Том 55, № 5 (2018)

The paper provides the results of experimental studies pilot studies of the moisture transfer and clay soil swelling characteristics and their mathematical description. An analytical solution is suggested to determine a stress-strain behavior within a body of soil with non-uniform moisture content interacting with underground structures (foundation, pile, etc.). It is shown that the swelling pressure depends on the type of the stress-strain behavior of soil, and under the compression conditions, exceeds the corresponding swelling pressure under the finite-width foundation base by several times. It was found that the pull-out force of the pile greatly depends on the modulus of deformation of the swelling soil, influence zone and pile diameter.

The grouting efficiency of cement milk injected into sandy soil is estimated by using an artificial neural network. In order to evaluate grouting efficiency, laboratory model tests were conducted on a dry sand bed. Based on the model test results, a neural network model was developed for use in computing normalized grout bulb diameter. A thorough sensitivity analysis was carried out to evaluate the parameters affecting grouting efficiency. Based on the weights of the developed model, a neural interpretation diagram is developed to find out whether the input parameters have direct or inverse effect on the output. A prediction model equation is established with the weights of the neural network as model parameters. The results of the experiment suggest that the developed model can predict grouting efficiency with reasonable accuracy.

To study the dynamic characteristics of carbon-fiber-reinforced soil, carbon fiber was uniformly dispersed into clay soil. A series of resonant column tests was carried out at constant soil dry density. Samples prepared with fiber contents of 0%, 0.05%, 0.10% and 0.15% and water contents of 12%, 16% and 20% were studied. Scanning electron microscopy was used to examine the carbon-fiber-reinforced clay soil at the microscopic level. The results show that the maximum dynamic shear modulus increases and the damping ratio decreases with decreasing soil water content. With increasing fiber content, the maximum dynamic shear modulus increases at first and then decreases; the optimal carbon fiber content was 0.10%. The damping ratio increases with increasing soil fiber content. Scanning electron microscopy analysis indicated two reinforcement mechanisms: friction effect and limiting lateral deformation. Results of this study indicate that carbon fiber is conducive to the dissipation of vibration energy.

The paper provides the results of natural studies of consolidation of weak water-saturated clay soils of large thickness performed at the experimental sites located within the Imereti lowland (Olympic objects, Media center, city of Sochi) and a stadium in the city of Kaliningrad (Oktyabrskii island). A development of deformations, stress conditions and variation of pore pressure within the bulk of the weak water-saturated soils were studies, and the calculation results were compared to the actual deformation data.

In this study, through some laboratory tests, the influence of the encasement (routine and ringy) and gravel mattress (with and without geotextile) on the behavior of stone columns is studied. The primary objective of the tests was to compare the effectiveness of vertical encapsulating of stone columns in the same conditions for various encasing patterns with that of the gravel mattress. A 2D-numerical approach also provides the opportunity to investigate the reasons for changes in bearing capacity of stone columns encased by routine and ringy patterns and the various replacement areas. Results present a better understanding of the load-settlement behavior of stone columns with various encasement types. Encasement is more effective in improving the column bearing capacity of larger diameter columns than smaller ones.

An engineering method of calculating the thawing depth of permafrost in a multilayer base is proposed. The method includes an exact analytical solution of the problem of nonstationary heat conduction in a multilayer medium, including efficient thermal insulation with phase transitions (Stefan's problem) with a stepped calculation for each layer. Comparing the computational results shows that the method can be used for preliminary engineering calculations of the thawing depth of the bases of airfield pavement laid together with a layer of efficient thermal insulation.