Universitas Musamus Researcher Reveals Dangers of Bentonite-Clay Soil Mixtures Under Soaked Conditions

Apriyani Multitach Publisher Kamis, Agustus 20, 2026

FORMOSA NEWS

MERAUKE, Formosa News – The bearing capacity of expansive clay soil mixed with bentonite drops drastically, making it unsuitable for use as a road pavement subgrade when submerged in water. This soil mechanics research was conducted by Hairulla, a researcher from the Department of Civil Engineering, Faculty of Engineering, Universitas Musamus. The key findings were officially published in July 2026 in the scientific journal International Journal of Advanced Technology and Social Sciences (IJATSS).

This study is crucial for providing technical guidance to infrastructure construction planners. The bearing capacity of the subgrade soil directly determines the durability of highways, buildings, and bridges. Misidentifying the expansive behavior of soil when exposed to water can trigger fatal cracking, foundation shifts, and structural subsidence.

The Threat of Expansive Soils in Road Construction

Expansive clay soil is highly sensitive to climate and moisture changes. Under dry conditions, this soil shrinks and hardens, but upon absorbing water, its volume swells dramatically. This high swelling-shrinkage behavior frequently causes severe damage to road structures.

Volume changes during low moisture content lead to non-uniform settlement, causing pavements to crack or collapse. Conversely, increased moisture content causes soil expansion, exerting upward pressure (uplift) that can lift structures built above it. Therefore, evaluating soil bearing capacity through California Bearing Ratio (CBR) testing is essential to measure subgrade resistance prior to road construction.

Laboratory Testing of Bentonite and Embankment Soil Mixtures

To evaluate the mechanical behavior of expansive soils, Hairulla collected embankment soil samples from Gowa Regency, South Sulawesi, and bentonite material imported from Bandung City. Physical and mechanical testing was conducted at the Soil Mechanics Laboratory, Faculty of Engineering, Universitas Hasanuddin.

The researcher prepared soil mixture variations containing 0%, 25%, 50%, 75%, and 100% bentonite. High bentonite concentrations were tested because its montmorillonite mineral content is known for exceptionally high water absorption and swelling potential. Tests were carried out using two standard soil bearing capacity methods:

-Unsoaked CBR Test: Measures soil strength and hardness under dry or normal moisture conditions.

-Soaked CBR Test: Measures soil strength after water immersion to simulate field flooding or rainwater ponding while measuring the swelling percentage.

Key Research Findings

Based on laboratory analysis, the study yielded several major insights regarding the physical and mechanical properties of the soil:

-High-Plasticity Clay Classification: Under the USCS classification system, all pure embankment soil and mixture samples were categorized as high-plasticity clay (CH). Under the AASHTO system, the soils were classified as A-7-5 clayey soils, with over 50% passing through the No. 200 sieve.

-Good Dry Performance (Unsoaked): In unsoaked conditions, the CBR values across all mixture variations ranged between 7% and 20%. According to road construction standards, this falls into the fair to good rating, making it theoretically suitable for subgrade use.

-Severe Drop Under Soaked Conditions: Once submerged in water, the CBR values for all bentonite-containing mixtures plummeted below 2%. The 25% bentonite mixture yielded a soaked CBR of just 2.0%, while 100% bentonite dropped to 1.3%. These values fall far below the minimum 6% CBR requirement for subgrade suitability.

-High Swelling Potential: Higher bentonite content directly correlated with greater soil expansion percentages. Compaction energy also influenced expansion; samples subjected to 56 blows exhibited swelling up to 5.9% due to the larger volume of compacted material.

Implications for the Construction Industry and Public Policy

These findings offer a critical warning for contractors, highway design consultants, and public works departments. Utilizing bentonite or soils with high montmorillonite content without additional chemical stabilization agents (such as lime, cement, or fly ash) poses severe risks if placed directly as road subgrades in flood-prone or high-rainfall regions.

Ignoring soaked CBR evaluations can result in premature structural pavement failure. The researcher recommends that highly expansive soils must be excavated and replaced or chemically stabilized before initiating pavement construction.

Author Profile

  • Hairulla, S.T., M.T.: Researcher and lecturer in the Civil Engineering Department, Faculty of Engineering, Universitas Musamus, Merauke, South Papua. His expertise spans geotechnical engineering, soil mechanics, and subgrade stabilization for transportation infrastructure.

Research Source

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