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44
Geotechnical News • September 2013
www.geotechnicalnews.com
FS = 1.5 on the passive earth pressure
coefficient, thus Kp(design) = 1.4.
Design of CBP Wall
By taking the summation of moment
of the base of the wall equal to zero,
the required embedded length of
the contiguous bored pile (CBP) is
14.44m. In practice, additional 20%
of the embedded length is provided
which gives the total pile length = 3.0
+ 1.2 (14.44) = 20.33m. Use bored
piles with diameter, D = 1200mm.
Shear force and bending moment
acting on the CBP wall was shown in
Figure 2.
Design of Anchored Steel Sheet
Pile Wall
Design of anchored steel sheet pile
wall carried out using the free earth
support method. All other condition is
similar as design of CBP wall. By tak-
ing the summation of the moment at
point where tie rod is tied, the required
embedded depth is 6.5m. Additional
20% of the embedded length is pro-
vided which gives the total pile length
= 3.0 + 1.2 (6.5) = 10.8m and ten-
sion in tie rod, T is found to be 94.48
kN/m length of the wall. From Figure
3(b), Mmax = 124.07 kNm/m and
the elastic modulus, Z is found equal
to 460 cm3/m. Use U-section with
the nearest elastic section modulus of
600 cm3/m. Tie rods will be installed
at every 5 piles (spacing, s = 3.0m
c/c of each rod). Tie rods will be
installed at 50° to the wall in order to
provide full passive resistance from
the anchor where the passive zone in
front of the anchor system is located
completely outside the active zone. By
introducing a factor of safety of 2.0
as suggested by Littlejohn, 1970, the
tensile force in the rod is 94.48x3x2/
sin 50° which gives 740 kN. The
result allows the use of tie rod of
60mm diameter. The fixed anchor
length, L and diameter of the anchor,
D for ground anchor system need to
be determined in order to provide
adequate soil resistance (principally
skin friction) against pulling force of T
= 740kN. Using equation suggested by
Littlejohn, 1970 Obtained B = 0.6m
and L = 3.0m.
Finite Element Modeling and
Analysis
PLAXIS software was used to analyze
the behavior of the failed slope before
and after slope repairing works. The
soil properties used in the analysis
were taken from the previous analysis
done by Teo, 2003. Factor of safety,
FOS of the slope was determined
using phi-c-reduction approach avail-
able in PLAXIS.
Analyses were carried out for three
different conditions which include
the modeling of original slope and
repaired slope using CBP wall and
anchored steel sheet pile wall respec-
tively for various groundwater level.
The deformed mesh for each analysis
was shown in Figure 4. Results are
shown in Table 1 and Figure 5.
Conclusion
The conclusions that can be drawn
(a) Depth of anchored steel sheet pile wall Vs shear force. (b) Depth of
anchored steel sheet pile wall Vs bending moment.
Figure 3. Shear force and bending moment acting on anchored steel sheet
pile wall.
(a) Deformed mesh of original slope profile. (b) Deformed mesh of original
repaired slope using CBP wall.
(c) Deformed mesh of repaired slope using anchored steel sheet pile wall.
Figure 4. Deformed mesh of original and repaired slope.