Yu. G. Fedoseev

Compressibility of sandy permafrost during thawing

Conclusions1. The compressibility of sandy permafrost deep deposits with a medium texture density is, as a rule, close to the compressibility of similar thawed deposits.2. The degree of saturation of frozen sandy soils may serve as an indicator of their compressibility during thawing. When Gf<0.91, the compressibility of frozen sands during thawing is equal to the compressibility of similar thawed soils.3. The compressibility of frozen sandy deposits during thawing, which increased as compared with ordinary thawed sands, should be expected in zones adjacent to the roof of soils with a low permeability.4. The refinement of the method and the high quality of the testing of thawing soils increases significantly the technicoeconomic effectiveness of construction on permanently frozen sandy soils, making it possible to reduce the volume of special measures taken to ensure the stability of buildings and structures, or eliminate them entirely.

Structural strength of frozen soils during thawing

ConclusionsFrozen clayey soils of semi-hard and hard consistency and sandy soils of medium density have a structural strength equal to the value of the actual pressure under complete saturation, and, consequently, the suspending effect of water, and their deformation is determined by the presence of ice striations and the extent to which the macropores that form after their complete thawing are interconnected.

Determination of the deformation characteristics of thawing permafrost soils in the construction of the urengoiskii grés complex

Conclusions1. The test thawing of soils in the test area in the Urengoiskii GRÉS construction sites made it possible to determine the deformation characteristics of permafrost in their natural occurrence and to estimate the rate of consolidation and distributive properties of preliminarily thawed soils.2. The calculation for the settlements of thawing soils with the use of results of compression tests and visual determination of the ice content led, in the given case, to values with are twice as much as the actual values.3. Permanently frozen sandy soils in the construction areas are practically noncompressible with thawing, whereas clayey soils are highly compressible with thawing and cannot be made use of as per principle II without preliminary thawing.

Correlation of results of plate and compression tests on frozen soils under thawing

Conclusions1. The coefficients of thawing A obtained from the plate and compression tests are not correlated.2. The coefficients of compressibilityap obtained from the plate tests significantly exceed the values ofac obtained from the compression tests. This must be taken into account in the revision of the GOST Norms for these tests.

Field investigations of negative friction forces in thawing soils

Conclusions1.The negative friction forces can be estimated by calculation with the use of the Shvedov-Bingham equation of deformation of a viscoplastic body on the basis of the results of pull-out testing of an experimental foundation with preliminary thawing of the frozen ground around this foundation.2.The negative friction forces exceed the ultimate shear strength of the thawed soil on the skin surface of the foundation and depend on the rate of mutual movement of the thawing soil and foundation.3.In connection with the decrease in the rate of thawing of permafrost under a structure with the course of time and the increase of the depth of thawing, the effect of negative friction forces should be checked for the most unfavorable combination of these parameters.4.The minimum values of the negative friction forces obtained in experiments for conditions of the movement of the thawing front parallel to the axis of the pile or support exceed by a factor of 2–3 their value set by the standards [1, 2].

Effect of ice content and cryogenic structure of frozen ground on the bearing capacity of a pile

Conclusions1. The limit resistance of piles in permofrost, especially of driven and bored-driven piles, is determined not only by the amount of ice IC but also by the character of ice distribution in the mass, i.e., by the cryogenic structure.2. Horizontally bedded structures as compared with vertically bedded and cellular, with like content of ice, provide higher bearing capacity of the piles (on an average, by 17%).3. The effect of structure in determining the bearing capacity of a pile may be considered by introducing the structure coefficient KT into the formula for calculation; the values of this coefficient for horizontally bedded structure have been given in Table 1. For vertically bedded and cellular structures, KT = 1 is recommended, and for massive soils, KT = 0.