Download 2 Param Agricultural Soil Surveys (M) Sdn Bhd, A4

Effects of soil fillers, vegetation lateral variation and basin ‘dome’ shape on tropical
lowland peat stabilization.
Mohamad Tarmizi Mohamad Zulkifley1*, Roslan Hasyim3, John Kuna Raj1, Ng Tham Fatt1,
Wan Hasiah Abdullah1, Azman Abdul Ghani1, Mustaffa Kamal Shuib1, Muhammad Aqeel
Ashraf1, Ahmad Farid Abu Bakar1, Jasmi Hafiz Abdul Aziz1, Nur Iskandar Taib1, Meor Hakif
Amir Hassan1, Nur Islami Rahman1, Ismail Yusoff1 & S. Paramananthan2
1Department
2Param
of Geology, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia
Agricultural Soil Surveys (M) Sdn Bhd, A4-3 Jalan 17/13, 46400 Petaling Jaya, Selangor, Malaysia
3
Department of Civil Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia
*Corresponding author: email address [email protected], [email protected], tel: +6016-5773114
Extended Abstract :
Field mapping involving observation, identification, characterization, classification (von
Post) to map and identify the natural extent and occurrence of tropical lowland peat deposits was
carried in the Kota Samarahan-Asajaya study area in West Sarawak (Malaysia). Field
identification and classification indicates that there is a lateral variation of peat humification
levels (von Post) in the form of dominantly occurring fibric, fibric to hemic, sapric and hemic to
sapric peat, occurring from margin and towards the centre of the tropical lowland peat dome or
basin (Engineering Geology Working Group, 2007). Cement-peat stabilization (Alwi, 2008;
Wong, 2010; Wong et al., 2008; 2009 and 2011) can be achieved or enhanced with the addition
of mineral soil fillers (silt, clays and fine sands) obtained from Quaternary floodplain deposits
and residual soil (weathered schist). Unconfined Compressive Strength (UCS) of the stabilized
cement-mineral soil filler-peat mix is observed to increase with the further addition of selected
mineral soil filler (msf) in increasing quantities.
Results indicate that there is a lateral variation of stabilized peat strength (UCS)
occurring on the top 0 to 0.5 metres layer, from margin towards the near-centre, of the tropical
lowland peat dome. This study indicates that these stabilized strength variations are at the
maximum near the dome/basin margin/periphery, followed by a decrease to a low (intermediate)
at the mid-section area and progressively increases back again further towards basin centre of the
peat dome. Almost all the stabilized cement-filler-peat mix specimens with added msf (silt, clay
and fine sands) that were tested, exhibited brittle or shear failures with no barrelling except for
the specimen with peat obtained from KS.TP.08 which exhibited dominantly more shear failure
than barrelling failure. In conclusion, topogenic, clayey, high-ash or shallow peats (with more
naturally occurring in-situ msf content) occurring near or at the margin/periphery of the peat
dome/basin have relatively higher UCS compared to the deeper intermediate topogenic to
ombrogenic, low-ash peats (with relatively lesser or no natural msf content) occurring at
midsection or towards the basin centre. Furthermore, stabilized peat specimens from topogenic,
marginal, shallow, transitional peat areas also exhibited relatively better, uniform and consistant
cylindrical shape, less deformation, are denser, are harder, has lesser cracks, lesser holes, less
indentations and lesser joints/discontinuities at the tamped layer planes. These observations may
probably reflect the enhanced field conditions of the stabilized peat columns if msf were applied
in the cement-filler-peat stabilization process and targetted at the marginal/fringe, topogenic,
shallow peat areas of the peat basin/dome.
Variations of UCS of stabilized tropical lowland peats occurring with varying distance
from periphery towards the centre of the peat dome in the current scope of this study, is
probably caused by a combination of factors due to variations of mineral soil or ash content in
the peat and the indirect effect of horizontal zonation or, lateral variation of dominant species of
plant assemblages (due to peat swamp forest successive vegetation zonations occurring from
periphery towards centre of the tropical lowland peat dome). These factors are further associated
to the shape of the peat basin or ‘dome’ shape (Anderson, 1964; Anderson and Muller, 1975).
The observed stabilized strength zonations are: (a) Fibric or fibric to hemic, topogenic, clayey,
shallow, transitional peats that usually occur near the basin margin or near the peat-soil
lithological boundary with relatively higher natural, mineral soil (naturally deposited
silt/clay/sand) or ash content that act as “natural fillers”, that may probably have contributed to
relatively higher UCS of cement-msf stabilized peat when compared to peats occurring at
locations intermediate and towards the centre of the peat dome; (b) Sapric, intermediate
topogenic to ombrogenic peats that occur at intermediate locations between basin margin and
towards the centre of peat basin with lesser “natural msf” or ash content that may likely produce
cement-msf stabilized peat with a relatively lower UCS; (c) Ombrogenic, sapric peat (from
decomposed hardwood fragments of tree logs, broken branches, bark and roots contributed by
dominant, hardwood, plant species (e.g. Shorea type)) that occur in these vegetation zones
(phasic community II to IV) towards and near the centre of the peat swamp forest, may produce
cement-msf stabilized peat with a relatively higher UCS compared to stabilized peats occurring
at the mid-section area (phasic community I) .
Hence, lateral or horizontal vegetation succession (phasic community zonation) which is
indirectly due to the tropical lowland peat basin “dome” shape and unconfined compressive
strength of the stabilized cement-mineral soil filler (msf)-peat mix may probably be associated in
tropical lowland peat basins/domes.
Keywords: tropical lowland peat dome or basin; mineral soil filler; cement-soil filler-peat
stabilization; topogenic to ombrogenic; unconfined compressive strength; lateral vegetation
succession
Acknowledgements: The authors greatly appreciate financial assistance from University of
Malaya IPPP research grant no PV018/2011A.
References:
Alwi, A., 2008. Ground improvement of Malaysian peat soils using stabilized peat-column
techniques. Ph.D thesis, University of Malaya, Kuala Lumpur(Malaysia). 260 pp.
Anderson, J.A.R., and Muller, J., 1975. Palynological study of a Holocene peat and Miocene
coal deposit from NW Borneo. In: Review of Palaeobotany and Palynogy 19(1975), 291-35.
Elsevier Scientific Publishing Company, Amsterdam, Netherlands.
Anderson, J.A.R., 1964. The structure and development of the peat swamps of Sarawak and
Brunei. Journal of Tropical Geography 18, 7-16.
Engineering Geology Working Group, 2007. Guideline for Engineering Geological Investigation
in Peat and Soft Soils. Minerals and Geoscience Department of Malaysia.
Wong, L.S., 2010. Stabilization of peat by by chemical binders and siliceous sand. PhD thesis.
University of Malaya, Kuala Lumpur (Malaysia). 260 pp.
Wong, L.S., Hashim, R. and Ali, F., 2009. Unconfined compressive strength of cemented peat.
Australian Journal of Basic and Applied Sciences 3(4), 3850-3856.
Wong, L.S., Hashim, R. and Ali, F., 2011. Unconfined compressive strength characteristics of
stabilized peat. Scientific Research and Essays 6(9), 1915-1921.
Wong, L.S., Hashim, R. and Ali, F., 2008. Engineering Behaviour of Stabilized Peat Soil.
European Journal of Scientific Research 21(4), 581-591.