پيش‌بيني تغييرشكل ماندگار لرزه‌يي شيب‌هاي خاكي با شتاب تسليم متغير به روش تحليلي وابسته

Coupled Seismic Permanent Displacement of Soil Slopes with Variable Yield Acceleration

روش‌هاي مبتني بر روش بلوك صلب نيومارك در تخمين تغييرشكل ماندگار شيب‌هاي خاكي تحت بار زلزله به دليل سادگي نسبت به ساير روش‌ها بيشتر مورد توجه مهندسان قرار گرفته‌اند. علي‌رغم مزايايي كه روش‌هاي ذكرشده دارند، محدوديت‌هايي در مباني آن‌ها نهفته است. يكي از اين محدوديت‌ها، ثابت‌بودن شتاب تسليم در حركت رو به پايين توده‌ي لغزش است. در اين نوشتار، تغييرشكل هندسي سطح لغزش در حين تغييرمكان لرزه‌يي به صورت وابسته مورد بررسي قرار گرفته است. نتايج نشان مي‌دهد كه كاهش طول گسيختگي منجر به كاهش تغييرمكان مي‌شود. همچنين نسبت دوره‌ي تناوب، ضريب گسيختگي، و پارامترهاي لرزه‌يي تاثير قابل‌توجهي در نتايج دارند. در ادامه، با استفاده از ركوردهاي زلزله مشتمل بر 1363 ركورد ميدان آزاد از 25 زلزله، تغييرمكان ماندگار شيب‌هاي خاكي توسط روش تحليلي وابسته به شتاب تسليم بررسي و مدل همبستگي در اين خصوص ارايه شده است.

As a simplified dynamic analysis, the Newmarkian sliding block and decoupled and coupled analyses have received considerable attention among geotechnical practitioners for estimating the earthquake-induced permanent deformation of earth slopes and embankments. However, some conceptual limitations might affect the estimated permanent displacements. Research work still proceeds to modify the basic sliding block approach in order to attain more precise estimates of seismic ground displacement. The original sliding block analogy assumes a constant yielding acceleration, while there must be variable yield acceleration due to the downward-stabilizing movement of the sliding soil mass. In this paper, yield acceleration is modified based upon the changes in the geometry of the sliding surface. An analytical coupled solution is done for a SDOF system with distributed mass and stiffness throughout the system height; whereas sliding displacement and dynamic system response are coupled. Numerical analyses reveal that consideration of the sliding mass rotation and modification of yield acceleration significantly affects the resultant permanent displacement, especially for small slip lengths. It is also shown that period ratio, yield acceleration, and input motion have a significant impact on the results. For better evaluation of the effect of seismic parameters on permanent displacement, a wide-ranging database of earthquake records containing 1363 records from 25 earthquakes, were employed, and permanent displacements were evaluated by the proposed coupled analysis with variable yield acceleration. A regression model is presented to predict permanent displacement, including, as a function of the seismic parameters, slip lengths, period ratio, and yield acceleration. The presented equation is compared with the models proposed by other researchers. The proposed equation is applicable for microzonation of landslide hazard.