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Keywords

Saline soil, Compaction, subbase, Crushed stone, Gravel, Maximum dry density, Optimum moisture content, Soil improvement, Soil strength

Document Type

Article

Abstract

Saline soils are widespread in southern Iraq and are generally characterized by low shear strength and poor compaction behavior, which limits their suitability for engineering applications. This study aims to evaluate the effectiveness of mechanical stabilization using locally available granular materials—subbase, crushed stone, and fine gravel—to improve the compaction properties and shear strength of saline soils. The experimental program included modified Proctor compaction tests conducted in accordance with ASTM D1557 and direct shear tests conducted in accordance with ASTM D6528 on untreated soil and treated soil mixtures prepared with additive contents of 7%, 15%, 30%, and 50% based on the dry weight of the soil. The compaction test results showed that the addition of granular materials had a significant effect on the optimum moisture content and maximum dry density of the soil. The lowest values for optimum moisture content and improved compaction behavior were obtained at a 15% ratio of subbase and 15% crushed stone, while the highest value for maximum dry density (1.99 g/cm3) was achieved at a 50% gravel content, indicating improved particle compaction and a reduction in void ratio. Direct shear test results also showed a marked improvement in shear strength coefficients after stabilization. The apparent cohesion increased from 82 kPa for untreated soil to 105.6 kPa when 15% of the subbase layer was added, and reached 122 kPa at a 50% gravel content. Similarly, the angle of internal friction increased from 11° to a maximum value of 21° when 15% crushed stone was added, as a result of improved intergranular bonding. The results indicate that stabilization with granular materials significantly improves the engineering behavior of saline soil by increasing density, reducing the moisture requirement under optimal conditions, and enhancing the soil's resistance to shear deformation. Among the tested mixtures, 15% subbase and crushed stone provided the most efficient improvement in compaction characteristics, while 50% gravel produced the greatest increase in apparent cohesion under the direct shear test conditions. Therefore, locally available granular materials can be considered a practical and economical mechanical stabilization option for improving the compaction behavior and shear strength characteristics of saline soils. However, further CBR, consolidation, permeability, and long-term durability tests are required before confirming their suitability for pavement subgrades, embankments, or shallow foundations.

DOI

10.30684/2412-0758.1574

First Page

19

Last Page

35

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