Comparative Analysis of the Geotechnical Properties of Soil for Road Subgrade in Anambra State: A Case Study of Onitsha, Nnewi, Awka, and Ihembosi

Abstract

Before commencing any engineering project, it is crucial to understand the geotechnical properties of the soil. The construction of buildings, roads, and bridges relies on solid and efficient design criteria, which require a thorough assessment of the soil’s characteristics at the construction site. Soil investigation is essential for determining the behavior and stability of different soil types under stress, ensuring the feasibility and durability of engineering projects. To determine whether the soil from Onitsha, Nnewi, Awka, and Ihembosi in Anambra State is suitable for use as road subgrade, this study examines its geotechnical properties. Laboratory tests conducted include particle size distribution, specific gravity, Atterberg limits, shear strength, permeability, and compaction characteristics. The findings provide insights into the soil’s engineering behavior, particularly regarding its load-bearing capacity and potential need for stabilization.

Introduction

The performance, durability, and sustainability of road pavements are heavily influenced by the characteristics of subgrade soils. In Nigeria—particularly in urbanizing regions like Anambra State—rapid urbanization, population growth, and increasing vehicle traffic accelerate pavement deterioration. Poor consideration of local soil properties during road design is a major contributor to early pavement failure.

2. Need for Localized Geotechnical Assessment

Studies (Ezeh et al., 2023; Ugwu et al., 2021; Agu & Okafor, 2022) stress the importance of conducting site-specific geotechnical evaluations to understand key soil properties such as:

• Particle size distribution

• Plasticity index (Atterberg limits)

• Compaction characteristics

• Moisture-density relationship

• California Bearing Ratio (CBR)

These parameters are critical for designing pavement structures that are both durable and cost-effective.

3. Regional Soil Variability in Anambra State

Significant variation in subgrade soil characteristics exists across locations like Onitsha, Awka, Nnewi, and Ihembosi, due to differing geological and environmental conditions. This variability affects the bearing capacity, compaction, and moisture sensitivity of soils, necessitating comparative studies to guide pavement engineering.

4. Previous Research and Recommendations

• Anene et al. (2023) recommended a storey car park at Eke Nibo to manage traffic, highlighting the role of soil analysis in structural planning.

• Obi et al. (2023) emphasized integrating soil characterization into modern pavement designs to reduce lifecycle costs.

• Okafor & Okeke (2022) showed that soils with low bearing capacity or high plasticity lead to increased maintenance, safety risks, and economic disruption.

5. Laterite Soils and Engineering Significance

Lateritic soils are commonly used in road construction in Nigeria. Their strength depends heavily on clay/silt content and proper classification. Past studies (Ayetey & Freping, Adeyemi & Wahab) confirm the reliability of well-characterized lateritic soils for pavement use.

Materials and Methods Summary:

A. Materials Used

• Laterite soil (sampled from Onitsha, Awka, Nnewi, and Ihembosi)

• Portable water for laboratory procedures

B. Laboratory Tests Conducted:

1. Moisture Content Determination

   • Measured the ratio of water to dry soil mass to assess water influence on soil behavior.

2. Particle Size Distribution (PSA)

   • Mechanical sieve analysis to determine grain sizes and classify soils using BS 1377 (1990).

3. Specific Gravity Test

   • Pycnometer method to determine the ratio of soil solids to water density—key for soil classification.

4. Atterberg Limits (LL, PL, PI)

   • Casagrande apparatus used to determine plasticity and consistency, essential for soil classification and construction suitability.

5. Standard Proctor Compaction Test

   • Established Optimum Moisture Content (OMC) and Maximum Dry Density (MDD), vital for construction compaction standards.

Relevance to Broader Construction Work

• In any civil engineering project, understanding soil behavior is fundamental—whether for buildings, roads, or other infrastructure. Soil properties influence load-bearing capacity, structural safety, and project sustainability.

• The text also highlights broader applications in concrete technology, including the use of alternative aggregates, fiber reinforcement, and supplementary cementitious materials (SCMs) like fly ash, rice husk ash, and nano-silica to enhance concrete performance.

Conclusion

The geotechnical assessment of lateritic soils from Anambra State showed that while some samples met the required AASHTO and Federal Ministry of Works and Housing standards, others did not. Sample C (Awka) is suitable as subgrade material in road construction, while Samples A (Onitsha), B (Nnewi), and D (Ihembosi) require the addition of admixtures to enhance their engineering properties. It is recommended that Sample C be used directly as subgrade material, and that Samples A, B, and D be considered with admixtures for improved performance. Further geotechnical investigations on lateritic soils from various locations and depths in Anambra State are suggested to better guide future road construction project in the region.

References

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Copyright

Copyright © 2025 Anene W.C, Ibekwe O.S, Okeke C.S. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.