Civil Engineering Reference
In-Depth Information
CHAPTER 12
GRADING AND OTHER SOIL
IMPROVEMENT METHODS
12.1 INTRODUCTION
Part 3 of the topic (Chaps. 12 and 13) discusses the various methods that can be used to
mitigate the effects of the earthquake on the structure. The next two chapters deal with
site mitigation methods such as grading and soil improvement (Chap. 12) and foundation
alternatives to resist the earthquake effects (Chap. 13).
The mitigation of slope hazards has already been discussed in Sec. 9.7.2. Options
include avoiding the slope failure, protecting the site from the failure mass, and reducing
the risk to an acceptable level by increasing the factor of safety of the slope. For slope haz-
ards dealing with liquefaction-induced flow slides and lateral spreading, Seed (1987)
states:
It is suggested that, at the present time, the must prudent method of minimizing the hazards
associated with liquefaction-induced sliding and deformations is to plan new construction or
devise remedial measures in such a way that either high pore water pressures cannot build up
in the potentially liquefiable soil, and thus liquefaction cannot be triggered, or, alternatively, to
confine the liquefiable soils by means of stable zones so that no significant deformations can
occur; by this means, the difficult problems associated with evaluating the consequences of lique-
faction (sliding or deformations) are avoided.
Types of stable zones that can be used to confine the liquefiable soils include robust edge
containment structures and shear keys (i.e., compacted soil zones). Examples of robust
edge containment structures that are capable of resisting failure or excessive displacement
under the seismic loading include compacted berms and dikes as well as massive seawalls or
retaining structures (R. B. Seed 1991). The construction of stable zones may need to be used
in conjunction with other methods that mitigate liquefaction-induced settlement, bearing
capacity, and ground damage (surface cracking and sand boils).
Other options for dealing with liquefaction hazards are as follows (Federal Emergency
Management Agency 1994):
Four general approaches apply to the mitigation of liquefaction hazards (avoidance, pre-
vention, engineered design, and post earthquake repairs). A prime way to limit the damage due
to liquefaction is to avoid areas susceptible to liquefaction. This approach is not always possible
12.3
