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:

  1. 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.

  2. Each shipment shall be accompanied by a bill of lading and by a certificate of compliance stating conformance to the applicable specifications.

  3. The Contractor's safety measures shall be in accordance with applicable OSHA standards.

MIXTURE COMPOSITION:

  1. 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.

  2. 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:

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  1. 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   

 

Metric Pay Unit Symbol
(English Pay Unit Symbol)


Asphalt Curing Seal

  ......................Mg (TON)


Lime

  ......................Mg (TON)


Lime Stablized Soil, _______
                     thickness

  ......................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.