A Geotechnical Exploration of Peat Soil : Engineering Classifications and Field Surveys

Adnan Zainorabidin

Assoc. Professor, Faculty of Civil and Environmental Engineering, Universiti Tun Hussein Onn , 86400 Batu Pahat, , Malaysia. [email protected]

Habib Musa Mohamad Universiti Tun Hussein Onn Malaysia. Faculty of Civil and Environmental Engineering Tabanac Street 91124, , Sabah, Malaysia. [email protected]

ABSTRACT Assessment and exploration of tropical peatland in Sabah, Malaysia forests requires a series laboratory and field analyses. The objective of this study is to carry out an in-depth study and to classify the engineering properties of Sabah peat soil in Lumadan area. Peat exhibits unique geotechnical properties, highly organic, extremely compressible and is known to be problematic for construction industries. This paper reviews and investigates the profiles with reference to the physical and geotechnical properties. Peat in this region is embedded at depth ranging between 1.5m to 3.0m beneath the ground surface and has massive thickness reaching 6m in some locations in Beaufort, Sabah especially in Batu 54. The laboratory experimental results showed Lumadan peat has high fibre and organic content and classified as hemic peat. KEYWORDS: peat; profile; engineering properties; depth; hemic.

INTRODUCTION Sabah or formerly known as is one of two Malaysia’s easternmost state besides where the states are founding members of the Malaysia federation. It is located on the northern portion of the island of Borneo and known as the second largest state in Malaysia. Sabah covers an area of about 73,619 KM2 and bordering the territory of Kalimantan, Indonesia in the southeast and neighbouring close to the international border with Brunei Darussalam sandwiched with Sarawak. Sarawak and Sabah are the states who make up the Malaysian part of the island of Borneo, and are separated from West Malaysia by the . Borneo Island is in the extreme southwestern part of the Pacific Ocean. It is the third largest island in the world, surpassed in size by only Greenland and New Guinea (Britannica, 2016). or formerly known as Jesselton is the capital of Sabah and often referred to as the “Land below the Wind”. Such as a perfect geography and generally mountainous, from the highest peak of

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Mount Kinabalu to lower land, is enriched with diversity. The geology of Sabah is well documented, contrast with geotechnical surveys that still under assiduity in engineering perspective. Thus, this paper is intended to prepare the orientation of a geotechnical engineering exploration of Sabah peat soil from the engineering classification and field surveys. In Malaysia, it is estimated that there are around 2.5 million ha of peat soil land (Teong et. al., 2015) with, Sabah supports the second largest area of peat soils in Malaysia about 4.76% or 116,965 ha According to Wetlands International, Malaysia (2010). However, natural peatlands in Sabah growing as options to development and converted to productive use. Draining and deforestation are often activities to create agricultural land. In Sabah, 2% or 29,000 ha of oil palm plantations occurring on peat land (Gunarso, 2013). The forest conversion to establish oil palm occurred in large scale in Sabah. The undisturbed and disturbed peat land in Sabah summed overall and 62% or about 714,000 ha (Gunarso, 2013). This conversion widely open including met the global demands for food and biofuels that drives forest clearance and the conversion of other land cover types, such as rubber plantations and pineapple agricultural project. Peat with high organic content with fibrous characterises is highly flammable. Peat in strict definition usually refers to the accumulation of a purely one hundred percent organic material and the distinction between soil and vegetative accumulation is not clear (Andriesse, 1988). Thus, in Sabah large areas of natural peat land were destroyed by severe fires in 1981-1982 and were subsequently converted for agricultural purposes continued in 1992, 1998 and 2005 including 12,000 ha of protected peat swamp forest in Binsuluk Forest Reserve (Wetlands International Malaysia, 2010). In general, there are two remaining sites which support the largest areas of peat soil in Sabah, on the and, in the –Segama Valleys. In Sabah, infrastructure construction such as roads in peaty soil is not a major issue since, associated peatland are mainly for an agriculture. A case study conducted by Vincent (2009), in some parts of Sibu, Sarawak the peat formations are well over than 10 meters depth. Hashim and Islam (2008) reported depth of tropical peatland in West Malaysia about 10m. However, the characteristic and behaviour from the engineering perspective of Sabah peat soil is similar to other tropical peat where found in Sarawak and Peninsular Malaysia. Peat poses serious problems in construction due to its long-term consolidation settlements even when subjected to a moderate load (Duraisamy et al., 2007). This study a preliminary surveys that conducted to study the peat soil profile of Sabah peat.

PEAT SOIL DISTRIBUTION The Sabah peat soil information from engineering perspective project was established in 2016. This study conducted to prepare the associated data for engineering purposes. Classification of peat and the index properties are presented in this paper and major focuses in peat soil profile. As an introduction to the Sabah peat soil distribution, classification, indexing and profiling, this study initiated in Lumadan, Beaufort, Sabah. Lumadan located in the Bukau Api-Api cluster area where peat deposit redundantly occurred.

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Lumadan peat, study area KLIAS FOREST RESERVE Borehole 1 Borehole 2 Borehole 3 Borehole 4 BUKAU API- API

PULAU NABAHAN FOREST RESERVE

KAMPUNG HINDIAN FOREST RESERVE

Figure 1: Distribution of Peatland in Sabah (Robert et. al., 1998; Hamzah and Rashid, 2015)

By far the most extensive area lies adjacent to the Padas and Klias Rivers in the Beaufort area, where the alluvium is associated with extensive peat swamps. Some 12,900 ha or equal to 32,000 ac (Robert et. at., 1976) and, have been mapped in that area as shown in Figure 1. Figure 1 in general shows the distribution of peatland in Sabah. In this study, there are 4 boreholes excavated in Lumadan as indicates in the maps for profiling purposes. Bukau Api-Api area in generally described as lowland with peat swamp forest (Robert et. al., 1998). Vol. 21 [2016], Bund. 20 6674

Peat soil distribution in Sabah mainly in Beaufort and Kinabatangan Accounting the largest portion of the area in Beaufort where mostly peat deposit occurred along the Klias Peninsula. Beaufort peat area highlighted and focused on the mapped (Robert et. al., 1998). In Beaufort itself, there few protected peat swamp forest from Klias Forest Reserve (KFR), Kampung Hindian Forest Reserve (KHFR) and Pulau Nabahan Forest Reserve (PNFR). Table 1 shows the major peat swamp forest reserve within Klias Peninsula with protected classes by Sabah’s state government. The Klias Peninsula historically supported 60,500 ha of peat swamp forest (Fox, 1972; UNDP/GEF, 2007). Currently, the Klias Forest Reserve consists of only 3,630 ha peat swamp forest and there are five forest reserves located in this wetland region, of which the largest are Padas Damit freshwater swamp with 9,027 ha and Binsuluk Forest Reserve is about 12,106 ha (Wetlands International Malaysia, 2010). Table 1: Major Peat Swamp Forest Reserve within Klias Peninsula (Matunjau and Ali, 2014)

Forest Reserve Class Area (ha) Soil Type Binsuluk Class I 12,106 Mixed peat swamp forest Klias Class I 3,360 Mixed peat swamp forest Mixed peat swamp forest Padas Damit Class IV 9,339 and nipah swamp Mangroves, mixed peat Kampung Hindian Class IV 580 swamp forest and Gymnostoma swamp forest

In the north bank of the intersect with Batu Puteh and Bilit, there are 14,000 ha of peat. Fortunately, this area lies within Kinabatangan Wildlife Sanctuary and was gazetted in 1999 with 27,000 ha as protected area. Lumadan, it forms part of the Beaufort District, Sabah. The studied peatland covers an area of 15 ha in the private property in commercial agricultural plantation adjacent to the Klias Forest Reserve (Peat Swamp) and 13 km away from the Beaufort township area. Sabah Peatlands mainly found in a thick water-logged that made up in decaying plant material. With high water table, it becomes suppler although composed of unidentified fibres. Lowland of peat areas in Sabah are often flooded and swampy. Most of the peat land area covered by mud and transferable organic particle transported by water flood. Essentially, Sabah peatland distribution are not lies in the area of urban settlement in general. It's just populated by small villages as centres of agricultural and non-developed municipal areas makes the post-construction problem that arises are not often reported. The natural peatland deposit effect to the construction has not yet been written, for only small part with principles of village economy with medium population are often to convert land used to fertile agricultural land. In geotechnical engineering field, are not yet well studied in this area. This paper prepared some preliminary information of peat soil in Sabah as a preliminary surveys in advancing the geotechnical exploration.

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PEAT SOIL PROFILE Data for this study are obtained from field surveys that have been conducted in Lumadan representing peat soil profile from Bukau Api-Api area and data that were collected from Sabah peat valley. Determining the size of the representative area, using peat depth measurements to estimate depth, and obtaining measurements of index properties in the associated area throughout the peat profile by vertical pit sampling using peat sampler technique. This soil profile are used to classify peat soil in Bukau Api-Api intersect area especially in Lumadan. Average insitu peat depth used to recognize the fibre content and structural that formed local peat soil. Known variation in all of these variables among peat types and depth profiles of single peat cores (Ballhorn et al., 2009). In Lumadan field, there are four peat boreholes with cores extracted up to the alluvial clay layer beneath fibrous peat layer. Each of these boreholes established from 40 m subplots along 100m to 150m transects by using Russian peat sampler (Craig, 2014). A 1.5 ha or 150m x 100m land area was studied in agricultural plantation area with parallelogram shape transect by the coordinates at latitude 5.29616940 and Longitude 115.69118810 located in Lumadan and accessible from mile 6 ½, Beaufort – roadway. Four points of boreholes data formed depth profiles illustrations and estimations as shown in Figures 2, 3 and 4. Peat core obtained up to the silty clay layer beneath peat layer. This sampling taken out for every 0.5m deep and finally indicates the insitu peat depth with associated pH value. Figure 2 shows the cross-section of north-south direction of peat deposit in Lumadan. Generally, the above ground land used for agricultural activities such as small medium plantation for pineapple project. Overall, peat depth in cross-sectional of north to south ranged from 1.5m to 3.0m across the area. Average depth in this section is about 2.13m. Peat sampler penetrated until the blueish silty clay found. A region of the peat layer that is to disassociate a stratum of the depth. pH value of peat averagely increased to the depth. This is due to concentration of organic decomposition and undrained conditioned of local peat area. At depth 1.5m, pH value recorded is 3.89 and up to 3.0m deep, pH increased to the 4.5. Observer depicted the peat land condition with irregular subsidence layer beneath peat layer soil profile making it as a region with stacking water and the difference in depth seems to form a basin beneath the ground. In other Borneo region, Kalimantan peat depth measured from peat cores ranging from 1.9m to 4.2m thick (Warren, et. al., 2012). The peat thickness of the Sebangau formation is known to exceed 10m (Jaenicke et. al., 2008). In Lumadan west-east cross sectional direction as shown in Figure 2, three transects boreholes were prepared. The peat layer ranged from 1.5 m to 3m. This profile described a slope beneath the peat layer to the silty clay layer. This conditioned constituted saturated permeable layer. At this section, it is really reflected the peat soil profile impounded by basin shape. Average gross depth about 2.17m. Peat thickness ranged from 2.41 to about 3.4m reported by Neuzil (1997). Huat (2004) stated that, in Malaysia the peat deposits occur at varying depths between 1-20m. While, Zainorabidin and Wijayasekera (2007) observed that, peat predominantly along the coastal area except in Sri Aman, Sarawak. Lumadan area redundantly with peat deposit and far from mountainous surface profile, flat in lowland area and found along Bukau River.

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Figure 2: Cross-section of north-south direction of Lumadan peat deposit Inter-section cross the southwest-northeast direction of Lumadan peat deposit and indicated that, form 10m distance with 1.5m peat depth gradually increased in depth to 2.0m in 40m away from borehole 1 to 3m depth in borehole 3 about 80m away from borehole 1. This cross-sectional depth depicted to slope shape where proven, that there is a basin shape profile beneath fibrous peat layer that increased water stagnant characteristic in peat soil. This increased the chances of high water content in peat and low shear strength due to the undrained peat bogs.

Figure 3: Cross-section of west-east direction of Lumadan peat deposit

Figure 3: Cross-section of west-east direction of Lumadan peat deposit Vol. 21 [2016], Bund. 20 6677

Figure 4: Cross-section of southwest-northeast direction of Lumadan peat deposit According to Jamil et al., (1989), where soil with peat depth of <1.0, 1.0-1.5, 1.5-3.0 and >3.0 m is classified as shallow, moderate, deep and very deep peat. Wong et al., (2008) conducted a test on peatland in Peninsular, Malaysia and found that the water holding capacity of this peat was very high. Sabah peat are categorized as tropical peat the same as Sarawak, Peninsula Malaysia and other parts in Borneo. Peat in Malaysia is categorised as a tropical peat (Anderiesse 1988). In other part of observation in Beaufort, excavation of peat layer found ranged 3m to 6m in Batu 54 near Limbawang, Beaufort. Vincent (2009) reported that, in Sibu, Sarawak peat formations are well over 10m depth. Basin shape profiles in Lumadan increased the acidity of soil to depth. Haider and Gary (2013) concerns that, the surround this of peat subsidence especially when acid sulphate soils which occur frequently underneath the peat, might surface.

PEAT SOIL CLASSIFICATION AND PROPERTIES Peat soil samples are collected from Lumadan intersect to Bukau Api-Api area in Beaufort Sabah. It is accessible by the Kampung Lumadan in Batu 6 by way of agricultural road and unpaved surfaced with gravel in palm estate 13 KM away from Beaufort town. The sampling site located near to the Klias Forest Reserve and peat swamp. Ground water level observed 0.5m from top soil and sample taken 0.4m beneath the ground level. Lumadan peat soil materials are classified using von Post scale of decomposition by visual observation. Characterization tests of peat soil were performed on each soil sample in accordance with accepted BS 1377: 1990 and ranges from three different type of peat according to the USDA classification system and Von Post Scale. The results of the characterization tests are in Table 3. A visual examination of peat have been done in site by squeezing the peat soil material in hand of an insitu undisturbed saturated clod of soil sample where water expelled and soil fibre material remained in hand. From the observation, Lumadan peat examined of the colour dark brown, hickory Vol. 21 [2016], Bund. 20 6678 and constantly brown colour. The residue of peat observed is very pasty and partially moderate- highly decomposed peat with indistinct plant structure. Core 1 and Core 2 categorized as H6. In some condition, peat a very faintly, very dark hickory and pasty with highly decomposed material. This characteristic owned by core 3 and core 4 peat samples were classified as H7 with all cores are hemic peat.

Table 3: Index Properties of Lumadan, Beaufort, Sabah peat soil

Properties Core 1 Core 2 Core 3 Core 4 Average Moisture Content (%) 491.16 489.09 985.30 887.88 713.35 Liquid Limit (%) 211 225 299.5 289 256.13 Organic Content (%) 55.82 53.97 95.51 55.58 65.22 Von Post Scale H6 H6 H7 H7 H6 Fibre Content (%) 76.85 66 79.40 61.61 70.97 Specific Gravity 1.44 1.37 1.28 1.25 1.34 Peat soil pH 4.0 4.8 4.9 4.7 4.6 Ground water pH 4.4 4.2 4.2 4.4 4.3

Peat type Fibric Hemic Fibric Hemic Hemic

A laboratory testing program has been conducted to analyse the index properties of peat soil. Moisture content variously found ranged from 489.09% (core 2) to highest 985.30% (core 3). Lumadan peat indicates high moisture and water content. This is can be related to the nature of Lumadan peat profile a basin with undrained peat bogs condition dominated the area. High water content due to the capability of peat in holding water. Wong et al., (2008) conducted a test on peatland in Peninsular, Malaysia and found that the water holding capacity of this peat was very high and it was found dark brown in colour and the soil was classified H4 according to Von Post classification system. The water content of peat researched in West Malaysia ranges from 200 to 700% (Hashim and Islam, 2008). The properties of peat are greatly dependent on the formation of its deposits and the organic content. The average organic content for Lumadan peat is about 65.22%. Lumadan peat has high organic content that formed its physical properties. Soil scientists have defined peat as a soil with organic content greater than 35% however; geotechnical engineers define the peat as soil with organic content greater than 20% (Huat 2004). Liquid limit are recorded averagely 256.13% this area. The liquid limit behaviour seems dependant on the moisture content of peat soil, the higher moisture content the higher liquid limit of peat itself. In Peninsular Malaysia, Huat (2004) stated that, the organic content in the range of 65 % to 97 % and the Atterberg limit was in the range of 200 % to 500 % as reported by Huat (2004). Kazemian et al., (2011) in their study described that, in fibrous peat, the force is taken by the fibres as it acts as reinforcement if the direction of the load is in the same direction as the fibres. Different with this Sabah tropical peat, the fibre content is only about 70.97%. Islam and Hashim (2008) in their research recorded the fibre content for Klang peat is about 90.39%. Lumadan has lower fibre content compared to Klang peat. Such fibres can be seen as a compressible solid, Lumadan peat observably pastier and very soft. The content of peat differs from location to location due to the factors such as the origin of fibre, temperature, climate, and humidity (Huat, 2004). Specific gravity ranged from 1.25 to 1.44 and relatively small. Hence, it makes the peat grains, plates, fibres or element is light and the particle of Vol. 21 [2016], Bund. 20 6679 peat is porous (Mesri et al., 1997). Lumadan peat has low acidity in pH scale ranged 4.0 to 4.9. Moore (1997) affirmed that, peatlands are ecosystems resulting from the successive accumulation of plant remains at sites where local conditions inhibit the decomposing activity of microorganisms, such as areas of excess moisture, low pH, lack of oxygen, and low temperatures. In soil classification system, peat can be classified into three distinguish degrees of decomposition which are fibric, hemic and sapric. The classification stated that, for more than 66% of fibre content it can be classified as fibric and 33% to 66% fibre content are classified under hemic peat. In this field surveys, peat found variously from fibric and hemic form. Core 1 and core 3 classified as sapric, core 2 and core 4 more hemic peat. This is due to the different peat bores location and different degree of decomposition. In engineering perspective, tropical fibric peat will cause highest settlements followed by hemic and sapric when subjected to any load over the time period (Duraisamy et al., 2007). Testing is carried out continuously from ground level to the final sampler depth. The continuous penetration profiles enable easy recognition of dissimilar layers and even thin strata by the observed variation in peat soil layer profile. Figures 5, 6, 7 and 8 shows the pictorial profile of peat soil in Lumadan, Beaufort. Table 4, describes the physical observation and characteristic of Lumadan, Beaufort peatland profiles. In general, peat soil profiles ranged from 1.5m to 3.0m depth in this area. Silty clayey soil found beneath the subsidence of peat layer. In the encountered region of peaty and silty clayey soil, there is a different colour observed from dark brown turn to brunette in colour.

Table 4: Physical observation and characteristic of Lumadan, Beaufort peatland profiles

Depth, m Von Post Colour Physical characteristic

Borehole 1 0 – 0.5 Hemic Dark brown Organic horizon, partly decomposed 0.5 – 1.0 Hemic Brown Mixed with humus and darkened 1.0 – 1.5 - Hickory Mixed peat with silty clay Borehole 2 0 – 0.5 Fibric Dark brown Organic horizon, partly decomposed 0.5 – 1.0 Hemic Dark brown Black, humified and loamy peat 1.0 – 1.5 Hemic Dark brown Mixed with humus and darkened 1.5 – 2.0 Hemic Brown Dark reddish brown and silty peat Borehole 3 0 – 0.5 Hemic Dark brown Loose, fibreless, loamy peat 0.5 – 1.0 Fibric Brown Fibrous, pasty and loamy peat 1.0 – 1.5 Fibric Brown Fibreless and very pasty 1.5 – 2.0 Hemic Hickory Fibreless, undecomposed wood 2.0 – 2.5 Hemic Umber Fibreless, very soft, succulent 2.5 – 3.0 Hemic Brunette Mixed peat with silty clay Borehole 4 0 – 0.5 Hemic Dark brown Organic horizon, partly decomposed 0.5 – 1.0 Hemic Brown Fibrous, pasty and loamy peat 1.0 – 1.5 Hemic Hickory Fibreless, mixed silty peat 1.5 – 2.0 Sapric Hickory Mixed peat with silty clay Vol. 21 [2016], Bund. 20 6680

Four boreholes representative profiles of the area of Lumadan and shown in Figure 5 for borehole 1 with 1.5m depth, Figure 6 represented borehole 2, 2.0m depth, Figure 7 borehole 3 with 3.0m depth and Figure 8 shows the peat soil profile associated for borehole 4 in 2.0m depth according to the homogeneity of layers. Through the peat soil profiles, it can be seen that the peat has fibrous characteristics with unrecognized material plants. Roughly, profiles from Figures 5 and 6, it can be concluded as decomposed plant materials with poorly decomposed material wood and muddy peat condition but its shows structure of peat. Well decomposed peat material observed in Boreholes 3 and 4 represented in Figures 7 and 8. Fibreless peat and the residue consist partially of woods, roots and unrecognised fibre structure. There are no significant differences among profiles in Lumadan peatland and layers were observed in samples under same regional characteristics. Furthermore, all layers observed differed physically from the fibric and hemic peat layer, which had different decomposition level. Averagely, the unrecognized material with moderate decomposition level are observed. Silty clay layer be found under 1.5m to 3.0m beneath fibrous peat layer. Silty clay seen occasionally with mixed peat. Depth of peat is 1.5 m and according to Jamil et al., (1989) classification system it can be classified moderate depth peat. Hashim and Islam (2008) stated, in Peninsular peat study, indicated that the soil was dark brown in colour and Lumadan peat similar to their findings, fibrous peat mixed with vegetal fibre, wooden chips inside and roots appear on top layer. Ground water table is below 0.3m from top surface and pure peat layer is up to 1.5m and below peat layer there is a slightly organic clay layer up to 6m depth. Past studies concluded that peat is a mixture of fragmented organic materials formed in wetlands under appropriate climatic and topographic conditions and it is derived from vegetation that has been chemically changed and fossilized (Edil and Dhowian, 1980). In natural state, peat consists of water and decomposed plant fragment with virtually no measurable strength (Munro, 2005).

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Figure 5: Lumadan peat soil profile from borehole 1 Depth 0 – 1.5m

Dark brown to peanut in colour. From 1.0m to 1.5m, mixed peat with

silty clay appeared. Overall, fibrous peat mixed with vegetal fibre,

wooden chips inside appears.

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Figure 6: Lumadan peat soil profile from borehole 2 Depth 0 – 2.0m Fibrous peat mixed with unrecognized fibre, wooden chips inside and moderate decomposition plants material

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Figure 7: Lumadan peat soil profile from borehole 3 Depth 0 – 3.0m

Fibreless, very soft, succulent and loamy peat with very pasty condition represents undrained peat bogs. Bottom layer observed mixed peat with silty clay. Partially decomposed wood materials appears occasionally.

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Figure 8: Lumadan peat soil profile from borehole 4 Depth 0 – 2.0m

Organic horizon and partly decomposed. Hemic peat with fibrous condition. Mixed peat with silty clay occasionally observed. Organic rich peat soil and crumbled structure. Vol. 21 [2016], Bund. 20 6685

CONCLUSION Based on the field and experimental data obtained in the laboratory, it can be concluded that Lumadan, Beaufort peat profile depth ranged from 1.5m to 3.0m and can be classified as moderate to massive peat depth. Averagely, the unrecognized material with moderate decomposition level are observed. Decomposed plant materials with poorly decomposed material wood and muddy peat condition but its shows structure of peat. Fibrous peat mixed with unrecognized fibre, wooden chips inside and moderate decomposition plants material appears in peat soil profiles. Moisture content variously found ranged from 489.09% to highest 985.30%. It is related to the nature of Lumadan peat profile a basin with undrained peat bogs condition dominated the area. Peat found variously from fibric and hemic form, generally found as hemic peat in Lumadan. Organic horizon and partly decomposed. Hemic peat with fibrous condition. Mixed peat with silty clay occasionally observed. Organic rich peat soil and crumbled structure.

ACKNOWLEDGMENT This research was supported by the research team and independently initiated to the research extend of peat soil in Malaysia. The authors gratefully acknowledge use of the services and private peatland owner Mr. Kurus and Mr. Albert to their supports in developing research in Sabah.

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© 2016 ejge

Editor’s note. This paper may be referred to, in other articles, as: Adnan Zainorabidin and Habib Musa Mohamad: “A Geotechnical Exploration of Sabah Peat Soil: Engineering Classifications and Field Surveys” Electronic Journal of Geotechnical Engineering, 2016 (21.20), pp 6671-6687. Available at ejge.com.