GSB METHODOLOGY & MIX-DESIGN DATA
CONTENTS
1. SCOPE OF WORK
2. MATERIALS
2.1. Physical requirements.
3. CONSTRUCTION OPERATIONS
3.1. Preparation of sub grade3.2. Mixing of Material3.3. Flow Chart for the Construction of Granular Sub-Base
4. SPREADING & COMPACTING
5. MIX DESIGN DATA
1. SCOPE OF WORK
This work shall consist of laying and compacting well-graded material on prepared subgrade in accordance with the requirements of Specifications.
The Grades-V material shall be laid in one layer as sub-base.
Lying shall be done as per cross sections shown on the drawings or as directed by the Engineer.
2. MATERIALS
The material to be used for the work shall be crushed stone & river sand.
Proportion is depending upon the grading required. The material shall be free from organic or other deleterious constituents and conform to grading.
1.1. Physical requirements.
Ø The material passing 425 micron (0.425 mm) sieve for all the grading when tested according to IS :2720 (Part -5) shall have liquid limit and plasticity index not more than 25 per cent and 6 per cent respectivelyØ Aggregate Impact value (AIV) < 40 %Ø CBR at 98% Dry Density > 30Ø FDD is at least 98 % of the MDD
2. CONSTRUCTION OPERATIONS
2.1. Preparation of sub grade
Immediately prior to the laying of sub-base, the subgrade already finished as applicable shall be prepared by removing all vegetation and other extraneous matter, lightly sprinkled with water if necessary and rolled with two passes of 8 -10 Ton smooth wheeled roller.
1.1. Mixing of Material
Ø The individual material shall be mechanically mixed by volume.
Ø The volumetric proportion shall be fixed by trial at site stock yard.
Ø After fix the mixing ratio of GSB material, prepare a stock of graded GSB material.
Ø The grading of the specified design shall be checked after preparing GSB material to ensure homogenous & uniform mix.
Sl No. | Test | Frequency |
1 | Gradation | One test per 400 m3 |
2 | Atterberg Limit | One test per 400 m3 |
3 | Moisture Content prior to compaction | One test per 400 m3 |
4 | Density of Compacted Layer | One test per 1000 sq.m |
5 | Deleterious Constituents | As required |
6 | CBR | As required |
Ø If test results are found satisfactory then GSB material shall be allow to spread at site.
2. SPREADING & COMPACTING
Ø The sub-base material of grading specified in the Contract shall be spread on the prepared sub grade with the help of grader of adequate capacity, its blade having hydraulic controls suitable for initial adjustment and for maintaining the required slope and grade during the operation or other means as approved by the Engineer.
Ø Moisture content of the loose material shall be checked in accordance with IS:2720 (Part II) and suitably adjusted by sprinkling additional water from a truck mounted or trailer mounted water tank and suitable for applying water uniformly and at controlled quantities to variable widths of surface or other means approved by the Engineer so that, at the time of compaction it is from 1 % above to 2 % below the optimum moisture content (OMC) corresponding to IS:2720 (Part VIII).
Ø Immediately thereafter, rolling shall start and for a compacted single layer up to 200 mm, the compaction shall be done with the help of a vibratory roller of minimum 8 to 10 Ton static weight capable of achieving the required compaction.
Ø Rolling shall commence at the lower edge and proceed towards the upper edge longitudinally for portions having unidirectional cross-fall and super elevation and shall commence at the edges and progress towards the centre for portions having cross-fall on the both sides.
Ø Each pass of the roller shall uniformly overlap not less than one third of the track made in the preceding pass. During rolling, the grade and camber shall be checked and any high spots or depressions which become apparent corrected by removing or adding fresh material.
Ø The speed of the roller shall not exceed 5 km per hour. Rolling shall be continued till the density achieved is at least 98% of the maximum dry density for the material determined as per IS:2720 (Part 7).
Ø FDD for the prepared layer determined as per IS:2720 (Part 28) on 1 test per 1000 sq.m.
Ø The surface of any layer of material on completion of compaction shall be well closed, free from movement under compaction equipment and from compaction planes, ridges, cracks or loose material. All loose, segregated or otherwise defective areas shall be made good to the full thickness of layer and re-compacted.
5. Mix-Design Data
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