2971
Technical Committee 214 /
Comité technique 214
each track area is up to 50 t/m². The foundation soil is 10 m
thick soft bluish clay with an average undrained shear strength
of 23 kPa from vane shear test results.
Figure 6. Rehabilitated fabrication yard in use.
In the calculations, the angle of load spread for the fill
material reinforced with TriAx geogrid within the MSL is taken
to be 1 vertical to 1 horizontal (i.e., 1V:1H) whereby the load
distribution through the geocell mattress was taken as 1 vertical
to 2 horizontal (i.e., 1V:2H) to model the very stiff nature of the
construction (Figure 7).
(a)
(b)
Figure 7. Geocell mattress and MSL platform (after Ong et al., 2011)
Five layers of TriAx geogrids were used to form the 2 m
thick MSL. Stiff uniaxial geogrids were used to form the
interlocking cells of the 1 m thick geocell mattress and a layer
of TriAx geogrid was placed at the base. The aggregate to be
used as backfill material for the MSL and geocell mattress was
specified as well graded granular material with particle size less
than 75 mm. Full scale plate bearing test (PBT) was conducted
to ascertain the performance of the geocell mattress in meeting
the acceptance criterion (i.e., total settlement less than 100 mm
under loading of 50 t/m²). The loading on the steel plate was
increase in six steps: 10 t/m², 20 t/m², 30 t/m², 40 t/m², 50 t/m²
and 60 t/m². Settlement versus applied load and settlement
versus time were plotted. It was found that the specified
settlement requirement was satisfied with total settlement of 41
mm under 60 t/m² load.
4 CONTAINER YARD IN GEBENG, KUANTAN
In this project, a working platform in the form of container yard
was built on soft subgrade with California bearing ratio (CBR)
of 1% to 2%. The container yard was designed to support the
following loadings:
6 m by 2.4 m container with maximum weight of 30 tonnes.
Maximum staking of containers was 2 containers.
Container handler machine with maximum axle load of 105
tonnes. Therefore maximum wheel load of 525 kN
including dynamic factors.
Total number passes of the container handler machine was
designed as 250,000 during service life.
The terms of reference are:
To reduce thickness of unbound granular layer platform.
To mitigate differential settlement.
To provide stable storage area and to increase load spread
using geocell mattress and mechanically stabilised layer
(MSL) with TriAx geogrids.
The analysis conducted indicated that the loadings from the
trafficking movement due to container staker would be more
critical than the static loadings due to the staking of 2
containers. Thus, the requirement for total platform thickness
was assessed based on heavy duty pavement design (Knapton,
2008). By using geocell mattress and MSL, the thickness of
granular fill required to construct the container yard has been
reduced up to 810 mm. This resulted in substantial savings in
terms of construction time and cost.
MECHANICALLY
STABILISED LAYER
(MSL)
GEOCELL MATTRESS
2.0 m
1.0 m
SOFT CLAY
EGL
MAX. CRANE TRACK
LOADING = 50 t/m
For the heavy duty pavement construction of the container
yard, 1 m high geocell mattress was placed on one layer of
TriAx geogrid at subgrade level. The geocell mattress is to
provide a firm and relatively rigid platform with a perfectly
rough interface between the mattress and the soft foundation.
This stiff platform is created by the high tensile strength of
polymer grid material used in the cellular construction to
confine the granular fill which enables an even distribution of
load onto the foundation. On top of the geocell mattress is MSL
of 500 mm to 750 mm compacted well graded granular fill with
3 layers of TriAx geogrids. Granular layers reinforced with
TriAx geogrids perform as composite due to the interlock
phenomenon. The configuration of the geogrid ribs and the
integral junctions provide lateral restraint to the aggregate
particles as they partially penetrate the apertures by a process of
interlock. This interlock effectively stiffens the aggregate and
enables any imposed load to be distributed over a wider area.
The container platform was finished with interlocking paving
blocks. The construction of the container yard is expeditious
starting from placement of TriAx geogrids, forming of geocells,
filling with granular materials according to prescribed grading
envelope, construction of MSL geogrid reinforced layers and
installation of the paving blocks (Figures 8 to 12).
GEOCELL MATTRESS
2.0 m
1.0 m
SOFT CLAY (bearing capacity = 131 kPa)
EGL
MAX. CRANE TRACK
LOADING = 50 t/m
TRIAX GEOGRID
TO FORM MSL
1V:1H
1V:2H
5 DISCUSSION AND CONCLUSION
Comparison is made in the pavement details and settlement
performance of the working platform (Table 1). From Table 1 it
can be seen that all the 3 platforms consist of soft clay layer of
thickness varying from 4.5 m to 10 m. The crane track pressure
exerted on the working platform was up to 500 kPa and axle
load exerted by the reach stacker on the working platform is 105
tonnes. Granular fill of varying thicknesses were used in all
three working platforms. It appears that MSL constructed using
biaxial and TriAx geogrids with granular fill with or without
geocell mattress performed satisfactorily in terms of platform
settlement performances to support the heavily loaded crawler
crane or stacker machine for the fabrication or container yard.
