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

309Frozen32t2.034S2 * 01.4520.34 3.1020.3 1.74iO. 251.44f0.03 3.90k0.2 1.50k0.25Sublimated9.7~0.5 1.45t0.01 2.00i0.1 1.73tO. 0510.2*0.5 1.45f0.01 1 e 35kO.l 1.27S0.05Note: Numerator stands for properties of undisturbed ground, denominatorstands for disturbed ground.after the test began. Deformations developing in the mineral framework, which can be determined bythe initial period are caused by elastic compression short-term tests for the strength of the sublimatecof the ground framework and by a predominantly ground samples.reversible relative shift of mineral particles along If we compare the proposed and existing methodsviscous films of unfrozen water, General creep for determining h5 we note that the first hasdeformation of the frozen ground is 15-20% depending obvious merits. In particular, it reduces teston the effective stress and is mainly plastic time since it allows us to determine the of the(reverse). That of sublimated samples is reduced frozen ground by conducting short-term tests ofto 3-5% with domination of the elastic component.When ground freezes its strength is sharplyincreased due to crystallization of porous watertheir sublimated analogues. Besides, sublimatedsamples are less sensitive to temperature variations,especially beyond the field of intensiveand formation of ice-cementing. This phenomenon is phase transformations (below-5'C).And finally,widely used in civil engineering, for instance,during tunneling or trenchingweak and watertheaccuracy of the test results for sublimatedsamples is higher (k4%) than for frozen samplessaturated ground by means of artificial freezing (k12 to 15%).(Vyalov et al. 1962). Ice-cementing depends onAt the same time, it should be noted that thethe amount of ice and the ground temperature; it is proposed method can be used only to determine theless stable than structural bonding. Ground loadingcauses a shift in the balance between the ice andof clay ground in massive cryogenic structures.The possibility of using this method at temperaunfrozenwater due to a concentration of stresses tures below -1OOC is also debateable because weat particle contacts. Under the influence of thegradient that arises, the unfrozen water, which ishave little knowledge about the rheology of lowtemperaturefrozen ground.replenished by melting ice, shifts to the less tensezone where it refreezes. Simultaneously, the icerecrystallizes and a basal plane reorientation ofCONCLUSIONScrystals occurs parallel to the shift forces.These processes cause a decrease in the frozen 1. To determine the of the frozen clayground's strength when the loading is prolonged. ground of a massive cryogenic structure. the sub-The load for clay samples Q is determined by (I) limated analogues can be used, because the strucandequals 0.45 to 0.5 (Table 2).ture of the mineral framework is not disturbedSublimated clay samples, as compared to frozen during the process of frost drying until CJ,., andsamples, do not demonstrate considerable decrease in its static fatigue limit corresponds to the condistrengthover time; their static fatigue resistance tional instantaneous strength of the sublimatedto compression is 0.85 to 0.9 of the conditional ground.instantaneous strength. of the frozen ground2. The proposed method for determining the FJLand % of the sublimated ground show considerable of frozen ground has certain merits as compared tosimilarity. Such coincidence seems to be regular existing methods. It allows a reduction in testif we assume % as maximal stress at which no defor- time, is not as sensitive to temperature variationsmation of the ground occurs during plastic-viscous (+3"C), and its results have high accuracy.flow or breakdown. A similar conclusion about the 3. Ice sublimation allows for more detailedphysical properties of the of capillary porous investigation into the nature of the strength andbodies was reached by Bykovsky (1954) when hedeformability of frozen ground. In particular, itanalyzed the after-effects of deformation of wood. allows us to determine the individual roles ofIf we treat the frozen ground as an elastic- structural bonding and ice-cementing in the formaplastic-viscousmedium pierced by an elastic spatial tion of their mechanical properties.grid, the system could be destroyed when the stresslimit is surpassed; as a result, further increaseof deformations in the frozen ground is no longerinhibited by its mineral framework. As far asREFERENCESinterground bonding is concerned, this stress limit Bykovsky, V. N., 1954, Definition of static fatiguecorresponds to the value of structural bonding oflimit of the wood by the after-effects deforma-