The prediction of the behavior of structures interacting with soil is one of the main challenges in structural design. Accurate evaluation of soil–structure interaction ensures a rational design solution for the superstructure and foundation of a building. In structural analysis, one of the key problems is the identification of relevant movements of the foundation considering the interaction between the superstructure, foundation and ground (the soil mass around the foundation). The correct assessment of soil–structure interaction contributes to the rational constructional design of the superstructure and foundation and allows avoiding violations of requirements for ultimate and serviceability limit states possible due to unpredicted additional stress on the structural system. Resistance predictions for pile group foundations is a complex problem, which may be the reason for scattered and insufficient information available despite numerous experimental and numerical studies, predominated by the focus on partial empirical relationships. This experimental study analyzed the prototype of a short displacement pile group with a flexible pile cap in terms of the bearing capacity and deformation behavior while subjected to static axial vertical load. In particular, attention was given to the resistance–stiffness evolution of single piles acting in a pile group with different spacing. Test results of short displacement pile groups were used to verify known models for the bearing resistance prediction of the pile group.

Nowadays it is possible to find many experimental and analytical studies aimed for better prediction of sand soil response during the installation and loading stages of displacement pile. The interaction between the soil and the pile is very complex, this is the reason why it is not exhaustively described, so far. Response of the soil, especially the ultimate state necessitates investigate the nature of soil response via tip and shaft as well as their relation. Qualitative evaluation of the stress state influence on pile behaviour serves for more clear description of the soil ultimate response mechanism. Current investigation presents the results of two specific instrumented piles tests. The 1 st type of the tests revealed the shear and normal stresses distribution at particular areas of short displacement pile interface during static vertical load test. The 2 nd type of the tests showed the radial stresses increment paths in the soil during the pile installation stage. The performed tests of the short displacement piles results cleared, that during the static load tests the highest shear stresses, on the pile skin, get concentrate near the pile tip and during the installation stage the radial stresses significant increase when pile tip gets near the push in load cells measurement plane.

Statyba Civii Engineering KÜGINIO STIPRIO IR GILIOJO SPRAUSTINIO PAMATO PAGRINDO LAIKOMOSIOS GALIOS BANDYMU, TAIP PAT KITAIS METODAIS NUSTATYTy DEFORMACIjy MODULiy PRIKLAUSOMYBÈS Tautvydas Statkus^ Váidas MartinkusV ilniaus Gedimino technikos universitetas El. pastas: 'Tautvydas.Statkus@vgtu.lt; ^Váidas.Martinkus@dohvgtu.ltSantrauka. Sio straipsnio tikslas yra nustatyti priklausomybes tarp gmnto kflginio stiprio ir grunto deformaeijii moduliij, gautii i § giliojo pamato pagrindo laikomosios galios bandymii duomenii, taip pat gmnto tyrimo [spraudziamaisiais horizontaliojo slégio matuokliais bei kompresiniu aparatu. Straipsnyje pateiktos tiriamojo orasausio smèlinio grunto fizinès ir mechaninés savybès nustatytos laboratoriniais ir lauko tyrimo metodais. Atlikus regresinç bandymii duomenii analizç straipsnio isvadose pateiktos minètii dydziii priklausomybes. Tydmo duomenys gali bûti panaudoti sudarant praktini metod^ giliqjil spraustiniii pamani smèliniii pagrindii nuosèdziams prognozuoti.© Vilniaus Gedimino technikos universitetas

One can find lot of the methods and theories to determine and interpret the nature of the bearing capacity of displacement piles in cohesion-less soil. The presence of many methods leads to the variety of results and yields that no general and relevant methods have been proposed yet. Many experimental investigations do not fit properly the results of known numerical simulations. These simulations yield that the shear stress near the end of the pile increases significantly, when compared with the rest of pile length. Current investigation presents the specific test results of the short displacement pile under vertical load in cohesion-less soil. The full scale test was performed and the vertical stresses beneath base and shear stresses along the pile have been measured, as a result the shear stress significant increase near the end of the pile was observed. The obtained results can be used for developing the shaft and tip bearing capacity evaluation method for the short displacement piles in cohesion-less soil.

Accuracy of numerical modelling of ground resistance of the displacement pile highly depends on proper evaluation of its states: prior loading and its changes during the loading. Evaluation of initial ground stage, its subsequent changes caused by pile installation and, finally, evolution of the loaded pile resistance are the modelling stages that require validation with specialized test results performed under controlled laboratory conditions. Selection of the proper physical soil model and its parameters should be also done in accordance with the relevant soil tests results. The first paper briefly introduces testing results of a displacement pile prototype. Tests were conducted in the created sand deposit in the laboratory pit. Determining pile resistance and ground stress-strain distribution in the vicinity of the pile allows selecting the physical model for the soil. Numerical calibration of the parameters for the physical model of the selected soil was performed. The second, following paper will introduce analyses of pile resistance. It involves creation of a discrete model and its parameters, numerical modelling of pile resistance against vertical load. The pile ground resistance modelling applying the physical model of the selected soil includes the following stages: evaluation at rest stage and assessment of residual effects of installation and displacement pile loading resistance. Numerical analyses results were validated with displacement pile prototype testing results.