博士 / 國立臺灣海洋大學 / 河海工程學系 / 101 / The sandy sediments filled with Taiwan western marine area, along with accelerating climate change in recent years caused the occurred frequency increasing of extremely waves. Due to sea level rise and the typhoon disasters, it could be caused the pore pressure of seabed may be sustained a build-up state below the coastal structures, and occurring and increasing the risk of the seabed liquefaction.
Therefore, the purpose of this study is to establish a typhoon wave type for Taiwan environmental characteristic, and understand the dynamic behavior of seabed subjected to multi-directional stresses combined with torsional shear stress. Meanwhile, a prediction model of pore pressure accumulation for seabed under long-term wave loading is also established, and it can assess the liquefaction potential under different time of cycles.
Most of the past related researches followed the relevant theory to study cyclic wave loading, including wave induced the single external stress or internal stress, number of cycles in seabed, and pore pressure generation model for earthquake mechanism. Therefore, the "Zone A" of Kaohsiung Harbor Intercontinental Container Center at second stage project is selected as this study area. And this study discusses and analyses these research findings, and the results can be suitable for the marine environment in Taiwan.
Hence, this study first collects and investigates the wave data during each typhoon attacked period. It makes the adopted typhoon wave duration to increase the accuracy and regionality. Based on the collection of wave data, we study and carry on the assessment of Taiwan typhoon wave type, and make sure the number of cycles, wave characteristics, and wave duration under cyclic typhoon wave loading. The equivalent loading can be obtained by number of cycles, and can be converted into stress condition and joint with the automatic control software system of Triaxial Cyclic Testing System.
Secondly, based on the parameters and characteristics of seabed soil, we consider the influence between different dynamic stress and bearing capacity, including vertical stress, horizontal stress, torsional shear stress and pore water pressure. A series of triaxial cyclic tests can simulate the wave loading, and deep understand the behavior of pore water pressure under different drained conditions. A pore pressure generation model for seabed under wave loading can be established.
On the other hand, this study compares relevant testing results with existing related theory. The applicability of existing theory can be understood and also discussed to investigate not considered factors in existing models. In addition, an evaluation method for liquefaction potential in seabed is established, which is based on pore pressure generation model by this study proposed to understand the variation of liquefaction depth under different time of cycles.
By use of the measured data to draw wave height distribution, the local typhoon wave type diagram was established in Taiwan marine areas. On the basis of typhoon wave type assessment, we can obtain the ladder type in Long-Dong, Chiku and Eluanbi, the triangular type in Hualien. With the regional differences, the number of typhoons cycles is about from 800 to 1320 cycles, the number of equivalent cycles is about from 267 to 440 cycles. The research results can provide to the coastal structure design and cyclic triaxial test applications in the laboratory.
From the related cyclic triaxial test results indicated that when the specimen is subjected to a horizontal torsional shear stress, the 3-D cyclic tests occur liquefaction failure average about 152 secs under undrained condition, i.e., Nc=13.2 when period is 11.5 secs. And the build-up value of pore pressure average is about 48.5 kPa. Similarly, the 3-D cyclic tests occur strain failure average about 1009 secs under drained condition, i.e., Nc=87.7 when period is 11.5 secs, and the build-up value of pore pressure average is about 46.9 kPa. It can be shown the torsional shear stress is an very important factor for wave induced seabed failure, and can be taken into account when a theoretical model assumptions and triaxial test simulation in the laboratory.
This study proposed an pore pressure accumulation model for seabed under long-term wave loading by the hyperbolic sine function, and suggest a testing parameter to predict the curve of pore pressure under different test conditions as Tp=0.005, 0.05 and 0.5. The model can be applied in assessment of wave induced seabed liquefaction potential. The maximum possible liquefied depth is about 4.6m when Tc=3200s in this study area, and provide the well marine geotechnical practical application for seabed stability.
| Identifer | oai:union.ndltd.org:TW/101NTOU5192022 |
| Date | January 2013 |
| Creators | Wen-Chien Tseng, 曾文謙 |
| Contributors | Lien-Kwei Chien, 簡連貴 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 217 |
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