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Most of the existing methods of pile settlement calculation, including normative methods, do not fully take into account the processes occurring in the soil when loads are transferred to them and the changes in the properties of the contact zone soils. This leads to underutilisation of the bearing capacity of the soil, and the calculated settlement value may differ several times from the real values. In this paper, a graph-analytical solution to the problem of interaction of a single pile with a three-layer soil foundation is proposed to determine the settlement, taking into account the complex nature of the pile operation and the processes occurring in the soil when loads are transferred to them. The proposed method allows to use the non-linear behaviour of the soil on the lateral surface and under the tip of the pile, the possibility of its detachment and slippage after reaching the ultimate strength of the soil, changes in the properties of the contact zone soils, and the load distribution on the pile between its lateral surface and the tip. To verify the proposed graph-analytical solution, a comparative analysis was performed with the numerical method in the Plaxis 2d software (version 21.00.01.7) and with the results of static tests of piles at the construction site. To determine the strength reduction factor at the contact of soils with concrete, laboratory tests were carried out on a direct shear apparatus. Based on the results of the performed calculations, graphs of the dependence of settlements on loads were plotted, conclusions were drawn about the possibility of using the graph-analytical method, and prospects for further development and improvement of the graph-analytical method were proposed. [ABSTRACT FROM AUTHOR]

The construction of high-rise building and structures has been widely developed recently in Vietnam. Pile foundations are considered one of the most suitable solutions when choosing the foundations for their construction, especially in difficult geological conditions, including seismic areas. According to many researches, geological conditions of Ho Chi Minh City are generally difficult. The occurrence of earthquakes there influences the conditions for the construction. Besides, many historical cases have shown that soil liquefaction is often manifested, negatively affecting the underground structures and foundation working. With an increase in investments of international construction companies and organizations in Vietnam, pile foundations can be designed according to domestic or foreign normative documents. Therefore, at present, a better understanding and detailed analysis of various existing normative documents and methods for designing pile foundations are required, especially when the influence of soil liquefaction is taken into account. This paper presents a review of various normative documents, including Russian, Vietnamese, American and Eurocode. The different methods in these normative documents for calculating the piles' bearing capacity are considered in 2 cases: with and without taking into account the soil liquefaction based on the hypothesis that the additional downward loads due to self-compaction of liquefiable soils affect piles. Finally, a comparison of the calculation results is presented. The comparison shows how these considering methods in these normative documents differ from each other and how much the pile's bearing capacity can be reduced when considering the soil liquefaction in calculations.

Vibratory piling technology does not require analytical tools to predict displacement rates and arising forces. The authors consider the problem of vibratory driving of a pile into a homogeneous unsaturated sandy massif under the action of static and dynamic loads. The purpose of this study is to develop a new analytical solution to the problem of the vibratory pile driving rate in a homogeneous sand base taking vibration creep into account. The solution is provided for the quasi-dynamic problem statement (inertial terms in equations of motion are neglected): the sand medium develops viscous properties due to vibration under the action of the dynamic component of the load, and a pile is driven into the viscous sand base due to the static component of the vertical load. The obtained mathematical model converges with the results of laboratory flume and field experiments performed by other researchers earlier, where the pile vibratory embedding rate increased along with an increase in static loading, the amplitude of dynamic load, and vibration frequency. It can be used to predict the pile or sheet pile driving rate into the unsaturated sand base under the action of vibration, and also to evaluate the necessary parameters of pile driving to obtain the required value of the pile embedding rate. [ABSTRACT FROM AUTHOR]

The article discusses the interaction of concrete structures with the soil, made on the basis of laboratory tests and numerical simulation. The objectives of the study were to obtain the strength characteristics at the contact of two different materials, to compare the obtained value of the strength reduction factor with the standard values, and also to determine the extent to which the interface must be taken into account when conducting numerical geotechnical calculations. The study was carried out using a direct shear test device, where the strength reduction factor was obtained, which characterizes the conditions of interaction between different materials at their contact. According to the results of numerical simulation, one can see how the consideration of the given characteristics of the material of the contact element affects the internal forces arising in the underground structure and its displacements. The test results showed that the particle diameter has a different effect on shear strength at the same level of normal stress. On the basis of the results obtained, conclusions were drawn on what needs to be paid more attention to when conducting laboratory tests, how strongly the consideration of contact elements with the correct set of properties affects the internal forces of the underground structure. Also, the remaining problems and factors not considered in this study determined the prospects for further research on the topic under consideration.

Contrary to the considerable experience of designing, construction and operation of hydraulic construction of the bulwark type, there are still emergencies that exceed the normative values of deformations, displacements, rotation angles, loss of stability both during the staged construction and at the completion of construction. The question of taking into account the interaction of various complicating factors in the system “retaining structure-soft saturated soil base” is currently fundamental when choosing the type of element of structures, technology and the time of their construction. As a task, the interaction of a thin-walled bulwark on a soft saturated soilbase with the ice and seismic impacts was considered. Numerical research performed using PLAXIS 2D. Prediction of the interaction of the berth construction with the soil base, taking into account the variety of loads and impacts, made it possible to identify exceedances of normative values of forces, bending moments, displacements, which requires further consideration of the issues of ensuring the safety operation phase of the berthing construction. The errors of designers to unfinished consolidation of soils, the non-linear behavior under various impacts will lead to emergency situations, especially in hydraulic engineering. The results of the article show the need to take into account the rate of loading of the base for correct accounting of the bearing capacity of soft soils.

At present, numerical methods of calculations, which are implemented in a large number of software complexes, are widely used in geotechnical practice and the definition of input parameters of the ground is very important and necessary to reflect the real work of the foundation of geotechnical structures [1-4]. There are often cases when the results obtained during laboratory tests of soils are not accepted by software complexes, errors are given, recommendations are proposed for changing the parameters in the direction of increasing or decreasing. In connection with these problems, the question arose about the need to optimize soil parameters obtained as a result of laboratory tests to compare and correct these parameters, based on the degree of approximation of model tests with laboratory tests [5]. Optimization of soil parameters can be carried out in the subroutine Soil test, incorporated in the PLAXIS geotechnical software [6]. Using the Soil test, the triaxial and compression tests are simulated based on the input parameters of the soil and the initial test data. The purpose of this study was to describe the methodology for optimizing the parameters of the Hardening Soil model and the Soft Soil Creep model using the PLAXIS 3D software geotechnical complex, as well as a comparative analysis of the results of laboratory soil tests with modeling results in software complex.

In process of designing foundations of circular form in plane, as well as bored piles of circular cross section, there is important to quantify the stress-strain state and the bearing capacity of the soils interacted with the foundations, as well as under the toe of piles. The article presents the formulation and solution of the problem of determining the initial critical load at the base of the circular foundation, which is also relevant for the design case of the soil under the toe of a circular bored pile. It is shown that the condition of limiting equilibrium arises both under the center of the loaded area and on the contour of the circular loading area, and primarily on the contour. A comparative estimate showed that the ratio of the initial critical load to the base soil of the circular foundation under the center of the site is 2 times greater than the corresponding load for the point at the edge of the site.

The article is devoted to the stability determining of the slopes, near which are being carried out works on the construction of the foundation of an automobile overpass. The methods of determining the landslide pressure on the retaining structures, accounting for the technological vibration load on the base, which occurs when the sheet pile is submerged into soil base during the excavation are considered. The analysis of the options for usage the strength undrained characteristics of the soil base under vibration influence on them is made. The risk of construction works near the slope is estimated with the forecasting of the safety coefficients and limiting slip surfaces obtained by the finite element method implemented in the PLAXIS geotechnical software. Many factors of influence on the safety of the slope were taken into account: the staging of construction, the change in the hydrogeological situation, the application of technological and vibrational loads. Based on the results obtained, possible types of work to increase the stability of the slope are presented, and conclusions are drawn on the need for additional studies in the field of undrained properties in case of vibrational loads.

One of the actual problems of modern construction is the development of methods for managing the stress state of the soil bases for its use in conditions favorable to the construction. Also, soil state management methods are used to protect existing buildings and structures from the negative impacts of new construction. One of the methods that can affect the stress-strain state is the technology of compensatory injection. The essence of the method consists in injecting an extra volume of a slowly hardening solute into the soil base placed in the path of propagation of an impact wave transmitted through the soil. Controlling the volume of the pumped material, a calculated stress-strain state of the soil massif is created, which ensures safe construction. The article contains theoretical foundations describing the processes and examples of numerical simulation of control processes of the stress-strain state of the base when tunneling under the building.

In the design of foundations for buildings and structures of various purposes, including improved risk, weak water-saturated clay soils with low mechanical characteristics are often found on a construction site. One of the possible ways of using them as a foundation is to seal them in various ways, including using pile drains of sand or rock stone material that are capable of both absorbing the load at the base and accelerating the process of filtration consolidation. This paper describes an analytical solution to the problem of interaction between the pile and the mattress with the surrounding soil of the foundation, taking into account the possibility of expanding the pile shaft. Solutions are obtained for determining the stresses in the shaft of the pile drain and in the soil under the mattress. The solution takes into account the influence of the pre-stressed state of the foundation after compaction on the formation of a stress-strain state during the erection and operation of structures. The solutions are relevant for consolidating pile drains made of rubble or for jet grouting piles, the rigidity of which is comparable to the rigidity of the surrounding soil. The paper describes the technique for determining the characteristics of the strength and deformability of the converted foundation and the results of large-scale tests at the experimental site for the construction of a large energy facility in Russia.

The article provides an analytical solution of the soil pile and surrounding soil cylinder interaction problem, with the possibility of extension of the pile shaft in its construction. Presents a closed solution for determination of radial and tangential stresses in the process of expansion of the pile shaft, as well as the minimum vertical force sufficient for the crushing of the pile material and move it in radial direction to the specified value. The problem is most actual for compacted soil bases with use of piles-drains of sand and sand-gravel mixture.