TABLE OF CONTENTS The components making up a retaining structure can be broadly classified into: facings and supports. The common type of facings include: Kingposts and planking (braced excavation), bored piles, diaphragms, and steel sheeting. Kingpost and planking include: steel H-sections (solider piles) with timber sheeting and bored piles with gunnite and mesh facings, and the contiguous, secant and tangent piles belong to the bored piles group. The main differences between the different types of walls are: the construction technology, the material in which they are made of, and the flexibility and rigidity of the wall. The feasibility of any construction method depends to a great extent upon the ground and groundwater conditions at the site, and upon locally available skill, equipment and experience. For excavations in normally consolidated soft clays, stiffer walls such as diaphragms and bored pile walls are usually recommended. However, even with stiffer walls, it is practically impossible to completely eliminate the ground movements in and around an excavation in soft soils (Palmer and Kenny 1972; Burland et al. 1979; Fujita 1994).
After statistically analysing the data from literature about construction and performance of deep excavation support systems since 1962, Duncan and Bentler 1998 reported that the percentage of excavations supported by sheet piles have decrease over time, while the percentage of excavations supported by diaphragm walls and other walls (mainly secant, tangent and contiguous pile walls) has increased steadily. They also found that settlements and horizontal movements...
