ABSTRACT
This chapter considers the design of gravity walls. Gravity and reinforced-concrete cantilever walls are commonly used for
relatively low retaining structures, although walls of up to 8-10 m are not unheard of. The design of this group of structures falls into ve stages:
1. Selection of suitable wall type (see Chapter 6) 2. Preliminary wall sizing and layout 3. Selection of soil parameters (see Chapters 2 and 7) 4. Calculation of external stability 5. Checks on internal stability, and wall detailing
9.1 PRELIMINARY DESIGN
Preliminary design involves two stages:
• Provision of drainage, to minimise loads on the wall • Initial sizing of the wall
Chapter 4 should be referred to for a wider discussion of the important effects of water on the pressures that need to be supported by retaining structures. Figure 9.1 illustrates some common methods of providing drainage behind a gravity retaining wall (see Teng 1962, pp. 316-317). These include using
a. Weep-holes in pervious backll b. Open-joint clay or perforated metal pipes in pervious backll c. Sub-vertical strips of lter material midway between weep-holes,
linked to a horizontal strip of lter material, in semi-pervious backll
d. Porous blocks or blanket of pervious material against the back of the wall in ne-grained backll
e. Blanket of pervious material extending into ll in ne-grained backll f. Multiple blankets of pervious material in expansive clay
Figure 9.2 denes some key dimensions that can be chosen during preliminary design on the basis of simple rules-of-thumb (see, for example, Cernica 1995) as summarised in Table 9.1, below.
