Quality Assurance Handbook for Rural Roads Volume-I - pmgsy

3. Section-300
3. Surface Levels
The tolerance in surface level for sub-grade will be (+) 20 mm and (–) 25 mm.
4. Surface Regularity
The maximum allowable difference between the sub-grade surface and underside of a 3 m straight
edge shall be 20 mm for the longitudinal profile and 15 mm for the cross profile.
5. Quality Control Tests
Subgrade material shall be tested as per tests given in Table 301.4 (B). If the material in the subgrade
has a density of less than 100% of maximum dry density (IS:2720 Part 7), the same shall be loosened
to a depth of 500 mm (depth could be reduced to 300 mm if insitu density is not less than 95% of
maximum dry density) and compacted in layers to 100% of maximum dry density. The density of
compaction shall be tested as per Table 301.5 and checked as per Table 301.6.
C. Do’s and Don’ts
1. Take precautions against soil erosion, water
pollution, etc. and for preservation of existing trees,
drains, sewers, pipes, conduits, poles or any other
structures.
2. Remove water, if met during excavation, from
springs, seepage or other causes, by suitable
diversions, pumping, or bailing out to keep the
excavation dry.
3. Rocks and boulders, which are likely to cause
differential settlement should be removed to the
extent of 500 mm below the formation level.
4. Take precautions during construction to ensure
stability and safety of slopes.
5. Near village settlements, trenches and foundation
pits should be securely fenced and provided with
caution signs in the interest of public safety.
6. Ensure that unsuitable and surplus material from
cuttings is disposed of as directed by the Engineer.
7. Ensure that proper longitudinal gradients as per
drawings have been achieved.
303. SUBGRADE CONSTRUCTION
Do’s Don’ts
1. Do not remove the bench marks, reference lines, stakes
etc. used for setting out of works without informing
the Engineer.
2. Do not let the loose material/ debris remain on the
slopes of cutting/ along the road.
3. Do not allow the rock to protrude above the formation
level at any point.
4. Do not stack stone boulders on embankment to ensure
free flow of traffic especially on hill roads.
5. Do not throw the debris on the valley side to avoid
damage to property/ environment.
The sub-grade is top 300 mm compacted layer in embankment or cutting just beneath the pavement
crust. The subgrade in embankment is compacted to a higher standard than the lower layers of the
embankment. In cutting, the cut formation, which serves as the subgrade, is treated similarly to achieve
the specified density to provide a suitable foundation for the pavement.
A Methodology
1. Setting out, dewatering, stripping of top-soil etc. for subgrade construction shall be the same as
for embankment construction described in sub-section 301.
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