Abstract
Deep excavations are intensively carried out in many cities in China and other countries. One of the major loadings in such construction work is the water pressure, and great effort is required to assess the seepage problem and the corresponding water pressure on the retaining wall for a good design and construction. Different methods used for the seepage analysis are discussed in this paper through a series of projects in Hong Kong. Some interesting phenomena from the seepage analysis will also be discussed. Two large scale seepage field tests in Hong Kong are also used for the illustration of the back analysis in seepage problems which are seldom carried out. The comparative studies demonstrate that a realistic seepage analysis is very important for deep excavation works, but it was not seriously considered in the past.
Highlights
In Hong Kong, China, and many developed cities in the world, deep excavations are necessary for the building foundations, basements, mass transit, subways, and other construction works [1,2,3,4,5]
The actual amount of water table drawdown is around 35 m depth; the maximum water pressure difference at the two sides of the diaphragm wall is about 35 × 9:81 = 343 kPa, which is about three times the soil active pressure
Based on the use of various numerical methods and computer programs, the authors view that the finite element method is the most versatile method among all, while the analytical method is sufficient for normal engineering problems
Summary
In Hong Kong, China, and many developed cities in the world, deep excavations are necessary for the building foundations, basements, mass transit, subways, and other construction works [1,2,3,4,5]. An ELS design submission includes (1) Lateral support system, e.g., sheet piles and diaphragm wall (2) Strutting (or tie-back) layout (3) Construction sequence (4) Supporting geotechnical documents (5) Ground water seepage analysis, control of ground water, and estimates of ground movements (6) Assessment of the effects of excavation and dewatering on adjoining structures (7) Monitoring proposal for the ground settlement and ground water level. For the Sheung Wan MTR Concourse, which is a 35 m deep diaphragm wall excavation in very poor soil, the water level has to be controlled to at least 2 m below the formation level during construction. To control the ground settlement in such a Geofluids poor soil condition, recharge wells have been used to restore the water table outside the diaphragm wall to a reasonable level. Many commercial codes are available for finite element seepage analysis, and this will not be discussed here
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