INTRODUCTION:-
This
work shall consist of cutting, removing and disposing of all materials such as
trees, bushes, shrubs, stumps, roots, grass, weeds, top organic soil not
exceeding 150 mm in thickness, rubbish etc., which in the opinion of the
Engineer are unsuitable for incorporation in the works, from the area of road
land containing road embankment, drains, cross-drainage structures and such
other areas as may be specified on the drawings or by the Engineer. It shall
include necessary excavation, backfilling of pits resulting from uprooting of
trees and stumps to required compaction, handling, salvaging, and disposal of
cleared materials. Clearing and grubbing shall be performed in advance of
earthwork operations and in accordance with the requirements of these
Specifications.
METHODS, TOOLS & EQUIPMENTS:-
If
the area has thick vegetation/roots/trees:- A crawler or pneumatic tyred dozer
of adequate capacity may be used for clearance purposes. The dozer shall have
ripper attachments for removal of tree stumps. All trees, stumps, etc., falling
within excavation and fill lines shall be cut to such depth below ground level
that in no case these fall within 500 mm of
the
subgrade.
ORIGINAL GROUND LEVEL:-
When
C & G work is done then that area shall be level by the grader. Basically,
rolling is done when excavation is complete. According to engineer, this work
shell be done. If there is a bumping problem then removed all the soils at that
place. When all soil is removed then good soil is used. Before density is
checking, the rolling is done according to morth.
EXCAVATION:-
It
is done where, there is requirement. This work shall consist of excavation,
removal and satisfactory disposal of all materials necessary for the
construction of roadway, side drains and waterways in accordance with
requirements of these Specifications and the lines, grades and cross-sections
shown in the drawings or as indicated by the Engineer. It shall include the
hauling and stacking of or hauling to sites of embankment and subgrade
construction, suitable cut materials as required.
EMBANKMENT:-
All embankments, sub
grades, earthen shoulders and miscellaneous backfills shall be constructed in
accordance with the requirements of these Specifications and in conformity with
the lines, grades, and cross-sections shown on the drawings or as directed by
the Engineer.
MATERIAL
USED FOR EMBANKMENT:-
The
materials used in embankments, subgrades, earthen shoulders and miscellaneous backfills shall be soil,
moorum, gravel, a mixture of these or any other material approved by the
Engineer. Such materials shall be free of logs, stumps, roots, rubbish or any
other ingredient likely to deteriorate or affect the stability of the
embankment/ subgrade.
1).
CLAY:- Expansive clay exhibiting marked swell and shrinkage properties ("free
swelling index" exceeding 50 per cent ) shall not be used as a fill
material.
2).
Any fill material with a soluble sulphate content exceeding 1.9 grams of
sulphate (expressed as SO3) per litre, but using a 2:1 water-soil
ratio shall not be deposited within 500 mm.
3).
The size of the coarse material in the mixture of earth shall ordinarily not
exceed 75 mm when being placed in the embankment and 50 mm when placed in the
subgrade.
4). The maximum particle, size shall not be more than
two-thirds of the compacted layer thickness.
DENSITY REQUIREMENTS OF EMBANKMENT AND SUBGRADE
MATERIALS
|
S.
No.
|
Type of Work
|
Maximum
laboratory dry unit
|
|
1
|
Embankments
up to 3 metres
|
Not less
than 15.2 kN/cu.m. height, not subjected to extensive flooding.
|
|
2
|
Embankments
exceeding 3 metres height or embankments of any height subject to long
periods of inundation
|
Not
less than 16.0 kN/cu. m.
|
|
3
|
Subgrade
and earthen shoulder
|
Not
less than 17.5 kN/cu. m.
|
GENERAL REQUIREMENTS:-
The materials for embankment shall be obtained from approved
sources with preference given to materials becoming available from nearby
roadway excavation.
BORROW MATERIALS:-
Where the materials are to be obtained from
designated borrow areas, the location, size and shape of these areas shall be
as indicated by the Engineer.
COMPACTION REQUIREMENTS FOR EMBANKMENT AND
SUBGRADE
|
||||||||||||||||
CONSTRUCTION
OPERATION:-
SETTING
OUT:-
The limits of embankment/subgrade shall be
marked by fixing batter pegs on both sides at regular intervals as guides
before commencing the earthwork.
The embankment/subgrade shall
be built sufficiently wider than the design dimension so that surplus material
may be trimmed, ensuring that the remaining material is to the desired density
and in position specified and conforms to the specified side slopes.
DEWATERING:-The removal of water
at the site.
STRIPPING & STORING TOP SOIL:-
In localities where most of the available embankment materials
are not conducive to plant growth, or when so directed by the Engineer, the
topsoil from all areas of cutting and from all areas to be covered by
embankment foundation shall be stripped to specified depths not exceeding 150
mm and stored in stockpiles of height not exceeding 2 m for covering embankment
slopes, cut slopes and other disturbed areas where re-vegetation is desired.
Topsoil shall not be unnecessarily trafficked either before stripping or when
in a stockpile. Stockpiles shall not be surcharged or otherwise loaded and
multiple handling shall be kept to a minimum.
Compacting ground supporting embankment/subgrade:-
Where necessary, the
original ground shall be levelled to facilitate placement of first layer of
embankment, scarified, mixed with water and then compacted by rolling so as to
achieve minimum dry density.
Spreading material in layers and bringing to appropriate
moisture content:-
1).The embankment and subgrade material shall be spread in
layers of uniform thickness not exceeding 200 mm compacted thickness over the
entire width of embankment by mechanical means, finished by a motor grader and
compacted.
2).The motor grader blade shall have hydraulic control suitable
for initial adjustment and maintain the same so as to achieve the specific
slope and grade.
3).Each compacted layer shall be finished parallel to the final
cross-section of the embankment.
4).Moisture content of the material shall be checked at the
site of placement prior to commencement of compaction; if found to be out of
agreed limits, the same shall be made good. Where water is required to be added
in such constructions, water shall be sprinkled from a water tanker fitted with
sprinkler capable of applying water uniformly with a controllable rate of flow
to variable widths of surface but without any flooding.
5). If the material delivered to the roadbed is too wet, it
shall be dried, by aeration and exposure to the sun, till the moisture content
is acceptable for compaction.
6).Moisture content of each layer of soil shall be checked,
making due allowance for evaporation losses, that at the time of compaction it
is in the range of 1 per cent above to 2 per cent below the optimum moisture
content.
7).Clods or hard lumps of earth shall be broken to have a
maximum size of 75 mm when being placed in the embankment and a maximum size of
50 mm when being placed in the subgrade.
COMPACTION:-
Smooth wheeled, vibratory, pneumatic tyred, sheepsfoot or pad
foot rollers, etc. of suitable size and capacity as approved by the Engineer
shall be used for the different types and grades of materials required to be
compacted either individually or in suitable combinations.
The compaction shall be done with the help of vibratory roller
of 80 to 100 KN static weight with plain or pad foot drum or heavy pneumatic
tyred roller of adequate capacity capable of achieving required compaction.
When compaction is completed then density & moisture is checked.
BUMPING PROBLEM:-
It is occurring due to the more water content present in the
soil. Due to this many problem comes like cracks in top soil, undulations and
many problems. The bumping problem shown in the figure:-
DRAINAGE:-
The surface of the embankment/subgrade at all times during
construction shall be maintained at such a cross fall (not flatter than that
required for effective drainage of an earthen surface) as will shed water and
prevent ponding.
REPAIRING
OF DAMAGES CAUSED BY RAIN:-
The
soil in the affected portion shall be removed in such areas as directed by the
Engineer before next layer is laid and refilled in layers and compacted using
appropriate mechanical means such as small vibratory roller, plate compactor or
power rammer to achieve the required density.
FINISHING
OPERATION:
Finishing operations shall include the work
of shaping and dressing the shoulders/verge/roadbed and side slopes to conform to the alignment, levels, 0f the
cross-sections and dimensions shown on the drawings.
Both the upper and lower ends of the side slopes shall be
rounded off to improve appearance and to merge the embankment with the adjacent
terrain.
The topsoil, removed and conserved earlier shall be spread over
the fill slopes as per directions of the Engineer to facilitate the growth of vegetation.
Slopes shall be roughened and moistened slightly prior to the application of
the topsoil in order to provide satisfactory bond. The depth of the topsoil
shall be sufficient to sustain plant growth, the usual thickness being from 75
mm to 150 mm.
When
earthwork operations have been substantially completed, the road area shall be
cleared of all debris, and ugly scars in the construction area responsible for
objectionable appearance eliminated.
GRANULAR
SUB-BASE (G.S.B):-
This
work shall consist of laying and compacting well-graded material on prepared
subgrade in accordance with the requirements of these Specifications. The
material shall be laid in one or more layers as sub-base or lower sub-base and
upper sub-base as necessary according to lines, grades and cross-sections shown
on the drawings or as directed by the Engineer.
MATERIALS
USED:-
The
material to be used for the work shall be natural sand, moorum, gravel, crushed
stone, or combination thereof depending upon the grading required. Materials
like crushed slag crushed concrete, brick metal and kankar may be allowed only
with the specific approval of the Engineer. The material shall be free from
organic or other deleterious constituents and conform to one of the three
grading.
GRADING FOR CLOSE-GRADED GRANULAR
SUB-BASE MATERIALS
|
IS Sieve
|
Percentage By Weight Passing the Is Sieve
|
||||
|
Designation
|
Grading I |
|
Grading II
|
|
Grading III
|
|
75.0 mm
|
100
|
|
__
|
|
__
|
|
53.0 mm
|
80-100
|
|
100
|
|
__
|
|
26.5 mm
|
55-90
|
|
70-100
|
|
100
|
|
9.50 mm
|
35-65
|
|
50-80
|
|
65-95
|
|
4.75 mm
|
25-55
|
|
40-65
|
|
50-80
|
|
2.36 mm
|
20-40
|
|
30-50
|
|
40-65
|
|
0.425 mm
|
10-25
|
|
15-25
|
|
20-35
|
|
0.075 mm
|
3-10
|
|
3-10
|
|
3-10
|
|
C.B.R.Value (Minimum)
|
30
|
|
25
|
|
20
|
GRADING FOR COARSE GRADED GRANULAR SUB-BASE MATERIALS
|
IS Sieve
|
Per cent by weight passing
the IS sieve
|
||||
|
Designation
|
Grading I |
|
Grading II
|
|
Grading III
|
|
75.0 mm
|
100
|
|
__
|
|
__
|
|
53.0 mm
|
|
|
100
|
|
|
|
26.5 mm
|
55-75
|
|
50-80
|
|
100
|
|
9.50 mm
|
|
|
|
|
|
|
4.75 mm
|
10-30
|
|
15-35
|
|
25-45
|
|
2.36 mm
|
|
|
|
|
|
|
0.425 mm
|
|
|
|
|
|
|
0.075 mm
|
<10
|
|
<10
|
|
<10
|
|
CBR
Value (Minimum)
|
30
|
|
25
|
|
20
|
STRENGTH
OF SUB-BASE:-
It
shall be ensured prior to actual execution that the material to be used in the
sub-base satisfies the requirements of CBR and other physical requirements when
compacted and finished.
When
directed by the Engineer, this shall be verified by performing CBR tests in the
laboratory as required on specimens remoulded at field dry density and moisture
content and any other tests for the "quality" of materials, as may be
necessary.
CONSTRUCTION
OPERATIONS:-
PREPARATION OF
SUB-GRADE:-
Immediately prior to the laying of sub-base, the subgrade
already finished. Removing all vegetation and other extraneous matter, lightly
sprinkled with water if necessary and rolled with two passes of 80 -100 KN
smooth wheeled roller.
SPREADING AND
COMPACTION:-
The
sub-base material of grading specified in the Contract shall be spread on the
prepared subgrade with the help of a motor 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. When the sub-base material consists of combination of
materials, mixing shall be done mechanically by the mix-in-place method.
MOISTURE CONTENT:-
Moisture content of the loose
material shall be checked 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 OMC. While adding water, due allowance shall be
made for evaporation losses. After water has been added, the material shall be
processed by mechanical or other approved means like disc harrows, rotavators
until
the layer is uniformly wet.
COMPACTION:-
When
water is spread out, then immediately thereafter, rolling shall start. If the
thickness of the compacted layer does not exceed 100 mm, a smooth wheeled
roller of 80 to 100 KN weight may be used. For a compacted single layer up to
225 mm the compaction shall be done with the help of a vibratory roller of
minimum 80 to 100 kN static weight with plain drum or pad foot-drum or heavy
pneumatic tyred roller of minimum 200 to 300 kN weight having a minimum tyre
pressure of 0.7 MN/m2 or equivalent capacity roller capable of
achieving the required compaction.
Rolling shall
commence at the lower edge and proceed towards the upper edge longitudinally
for portions having unidirectional crossfall and super-elevation and shall
commence the center at the edges and progress towards for portions having
crossfall on both sides.
During
rolling, the grade and crossfall (camber) shall be checked and any high spots
or depressions, which become apparent, corrected by removing or adding fresh
material. The speed of the roller shall not exceed 5
km per hour.Rolling shall be continued till the density achieved is at least 98
per cent of the maximum dry density for the material determined. 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.
CONTROL OF ALIGNMENT:
- All works performed shall conform to the lines, grades, cross sections and
dimensions shown on the drawings.
1).HORIZONTAL ALIGNMENT:-
Horizontal alignments
shall be reckoned with respect to the centre line of the carriageway as shown
on the drawings. The edges of the carriageway as constructed shall be correct
within a tolerance of± 10 mm there from. The corresponding tolerance for edges
of the roadway and lower layers of pavement shall be ± 25 mm.
2).SURFACE LEVELS:-
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