Fig. 8.11. Compression curve for ice-rich frozen soil (f = constant) (according to A.G. Brodskaya).
Fig. 8.12. Consolidation curves for soils of different granulometry and mineral composition at t = —1.5 °C, P = 0.3 MPa: 1-3 - clays (1 - montmorillonite, 2 - polymineral, 3 - kaolinite); 4 - sandy silty material; 5 - sand.
The compressibility of frozen soils of different lithologic type and salinity as well as length of time of consolidation, is reduced at lower negative temperatures. The reduced compressibility is explained by the reduced content of unfrozen water and thinning of the unfrozen water films, stronger bonds at contacts of structural elements and the higher strength of ice and frozen material in general.
The strength of frozen soils determines their capacity to resist disturbance. Disturbance occurs by development of microshears and microfissures in the frozen soil which accumulate to give rise to big fractures that completely break the frozen soil. Strength properties of frozen soils include the following: temporary and long-term resistance to compression (<5tcom, tensile or rupture strength (<5trup, shear strength (St, Slon) and equivalent cohesion determined by a cone penetrometer (Cteq, Cf0qn).
Shear resistance of frozen soils is dependent on normal pressure P and, accordingly, is determined not only by forces of cohesion but also by
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