Investigation of liquefaction behaviour with UBCSAND model

Liquefaction and lateral spreading, which occur in saturated loose sandy soils and cause a considerable part of the structural damage during earthquakes, are among the leading research topics in recent years. There has been significant success in constitutive modeling developed to study liquefaction-induced deformations and failure. Verification of such modeling studies is possible by comparing the results of the numerical analyses to the laboratory and field data. In this thesis, numerical analyse have been purposed to do, using a numerical liquefaction model designated as UBC3D-PLM, and formed by user-defined integration of the UBCSAND module developed for analysis of saturated loose sandy soils to Plaxis FE software. The UBC3D-PLM is a simple, fully-coupled effective stress model for analysis of the liquefaction behavior of sands. In the study, the results of VELACS-1 centrifuge model have been compared to the pore pressure increase, acceleration and displacement values obtained from numerical modeling, and the effect of the input parameters has been investigated. In addition, the results of centrifuge tests for sloping ground have been compared to those obtained from the numerical analyses performed with UBC3D-PLM. It has been found that the pore pressures and accelerations found by the two different methods are in agreement. On the other hand, the numerical analysis has calculated higher displacements in case of sloping ground. Wildlife field data including measured values of pore pressures and accelerations which were taken during the Superstition Hills earthquake in the USA, have been compared to the results of the numerical model of the Wildlife field. Althoug the results of the current study as well as the previous research on the topic are in concurrence with the field data, a delay in the increase of pore pressures compared to the results of the numerical analysis is observed. Furthermore, the SPT (N1)60 input values on the site have been increased and various analyses performed to model and evaluate the behavior of dense sands. Further analyses with the Wildlife model have been carried out by reducing the earthquake data by 20%, 40% and 60%. In these analyses, the cause of the delay in the increase of pore pressure has been investigated. The CarrefourSA site (Kocaeli, Turkey) had experienced liquefaction during the 1999 Kocaeli earthquake. In an area on the site, soil improvement with jet grouting colums had been carried out before the earthquake and no liquefaction occurred in that particular area during the seimic event. This case history clearly shows the positive effect of soil improvement on the site behavior. In that project, improvement had been carried out to include liquefiable sand layer in silty clay layers. In the thesis study, numerous numerical analyses have been carried out by modeling that site and trying various improvement ratios and using various shear modulus ratios. The effect of the soil improvement with jet grouting columns on the liquefaction behavior has been investigated. In the thesis, it has been aimed to determine the reliability of the UBCSAND model, and also to investigate the behavior of the soil improved by the widely used method of jet grouting columns.