Soil Stabilization for Road Construction

The growth and sustainability of human civilization depend heavily on the road infrastructure. A nation’s overall progress and the health of its economy are reflected in the quality and condition of its road network.

The construction and growth of National/State Highways, Expressways/Access Controlled Highways, Rural Roads, Urban Roads, Flyovers, Tunnels, elevated Corridors, ROBs, VUPs, pedestrian facilities, etc. have all advanced significantly during the past 20 years across the nation.

The quality and user experience of the road and highway infrastructure have been actively improved by the efforts of the government and the road construction sector. Furthermore, technology improvements combined with indigenous ideas enable the completion of the most difficult road projects in a timely and ecologically sensible manner, with a lower lifecycle cost.

History

The first paved road was created in the ancient Mesopotamia kingdom in BC 4000. Following that, about 3300 BC, log roads/timber tracks were constructed in Glastonbury, England as an upgrade over mud or dirt roads.

Brick-paved roads were developed in the Indian subcontinent’s Indus Valley Civilization at the same period. Paved roads were built in the Middle East and Greece as stone-cutting skills improved.

Around 2000 BC, the Minoans built a 50-kilometer-long paved road through the mountains from Knossos in North Crete to Gortyn and Lebena, a port on the island’s south coast, with side drains, a 200-mm-thick pavement of sandstone blocks bound with clay-gypsum mortar, covered by a layer of basaltic flagstones, and separate shoulders.

Material

The modern approach to road and highway infrastructure planning, design, construction, and maintenance is primarily concerned with durability, safety, sustainability, economy, environmental protection, and so on. A number of materials and technologies are used in the construction and maintenance of roads, highways, and associated infrastructure.

Road construction and maintenance operations make use of both natural and man-made resources, and the road industry is a key consumer of aggregates and other materials. Crushed stone is the most widely used aggregate material, followed by gravel, sand, and other aggregate materials.

Due to the rapid increase in road development programmes in the country, the supply of high-quality aggregates is becoming a cause for concern. Apart from concerns over decreasing reserves of limited natural resources, the environmental consequences of aggregate exploitation are a major cause of concern across the country.

It is also well known that environmental degradation has a high societal cost as well as other consequences. These effects include loss of green cover, noise, dust, blasting, and pollution issues that contribute to environmental deterioration, among other things.

Development of Road

Civil engineering constructions, such as roads and highways, are preferably built on strong and stable soil. Soil or gravelly material is utilized as the primary component of pavement layers in road construction projects.

To have the required strength against tensile stresses and strains, as well as other qualities such as volume stability, compressibility, permeability, durability, and so on, the soil used to make pavement must meet the specifications set by MORTH/MORD and IRC.

However, it is difficult to construct roads on poor sub grade, particularly soft/expansive soil, which lacks sufficient strength and endangers the safety, durability, and serviceability of civil engineering structures.

When subjected to even slight load increases, soft/expansive soil is less stable and vulnerable to significant primary and long-term consolidation settlements, generating fractures and early distress, leading to premature failure of the road surface or structure.

Resolution

The difficulty of improving unsuitable soils has continually forced engineers to develop new methods and ways to achieve this objective. The notion of improving soil qualities by stabilization with various sorts of additives goes back over 5000 years, when soil was stabilized with lime or pozzolans, among other things.

However, it is crucial to highlight that stabilization is not a magic spell that can enhance all soil qualities to obtain the required attributes. The decision to use technology is based on which soil properties must be modified. Pavement design is based on the idea that each layer of material in the pavement system will reach a minimum specified structural quality.

Each layer must be able to withstand shear loads, avoid extreme deflections that produce fatigue cracking within the layer or in overlying layers, and avoid excessive permanent deformation due to densification.

As the quality of a soil layer improves, so does its capacity to distribute the load over a larger area, allowing for a reduction in the required thickness of the soil and surface layers.

We know that soil stabilization of sub grade soils and aggregates by mechanical means of addition of various types of admixtures stabilization material such as lime, cement, fly ash, rice husk, bitumen, geotextiles, chemical, recycle & waste product, or their combination is a common practice around the world.

However, for appropriate stabilization technology selection, it is necessary to focus on aspects such as the type of soil to be stabilized, the purpose for which the stabilized layer will be used, the type of soil improvement desired, the required strength and durability of the stabilized layer, and the cost and environmental conditions.

Types of Stabilization

Mechanical Stabilization improves soil properties by altering its gradation, mixing, and proper compaction using mechanical energy from rollers, graders, rammers, and other tools.

In contrast, in the admixture stabilization process, several types of additives are added in appropriate percentages to a soil or earth material to act as a modifying agent and improve its properties. Because of its intrinsic benefits, cement has been one of the most extensively recognized and utilized binding admixtures in soil stabilization technology since the 1960s.

The cement stabilization process is completely water dependent, and when the cement hydrates and gains strength, the soil-cement becomes a hard and durable substance. Because cement fills the voids between soil particles, the void ratio of the soil is lowered. Cement also assists in lowering the liquid limit, raising the plasticity index, and improving the workability of clayey soil.

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