Construction Techniques

Module 3: Construction Techniques 

1. Earthwork & Grading

Earthwork prepares the roadbed by shaping the natural terrain to support pavement layers. Key activities include:

• Cut-and-Fill Optimization

• Cut: Excavating soil from high areas to achieve desired road elevation.

• Fill: Depositing excavated soil in low areas to build embankments.

• Balanced Earthwork: Minimizes material transport by matching cut/fill volumes.

• Equipment: Bulldozers, scrapers, and excavators for efficient material handling.

• Soil Stabilization Methods

• Mechanical Stabilization: Compaction (using rollers) to increase density.

• Chemical Stabilization:

• Lime/Cement Treatment: Reduces plasticity in clayey soils.

• Bitumen Emulsion: Binds granular soils for temporary roads.

• Geosynthetics: Geotextiles/geogrids reinforce weak subgrades.

2. Pavement Layers

Road pavements are categorized as flexible (asphalt) or rigid (concrete), each with distinct construction methods.

• Flexible Pavement Construction

• Layers: Subgrade → Sub-base → Base → Binder → Wearing Course.

• Process:

1. Prime Coat: Low-viscosity bitumen sprayed on base to enhance bonding.

2. Tack Coat: Bitumen emulsion applied between asphalt layers.

3. Hot Mix Asphalt (HMA) Placement: Paved using asphalt finishers, compacted with rollers.

• Rigid Pavement Construction

• Layers: Subgrade → Sub-base → Concrete Slab (PCC).

• Process:

1. Formwork Setup: Wood/steel molds for slab edges.

2. Concrete Pouring: Dowels/tie bars inserted for joint integrity.

3. Curing: Moisture retention (e.g., wet covers) for 14+ days.

• Surface Treatments

• Seal Coats: Thin asphalt + aggregate layers protect against water/oxidation.

• Slurry Seal: Mixture of emulsion, aggregates, and filler for minor repairs.

3. Drainage Systems

Effective drainage prevents water damage and extends pavement life. Key components:

• Surface Drainage

• Side Ditches: V-shaped channels along road edges to divert runoff.

• Cross Slope: Pavement camber (2–4%) directs water to ditches.

• Subsurface Drainage

• French Drains: Perforated pipes wrapped in geotextile, buried in granular trenches.

• Permeable Base Layers: Open-graded aggregates under rigid pavements.

• Culverts

• Types: Pipe (corrugated metal/concrete) or box culverts.

• Placement: Installed under road embankments for water flow.

Key Takeaways:

• Earthwork balances cut/fill volumes and stabilizes soils for a stable foundation.

• Flexible pavements use bituminous layers, while rigid pavements rely on concrete slabs.

• Drainage systems (culverts, ditches, subsurface pipes) prevent water-induced failures.