中 英 文 对 照 外 文 翻 译
(文档含英文原文和中文翻译)
Deep E x ca v a t ion s
ABSTR ACT ： All major topics in the design of in-situ retaining systems for deep excavations in urban areas are outlined. Type of wall, water
related problems and water pressures, lateral earth pressures, type of support, solution to earth retaining walls, types of failure, internal and external stability problems.
KEYW OR DS: deep excavation; retaining wall; earth pressure;
INTR ODUCTION
Numbers of deep excavation pits in city centers are increasing every year. Buildings, streets surrounding excavation locations and design of very deep basements make excavations formidable projects. This chapter has been organized in such a way that subjects related to deep excavation projects are summarized in several sections in the order of design routine. These are types of in-situ walls, water pressures and water related problems. Earth pressures in cohesionless and cohesive soils are presented in two different categories. Ground anchors, struts and nails as supporting elements are explained. Anchors are given more emphasis compared to others due to widespread use observed in the recent years. Stability of retaining systems are discussed as
internal and external stability. Solution of walls for shears, moments, displacements and support reactions under earth and water pressures are obtained making use of different methods of analysis. A pile wall supported by anchors is solved by three methods and the results are compared. Type of wall failures, observed wall movements and instrumentation of deep excavation projects are summarized.
1. TYPES OF EARTH R ETAINING WAL L S
1.1 Introduction
More than several types of in-situ walls are used to support excavations. The criteria for the selection of type of wall are size of excavation, ground conditions, groundwater level, vertical and horizontal displacements of adjacent ground and limitations of various structures, availability of construction, cost, speed of work and others. One of the main decisions is the water-tightness of wall. The following types of in-situ walls will be summarized below;
1. Braced walls, soldier pile and lagging walls 2. Sheet-piling or sheet pile walls
3. Pile walls (contiguous, secant)
4. Diaphragm walls or slurry trench walls
5. Reinforced concrete (cast-in-situ or prefabricated) retaining walls
6. Soil nail walls
7. Cofferdams
8. Jet-grout and deep mixed walls
9. Top-down construction
10. Partial excavation or island method
Br aced Walls
Excavation proceeds step by step after placement of soldier piles or so called king posts around the excavation at about 2 to 3 m intervals. These
may be steel H, I or WF sections. Rail sections and timber are also used. At each level horizontal waling beams and supporting elements (struts, anchors,
nails) are constructed. Soldier piles are driven or commonly placed in bored holes in urban areas, and timber lagging is placed between soldier piles during the excavation. Various details of placement of lagging are available, however, precast units, in-situ concrete or shotcrete may also be used as alternative to timber. Depending on ground conditions no lagging may be provided in relatively shallow pits.
Historically braced walls are strut supported. They had been used extensively before the ground anchor technology was developed in 1970 s. Soils with some cohesion and without water table are usually suitable for this
type of construction or dewatering is accompanied if required and allowed. Strut support is commonly preferred in narrow excavations for pipe laying or similar works but also used in deep and large excavations (See Fig 1.1). Ground anchor support is increasingly used and preferred due to access for construction works and machinery. Waling beams may be used or anchors may be placed directly on soldier piles without any beams.
Sheet-piling or Sheet Pile Walls
Sheet pile is a thin steel section (7-30 mm thick) 400-500 mm wide. It is manufactured in different lengths and shapes like U, Z and straight line sections (Fig. 1.2). There are interlocking watertight grooves at the sides, and they are driven into soil by hammering or vibrating. Their use is often
restricted in urbanized areas due to environmental problems like noise and vibrations. New generation hammers generate minimum vibration and
disturbance, and static pushing of sections have been recently possible. In soft ground several sections may be driven using a template. The end product is a watertight steel wall in soil. One side (inner) of wall is excavated step by step and support is given by struts or anchor. Waling beams (walers) are frequently used. They are usually constructed in water bearing soils.
Steel sheet piles are the most common but sometimes reinforced concrete precast sheet pile sections are preferred in soft soils if driving difficulties are not expected. Steel piles may also encounter driving difficulties in very dense, stiff soils or in soils with boulders. Jetting may be
accompanied during the process to ease penetration. Steel sheet pile sections used in such difficult driving conditions are selected according to the driving resistance rather than the design moments in the project. Another frequently
faced problem is the flaws in interlocking during driving which result in leakages under water table. Sheet pile walls are commonly used for temporary purposes but permanent cases are also abundant. In temporary
works sections are extracted after their service is over, and they are reused after maintenance. This process may not be suitable in dense urban environment.
Pile Walls
In-situ pile retaining walls are very popular due to their availability and practicability. There are different types of pile walls (Fig. 1.3). In contiguous (intermittent) bored pile construction, spacing between the piles is greater
