DESIGN AND CONSTRUCTION OF HIGHRISE BUILDING FOUNDATIONS(1) -85-STOREY T&C TOWER IN KAOSHIUNG
本文檢討位於高雄市苓雅區東帝士國際廣場大樓(T & C Tower)，地上85層地下5層之超高大樓基礎之規劃，設計至施工之考量過程與儀器監測結果。該大樓採用均勻對稱三管式結構，基礎則基於地層特性、施工技術、鄰房狀況與施工工法之考量而採用框格式地下連續壁牆，監測結果顯示大樓平均沉陷相當均勻在中央區約5-6公分，四周約3-5公分，地下水壓於營造至約35樓停止降水後，隨樓層之增高逐漸回升，於完成時回升至原地下水壓狀態。
This paper describes the process of design and construction and monitoring results of the foundation system for T & C Tower, an 85-storey highrise building with 5 levels of basements in kaoshiung, southern Taiwan.
The structure system design is a triple tube in series with 8 mega columns each to support loads up to 40,000 metric tons; Considering the soil conditions, construction techniques available at the time, safety of vicinity buildings and method of construction, a grid pattern of slurry walls underneath the floating raft foundation system was used. Monitoring results indicate that after completion of 85 stories, the settlements at the central portion and periphery of the building are 5-6cm and 4-5cm, respectively; while the ground water pressure at the bottom of the raft after stopping dewatering when construction reached 35F, it increased gradually towards its natural level as construction progressed towards 85F.
Evaluation of parameters is of great importance in the retaining and bracing system analyses of deep excavation. The sensitivity of the design parameters should be carefully handled and the improper construction behavior should be avoided to have the situation in control beforehand, although the safety of the bracing system is directly related to the quality of construction management and must rely upon monitoring system to thoroughly comprehend the excavation behavior.
This study is based on data from soil laboratory testing, construction arrangement and monitoring results in a site of Taipei basin . All the design parameters used in the analysis are examined one by one for the sensitivity study of the stress and strain in the retaining and bracing system.
Stability and deformation analysis should be preformed prior to excavation. This study investigates various factors affecting results of stability analysis. It is found that cohesion between retaining wall and surrounding soil is highly related to the stability analysis results. Based on ten case studies, reasonable cohesion between retaining wall and surrounding soil and factor of safety against push-in are obtained. Case studies also reveals that the method suggested by Specification for basal heave yields reasonable results. In addition, this study proposes a method to predict ground surface settlement induced by deep excavation. Case studies exhibits that the proposed method can accurately predict the ground surface settlement.
Diaphragm wall with buttresses is often used in deep excavation projects to reduce its displacement. The overall stability of excavation is increased as well. The behavior of buttress is a highly complicated one and of soil-structure interaction nature, which can not be easily modeled by commercially available soft wares. As a result, some simplifications have to be adopted in order to analyze and design the buttress. It is suggested that the buttress be regarded as a certain type of soil improvement. The existence of buttress increases the equivalent stiffness and strength parameters of soil within excavation zone. The displacement, moment and shear of the diaphragm wall are reduced as a result, and the amount of reduction is pending on the number, length and depth of the buttress. Buttress is built the same way as the diaphragm wall, and the construction quality has a profound effect on its field behavior. It is noted that the joint between buttress and diaphragm wall has to be carefully constructed to ensure that the buttress behaves as originally conceived.
The objective of this study is to develop a simplified method to better evaluate the ground settlements caused by deep excavation in clay. The proposed method differs from others by incorporating the effects of small strain on the elastic soil modulus. Three field cases located in thick clay layers are then analyzed. Analytical results show good agreement with the measured results, including ground settlements and wall displacements. The proposed method also provides a reasonable tool for the evaluation of subsurface soil settlements induced by excavation.
This paper is to evaluate the effect of strength anisotropy on the current design method on the base stability of deep excavation in clay. Basically, the current method is an isotropic strength method and does not consider the effect of strength anisotropy. However, the direction of major principal stress changes along the slip surface beneath the base of excavation. To evaluate the effects of soil strength anisotropy on the calculated factor of safety against basal heave, an anisotropic strength criterion for soft clay is adopted here. After combining this strength criterion with the failure mechanism of the current design method, a modified method for analyzing the base stability of excavation can be established. The suitability of the proposed method has been verified by comparing with the numerical study results of deep excavations in Boston and a base failure case in Taipei. Finally, the results obtained from the proposed anisotropic strength method and the current isotropic strength method are compared. The range where the strength anisotropy of clay has little effect on the result calculated from the isotropic strength method under vavious construction conditions are identified also.
The Chung-Ho line of Taipei MRT system from station O18 to station O19 are connected with two bored tunnels. The outer diameter of the tunnel is 6.1 m and the average length 242m. The bored tunnels begin as two stack single tunnels leaving station O18. The stack tunnels entering the station O19 by changing to side-by-side tunnels with the curvature radius 200m and 210m respectively. The overburden of the tunnels varies from 10 to 13 m. The clearance between two tunnels varies from 4 to 4.5 m. The twin tunnels run underneath the existing old buildings.
Two test grouting works were carried out in the clay layer prior the tunneling work, to ensure the integrity of the building and reduce the settlement. Two test grouting works included the single tube, double tube and triple tube grouting program and the horizontal directional drilling (HDD) program. Both methods are not suitable for the project after reviewing the test results. Finally the secondary compensation grouting system of tunneling were adopted and the tunneling work was finished successfully.
This article presents these three methods of soil improvement, the method statement, construction sequence, parameters and monitoring results to serve for future engineering practice of tunneling works.
In Taiwan, diaphragm walls have been the most commonly used retaining walls for deep excavations in both private construction sites and major public construction projects (e.g. MRT, TRUC, etc.).
Deep excavations have been successfully undertaken using soil mixed pile walls (SMPW) as retaining walls in Japan. Limited experience of SMPW in the areas of data monitoring, back analyses and research have meant that SMPW are rarely adopted in Taiwan,
This paper presents a case study of deep excavation site in central Taiwan, where SMPW is used as a retaining wall for deep excavation. Design concepts and the considerations on retaining wall system, together with safety evaluation and protection measure design for adjacent buildings utilizing soil improvement are introduced.
In addition, construction procedures and remedial measures for the accident are also presented. Comparisons between a monitoring system and a back analysis are also summarized in this paper. The aim of the paper is to help contractors and consultants who may wish to undertake similar projects in Taiwan in the future.
This study presents different types of structural configurations with diaphragm walls, and the variations of structure and their loading condition corresponding to each stage. The structural behavior of a permanent diaphragm wall, which is the condition now commonly used in current analysis, is also discussed.