Malaysia, namely Tanjung Dua Belas and Air Hitam, to determine their suitability as compacted landfill liner

materials. An integrated laboratory investigation was conducted to determine key physical properties,

compaction behaviour under varying energy levels, consolidation characteristics, and stress-dependent hydraulic

conductivity. The results reveal clear differences in engineering performance between the two soils. The Air

Hitam soil achieved higher Maximum Dry Density (MDD) values ranging from 1.832 to 1.987 g/cm³ at lower

Optimum Moisture Contents (OMC) between 11.92% and 14.81%, demonstrating more efficient particle

packing and compaction response compared to the Tanjung Dua Belas soil, which recorded MDD values between

1.410 and 1.565 g/cm³ with higher OMC ranging from 18.56% to 22.56%. Consolidation analysis further

indicated lower settlement for Air Hitam (1.401 mm) relative to Tanjung Dua Belas (1.583 mm), reflecting

improved stiffness and reduced compressibility. Hydraulic conductivity decreased with increasing applied stress

Malaysia’s rapid population growth and industrialisation have significantly increased municipal solid waste

(MSW) generation, thereby intensifying reliance on landfilling as the primary disposal method [1]. The

performance of landfill facilities depends largely on the engineering behaviour of liner and cover materials,

where geotechnical parameters such as compaction, settlement, and hydraulic conductivity play critical roles in

maintaining structural stability and preventing environmental contamination [2]. Properly designed liner systems

must demonstrate adequate density, minimal compressibility, and low permeability to effectively restrict leachate

migration. Therefore, this study evaluates the relevant physical and engineering properties of selected soils and

examines their influence on compaction characteristics, settlement behaviour, and hydraulic conductivity in

order to establish meaningful correlations that can enhance landfill liner design and minimise environmental

comprehensive data linking index properties with compaction response, consolidation behaviour, and hydraulic

performance has introduced uncertainty in predicting the long-term behaviour of landfill liner materials [5]. This

challenge is particularly significant in tropical regions such as Selangor, where fluctuations in moisture content

and variations in mineral composition may substantially alter soil behaviour under load [6]. Consequently, a

systematic assessment of the interrelationship between soil properties and engineering performance is required

to reduce design uncertainties and improve landfill management strategies. This study aims to address these gaps

by determining the physical properties of soils obtained from the Tanjung Dua Belas and Air Hitam landfill sites.

It further evaluates the compaction characteristics, consolidation behaviour, and hydraulic conductivity of the

selected samples. In addition, the study analyses the relationships between physical properties and engineering

are therefore representative of laboratory-scale evaluation and may not fully replicate field-scale performance.

Furthermore, the conclusions drawn are specific to the selected landfill sites and may not be directly

generalisable to all landfill conditions in Malaysia. Nonetheless, this study provides valuable insight into the

interaction between material properties and engineering performance in landfill liner applications. While the

present investigation is limited to two landfill sites, the selected soils provide useful comparative insight into the

engineering response of tropical landfill soils under controlled laboratory conditions. The selected test

programme was designed to capture the most critical engineering parameters governing landfill liner

performance, namely compaction efficiency, settlement response, and resistance to fluid migration, while also

environments, supporting the suitability of this location for evaluating compaction response and permeability

The second study location was the Air Hitam Sanitary Landfill in Puchong, Selangor, situated at 3°00′21″N,

101°06′26″E, as presented in Figure 2. This landfill has been operating since 1995 and has received an estimated

6.3 million tonnes of municipal solid waste. In contrast to Tanjung Dua Belas, the subsurface conditions at Air

Hitam are associated with granitic residual soils exhibiting variable degrees of weathering and mineralogical

opportunity to compare two distinct residual soil profiles that are commonly encountered in landfill

environments within Selangor, thereby improving the comparative assessment of their engineering suitability

for landfill liner applications. Approximately 90 kg of soil was excavated from a depth of about 0.5 m to represent

the active zone influenced by leachate movement. The selected depth was considered appropriate to represent

the near-surface soil layer most likely to be affected by landfill leachate infiltration and environmental exposure.

Bulk disturbed samples were collected from each site to provide sufficient material for the full suite of laboratory

A series of laboratory tests were conducted to determine the basic physical properties of the collected soil

samples, including pH, particle density, particle size distribution, Atterberg limits, and shrinkage limit. The pH

value was determined using a 1:2.5 soil-to-water ratio following BS 1377-3:1990, to assess the acidity or

alkalinity of the samples. Particle density was obtained using the pycnometer method in accordance with BS

1377-2:1990. The particle size distribution was analysed through combined wet sieving and hydrometer analysis

following BS 1377-2:1990 to classify the proportions of gravel, sand, silt, and clay. The Atterberg limits,

including liquid limit, plastic limit, and plasticity index, were determined using BS 1377-2:1990 to evaluate the

soil’s plasticity characteristics. The shrinkage limit was measured in accordance with BS 1377-2:1990 to assess

conducted, namely Standard Proctor Compaction (SPC), Reduced Proctor Compaction (RPC), and Modified

Proctor Compaction (MPC), in accordance with BS 1377-4:1990, as differentiated in Table 1. For each method,

soil passing through a 4.75 mm sieve was prepared, and the water content was adjusted at different intervals to

determine the Optimum Moisture Content (OMC) and Maximum Dry Density (MDD). In the Standard Proctor

Test, soil was compacted in a 1-litre mould in three layers, each subjected to 25 blows using a 2.5 kg rammer

dropped from a 300 mm height. The Reduced Proctor Test adopted the same configuration but used 15 blows

457 mm drop height, compacting the soil in five layers of 25 blows each to replicate higher energy compaction

conditions. After compaction, the bulk and moisture contents were determined to compute dry density values,

apparatus to simulate the pressure typically exerted on landfill liner materials shown in Figure 3. A saturated

specimen was placed within a consolidation ring and sandwiched between porous stones to facilitate even

drainage. A seating pressure of 6 kPa was first applied to ensure full contact, followed by incremental loads of

12, 25, 50, 100, 200, and 400 kPa, each maintained for one hour. Deformation readings were recorded using a

dial gauge throughout the loading period. The unloading phase was conducted in two stages to assess rebound

potential. Upon completion, the specimens were oven-dried to obtain their moisture content. The Coefficient of

Consolidation (Cv) was determined using the square root of time approach, while the Compression Index (Cc)

was calculated from the linear segment of the void ratio–log pressure (e–log p) relationship. The total

respective OMC values, and vertical pressures of 25, 50, 100, and 200 kPa were applied to replicate field

overburden stresses. The flow rate through the saturated soil was recorded over a specified period, and hydraulic

conductivity was computed using Darcy’s law. This procedure provided an assessment of soil permeability under

controlled stress conditions, reflecting the influence of density and structure on fluid migration within landfill

do not fully account for field-scale variability such as construction heterogeneity, climatic exposure, wet–dry

cycling, and long-term waste loading. Therefore, the engineering behaviour reported in this study should be

The chemical condition of the investigated soils was assessed through pH testing using a 1:2.5 soil-to-water ratio

in accordance with BS 1377-3:1990. The measured values indicate that both soils exhibit strongly acidic

behaviour, which is commonly associated with landfill environments subjected to prolonged leachate exposure.

As shown in Table 2, the average pH recorded for the Tanjung Dua Belas sample was 2.81, while the Air Hitam

sample exhibited a slightly higher value of 3.65. These results classify the soils as highly to very strongly acidic.

Such acidity is typically linked to the presence of decomposed organic matter and sulphate-bearing compounds

generated from municipal solid waste degradation. Previous investigations have reported comparable acidic

characteristics in soils surrounding Malaysian landfill sites, indicating that continuous interaction with leachate

Similar pH conditions have also been documented at the Air Hitam landfill, confirming that acidic soil behaviour

composition, soil fabric, and long-term engineering performance, particularly in liner systems where chemical

other Malaysian landfill liner materials, stabilization or treatment measures may be necessary to enhance their

The particle density of the investigated soils was determined in accordance with BS 1377-2:1990 using the small

pycnometer method to evaluate the mineralogical characteristics of the samples. The measured values indicate

variation between the two landfill sites, reflecting differences in material composition. As shown in Table 3, the

particle density of the Tanjung Dua Belas soil was 2.22 Mg/m³, whereas the Air Hitam soil recorded a higher

higher organic content or lighter mineral constituents within the soil matrix. This difference is important because

particle density affects the solid-phase mass per unit volume of soil, which in turn influences dry density,

compressibility, and the ability of the soil skeleton to resist deformation under loading. In contrast, the higher

particle density observed at Air Hitam implies a greater proportion of heavier mineral components, potentially

including iron oxides or denser silicate minerals. Previous studies have reported that soils containing elevated

organic matter typically exhibit reduced particle density values due to the lower specific gravity of organic