During August 06～09, 2009, Typhoon Morakot brought breaking records of rainfall and discharge both over 200-yr return-period. Large-scale debris flows occurred along both banks of most wild creeks of three tributaries in Gaopin River basin. Many serious disasters of the landslips, floods and bridge damages occurred in Gaopin River basin. Therefore, the purpose of this study is to collect the database of these bridges that damaged during Morakot typhoon, and also to focus on the analysis of disaster cause and damage process of these bridge structures. According to the investigation, very complex multi-hazard encountered, including debris flow, debris dam break flow, massive rafting upon pier or girder, scour induced by very torrential flood.
Kinmen Bridge is a cross-sea bridge going across the Kinmen channel and then linking Kinmen and Lieh-yu island. Taking into account the water depth, the bridge is divided into three sections which are main section, side section and approach section, respectively. The road corridor, configuring the main section and side section of bridge, will cross over the widest trench area of about 1.6km in length. In the deep trench area, the middle tide water level depth at bridge pier ranges from 15m to 20m. In consideration of the influence factors, such as structure type, marine conditions, geology, corrosion, landscape, construction conditions, workability, working period and budget, the comprehensive study has been done to select the most appropriate foundation type at the deep trench area. In addition, Kinmen is located at the geology of granite and the depth of overburden is dramatically changed which has greatly increased the difficulties in the engineering practice. Taiwan has no such experience before so that Hong Kong specifications possessing the experience with granite geology have been taken as the basis for the reference in the analysis and design.
The geology of Taiwan is complex, and the terrain is steep. The rivers are short and steep, and the rainfall is concentrated. Under extreme climate condition, in order to satisfy the requirements for bearing capacity, settlement, scouring and earthquake resistance, the bridge foundation has increased in size and depth. The design of bridge foundation faces major challenges, including scouring, foundation selection, deep excavation, limited working space, underwater construction, piling in gravel and rock, etc. This article explains the current problems of river bridge foundation in Taiwan, and three case studies on foundation design are presented here for reference.
In the past decades, the heavy rain frequently caused the scoured bridges collapse during typhoon period in Taiwan. To get a better warning system, this paper first concluded three fundamental parameters including the water level, the scoured depth of the bridge foundation and the flood velocity sensitive to the failure of the bridges and proposed an analysis process in determining the safety level.
In this study, various possible failure modes of the pile-foundation and caisson-foundation were classified and employed as the check-point of the governed issue during the analysis. Through the 3D finite element software of MIDAS-GTS, the stresses concerned during various situations of scoured riverbed are able to be determined and, accordingly, the most possible failure mode of the bridge foundation can be detected through the choice of minimum ratio of capacity to stress. As a result, different kinds of safety level represented by the surfaces composed of the parameters could benefit the bridge engineers a good decision making on management of the scoured bridges.
Bridges in Taiwan usually confront flood challenges induced by typhoons and storms. The keys of flood mitigation for bridges are associated with both integrating relevant professional knowledge and evaluating flood resistant capacity efficiently. This paper reviews the researches and their trend related to flood resistant capacity for bridges in past decade. This paper integrates current hydraulic, structural, geotechnical, and inspection professional knowledge and establishes archives and quantitative evaluation technology for assessing flood resistant capacity. A cause investigation on Shuang-Yuan Bridge is given as a demonstrative example to describe the proposed evaluation method in detail. Quantitative evaluation of flood resistant capacity on bridges is linking as a continuous numerical simulation chain initiating from one-dimensional and two-dimensional hydraulic computations, fluid-solid coupled simulation, to stability analysis on bridge foundations. Alert and critical state charts for bridge flood resistant capacity are action indices for defining current bridge performance based on tri-parameters, scouring depth, representative velocity, and representative stage. The future applications are also mentioned.
With the expansion of transportation network, the number of bridges has been increasing in Taiwan. The design and construction technology of bridge building have become more mature and the awareness of maintenance has been raised. Old bridges are under long-term management for safety and endurance in order to fend off potential disasters. Furthermore, Taiwan is prone to earthquakes, typhoons and floods; overloaded vehicles are also an issue to be considered. To understand the cause for anomalies and deterioration factor, it is imperative for highway administration agencies to establish an effective system of examination and maintenance. The study used substructure replacement of Wanda Bridge as an example to explain safety evaluation and improving methods for bridges, so that readers will have a better understanding of currently enforced bridge management, as well as flood- and earthquake-prevention and reinforcement. The study also hopes to serve as a reference for bridge management in the future.
This paper will use the Cheng-Kung porous basket (CKPB) structure to reduce the pier scour depth. The method tested and verified is a good effect to protect the pier against scour. Now, we will apply the CKPB to the Tai-Po Bridge located at the Jishuei River. The CKPB is set upstream the pier with a triangle shape according to the flow direction. The set of the CKPB has six piles and 2 m height. From 2009 to 2010 it was gone many large flows and two typhoons, Morakot and Fanapi. The results show a better protection for the piers against scour. The piers can be impacted with a low velocity when the flow passes through the CPKB. The level of the bed bottom at pier is higher than at the main channel. The high velocity flow passes through among two piers and the low velocity flow happens at the upstream pier. The piers are stuck nothing because many drifters are obstructed by the CKPB.
A bridge-closure procedure was proposed in this research because some cross-river bridges collapsed and caused casualty due to the foundation scouring in the typhoon events. Three major processes were performed including (1) one- and two-dimensional hydraulic simulations; (2) the structure analysis and (3) the eroded depth around the piers. According to the past experience, closing a bridge takes two hours in average, therefore, the warning water stage is defined correlating to the increasing rate of the water stage. Finally, the procedure developed in this research has been implemented on two bridges and properly works.
Ground anchors’ damage behaviors are complicated and influenced by multiple causes. Although at the initial stage the damage causes can be detected from visual inspect of structural appearance changes, they, as the complete generator to damages, are not easily diagnosed and their degrees are also hard to be recognized by single equipment. Due to the above reasons mentioned, damages occurred without pre-warning. In view of this, to prevent the future occurrence of damages to anchor slope and anchor supported structure, the ground anchor’s safety and function evaluation at its usage stage becomes more important. By simultaneously applying lift-off test and acoustic monitoring test, this study explains the application of acoustic monitoring technology in defects diagnosis and damage pre-warning. Other than this, this study uses numerical modeling and signal processing to discuss in a broad sense the relationship of anchor damages with the parameters change in anchor design practice, development of anchor disaster, and signal characteristics. Finally, this study illustrates the research results, expecting to be as reference for future anchor’s maintenance and damage pre-warning.