Creep and strength parameters of frozen clayey soils in the Bovanenkovsk gas-condensate field

Abstract

The Bovanenkovsk gas-condensate field is situated in the cryolithozone with an expanse that is continuous in terms of area and monolithic in terms of section. The mean annual temperature of the rock depends on factors controlling the thickness of the snow cover, and ranges from 0 to −8 o C with a background value of −5-6 o C. The cover formations are composed of rocks that differ in terms of composition ! from sands to clayey loams and clays. Salinity with a marine type of salt is a characteristic feature of their physical properties.The situation in the gas field, and also on other projects where foundations are installed in permafrost soils dictates the need to account for their performance in a complex stress state, i.e. it is required to determine the creep and strength characteristics in triaxial compression.To acquire these characteristics, we employed a type "A" stabilometer in which vertical stresses were created by a lever system, and three-dimensional (lateral) stresses by the pressure of a nonfreezing liquid. The cylindrical soil specimens were 140-160 mm high and 71.5 mm in diameter. Tests were conducted in accordance with a consolidated-drained scheme with preliminary compaction by a three-dimensional pressure prior to conditional stabilization of deformations. All tests were conducted at negative temperatures below the freezing point of the soil being tested. The temperature in the cryochamber was maintained with an accuracy to 0.1 o C.In testing for creep, an axial load σ 1 was applied to the soil specimen after stabilization of deformations with a simultaneous reduction in the three-dimensional pressure σ 2-3 while observing the condition (σ 1 + σ 2 + σ 3 )/3 = const. From our viewpoint, tests conducted for this load path simulate most authentically the deformation of frozen soils, making it possible to isolate creep deformation "in pure form," since observance of the constancy of the average principal stress during the course of the test does not lead to compaction of the soil specimen, but only to variation in its shape.The parameters m, ξ, and α of the equation derived by Vyalov [1] on the basis of the theory of aging, which is widely employed to predict the deformation of frozen soils during the in-service period of structures, considering the manifestation of their rheologic properties ε m = σ t α /ξ,