Often foundation construction of urban renovation projects would encounter difficulties including limited workspace, complicated interfaces with adjacent buildings, and risks of demolishing existing foundations. These decadent factors are not only challenges for design, but also for safety monitoring and construction management. In this paper, the authors are in an attempt to raise such design and construction issues and to provide available construction technologies and countermeasures. It is hoped to be helpful to engineers in practice.
After several decades of urban development, the less of original land suitable for new building, the more of demand for reconstruction of old building. In Taipei, there have accumulate quite a lot of renewal projects, in these cases, the main geotechnical problem is how to construct the new retaining wall or pile and demolish the underground structures of old building safely. In general renewal cases, the underground part of existing structure was treated as obstruction, therefore the main engineering technology issue is the eliminating of obstacles and influence on ground and neighboring buildings as new retaining wall is constructed. The case studied is a less than 20 years old building with a basement not much difference between the new building, for this reason, the design concept of new basement not regard existing basement as obstruction but utilize the existing basement to form a combined retaining wall for new basement excavation. The new basement construction is firstly keeping the same basement depth with existing one to take advantage of utilizing most part of the old slurry wall to connect old basement structures of the old building to complete excavating new basement without braced system. Because it would increase the degree of difficulty and technical requirements under the condition that the new and old basement 75% overlap, the construction process has to reuse old basement as much as possible, such as reusing for slurry and waste pits and staff lounge. This article illustrates the design and construction principles and the solutions in the reconstruction in this renewal project.
The government urban renewal policy proposes that many residential or business buildings that were built twenty to thirty years ago in Taipei city are to be renewed. Planning and construction of the foundations of these to-be-renewed buildings is influenced by the existing foundation of the old structures and retaining structures, such as slurry walls or drilled shafts.
This paper reports a building renewal case in Taipei. The building site has an area of 900m2 and is divided into two parts. On one side of the area is an old building with a single-story basement and on the other side of the site is a ten-story building with a two-story basement. The ten-story building has a total perimeter of 70m and a foundation that reaches 10.4m below the ground surface. The slurry wall of this ten-story building is 60cm thick and 17.5m deep. The newly planned building has a total perimeter of 111.5m and is 15 stories high, with a six-story basement. The foundation will use the Top-down method to excavate down to 23.5m deep and incorporate a slurry wall that is 90cm thick , 46.7m deep and uses barrette piles that are 90cm thick, 2.5m wide and 57m deep. The construction of the new building has some difficulties, such as the conflict between the old and the new slurry walls, highly permeable sandy soils and a very limited working space between the new structure and the neighboring building. The planning and construction procedures are detailed in this paper. The monitoring System and slurry wall deflections are also presented in this paper. The 3-D corner effect has a great effect on the slurry wall deflections.
In recent years, top-down method is often adopted to construct basement for high-rise buildings in urban area. In these cases, huge column loads are often encountered that requires the use large diameter bored piles in conjunction with the installation of steel column at the stage of pile construction. Another major pile construction issue for urban renewal project is how to overcome the obstacle presenting by the existing old basement structure.
This article outlines possible difficulties that may be encountered when constructing piles on top of existing basement structure, either by reverse circulation drilling, cased drilling, long-bucket grabbing, or earth drilling method. Solutions or measures to overcome these difficulties are also provided. Other details, including the removal or strengthening of existing basement structure, borehole collapsing prevention, installation and adjustment of steel columns are also addressed.
MRT construction in the metropolitan area inevitable involved underground construction. However, land acquisition for the space of the entrances and ventilation shaft of underground station is difficult. This paper presented a case study of MRT station design which the entrance and ventilation shaft were jointly developed with private landowners. Because the MRT entrance and ventilation shaft were close to buildings, the bottom sealed grouting, protection measures, and instrumentations were used to keep the safety of nearby buildings, reduce the time and the risk of construction. The joint development of MRT entrance and ventilation shaft not only increased the convenience using the MRT but also improved the urban landscape. Apparently, this is a win-win benefit strategy.
The Nangang Extension Project of underground railway engineering in Taipei City was finished in 2008. The railway in Taipei area has been transferred to underground operations. This achievement made a significant upgrade of urban transportation, environmental landscape and economic benefits. Nangang Underground Railway Station, containing Taiwan railway station, high-speed rail station and connection passage to underground MRT station, is not only the biggest engineering of this project, but also the largest station in Taipei. In addition to transportation purpose, it combines with shopping mall and commercial hotel to provide complete functionality of a modern station.
This article describes the planning concept of the station and the prepared the ground for the future development. The technical problems and solutions associated with the geotechnical engineering during the construction process are highlighted.
The main design criterion of deep excavation is to minimize the influence to the nearby building. From recent experiences, engineers could adopt soil improvement or increase the supporting system stiffness to reduce ground deformation and settlement. This paper introduces case study of a deep excavation site in Kaohsiung. The site is near a square shape with a dimension of about 73m. The maximum excavation depth is 20.2m. There are no adjacent buildings. During the excavation, the maximum accumulated deflection of slurry wall is about 14.0cm, and the maximum settlement is 13.94cm. Referred to other deep excavation cases, the amounts of the deflection and settlement measured in this site are very large. The loosely packed silty fine sands behind the slurry wall may be one of the main causes of the measured large deformation. Significant local failure zone was developed during excavation. Accordingly, the strength and stiffness of soil reduced within the local failure zone. Besides, the large excavation width may be another important cause of the measured large deformation. Based on this valuable case history, suggestions for analysis and design of deep excavation were proposed.
In recent years, cross walls and buttress walls are extensively used in deep excavations in an effort to reduce the lateral deformation of diaphragm wall. This paper presents a deep excavation case, which is close to MRT Xindian line and Zonnghe line, that is very sensitive to excavation induced deformation. In this case, diaphragm walls, cross walls, buttress walls and barrette piles are all incorporated to optimize the design in minimizing the excavation induced deformation and foundation settlement. As indicated by inclinometer readings, the displacements of diaphragm walls are well within the design values. Since this site was heavily affected by 3D effect, we tried to establish a simplified approach that use 1D FEM program (TORSA) in conjunction with Plane Strain Ratio (PSR) chart or the corner effect to estimate the displacement of diaphragm at various locations. It is hoped that this approach can be used in similar urban excavation cases to better predict the possible wall deformation.
It is not uncommon to use sheep piles as the retaining structure for deep excavations in southern region of Taiwan, though the vibrations induced by installation of sheet piles often results in damage to adjacent buildings. A new installation technique that induces relatively low vibration levels has been adopted in recent years, which greatly enhances the capability of sheep piles to serve as the retaining wall for deep excavations. This paper presents a deep excavation case in southern Taiwan. Details as vibration and noise mitigation of sheet pile installation, budget and construction schedule control of the overall project, etc., are addressed. The inclinometer readings are also delineated by the use of TORSA2 computer code to reveal the difficulties and blind spots that may be encountered in design stage.