How many grades are there in GSB?
Out of six GSB grades Grade III, Grade IV, Grade V and Grade VI obtained permeability values are more than predicted values.
Is code for GSB material?
Grading for Granular Sub-base Materials (GSB) (Grading – IV) IS:2386 (Part-I)
How can I check my GSB gradation?
In a gradation and size analysis, a sample of dry aggregate of known weight is separated through a series of sieves with progressively smaller openings. Once separated, the weight of particles retained on each sieve is measured (Figure 2) and compared to the total sample weight.
What is the ratio of GSB?
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%.
What is GSB material?
Granular Sub Base(GSB) is natural or designed construction material, used for road construction as a sub-base layer. Granular Sub Base is a layer in road foundation just above the compacted sub-grade layer. Secondly, it works like a drainage layer where water can pass without damaging other road layers.
What is the compaction factor for GSB?
Specified compaction for GSB – 98 % of MDD (MDD by IS 2720 Part – 8). There is a possibility of getting a higher compaction which results normally upto 104% due to the presence of coarse crushed material.
How do you mix GSB?
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 the minimum CBR value for subgrade?
According to the subgrade characterization which recommends 10% as minimum CBR value for the layer , the subgrade material proved adequate as this value appears to have been exceeded by a wide margin at most of the sections along the road. …
What is the purpose of GSB?
INTORDUCTION The Granular Sub Base (GSB) layers are used in the flexible pavements to provide a stress-transmitting medium to spread the surface wheel load to a large area so as to prevent the shear and consolidation deformations.
What is a good CBR value?
A clayey soil generally has a low CBR value (less than 8). Sands are more granular and drain better and will generally have CBR values between 15 and 35. Gravel will have the best CBR values, generally 25 and up. That is why it is suggested to save the best material to cap the subgrade.
What is the minimum CBR value?
1 Answer. Min. CBR Value is 6. If the value for subgrade is less than 4, 300mm thick bolder solling is required (Base Corse).
How to apply GSB material on approved sub-grade?
Approved sub-grade layer is rolled with two passes by smooth wheel roller with slight sprinkle of water. 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.
What is GSB in road construction?
Granular Sub Base (GSB) is natural or designed construction material, used for road construction as a sub-base layer. Granular Sub Base is a layer in road foundation just above the compacted sub-grade layer.
What is GSB (granular sub base)?
Granular Sub Base is a layer in road foundation just above the compacted sub-grade layer. GSB or granular sub-base prevents capillary water from rising; its particle size is so designed that the capillary action stops and cant go beyond GSB layer. Secondly, it works like a drainage layer where water can pass without damaging other road layers. 1.0
What is the maximum thickness of GSB?
Spreading and Grading: The material shall be mechanically (viz grader, etc.) spread in uniform layers such that compacted thickness not exceeding 200mm – 250mm with due consideration to loose thickness (compaction factor) of GSB.