據說營造廠有三件害怕的事情，一是深開挖，二是搭鷹架，三是交屋。深開挖忝為其首，尤其是都會區中的深開挖更是令人寢食難安，深怕會有想像不到的狀況產生。但根據莫非定律(Murphy′s Law)所言，凡有可能出錯的事情必然會出錯(Anything that can go wrong will go wrong)，都會區的深開挖也難逃莫非定律的魔咒，甚至不可能出錯的事情也會出錯。姑且不談由莫非定律主控的工程實務，純由學術研究的角度而言，深開挖是一個引人入勝的主題，複雜的土壤依時行為、三向度效應及多變的施工程序，乍看之下似乎可以用高階之土壤組成律配合高等數值分析程式解決之。但現場有太多牽一髮動全身的施工細節，致使分析結果與實際行為始終有所出入。施工細節的變化可能使開挖實際行為比預期結果來得好、變得差、或者完全脫離設計者或施工者的掌控。也因為施工細節的變化，每個深開挖工地都是獨一無二的，你必須帶著分析程式、走進工地、待在工地、注意所有的細節、看著每階段的變化、不斷的累積及修正開挖經驗，或許有一天你終會了解深開挖。
The site locates near Kaohsiung Harbor area, the characteristics of site geology is soft and loose soil with high and tide-influenced ground water table, The soil is mainly composed of slity sand, sandy silt and clayey silt stratum mixed with sandy silt layer. This paper illustrates an actual case on deep excavation for a high-rise building in seafront area.
The project is a 41-story high-rise building with 5-level basement, the basement was built by top-down construction method. Diaphragm wall with cross and buttress walls, which connected to the B4F slab, is adopted to reduce the
deflection of diaphragm wall and enhance the stability during excavation. The steel column embedded in 75-meter-long barrette piles were used to support the whole steel structure. A pile test for the barrette pile was conducted at site to
ensure adequate capacity. In addition, the bore hole data were reviewed to understand the possible permeable layer, and the pumping test was carried out at site to obtain the relevant hydraulic parameters in order to design additional deep
wells to deal with the ground water issues. This study would be a good reference for the design and construction of similar difficult project near Kaohsiung Harbor area in the future.
The needs for urban building are especially big in recent years. Though most of the core areas have already been highly developed, it still cannot fulfill the needs and lead to the sky high costs of the land as well as building. Due to the scarcity and the high cost of the land, many new developing projects have spread from the plains into the foothills. And construction with deep excavation with ground elevation difference is inevitable.
This article uses a real case on the deep excavation with ground elevation difference to demonstrate the complexity and variability on design, analysis, and construction in the geotechnical engineering issues on stratigraphical distribution, retaining structures, strutting systems etc., compared to those projects on the same ground level.
Case Histories on the Narrow Lane Effects for Deep Excavations in Urban Area
本文討論都會區深開挖工程一類較為異常之現象，即所謂之「窄巷效應」(Narrow lane effect)。窄巷效應乃是因都會區相鄰深開挖基地間往往僅有一巷之隔，兩基地開挖之主被動區交互重疊，且土壤受到兩次擋土及開挖作業之擾動，致使後施工開挖基地之擋土結構變位遠大於預期，且兩深開挖基地間窄巷之地表沉陷較經驗值亦超過甚多。就土壓力理論而言，兩基地間所夾之土壤為有限寬度之土體，且受巷道兩側擋土牆之束制，其作用於新建工程擋土牆之土壓力應低於理論主動土壓力，故新建工程窄巷側之擋土壁側向變位應低於預期，而壁體變位所引致之地表沉陷亦應低於預期。但有某些相鄰深開挖工程所表現之行為與預期狀況相反，窄巷側之壁體變位及地表沉陷皆遠超過其他側之數值。本文以實際案例呈現窄巷效應所造成之影響，希能提供學術研究及設計者對深開挖行為分析的新思考方向。
This paper presents a less known phenomenon in the field of deep excavation, namely, the narrow lane effect. The narrow lane effect describes the overlapping effects on the active and passive pressures of two adjacent deep excavation sites separated only by a narrow lane. As noted in the field, the lateral deformation of retaining wall and the associated ground settlement as a result of the narrow lane effect often exceed the empirical values by a large margin. It is a general belief that the soil mass sandwiched between two adjacent sites tends to yield less active pressure compared to that of an unconfined soil mass, and as a consequence, the resulting lateral wall deformation and ground settlement should be less than expected. However, the field behaviors of some deep excavations show the contrary, wall deformation and ground settlement on the narrow lane side are much higher than other sides free of the effects of adjacent basement. This paper presents case histories that exhibit narrow lane effects. It is hoped that these data serve as a good reference to designers and can be used by academic field as a basis for future researches.
Underground railway is an important index for a city step toward modernizing. Because of densely population, build-up area and small hinterland in urban area, the safety of construction and time management should be specially considered in design stage. Domestic underground railway in general is to adopt the cut and cover method, which is against the operating TRA railway. In order to protect guide ditch of diaphragm wall and to ensure safety of deep excavation, there
are some measures adopted including 1) using CCP to protect guide ditch of diaphragm wall at intersection and bridge pier; 2) working out small unit of diaphragm wall to shorten work schedule; 3) all panels covered with canvas to reduce interfacial adhesion between clay and diaphragm wall; 4) embedded PVC in diaphragm to help using ultrasonic testing the quality of diaphragm wall and in accordance with testing result to assess whether to strengthen the wall or not. Moreover, canceling post and re-strut can reduce construction interfaces to shorten the time schedule. TRA Kaohsiung underground railway project needs to pass through the 75m Love-river and the river-crossing section of tunnel is adopted the three stages of cofferdam construction method. To cope with the regulations of authority about avoiding construction in river during flood season, river slab of semi-top down construction method is designed, and it can be benefited at TRA tunnel excavation under river slab.
This paper reports renovation of a building project, 12-story high added by a 3-story underground basement covering area of 583 m2 in Taipei. Perimeter of the planned site is 80m. The foundation depth and the slurry wall depth are 14.2m and 25m, respectively. In addition, the slurry wall thickness of this old building is 70cm. The new building foundation planned to sit inside the slurry wall area of the old building. New building is expected to excavate down to 21.5m, with drilled shafts H414×405×18×28mm installed down to 34m. The new foundation construction is firstly by taking advantage of the available basement structures of the old building and old slurry wall and by incorporating with the to-be-installed drilled shafts inside the basement and water tight cylindrical ground improvement piles to increase the strength of clay in the passive resistance zone. In addition, combining the top-down and bottom-up construction procedures by taking advantage of utilizing part of the floor slab to connect old slurry wall and newly installed drilled shafts to complete the building project.
In Taipei City， a large area underground structure construction is seldom seen recently. The Twin Tower project is the one. Two high rise buildings, one is 56 floors and the other is 76 floors, were planned. They were planned to use one
basement which has 4 floors underground. This underground structure is also the starting station of Taoyuan airport rapid transit system and it has been constructed before the two towers. Because of the large excavation area, 25,775m2, the excavation and construction met a different problems from ordinary underground structure. This paper introduced the design and construction ideas. The hydraulic pressure released via dewatering in the Chingmei Gravel Layer are also introduced. When large amount of soil were removed in this case, monitoring data indicated that heavings occurred. This data was also introduced in this paper.
Cross walls and buttress walls have been widely adopted, with many successful cases, in soft ground excavation work. The field instrumented displacement data indicated that cross walls and buttress walls could effectively reduce the lateral displacement of diaphragm wall and thus enhance the stability of the excavation work. The interaction between the soil/cross/buttress- and diaphragm walls is a three dimensional problem but in practice, due to the complexity of three-dimensional analysis, the problem is commonly simplified into a two-dimensional problem. This study aimed at examining the influence of the space of the cross/buttress walls on the displacement of diaphragm wall via a series of
three-dimensional FE analysis. The numerical procedure was first calibrated against the field data obtained from a 16m deep excavation real case in Taipei city. The FEM simulated results were consistent with the field monitored data. The
basic model was then used in the subsequent parametric study to evaluate the efficiency of buttress walls and cross walls in deep dxcavation. It was found that the cross walls were more efficient than the internal buttress walls on reducing the
displacement of the diaphragm wall. These results were evaluated and compared through the so-called displacement reduction ratio (DRR). The results indicated that the DRR of buttress walls and cross walls were 50% (for SBW/He=0.375)
and 77.5% (for SCW/He=0.55), respectively.
The rocking response of a footing or spread foundation is essential to its stability and performance. The analytical dimensionless performance curves of a rigid footing are presented in this paper for the cases of elastic and elastoplastic
soils. Based on that, performance-based design criteria for the rotational response of a rigid footing are suggested for engineering applications. The rotational yield point of a footing shall be set at the condition when the foundation contact area has been reduced to 50% of the total foundation base area. Beyond this point, the slope of the performance curve becomes very gentle, so the moment resistance of the footing cannot increase much with respect to larger rotations. In addition, the axial force is an important factor influencing the rotational resistance of the footing, in which the case with low axial force is a disadvantage design condition.
This paper study the earth pressure and member forces acting upon Taipei MRT shield tunnels RC lining based on real time monitoring results. Planning of installations of earth and water pressure cells , rebar strainmeters for RC lining,
as well as methodology for axial forces and bending moments calculated in RC lining, the monitoring results during the assembled of lining, back-fill grouting ,close proximity constructions and long term real time records about 400 days for CG290 projects and 800 days for CG291 projects were discussed.