Bases and Foundations

The use of planar and three-dimensional calculation models for the numerical modeling of retaining walls in conditions of dense urban construction

2024-09-05T22:05:45+03:00

In modern realities, the construction of multi-story buildings increasingly has to be carried out in the conditions of dense urban development. Since high-rise buildings are characterized by the presence of deep pits, there is a need to select the parameters of the enclosing structures (retaining walls) and take into account the influence of the pit arrangement and enclosing structures on the existing building.

Numerical simulation of the stress-strain state (SSS) of the elements "soil base - existing structures - pit enclosure" was performed to assess the impact of choosing the dimensions of the calculation scheme when designing a deep pit and assessing its impact on existing buildings and selecting effective parameters of enclosing structures. with different dimension options (flat two-dimensional and spatial three-dimensional) calculation scheme.

Modeling was performed using the finite element method using a nonlinear model of soil deformation in the Plaxis software package.

Since the soil conditions within the construction site are complex (the presence of a significant layer of plastic and flowing clay soils and powerful aquifers), the level of groundwater within the construction site was taken into account in the modeling and the effect of water lowering during the development of the pit was modeled accordingly for a more correct assessment of the stress-strained state of pit enclosure elements and the impact on existing structures.

Numerical calculations of retaining walls provide for taking into account the technological sequence of the construction of retaining walls and modeling of the step-by-step development of the pit.

Studies have shown that the use of a spatial finite-element model of the system "soil base - existing structures - pit enclosure" provides an opportunity to more correctly and effectively assess the stress-deformed state of system elements due to taking into account the spatial rigidity of the elements of the pit enclosure and the foundations of existing structures.

The values of the displacements of the retaining walls obtained by the calculation of the spatial finite element model (FEM) are 20% smaller than the values obtained using the plane FEM. The values of the bending moments obtained by the calculation of the spatial FEM are 10% smaller than the values obtained using the plane FEM.

A soil base model of adjacent various story structures

2024-09-07T13:40:21+03:00

In modern geotechnical engineering, owing to the development of information technology and availability of powerful packages for the calculation of the entire base - foundation - structure system, one of the main research areas is to develop, improve and investigate soil base models to ensure the adequate interaction between the components of the system during the construction and operation of buildings and structures (hereinafter referred to as the “structures”).

The paper proposes an improved soil base model in the form of a continuous layer of finite distribution capability to simulate and calculate adjacent multistory structures in the base - foundations - structures system using powerful calculation packages such as SOFiSTiK, ABAQUS, PLAXIS, SCAD, Lira and others. The improved model considers the parameters of the stress-strain properties of the soils of the bases, the geometric profile taking account of the distribution capability of the base and different boundary conditions, but differs from the existing models in that it has a stepped geometric profile at the lower boundary of the model because of different compressible layer depths under each foundation of the structures. The use of this model improves the accuracy of simulating a soil base for large-sized foundations of adjacent structures to obtain reliable results of the stress-strain state of the base - foundations - structures system.

An example demonstrates how to simulate and calculate raft foundations of a two-section multistory building in the base - foundations - structures system that interacts with an improved soil base model (linear strains of soils under loads are considered here) with reference to different numbers of stories of the sections. The numerical study results show on a specific calculation example that considering different compressible layers depths in the model under differently loaded foundations results in an increase in moment forces of up to 65% as compared with simulating the whole compressible layer, which may lead to the disruption of large-sized raft foundations.

Geotechnical issues of investigation of the technical condition of the structure on weak soils according to the boundary element method

2024-09-07T19:08:17+03:00

The article considers the controversial issue of the need to take into account the increasing coefficient to the soil deformation modulus obtained on the basis of compression studies for the design of loess frozen soils. It is well known that weak soils can have low bearing capacity and high compressibility, which makes them difficult to construct and operate structures.

It is known that in laboratory conditions, the modulus of soil deformation is usually determined by compaction with a static load without the possibility of lateral expansion in a rigid ring. The disadvantage of the compression device is the low accuracy of measurements, which is emphasised by many researchers due to the fact that the friction forces of the soil sample on the ring walls reduce, depending on the moisture content and soil type, the vertical pressure applied to the sample during the test. This leads to a false decrease in the actual value of the soil deformation modulus.

To determine the reliability of the two approaches to determining the soil deformation modulus, the settlements of the foundations of grain storage silos on dangerous degraded loess soils were calculated by the numerical method of boundary element (MBE) using an elastic-plastic model, with and without taking into account the soil deformation modulus.

It has been found that solving the problems of assessing the technical condition of a building is associated with geodetic and engineering-geological surveys and the analysis of these results, since the stress-strain state of the building-foundation system and the peculiarities of deformation of the soil base depend on them. After all, the problem of protecting a building from rolling is quite relevant. The design or reconstruction of structures on foundations with weak soils (with a deformation modulus E < 5 MPa) is also associated with the problem of ensuring that the calculated deformation values do not exceed their maximum permissible values for the experimental structure.

The results of numerical studies are compared with the method of finite element (MFE) calculation and experiment.

Influence of soil base deformation methods on the formation of the stress-strain state of retaining walls

2024-09-04T17:23:57+03:00

The results of numerical modeling of the interaction between a pile retaining wall and the soil base using the software complexes "Plaxis" and "LIRA-SAPR" are presented. A comparison of the stress-strain state of retaining walls using different calculation methods, taking into account the presence of rock soil, has been performed.

In the first variant, the active pressure on the wall was determined manually in accordance with the current standards [3], and the subsequent calculation was carried out in the "LIRA-SAPR" software complex. The "pile-soil" system was modeled using FE 57, which are interconnected by FE 10 (rod), and the values of horizontal stiffness (Rx,y) were determined according to the requirements of [3].

In the second variant, the retaining wall calculation was performed in "Plaxis 2D". The soil behavior model is "Mohr-Coulomb", and for rock - "Hoek-Brown". It was considered that rock soils lie at the base of the retaining wall, which revealed significant differences in the distribution of bending moments along the length of the retaining wall.

It was established that the stress-strain state in the first variant significantly differs from the second. The difference in maximum horizontal displacements after the calculation by the first and second methods was shown. Differences and variations in the values of bending moments occurring in the retaining wall were investigated. The importance of using modern geotechnical calculation software complexes for a more detailed and accurate analysis of structures and foundations was demonstrated.

Additionally, an assessment of the impact of variations in the parameters of the soil and retaining wall models on the calculation results was conducted. The research results allow recommending the use of a comprehensive modeling approach to enhance the reliability and efficiency of retaining wall design. The analysis also shows that the application of different soil behavior models can significantly affect the final calculation results, highlighting the need for careful selection of modeling parameters.

The obtained results have significant practical value for engineers and designers, as they allow for more accurate prediction of the behavior of retaining walls under various operating conditions. This contributes to improving the safety and cost-effectiveness of construction projects.

Analysis of the effectiveness of the use of short piles as part of a columnar pile foundation

2024-09-07T21:32:45+03:00

The realization of the operation of the grid and piles as a part of the columnar pile foundation, depending on the length of the piles, the method of arranging the piles, the distance between the piles and the type of soil with a constant number of piles, has been studied. The degree of implementation of the load-bearing capacity of the piles and the degree of implementation of the grid work as part of the pile foundation were analyzed. To solve the tasks set in this work, mathematical modeling by the finite element method of the joint operation of the pile foundation elements with the soil base and the separate operation of the pile and grid as a shallow foundation was performed in the "Plaxis 3D Foundation" software complex. It was established that the implementation of the load-bearing capacity of piles in the composition of the foundation with a large distance between the piles is much better. The length of the piles also affects the degree of their implementation. When the length increases, the bearing capacity of the piles is realized less. The greatest implementation of the load-bearing capacity of piles in the composition of the foundation is observed for short piles. The realization of the pressure under the sole of the grid with an increase in the pitch of the piles also improves, the realization of the load-bearing capacity of the grid is from 8 to 50%, which allows to raise the load-bearing capacity of the foundation. For sandy and clay soils, the nature of the redistribution of forces between the elements of the columnar pile foundation is similar. For foundations made of drilled piles, the degree of realization of pressure under the sole of the grate, as well as the degree of realization of the load-bearing capacity of the piles, is higher than for foundations made of driven piles. The guiding factor is the length of the piles.

The economic efficiency of the transition in homogeneous soils from a bush made of long piles with a standard minimum step to a bush made of short piles with an increased distance between the piles was investigated. By taking into account the joint operation of piles and grid, a bush made of short piles with larger dimensions of the grid provides the same bearing capacity as a bush made of long piles with a compact grid.

Despite the significant increase in the volume of concrete grating and the number of fittings with an increase in the pitch of the piles, cost savings on the cost of piles provide an economic effect of using bushes from short piles with wide gratings up to 35%.

Interpretation of the data of modern methods of field soil research

2024-09-07T21:57:14+03:00

This study examines modern in-situ testing methods for soils; it investigates the impact of interpreting these methods on the calculated strength and deformation parameters of soils and compares them with tabulated values according to the DSTU (Standard of Ukraine).

In today's world, there is an urgent need for accurate and prompt soil investigations, which are crucial for design and construction. Although laboratory methods are reliable, they often require significant time and resources. The advantage of in-situ methods lies in the fact that testing is performed directly in the soil mass, meaning that the results are not influenced by the transportation and preparation of samples. Conducting tests directly in the soil massif allows for the acquisition of information about soil characteristics and their classification, providing data on soil stratification.

This publication reviews modern methods of in-situ soil investigations, specifically CPTu (Cone Penetration Test) and DMT (Dilatometer Test) [1, 2]. These methods are widely used in Europe, while in Ukraine, they are relatively new and are just beginning to gain popularity. Therefore, it is relevant to compare these methods with the tabulated values provided in Ukrainian reference guides.

The deformation and stress values were compared using three calculation models based on CPTu, DMT, and DSTU data. A comparative analysis of the foundation slab deformations was conducted using models with elastic and elastic-plastic model.

For this purpose, a foundation slab was designed, and a finite element model of the building was developed, examining the foundation on a soil massif with inclined stratification, using both elastic and elastic-plastic soil models.

Numerical studies of the distribution capability of a continuous linear strain soil base model for largesized raft foundations

2024-09-07T22:16:00+03:00

The paper examines the existing methodology for determining the main design parameters of the model in the form of a continuous linearly strained layer of finite distribution capability (the design thickness of the layer H₀ and design stress-strain modulus E₀) to simulate the adequate interaction between soil bases and large-size slab foundations. The aim of this work is to numerically study the stress-strain state of a uniformly loaded flexible rectangular foundation slab when the thickness of the soil base model layer is reduced in the form of a continuous linearly deformed layer of finite distribution capacity. Numerical studies of the effect of the thickness of the layer of the specified soil base model that interacts with a large-size flexible slab foundation of various rectangular shapes in plan were conducted in the SCAD package using the finite element method. The numerical study results have shown that when the ratio H₀/H_a (the design thickness of the layer of the soil base model H₀ to the actual compressible thickness of the soil base H_a) decreases, the maximum moment forces along the orthogonal axes of rectangular foundations decrease to 50% because of the decrease in the distribution capability of the soil base model and, accordingly, in the edge reactions R under the slab at equal average settlements of the slab s_aver. Numerical studies have shown interesting results on the distribution of moment forces in flexible rectangular slabs, where the maximum is outside the center of gravity of a uniformly loaded raft, which confirms the peculiarity of the interaction of flexible slabs with relatively narrow compressible layers under the sole. With an appropriate in-situ experimental justification, the use of the soil base model in the form as a continuous linearly strained layer of finite distribution capability with the design parameters (H₀ and E₀) rather than with the actual parameters (H_a and E_a) in calculations of large-size slab foundations can be of fundamental practical importance in their rational design, as the reinforcement can be reduced to 50%

Study of the stress-strain state of the loess soil base of an eccentrically loaded tower foundations, with taking into account the possible water saturation of the soil

2024-09-07T22:28:06+03:00

This article provides the design of the tower shallow foundations using numerical simulation in the "Midas GTS NX" software. The foundations are four separate structures that perceive the bearing reactions from the tower supports. Depending on the wind load direction, the support reactions change both quantitatively and qualitatively. So, one foundation can accept a compressive force, the other one can accept a pull-out force. In this study, two variants of wind loading are considered: the wind load acts on the tower face or on the tower edge.

The geological conditions of the research site are taken as simplified. The soil base consists of one engineering-geological element, which is a loess soil. Numerical simulation of the soil massif was implemented by using volumetric finite elements. An elastic-plastic deformation law and a Mohr–Coulomb failure criterion were applied for these finite elements.

The design provided for the calculation of the tower foundation on a natural basis and with the arrangement of a compacted sub-base.

Research was carried out for the foundations of the tower construction in four stages: 1) soil base in its natural state; 2) arranged compacted sub-base; 3) natural basis with local water saturation of the soil; 4) compacted sub-base with local water saturation of the soil massif.

Simulation of the arrangement of the compacted sub-base occurs by replacing the stiffness of the finite element at a certain stage of the calculation. The soil water saturation simulation algorithm is performed in a similar way - there is a change in the physical and mechanical characteristics of certain finite elements. The localization of saturation zones was chosen from the conditions of the most unfavorable combinations of loads and vertical movements of the foundations.

An analysis of the stress-strain state of the soil base of foundations under the tower on a natural base and with the arrangement of a compacted sub-base was performed. The scheme of the applied load on the foundation and the possible local water saturation of the loess soil at the base of the foundations were taken into account

Stress-strain state of building structures taking into account possible local failure of the element

2024-09-08T08:56:15+03:00

The issue of choosing a structural design and material for supporting structures is an important technical and economic task at the stage of developing a design solution. It depends on a number of factors: consequence class of the structure, reliability of the design solution, savings in basic building materials.

The publication provides a classification of design schemes and types of load-bearing structures used in the corresponding solutions. The disadvantages and advantages of using prefabricated and monolithic structures for the installation and subsequent operation of the structural scheme of buildings and structures are considered.

Modern design requirements include ensuring the ability of a damaged structure to adapt to new conditions while continuing to function while ensuring the integrity of human life, property and equipment. New conditions mean the consequences of the occurrence of a certain emergency situation, accompanied by weakening or overloading of the load-bearing structures of a structure or soil foundation: a change in the structural design, a combination of new existing loads and a redistribution of internal forces.

The publication reflects the results of assessing the redistribution of the stress-strain state of the elements of the “base - foundations - load-bearing structures” system as a result of the implementation of a hypothetical emergency situation with the exclusion of the load-bearing structure from operation.

The case of the collapse of one of the vertical load-bearing elements (local failure of the pylon) of an underground floor, which can be used as a dual-use structure, is considered.

Calculations for the stability of the structure against progressive collapse were carried out by numerical modeling in the LIRA SAPR-2019 software using a quasi-static calculation and the method of direct integration of dynamics over time.

It has been demonstrated that the method of numerical modeling the joint work of a building with a soil base affects the results of a calculation of the progressive collapse of the building frame.

The influence of local collapse of a vertical load-bearing element on the redistribution of stresses and strains in the foundation structures of a building section is assessed.

The load on the piles under the pylons around the element removed under the local failure scenario is expected to increase by 15...25%.

Strengthening of the soil base - preparation for the road surface of the existing enterprise

2024-09-08T09:01:27+03:00

The issue of constructing new and restoring existing complexes for the storage and processing of agricultural products, as well as logistics complexes, holds significant importance in today's conditions as an integral component of ensuring the normal functioning of our economy. Historically, in Ukraine, when developing regulatory documents, the primary requirements were outlined for the design and construction of civil and industrial buildings and structures: residential and administrative buildings, industrial facilities, and objects of transport, energy, and critical infrastructure. These requirements are based on ensuring strength, reliability, durability, safety, and cost-effectiveness.

For projects involving the construction of logistics complexes or agricultural facilities, the regulatory documents in Ukraine contain significantly fewer detailed instructions and requirements [1, 2]. Therefore, when implementing this class of projects, design solutions are often based on requirements outlined in construction regulatory documents from other countries, such as Eurocodes (EN) [10], British Standards (BS), or the standards of the United States (ASTM), where considerable experience has already been accumulated in the reliable operation of such facilities.

The issue of requirements for the engineering preparation of territories for industrial or agricultural projects during the development of comprehensive building plans is not sufficiently covered in national regulatory documents that establish requirements for the calculation of building structures, road construction, or comprehensive territory planning – these documents are too general and lack the necessary detailed information or clear requirements for the application of reliable design solutions.

As a result, there are often cases where deformations of the surrounding surface and access roads to these facilities significantly complicate and/or render their normal operation impossible.

This article focuses on the study of soil preparation as the foundation for access roads for a group of buildings and structures in a grain storage complex: assessing the condition of the foundation during the operation of the complex; identifying the causes of significant deformations; selecting methods for strengthening and stabilizing the foundation; and geotechnical quality control of the performed foundation strengthening work.

Practical experience of installing an artificial base for industrial floors

2024-09-08T11:04:51+03:00

The installation of artificial foundations for industrial buildings and constructions (industrial floors) is becoming more and more relevant in modern construction, as the number of satisfactory sites for development is decreasing, territories with complex geological and hydrogeological conditions are increasingly being used. A high-quality installation of an artificial base should ensure the durability, strength and stability of the structure.

When preparing the site and arranging the artificial base, it is necessary to take into account such important factors as the type of soil, the level of groundwater, the expected load on the floor and the type of floor covering. Compliance with the requirements of regulatory and technical documentation, the use of quality materials and professional execution of work are critical for the successful construction of industrial floors.

As part of the study, an overview and detailed description of the process of installing an artificial base for industrial floors was carried out on the example of a real construction, a warehouse complex with an area of 35,000 m² in the south-western outskirts of the city of Kyiv.

The article highlights that the foundation installation process includes two main stages: site preparation and creation of artificial foundation layers.

The preparation of the site includes cleaning and planning of the territory, removing and removing the fertile layer of soil, conducting engineering and geological studies and implementing measures for the engineering protection of the territory.

The arrangement of the artificial base includes the compaction of the existing soil layers, the creation of new artificial base layers and their mechanical compaction in combination with the reinforcement of the layers with geosynthetics materials (geogrids).

This study emphasizes the importance of a comprehensive approach to site preparation and artificial base installation, which allows for reliable and long-term operation of industrial floors, minimizing the risks of deformation and damage.

Peculiarities of using small-diameter bored piles for effective solving of geotechnical problems

2024-09-08T09:18:15+03:00

Abstract. The peculiarities of the use of small-diameter drill piles in modern construction considered, with an emphasis on their advantages and areas of application in specific conditions. Two main types of piles distinguished: cast-in-place, which characterized by continuous reinforcement and filling with concrete or cement mortar, and composite, where the load transfers to reinforcing elements. Main advantages of small-diameter bored piles noted, including the possibility of performing work in confined spaces, reducing the level of noise and vibrations, a variety of drilling technologies, the possibility of application in geological conditions of varying complexity, etc.

Particular attention paid to the areas of application of small-diameter bored piles, including the installation of new foundations, underpinning of existing structures, soil improvement and land-slide protection. The main groups of factors that can influence the choice of small-diameter bored piles as the main design decision for various fields of application considered, including:

- physical factors (restricted access, remoteness of the area, distance of piles to existing structures);

- subsoil factors (difficult geological conditions, soil liquefaction tendency);

- environmental factors (sensitivity to vibration/noise, hazardous or contaminated soils);

- necessity of adaptation to existing structures;

- load/settlement requirements;

- economic factors.

Limitations for the use of small-diameter drill piles from the point of view of their efficiency described.

An example of the effective practical use of small-diameter bored piles in the confined conditions of dense urban development in close proximity of metro tunnels with increased requirements regarding the level of vibrations and noise considered. The task of minimizing subsidence of the designed residential and office complex and the impact on surrounding buildings and structures solved. The compliance of the adopted design decisions confirmed by means of field tests, as well as using the results of settlements monitoring. Attention focused on the need for further improvement of design approaches and technological solutions to optimize the efficiency of small-diameter bored piles for solving geotechnical problems.