Исследование напряженно-деформированного состояния песчаного основания коротких буронабивных свай из напрягающих бетонов в большом геотехническом лотке и при помощи ПК Plaxis 2D

INVESTIGATION OF THE STRESS-STRAIN STATE OF THE SANDY BASE OF SHORT BORED PILES FROM EXPANSIVE CONCRETE IN A LARGE GEOTECHNICAL TRAY AND WITH USING THE PLAXIS 2D PROGRAM A. NEVEIKOV, V. DEDOKПредставлена оценка напряженно-деформированного состояния и несущей способности буронабивных свай из напрягающих бетонов по результатам натурных исследований в большом геотехническом лотке и численного моделирования в ПК Plaxis 2D. Дано краткое описание методики проведения натурных экспериментов и создания их конечно-элементных моделей в ПК Plaxis 2D на основе упругопластической модели Мора – Кулона. Выводы базируются на сопоставлении результатов натурных исследований буронабивных свай и данных численных расчетов в ПК Plaxis 2D.= The article defines the stress-strain state and load-bearing capacity of bored piles made of expansive concrete based on field studies in a large geotechnical tray and of numerical tests simulation in Plaxis 2D program. This article describes the routine full-scale experiments and their finite element schemes using Plaxis 2D program and the elastic-plastic Mohr – Coulomb model. The implications are based on the comparative analysis of the results obtained from the held studies of bored pile test and calculation data in Plaxis 2D program

Vertical facing panel-joint gap analysis for steel-seinforced soil walls

This paper reports the results of a numerical parametric study focused on the prediction of vertical load distribution and vertical gap compression between precast concrete facing panel units in steel-reinforced soil walls ranging in height from 6 to 24 m. The vertical compression was accommodated by polymeric bearing pads placed at the horizontal joints between panels during construction. This paper demonstrates how gap compression and magnitude of vertical load transmitted between horizontal joints are influenced by joint location along the height of the wall, joint compressibility, and backfill and foundation soil stiffness. The summary plots in this study can be used to estimate the number and type (stiffness) of the bearing pads to ensure a target minimum gap thickness at the end of construction, to demonstrate the relative influence of wall height and different material component properties on vertical load levels and gap compression, or as a benchmark to test numerical models used for project-specific design. The paper also demonstrates that although the load factor (ratio of vertical load at a horizontal joint to weight of panels above the joint) and joint compression are relatively insensitive to foundation stiffness, the total settlement at the top of the wall facing is very sensitive to foundation stiffness. This paper examines the quantitative consequences of using a simple linear compressive stress–strain model for the bearing pads versus amultilinear model that is better able to capture the response of bearing pads taken to greater compression. The study demonstrates that qualitative trends in vertical load factor are preserved when a more advanced stress-dependent stiffness soil hardening model is used for the backfill soil as compared with the simpler linear elastic Mohr–Coulomb model. Although there were differences in vertical loads and gap compressionwith the use of both soilmodels for the backfill, the differenceswere small and not of practical concern.Peer ReviewedPostprint (author's final draft

Numerical investigation into the effect of various surcharge loadings on propped wall excavations and embankments

Several guidance and formulation have been developed in the literature to account for the analysis of external surcharges adjacent to a propped excavation but less attention has been paid to the presence of sloping ground or embankments. However, CIRIA C760 states that the actual ground profile should be modelled and analysed as a series of surcharge loading over the extent of the active side of the wall. In this research, two braced excavation models were analysed of which one was the actual ground profile and the second with a series of surcharge loading representing the embankment adjacent to the excavation. The accuracy, efficiency, and conservation of the proposed approaches were examined on a propped cantilever wall excavation using a finite element geotechnical analysis software PLAXIS 2D. The models were analysed and examined in terms of the bending moment and deflection of the diaphragm wall and the prop load, the model with the actual ground profile was also investigated for any thrust load on the support system should the embankment or sloping ground fail in shear. The results were presented, and comparisons were made. Merits and advantages of the proposed numerical approach were discussed

Analysis of a shaft using 2D & 3D finite element programs

Εθνικό Μετσόβιο Πολυτεχνείο--Μεταπτυχιακή Εργασία. Διεπιστημονικό-Διατμηματικό Πρόγραμμα Μεταπτυχιακών Σπουδών (Δ.Π.Μ.Σ.) “Σχεδιασμός και Κατασκευή Υπόγειων Έργων

Securing of Foundation Pit for Construction of Power Station in Štětí

Práce je zaměřena na zajišťování hlubokých stavebních jam. V první části jsou zmíněny možné způsoby zajištění a jejich výhody i nevýhody. Následuje statické posouzení pažící podzemní železobetonové stěny v programu Plaxis 2D. Nakonec je zpracován technologický postup provádění této konstrukce.Bachelor´s thesis is about securing of deep foundation pit. In first part there are explained types of securing, their advantages and disadvantages. In second part there is static appraisal of diaphragm wall in software program Plaxis 2D. In the end of this thesis there is technological process of building this diaphragm wall.

Seismic behavior of triple tunnel complex in soft soil subjected to transverse shaking

Combining multiple tunnels into a single tunnel complex while keeping the surrounding area compact is a complicated procedure. The condition becomes more complex when soft soil is present and the area is prone to seismic activity. Seismic vibrations produce sudden ground shaking, which causes a sharp decrease in the shear strength and bearing capacity of the soil. This results in larger ground displacements and deformation of structures located at the surface and within the soil mass. The deformations are more pronounced at shallower depths and near the ground surface. Tunnels located in that area are also affected and can undergo excessive distortions and uplift. The condition becomes worse if the tunnel area is larger, and, thus, the respective tunnel complex needs to be properly evaluated. In this research, a novel triple tunnel complex formed by combining three closely spaced tunnels is numerically analyzed using Plaxis 2D software under variable dynamic loadings. The effect of variations in lining thickness, the inner supporting structure, embedment depth on the produced ground displacements, tunnel deformations, resisting bending moments, and the developed thrusts are studied in detail. The triple tunnel complex is also compared with the rectangular and equivalent horizontal twin tunnel complexes in terms of generated thrusts and resisted seismic-induced bending moments. From the results, it is concluded that increased thickness of the lining, inner structure, and greater embedment depth results in decreased ground displacements, tunnel deformations, and increased resistance to seismic-induced bending moments. The comparison of shapes revealed that the triple tunnel complex has better resistance against moments with the least amount of thrust and surface heave produced

Anisotropy effects on the undrained stability of cuts in clays

It has long been recognised that soils are generally anisotropic with some of their properties varying depending on the direction of measurement. In particular, strength anisotropy should be a main concern in relation with the stability assessment of geotechnical cases. Nevertheless, the incorporation of this feature is rarely considered in routine slope stability analyses in spite of the fact that its absence may lead, in some cases, to an overestimation of the factor of safety. In the paper, the effects of strength anisotropy on the undrained stability of cuts in clays are examined. A literature review reveals that clays have different patterns of undrained strength anisotropy depending on their overconsolidation ratio. A constitutive model is introduced, able to account for the different observed variations of undrained strength with loading direction. A series of numerical stability analyses have been performed to explore the effects of the type of undrained strength anisotropy on the stability of cuts. The effects of slope inclination, bedding orientation, and pattern of undrained strength anisotropy on factors of safety and failure mechanisms are examined and discussed. In addition, a real case study of the failure of an underwater cut is analysed showing that undrained strength anisotropy is able to explain satisfactorily the collapse observed.Postprint (published version

Analysis of circular ventilation shaft with 2D and 3D finete element models (FEM)

Εθνικό Μετσόβιο Πολυτεχνείο--Μεταπτυχιακή Εργασία. Διεπιστημονικό-Διατμηματικό Πρόγραμμα Μεταπτυχιακών Σπουδών (Δ.Π.Μ.Σ.) “Σχεδιασμός και Κατασκευή Υπόγειων Έργων