Abstract:
The pavement subgrade acts as foundation for a pavement structure. The life and performance of a pavement structure is greatly dependent on the strength properties of subgrade layer. It is common for pavement engineers to encounter weak subgrade soil conditions, not suitable for highway construction. Depending on the soil type, one of the techniques available to enhance the in-situ strength and durability of subgrade soils is by stabilization. The stabilization process constitutes mixing of additives like lime, cement, fly-ash and asphalt, depending on the soil type during the construction stage to improve the strength properties. Incorporation of subgrade stabilization in pavement design reduces the thickness of subsequent pavement layers and is thereby an economical practice.
The subgrade soils of Gujranwala–Lahore section of National Highway-5 (N-5) are mostly low plastic clayey soils. The clayey soils with poor drainage properties coupled with non-provision of proper drainage structures results in collection of surface runoff along the road alignment, particularly during rainy season. Unsuitable subgrade soil and POOR drainage conditions are one of the reason causing distresses in the pavement structure, primarily rutting. During the recent past, pavement in this section has been rehabilitated a number of times without significant improvement in durability/performance.
The study has been carried out to investigate the stabilization potential of the subgrade soil of said section of N-5. Lime and a combination of lime and bagasse ash have been used as additives. Bagasse ash is a by-product of sugar industry, while bagasse is burnt for the purpose of electricity generation. Bagasse ash contains high silica and alumina contents and is therefore a pozzolanic material, reacting with calcium to form cementitious calcium silicate and aluminate hydrates. Result of unconfined compression tests show an increase of almost 50 times in soaked strength when lime alone was used and 64 times when a combination of lime-bagasse ash was used for stabilization (strength increased from 4 psi to 194 psi and 257 psi with lime and lime-bagasse ash respectively). Soil also experienced an increase in CBR value by almost 3.5 and 4.5 times with lime and a lime-Bagasse ash combination respectively. Swell potential of the soil also reduced from 2.5 percent to almost zero.
The study shows that strength and durability of soil increased significantly with lime stabilization. The use of Bagasse ash in combination with lime further enhanced the strength and durability of subgrade soil with the most significant influence on CBR on wet of optimum. Thus soil stabilization can be carried out effectively by careful monitoring of mixing and curing arrangements in the field.
