Civil Engineering Reference
In-Depth Information
Downdrag load
(pile perimeter) (layer thickness) (
h
tan
)
(0.3 m) (4.5 m) (24.6 tan 28°)
55.5 kN
Total downdrag load
5.2
55.5
61 kN
13.3
Soil will liquefy down to a depth of about 20 m. Thus the piles should be at least
20 m long.
CHAPTER 14
14.1
In Fig. 10.5, the soil is described as “sand backfill.” From Table 14.10, the active
earth pressure is 30 psf/ft for both well-graded clean sands and poorly graded clean sands.
Hence use this value of equivalent fluid pressure (EFP) of 30 psf/ft:
P
H
1
2
(EFP)(
H
)
2
1
2
(30)(20)
2
6000 lb/ft and
P
V
0
From Fig. 10.5:
P
H
5660 lb/ft and
P
V
3270 lb/ft
14.2
In Fig. 10.5, the soil is described as “sand backfill.” In Table 14.10, for restrained
wall, use at-rest pressure. The at-rest pressure is 60 psf/ft for both well-graded clean sands
and poorly graded clean sands. Hence use this value of equivalent fluid pressure (EFP) of
60 psf/ft:
2
(EFP)(
H
)
2
1
2
(60)(20)
2
12,000 lb/ft and
P
V
0
P
H
1
Using:
k
0
1
sin
1
sin 30°
0.5
P
H
1
2
(
k
0
)(
t
)(
H
)
2
1
2
(0.5)(110)(20)
2
11,000 lb/ft and
P
V
0
14.3
The standard penetration test data indicates that for the design earthquake, there
are three zones of liquefaction from about 2 to 11 m, 12 to 15 m, and 17 to 20 m below
ground surface. From Table 14.11, the site is considered to be site class F.
14.4
The procedure is as follows:
Step 1: Check site class F, which must have one or more of the following character-
istics:
a. Soils vulnerable to potential failure or collapse under seismic loading such as
liquefiable soils, quick and highly sensitive clays, collapsible weakly cemented
soils.
b.
Peats and/or highly organic clays (
H
10 feet of peat and/or highly organic clay
where
H
thickness of soil).
c.
Very high plasticity clays (
H
25 feet with plasticity index PI
75).
d.
Very thick soft/medium stiff clays (
H
120 feet) with
s
u
1000 psf.
None of these requirements are met; hence, it is not a site class F.
