What Is GSB In Road Construction?

Charlotte Miller

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Are you curious to know what is GSB in road construction? You have come to the right place as I am going to tell you everything about GSB in road construction in a very simple explanation. Without further discussion let’s begin to know what is GSB in road construction?

The construction of roads is a fundamental aspect of infrastructure development, connecting people, places, and markets. Building a reliable road network requires careful planning and the use of various materials, one of which is Granular Sub-Base (GSB). In this blog, we will explore what GSB is, its significance in road construction, and its role in creating robust and enduring roadways.

What Is GSB In Road Construction?

GSB, or Granular Sub-Base, is an essential component of the road construction process. It serves as the foundation layer upon which the road’s structure is built. GSB is a layer of granular material made up of a mixture of soil, aggregates, and sometimes bitumen or cement. It is placed directly on the natural soil or sub-grade to create a stable and durable base for the road.

Key Aspects Of GSB In Road Construction

  1. Composition: GSB is typically composed of crushed stone aggregates, sand, gravel, or a combination of these materials. The specific composition may vary depending on the road’s location, traffic load, and engineering requirements.
  2. Thickness: The thickness of the GSB layer can vary according to the project’s design and specifications. It is often between 100 mm to 200 mm, but in some cases, it can be thicker.
  3. Role: The primary role of GSB is to provide a stable and load-bearing foundation for the road. It distributes the traffic load evenly and prevents deformation or settlement of the road’s surface.
  4. Compaction: Proper compaction of GSB is essential to ensure its density and strength. Compaction involves the use of heavy machinery like rollers to compress the material, making it more resistant to settling.

Significance Of GSB In Road Construction

  1. Load Distribution: GSB serves as the load-distributing layer for the road. It spreads the weight of vehicles and prevents the underlying soil from getting compressed, which can lead to road failures.
  2. Preventing Moisture Infiltration: GSB acts as a barrier to prevent water from infiltrating the road’s foundation and causing soil erosion. Proper drainage is crucial to the longevity of road surfaces.
  3. Stabilization: GSB stabilizes the road surface and prevents rutting, potholes, and other deformations that can occur due to traffic loads.
  4. Enhancing Durability: Roads constructed with a robust GSB layer tend to have a longer service life and require less maintenance.
  5. Improving Surface Smoothness: GSB contributes to the overall smoothness of the road surface, enhancing driving comfort and safety.

Construction Process

The construction process involving GSB generally includes the following steps:

  1. Site Preparation: The sub-grade is prepared by removing any organic materials or debris and compacting the natural soil.
  2. Placement of GSB: The GSB layer is laid on the sub-grade and spread evenly to the specified thickness.
  3. Compaction: Heavy compaction equipment is used to compress the GSB layer, increasing its density and strength.
  4. Quality Control: Regular quality checks are conducted to ensure the GSB layer meets the engineering specifications and standards.


Granular Sub-Base (GSB) is a critical component in road construction, providing the stable foundation upon which road surfaces are built. It plays a vital role in distributing traffic loads, preventing settlement, enhancing road durability, and improving driving comfort. Roads constructed with a well-engineered GSB layer not only last longer but also require less maintenance, contributing to the overall efficiency and safety of the transportation network. As the backbone of road construction, GSB remains an indispensable element in the development of reliable and resilient roadways.


Why Is GSB Used In Road Construction?

To spread the surface wheel load over a large region and prevent shear and consolidation deformations, the Granular Sub Base (GSB) layers are utilised in flexible pavements. GSB serves as a load-bearing and pavement-strengthening element. The subgrade layer is subjected to less stress as a result.

What Is GSB Material For Road?

GSB material is a mix of sand & gravels, crushed stone & broken rock. GSB material typically contain crushed stone > 50%. Material having CBR > 30% & PI < 6%. Water absorption < 2% & Agg impact value (AIV) < 40%.

What Is GSB Road Construction Process?

The GSB Material is spread with the help of motor grader on the approved layer of Sub-grade in single layer of 200 mm with Grading either IV or V. During spreading and mixing by grader in site, water is sprinkled over the material by water browser mounted on water tanker.

What Is GSB And Wbm?

The subgrade is a compacted soil layer. The base and sub-base course could be made up of bound or unbound granular layer. As per Indian specifications (MORT&H 2001), some examples of base or sub-base layers are: Granular sub-base(GSB), Water Bound Macadam (WBM), Wet Mix Macadam (WMM) etc.

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