The construction of bridges passing through steep hillsides is an inevitable trend in Taiwan. There are several disadvantages of the traditional foundation excavation method, including a larger excavation area, a higher cost and significant environmental impacts. In this project, tender no. DE01 of airport access MRT system , “Bamboo Shape”excavation and support method was used at steep slopes to reduce the disturbance range. Because of the confined working space of this method, the impact to environment can also be reduced to a minimum. Therefore, in the aspects of landscape preservation, environmental protection, constructability, control of project cost and safety and so on, this method is superior compared to traditional methods. This method can also be considered as an alternative for excavations at steep slopes and enhancing the construction technology of bridge foundations.
To comply with the requirements of Taoyuan underground railway project, the crossover elevation of Taoyuan Airport MRT Extension Line has to be lowered by 3.21m, but the diaphragm wall of the crossover area had been completed according to the original design. To ensure the safety of excavation, we have to add the strutting and cross walls in crossover excavation area. The crossover excavation area is located at downtown, there are lots of stores on both sides, so we use full-casing secant piles to replace diaphragm walls, and adopt a two-phase construction scheme to reduce the influences on traffic. In addition to reduce the displacement caused by deep excavation, the strutting has to be promptly installed immediately after excavation and it will help in reducing the deformation of adjacent buildings. Automatic monitoring system is also used in order that appropriate emergency measures can be implemented in time to ensure the safety of adjacent buildings and utilities.
In recent years, construction of Taipei Mass Rapid Transit (MRT) underground stations has led to many cases of deep excavation which has also enhanced the technology of deep excavation. In this article, the case study on deep excavation for the construction of Nanjing Sanmin Station of Songshan Line of Taipei MRT will be discussed. We will report the design analysis of the deep excavation and the considerations taken for nearby structural protection. On-site monitoring data were compared with the predictions from our analyses. To protect the nearby structures, buttress-wall type ground improvement was considered. Both the analysis results and monitoring data showed that the deformation of the wall with ground improvement was smaller than that without improvement. This suggests that buttress-wall type ground improvement is an effective way to reduce deformation of nearby structure caused by deep excavation.
Verification of Back Analyses of Deep Excavations and Applications of Wall Deflection Paths
Moh and Hwang (2005)建議將各開挖階段擋土牆的最大側向位移與開挖深度的關係以雙對數之方式圖示之，並命名此關係式為「位移路徑」。本文以台北捷運板南線善導寺站開挖為例，分析連續壁的側向位移、並建立足以代表台北盆地T2地質分區之「參考位移路徑」，用以量化土壤強度、開挖區寬度、連續壁厚度、以及地中壁以及鄰近結構物對連續壁側向位移之影響。而後，再以小南門站及其東之明挖覆蓋隧道開挖過程中所得監測資料驗證分析所得結果。此外，並以新加坡尼誥大道崩坍案例，作為設計及施工品質影響連續壁側向位移之佐證。同時，以京華城開挖為例，比較逆打工法施作所得側向位移較順打工法施作所得側向位移之不同。這些實例證明連續壁位移路徑的確可作為研判連續壁行為的有效工具。
Structures adjacent to excavations were often damaged as a result of ground movements mainly due to the deflections of the retaining walls of the excavations. Therefore, it is vital to identify the factors affecting wall deflections and quantify their influences on wall deflections.
Moh and Hwang(2005) suggested to plot the maximum wall deflections obtained in various stages of excavation versus the depths of excavation in a log-log scale and designated these plots as wall deflection paths. Back analyses were performed for the wall deflections obtained at Shandao Temple Station of Taipei Metro and established the reference wall deflection path for this site and for the T2 Zone of the Taipei Basin. The influences of soil strength, width of excavation, and thickness of wall on wall deflections are quantified. The results obtained were verified by the wall deflections observed at the cut-and-cover section to the east of Xiaonanmen Station. In addition, data obtained at the cut-and-cover tunnels along Nicoll Highway of Singapore Metro and those obtained at the excavation using the top-down method of construction at Core Pacific City in Taipei were used to illustrate the applications of the concept of wall deflection paths. Based on the data presented, it is concluded that the wall deflection paths are indeed useful in the evaluation of the performance of retaining walls in deep excavation in soft ground.
In early construction of Taiwan Mass Rapid Transit (MRT), shield tunnel method was majorly applied in soft sediment layer. Due to development and expansion of urban areas, shield tunnels were constructed to pass through rivers, foothills and gravelly layer which are commonly found in the terrace. In Taiwan, there are several shield tunnels traversing through gravelly layer, such as Taiwan Power Company’s underground electric transmission system, sewage pipe system in Science-based Industrial Park, and the 7.2-kilometer shield tunnel for Taoyuan International Airport MRT (Project No. CU02A). Using the planning, design and construction experience of the shield tunnel for Taoyuan Airport MRT, this article will report 1. the geological survey of the gravelly layer, 2. design consideration, requirement and construction difficulty, 3. design and selection of shield machine, 4. construction planning and management, 5. feedbacks and advices for future shield tunnel construction in gravelly layer. We hope that the experience shared in this article can provide insights for future design and construction of shield tunnels that shall pass through gravelly layer in Taiwan.
This paper presents a failure case which took place during the construction of shield tunnels at Ventilation Shaft A of Panchiao Line of Taipei Rapid Transit Systems (Project No. CP262). When advancing the tunnel face for the up-track tunnel, piping suddenly occurred and there was influx of high-pressure groundwater (along with subsoils) into Shaft A. The surrounding ground settled by as much as 5 m and the tunnel boring machines for both up and down-track tunnels were flooded. In this paper, the following aspects of the construction project CP262 and the aforementioned accident are reported: general project brief, geological and geotechnical conditions, operations performed at the tunnel-shaft interface prior to the accident, emergency rescue actions taken by the contractor, damage assessment, failure investigation and analysis, and restoration and rehabilitation of the shaft and tunnels. Based on the investigative studies, the accident may be due to the following causes (which may occur concurrently): presence of drift woods in the improved ground (by soilcrete) around the tunnel, non-verticality of routing rods, and the cleavage between soilcrete and the diaphragm wall at shaft A.
New Ziqiang Tunnel is located in the East Rift Valley of Taiwan. The tunnel, which is 2,667 m in length and 11.3 m in width, is a single-tube double-track railway tunnel traversing the Wuhe Terrace. In general, the thickness of the overburden ranges from 10 m to 95 m. Besides, the tunnel passes through the LunShan Slate, Wuhe Conglomerate, YuLi Schist, and a silt layer with thickness of 10 m or more. The silt layer is known to be an extraordinarily poor stratum in Taiwan. The tunnel construction project began in January of 2010. Serious cave-ins, squeezing, and groundwater inflow were encountered when advancing the tunnel through the silt layer. By using countermeasures such as central pilot tunnel method, pre-reinforcement of tunnel heading, compound grouting and mini bench cut, the tunnel was successfully advanced through the 300-m long silt layer in December of 2015. The construction of New Ziqiang Tunnel is considered to be a valuable engineering experience as it is very rare for a tunnel to extend across a silty layer. In this paper, difficulties encountered during the construction of New Ziqiang Tunnel and countermeasures taken to overcome such difficulties are presented.
Tunnel maintenance and management tasks are aimed to identify the variability or development of anomalies that affect tunnel service, and evaluate their influences on tunnel functionality, serviceability, structural safety and durability in order to respond in accordance with the idea of sustainable development as soon as possible. To achieve the goal of complete life cycle maintenance and management for modern railway tunnel, factors including the surrounding environment, geological conditions, construction quality, conditions of lining structure, possible loading variation during operation, requirements for maintenance and management were all considered to outline the basic requirements to serve as a reference for tunnel maintenance, management and inspection . This outline can further be modified according to specific needs and conditions to incorporate supporting measures and detailed commentates. This paper provides a report of the state-of-the-art progress and preliminary application of this guideline in Taiwan.
The implementation of maintenance and management strategy for MRT structural facilities has gradually become a critical issue for the operations management unit of rapid transit corporation in recent years. This article firstly elaborated the theory of total life-cycle maintenance and management for structural facilities, which includes definitions of different types of maintenance management, workflow process of maintenance management, data feedback mechanism, as well as the initiation and promotion of maintenance management concept during the completion stage of new facilities. This article
then explored the design of data warehouse for facility maintenance and management, as well as the functionalities of the management system. To demonstrate how maintenance strategy and practice can be integrated in the maintenance and management of MRT structural facilities, a shield tunnel structural inspection project conducted by the Taipei Rapid Transit Corporation utilizing LiDAR scanning will be discussed in this article.