• The Journal of the Acoustical Society of Korea
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• v.35 no.6
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• pp.480-490
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• 2016

As wind turbines become larger and lighter, they are likely to respond sensitively by dynamic loads applied on them. Since the responses at resonances are particularly interested, it is required to be able to predict natural frequencies of wind turbines reliably at early design stage. To achieve this, the foundation-soil analysis is needed to be carried out and a finite element approach is adopted in general. However, the finite element approach would not be appropriate in early design stage because it demands heavy efforts in pile-soil modelling and computing facilities. On the contrary, theoretical approaches adopting linear approximations for soils are relatively simple and easy to handle. Therefore, they would be a useful tool in predicting a pile-soil interaction, particularly in early design stage. In this study an analysis for a pile inserted in soil is performed. The pile and soil are modelled as a beam and continuum medium, respectively, within an elastic range. In this analysis, influence factors at the pile head for lateral loads are predicted by means of this continuum approach for various length-diameter ratios of the pile. The influence factors predicted are validated with those reported in literature, proposed from a finite element analysis.

• Journal of the Korean Geotechnical Society
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• v.33 no.2
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• pp.17-26
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• 2017

Pile foundations that support offshore structures or transmission towers are dominantly subjected to cyclic lateral loads due to wind and waves, causing permanent displacement which can severely affect stability of the structures. In this study, a series of cyclic lateral load tests were conducted on a pre-installed aluminum flexible pile in sandy soil with three different relative densities (40%, 70% and 90%) in order to evaluate the permanent displacement of a cyclic laterally loaded pile. Test results showed that the cyclic lateral loads accumulated the irreversible lateral displacement, so-called permanent displacement. As the number of cyclic lateral load increased, accumulated permanent displacement increased, but the permanent displacement due to one loading cycle gradually decreased. In addition, the permanent displacement of a pile increased with decrement of relative density and decreased by soil saturation. From the test results, the normalized permanent displacement defined as the cumulative permanent displacement to the initial permanent displacement ratio was investigated, and empirical equations for predicting the normalized permanent displacement was developed in terms of relative density of the soil and the number of cyclic lateral load.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.34 no.5
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• pp.144-155
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• 2022

The Korea Coast Guard evaluates the risk of major coastal activity places to prevent coastal accidents, and patrols and manages them based on that, but it is not responding properly to the continuously increasing number of coastal accidents. The reason for this is that, despite the gradual expansion of coastal activity places, there is a lack of manpower to manage and supervise them, resulting in blind spots in coastal accident safety management. Therefore, in order to solve this problem, it is necessary to prepare more efficient and effective measures that check and supplement the current coastal safety management system. Coastal accidents show different characteristics of accident causes and places due to differences in the activity characteristics of users according to time. As a result of analyzing coastal accident data (2017~2021), the frequency of daytime accidents is high in the case of sea rock, beach, and offshore, where family leisure activities are frequent. In the case of wharf, tidal flat and bridge, where accidents due to drinking, disorientation, and suicide mainly occur, the frequency of accidents at night is high. In addition, there were more accidents on weekends when the number of users increased compared to weekdays. This trend indicates that the user's temporal activity characteristics must be reflected in the risk assessment of coastal activity places. Therefore, in this study, based on the case of coastal accidents, the characteristics of accidents at coastal activity places according to time were identified, and the criteria were presented for risk evaluation by grading them. It is expected that it will be possible to lay the foundation for reducing coastal accidents by efficiently managing and supervising coastal activity places over time using the presented evaluation criteria.

• Journal of the Korean Geotechnical Society
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• v.26 no.11
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• pp.63-73
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• 2010

Monopiles, used as one foundation option for offshore wind turbines, are usually subjected to great cyclic lateral loads due to wind and wave. In this study, model pile load tests were performed using calibration chamber and three model piles with different pile lengths in order to investigate the behavior of laterally cyclic loaded piles driven into sand. Model test results show that the first loading cycle generates a bigger displacement than the following ones, and the permanent displacement of piles by one loading cycle decreases with increasing the number of cycles. 1-way cyclic loading causes the permanent displacement in the same direction as cyclic loading, whereas 2-way cyclic loading causes the permanent displacement in the reverse direction of initial loading. It is also observed that the permanent displacement of piles due to cyclic lateral loads increases with decreasing relative density of soil and with increasing the magnitude of cyclic loads. However, it is insensitive to the earth pressure ratio of soil and embedded pile length. In addition, based on the model pile load test results, equations for estimation of the permanent lateral displacement and rotation angle of piles due to 1-way cyclic lateral loads are proposed.