مهندسی عمران شریف (May 2016)
COUPLED SEISMIC PERMANENT DISPLACEMENT OF SOIL SLOPES WITH VARIABLE YIELD ACCELERATION
Abstract
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.
