Civil Engineering Reference
In-Depth Information
factor of safety so that there is ample resistance against a bearing capacity failure. This is
discussed further in Chap. 8.
●
Buoyancy effects:
Consider possible buoyancy effects. Examples include buried stor-
age tanks or large pipelines that are within the zone of liquefied soil. Instead of settling,
the buried storage tanks and pipelines may actually float to the surface when the ground
liquefies.
●
Sloping ground condition:
Do not use Figs. 7.1 and 7.2 when there is a sloping ground
condition. If the site is susceptible to liquefaction-induced flow slide or lateral spreading,
the settlement of the building could be well in excess of the values obtained from Figs.
7.1 and 7.2. This is discussed further in Chap. 9.
●
Liquefaction-induced ground damage:
The calculations using Figs. 7.1 and 7.2 do not
include settlement that is related to the loss of soil through the development of ground
surface sand boils or the settlement of shallow foundations caused by the development
of ground surface fissures. These types of settlement are discussed in the next section.
7.3
LIQUEFACTION-INDUCED GROUND DAMAGE
7.3.1
Types of Damage
As previously mentioned, there could also be liquefaction-induced ground damage that
causes settlement of structures. This liquefaction-induced ground damage is illustrated in
Fig. 7.3. As shown, there are two main aspects to the ground surface damage:
1.
Sand boils:
There could be liquefaction-induced ground loss below the structure, such
as the loss of soil through the development of ground surface sand boils. Often a line of
sand boils, such as shown in Fig. 7.4, is observed at ground surface. A row of sand boils
often develops at the location of cracks or fissures in the ground.
2.
Surface fissures:
The liquefied soil could also cause the development of ground sur-
face fissures which break the overlying soil into blocks that open and close during the
earthquake. Figure 7.5 shows the development of one such fissure. Note in Fig. 7.5 that
liquefied soil actually flowed out of the fissure.
The liquefaction-induced ground conditions illustrated in Fig. 7.3 can damage all types
of structures, such as buildings supported on shallow foundations, pavements, flatwork,
FIGURE 7.3
Ground damage caused by the liquefaction of an underlying soil layer. (
Reproduced from
Kramer 1996, originally developed by Youd 1984.
)
