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中英文对照外文翻译
(文档含英文原文和中文翻译)
原文:
Safety Assurance for Challenging Geotechnical Civil
Engineering Constructions in Urban Areas
Abstract
Safety is the most important aspect during design, construction and service time of any structure, especially for challenging projects like high-rise buildings and tunnels in urban areas. A high level design considering the soil-structure interaction, based on a qualified soil investigation is required for a safe and optimised design. Due
to the complexity of geotechnical constructions the safety assurance guaranteed by the 4-eye-principle is essential. The 4-eye-principle consists of an independent peer review by publicly certified experts combined with the observational method. The paper presents the fundamental aspects of safety assurance by the 4-eye-principle. The application is explained on several examples, as deep excavations, complex foundation systems for high-rise buildings and tunnel constructions in urban areas. The experiences made in the planning, design and construction phases are explained and for new inner urban projects recommendations are given.
Key words: Natural Asset; Financial Value; Neural Network 1. Introduction
A safety design and construction of challenging projects in urban areas is based on the following main aspects:
Qualified experts for planning, design and construction;
Interaction between architects, structural engineers and geotechnical engineers; Adequate soil investigation;
Design of deep foundation systems using the FiniteElement-Method (FEM) in combination with enhanced in-situ load tests for calibrating the soil parameters used in the numerical simulations;
Quality assurance by an independent peer review process and the observational method (4-eye-principle).
These facts will be explained by large construction projects which are located in difficult soil and groundwater conditions.
2. The 4-Eye-Principle
The basis for safety assurance is the 4-eye-principle. This 4-eye-principle is a
process of an independent peer review as shown in Figure 1. It consists of 3 parts. The investor, the experts for planning and design and the construction company belong to the first division. Planning and design are done accordingto the requirements of the investor and all relevant documents to obtain the building permission are prepared. The building authorities are the second part and are responsible for the building
permission which is given to the investor. The thirddivision consists of the publicly certified experts.They are appointed by the building authorities but work as independent experts. They are responsible for the technical supervision of the planning, design and the construction.
In order to achieve the license as a publicly certified expert for geotechnical engineering by the building authorities intensive studies of geotechnical engineering in university and large experiences in geotechnical engineering with special knowledge about the soil-structure interaction have to be proven.
The independent peer review by publicly certified experts for geotechnical engineering makes sure that all information including the results of the soil investigation consisting of labor field tests and the boundary conditions defined for the geotechnical design are complete and correct.
In the case of a defect or collapse the publicly certified expert for geotechnical engineering can be involved as an independent expert to find out the reasons for the defect or damage and to develop a concept for stabilization and reconstruction [1].
For all difficult projects an independent peer review is essential for the successful realization of the project.
3. Observational Method
The
observational method is practical to projects with difficult boundary
conditions for verification of the design during the construction time and, if necessary, during service time. For example in the European Standard Eurocode 7 (EC 7) the effect and the boundary conditions of the observational method are defined.
The application of the observational method is recommended for the following types of construction projects [2]:
very complicated/complex projects;
projects with a distinctive soil-structure-interaction,e.g. mixed shallow and deep foundations, retaining walls for deep excavations, Combined Pile-Raft Foundations (CPRFs);
projects with a high and variable water pressure;
complex interaction situations consisting of ground,excavation and neighbouring buildings and structures;
projects with pore-water pressures reducing the stability; projects on slopes.
The observational method is always a combination of the common geotechnical investigations before and during the construction phase together with the theoretical modeling and a plan of contingency actions(Figure 2). Only monitoring to ensure the stability and the service ability of the structure is not sufficient and,according to the standardization, not permitted for this purpose. Overall the observational method is an institutionalized controlling instrument to verify the soil and rock mechanical modeling [3,4].
The identification of all potential failure mechanismsis essential for defining the measure concept. The concept has to be designed in that way that all these mechanisms can be observed. The measurements need to beof an adequate accuracy to allow the identification ocritical tendencies. The required accuracy as well as the boundary values need to be identified within the design phase of the observational method . Contingency actions needs to be planned in the design phase of the observational method and depend on the ductility of the systems.
The observational method must not be seen as a potential alternative for a comprehensive soil investigation campaign. A comprehensive soil investigation campaignis in any way of essential importance. Additionally the observational method is a tool of quality assurance and allows the verification of the parameters and calculations applied in the design phase. The observational method helps to achieve an economic and save construction [5].
4. In-Situ Load Test
On project and site related soil investigations with coredrillings and laboratory
tests the soil parameters are determined. Laboratory tests are important and essential for the initial definition of soil mechanical properties of the soil layer, but usually not sufficient for an entire and realistic capture of the complex conditions, caused by the
interaction of subsoil and construction [6].
In order to reliably determine the ultimate bearing capacity of piles, load tests need to be carried out [7]. Forpile load tests often very high counter weights or strong anchor systems are necessary. By using the Osterberg method high loads can be reached without install inganchors or counter weights. Hydraulic jacks induce the load in the pile using the pile itself partly as abutment.The results of the field tests allow a calibration of the numerical simulations.
The principle scheme of pile load tests is shown in Figure 3.
5. Examples for Engineering Practice
5.1. Classic Pile Foundation for a High-Rise Building in Frankfurt Clay
and Limestone
In the downtown of Frankfurt am Main, Germany, on aconstruction site of 17,400 m2 the high-rise buildingproject “PalaisQuartier” has been realized (Figure 4). The construction was finished in 2010.
The complex consists of several structures with a total of 180,000 m2 floor space, there of 60,000 m2 underground (Figure 5). The project includes the historic building “Thurn-und Taxis-Palais” whose facade has been preserved (Unit A). The office building (Unit B),which is the highest building of the project with a height of 136 m has 34 floors each with a floor space of 1340 m2. The hotel building (Unit C) has a height of 99 m with 24 upper floors. The retail area (Unit D)runs along the total length of the eastern part of the site and consists of eight upper floors with a total height of 43 m.
The underground parking garage with five floors spans across the complete project area. With an 8 m high first sublevel, partially with mezzanine floor, and four more sub-levels the foundation depth results to 22 m below ground level. There by excavation bottom is at 80m above sea level (msl). A total of 302 foundation piles(diameter up to 1.86 m, length up to 27 m) reach down to depths of 53.2 m to 70.1 m. above sea level depending on the structural requirements.
The pile head of the 543 retaining wall piles (diameter1.5 m, length up to 38 m)