Civil Engineering Reference
In-Depth Information
(1)
(2)
Initial excavation
Proposed
excavation
First nail
installed
(3)
(4)
Shotcrete facing applied
Shotcrete
Soil nails
Completed excavation
Fig. 8.22
Construction stages of a soil nailed wall.
There are two methods of forming the nail:
drill and gout
and
driving
. With the drill and grout method,
steel bars are installed into pre-drilled holes and grout injected around them to bond them fully into the
soil mass. This generates a reasonably large contact area between the grout and the soil thereby provid-
ing a high pull-out resistance. With the driving method, nails are either driven into the soil using a hydraulic
or pneumatic hammer, or fired into the soil from a nail launcher which uses an explosive release of com-
pressed air. This method of installation requires the nails to be relatively robust and to have a reasonably
small cross-sectional area. Details of the driving technique are given by Myles and Bridle (
1991)
and full
details of soil nail techniques and design methods are given by Gassler (
1990
), Schlosser (
1982)
, Schlosser
and de Buhan (
1990)
and RDGC (
1991)
and a recent extension of the technique is described by Pokharel
and Ochiai (
1997
).
Exercises
Exercise 8.1
A reinforced concrete cantilever retaining wall, supporting a granular soil, has
dimensions shown in Fig.
8.23.
Using a gross factor of safety approach, calculate the factors of safety against
sliding and overturning and check the bearing pressure on the soil beneath the wall
if the allowable bearing pressure is 300 kPa. Take the unit weight of concrete as
23.5 kN/m
3
and assume that the friction between the base of the wall and the soil
is equal to
φ
′
. Ignore any passive resistance from the soil in front of the wall.
Answer
F
s
=
2.19; F
o
=
3.63; p
max
=
135.5 kPa {
<
300
⇒
OK}
