Civil Engineering Reference
In-Depth Information
max
Maximum shear strain
t
Total unit weight of soil
max
Earthquake-induced total settlement of foundation
v
0
Total vertical stress
m
Mean principal effective stress
vm
Maximum past pressure, also known as preconsolidation pressure
v
0
Vertical effective stress
1
Major principal effective stress
2
Intermediate principal effective stress
3
Minor principal effective stress
v
Increase in foundation pressure due to earthquake
cyc
Uniform cyclic shear stress amplitude of earthquake
eff
Effective shear stress induced by earthquake
max
Maximum shear stress induced by earthquake
7.1 INTRODUCTION
As discussed in Sec. 4.2, those buildings founded on solid rock are least likely to experi-
ence earthquake-induced differential settlement. However, buildings on soil could be sub-
jected to many different types of earthquake-induced settlement. This chapter deals with
only settlement of soil for a level-ground surface condition. The types of earthquake-
induced settlement discussed in this chapter are as follows:
●
Settlement versus the factor of safety against liquefaction (Sec. 7.2):
This section dis-
cusses two methods that can be used to estimate the ground surface settlement for vari-
ous values of the factor of safety against liquefaction (FS). If FS is less than or equal to
1.0, then liquefaction will occur, and the settlement occurs as water flows from the soil
in response to the earthquake-induced excess pore water pressures. Even for FS greater
than 1.0, there could still be the generation of excess pore water pressures and hence set-
tlement of the soil. However, the amount of settlement will be much greater for the liq-
uefaction condition compared to the nonliquefied state.
●
Liquefaction-induced ground damage (Sec. 7.3):
There could also be liquefaction-
induced ground damage that causes settlement of structures. For example, there could be
liquefaction-induced ground loss below the structure, such as the loss of soil through the
development of ground surface sand boils. The liquefied soil could also cause the devel-
opment of ground surface fissures that cause settlement of structures.
●
Volumetric compression (Sec. 7.4):
Volumetric compression is also known as
soil den-
sification.
This type of settlement is due to ground shaking that causes the soil to com-
press together, such as dry and loose sands that densify during the earthquake.
●
Settlement due to dynamic loads caused by rocking (Sec. 7.5):
This type of settlement
is due to dynamic structural loads that momentarily increase the foundation pressure act-
ing on the soil. The soil will deform in response to the dynamic structural load, resulting
in settlement of the building. This settlement due to dynamic loads is often a result of the
structure rocking back and forth.
