تاثير تغيير مشخصات لايه‌هاي خاك بر پاسخ سيستم خاك ـ شمع تحت بار زلزله

THE EFFECT OF SOIL MECHANICAL PROPERTIES ON THE RESPONSE OF SOIL-PILE SYSTEMS UNDER EARTHQUAKE LOADING

در اين مطالعه با استفاده از نرمافزار تفاضل محدود FLAC3D، اثر تغيير مشخصات خاك به‌صورت تغيير پارامتر سختي در دو لايه‌ي رسي نرم و سخت بر رفتار خاك ـ شمع تحت بار زلزله بررسي مي‌شود. تحليل ديناميكي با استفاده از شتاب نگاشت ورودي سنگ بستر براي بررسي عوامل موثر در اندركنش انجام مي‌شود. نتايج حاصل از تحليل به‌صورت تاريخچه‌ي زماني شتاب، و نيز تبديل فوريه‌ي سريع شتاب سرشمع نسبت به ميدان آزاد در حوزه‌ي فركانسي ارايه مي‌شوند. براساس نتايج حاصل از تحليل، تفاوت سختي لايه‌هاي خاك تاثير به‌سزايي در اندركنش خاك ـ شمع دارد، به‌طوري كه دو‌لايه در نظر گرفتن خاك (لايه‌ي نرم بر روي لايه‌ي سخت) ــ علي‌رغم افزايش سختي آن ــ حالت بحراني‌تري از خاك يك‌لايه‌ي نرم را نشان مي‌دهد و كم‌ترين ميزان اندركنش، جابه‌جايي و لنگر بيشينه مربوط به حالت خاك يك‌لايه است.

In the last few years, although considerable progress has been made in developing methods of analysis and understanding of phenomena related to dynamic soil-pile interaction, much has still to be learned through systematic parametric studies. Due to the progressing knowledge and capabilities of computer software and hardware, a significant amount of study has been conducted to investigate the effect of changes in environmental conditions around the piles on the soil-pile behavior under dynamic analysis. The necessity of evaluating the effects of changes in the soil profile around the pile has significant importance. In this research, dynamic interaction between pile and soil has been examined, and the current methods were introduced. With the aim of a better understanding of the problem, first, a brief review was made on previous research. Then, the behavior of pile-soil under earthquake load and with geotechnical problems has been discussed using Finite Difference Software i.e., FLAC3D. Through using different types of accelerogram, dynamic analysis was conducted to evaluate the effective factors on interaction, such as a comparison of elastic and Mohr-Coulomb elastoplastic behavior. In order to obtain the above-mentioned goals, kinematic effects are described by frequency dependence on the transfer function. The transfer function is defined in the frequency domain as the relative movement of the foundation to a free field in the absence of a structure. The obtained results from analysis are presented as an acceleration time history, as well as the Fast Fourier Transformation of the acceleration of a head pile in relation to a free field in the frequency domain. Maximum shear force and flexural moment applied to the pile have been compared in different modeling. Based on the analysis results, the difference in the stiffness of soil layers may have an appreciable influence on the soil-pile interaction. It should be mentioned that the condition of two-layer soil is more critical than one-layer soft soil, and the lowest interaction, displacement and maximum moment were observed in one-layer soil.