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Journal of Korean Society of Coastal and Ocean Engineers > Volume 30(6); 2018 > Article
J Korean Soc Coast Ocean Eng 2018;30(6): 306-318. doi: https://doi.org/10.9765/KSCOE.2018.30.6.306
직립식 방파제 성능기반 내진 설계 Platform 개발을 위한 기초연구 - 전단파 횟수 누적에 따른 지반 강도 감소를 중심으로
최진규, 조용준
서울시립대학교 토목공학과
Preliminary Study on the Development of a Performance Based Design Platform of Vertical Breakwater against Seismic Activity - Centering on the Weakened Shear Modulus of Soil as Shear Waves Go On
Jin Gyu Choi, Yong Jun Cho
Department of Civil Engineering, University of Seoul 163 Seoulsiripdaero, Dongdaemun-gu, Seoul 02504 Korea
Corresponding author: Yong Jun Cho ,Tel: +82-2-6490-2427, Fax: +82-2-6490-2424, Email: young@uos.ac.kr
Received: December 8, 2018;  Revised: December 26, 2018.  Accepted: December 27, 2018.
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ABSTRACT
In order to evaluate the seismic capacity of massive vertical type breakwaters which have intensively been deployed along the coast of South Korea over the last two decades, we carry out the preliminary numerical simulation against the PoHang, GyeongJu, Hachinohe 1, Hachinohe 2, Ofunato, and artificial seismic waves based on the measured time series of ground acceleration. Numerical result shows that significant sliding can be resulted in once non-negligible portion of seismic energy is shifted toward the longer period during its propagation process toward the ground surface in a form of shear wave. It is well known that during these propagation process, shear waves due to the seismic activity would be amplified, and non-negligible portion of seismic energy be shifted toward the longer period. Among these, the shift of seismic energy toward the longer period is induced by the viscosity and internal friction intrinsic in the soil. On the other hand, the amplification of shear waves can be attributed to the fact that the shear modulus is getting smaller toward the ground surface following the descending effective stress toward the ground surface. And the weakened intensity of soil as the number of attacking shear waves are accumulated can also contribute these phenomenon (Das, 1993). In this rationale, we constitute the numerical model using the model by Hardin and Drnevich (1972) for the weakened shear modulus as shear waves go on, and shear wave equation, in the numerical integration of which Newmark-β method and Modified Newton-Raphson method are evoked to take nonlinear stress-strain relationship into account. It is shown that the numerical model proposed in this study could duplicate the well known features of seismic shear waves such as that a great deal of probability mass is shifted toward the larger amplitude and longer period when shear waves propagate toward the ground surface.
Keywords: weakened shear modulus, equivalent PSD, lengthened shear waves, vertical type breakwater, seismic capacity evaluation
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