1948
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
Critical to the design of the soil nail slope is the assumptions on
the skin friction between the ground and the grouted body of
soil nail and as such, a series of instrumented pull-out tests on
preliminary soil nails (non-working soil nails) were carried out
at site to verify the design assumptions. The soil nails adopted
at site generally consists of 4m to 18m length soil nails with
16mm to 32mm diameter galvanized high yield reinforcement
(yield strength = 460N/mm
2
) slotted inside a 150mm diameter
hole formed by open hole construction (without temporary
casing) and filled with Grade 30 non-shrink grout.
3.1
0B
Soil nail pull-out tests
A total of six numbers of instrumented pull-out tests on
preliminary soil nails (non-working soil nails) were completed
at the time this paper is prepared and the details of the pull-out
tests are summarized in Table 1. All the soil nails are 6m length
with 5m grouted length and 1m ungrouted length (free length) at
the top. Typical set-up for the pull-out tests is shown in Figure 2
while details of the instrumented preliminary soil nails are
shown in Figure 3.
Figure 2. Typical set-up for pull-out tests.
Table 1. Details of instrumented pull-out tests on preliminary soil nails
(non-working soil nails).
Nail No.
Bar Diameter
(mm)
Maximum test load
achieved (kN)
Nearest
borehole
Y-7
(RL 75.19)
25
175.0
BH-15
W/X-16
(RL 71.40)
25
140.0
BH-13
Y-10*
(RL 73.24)
25
131.2
BH-15,
NBH-3
Y-13*
(RL 74.50)
25
148.8
NBH-3
Y-7*
(RL 73.24)
25
78.8
BH-15
Y-1/2
(RL 74.00)
32
286.0
NBH-7
Note:
1. Different maximum test load is achieved primarily due to
various site issues such as improper test set-up where the
dial gauge has reached its maximum travel distance,
malfunctioning of the load cell, etc. and not due to
inadequate bond strength of the soil.
2. * - Results ignored due to improper preparation of free
length at the soil nail head which interferes with
instrumentation results.
Figure 1. Borehole profiles relevant to soil nail slope.
