DEFINITIONS
(1) Formation Level
The level of the top surface of the subgrade upon which
pavement structures is built up.
(2) Subgrade
Up to 500 mm below formation (Lowest level of pavement
crust) level is designated as “subgrade”.
(3) Capping Layers
Capping layers are layers of specified materials to be laid
and compacted in the subgrade and below as required, in replacement of in-situ
materials to achieve CBR conforming to Clause 609, Table 6.2.
(4) Stabilizer
The selected natural or crushed material, lime, cement and
other similar materials to be mixed into the in-situ material of the subgrade
is defined as the “stabilizer”.
(5) Mechanical Stabilization
The addition and mixing of natural or crushed material to
improve the in-situ material of the subgrade. (6) Lime Stabilization
The addition and mixing of lime to improve in-situ material
of the subgrade such as in-situ material with a CBR is less than 5% or
saturated soils.
(7) Treated Materials
Following the addition of stabilizer to the in-situ
materials, the material is referred to as “treated material”. Treated materials
may be either mechanically stabilized, lime stabilized, cement stabilized, or
so on.
1003. PREPARATION AND SURFACE TREATMENT OF FORMATION
Preparation and surface treatment of formation shall be
carried out only after completion of all drainage works unless otherwise agreed
by the Engineer and prior to laying the sub-base or the base where no sub-base
is required. The sequence of operations shall be as follows:
(1) Formation of Loose Untreated Materials
Materials for use in the subgrade shall not contain
particles larger than 60 mm. In addition, the material shall have a CBR of not
less than 5% measured after a 4-day soak on a laboratory mix compacted to 95%
MDD (heavy compaction), a swell of less than 1%, a plasticity index of less
than 40% and an organic matter content less than 3%. In-situ material in the
subgrade in cutting that does not meet these requirements shall either be
spoiled or, if suitable, placed in the embankment. The spoiled material shall
be replaced with material meeting the requirements for loose material in the subgrade.
In fill areas, and in cutting except otherwise instructed by the Engineer,
according to the material encountered, loose materials of the embankment and cuttings
shall be deposited in the layers of 150 mm compacted depth. Each layer shall
extend reasonably more than the full width of the embankments or cutting and
shall be compacted in accordance with requirements as specified hereunder: -
(a) The material shall be broken down to the above specified
grading and any oversize material which cannot be broken down to the require
size shall be removed and disposed off. The material shall be scarified and the
moisture content shall be adjusted by either uniformly mixing in water or
drying out the material such that the moisture content during compaction is
between 95% and 100% of the Optimum Moisture Content. The moisture content
shall be kept within these limits until compaction is complete except where
otherwise instructed by the Engineer.
(b) Each layer shall be compacted to a dry density equal to
at least 95% MDD (heavy compaction).
(c) In accordance with Section 500, the Contractor shall
submit to the Engineer his proposals for the compaction of the material to be
used in the subgrade. The proposal shall be based on the type of plant, the
range of passes and the loose depth of the layer. The Contractor shall carry
out site compaction trials, supplemented by necessary laboratory
investigations, and shall satisfy the Engineer that all the specified requirements
regarding compaction shall be achieved. Site compaction trials shall be
completed and approved by the Engineer before the permanent Works commences.
(d) Testing to be carried out during the construction of subgrade
shall include the following:
i. The MDD (heavy compaction), Field density and OMC shall
be determined for each new material encountered as specified in Table 5.2. The
test of field density shall be conducted in staggered manner i.e. at left, at
crown and at right in the carriageway.
ii. The soaked CBR of material in the subgrade shall be
determined as per Table 5.2 for each layer.
The Contractor shall request in writing for the Engineer’s
approval for each layer in accordance with Sub-clause 509 (1) and such request
shall be accompanied by the tests results of the above described testing and
all additional relevant information required. If the results are as specified,
he will approve for addition of another layer or will ask for further tests or
rework to meet the requirements.
(2) Formation of Loose Treated Materials
The sequence of operation shall be as described in Clauses
1005 to 1006 of this Specification.
(3) Formation in Rock Cutting
The subgrade in rock cutting shall be regulated after trimming
the rock excavation by a regulating course of minimum 150 mm compacted depth of
natural complying with the requirements of natural material for sub-base as
specified in Sub-clause 1201 (3). The regulating course shall be laid,
compacted and tested in accordance with Clause 1201 and the surface regularity
shall meet the requirements of Clause 1101.
(4) Preparation of Formation for Rehabilitation Works
After reinforcement of any soft areas, all surface below carriageways,
lay-bys, cycle tracks, footways and hard shoulders shall be well cleaned and
freed from mud a slurry.
(5) Surface Regularity and Tolerances
The surface regularity and tolerance of the subgrade shall
meet the requirements of Clause 1101.
When each layer is completed the Contractor shall comply
with the requirements of Clause 510 for requesting the Engineer’s approval and
protecting the layer.
1004. CAPPING LAYER
Where shown on the Drawing or where in-situ material in the
subgrade in cutting does not meet the requirements, in-situ materials shall be
replaced with selected material from cuttings or borrow pits. Where materials
of differing quality are available for placing in the embankments, the Engineer
may also instruct that certain materials should be excluded from the subgrade
and that certain materials should be set part or obtained from borrow pits for
use in the upper layers. When materials for subgrade are extracted from borrows
to form the capping layer, they shall be natural material complying with the
following requirements: -
(1) Material classification
Materials used for use in capping layers shall be selected
among soils classified as GW, GP, GC, and SW in the General Classification of
Soils, described in Clause 609.
(2) Material Requirements
Material for use in the capping layers shall not contain
particles larger than 75 mm and their percentage passing by weight the 0.075 mm
sieve shall be less than 15%. The material shall have a CBR of not less than
15% measured after a 4-day soak on a laboratory mix compacted to 95 % MDD
(heavy compaction), a swell of less than 1%, a plasticity index of less than
12%.
(3) Laying and Compaction
The material shall be deposited in the layer of 150 mm
compacted depth. Each layer shall extend over the full width of the embankments
or cutting and shall be compacted in accordance with the requirements specified
in Sub-clause 1003 (1) (a) to (d).
(4) Tolerances
Tolerances of capping layers shall be in accordance with
Sub-clause 1003 (5) When each layer is completed the Contractor shall comply
with Clause 510 for requesting the Engineer’s approval and protecting the
layer.
1005. MECHANICAL STABLISATION
(1) General
The extent of the mechanical stabilization shall be detailed
in the Special Specification or shown on the Drawing. In-situ subgrade
materials subject to mechanical stabilization shall be generally soils classified
as SM, ML, CL, MH, CH in the General Classification of Soils described in Clause
609 with a CBR less than 5% or a moisture content close to saturation or too high
moisture content to meet the compaction requirements as set out in Sub-clause 1003
(1).
(2) Material Requirement
(a) Stabilizer (Additive Material)
Additive material shall be gravel, crushed stone/gravel or
sand, according to the type and characteristics of the in-situ soil as shown in
the Table 10.1. It may be crushed stone/crushed gravel, (CS) discarded material
from primary crushing, or screened stone (SS) from debris and screes. Sand may
be soils classified as SP, SW in the General Classification of Soil described
in Clause 610 or Sand (SSFF) obtained by screening the discarded fine fraction
of primary crushing. Gravel 12/40 shall have a percentage in weight passing the
12 mm sieve less than 20% and a percentage in weight passing the 40 mm sieve
more than 85%. Sand shall have a Sand Equivalent more than 60.
Table 10.1: Type of Additive Material
(b) Stabilized Material Requirements
The amount of stabilizer shall be determined by the Engineer
after laboratory test
The mechanically stabilized materials after mixing and
compacting shall conform to the following
Maximum size of particles 60 mm
Uniformity Coefficient min 5
CBR at 95% MDD (heavy compaction) measured after 4 days’
soak min 25 %
Swell max 1%
(3) Amount of stabilizers to be added
The amount of stabilizer to be added shall be generally
between 15% and 25% in weight of the in-situ material and shall be determined
by the Engineer following laboratory trials, and site trials to be carried out
by the Contractor in accordance with Section 500. During the site trials, the
control testing requirements shall be in accordance with Clause 507 and in
addition, each set of test shall include the following:
The MDD (heavy compaction) and OMC determined on the mixed
material before compaction.
The CBR at 95% MDD (heavy compaction) after 4 days’ soak.
(4) Mixing
(a) Mixing Equipment
The equipment for scarifying the in-situ material and mixing
it with the stabilizer, such as scarifies and grades, shall be capable of
scarifying the materials and mixing it with the stabilizer to the full depth of
the loose layer necessary to give the specified thickness of compacted material
mixed and compacted in accordance with this Clause. The equipment shall be only
acceptable, if during the site trials carried out in accordance with Section
500, it produces the material to the specified requirements.
(b) Preparation of the Layer
Before the stabilizer is applied, the material to be treated
shall be scarified. If required or instructed by the Engineer, oversize
material shall be removed or broken down so that the maximum size of the
particles is not more than specified.
(c) Spreading the Stabilizer
After the layer to be treated has been prepared, the
stabilizer shall be uniformly spread over the width to be worked at the
specified rate.
(d) Mixing and Watering
After the stabilizer has been spread, it shall be thoroughly
and intimately mixed into the material for the full depth of the layer. Mixing
shall continue until the resulting mixture forms a homogeneous filth. Care
shall be taken both during mixing and subsequent watering operations so that
the underlying layer is not disturbed. No material from the underlying layer is
mixed with that being processed.
If watering is necessary to bring the mixture to the
required moisture content, this shall be done after spreading and mixing with
the stabilizer. Water shall be added in a uniform and controllable manner and,
where necessary, in successive increments. Each increment shall be mixed in as
a separate mixing operation. Concentration of water at any point or a flow of
water over the surface shall be avoided. Any part of the mixture which becomes
too wet for compaction shall be allowed to dry out until its moisture content
is satisfactory for compaction. Throughout the process of mixing the stabilizer
and watering, a uniform thickness of the mixture shall be maintained and, if
necessary, the mixture shall be graded to maintain the correct un-compacted
thickness and shape. Any part of the mixture that becomes segregated shall be
removed and replaced.
(5) Compaction
(a) Thickness of Layers
The subgrade shall be constructed in the layer of 150 mm
compacted depth.
(b) Compaction Requirements
The minimum density for mechanically stabilized materials
shall be 95% MDD (Heavy compaction). The moisture content at the time of
compaction shall be between 97% and 103% of Optimum Moisture Content.
(c) Finishing
The surface finish after compaction of any treated layer
shall be free from ridges, compaction planes, laminations, loose and
segregated material and other surface irregularities and shall be to the
line and the level within the tolerances as specified in Clause 1101. If
the surface fails to meet the requirements of this Specification, the
Contractor shall take the action set out in the appropriate part of
Section 1100 or such other action as the Engineer may instruct, or agree.
(6) Construction Control Testing
(a) In-situ Material
The following properties of subgrade material shall be
determined as per Table 5.2.:
Grading,
Moisture Content,
Atterberg limits,
The MDD (heavy compaction) and MOC,
The CBR at 95% MDD (heavy compaction) after 4 days’ soak.
(b) Stabilizer
The following properties of the additive material shall be
determined as per Table 5.2 and when in opinion of the Engineer the nature of
the material is changed
Grading,
SE
(c) Control of Mixing
Prior to compaction in every 400 m2 or part thereof the
following properties shall be determined on each new treated material used
after mixing for subgrade of each layer.
The MDD (heavy
compaction) and OMC,
The CBR at 95% MDD
(heavy compaction) after 4 days’ soak.
(d) Control after Completion of Each Layer
The field dry density shall be determined as specified in
Table 5.2 of compacted subgrade in staggered manner i.e. at left, at crown and
at right in the carriageway.
(7) Tolerances
(a) Geometric Tolerances As specified in Clause 1101.
(b) Amount of Stabilizer
The average amount of stabilizer, measured before mixing,
over a length of 100 m, shall not be less than the amount specified. The
average amount of stabilizer, in the treated material, measured at five points over
a length of 100 m, shall not be less than the amount specified.
1006. LIME STABILISATION
(1) General
The extent of lime stabilization shall be as detailed in the
Special Specification or as shown on the Drawing In-situ subgrade materials
subject to lime stabilization shall be generally soils classified as ML, CL,
MH, CH in the General Classification of Soil described in Clause 609, with a
CBR less than 5% or a moisture content close to saturation.
(2) Material Requirements
(a) Lime
Lime shall comply with the requirements of Clause 615. Quick
like shall be used on in-situ materials which have a CBR less than 2% and which
moisture content is close to saturation. Hydrated lime shall be used on in-situ
materials which have CBR between 2% and 5%.
(b) Storage and Handling
All lime shall be kept under cover and protected from
moisture. Consignments shall be use in the same sequence as they received at
the site. Damaged stocks or stored on the site for more than 3 months shall not
be used. The Contractor shall replace them at his own cost. Operators and labour
shall be provided with protective shoes, clothing, masks, gloves and goggles
when they work with lime.
(c) Requirement of Lime Treated Materials
The lime treated materials after mixing and compacting shall
conform to the following requirements:
Maximum size of particles : 20 mm
CBR at 95% MDD (heavy compaction) measured after 4 days’
soak : min 15%
Swell : max. 1%
(3) Amount of Lime to be added
The amount of lime to be added shall be determined by the
Engineer following laboratory and site trials to be carried out by the
Contractor in accordance with Section 500. For the laboratory trials, the
requirements of lime treated materials shall be as specified in Sub-clause 1006
(2) (c) except for that the CBR at 95% MDD (heavy compaction) measured on a
laboratory mix after 3 days curing at ambient temperature and 4 days’ soak
which shall not be less than 30%. During the site trials, the control testing
requirements shall be in accordance with Clause 507 and in addition, each set
of test shall include the following: The MDD (heavy compaction) OMC determined
on the mixed material before compaction, The CBR at 95% MDD (heavy compaction)
after 3 days curing at ambient temperature and 4 days’ soak shall not be less
than 15%.
(4) Mixing
(a) Mixing Equipment
The equipment for pulverizing the in-situ material and
mixing in the stabilizer shall be purpose-built equipment capable of pulverizing
the materials and mixing in the stabilizer to the full depth of the loose layer
necessary to give the specified thickness of compacted material mixed and
compacted in accordance with this Clause. The equipment shall be only
acceptable, if during the site trials carried out in accordance with Section
500, it can produce the material of the specified requirements.
The mixers shall be equipped with a device for controlling
the depth of processing and mixing blades shall be maintained or reset
periodically so that the correct depth of mixing is obtained at all times. Mixing
by grader shall not be permitted.
(b) Preparation of the Layer
Before the stabilizer is applied, the material to be treated
shall be scarified and/or spread and broken down and oversize material shall be
removed or broken down so that the maximum size of the particles is not more
than the specified. The material shall first be pulverized to the required
filth by successive passes. Then it shall be shaped true to line, grade and
cross Section and, if required, lightly
compacted. The loose thickness shall be such as to give
specified thickness after full compaction has been carried out. The moisture
content of the layer before addition of the stabilizer shall be adjusted to
within the range of 80% to 90% of the OMC.
(c) Spreading the Stabilizer
After the layer to be treated has been prepared to the
satisfaction of the Engineer, the stabilizer shall be uniformly spread at
specified rate over the width to be worked at a time. If a spreader is used to
spread the stabilizer ahead of the mixer, it shall be fitted with a device to
ensure a uniform and controllable rate of spread both transversely and
longitudinally. Only sufficient stabilizer for immediate use shall be spread
ahead of the mixing operation. If, in the opinion of the Engineer, any part
becomes defective, the Contractor shall replace the material of that part as
his own cost and shall rework to meet the requirements. Only equipment actually
used in the spreading or mixing operation shall be allowed to pass over the
stabilizer, when so spread before it had been mixed into the material to be
treated.
(d) Mixing and Watering
Immediately after the stabilizer has been spread, it shall
be thoroughly and intimately mixed into the material for the full depth of the
layer. Mixing shall continue until the resulting mixture forms a fine and
homogeneous tilth. The mixing machine shall be set so that it cuts at least 100
mm into the edge of any adjoining lane processed previously so as to ensure
that all the material forming the layer has been properly processed. Care shall
be taken during mixing and subsequent watering operations that the underlying
layer is not disturbed and that no material from the underlying layer is mixed
with that being processed. If watering is necessary to bring the mixture to the
required moisture content, then this shall be done after spreading and mixing
in the stabilizer. Water shall be added in a uniform and controllable manner
and, where necessary, in successive increments. Each increment shall be mixed
in as a separate mixing operation. Concentration of water at any point or flow
of water over the surface shall be avoided. Any part of the mixture becomes too
wet after the stabilizer has been added and/or before the mixture is compacted
shall be allowed to dry out until its moisture content is satisfactory. This
part shall be retreated with fresh stabilizer and finished off in accordance
with this Clause. Throughout the process of mixing in the stabilizer and water,
a uniform thickness of the mixture shall be maintained and, if necessary, the
mixture shall be graded to maintain the correct un-compacted thickness and
shape. Any part of the mixture that becomes segregated shall be replaced by new
one.
(e) Manual Mixing
Where manual mixing is permitted the soil from borrow area
shall be freed of all vegetation and other deleterious matters and placed on
the prepared surface. The soil shall then be pulverized by means of crow bars,
pickaxes or other means approved by the Engineer. Water in requisite quantities
may be sprinkled on the soil for aiding pulverization. On the pulverized soil
the blending material (lime) in requisite quantities shall be spread uniformly
and mixed thoroughly by working with spades or other similar tools till the
whole mass is uniform. After adjusting the moisture content to be within the
limits mentioned later the mixed material shall be levelled up to the required
thickness so that it is ready to be rolled.
(5) Compaction and Finishing
For lime treated materials, final compaction and finishing
shall be completed within 4 hours after the lime comes into contact with the
material to be treated.
(a) Thickness of Layers
The subgrade shall be constructed in the layers of 150 mm
compacted depth each.
(b) Compaction Requirements
The minimum density for lime treated materials shall be 97%
MDD (Heavy compaction). The moisture content at the time of compaction shall be
between 95% and 100% of Optimum Moisture Content.
(c) Finishing
The surface finish after compaction of any treated layer
shall be free from ridges, compaction planes, laminations, loose and segregated
material and other surface irregularities and shall be to the line and the
level within the tolerances as specified in Clause 1101. If the surface fails
to meet the requirements of this Specification, the Contractor shall take
appropriate action to set out to comply with the requirements of the Section
1100 or agree with other action as the Engineer may instruct.
(6) Joints between New and Existing Work
The forming of construction joints and the protection of
previously treated or other work shall be carried out so as to produce a uniformly
compacted and homogeneous layer free from ridges or other irregularities. Full
working width, without longitudinal joints, will generally be required. Half working
width may be instructed by the Engineer to pass traffic. When forming longitudinal
joints at least 100 mm of the first laid half-width layer shall be retreated and
mixed in with the layer of second half-width. When forming transverse joints, at
least 1.0 m length of the previously laid work shall be incorporated into the
new treated layer and the Engineer may instruct that the percentage of
stabilizer be increased at these places.
(7) Protection and Curing
Treated layers shall be kept continuously damp by lightly
spraying with water or adhering to one of the curing systems specified below. Treated
layers shall be protected, within 8 hours of completion by one of the following
methods:
(a) Completely covering the layer with clear or light-coloured
approved polythene sheeting of minimum thickness 0.1 mm. The sheeting shall be
laid to cover the whole of the surface of the layer. At joints the sheeting
shall be lapped by at least 500 mm and any damaged sheeting shall be replaced
at the Contractor’s expense. The sheeting shall be securely held in contact
with the layer by an approved method.
(b) Completely covering the treated material with a layer of
damp uncompact gravel or soil material of minimum thickness 100 mm. The
material which may form part of the next layer, shall be kept continuously
damp. Plant used for dumping and spreading material, and spraying water shall
be approved by the Engineer and shall have individual axle loads not exceeding
6 tons.
Immediately prior to application of a curing system the
surface of the treated layer shall be made thoroughly damp by lightly spraying
water. The curing system shall be kept in place and intact for a minimum of 7
days after completion of compaction. Some areas may be temporarily removed for
the purposes of carrying out control testing but only for the minimum amount of
time required for the testing.
(8) Construction Control Testing/Process Control Testing
(a) In-situ Material
The following properties shall be determined for the
subgrade material as per
Table 5.2:
Grading, Moisture Content, Atterberg limits,
The MDD (heavy
compaction) and OMC.
The CBR at 95% MDD (heavy compaction) after 4 days’ soak.
(b) Lime
Lime shall be tested in accordance with Clause 615 for each
consignment delivered at the site.
(c) Control of Mixing
The following properties shall be determined after mixing on
every new treated material used for subgrade and in every 400 m2 and part
thereof of each layer of mixed material prior to compaction:
The MDD (heavy
compaction) and OMC
The CBR at 95% MDD (heavy compaction) after 3 days curing
at ambient temperature and 4 days’ soak which shall be not less than 15%.
(d) Control of Compaction
The field dry density shall be determined in each layer of
compacted subgrade in a staggered manner i.e. left, at crown and at right in
the carriageway.
(9) Traffic
Traffic or equipment other than that actually engaged in the
various treatment or protection processes, shall not run over the layer bring
processed or compacted. On compaction or curing, no traffic or equipment shall
be allowed on the treated layer with the exception of that required for priming
or construction of the subsequent layer.
(10) Tolerances
(a) Geometric Tolerances
The work shall be completed within tolerance as specified in
Sub-clause 1003 (6).
(b) Amount of Stabilizer
The average amount of stabilizer, measured before mixing,
over a length of 100 m, shall not be less than the amount instructed by the
Engineer. The average amount of stabilizer, in the treated material, measured
at five points over a length of 100 m, shall not be less than the amount
instructed by the Engineer
The amount of stabilizer, measured at any point after mixing
may vary within ± 3 % of the amount instructed by the Engineer.
(c) Determination of Stabilizer Content
The lime content in mixed materials shall be determined
according to IS: 2720.
1007. MEASUREMENT
(1) Subgrade construction with loose untreated/treated
materials, formation in rock cutting shall be measured in cubic meter by taking
cross Sections at intervals of 10 meters or as directed by the Engineer in the
original position before the work starts and after its completion and computing
the volumes of the respective work in cubic meters by average end area method.
(2) Preparation of formation for rehabilitation works shall
be measured in square meter.
(3) Capping layer shall be measured in cubic meter by end
area method as described in Sub-clause 1007 (1).
(4) Mechanically stabilized subgrade shall be measured in
cubic meter as described in Sub-clause 1007 (1) and shall be exclusive of the
measurement on the stabilizer. Stabilizers (additive material) such as gravel,
crushed stone/gravel or sand shall be measured in cubic meter as per procedure
described below.
(a) Before mixing the stabilizer (i.e. gravel, crushed
stone/gravel sand) quantity to be used shall be measured in stacks or in the
body of transporting trucks/trippers, if it can be measured.
(b) In a length of 100 m five standard holes at the equal
distances shall be dig up and materials shall be collected separately from each
hole. The average percentage of stabilizer obtained from each hole shall be
worked out. Based on average percentage of stabilizer and volume treated total
quantity of stabilizer used shall be computed.
Least of the quantities computed in (a) and (b) above shall
be accepted for payment.
(5) The volume of lime stabilized material shall be measured
in cubic meter as per end area method inclusive of lime used. The lime used
shall be measured in ton.
(6) Quick lime/Hydrated
Lime (stabilizer) shall be measured in ton as per actual
consumption.
1008. PAYMENT
The subgrade construction with loose untreated/treated
materials, formation in rock cutting, additive materials and stabilizers,
preparation of formation, capping layer, mechanically stabilized subgrade, and
lime stabilized material shall be paid at their respective contract unit rate
which shall be the full and the final compensation to the Contractor as per
Clause 112 and also for the cost of:
(1) Arrangement of land as a source of supply and material
required
(2) Compacting the ground supporting subgrade where removal
and replacement of unsuitable material or loosening and re compacting is
involved.
(3) Watering or drying of material in the subgrade as
required.
(4) Mixing, spreading in layers brining in appropriate
moisture content and compacting to the requirement of Clause 1003.
(5) All other operations including incidental costs
necessary to complete the item as per this Specification
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