Destructuring settlements due to frost heave during the structures’ exploitation are often not taken into account at the designing stage, although they are indirectly related to the bearing capacity of the soils. The objective of this research was analyzing the effect of the number of freezing-thawing cycles on the strength characteristics of soils. A paired experiment with various initial parameters (void ratio, initial moisture content, and the number of freezing-thawing cycles) was carried out. According to the experimental results, the cohesion largely depends on the above parameters which might lead to its decrease by up to three times. The angle of internal friction demonstrated an indefinite behavior during the freeze-thaw cycles, which is confirmed by a literature review. Freezing–thawing cycles significantly decrease the soil bearing capacity: up to 44% after 10 freezing-thawing cycles for soil with $e=0.55$ and $w=16.5\%$. However, in the case of $e=0.75$ and $w=22.6\%,$ it increased by 33%. A program based on the least-squares method was used to calculate the approximation coefficients of the dependence describing the changes in strength characteristics from the abovementioned parameters. Changes in strength characteristics must be taken into account when designing structures, as they can lead to additional settlement or even subsidence of the foundations.

ИССЛЕДОВАНИЕ РАБОТЫ СПИРАЛЕВИДНОЙ МИКРОСВАИ С ГРУНТОМ

Excavation of pits, trenches for foundations of civil buildings and industrial structures in saturated clayey soils often leads to soil structural change and great decrease in the soil strength and deformation characteristics. In some cases, an artificial sand base is used as a method for construction on saturated clayey soils. However, technology violations and unsuitable material used during construction can be the reason for excess settlement of the erected facilities. The study includes a real example of an emergency situation at gantry crane railways with three hundred meters in length in the town of Tobolsk. The artificial base was made using local sand with specific properties such as subsidence and frost heaving, which were not taken into account in the design process. The observed excess non-uniform base deformations were up to 240 mm. The base properties of the silty sand were analyzed in a laboratory study. Two tests were carried out to simulate possible impact on the artificial sand base. They showed that the values of the initial compaction factor K_com of sand base were found in the range of 0.87-0.92. So, the base subsidence was about 12% of the actual base deformation and the total base settlement under the total operation loading made about 19%.

Усиление грунтовых оснований методом гидроразрыва при горизонтальной проходке