ارايه‌ي روابطي براي تعيين تغيير مكان لرزه‌يي ماندگار شيرواني‌ها، براساس داده‌هاي لرزه‌خيزي ايران

PROPOSED EQUATIONS FOR PERMANENT SEISMIC DISPLACEMENT OF SLOPES ACCORDING TO IRAN SEISMIC DATA

در اين نوشتار به‌منظور ارايه‌ي روابطي براي تعيين تغيير مكان ماندگار لرزه‌يي شيرواني‌ها، با توجه به داده‌هاي لرزه‌خيزي كشور ايران، ابتدا مدلي هندسي براي دامنه‌هاي طبيعي با مصالح مختلف در نظر گرفته شده است. سپس تعدادي از شتاب‌نگاشت‌هاي زلزله‌هاي به‌وقوع پيوسته در ايران انتخاب شده و با انجام تحليل ديناميكي، پاسخ شتاب زلزله در توده‌ي لغزنده‌ي شيرواني برآورد ‌شده، و تغيير مكان ماندگار شيب با استفاده از روش بلوك لغزشي نيومارك به دست آمده است. با استفاده از روابط به دست آمده مي‌توان طراحي شيرواني‌ها را براساس تغيير مكان مورد نظر انجام داد. همچنين اين روابط براي برآورد ضريب نيمه‌ايستاي مناسب در طراحي‌هاي لرزه‌يي قابل استفاده‌اند. نتيجه‌ي بررسي‌هاي اين تحقيق ميزان تاثير پارامترهاي مختلف را در ميزان تغيير مكان شيرواني‌ها نشان داده و مبين آن است كه پارامتر بدون بعدِ نسبت شتاب بحراني به شتاب بيشينه‌ي شتاب‌نگاشت (kmax/ (ky بيشترين تاثير را در رابطه‌ي تعيين تغيير مكان ماندگار شيرواني دارد. همچنين مقايسه‌ي رابطه‌ي پيشنهادي در تحقيق حاضر با رابطه‌ي پيشنهادي راهنماي ارزيابي خطر لرزه‌يي شيب‌ها در كاليفرنيا حاكي از آن است كه تغيير مكان‌هاي ارايه‌شده در آن دستورالعمل از تغيير مكان‌هاي به دست آمده در كشورمان بزرگ‌ترند.

Every year, a great deal of financial damage and many casualties occur during earthquakes, due to the sliding of slopes in various parts of the world. Iran is a mountainous country located on a seismic zone, where many buildings are constructed on natural slopes. Seismic slope stability analyses mainly consist of pseudo statistical methods, dynamic analysis and simplified methods, which are based on estimation of an index displacement. In this paper, a number of relations for determining the permanent seismic displacement of slopes is proposed based on the available seismic data of Iran. The study was conducted based on dynamic analysis of different slopes, evaluation of earthquake acceleration in a sliding mass, and calculating the permanent displacement of the slope, using the Newmark sliding block. A two dimensional model of a typical slope was considered, and, by conducting dynamic analyses, the slope performance was studied for different geometries, strength parameters and shear wave velocities. Such a performance has been studied by assessing the record of acceleration in a sliding mass (the mass above the critical sliding surface), and calculating the slope displacement, using the Newmark method. Due to the limited number of strong ground motion records for a specific area in Iran, records related to the earthquake events in the whole country were gathered, 14 of which, related to 6 earthquakes with the largest magnitudes and accelerations, were chosen for dynamic analyses. A range of soil strength parameters and shear wave velocities were considered and the slopes were analyzed. The proposed relations in this paper can be used in the seismic design of slopes by choosing an allowable displacement and determining the proper pseudo-static coefficient. Results of this study show that the seismic permanent displacement of a slope is mainly affected by the ratio of critical acceleration to maximum acceleration in the sliding mass (kmax/ ky). Also, it was found that seismic permanent displacements by the proposed relations are less than those proposed by the “Guidelines for Analyzing and Mitigating Landslide Hazards in California”.