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6-24-97
LIME STABILIZATION OF SOILS
207-R-335
DESCRIPTION: This work shall consist of
stabilizing the subgrade soils by uniformly mixing lime with the
soils. This may be used to stabilize the natural ground under
embankments and the immediate subgrade under pavements.
MATERIAL: The materials shall be in
accordance with the following:
Hydrated
lime.............. 913.04.
Water..........................913.01.
Asphalt material for curing seal shall be AE-150 Type I
in accordance with 404.
Reactive Soils are those soils
which, when mixed thoroughly with at least 3 percent lime,
compacted in accordance with AASHTO T 99 Method C, and cured for
48 hours at 49E C (120E F), shall show a strength gain of at
least 345 KPa (50 psi) greater than that obtained for similarly
prepared untreated control specimens.
EQUIPMENT: The machinery, tools and equipment
necessary for proper execution of the work shall be available on
the project site and approved by the Engineer prior to the
commencing of construction operations.
STORAGE AND HANDLING:
- Hydrated lime shall be stored and handled in closed
weatherproof containers until immediately before
distribution on the subgrade. Hydrated lime in bags shall
be stored in weather protected conditions with adequate
protection from ground dampness. The storage facility
shall be approved by the Engineer prior to commencement
of any lime work.
- Each shipment shall be accompanied by a bill of lading
and by a certificate of compliance stating conformance to
the applicable specifications.
- The Contractor's safety measures shall be in accordance
with applicable OSHA standards.
MIXTURE COMPOSITION:
- Sample: The Contractor shall provide 5 kg
(11 lb), minimum, samples of the soil to be stabilized,
and 50 kg (110 lb), minimum, samples of the lime to be
used at least 20 days prior use of the lime.
- Mix Design: Lime shall be proportioned
within, but not limited, to an approximate range of 3 to
6% of soil as determined by the oven - dry basis. The
required proportion of lime shall be established by the
Engineer prior to construction, using samples of soil and
lime, and the Department's laboratory design procedure
for lime stabilized soil. The Engineer reserves the right
to make such adjustments of lime proportioning as are
considered necessary during the progress of the work.
The source or type of lime shall not be changed during
the progress of the work without permission of the
Engineer. However, the Engineer may choose, based on
laboratory test results, to use different types of lime
on different portions of the project. The different types
shall not be mixed in the same project portion.
CONSTRUCTION REQUIREMENTS:
- Temperature and Weather Limitations: Lime
modification shall be performed only with a minimum soil
temperature, measured 100 mm (8 in.) below the surface,
of 7E C (49E F) and with the air temperature rising. Lime
shall not be mixed with frozen soils or with soil
containing frost.
- Preparation of existing ground or subgrade:
All deleterious material, such as stumps, roots, turf,
etc. and aggregate larger than 75 mm (3 in.) shall be
removed. All soft organic soils shall be removed as
directed by the Engineer.
- Scarification and Pulverizing: The subgrade
shall be scarified to the required depth by a machine of
such design that a visible indication is given at all
times that the cutting is to the required depth. Moisture
shall be added if necessary.
- Lime Application: The Department reserves
the right to increase or decrease the quantity of the
lime used based on test results, as determined by the
Engineer.
If considered necessary by the Engineer for plastic clays
with a PI greater than 25, the lime shall be placed in
two applications. The first application shall consist of
2/3 of the lime specified and a curing period of 72
hours. The second application shall consist of the
remaining 1/3 of the lime specified and a curing period
of 96 hours. At the discretion of the Engineer, curing
periods may be extended to one week if the gradation is
not being achieved. Lime shall be spread only on that
area where the initial mixing operation can be completed
during the same working day.
All lime that has been exposed to the open air for six
hours or more before mixing will not be accepted unless
approved by the Engineer.
Heavy traffic or equipment shall not be permitted on the
spread lime other than that required for spreading,
watering, or mixing.
Hydrated Lime: Hydrated lime shall be spread at
the specified rates using either dry or slurry methods.
Dry lime may be used when specified on the plans or when
approved in writing by the Engineer. If dry lime is
employed, it shall be sprinkled lightly with an approved
sprinkler to reduce dusting. If bagged lime is used, the
lime piles shall be leveled by hand raking or with a drag
before mixing commences. Graders shall not be used for
this purpose. The Engineer may suspend the spreading of
dry lime under windy conditions.
To prevent loss and minimize lime carbonation, the lime
shall be covered or mixed into the soil within six hours
after application. Prior to mellowing, the mixture shall
be lightly compacted using a rubber tired roller to
minimize carbonization.
Slurry Placing: If hydrated lime or quick lime is
to be placed in a slurry, hydrated lime shall be mixed
with water in a central mixing tank or in a jet mixer
such that the dry solids content, by weight, will be at
least 31%, or as designated by the Engineer. The
distributor shall be equipped to provide the slurry from
the mixing site until the slurry is applied to the soils.
The slurry shall be spread over the scarified subgrade
through tank truck spray bars. The slurry shall be
distributed by one or more passes over a measured area
until the specified percentage, based on lime solids
content, is obtained. Run off and subsequent non-uniform
lime distribution shall be prevented.
The slurry shall be spread within 1/2 hour after final
mixing at the central plant. The slurry and soils shall
be mixed within 2 hours after spreading.
This type of application shall not be used to dry out the
soil.
- Moisture Control: At all times during the
period from immediately prior to application of the lime
until final curing is completed, the moisture content of
the lime-soil mixture shall be maintained at no less than
its specified optimum but not more than 3% over optimum.
Continual application of water during mixing may be
necessary even when the material is at optimum moisture
when mixing begins.
- Test Section: The first section of each
mixing operation, both primary and final, shall be a test
section to demonstrate the acceptability of the
Contractor's equipment and methods, and to provide a
check of the resulting finish grade elevation and the
compacted thickness of the stabilized layer. The length
of the section shall be as long as necessary to use one
truck of lime . Changes in equipment shall be made as
needed based on the results of the test section. If
changes in methods or requirements are made, additional
test sections shall be constructed, as required by the
Engineer. A minimum of one test section per project shall
be provided, and additional test sections shall be
constructed if recommended in the Geotechnical Report.
Test sections may be waived by the Engineer.
- Mixing: The mixing procedure shall be the
same for dry placement or slurry placement. The soil and
the lime shall be mixed by an approved road mixer or
other approved equipment, and the mixing continued until
a homogeneous friable mixture of soil and lime is
obtained as determined by the Engineer. The friable
mixture of soil and lime shall be free from clods or
lumps exceeding 50 mm (2 in.) in size. After initial
mixing, the lime treated layer shall be shaped to the
approximate section and compacted lightly prior to curing
to minimize the evaporation loss, lime carbonation, and
to prevent excessive wetting from possible rain. The
surface shall be crowned to provide proper drainage.
- Mellowing: The lime-soil mixture shall be
cured for 48 hours. The duration of this curing may be
extended up to approximately 7 days for heavy clay. The
characteristics of the soil, temperature, and rainfall
may influence the curing period. During mellowing, the
surface of the material shall be kept moist to prevent
drying and cracking.
- Final Mixing and Pulverization: Within 72
hours after completion of the mellowing, the stabilized
materials shall again be completely mixed and pulverized
to the full depth of stabilization such that 100% of the
mixture passes a 25 mm (1 in.) sieve and 60% passes a
4.75 mm (No. 4) sieve, excluding the non-slaking
fraction, and then recompacted. It may be necessary to
raise the moisture to optimum moisture content prior to
compaction.
- Compaction: Compaction of the mixture shall
begin immediately after the final mixing process is
complete. Prior to the beginning of the compaction, the
mixture shall be in a loose condition for its full depth
and width. The mixture shall then be compacted, using
either a sheepfoot or steel wheel roller for the entire
width, to at least 100%, within the special subgrade
treatment zone or to 95 percent below special subgrade
treatment zone, of the maximum dry density of the lime
stabilized mixture in accordance with AASHTO T 99 or the
one point proctor, AASHTO T 272. The density of the
soil-lime mixture will be determined by the Engineer near
the end of the finishing operations. If the required
density cannot be achieved in the field, a one point
proctor in accordance with AASHTO T 272 shall be
performed to verify the target density. Any portion of
the
soil-lime mixture having density less than specified
shall be corrected or removed and replaced. The in-place
dry density shall be determined by the Engineer in
accordance with AASHTO T 191 or T 239.
The average compacted thickness of modified soils
constructed shall be within 10% of the specified
thickness, except that the thickness at any one place may
be within 15% of that specified.
The Department reserves the right to determine the actual
thickness of the completed and cured layer by coring, use
of a phenolphthalein solution, or by other means. The
Engineer will perform at least one test every 280 m2
(335 syd) for each compacted lift to insure that the lime
is spread at the specified rate. All deficient areas
shall be corrected.
Throughout this operation, the shape of the course shall
be maintained by blading and the surface shall be sloped
to the required lines, grades and cross-sections.
Compaction shall be continued using a steel wheel roller
until the minimum specified density is obtained.
- Curing and Protection: After the soil
stabilization has been finished as specified, it shall be
protected against drying for seven calendar days. The
surface shall be maintained in a moist condition by
sprinkling for the above mentioned period or until a seal
coat is placed, whichever occurs first. Equipment used to
apply the curing seal and curing water shall be of a size
and weight such that the subgrade is not damaged.
Heavy traffic or equipment other than curing equipment
shall not be allowed on the finished subgrade until
completion of curing, unless permitted by the Engineer. A
satisfactory curing day shall be any day when the
temperature of the completed subgrade does not fall below
7E C (49E F). All damage to the curing seal prior to
completion of curing shall be immediately resealed.
The curing seal shall consist of the asphalt material
specified and shall be uniformly applied at the rate of
approximately 1 kg/m2 (2 lb/syd) with approved
distributing equipment. Other acceptable curing material
or methods may be used upon written permission of the
Engineer. The actual rate and application temperature of
the curing material will be determined by the Engineer.
If the asphalt material is tacky, a sand blotter material
shall be applied at a rate of 3 kg/m2 (5
lb/syd), when directed by the Engineer.
The stabilized subgrade shall be protected from freezing
for a period of seven calendar days after placement.
The stabilized subgrade shall be completely covered with
the specified pavement courses before work is suspended
for the winter months. When the stabilized subgrade is
not completely covered by the specified pavement courses,
the Contractor shall be responsible for all work and
materials necessary to protect and maintain the
uncompleted work during the winter months. The contractor
shall acceptably repair or restore the uncompleted work
before the beginning of spring paving operations.
METHOD OF MEASUREMENT: Lime stabilized soils will be
measured in square meters (square yards) of the thickness
specified complete in place. The width for measurement shall be
as shown on the plans. Water will not be measured for payment.
Lime shall be measured in megagrams (tons). The lime may be
weighed in trucks or freight cars. If the lime is shipped in
trucks, it may be weighed at the place of loading, at the place
of unloading, or at such other place as the Engineer may
designate. The Engineer may accept original signed bills in lieu
of weighing. The asphalt material used as a curing seal will be
measured in megagrams (tons).
Extra earth
excavation or embankment due to the Contractor's method of
construction requiring more than one lift to construct the lime
stabilized soil layer as shown on the plans will not be measured
for payment.
- Contract Quantities: If the project is
constructed essentially to the lines, grades or
dimensions shown on the plans and the Contractor and
Engineer have previously agreed in writing that the plan
quantities are accurate, no further measurement will be
made. If errors are discovered after work has started,
corrective measurements will be made.
If the plans have been altered or if disagreement exists
between the Contractor and the Engineer as to the
accuracy of the plan quantities, either party shall,
before any work which would affect the measurement is
started, have the right to request in writing and thereby
cause the quantities involved to be measured as
specified.
BASIS OF PAYMENT: Lime stabilized soils will be
paid for at the contract unit price per square meter (square
yard) at the thickness specified complete in place. Lime will be
paid for at the contract unit price per megagram (ton). Asphalt
curing seal will be paid for at the contract unit price per
megagram (ton).
Payment will be made under:
Pay
Item
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Metric Pay Unit
Symbol
(English Pay Unit Symbol)
|
Asphalt Curing Seal
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......................Mg (TON) |
Lime
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|
......................Mg (TON) |
Lime Stablized Soil, _______
thickness
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|
......................m2 (SYD) |
The costs of
furnishing and placing the sand blotter; the extra materials,
methods, and construction techniques required to protect,
maintain, or repair protions of the uncompleted work left during
the winte months; the maintenance of the lime stabilized soil
mixture; the water used for lime stabilization; and all extra
earth excavation or embankment due to more than one lift being
required to construct the lime stabilized soil layer shall be
included in the costs of the pay items.
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