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

28 8Depending upon the vertical levelling done for embankment will be 10 m or m ore in the case of bigthe engineering preparation of the site and the use skeleton soils.of sluiced materials as the foundation bed, three The deformation requirements for the srructuralscenarios can be distinguished (Figure 1) :properties of the sluiced and underlying soils areI. The foundation does not exert load on the the same as for scheme 111. If underground ice,embankment fill; it functions as the levelling ice-rich soils, frozen peat and other types of soil,layer.which undergo considerable settling during thawing,11. The foundations of structures exert loads on are found in the underlying natural layer sluicingthe embankment fill and its natural underlying must be done with an eye toward restriction of itslayer.thermal effect on the underlying soil. The possi-111. The embankment fill accepts all of the loads bility that the underlying soil could thaw duringexerted on it by the foundations and structures. the construction and operation of buildings must beThe underlying layers are not affected by the completely eliminated. The third scheme expandsfoundation loads.the limits of application of the second principleIn the first scheme the use of a fill embankment, of soil use as a foundation bed, because the depthirrespective of the use of foundations, requires of the layer of sluiced materials promotes thethat there be no evidence of heave in the sluice; formation of an extensive, positive temperaturegravel, sand or a combination of both are used. thaw zone. Under natural conditions it can takeIt is necessary to provide high load bearing more than 15 years for this layer to freeze.capacity of the natural ground. It is compressed Measures designed to accelerate this freezing prounderthe sluiced layer and frozen in the com- cess are frequently ill-advised due to technicalpressed state, which improves its structural and economic considerations.properties. As for Yakutsk, when scheme 1 is used, The choice of scheme depends upon the thicknessfreezing takes place over the course of one winter of the fill and the characteristics of the naturalif the fill height does not exceed 2 m.topography of the area being developed. Therefore,If foundation works for the account of soil in the engineering preparation for future construcfreezingalong the lateral surface, it is recom- tion on the Yakutsk Lena River floodplain, allmended to use fine-grained soils. Their highest three schemes could be adopted.load bearing capacity will be reached under con- When the fill embankments are constructed by theditions of rota1 moisture capacity and maximum sluice technique in permafrost and severe climaticdensity. Maximum density is provided by theconditions, the problem of choosing the correctspecial selection of fractions. The best degree scheme for the use of sluiced materials as a founof pore filling in the mixture of two fractions dation bed is of particular importance. Thisis obtained when the small fraction weight 30% is problem has evoked considerable controversy among(Bannik 1976). Filter particles must not be frost- specialists. The problem, first of all, relates toheaved and have a dimension greater than 0.1 rn acceleration of the time required to freeze the(Dalmatov and Lastochkin 1978).sluiced materials, while increasing the thicknessWhen scheme I1 of sluiced fill use has been of this layer. In addition, the engineers arechosen, it is necessary that maximum load bearing interested in obtaining a frozen foundation bed ascapacity of both the sluice materials and the fast as possible. Periods of freezing and stabiliunderlyingground be maintained. Under sluicing zation of the temperature depend on the intensitythis soil thaws, but under the weight of the sluiced of sluicing, the season when the work is beingmaterials it is compacted and a redistribution of performed, moisture content of the alluvial fillmoisture takes place. It is recommended to take and also upon the design of building foundations.measures for draining the thawed layer in order to In order fo use permafrost as a foundation bed (inprevent frost heave. Experiments show that sandy thawed or frozen state) it is recommended to gosoil compresses during the thawing period. When with the natural development of cryogenic processescompression is completed they might be used as beds. in the new fills. Technological and engineeringThe calculation of strain deformation must be done solutions must facilitate intensification of theseaccording to norms established for two-layered processes and under no circumstances impede orfoundation beds. In the case of Yakutsk, theoppose them. This makes it possible to provide thedegree of settling under working loads does not necessary reliability of the beds and stability ofexceed allowable standards. Strain deformation of building and structures.the underlying soil can be reduced when the warming Insofar as temperature regime of the fill soileffect of sluicing decreases. Depth of thawing can affects the condition of the ground water, itbe diminished by depositing sluiced materials on determines to a great extent the soil's COnStructhefrozen ground in the spring, increasing the tion properties. In connection with this, thesluicing intensity and by thermal insulation of the prediction of fill thermal conditions is particunaturalsurface. In some cases, it appears to be larly important for differant technological schemesfeasible to obtain maximum depth of thawing ofof the use of sluiced materials, thickness of thenatural soils for their melioration in the sluicing alluvial layer and conditions of thermal exchangeprocess. The technical and engineering techniques between the alluvial layer and the underlying soilthat allow for the control of this process within in the bottom of fill and the atmosphere. For thedefinite limits in a prescribed direction are well conditions in Yakutsk, the problem of such predicknown.tion was solved for the firSK time using hydro-When scheme 111 for the use of sluiced materials integration and computer technology at the Permaisadopted, the thickness of working layer exceeds frost Institute of the USSR Academy of Sciencesthe computed thickness of the linearly deforming (Konstantinov and Votyakova 1981).layer. Therefore, the total depth of the sluiced