ONE DIMENSIONAL SITE RESPONSE ANALYSIS OF A POWER PLANT SITE BEFORE AND AFTER GROUND IMPROVEMENT

Abstract

The purpose of this research is to measure amplification factor of a power plant site before and after ground improvement. Eight earthquakes with different frequency content (ChiChi, Coyote, Kobe, Loma Girloy, Nahani, Northridge, Mammoth, & Parkfield earthquakes) were selected to do the analysis. The analyses were mainly based on shear wave velocity. Soil parameters and other data were collected from the Power Plant Site. In this location Ground Improvement was done by deep mixing with cement. Soil model before ground improvement mainly considered as silty fine sand with shear wave velocity of 160 m/s at ground level to 640 m/s at 120m depth. Similarly, after ground improvement shear wave velocity was 1100 m/s at ground level to 640 m/s at 120m depth. For estimating site amplification factor, computer program DEEPSOIL was used. With soil layer depth, unit weight (γ) and shear wave velocity (Vs) as inputs, soil amplification by equivalent linear analysis was estimated. Amplitude ratio versus frequency (Hz), Peak Ground Acceleration (PGA) versus depth, Acceleration versus time, normalized Peak Surface Acceleration (PSA) versus period were plotted both for the above two models. After combining all the earthquakes, the mean value amplitude ratio decreased from almost 12 before ground improvement to 9 after ground improvement though the frequency was the xv same. PSA value decreased from 0.6 to 0.3 within the same period of time. We cannot find any significant change in the normalized PSA value. After ground improvement the mean PGA value of all the earthquakes decreased to 0.15g from 0.30g which is a significant amount