Stress-strain state of the building foundations with taking into account the possible water saturation of loess soils

In Ukraine, the problem of construction on loess soils is relevant due to the widespread use of these soils and their negative property - the ability to give additional deformations of subsidence during water saturation. Flooding of territories by groundwater, emergency leaks from aquifers cause significant problems during the exploitation of buildings and engineering structures on such soils. Computer simulation of the interaction of the building with the soil base allows to investigate the influence of all negative factors on the change of the stress-strain state of both the soil base and the load-bearing structures of the building. The study of the interaction of the building with the foundation was performed using the software package LIRA-CAD. The interaction of the building with the soil base, the soils of which are able to reduce their mechanical properties with increasing humidity and give additional subsidence deformations, was studied. A variant design of the foundations was performed taking into account the occurrence of uneven deformations during subsidence of the loess soil due to its moistening in case of possible emergency losses from aquifers. The change of stress-strain state of the foundations of the building depending on the spatial rigidity of the foundation, the location of the soaking zone within the building spot, the shape and size of the zone of soil moisture is analyzed. It is shown that taking into account the possible water saturation of loess soils when calculating the collaborate of the building with the soil base, allows to obtain stress-strain state of foundations and load-bearing structures of the aboveground part of the building for the most unfavorable conditions that may occur. The search for the optimal variant of the foundation structures of the building, which, while remaining cost-effective, provides reliable operation of the building in conditions of possible occurrence of uneven deformations of subsidence of the soil base during water saturation of the layer of loess soils. According to the research results, a rational variant of the foundation structures has been designed taking into account the possible occurrence of non-uniform deformations.

Influence of the sequence of erection of build-ings on the formation of the stress-strain state of the system «base-foundation-overhead structures»

The influence of the order of construction of houses on the formation of the stress-strain state of the system "foundation-foundation-above-ground structures" is investigated For this purpose, several options for setting tasks for the phased construction of multi-section building sections are considered. With this in mind, it should be noted that the construction of each subsequent section has an impact on the built entirely or partially adjacent section. That is why this effect should be investigated to predict how serious this impact may be, and to draw appropriate constructive decisions. Thus, the main objectives of the study are: Creation of SEM without taking into account the stages of construction of the house; Calculation of a house with a phased loading of 5 floors. Taking into account changes in the order of construction of sections; Formation of SEM taking into account the sequence of erection of sections without including the sequence of erection of floors within the boundaries of the current section; Research of the impact of the calculation of sections of a multi-section building without and taking into account the summary of subsequent sections. The research of the impact of the sequence of construction and installation of the object will allow us to assess the stress-strain scheme at all stages of construction, so changes in the behavior of the scheme will be recorded at all stages of construction specified by the designers. To do this, the change in the stress-strain state (VAT) of the system "foundation - foundations - above-ground structures" must be modeled with different options for stages of construction, taking into account the real parameters of the soil base and so on. The interaction of piles in different zones of sections, the work of grids in the foundations of high-rise buildings are considered. The research was carried out with the help of numerical modeling of the system "foundation - foundations - aboveground constructions". The redistribution of forces in the piles depending on the formulation of problems on the stages of construction of sections and design parameters (location of piles in characteristic zones, the influence of the stiffness of the aboveground part on the redistribution of forces). Characteristic zones in the foundation are distinguished: they are central, lateral, angular and especially at the joints of adjacent sections. The redistribution of efforts between piles and a grid is revealed.

Influence of the choice of the base model on the stress-strain state of the vertical load-bearing elements of a monolithic-frame house

Comparison of the stress-strain state of vertical elements of the frame of a monolithic house (basement, first and fourth floors), depending on the method of modeling the soil environment and piles, is carried out. The use of pile foundations is due to the fact that they provide the transfer of loads to deeper soil layers and, as a rule, a greater bearing capacity compared to shallow foundations. In the design of foundations, engineers face the question of how to model the soil environment and piles? This paper presents the influence of the decision taken (the selected soil model and the method of modeling piles) on the stress-strain state of the vertical load-bearing elements of the house frame. Comparison of the stress-strain state of vertical elements of the frame (basement, first and fourth floors), which were obtained using the following models of the system «base - pile foundation - overhead supporting structures»: 1) the piles are modeled by single-node finite elements, have only vertical stiffness according to the results of testing the piles for vertical static pressing loads, the mutual influence of piles and soil characteristics are not taken into account (FE-56 hereinafter, this is the number of the finite element in the library of elements of the PС «Lira -SAPR») 2) the piles are modeled by single-node finite elements, are located with a given step along the length of the pile and have rigidity in different directions and approximately take into account the surrounding soil around the pile and under its tip (FE-57); 3) the soil environment is modeled by volumetric elastic finite elements; piles - rod finite elements. It is shown that the choice of the foundation model carries stress-strain state not only for the foundation structures, but also for the vertical bearing elements of the house. When using various options for modeling the base: using a single-node finite element that simulates a smoke like elastic ligature (FE-56), using a chain of single-node skinned elements (FE-57), or a volumetric soil massif, it is possible to obtain quantitative differences in stresses from 2 to 20%, and a qualitative change, which is observed in a change in the sign of bending moments.

Physical modeling of steel tubular piles installation into sandy soil

Modern marine structures (berths, breakwaters, offshore platforms, etc.) often include steel tubular piles of essential length (80-100 m and more) that should provide high bearing capacity in case of external axial loads application. Interaction between elements of the system “piled structure – soil media” is not yet studied sufficiently. It relates also to the bearing capacity of the long steel tubular piles of large diameter. One of the interesting peculiarities of long tubular piles’ behavior is the formation of soil plug at the piles’ tip. There are a lot of suggestion and methods aimed to increase piles bearing capacity under static pressing load. One of them relates to use of the additional structural element, i.e., the internal diaphragm welded to the internal surface of the pile’s shaft. Such approach has been applied in some practical cases of marine construction and demonstrated its effectiveness. At the moment there are no researches focused on study of the peculiarities of internal diaphragm application. So proposed research aimed to study two connected processes during steel tubular pile driving: soil plug formation at the tip of the open-end pile and soil behavior under the internal diaphragm fixed inside the tubular pile’s shaft. To study mentioned processes we provided several series of laboratory experiments fulfilled at the Geotechnical laboratory of the Department “Sea, River Ports and Waterways” in Odessa National Maritime University. In these experiments the model of steel tubular pile has been driven (pressed) into fine sand by mechanical jack. The first series was devoted to determination of the conditions related to the soil plug formation at the pile’s tip (results are presented in this paper). The next series were aimed to study the influence of the rigid diaphragm inside the pile’s shaft (to be presented in the further publications). Obtained experimental results allow to conclude that (a) in the fine sand the plug is formatted at the comparatively early stage of pile installation (in case of our modeling - at the penetration depth of some 4-5 pile’s diameter); (b) our empirical assessment of the conditions of soil plug formation corresponds to the approaches based on PLR and IFR characteristics; (c) formation of soil plug at the pile’s tip is followed by decreasing of soil level in the pile’s shaft relatively its initial value (on completing the plug formation the soil level in the shaft become stable); (d) regarding above mentioned, we may note that in case of use of internal diaphragm on the recommended depth (5-7 pile’s diameters) there may be no contact between diaphragm and the soil inside the pile and the diaphragm does not come up with the soil. So, for the next series of our experiments, it should be foreseen assured contact of the diaphragm’s surface with soil underneath. As proved by previous studies, one of the interesting features of the behavior of long tubular piles is the formation of a soil plug at the lower end of the pile. From this point of view, it is important to study the effect of soil plug not only on the bearing capacity at the lower end of the pile, but also on the behavior of the soil inside the pile. It is shown that in fine-sandy soils a plug is formed at a relatively early stage of pile immersion (in this case - at a depth of immersion of about 4-5 pile diameters). The process of forming a soil plug at the lower end of the tubular pile during its immersion is accompanied by a decrease in soil surface level in the pile trunk relative to its initial value (upon completion of plug formation the soil surface level in the pile trunk stabilizes).

Numerical analysis of methods for calculating the soil base and methods for determining bed coefficients

Despite significant progress in the development of methods for calculating the soil base in a single calculation model with structures and the ability to perform calculations in three dimensions, the most popular in the community of design engineers remains the calculation model of the slab on an elastic basis. This is due to the simplicity of such a model. Probably, the greatest difficulty in applying such a model is to determine the coefficients of flexibility of the base (bed coefficients). In this paper, a study of the reliability of different methods for determining the coefficients of the bed under different variants of soil conditions The paper determines and compares the characteristics of the stress-strain state (sedimentation values, reactive pressure and forces) in three foundation slabs of different geometry and under different engineering and geological conditions of the construction site. A homogeneous base composed of loess soils, an inhomogeneous base composed of alternating layers of both cohesive (loam and sand) and incoherent (fine sand) soils and a close to homogeneous base composed of sand and soils are considered. The research was conducted using the software and computer system LIRA SAPR 2016. Implemented three methods for determining the coefficients of the bed (the flexibility of the base): - Pasternak model with two bed coefficients, which for inhomogeneous soils are determined by the values of the deformation modulus and Poisson's ratio averaged within the depth of the compressible thickness; - Winkler model with one bed ratio; - Pasternak model with two bed coefficients, which are determined by the average values of the deformation modulus and Poisson's ratio when introducing the correction factor to the deformation modulus. The convergence of the absolute values of the controlled parameters obtained using the above methods, depending on the type of soil base and the nature of soil layers within the compressible layer, is analyzed. The dependence of the convergence of the characteristics of the stress-strain state of the slab obtained by different methods on the homogeneity of the base soils is established.

Improving the test methodology of design piles on a construction site

Reliable solutions for the design of tall buildings with pile foundations depend on the correctness of the load-bearing capacity. In some cases, you need to know that it is impossible to determine the ability on the side surface and under the sole. To do this, it is proposed to develop a special technique that combines tests to remove and pull out and educate the nature of the downloads (static or kinematic).Тhe publication proposes a method of testing piles in the field, which simulates the processes that accompany the interaction of the pile with the soil base in real situations of operation of the technical object: for example, emergency soaking of soils when there is no time for stabilization deformations under load from a building or structure. It is shown that the value of friction on the side surface of the piles significantly depends on the nature of the loads. The analyzed results of the test schedule allow to separate these two components in the case when unloading is carried out continuously and the beginning of the pile movement in the opposite direction gives the value of soil resistance on the side floor. This simulates the real behavior of the pile at the base of the building, because in real objects there is no time for stabilization.It is offered to carry out tests of piles before loading which causes continuous indentation of piles, and division into components - bearing capacity on lateral surface Fdf and bearing capacity under the sole of the pile FdR will allow to accumulate the calculated soil supports in the respective zones, which makes it possible to create tables «R» and «f» for soil conditions of Ukraine.Taking into account the peculiarities of the construction of the pile test schedule and the proposed approaches will allow to correctly determine the components used in determining the bearing capacity of the pile. The accumulation of test results in the future will clarify the calculated soil supports of Ukraine. Reliable values of the calculated resistances will reduce the amount of static tests, which are time consuming and expensive.

On the requirements for articles published in the scientific and technical journal «Bases and foundations»

Before starting work on the article, you should get acquainted with the requirements for the publication of articles in the Scientific and Technical Journal «Bases and foundations», founded by the Kyiv National University of Construction and Architecture. The journal includes the articles on topical challenges of geotechnics. There are the results of interaction between elements of the system «base – foundation – superstructures», influence of seismic or other dynamic loads; designing foundations on weak soils, exploration of the deep foundations, retaining structures, assessment of the slope stability of landslide areas, determination of soil parameters by in-situ and laboratory tests. The journal is designed for scientific, engineering and technical specialists of scientific, research, design and construction organizations. The journal publishes in the following specialties: 192 «Construction and civil engineering», 194 «Hydraulic engineering, water engineering and water technologies». The article submitted to the editorial board must clearly meet the goals and specializations of the journal, must be written and designed in accordance with the requirements set out in this article. Original research and discussion materials are accepted for publication. Articles are subject to double review, including by independent experts. It is recommended to submit a scientific article only in one journal, which meets the requirements of International Ethical Standards, which prohibit the simultaneous publication of the article in different publications. Articles must be pre-reviewed before publication in the journal. After confirmation of the article's compliance with the general requirements and the availability of a complete package of documents, the article is submitted for review and undergoes internal editorial processing. The editors reserve the right to make minor edits and reductions, while maintaining the main results and author's style. The article is returned to the author for revision or correction if the members of the editorial board (scientific editors in the relevant areas) have questions to the author regarding certain provisions of the article. The Editorial Board is not responsible for the content and authorship of the material of the article used, but reserves the right not to allow the article to be published in case of non-compliance with the above requirements.

Formation of stress-strain state in the founda-tions of grain drying complexes when chang-ing soil parameters

The work of the pile foundation of the grain drying complex when changing the parameters of soils determined by laboratory and field methods has been studied. Two variants of calculations with the help of numerical modeling by the finite element method were carried out: 1) using the characteristics of soils, which were determined by laboratory methods; 2) using the characteristics of soils, which are determined by field methods. The stress-strain state of the foundation structures of the grain drying complex is analyzed in the work, namely: redistribution of forces in the piles, subsidence of the foundation structures, bending moments and the area of working reinforcement in the foundation slab. The paper emphasizes the use of pile foundations for grain drying complexes due to the emergence of many negative factors in the installation of slab foundations. The main ones are: low soil indicators in the upper zone of the soil massif; construction of several silos next to each other, which determines their interaction; uneven loading - unloading of silos; the choice of calculation method, which correctly describes the parameters of the soil and the stages of loading and unloading of silos. The paper also presents problematic issues in the design of pile foundations for grain dryers. The results of the study of the formation of the stress-strain state of the foundation structures at different soil parameters are presented. The study was conducted in clay soils of solid and semi-solid consistency. The pile foundation is based on hard sandy loams and soft-plastic loams. The paper shows that with increasing soil parameters of the base decreases the subsidence of the foundation slab. The redistribution of forces between the piles has a similar character, but due to the increased rigidity of the base, the foundation plate transfers the load to the base, so almost all piles are unloaded within 5… 10%. At the same time bending moments in the base plate are reduced that demands reduction of reinforcement by working armature. This allows you to design reliable and economical solutions for pile foundations of grain dryers.

Numerical simulation of the stress strain state of base of the multi-helix screw pile under static loading in clay soil

A full-scale experiment was conducted to study the operation of a multi-helix screw pile under static pressing and pulling load in dusty clay soil. Based on the full-scale test of a multi-helix screw pile under static loading in dusty clay soil, numerical modeling of the stress-strain state of the base of the multi-helix screw pile was performed. Multi-helix screw piles are actively used all over the world, and have also become widespread in Ukraine. Foundations made of multi-helix screw piles are often used for industrial construction as well as the foundations of low-rise buildings and structures. Despite the growing demand for the use of multi-helix screw piles in modern construction, there is no official document calculating the features of their design and bearing capacity of a multi-helix screw pile. This poses a number of new tasks for engineers and geotechnical: a) development of new modern calculation methods; b) development and use of modern normative documents and recommendations for the calculation of foundations from multi-helix screw piles in various soil conditions; с) use of computer-aided design systems for calculation of complex geotechnical tasks; d) development of calculation models that will take into account nonlinear models of deformation of materials and soil base. Foundations made of multi-helix screw piles are a promising direction in the field of foundation construction due to the reduction of the duration of the foundation and its economic. This requires the development of regulations with recommendations for the calculation and use of multi-helix screw piles in the field of foundation construction, development of modern calculation models for the calculation of bearing capacity and settling of multi-helix screw piles in different geological conditions. Based on the results of the field study of the work of multi-helix screw piles in clay soils, numerical modeling of the stress-strain state of the base of the multi-turn pile was performed, and their results were compared.

Influence of house bearing construction rigidi-ty of precast reinforced concrete on stress-strain state Continuous Flight Auger (CFA) piles foundations

At present, the tendency to build multi-storey residential buildings has become widespread in Ukraine. This is due to a number of reasons: significant increase in land prices in cities, dense urban development and the availability of appropriate equipment for the construction of such structures. One of the most common materials for multi-storey buildings is monolithic reinforced concrete. The main advantage of monolithic structures is the possibility of free spatial planning and the possibility of uniform redistribution of forces in the elements of the frame - the house works as one rigid entire structure. On the other hand, such structures require a long construction time and appropriate highly qualified control of monolithic works. Therefore, as an alternative, prefabricated reinforced concrete structures are used to accelerate the pace of construction. In this work, the influence of the rigidity of a precast reinforced concrete house on the stress-strain state of CFA piles foundation is investigated. The stress-strain state of a precast reinforced concrete building with two basement options is analyzed: precast and monolithic. The numerical modeling of the interaction of the system elements is used as a research method: soil base - foundation - aboveground structure. It was found that the replacement in a prefabricated house only one basement floor of precast concrete on a monolithic one affects the redistribution of forces, so the self-supporting wall is loaded 2.6 times, and the busiest wall, which rests on both sides of the floor slab, is unloaded to 2.1 times. It was found that in the case of a basement made of precast reinforced concrete with a precast basement the difference efforts in pile heads (under the load-bearing walls) can differ 1.98 times, and in the case of a monolithic one 1.17 times. So it is mean, the monolithic foundation redistributed of efforts between the piles is more uniform. It is established that the monolithic reinforced concrete basement, in comparison with the prefabricated one, reduces the uneven settlement of the foundation by 2.4 times. When designing large-panel houses, it is advisable to provide a basement floor monolithic - this will allow to load the fundamental constructions more evenly, which in its reduction reduces the relative deformation of buildings and reduces their cost.