Presentation on gsb

GSB and its importance in Road

1. Prepared by M.Sreekanth Reddy Granular Sub Base and its Role in Pavement. ( Focus on Permeability of GSB Grades )

2. Act as Drainage Layer Act as Load Distribution Layer Load Distribution & Drainage Layer Functions of Granular Sub Base

3. Source of Moisture

4. Weakening of Pavement Layers Loss of bond between layers Loss of Strength and durability of asphalt mixtures. Cause for pavement distresses such as ravelling, rutting and stripping. What happens to pavement if drainage layer is not provided .

5. How to protect pavement from moisture damage?

6. It can preventing capillary water to rise to top road layers ( Particle size of drainage layer is planned in such way that the capillary action stops and can not go beyond drainage layer ) It has to act as a medium where water can pass through without damaging other road layers. By Providing Drainage Layer(GSB)

7. Granular Sub Base Grades as per MORTH

8. Grade of GSB Permeability at 2.5% slope m/day Permeability at 3.5% slope m/day Grade I No Flow was observed Grade II No Flow was observed Grade III 3675.66 3056.23 Grade IV 2418.28 1698.74 Grade V 2423.14 1930.83 Grade VI 1293.62 1297.34 Grade III+V 3049.40 2493.53 Grade III+ VI 2432.37 2212.83 Grade IV + V 2366.20 2040.49 Grade IV + VI 1605.64 1489.04 GSB Grade I,II - Densest Graded III,IV – Open Graded GSB Grade V & VI - Close Graded

9. AS from the previous table , The GSB Grade III, Grade V, Grade III+V have maximum hydraulic conductivity at 2.5 % slope. Hence 2.5% camber for GSB is required to prevent moisture damage to the pavement. Grade III - 3675.66 m/day Grade V - 2423.14 m/day Grade III+V – 3049.40 m/day Importance of GSB Camber

10. Densest grades among all grades specified in MoRTH . Having 65 % of 4.75 mm passing material. These grades showed good structural stability than drainage property. It is used in areas where there is need of structural support to pavement rather than drainage requirement. GSB Grade I & II

11. Grade III GSB act as only drainage layer. Highest coefficient of permeability among all gradations specified in MoRT&H for GSB at optimum gradient 2.5%. So Grade III can be effectively used for heavy monsoon regions as a Drainage layer. Structural stability of this grade can be improved by working on combination grade III+V . Grade III GSB

12. It can be used as drainage cum structural layer Fulfil the drainage requirement with providing full thickness of 300mm But while providing these grades camber provision must be verified. Grade V is having approximately 50% finer material i.e 4.75 mm sieve passing , so this grade is considered as Close graded. Grade V GSB

13. Field Setup of Horizontal Permeability Chamber

14. Elevation of Permeability Chamber