-FOURTH IN THE SERIES OF TRANSLATIONS PREPARED FOR THE DIVISION OF BUILDING RESEARCH

TRADUCTION NUMERO 224 DE LA SERlE PREPAREE POUR LA DIVISION DES RECHERCHES EN BATIMENT

OTTAWA 1976

1+

National Research Council Canada Conseil national de recherches Canada

The most recent standard (code of practice) for the design of foundations in permafrost areas in the Soviet Union (Construction Standards and Regulations, Part IT, Section B, Chapter 6 - referred to as SNiP 11-13.6-66 - "Bases and Foundations of Buildings and Other Structures on

Permafrost: Design Standards") was issued in 1967 by the State Committee of

the Council of Ministers for Construction, USSR. This was followed by the

publication in 1969 of a "Handbook For The Design of Bases and Foundntions of Buildings and Other Structures on Permafrost".

This translation of the "Handbook", which provides a detailed explanation of all sections in the original Standard (SNiP II-B.6-66) and illustrates the present approach to foundation design used in the USSR, is of particular interest to the Division of Building Research in its investi-gations of permafrost and building problems in northern Canada.

This is the fourth Russian code for design and construction in

permafrost regions that has been translated for the Division. The first

three dealt with tile design of all types of foundations in permafrost areas (TT-I033), the design of foundations in the zone of discontinuous permafrost (TT-1298) and the design and construction of pile foundations in permafrost

(TT-1314).

The Division is most grateful and wishes to express its sincere

thanks to Mr.

V.

Poppe, Translation Services, Canada Institute for

Scientific and Tec h ni c a I Information, NRCC who translated the "Handbook"

and to Mr. (;.11. Johnston of the Division of Building Research who checked

the translation.

() ttｾｉ｜ｾ a

ｾｬ｡ｹ 197()

C.B. Crawford, Director.

NATIONAL RESEARCH COUNC IL OF CANADA CONSEIL NATIONAL DE RECHERCHES DU CANADA

TECHNICAL TRANSLATION TRADUCTION TECHNIQUE 1865 Title/Titre: Editors/Redacteurs: Publisher/Editeur: Translator/Traducteur:

Handbook for the Design of Bases and Foundations of Buildings and Other Structures on Permafrost

(Posobie po proektirovaniyu osnovanii i fundamentov zdanii i sooruzhenii na vechnomerzlykh gruntakh)

S.S. Vyalov and G.V. Porkhaev

Nauchno-issledovatel'skii institut osnovanll 1

podzemnykh sooruzhenii Gosstroya SSSR (Research Institute of Bases and Underground Structures, Gosstroi, U.S.S.R.)

Izdatel'stvo literatury po stroitel'stvu. Moscow,

1969.l29pp.

V. Poppe, Translation Services/Service de traduction

Canada Institute for Scientific and Technical Information Institut canadien de l'information scientifique et technique Ottawa, Canada KIA OS2

INTRODUCTORY NOTE

All sections from the original Standard (SNiP II-B.6-66), are

reproduced in the "Handbook". In this translation these sections have been

typed in italics to distinguish them from the explanatory notes and examples. The following Russian Construction Standards and Regulations are referred to in the Ilandhook:

(I) SNiP II-A.6-62 - Building Climatology and Geophysics: Design

Fundamentals.

(2) SNiP II-A.7-62* - Building Heat Engineering: Design Standards.

(3) SNiP II-A.lO-62 - Structural Elements and Bases of Buildings and Other

Structures: Basic Design Principles.

(4) SNiP II-A.11-62 - Stresses and Loads: Design Standards.

(5) SNiP II-A.12-62 - Construction in Seismic Regions: Design Standards.

(6) SNiP II-B.1-62* - Bases of Buildings and Other Structures:

Design Standards.

(7) SNiP II-B.5-62 - Pile Foundations: Design Standards.

(8) SNiP 11-8.5-67 - Pile Foundations: Design Standards.

(9) SN 289-64 - Instructions for the Design of Buildings and Other

Structures in NeWly Developed Regions.

(IO) SN 258-66 - Instructions for the Design of Townsi tes, Factories, Buildings and Structures 1n the Northern Construction-Climatic Zone.

(11) RSN 14-62 - Guide for the Design and Construction of Pile Foundations in Permafrost.

(12) RSN 30-67 - Instructions for the Design and Construction of Pile Foundations in Plastic Frozen Soils (Vorkuta Region). Documents 10 and 11 were translated by the National Research

Council of Canada and issued some time ago as Technical Translations 1547 and

]311, respectively. None of the others have been translated to our knOWledge.

With the exception of items 7 and 9, copies (in Russian) of the other documents listed ahove (or more recent, revised issues of them) arc

held in the Library of the Division of Building Research, National Research

Council of Canada, Ottawa. The Russian Construction Standard and Regulation

SNiP II-B.6-66, upon which the Handbook is based, is also held in the DBR/NRC Library.

In the September-October, 1973 issue (No.5) of the Russian Journal "Bases, Foundations and Soil Mechanics" (Osnovaniya, Fundamenty i Mekhanika Gruntov), several changes to sections in SNiP II-B.6-66 and the

Handbook were noted. This article is reproduced as follows:

T. The Government Committee for Construction (Gosstroi) of the USSR

approved the following changes 1n the Chapter SNiP II-B.6-66, which were put in force on July 1, 1973.

1. Note 2 of Point 1.1 is set forth as follows: "2. In the des ign of

bases and foundations on permafrost soils, in addition to the requirements established in this chapter of the SNiP norms, it is mandatory to fulfill the requirements stipulated 1n other normative documents approved by or

coordinated with the Gosstroi of the USSR. In particular, in the design of

bases consisting of permafrost soi Is with a high ice or salt content, it is mandatory to apply the requirements contained in the "Instructions for

Design of Bases and Foundations on Permafrost Soils Having High Ice and Salt Contents (SN 450-72)."

2. The fi rst paragraph of Point 1.2 is invalidated.

3. Point 2.6 is complemented with the following paragraph: "Permafrost

soils arc considered to have a high ice content when L > 0.4."

w

4. Point 2.11 is set forth as follows: "2.11. The salt content of

permafrost soils is determined as the ratio of the weight of the salt in the soil to the weight of the soil skeleton (including the weight of the salts in the soil), expressed as a percentage.

"Permafrost soils are considered to be of a salty nature if their degree of saltiness exceeds the following values:

for silty sands. . . 0.05%

for fine, medium, coarse, and gravelly sands 0.10%

for ordinary and sandy l oams 0.159"

5. Note 3 in Table 5 is phrased as follows: "3. The normative

strengths ｾｩ presented in Table 5 do not apply to permafrost soils having

a high ice (Point 2.6) or salt (Point 2.11) content."

6. Note 6 in Table 6 is phrased as follows: "6. The normative

strengths Rn presented in Table 6 do not apply to permafrost soils having a

high ice (Point 2.6) or salt (Point 2.11) content."

7. References to the chapters SNiP II-A.6-62; II-A.7-62; lI-A.10-62;

II-B.I-62; II-B.5-67 are replaced by refcrences to chapters SNiP II-A.6-72; II-A.7-71; II-A.IO-71; II-B.I-62*, and II-B.5-67*, respectively.

II. In connection with the approval, on the part of the Gosstroi of the

USSR, of the new construction norms SN 450-72 "Instructions for Design of Bases and Foundations on Permafrost Soils Having High Ice and Salt Contents," prepared by the Scientific-Research Institute for Foundations and the

LenZNIIEP, with the participation of the Krasnoyarsk Promstroiniiproekt, the Fundamentproekt, and the Leningrad Branch of the Aeroproekt Institute, which wcre put in force on July 1, 1973, Tables 18 and 19 as well as all the

instructions on salty soils given in the "Handbook for Design of Rases and Foundations of Buildings and Structurcs on Permafrost Soils" are invalidated.

Sections affected by the above notcd changcs have been identified

with a

t

in this translation of the Handbook.

G.H. Johnston DBR/NRC

ABSTRACT

The Handbook examines the application of concepts outlined In the SNiP 11-8.6-66 "Bases and foundations of buildings and other

structures on permafrost: Design standards" used in design practice.

A detailed treatment of methods of designing bases and foundations

(including piles) on permafrost is given. The criteria used are the

limiting states, i.e., bearing strength and deformations. The heat

engineering designs of foundation soils are given also.

The Ilandbook is intended for a broad spectrum of specialists engaged in foundation construction, desfgn and research in

Foreword 1. 2. 3. 4. 5. TABLE OF CONTENTS General Provisions

Nomenclature of Foundation Soils

Basic Methods of Design ...•...•...•...

The Use of Foundation Soils in a Frozen State (Method I) .

Use of Thawing or Thawed Foundation Soils (Method II) .

Selection of the Method of Using Perennially Frozen

Foundation Soi 1s .

Depth of Foundations Design of Foundations

General Instructions

Design for Bearing Strength .

Examples of Base Designs for Axial Loads .

Stability and Strength of Foundations Subjected to

PAGE 10 1-1 2-1 3-1 3-4 3-43 3-49 4-1 5-1 5-1 5-5 5-35 Heaving Forces

Design for Deformation of Foundation Soils Li tera ture

Appendix - Determination of the Depth of Thawing and Freezing

Figures 1 to 48

5-58 5-74

Foreword

This Handbook has been compiled by the Research Institute of Bases and Underground Structures, of The Gosstroi, USSR, with the participation of the Leningrad Design and Research Institute of Marine Transportation, USSR Ministry of Merchant Marine, and the State Institute for the Planning of Foundation and Substructures, USSR Ministry of Prefabricated and Special Construction. The Handbook serves as a further development of the chapter of SNiP II-B.6-66 "Bases and foundations of buildings and other structures on permafrost: Design standards". For convenience the original paragraphs of SNiP 11-B.6-66 are repeated in this Handbook in italics and each paragraph is explained. The explanations give the reasons for the instructions

outlined in the standards and recommendations concerning the use of these instructions. Wherever required, they also contain diagrams, tables and calculation methods with examples. The bracketed numbers of equations, tables and figures indicate the corresponding numbers in the original standards.

The Handbook was developed by Dr. S.S. Vyalov, G.V. Porkhaev, V.F. Zhukov (The Research Institute of Bases and Underground Structures) and V.V. Dokuchaev (The Leningrad Design and Research Institute of Marine

Transportation), with the assistance of Dr. M.V. Malyshev, A.M. Fish and 0.1. Fedorovich (The Research Institute of Bases and Underground Structures), N.r. Bclousov and A.A. Kolesov (The State Institute for the Planning of

Foundations and Suhstructures), Yu.

Va.

Velli, n.R. Sheinkman, C.S. Faktorovich and P.A. Grishin (The Leningrad Design and Research Institute of Marine

Transportation).

General supervision and editing were undertaken by Dr. S.S. Vyalov and G.V. Porkhaev.

All comments and suggestions should be addressed to: Moscow Zh-389,

2-ya Institutskaya ul. 6,

NIl osnovanii i podzemnykh sooruzhenii Gosstroya SSR. U.S.S.R.

1.

GENERAL PROVISIONS

1.1

Thece standards apply to the design of bases and foundations of

buildings and other structures erected in permafrost regions [Fig.

7(1)].

Notes

1.

The present standards do not apply to the design of bases

of hydraulic ebruaburee ,

rai.Lroade

and

ｨｩｧｨｷ｡ｹｳｾ br-idqee,

pipelines and

airfield pavements.

t2.

The bases and foundations of buildings and other structures

erected in seismic regions and mining areas should be designed with

allowances for the additional requirements given in SNiP II-A.

12-62

"Construction in seismic regions.

Design

ｳｴ｡ｮ､｡ｲ､ｳｾＢ

and "Instructions for

the design of buildings and other structures in newly developed regions"

(SN

289-64).

Re 1.1 The permafrost map shows the southern boundary of the permafrost region and the areas with different temperature and thickness of permafrost. In practice the southern boundary represents a strip tens of kilometres in width, within which there are only occasional areas with permafrost at a temperature close to 0

°e.

Here, even short-lived (lasting a few years) climatic fluctuations result in the formation or thawing of permafrost.

North of the southern boundary the temperature of permafrost drops to -12

°e

and its thickness reaches 500 m or more. However, even in the northern regions (e.g., at the latitude of Noril'sk and further north) there are occasional occurrences of thawed soils.

The map shows the isolines of soil temperatures at a depth of 10 m. At this Jepth the temperature changes little throughout the year and

therefore it can he taken as the mean annual ground temperature.

t 1.2

The bases and foundations of buildings and other structures in

permafrost regions should be designed in accordance with SNiP II-A. 10-62

Ｇｾｴｲｵ｣ｴｵｲ｡ｬ

elements and bases of buildings and other structures.

Basic

design

pi-inci.pl.ee",

II-B.1-62* "Bases of buildings and other structures.

Design standards", II-B.5-67 "Pile foundations.

Design standards",

'7nstructions for the design of settlements, industrial enterprises,

buildings and other structures in the northern construction-climatic zone"

(SN 353-66J,§

and the present chapter of SNiP.

The designs should be based on the engineering, geological,

hydrogeological and permafrost investigations carried out in accordance with

the existing standards.

Dcci.eionc concerrn.nq t.hc use of conebruction ei.tec

r;ubJee tcd to

soil

ci-ccp , karnt., thermokaret.i}

icing and solifZuction

2

_{should be based on}

the results of special investigations.

Re 1.2 In addition to information on the construction site, the

investigations should provide data on environmental conditions in the region as a whole. Furthermore, they should also reflect local construction

experience, if buildings and other structures, similar to those being designed, are already present in the region.

'l'havmokar-t: l: L;; i.ha [ormat-ion of

an

uno iab Lc noi. L pro

Ii

Lc

due

to thaiainq 01 i

ce-cat.urat.ed peprnafr'ost

or

buried

t.ce ,

2

Solifluction is the flow of soil along a slope caused by seasonal freezing

or

thawing.

Footnotes:

t

See Introductory Note.

'* Means that the original SNiP has been revised.

§

NRCC Technical Translation No. TT-1547

The instructions in 1.2 do not exclude the use of construction sites where the aforementioned frozen soil phenomena are present. For example, thermokarst may occur on any site composed of soils with a high ice content.

It follows from the instructions that, on using such sites, it is essential to carry out special investigations in order to arrive at a design which would exclude the dangerous consequences of such phenomena as thermokarst.

1. ;) The bases and foundations ehoul.d be designed with allowances for

thermal and mechanical interactions of structures with foundation soils

arising from structural characteristics and ｰ｡ｲ｡ｭ･ｴ･ｲｳｾ as well as the

purpose and the operational regime of the structures; information supplied by exploration and investigations should be considered also.

The design must allow for possible changes in the ground conditions

and the temperature regime of the ｰ･ｲｭ｡ｦｲｯｳｴｾ which may ｯｾ｣ｵｲ as a result of

the development of the construction ｳｩｴ･ｾ operation of structures erected on

it and adjacent ｬｯ｣｡ｴｩｯｮｳｾ buried pipelines and ｣｡｢ｬ･ｳｾ removal of vegetation

and ｓｮＰＱｊｾ construction of ditches and reeemioi.re, etc.

Re 1.3 The thermal and mechanical interactions of buildings and other structures depend on a number of factors arising from their structural and technological characteristics and the natural soil regime (see 5.23).

Furthermore, the temperature regime of soils under individual buildings and the ground conditions on the construction site as a whole, are affected by the following factors:

snow which accumulates In various ways around buildings depending on the wind direction;

ground and surface water whose regime changes as a result of ocvclopmcnt work on the construction site;

density of buildings and their orientation;

Pipes and cables, their location and mode of installation (whether below or on the surface of the ground, with or without insulation, etc.) .

The changes in ground conditions on construction sites are subdivided into general and local.

The general changes consist mainly in the increase or decrease of mean annual soil temperatures, changes in the depth of seasonal thawing or freezing, formation of pereletoks (see 2.1), etc. They are caused by the increase in the depth of snow on, or its removal from, the construction site, provision of green belts, drainage, etc.

Apart from information concerning ground conditions on the site prior to development, the engineering and geological investigations must provide data on possible general changes in ground conditions during development and construction.

Local changes are caused by local sources of heat or cold (heated and unheated buildings, pipelines, etc.) and extend over small areas (under buildings, around pipelines, etc.). The analysis of local changes is carried out when designing the bases and foundations.

1.4 The ground and hydrogeological conditions on the construction site

QY'e charact.er-i.zed by:

a) extent and occurrence of permafrost;

d) thickness

of

layers

of

seasonal freezing and thawing; [see 2.1

for

definitions]tt

e) physico-mechanical propei-tiee

of

soils;

1')

[r-ozcn coi.L phenomena (heairinq , t.ct.nq, bhcrmokaretz, ｄｯｬｩｦｬｵ｣ｴｬＺｯｮｾ

crack formations;

g) occurrence and type

of

ground water;

h) climatic conditions "n the construction region.

Re 1.4 Under certain conditions permafrost may be discontinuous on the construction site or may occur in patches. It may be close to the ground surface immediately below the layer of seasonal freezing and thawing, or at various depths below this layer.

The soil composition is characterized by the relative content of mineral particles of various sizes and 1S used to classify the soil in

accordance with the nomenclature given in SNiP II-B.1-62*.

Soil texture depends on the distribution of soil particles, while layering determines the soil structure. Furthermore permafrost is

characterized by the occurrence of ice inclusions and layers giving rise to a specific cryogenic texture (see 2.7).

The main features of the temperature regime of permafrost are its

ｴ｣ｭｰ･ｾｬｴｵｲ･ at a depth of 10 m and the thickness of the layer of seasonal freezing and thawing. This thickness varies in different parts of the

permafrost region. North of the Arctic circle the average depth of seasonal thawing is 0.5 - 1.5 m, while below the moss-peat cover in the tundra zone it

may even be less than 0.2 - ().:; m. The freezing of thawed soi1 in w.inter 1.S

completed in December - January, after which the underlying permafrost coolso

In the central parts of the permafrost region, the layer of seasonal thawing is, on the average, 1.5 - 2.5 m thick and its freezing is completed in January - March. In the southern parts of the region, the depth of seasonal freezing and thawing is, on the average, 2 - 3 m, while in the areas free of snow (Transbaikal region, the area around Bratsk) it may reach 4 - 5 m or more.

Frozen soil phenomena result from freezing and thawing of wet soils.

Heaving (increase in the soil volume on freezing) is especially rapid if ground water is flowing towards the freezing front. It raises the ground surface an average of 10-15 cm. This uplift is uneven and in some cases leads to the formation of frost boils which may be several meters in height. There are occasional perennial frost boils 10 to 12 m or more in height.

Icing is formed due to pressure exerted by suprapermafrost water (see 2.10) as a result of a reduction in the cross-section of the ground water flow (ground icing), or owing to a reduction in the cross-section of a river on freezing (river icing). Icing may be caused by ground water springs. Water which gr:I(Jually flows out, due to fracturing of soil or icc, freezes and

forms an ice crust.

Thermokarst is developed in areas underlain by icc rich permafrost, when seasonal thawing exceeds the average depth and penetrates permafrost. This may occur, for example, when the vegetation cover is removed. Thermokarst results in the formation of depressions of various shapes, which are usually filled with water, but may be dry in dry regions (e.g., in central Yakutiya).

Solifluction occurs where soils are oversaturated with water and contain numerous silty particles.

Vertical cracks from 2 - 3 to 10 - 20 cm or more in width and up to 3 - 4 m or more in depth occur upon seasonal freezing of soil, as a result of sharp temperature fluctuations in its upper layer. Such fractures are

dangerous mainly in the case of buried pipelines and cables. Damage to foundations caused by fractures are extremely rare.

For explanation of 1.4(e) see 2.5 and of 1.4(g) see 2.10.

J.5 It ＱｾＺ［ cocent.ial. to check the condition of et.rucbureo, as iael.l. as the temperature Y1egime of foundation soils and the ground water regime both during construction and operation of buildings and other structures in the

permafrost region. A program of observations is set up by the design

organization and depends on the use of the ｳｴｲｵ｣ｴｵｲ･ｳｾ their type and

structural ｣ｨ｡ｲ｡｣ｴ･ｲｩｳｴｩ｣ｳｾ as well as ground conditions and the adopted

method of using the soils as foundations (see 3.2).

In the case of large construction projects estimated at a cost of

more than 10 million ｲｵ｢ｬ･ｳｾ a field laboratory should be set up for

observation purposes at the start of construction. This should be done by

the oumcre of Lhc project .

Re 1.5 Construction of large huildings and other structures in the permafrost regions has taken place on a large scale for the last 30 to 35 years. In this region it is essential to check the need for and the mode of application of measures outlined in the design both during construction and operation of buildings and other structures.

In the course of preliminary investigations on large construction sites it is essential to organize field stations for the observation of the temperature regime of soils (both on undisturbed sections and where

conditions have been changed; e.g., areas without vegetation, with artificial covers, etc.). It is also essential to observe the ground water regime, frozen ground phenomena, etc.

The temperature and water regimes of soils are observed ln the course of construction and operation of structures, as well as the settlement of foundations, if allowances have been made for thawing of perennially frozen foundation soils or if the base consists of plastic frozen soils (sec 2.3).

The extent and nature of field investigations are outlined by the design organization. The investigations should be supervised by a research institution.

2.

NOMENCLATURE OF FOUNDATION SOILS

2.1 All soils ape tePmed fpozen if theip tempepature is below OP equal to

zepo (OC) and they contain ice; such soils ape tePmed pepennially fpozen if

they pemain in a fpozen state fop many yeaps (at least thpee).

The supface layep of soil in the pCPmafpost pegions subjected to seasonal thawing and fpeezing is tePmed as follows:

seasonally ｦｰｯ＿･ｮｾ if it thaws in the summep and fpeezes ｾｮ wintep without

mepging with the main body of pePmafpost;

seasonally ｴｨ｡ｷ･､ｾ if it thaws in the summep and fpeezes in wintep until it

mepges completely with the main body of pePmafpost.

Note. The soil layeps which fpeeze ｾｮ wintep and do not thaw fop one OP two

yeaps ape tePmed pepeletoks.

2.2 Fpozen soils ape classified accopding to the nomenclatupe given ｾｮ

SNiP II-B.1-62* "Bases of buildings and othep stpuctures. Design standapds"

(papa. 2.1 - ＲＮＴｾ 2.6 - 2.8 and ＲＮＱＰＩｾ depending on theip chapactepistics

aftep thawing.

In contpast to the nomenclatupe given in SNiP ｉｉＭｂＮＱＭＶＲＪｾ the

additional t.emn "silty" is used to deecx-ibe fpozen clayey soils containing mope than 50% of papticles 0.05 - 0.005 rron in size.

Re 2.1 and 2.2 The bases of buildings and other structures in the

permafrost region may be in a frozen, thawing, thawed, unfrozen or freezing

state. lienee, foundation soils are more varied here, as far as their

properties arc concerned, than outside the permafrost region, even though their composition and moisture content may be the same.

The silty particles in permafrost result from specific environmental conditions and are a product of physico-chemical weathering. Silty soils are widely present in the permafrost regions. In a thawed state these soils have thixotropic properties and a low coefficient of permeability, are often in a state of flow and are most subject to heaving on freezing.

2.3

Frozen soils are classified according to their state as follows:

lulrd frozen - soils which are firmly cemented with

ＧＦ｣･ｾ

are subject to a

relatively brittle failure and exhibit practically no compression under loads

exerted by the structur'e; hard fr'ozen soils include sandy and clayey

ｳｯｩｬｳｾ

if

their' temperatur'es are below the following values:

silty sands

-0.3

°c

sandy loams

-0.6

°c

clay loams

-1

°c

clays

-1.5

°c

plastic frozen - soils cemented by ice but with viscous properties (due to a

high unfrozen water content) such that they are subject to compression under

loads exerted by the structure;plastic frozen soils include sandy and clay

ｳｯｩｬｳｾ

if the degree of saturation of their pores with ice and unfrozen soil

(G) '&$

equal to

or

less than 0.8 and their temperature lies between

0

°c

and

the valur?$ Uivcn

[o»

the

har-d

fY'ozcn eoi.l.c;

G

is found from equation

[5 (5)];

-if

G >

o.

Ｘｾ

or' if the salt content of soil (see

2.11)

exceede

O.ＲＵＥｾ

the state

of the soil

'&s

determined by special investigations;

friable jrozen - sandy and coarse-grained soils not cemented by ice due to a

low moisture content.

Rc 2.3 The subdivision of frozen soils into hard frozen, plastic frozen and friable frozen is based on their different compressibilities under a load.

Hard frozen soils have a coefficient of compressibility of from 10-3 to 10-4 cm2/kg; plastic frozen soils from 10-2 to 10-3 cm2/kg and the compressibility of friable frozen soils is the same as for unfrozen soils having the same composition, moisture content and unit weight.

A change ln the temperature of the frozen soil will change the

amount of unfrozen water in it, so that hard frozen soil may be transformed to plastic frozen (if the temperature rises) and vice versa.

2.4 As a ｲｵｬ･ｾ friable frozen soils and monolithic rocks do not change their mechanical properties and do not settle when the temperature changes from

negative to positive. When using such soils as ｢｡ｳ･ｳｾ allowances should be

made for the requirements given in SNiP II-B. 1-62*.

Fissured rocks and coarse-grained soils with fissures and voids

filled with ice may change their mechanical properties and ｳ･ｴｴｬ･ｾ which should

be considered in the ､･ｳｩｧｮｾ as outlined in the present chapter of SNiP.

Re 2.4 It is known from experience gained in construction on permafrost that structures erected on coarse-grained soils or fissured rock may undergo

considerable deformation. Detailed examinations of foundation soils under deformed structures revealed the presence of ice in fissures and voids, which had not been discovered during the preliminary investigations. The drilling of boreholes in such soils results in strong heating of the drill, which melts the ice prior to extraction of the core.

:1.5 The [ol.Lourinq are the additional factors characteristic of frozen eoi.lc, as compared iaith. normal. unfrozen soils:

a) total moi.c turc content including al.L [orme of ioat.er t.n the

fr'ozen coi.l., and bhe bot.al. ice content: (see 2.6);

c) the extent to which the pores are filled with ｾ｣･ and unfrozen water (see 2.8);

d) unit weight of the skeleton of frozen soil;

e) relative settlement of frozen soil on its transition to a thawed

state (see 2.9);

f) the C01:L charact-cr-ie t.ice required to calculate the strength and

ntability of [r-ozen and thawing foundation soils (see 5.5 - 5.13);

g) the soil characteristics required to determine the stability and

strength of bases and foundations subjected to heaving forces (see 5.14 - 5.21);

h) the soil characteristics required to determine the deformation

of frozen and thawing bases (see 5.22 - 5.39);

i) the thermo-physical soil characteristics: the coefficients of

thermal conductivity and specific heat in frozen and thawed states (see para. 2 of the Appendix);

j) salt content (see 2.11).

Re 2.5 For explanation see paragraphs given in the brackets above.

-r2.6 Thc total moisturc eontcnt ｗ｣ｾ expveeeed as a ratic of the ｉｊ･ＱＺｾＷｨｴ

of all types of water eontained in frozen soil to the weight of the soil

ｳｫ･ｬ･ｴｯｮｾ is equal to:

W',=-: 1111\T Wll

+

Wll =

= Wu

+

w.,

_{[1 (1)]}

I,JheY'C: Wu Mjthe moisture content due to pore iceｾ i. e.ｾ ice

W

B ｾｳ

the moisture content due to ice

ｩｮ｣ｬｵｳｩｯｮｳｾ ｩＮ･Ｎｾ

ice layers and lenses;

W

H

is the moisture content due to unfrozen water &n

frozen soil at a given temperature;

W

=

W

+

W

H

is the moisture content of frozen soil

r u

between the ice inclusions;

All

these factors are expressed as fractions;

Wｾ W

and

W_r

c H

are determined

exper-imental.lq,

while

Wu

and

W

B

are calculated

from equation

[1 (1)]. W

H

may be found from the following

equation:

= k

w

H P [2 (2)]

where:

W

&s the moisture content of soil at the

p

plastic limit expressed as a fraction;

is a coefficient

depending on the

plasticity index

frozen soil.

taken from Table

1 (1)

type of

ｳｯｩｬｾ

the

W

and the temperature

Table 1 (1)

Values of k_H

k

H at soil temperature of (OC)

Soil Plasticity index

-0.3 -0.5 -1 -2 -4 -_10 1. Sand _Wn < 1 0 0 0 0 0 0 2. Dandy loam 1 <

W

< 2 0 0 0 0 0 0 - _n ,3. Sandy loam 2 <

W

_n < 7 0.6 0.5 0.4 0.35 0.3 0.25 : 4. Clay loam 7 <

w:

< 13 0.7 0.65 0.6 0.5 0.45 0.4 n 5. Clay loam 13 <

W

< 17

_*

0.75 0.65 0.55 0.5 0.45 n 6. Clay ｾ > 17

_*

0.95 0.9 0.65 0.6 0.55 n

*

The pores contain unfrozen water only.

t.e expreeeed as a r-at-io of the ooLumc of

"ee

The total ice content 11

c

in [rozen eoi.L to the volume of the latter:

where: 11

,,3

the ice content due to pore "ce expressed as a

11,

fraction;

[3 (3)]

11 is the ice content due to ice inclusions expressed as a

B

[4 (4)]

whcY'e:

_Yll, '&8

the density of mincY'al soil paY'ticles in

kg/cm ;

:3

thc density of ice taken as

:3

YJl &0

0.0009 kg/cm ;

ｗｂｾ W

and

W

H

aY'e the same as in

[1 (1)] .

c

Note.

TI

may be found diY'ectly fY'om the measuY'ements of ice

B

inclusions in the couY'se of investigations of foundation soils on the

constY'Uction site.

2.7

CY'yogenic stY'UctUY'e is the stY'UctuY'e of fY'ozen soil Y'esulting fY'om

fY'eezing of wateY' contained in it and chaY'acteY'ized by the

ｳｨ｡ｰ･ｾ

8ize and

distY'ibution of ice inclusions.

DiffcY'entiations aY'e made between

ｭ｡ｳｳｩｶ･ｾ

layeY'ed and Y'eticulate

et.rucburee,

Massive stY'UctuY'C is chaY'acteY'ized by the pY'edominant pY'esence of

poY'C ice

(l\

<

0.03) .

LayeY'ed and Y'eticulate stY'UctuY'es ar>e characterized by the presence

of ice lenses and layers

(TI

B >

0.03).

In soils with a reticulate stY'Ucture

these inclusions are present in the form of a

ｮ･ｴｾ

while in soils having a

layered stY'Ucture the ice inclusions occur' as layers and lenses alternating with

mineral layers.

The mineral layers are characterized by a massive stY'Ucture.

Re 2.6 and 2.7 Freezing of soil is accompanied by a redistribution of

pore moisture. The intensity of this process depends on the type of soil and its initi:ll total moisture content, the level of the ground water table, and the rate of freezing of the soil. As a result, some moisture accumulates here and there in the form of large crystals, lenses and layers of ice.

Some moisture freezes in the pores between the mineral particles and cements them together to form a monolithic mass. The resulting icc is termed icc-cement. The remaining moisture coating the mineral particles and f i I ling the smallest pores remains unfrozen. The amount of unfrozen water depends on the temperature, composition and salt content of the frozen soil. With a decrease in temperature some of this water in clay soils is transformed into ice-cement; which melts when the temperature rises.

Each type of moisture and ice affects the properties of soils in the frozen state and after thawing.

The icc inclusions, which arc quantitatively dependent on W B and

n

B, give an idea of the settlement of soil under its own weight after thawing

(without an external load). The factor Jl characterizes the amount of ice

B

in frozen soil due to icc inclusions. For example,

n

B = 0.2 means that a

100 em thick layer of frozen soil contains ice layers with a total thickness of 20 cm. On thawing the maximum possible settlement of frozen soil under its own weight 1S equal to the total thickness of ice inclusions.

The coefficient of permeability of thawing soils containing ice inclusions exceeds that of normal unfrozen soils of the same composition and density by two or three orders of magnitude, since on thawing the moisture migrates along the voids which originally were filled with ice.

The type of icc inclusions and their location determine the cryogenic structure of frozen soils. Distinctions arc made between three types of

cryogenic structures: massive with a uniform distribution of ice inclusions, layered and reticulate. The layered and reticulate structures are shown in l-ig . 2. The settlement of frozen soil depends on its structure. It is greatest in the case of reticulate and layered structures.

The ice-cement and unfrozen water (Wand W) define the settlement

u; H

of soil under an external load after thawing. In the majority of cases this settlement is considerably less than the settlement of soil under its own weight when the ice inclusions have thawed. Furthermore, W

H defines the state of frozen soil (hard frozen or plastic frozen) and is taken into account in heat-engineering calculations (see Appendix).

In cases where the water content of frozen soil _Wr = W

H cannot he Jetermined experimentally, it may be taken as approximately

W, where W is the water content of soil at the plastic limit.

p p

+

W

u

equal to

If

n

of sandy soil is less

u

cemented by ice or represents

The ice content Jl determines the adfreezing strength of mineral u;

soil particles. In the case of sandy soils, Jl cannot exceed their porosity. n

than its porosity, such soil is either weakly a friable mass (the soil is in a friable frozen state) .

2.8 The extent to which the pores of frozen soil are filled with &ce and

unfrozen water (G) is found as follows:

G - -J --- --(1,1li'11-!-ＭＭｾＭＭＭＭＭＭＭ \1'11)1'"

EM )'11

(5 (5)]

iohcvc : W, Wand YTT aY'e the same as t.n equations [1 (7)],

U; H >->,

r

2 ( 2)] and [4 (4

Jl ;

ｌｾＱ &0 the eocffl:el:cnt of ｲＩＨｊｙＧｭｾＧｕ［ｹ of miner-at

layers of undisturbed frozen SOl:l.; YB ＷｾＰ

the density of water taken as equal to

3

0.001 kg/cm .

Re 2.8 The extent to which the pores of frozen soil are filled with ice and unfrozen water IS used in determining the plastic frozen state of soils (see 2.3) and in estimating the adfreezing strength of soil particles. I f G is

very small, the soil may fail easily under an impact load and be in a friable frozen state. The large values of this coefficient, i.e., G > 0.9, define the heaving of frozen soil and hence its higher compactibility after thawing.

2.9

The relative settlement of frozen soil on its transition

to

a thawed

state

(0)

represents a ratio of the change in the thickness of the soil layer

on thawing under a load

to

its initial thickness:

[6 (6)]

ｾｨ･ｲ･Ｚ

h

M

is the thickness of the layer of frozen soil in cm;

h

_T

&s the thickness of the same soil after

ｴｨｾｮｧ

under

conditions eliminating the possibility of lateral

.

t

.

.

k / 2

expans&on a

a g&ven pressure

p

&n

g cm .

The relative settlement of

ｴｨ｡ｾｩｮｧ

foundation soil is determined &n

accordance

ｾｩｴｨ

paras.

5.36

and

5.39

of the present Standards.

Re 2.9 The relative settlement of frozen soil on its transition to a thawed state changes within a very wide range of values depending on the presence of ice (Table 2).

Table 2

The average values of relative settlement of thawing soils at

2 p = 1 kg/cm Soil Coarse-fragmented Sand Sandy loam Clay loam Clay Massive 0.003 - 0.03 0.005 - 0.04 0.01 - 0.05 Cryogenic Structure Layered 0.03 - 0.1 0.04 - 0.15 0.06 - 0.2 Reticulate

I

0.06 - 0.2 0.08 - 0.25

The relative settlement of frozen soil may exceed the values given in Table 2.

A 11reliminary estimate of the relative settlement of layereJ and reticulate frozen soils after thawing, in order to compare the compressibility of soils when selecting a construction site, may be done as follows:

(7)

where: YCK.r1 H IS the unit weight of the soil skeleton between the

ice inclusions (for sand - the unit weight of the skeleton of compacted soil) in kg/cm3;

W is the water content of frozen soil between the ice

r

inclusions expressed as a fraction;

IS the density of water equal to 0.001 kg/cm3;

W

c IS the total water content of soil expressed as a

fraction.

Equation (7) is used to find the maximum possible relative settlement of frozen soil on thawing under a load, since it is derived from the assumption that the density of soil after settlement will be equal to the density of the soil aggregates. The actual settlement will be less (see 5.35).

::. I () Ct-ound iaa Lc:f' t.n the _{pcr'maj"r'olJt region may} be cl.ace if'ied as ;:Lipr'uu!' rn«lff'!);;L, ij" 'U t.. ; be iioccn the Dcaconally frozen layer' and the

/!('Y'muj"f'o;:L La!'/I', or: i.n Ow Dcacorzally U1CXI,Jed layer; i.nbcrpcrmaj'roct.,

i f 'if; 'I;; miuYuf;'inU al.oruj Ow t.alikr: ioil.hin pcrmaj'roct.; and :;ubpcr7najhJ:;[;,

Re 2.10 Suprapermafrost water is, as a rule, connected to the nearest water basin (swampy depressions, ponds, lakes and rivers). Its horizontal migration takes place usually along sandy soils. The level of the

suprapermafrost water is unstable, since it depends on its source of supply (usually atmospheric precipitation) and the ground water flow. In winter or

in a dry period, the level of suprapermafrost water falls.

The chemical composition of suprapermafrost water may vary sharply, which may be due to the fact that atmospheric precipitation on entering the

soil will mix with industrial wastes, migrate through coal and ore dumps, etc. In such cases non-aggressive water may become aggressive as the area (region) is developed.

Subpermafrost water is found below permafrost. Its chemical composition, pressure and flow level remain constant throughout the year.

Ground water may migrate along thawed zones in permafrost and is then called interpermafrost water.

-r2.11

The c.alinity of soil is defined as a ratio of the UJeight of salts

in the soil to the UJeight of the soil skeleton and is expressed in percent.

The soils are saline if their salinity exceeds 0.25%.

Re 2.11 Salts, if present in the soil, change its freezing (or thawing) temperature, the amount of unfrozen water in frozen soil (see paras. 1 and 2 of the Appendix), its compressibility and bearing capacity. A salinity of up to 0.25% has practically no effect on the physico-mechanical properties of frozen soils. Saline soils are found most frequently on the northern sea coasts.

3. BASIC METHODS OF DESIGN

3.1

The design of bases and foundations should provide for the required

operational characteristics and long service life of buildings and other

structures.

This is achieved by selecting

or

providing a reliable base which

will prevent excessive deformation.

If

ｵｮ｡ｶｯｩ､｡｢ｬ･ｾ

use may be made of

structural designs adapted to considerable differential settlements.

Re 3.1. A reliable base is the foremost requirement with respect to the

operational characteristics and long service life of buildings and other

structures. In other words, the main objective should be the selection or

provision of a base which will prevent excessive deformations, rather than

adaptation of structural elements to such deformations. This is achieved by

adopting the measures outlined in paras. 3.2 - 3.21, the aim of which is to

provide the foundation soils with the required characteristics. Para. 3.1

emphasizes the importance of finding sites with reliable soils, which do not

require any special improvement. It is also possible to use structural

designs adapted to considerable differential settlements.

3.2

One of the following two methods of using permafrost as foundation

soil may be

｡､ｯｰｴ･､ｾ

depending on the environmental conditions and the

characteristics of buildings and other structures.

Method I - the foundation soils are used in a frozen state throughout

the entire service life of a building

or

structure.

Method II - the foundation soils are used in a thawing

or

thawed

state.

Note.

Undisturbed thawed soils may be used as a base in accordance

with requirements given in SNiP

ｉｉＭｂＮＱＭＶＲＪｾ

providing no freezing of

Joundation soils will be permitted throughout the period the building

or

Re 3.2. A distinction should be made between the methods of using the soil as a base and the methods of preparing the base [foundation soil.]*

The method of using the soil as a base has a direct bearing on the nature of engineering exploration, the investigation of permafrost, the estimates of the limiting conditions in the base, the rules for and methods of all work below ground level, and the use of buildings and other structures.

Methods for preparing the frozen soil base may consist in

preliminary lowering of the soil temperature, freezing of occasional thawed patches or raising the permafrost table, if the permafrost does not merge with the layer of seasonal freezing or is thawing everywhere within the construction site.

When thawed foundation soil is used, the actual thawing may be done prior to construction, or the soils may thaw while the building or structure

is in use. Preliminary thawing is normally done to a certain depth only and

all further thawing occurs when the building or structure is in use (see paras. 3.14 - 3.17).

3.3 As a ｲｵｚ･ｾ onZy one method of using permafrost as a base shouZd be

considered for each construction site. The combined use of both methods is

permitted onZy on condition that the stabiZity of buiZdings and structures

uJiU not be diet.urbed as a reeul.t: of their mutual t.hermal. effect on the

foundation soils. The appZication of different methods for individuaZ

sections of the same buiZding or structure (except very; long structures) ｾｳ

not pc rmitted, These requirements should be considered al.so iohen new

bui. Ldi.nqc or' n truct.urec are erect.ed i.n buil.t-up areas.

Re 3.3. Different methods of using permafrost as a base on the same

construction site may be applied only if this is justified by calculations or previous construction experience in the given region.

In the case vrhere very long structures cross different areas

with different permafrost conditions the application of different methods is

unavoidable. At the same time, special structural modifications must be

adopted on transition sections to ensure normal operation of the entire structure.

The prescribed regime of foundation soils must be maintained, even if the buildings or structures are modified later or new structures are

erected nearby. For example, in the case of method II, new additions to a

workshop will increase the depth of thawing of its foundation soils and hence

lead to additional settlement of the entire structure. In the case of

method I, an addition to a building may, for example, affect the ventilation of the cold crawl space (see 3.5), and thus may reduce the bearing capacity of the foundation soils.

3.4 The design of bases and foundations should provide for the retention

of the prescribed thermal regime of foundation soils throughout the

construction and use of buildings and other structures. Instructions

outlining the basic requirements should be incorporated in the design.

Working drawings of foundations must contain cross sections of the permafrost and basic information on the properties and the temperature of both undisturbed and disturbed foundation soils.

Re 3.4. The adopted method of utilizing permafrost as foundation soil must

be followed right from the start of construction work. With this in mind,

the measures designed to retain the specified temperature regime of foundation soils in the course of construction must be developed during the planning

stage. For example, in the case of method I, provisions should be made for

the retention of permafrost and, if possible, the lowering of its temperature

in the course of construction. For this, permafrost in excavations should be

prevented from thawing in the summer, while in winter provisions should be

made for the cool ing of permafrost hy preventing snow from accumulating in

excavations and on the site in general.

be incorporated in the design. Furthermore, the design should also contain a list of required observations as outlined by the design organization.

The use

of

foundation soils &n a frozen state (method I)

3.5 The

1'0

llourinq ins l.al l.at ione ar-c used to retain the [oundat.i.on

S01:

ls

t.n a frozen state and mai.ni.ai.n their specified thermal y-e!J1:me: cold cr-aial.

spaces (see ｊＮＶＩｾ cold main floors (see ＳＮＷＩｾ ventilation pipes and ducts

(see ＳＮＸＩｾ and insulating layers.

Note. Frozen foundation soils may be retained under heated buildings

built to allow for the formation

of

a thawed zone and without the use of

installations outlined &n paras. 3.6 - ＳＮＹｾ if the foundations are laid in

permafrost below the estimated depth of thmJ. This method is expedient when

the buildings are narrow and the temperature of permafrost is ｬｯｷｾ but each

case must be ｾＷｩｶ･ｮ 1:nd1:vidual consideration.

Re 3.5. The retention of a frozen base and the maintenance of specified soil

temperatures arc usually achieved by ventilation. Ventilation methods are

subdivided into surface and huried installations, depending on their location

relative to the surface of the ground. Surface installations include cold

crawl spaces, ventilation ducts along the perimeter of a building or other

structure, and duct systems immediately below the floors. Buried

instal-lations include various sytems of ventilation pipes or ducts in the foundation soils or pads on which the buildings are erected (see 3.8).

In summer, the ground heneath ventilated buildings and structures thaws to a certain depth; in winter, the thawed layer freezes again.

Additional cooling must ensure that the specified temperatures of foundation soils are reached (paras. 5.8 and 5.10).

Depending on the duration of additional cooling and the air

temperature within the ventilation device, this cooling Play be used to control

the mean annuaI t cmpcrut ur-c of permafrost and the specified temperature of the

capacity of permafrost, or raise them to reduce the heat losses in the building if the temperature of permafrost is very low).

The lower the temperature of the ground, the cheaper the foundation. In this case, however, it is essential to maintain very low temperatures in the ventilation devices during the winter. To do so the thermal resistance of the perimeter wall above the ventilation device must be increased and

consequently the cost of the wall and the cooling system becomes more

expensive. The optimum solution may be found by comparing various possibil-ities.

Unheated main floors of buildings may be used for ventilation

purposes, if their temperature regime will maintain the specified temperatures for the foundation soils.

In some cases the ground under buildings may be retained in a frozen state without ventilation. For example, if the area occupied by a building is relatively small and the thermal resistance of the lower perimeter wall is high and the temperature of permafrost is low, the thawed zone under the building will not exceed 2 or 3 m in depth, or the permafrost table may even rise, i.e., the depth of thaw under the building will be less than on the surrounding site. For example, the thawed zone under residential buildings in Yakutsk is not excessive and in most cases there is no need for a ventilated crawl space.

The possibility of retaining the ground in a frozen state without ventilation is determined by calculations given in the Appendix. If use is made of insulating layers in the form of pads of gravel or sand, the ground is cooled through the surface and the slopes of the pad outside the building. This process, however, is efficient only in the case of buildings occupying a small area and if the mean annual temperatures of the soils are low

(helow -3°C). The depth of thaw under a building or structures with an insulating pad is found by calculations given in the Appendix. The thermal

hn

resistance of the floor should be increased by a factor AIl (where ｾ is the thickness of the pad in m;

>n

is the thermal conductivity of the pad in kcal/m x hr x deg.) .

3.6 A cold crawl space with natural ventilation all the year round (or

forced ｶ･ｮｴｩｬ｡ｴｩｯｮｾ if natural ventilation is not possible) is the main method

of maintaining the ground under heated structures in a frozen state. Cold

crawl ｳｰ｡｣･ｳｾ unventilated in ｷｩｮｴ･ｲｾ are also permissible.

The choice of crawl space and ventilation method is based on

calculations or local construction ･ｸｰ･ｲｩ･ｮ｣･ｾ with allowances "Instructions

for the design of ｳ･ｴｴｬ･ｭ･ｮｴｳｾ ･ｮｴ･ｲｰｲｩｳ･ｳｾ buildings and other structures

in the northern construction-climatic zone" (SN 353 - 66).1

Re 3.6. Cold crawl spaces provide the simplest and most reliable means of ventilation. In this case the floor of the first storey is raised above the graded surface of the ground. The floor must satisfy the requirements in

SNiP II-A.7-62* and SN 353 - 66. The perimeter walls of the crawl space in

stone buildings is usually made of suspended plates of reinforced concrete, and, in timber buildings, of planks.

Depending on the cooling regime and ventilation, cold crawl spaces are classified as follows:

- ventilated the year round; ventilated in summer only; - unventilated.

In cold, unventilated crawl spaces heat is removed through the perimeter walls and the foundation soils. Heat removal through the perimeter wall should be considered only if a building occupies a small area and has a high crawl space. The possibility of condensation in unventilated crawl spaces in the summer, due to infiltration of warm external air, limits the uses of such crawl spaces still further.

From the point of view of heat engineering, the role of an

unventilated crawl space is reduced to that of additional insulation of the ground. Whether or not an unventilated crawl space can be used to retain

the ground in a frozen state lS determined by calculations (see Appendix). In these calculations the thermal resistance of the horizontal layer of air

between the bottom of the floor and the ground surface is included in the total thermal resistance of the floor.

In crawl spaces ventilated in the summer only, heat from the building is removed in winter through the perimeter wall and the foundation soils, while in summer the crawl space receives additional heat from the warmer external alr. This type of crawl space may be used in buildings occupying very small areas and if the soil temperatures are below _3°C.

Best results have been obtained with crawl spaces ventilated

throughout the year. In this case the ground is cooled mainly by ventilation with cold external air in winter. The height of crawl spaces is determined in accordance with SN 353 - 66.1

Depending on the method of ventilation, these crawl spaces are classified as follows:

- crawl spaces ventilated through openings in the perimeter wall or a space between the wall beam and the surface of the ground (open crawl

spaces);

- crawl spaces ventilated through exhaust pipes.

The method of ventilation used depends mainly on snow conditions. If average wind velocities in winter are less than 4 to 6 m/sec, the crawl spaces should be ventilated through openings in the perimeter wall or by leaving them open. In the case of high wind velocities, the use of openings or open crawl spaces is difficult due to snow drifts. In this case, the openings should be located above the snow surface, while open crawl spaces should be high enough for free passage of snow under the building. The latter can be ensured only for narrow structures well separated from other buildings. If the snow depth exceeds 30 ems, the openings should be provided with ducts with inlets and outlets located 40 to 50 cms above the snow surface.

In the absence of special snow protection measures, crawl spaces of buildings located in regions where the average wind velocity in winter exceeds

4 to 6 m/sec, should be ventilated by means of exhaust pipes. The inflow of

air occurs through inlet pipes with openings located above the maximum height

of snow near the building wall. The mouth of the exhaust pipes is located

above the apex of the roof and is provided with baffles. The ventilation in

this case occurs mainly as a result of wind pressure. Thermal pressure may

be ignored in calculations.

F,xhaust pipes should not be located within the building to increase the thermal pressure, since the outer surface of such pipes may be covered

with condensation. To avoid condensation problems, the thermal resistance of

the pipe wall should be close to that of the floor above the crawl space. This brings ahout a considerable reduction in the thermal pressure and makes

the exhaust system more complicated and expensive. The thermal pressure may

be increased also by installing special heaters in the exhaust pipes. In the

majority of cases, it is sufficient to install baffles without any special provisions for forced ventilation.

Exhaust pipes should be installed in such a way as to ensure uniform ventilation of the crawl space.

Ventilation must provide the specified ground temperatures without

excessive cooling of the crawl space. This makes it necessary to increase the

thermal resistance of the floor. It would also have a detrimental effect on

living or working conditions in the building.

The ventilation regime and the design of the crawl space are hased

on calculations or local construction experience. When using local experience

as a guide, it is essential to have data on the ground thermal regime heneath a building already in use, or a structure with a ventilated crawl space. Allowances should be made for the fact that the depth of seasonal thawing of soil beneath an operating building may be less than the depth of seasonal

thawing under natural conditions. At the same time, the maximum temperatures

of foundation soils may rise and even approach DoC. The main criteria of the

reliahility of ventilation are the maximum ground temperatures measured in late fall or early winter.

A ventilated crawl space may be designed by the method suggested by

G.V.

Porkhaev. The ventilation modulus

M

is a factor which determines the thermal regime of the crawl space:

M F B F c [8]

where: is the total area of air vents (for crawl spaces with air vents),

or (for open crawl spaces) the area of the ventilation space equal to the product of the perimeter of the building and the distance from the bottom of the wall beam to the surface of the ground, or the total area of exhaust pipes (for crawl spaces with exhaust pipes) in sq. m;

F is the area of the building measured along the perimeter, in

c

sq. m.

In the case of open crawl spaces and those ventilated through air vents in buildings with the internal air temperature not exceeding 20°C, the ventilation modulus is calculated as follows:

M= k tn - tn.1I

+

_N n _{300R o}V_{r p (tn.n -} [H.B) , [9] where: k Il

v

_cp t_{H. B}

is a coefficient which depends on the distance between the buildings;

is the air temperature within the building, in

DC;

is the mean annual air temperature in the crawl space, in

DC;

is the thermal resistance of the floor above the crawl space, in m2 x hr x dag/kenl;

is the average annual wind velocity in m/sec;

is the mean annual temperature of the external air, In DC. Factor N in equation [9] accounts for the effect of heat emitting pipelines in the crawl space on the thermal regime of the crawl space. N is calculated as follows:

n

where: is the number of heat emitting pipelines in the crawl space;

is the length of the i-th pipeline, in m;

is the temperature of the heat transfer agent in the i-th pipeline, in deg;

TTi is the duration of operation of the i-th pipeline throughout

R . Tl. T F R c

a

and t B

.n

the year, in hrs;

is the thermal resistance of insulation on the i-th pipeline, in m x hr x deg/kcal;

is the duration of the year equal to 8760 hr; are the same as in equations [8] and [9].

The values of k for crawl spaces with air vents and open crawl spaces

n

are taken in relation to the distance between the buildings £ and their height

h. At £ ｾ 5h, k_n 1; at £

=

_{4h, kn}

=

1.2 and at £

=

3h k

n

=

1.5.

The mean annual air temperature in the crawl space is estimated as follows:

- if the ground under the building has the same mean annual temperature as the mean annual temperature of undisturbed soil, then

[11 ] - if the ground consists of plastic frozen soils, then according to

para. 3.24 the temperature of the soil must be lowered. In this case

npH

to

ｾ

--

0,50

C tn ll ｾＭ］ 4to:

1

npn

to

< ---

O,[)O C t-;« = 'JIll.

f

r

121 .

1\t very low mean annual temperatures of undisturhed permofrost the required hearing strength of foundation soils may he maintained at higher

temperatures in a numher of cases. If the design provides for these higher

temperatures (they will be reached while the building is in usc), and having specified an appropriate ventilation regime for the crawl space, the thermal and moisture regimes of the floor above the crawl space may he considerably

improved. In this case, the mean annual air temperature in the crawl space, which will be higher than that required to retain the natural mean annual

temperatures of foundation soils, is based on the soil temperatures t k

Ma c

required to attain the specified bearing strength (see 5.8 and 5.10).

and t

3

The mean annual air temperature in the crawl space is then determined as

outlined below. The values of t k and t

3 are given and the thermal effect

Ma c

of the building on the temperature regime of the foundation soil is calculated as follows:

- for post foundations k t - for pile foundations k

t

[13 ]

The values of at and a are given in paras. 5.8 - S.IO.

3

The values of k

t and the curves in Figs. 11 and 14 are used to find

t'

the ratio -9_ where t' is the mean annual temperature at the base of the

to

,

0

seasona 11Y thawed layer under the bui l ding . The rne.m annua 1 ;1ir t l'lIl]1l'ra ture

in the crawl space is then:

[14]

Here, the values of t are somewhat increased, since the actual

B.n

mean annual soil temperature will be lower than the mean annual air temperature in the crawl space (by 0.2 - 1.2°C).

The floor above the crawl space must satisfy the requirements given

In SNiP 1 I-A.7-()2* (concerning thermal resistance, thermal stability, air

penetration and moisture regime). To determine these factors, it is essential

to know the summer and winter temperatures of the air in the crawl space, which arc related to the seasonal freezing of soil under the huilding.

In buildings with a high heat loss, the air temperature in the crawl space in the summer will be higher than the temperature of the external air.