2 Volumes Final Proceedings - Washington 1984.pdf - IARC Research

17- streamlining pile design so that variabletemperatures and loading are taken into account.Allowance for Variable Temperature and LoadingThe existing method of structural analysisrelies on the least favorable conditions, pilesbeing designed on the assunption that the permafrosttemperature is high and the loading givesrise to high forces and mornents. In fact, thepermafrost temperature varies with time, dependingon the air temperature and the chilling effect ofbasements, channels, and thermopiles. Pile loadingsalso vary with time, being law during theperiod of construction and susceptible to transientforces, in particular those of climatic origin(snow, wind, soil heaving). All in all, maximumloading is never timed to occur simultaneouslywith the soil's minimum bearing capacity. For example,loads due to snow, wind, and soil heavingare at the maximum in autumn and winter, whereasthe soil has a minimum bearing capacity in summer.This fact is of particular importance in designinglight engineering structures (pipelines, flyovers,power lines) and buildings of light-weight materialwhere transient loads account for a significantfraction of the total loading sustained.Sone design methods consider simultaneouslyloading, soil temperatures, the long-term strengthof eo11 and soil settlement, all varying withtimePiles for Use in Specific Permafrost ConditionsMethods have been developed for designing anddriving piles in ice-rich ground, subtesraneanice, saline permafrost, and thawing ground. Atthe sites where permafrost-thawing techniques areused, preference is coTnly given to staggeredpiles of considerable length and to molded-inplacepiles. Floating piles find application inconjunction with local pre-thawing of permafrost,which is then compacted as the pile is driven intoplace.PILE TESTING PROCEDURESLaboratory tests based on the kinetic theoryof strength have revealed the influence of thesize of the pile model on the adfreeze strength.4 method of allowing for this scale factor hasbeen developed.#Field tests of piles are performed at alllarge construction sites, and a standard procedurehas been established in this connection.A novel accelerated test technique has beendeveloped that relies on a "dynamowtric" apparatusas a means of applying load to the pile. Aninitial stress set in the gauge decreases with thesinking of the pile into the soil. The stress recordedwhen no further settlement of the pile isevident is adopted as the long-term ultimatestress.IMPROVING DURABILITY OF REINFORCED CONCRETE PILESThe extreme conditions of temperature and humidityin the Arctic, where temperature variationsand recurrent seasonal freezing and thawing of thesurface layer cause the high moisture content ofconcrete and freeze and thaw water in the voids ofthe concrete, have an adverse effect on reinforcedconcrete piles. Means are available to preventthe low-temperature destruction of concrete thatextend the service life of reinforced concretepiles.RESEARCH PROGRAMme following problem require further attention:- Improving the techniques of pile driving inpermafrost (especially coarse fragmental perma-frost);- Producing piles of advanced construction;- Streamlining the techniques of emplacingmolded piles;- Widening the field of application of pileswith pre-thawing of permafrost;- Improving the durability of reinforced concretepiles;- Streamlining methods fox computing thebearing power of piles (compiling new tables, constructingnew alignment charts, etc.);- Developing a single methodology of piletesting to be recommended for use in all countries;- Collecting a wealth of experirnental data onthe strength of freezing and the bearing power ofpiles under various conditions with an eye to providingdesign criteria for practical use on analyzingthese data (achievable if researchers fromall countries pool their efforts).