Practical knowledge and technical specifications about the Roads (Highways & Expressways) and Building work as per MORTH, Indian standard,IRC and CPWD.
SUB BASE (GSB)β The full form of GSB is granular sub base.it is being laid in road work because it plays two major roles
1- it works as drainage layer
2- it provides a good sub base to laid base layer on it.
How to calculate the quantity, compaction factor value and loose thickness of GSB? To know more information kindly visit on below link π
Material β
The material to be used for the work shall be natural sand, crushed gravel, crushed stone, crushed slag, or combination thereof depending upon the grading required use of material like brick metal, kankar and crushed concrete shall be permitted in the lower sub base. The material shall be free from organic or other deleterious constituents.
Grading III and IV shall be used in lower sub base. Grading V and VI shall be used as sub-base-cum-drainage layer.
Where the sub-base is laid in two layers as upper sub-base and lower sub-base, the thickness of each layer shall not be less than 150mm.
If the water absorption of the aggregates determined as per IS: 2386(part-3) is greater than 2 %, the aggregates shall be tested for wet aggregate impact value (AIV) (IS: 5640). Soft aggregates like kankar, brick ballast and laterite shall also be tested for wet AIV.
CONSTRUCTION OPERATION -
Spreading and compacting- the sub base material of the specified grading shall be mixed homogenously with the help of motor grader .the required water content shall be determined in accordance with IS:2720 (part 8).
Moisture content of the mix shall be checked in accordance with IS: 2720 (part 8) and adjusted so that, at the time of compaction, it is from 1 to 2 % below the OMC.
Immediately spreading the mix, rolling shall be done. If the thickness of the compacted layer does not exceed 100mm, a smooth wheeled roller of 80 to 100 KN weight may be used. For a compacted single layer up to 200mm the compaction shall be done with the help of a vibratory roller of min. 80 to 100KN.Rolling shall commence at the lower edge and proceed towards the upper edge longitudinally for portion having unidirectional cross fall or on super elevation. For carriage way having cross fall on both sides, Rolling shall commence at the edges and progress towards the crown.
To know more about WMM (wet mix macadam) ,kindly click on below link πEach pass of the roller shall uniformly overlap not less than one βthird of the track made in the preceding pass. The speed of roller shall not exceed 5 KM per hour.
Rolling shall be continued till the density achieved is at least 98% of the max. Dry density for the material determined as per IS: 2720 (part8).
All loose, segregated or other defective areas shall be made good to the full thickness and re-compacted.
Measurement - Granular sub βbase shall be measured as finished work in position in cubic metres.
Types of treatment for soil to make suitable for sub-base
(I) Lime treated soil for improved sub-grade/sub-base
To know more about cement treated soil and cement flyash treated sub-base, kindly click on below link π
(III) Crushed cement concrete sub-base
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Gyanofengineering
(Mukesh Kumar)
In this article we shall discuss three important points about granular sub base (GSB) 1- How can we calculate the required GSB quantity? 2 - What is value of compaction factor for GSB? 3- How much loose thickness of GSB should be taken to get proper compacted layer thickness ? 1- How can we calculate the required GSB quantity? Let us consider Length of GSB bed (L) = 500 Met. Breadth of GSB bed (B) = 7 Met. Thickness of GSB Layer (T) = 150 mm =0.150 Met. Max. Dry Density (MDD) =2.221 Gram/ Cubic Centimeter = 2221Kg/ Cubic metre Note - The value of MDD is calculated by conducting proctor density test as per IS 2720 (part -28) : 1983 (Reaffirmed - May 2015). Then Volume of GSB Layer = ( Length of GSB Bed X Width of GSB Bed X Thickness of GSB Layer) Volume of GSB Layer = L X B X T Volume of GSB Layer = 500 X 7 X 0.150 Volume of GSB Layer = 525 Cubic Metre We Know That Mass = Volume X Density in this case - Mass = Volume X MDD Putting
Wet Mix Macadam (WMM) quantity / Compaction Factor value for WMM / Loose thickness of WMM Layer In this article we shall discuss three important points about wet Mix Macadam (WMM) 1- How can we calculate the required WMM quantity? 2 - What is value of compaction factor for WMM? 3- How much loose thickness should be taken to get proper compacted layer thickness ? 1- How can we calculate the required WMM quantity? Let us consider Length of WMM Bed(L) = 1 Km = 1000 Met. Breadth of WMM Bed(B)= 7 Met. Thickness of WMM Layer (T) = 150 mm =0.150 Met. Max. Dry Density (MDD) =2.230 Gram/ Cubic Centimeter = 2230KG/ Cubic metre Note - The value of MDD is calculated by conducting proctor density test as per IS 2720 (part -28) : 1983 (Reaffirmed - May 2015). Then Volume of WMM Layer = ( Length of WMM Bed X Width of WMM Bed X Thickness of WMM Layer) Volume of WMM Layer = L X B X T Volume of WMM Layer = 1000 X 7 X 0.150 Volume of WMM Layer = 1050 C
Dense Bituminous Macadam (DBM) or Bituminous Concrete (BC) quantity / Compaction Factor value for DBM or BC / Loose thickness of DBM or BC Layer In this article we shall discuss three important points about Dense Bituminous Macadam (DBM) or Bituminous Concrete (BC) 1- How can we calculate the required DBM/BC quantity? 2 - What is value of compaction factor for DBM/BC? 3- How much loose thickness should be taken to get proper compacted layer thickness ? 1- How can we calculate the required DBM/BC quantity? Let us consider Length of DBM/BC layer (L) = 1 Km = 1000 Met. Breadth of DBM/BC Layer (B)= 5 Met. Thickness of DBM/BC Layer (T) = 50 mm =0.050 Met. Max. Dry Density (MDD) =2.441 Gram/ Cubic Centimeter = 2441KG/ Cubic metre Note - The value of MDD is calculated by conducting suitable test . Then Volume of DBM/BC Layer = ( Length of DBM/BC layer X Width of DBM/BC layer X Thickness of DBM/BC Layer) Volume of DBM/BC Layer = L X B X T Volume o
WET MIX MACADAM (WMM) sub β base /base:- Wet mix macadam (WMM) act as a base course just below the bituminous layer (bitumen base course or surface course). The thickness of a single compacted Wet mix macadam(WMM) layer shall not be less than 75mm.when vibrating or other approved types of compacting equipment are used, the compacted depth of a single layer of the sub-base course may be up to 200mm. How to calculate the loose thickness of WMM, compaction factor and quantity of WMM ? Kindly visit on below link π WMM- loose thickness,quantity and compaction factor Physical requirements Material finer than 425 micron shall have plasticity index (PI) not exceeding 6. To determine this combined portion, the flaky stone from a representative sample should first be separated out. Flakiness index is weight of flaky stone metal divided by weight of stone sample. Only the elongated particles are separated out from the remaining (non-flaky) stone metal. E
DENSE BITUMINOUS MACADAM(DBM) DBM acts as a bituminous base course and thickness of a single compacted layer shall be 50 mm to 100 mm. In this article we shall discuss about Technical specifications of DBM (Dense Bituminous Macadam), layer thickness, physical requirements, aggregate size, grades and its measurements A-Scope : The work shall consist of construction in a single layer of DBM on a previously prepared base or sub-base. The thickness of a single layer shall be 50 mm to 100 mm. B - Material : The choice of binder material shall be stipulated in the contract or by the engineer, where viscosity grades of bitumen are specified, they are referred to by a designation in accordance with IS: 73. Where modified bitumen is specified, it shall conform to the requirements of IRC:SP:53 and IS:15462. Selection criteria for viscosity grade bitumen based on highest and lowest daily mean temperatures at a particular site are ]given in table no -1. 1-Coarse Agg
