Bases and Foundations

Peculiarities of using the hypothesis of S.O. Kulon for soil dispersed sediments

Igor Boyko — 2023-12-29

The publication is devoted to the outstanding French scientist Charles Auguste Coulomb, who 250 years ago (1773) proposed a hypothesis that relates tangential and normal stresses through the angle of internal friction of soils. This hypothesis provides reliable results while maintaining Hooke's law. Beyond this law, it is necessary to take into account the property of the soil medium, namely the change in volume during shearing or displacement of soils, which requires the introduction of additional dilatancy parameters.

It is known that there are two types of friction in nature: sliding and rolling friction. At certain values of deformation in the soil medium, sliding friction, which is characterised by the traditional value of the internal friction angle, initially appears in certain zones of the soil medium at low deformations. Further increase in deformation causes rolling friction, which is characterised by a different value of the internal friction angle, almost one third less than the traditional value of the internal friction angle of the soil. This fact must be taken into account when performing numerical modelling of a dispersed soil medium from the beginning of loading to its failure. In this publication, we discuss the methodology for finding the parameters of the dilatancy theory to reveal the elastic-plastic deformation of cohesionless soils based on experimental results. Recommendations are given on the use of the Coulomb hypothesis in engineering calculations and on the relationship between tangential and normal stresses through the angle of internal friction of soils. For a correct description of the nonlinear process of soil deformation, it is necessary to use the parameters of the dilatancy theory, which can be investigated on an axisymmetric shear tester.

The results of tests of sand of medium size, medium density, low-moisture, homogeneous on several devices showed that the values of the angle of internal friction of soils differ depending on the design of the device. This fact is recommended to be taken into account when designing geotechnical facilities.

Investigation of the stress-strain state of foundation structures in determining the vertical stiffness of piles using different software systems

Vasyl Pidlutskyi — 2023-12-29

The results of numerical modeling of the interaction between a multi-storey building on a pile foundation and the soil base in the "Lira-SAPR" software are presented. A comparison of the stress-strain state of foundation structures was performed using different methods for determining vertical stiffness (Rz) in single-node FE 57 (this element is designed to model the behavior of a pile together with the surrounding soil, similar to FE 56, and can implement the interaction with the "SOIL" system). Piles were modeled by a chain of single-node FE 57 connected by vertical bars.

In the first variant, the calculation of the building was performed in the "Lira-SAPR" software. To determine the vertical stiffness in FE 57, a soil model with physical-mechanical characteristics was created, and layering was defined according to the engineering-geological cross-section in the "SOIL" system. The calculation of vertical stiffness took into account mutual influence and the model of the conditional foundation.

In the second variant, the determination of vertical stiffness (Rz) in FE 57 was carried out using the "Plaxis 3D" software. The overall model of above-ground structures, foundations, and all necessary loads were created in the "Lira-SAPR" software. Subsequently, an export to "Plaxis 3D" was performed, where the soil was previously modeled as a three-dimensional soil mass (with characteristics and strengths of layers similar to those created in the "SOIL" system) using the "Hardening soil" behavior model. After the import into "Plaxis 3D," the analysis of the "Soil-Foundation-Structure" system was conducted, and the obtained values of vertical stiffness (Rz) in FE 57 were exported back to "Lira-SAPR". After the export of "refined" values of vertical stiffness to "Lira-SAPR", a general static analysis and comparison of the stress-strain state of foundation structures with the first calculation variant was performed.

It was established that the vertical stiffness in
FE 57 in the first variant is higher than in the second, accordingly, the total displacements for the first variant are smaller. The importance of using the connection between "Lira-SAPR" and "Plaxis 3D" or other specialized geotechnical software complexes was demonstrated to obtain more accurate results of the interaction of the "Soil-Foundation-Structure" system due to the possibility of using nonlinear soil models to better describe the behavior of the foundation.

Structures of bored piles: features of installation technology

Oleksandr Havryliuk — 2023-12-29

Currently, pile foundations are often used in engineering practice. Among the modern types of piles used for foundation structures, the option of foundations made of bored piles is definitely popular. They are used for various types of structures: bridges as part of highways, urban ring roads or high-rise buildings. The main problem in these cases is related to a reliable assessment of the bearing capacity of the pile and the development of a cost-effective design solution for foundation structures.

The studies carried out in this direction confirm that the issue of determining the load-bearing capacity of piles remains relevant both at the stage of developing reliable design solutions and in the process of searching for an economically efficient option of the foundation constructions of buildings and structures.

Taking into account the design features of bored piles and their installation technology add certain difficulties to the analytical methods of determining the soil bearing capacity of a single pile.

The practice of using bored piles on construction sites followed by observation of deformations showed that the soil bearing capacity of the piles, determined by the analytical method of standards used at the stage of developing design solutions for foundations, is underestimated. Therefore, the total number of piles in the foundation needs to be optimized according to the results of further field tests. Geometric parameters of piles, such as length and diameter, in some cases can also be reduced at the stage of rationalization of the design solution of the pile foundation, based on the results of field tests. So, as a result, the underestimated value of the load-bearing capacity of bored piles causes an increase in the cost of construction materials, an increase in the cost of installing foundation structures and an increase in the cost of housing for the end consumer.

The problem of reliable assessment of the soil bearing capacity of piles remains a relevant issue at the moment, as evidenced by the practice of designing foundation structures.

The paper presents the results of the analysis of the structural features of bored piles, which are aimed at increasing their bearing capacity. Also, the paper examines the features of the technology of installing bored piles, which are determined by both the hydro-geological conditions of the construction site and the need to install the constructive features of the bored pile.

Comparison of the bearing capacities of a small-diameter bored pile obtained from the results of field tests and numerical modeling

Pavlo Soroka — 2023-12-29

Abstract. The paper compares the results of modeling static soil tests with a small-diameter drill pile with the data obtained from field tests. The calculations were performed by numerical modeling using the PC software "Plaxis", which is based on the finite element method. This problem was solved in a flat (2D) formulation for an axisymmetric model, which makes it possible to analyze the stress-strain state (SSS) and the interaction of elements of the pile-soil environment system.

Separate computational models were created for two types of piles made using different technologies: a bored- CFA pile and a drilled pile with partial soil displacement. In order to take into account the preload history in order to maximize the models' approximation to real conditions, the calculations were performed in 4 stages in accordance with the construction sequence: Stage 1 - initial stage (determination of the initial stresses in the soil massif in the natural state), Stage 2 - excavation to the design mark of the pit bottom, Stage 3 - testing of the soils with a pile by static load. Stage 4 - pile unloading. Based on the results of the calculations, the SSS and the interaction of the elements of the "pile-soil environment" system have been analyzed and compared the settlement graphs obtained from the results of the calculations with the data of field tests.

It is shown that the use of a plane axisymmetric FEM is a sufficiently effective approach for assessing the stress-strain state and understanding the interaction of elements of the pile-soil system, as well as predicting the bearing capacity of piles for further design of the pile foundation before obtaining the results of field tests. In addition, the labor intensity and time consumption of this approach are relatively low compared to other alternative methods.

With appropriate experience in using this approach in different soil conditions with appropriate comparison with field test data, it can be applied in the feasibility study and final decisions on the choice of a particular type of foundation.

Assessment of the impact of a high-rise building on the stress-strain state of the foundation and structures of existing buildings in dense development

Viktor Nosenko — 2023-12-29

One of the most progressive problems of modern urban planning is the gradual decrease in areas suitable for construction, especially within the historical districts of cities. This prompts developers to increasingly develop sites in difficult engineering and geological conditions, which are often located within dense buildings.

Today, the construction of multifunctional residential complexes combines the construction of high-rise residential sections and commercial real estate buildings with multi-level parking lots, which are often located in close proximity to each other. Often, the sequence of construction of these buildings is stretched over years or even decades, for example, due to an unfavorable economic climate or the instability of the political situation in the country, which leads to the commissioning of only certain stages of construction. The subsequent resumption of construction work requires taking into account the mutual impact of new construction and observations of previously constructed buildings during the construction of new structures.

The execution of deep pits at the stage of laying the foundations of new buildings, as well as the substantial weight of high-rise buildings, causes a change in the stress-strain state of the adjacent soil massif, so designers face the task of determining the impact of such construction on the adjacent buildings.

This article presents the results of a study of the change in the stress-strain state of load-bearing structures and foundations an existing building, taking into account the mutual impact of an adjacent high-rise section of a residential complex.

The calculations were performed in two independent software systems Plaxis 3D and LIRA-FEM, in the spatial formulation of tasks, for a comprehensive assessment of the SSS of the system "soil base-foundation-superstructure".

The zone of impact of new construction on the adjacent buildings, the values and character of additional displacements of foundations of adjacent structures are determined. The regularities of changes in the calculated forces in piles are shown, which indicate a decrease in axial forces in piles up to two times at the interface with the foundations of the new building and an increase in the load on the piles of the central zone by up to 17%. The obtained results show a tendency to redistribute stresses in the foundation slab from the bearing zones to the span zones, as well as in the bearing vertical structures of the lower floor of the existing building.

Identification of calculated parameters of the Hardening Soil model based on laboratory soil tests

Viktor Nosenko — 2023-12-29

The modern soil model Hardening Soil, which is used in many software complexes intended for solving geotechnical problems, is considered. The model makes it possible to take into account changes in deformation parameters of soils depending on the level of applied stresses and to describe the deformation processes of cohesive soils under complex loading/unloading trajectories.

The paper also presents tables and graphs obtained during laboratory studies of semi-hard clay "Kyiv marl" in a triaxial system and an oedometer. Based on these data, the soil strength parameters с' and φ', as well as the stiffens modules , , were determined.

To correlate the results of numerical simulation with the real behavior of clay soil in the Plaxis software complex, using the SoilTest virtual laboratory, a test in a triaxial compression device was simulated and soil parameters were identified. This approach makes it possible to increase the accuracy and quality of calculation results.

During identification, the parameters that most affect it were analyzed, which made it possible to better understand which parameters and in which ranges to vary in order to achieve the desired result.

It was determined that the most sensitive parameters are the section modulus of rigidity and the coefficient of destruction R_f. Their percentage sensitivity is 65.9% and 32%, respectively.

By varying the c' and φ' characteristics during the tests in the virtual laboratory, the destruction of the sample was simulated in accordance with real soil studies. Therefore, it is very important to correctly determine these parameters, because this can lead to an underestimation or, on the contrary, an overestimation of the strength of the soil base.

Assessment of the reasons for the loss of stability of the retaining wall and the choice of slope stabilization options, taking into account the use of retaining walls of different rigidity

Viktor Nosenko — 2023-12-29

An assessment of the reasons for the loss of stability of the sliding slope and the manifestation of significant movements of the existing retaining walls is presented, as well as the selection of measures to stabilize the slope by installing one of the variants of retaining walls of different rigidity is performed.

To assess the stability of the slope and select the effective parameters of the retaining walls, a numerical simulation of the stress-strain state (SSS) of the elements "soil massif of the slope - retaining walls" was performed. Modeling was carried out by the method of finite elements using the "Plaxis" software complex in a non-linear setting, taking into account changes in the parameters of structures and soils at different stages of modeling.

An assessment of the real movements of the retaining walls and the reasons for the loss of slope stability at the initial stage was carried out using geodetic monitoring.

A characteristic engineering-geological section in the zone of the greatest deformations of the existing anti-slide structures was chosen for modeling the calculation scheme.

Numerical calculations of the retaining walls, which were carried out using the finite element method, involve taking into account the technological sequence of the construction of the retaining walls and modeling the step-by-step development of the pit. Modeling was performed in several stages:

1) Formation of soil SSS in the current natural state;

2) Assessment of the stability of the slope before the start of construction, in the presence of an old massive retaining wall made of limestone blocks.

3) Assessment of the stability of the slope in the version of the original design solution with a retaining wall made of short bored piles with a diameter of 820 mm and taking into account the development of the pit to the design mark.

4) Modeling of SSS elements "soil array of the slope - retaining walls" with different options of the new retaining wall in order to choose an effective option that will ensure the possibility of developing the pit to the design marks and stabilizing the slope.

Based on the results of numerical modeling of slope stabilization options with retaining walls of different designs and rigidity, the consumption of materials for each of the options was determined and the most effective option was selected.

Studies have shown that depending on the change in the spatial rigidity of the retaining walls by introducing additional elements (buttresses, struts) it is possible to obtain an optimal solution and, in the future, to effectively design a complex of anti-landslide structures.

Factors affecting the operation of the floor of industrial buildings

Oleg Malyshev — 2023-12-29

In recent years, a high rate of construction of industrial facilities, located not only outside the city limits, but also in the conditions of urban development, in most cases on the outskirts of cities, has been observed. Such buildings include: production, transport, logistics or warehouse complexes. The latter, moreover, play a rather important role in the life cycle of any city.

For the reliable and efficient operation of such structures, in addition to ensuring the requirements for their strength, reliability and durability, which are put forward to the supporting and enclosing structures, it is also necessary to ensure the long-term, trouble-free and safe operation of floors subjected to various influences.

In recent years, the use of industrial concrete floors, which can be found quite often not only in industrial buildings, but also in places with a high traffic load, for example, floors in warehouses or factories, sales halls, hangars, airports, railway stations, stations, is gaining relevance maintenance, laboratories, which is explained by their high technical and economic indicators, as well as their resistance to the load from equipment and transport, the fall of heavy objects, thermal, vibration, chemical, temperature effects and abrasion.

In addition, industrial floors should be characterized by high strength, wear resistance, a long service life, maintainability, unpretentiousness in care.

However, along with this, there are also negative factors regarding the use of concrete industrial floors. Thus, due to the presence of a porous structure, the concrete floor covering is prone to destruction during operation. This leads to the formation of dust, which can rise into the air and fall into respiratory organs. Also, concrete floors are not resistant to chemical solutions that affect resistant to chemical solutions that affect the formation of cracks. Of course, there are methods of combating these negative factors, such as wet cleaning or using a special topping.

The influence of the parameters of engineering protective structures on the effectiveness of their use in densely built-up territory

Vitalii Ruchkivskyi — 2023-12-29

A study of the influence of application of an engineering protective screen made of small-diameter driven piles on the existing building deformations, caused by the arrangement of the pit fence made of bored piles, was carried out. The study was carried out with the help of numerical modeling using the method of finite elements, which allowed to display the work of the system "soil base - engineering protective structures - the foundation of the existing building" with different parameters of the protective screen. The influence of the following parameters is shown:

1) the depth of laying the protective screen L in relation to the depth of the compressible soil zone (Hst).

2) the position of the protective screen between the retaining structures of the pit and the existing building.

3) rigidity of the screen – the ratio of the step to the diameter of the piles of the engineering protective screen.

4) the distance between the existing building and the pit in relation to the depth of the enclosing structures of the pit of the new construction.

The tasks were modeled in a spatial arrangement with the task of the system "soil base - enclosing constructions of the pit - protective screen - foundations of the existing building". The soil environment was modeled using the Hardening Soil Model. The calculation was carried out in stages.

The variation of the parameters of the protective screen was carried out for the historical building, which in most cases was made according to a rigid wall construction scheme with strip foundations.

The foundation depth is 1.2 - 3.0 m and the foundation width is 1-2 m. The average pressure under the foundation is 150-250 kPa.

The rational depth of the foundation and the position of the protective screen between the existing building and the pit of the new construction were established.

The area of effective application of the protective screen was revealed, depending on the distance between the building and the pit fence.

The effective stiffness is established depending on the change in the relative distance between the poles of the protective screen.

The effect of an explosive shock wave on the plate of a protective structure of a critical infrastructure

Volodymyr Sakharov — 2023-12-29

The article presents the outcomes of an analysis on the stress-strain conditions of reinforced concrete structures subjected to an explosive shock wave resulting from the detonation of a combat unit from a kamikaze drone against a protective screen. When designing protective structures for critical infrastructure, employing computer simulation enables an assessment of the genuine impact of explosive loading on the structural elements' strength. The active phase of explosive loading is exceptionally brief, lasting only a fraction of a second. Under such circumstances, modeling is best performed using explicit methods of direct integration in time.

The structure considered in this work is a reinforced concrete slab supported by a metal beam cage with I-beam cross-sections, topped with a sand backfill. The study was executed within the SIMULIA Abaqus software suite, incorporating models depicting nonlinear material behavior in a three-dimensional context. Discretely positioned reinforcement was considered for reinforced concrete structures, and the "Concrete Damage Plasticity" model was applied for concrete, accounting for damage accumulation. The devised computational scheme for the shelter represents a section of the protective structure's roof under conditions of cyclic symmetry.

The article elucidates the core principles of incorporating explosive loading according to algorithm CONWEP.The results demonstrate that during the detonation of a kamikaze drone, an explosive wave created a crater in the sand backfill, exposing the slab. The study illustrates the development of damage in the reinforced concrete slab at various time intervals. Despite the identified damage to the slab, the protective structure overall withstood the explosive load. The intensity of the explosive shock wave diminishes significantly as it propagates away from the explosion site.

Features of interaction bored pile with the soil base in the presence of structurally unstable soils

Igor Boyko — 2023-12-29

During the construction of pile foundations, the pile testing process is necessary and mandatory. Therefore, there is a need for a correct assessment of the interaction elements of the "foundation-pile" system with the provision of a reliable and effective design solution.

If the soil parameters provided in the reports on engineering and geological searching are used without their prior refinement, this leads to a significant discrepancy in the results of numerical modeling of the interaction of piles with the base and data from field tests. In this regard, there is a need to identify the design parameters of the adopted soil model in order to match the modeling results with the results of experimental studies in a wide range of loads.

The Hardening Soil Model was chosen to describe the interaction behavior of the elements of base-pile system in this study. The nature of the influence of the three modules identified in the above model was investigated: modulus deformation at 50% of the base strength ( ); compressive strain module ( ); strain module at unloading ( ). The influence of the effect of dilatancy of the sand base was also analyzed.

At the initial stage of loading, the values of the and modules make a significant contribution to its performance. With further increased loads in the soil, significant plastic shear deformations occur, and accordingly, the parameters of soil strength (c, φ) are the leading parameters. Due to the fact that the upper part of the bored pile is located in structurally unstable soils (bulk soil and plastic sandy loam), and the lower part of the pile is located within sandy soil for a significant part of its length, it is also important to take into account the effect of soil dilatancy (ψ).

It was found that an increase in the unloading module ( ) reduces not only the settlement along the unloading curve, but also along the load curve.

The results of comparison of full-scale testing of a bored pile and its numerical modeling of interaction with structurally unstable and sandy soils are presented, and the design parameters of the soil environment model are identified in order to match the modeling results with experimental data at the corresponding specified loads.

The obtained convergence is within 5% in a wide range along the curve of the load on the bored pile.