Vol 55, No 3 (2018)

The development of the stress-strain state of the soil mass, represented by argillite-like clays and sandstones, at the base of bored end-bearing piles is examined. A method is developed for conducting experimental studies. Stamp tests showing the load-settlement relation were performed and three phases of development of the stress-strain state were identified. Recommendations are formulated for designing bases comprised of argillite-like clays and sandstones.

In this paper, the momentum equilibrium equation, the continuity equation, and the energy equation for the coupled heat and moisture transfer-deformation model are improved for frozen soil conditions through the introduction of the Clapeyron equation to describe moisture migration in a freezing zone under a temperature gradient. The AFEM program for the coupled model under plane strain conditions is established for engineering problems in cold regions. The results of calculations for Penner’s lab heaving test conditions are analyzed to validate the proposed model's rationality and reliability. The predicted frost heave deformations, temperature, and moisture distribution are consistent with experimental data, and it is demonstrated that the presented approach is valid for studying coupled heat-mass-transfer and deformation behavior of freezing soils with phase transitions.

Difficulties in obtaining high-quality undisturbed soil samples have necessitated the increased use of cone penetration test (CPT) or piezocone penetration test (CPTU) to determine soil properties at geotechnical engineering sites. Undrained shear strength (a key parameter for most clay investigations) traditionally is evaluated by cone tip resistance or effective cone tip resistance. In this paper a method of using the clay's excess pore pressure was used to estimate the undrained shear strength. A correlation of pore pressure ratio and cone factor was discovered and compared with results from the published literature and with those from field vane tests.

The compressibility parameters such as the compression index and the recompression index are necessary in the settlement calculation for fine-grained soils that is essential to geotechnical designs. However, determination of the compressibility parameters from odometer tests takes a relatively long time and leads to a very demanding experimental working program in the laboratory. Geotechnical engineering literature involves many studies based on multiple regression analysis (MLR). This study was aimed at predicting the compressibility parameters by soft computing methods such as artificial neural networks (ANN) and the quasi-Newton algorithm developed with the differential evolution method (QN-DE). The selected variables for each method are the index parameters of natural finegrained soils such as natural water content and initial void ratio. The results obtained from MLR, ANN, and QN-DE models were compared with each other at the end of the study.

The solutions of the equations of planar vibrations of massive bodies upon arbitrary timevarying horizontal displacement of the base are constructed using transfer functions (TF) and impulse response functions (ITF) of linear dynamic systems. This approach makes it possible to obtain the closed-form solutions with harmonic and free vibrations and to construct stable algorithms for calculating systems arbitrary displacement of the base. The solutions are written in the form of an expansion in 'normal forms' directly in generalized coordinates. An example of a calculation is presented for the response and operating regimes of the vibrations due to an instantaneously applied harmonic perturbation.

A study of the shear strength of expansive soil treated with ionic soil stabilizer during freeze-thaw cycles is presented. The shear strength of treated expansive soil is greater than that of untreated expansive soil at room temperature, and it is evident that the moisture content plays a leading role in this result. After a freeze-thaw cycle the shear strength changes little for untreated soil, but decreases gradually after ionic soil stabilizer treatment. Shear strength reaches the lowest values after seven freeze-thaw cycles. Finally, the influence of freeze-thaw cycles on the porosity of expansive soil is analyzed using scanning electron microscopy, which shows that the porosity of both treated and untreated soil increases with the number of freeze-thaw cycles, although porosity of the treated sample changes little.

We analyze the characteristic errors of the finite-element modeling of soil massifs by an example of the problem of vibrations of a layer on the rocky base for various types of fastening of the lateral boundary: rigid fixture, free boundary, acoustic boundary, and acoustic boundary with a column of the base. The first error is connected with the assumption that, for large distances of the boundary from the structure, the boundary conditions do not affect its behavior. The second error is caused by the use of a constant in height) elasticity modulus for a homogeneous layer of soil. The size of the domain used for modeling guaranteed the boundedness of the zone of dislocation displacements near the boundary and constant displacements in the central part of the layer. However, these displacements differed from each other and from the exact solution given by the elasticity theory. This is explained by the specific features of taking into account the effect of damping within the framework of the applied software.