Art. 301.12 Soil Modification
301.12 Basis of Payment. When the contract includes paving on a
pregraded section, this work will be paid for at the contract unit price per unit for SHAPING AND GRADING ROADWAY. Excavation for the removal or placement of material outside the 2 in. (50 mm) tolerance specified in Article 301.11(b) will be paid for according to Article 109.04. Additional drying and compaction beyond the three steps listed in Article 301.04 will be paid for according to Article 109.04. Excavation and replacement of material declared unsuitable, as specified in
Article 301 — 04, will be classified and paid for according to Article 104.02.
SECTION 302. SOIL MODIFICATION
302.01 Description. This work shall consist of constructing a modified soil
layer composed of soil, water, and a modifier.
302.02 Materials. Materials shall be according to the following.
Item Article/Section
a.Type I Portland Cement .......................................................................... 1001
b.Type IS Portland Blast-Furnace Slag Cement ........................................ 1001
c.Water ...................................................................................................... 1002
d.Hydrated Lime ................................................................................... 1012.01
e.By-Product, Hydrated Lime ................................................................ 1012.02
f.By-Product, Non-Hydrated Lime ........................................................ 1012.03
g.Lime Slurry ........................................................................................ 1012.04
h.Fly Ash .................................................................................................... 1010
i.Soil for Soil Modification (Note 1) ....................................................... 1009.01
j.Bituminous Materials (Note 2) ................................................................ 1032 Note 1. This soil requirement only applies when modifying with lime (slurry or dry). Note 2. The bituminous materials used for curing shall be emulsified asphalt RS-2, CRS-2, HFE 90, or HFE 150; rapid curing liquid asphalt RC-70; or medium curing liquid asphalt MC-70 or MC-250.
302.03 Equipment. Equipment shall be according to the following.
Item Article/Section
a.Distributor (Note 1)
b.Rotary Speed Mixer ........................................................................... 1101.06
c.Disk Harrow (Note 2) ......................................................................... 1101.02
d.Lime Slurry Equipment (Note 3) Note 1. The distributor shall be a mechanical type and shall be approved by the Engineer. Soil Modification Art. 302.07 Note 2. A disk harrow may be used for soil modification with portland cement, slag-modified portland cement, or lime (slurry or dry) when permitted by the Engineer. Note 3. The equipment used for mixing, transporting, slaking, and placing lime slurry shall be approved by the Engineer. CONSTRUCTION REQUIREMENTS
302.04 General. The modified soil shall be constructed when the temperature
of the soil, measured 6 in. (150 mm) below the surface is above 50 F (10 C) and the ambient air temperature in the shade is above 45 F (7 C). The quantity of modified soil constructed shall be limited to that which can be covered by the full thickness of PCC pavement or HMA binder during the same construction season.
302.05 Proportioning. Proportioning shall be as follows.
a.Samples. Samples of the soil modifier(s) and the project soil(s) shall be obtained and submitted to the Engineer at least 45 days prior to the construction of the modified soil. Sample sizes shall be a minimum of 25 lb (11 kg) for the modifier(s) and 200 lb (90 kg) for the project soil(s).
b.Mix Design. The actual proportions of modifier, soil, and water will be determined by the Engineer prior to construction using the submitted samples. The Engineer reserves the right to make such adjustments in proportions as are considered necessary during the progress of the work. In no case shall proportions or type of modifier be changed during the progress of the work without permission from the Engineer.
302.06 Preparation of Subgrade. The area to be processed shall be shaped
to the proper grade and cross section. All vegetation and other objectionable material shall be removed from within the limits of modification. In cut or at grade sections, the subgrade shall be prepared according to Articles 301.03 and 301.04; except the minimum immediate bearing value (IBV) of the soil below the soil to be modified, shall be according to the Department’s “Subgrade Stability Manual”.
302.07 Application of Modifier. The modifier shall be applied uniformly on
the soil. The application of modifier shall be limited to that amount which can be mixed with the soil within the same working day. After application of dry modifiers, but before the addition of any water, the surface of the subgrade shall be lightly scarified or disked. When lime slurry is used, the surface of the subgrade shall be lightly scarified or disked prior to the application of the slurry. Dry modifiers shall not be applied when wind conditions are such that blowing modifier becomes objectionable to adjacent property owners or creates a hazard to traffic on adjacent highways, as determined by the Engineer. Art. 302.07 Soil Modification Lime slurry shall be applied within 30 days of preparing and mixing the slurry, and shall be thoroughly agitated prior to application. Modifier which has been damaged by hydration due to rain prior to or during the mixing operations, or has been displaced by the Contractor’s equipment or other traffic after application, shall be replaced.
302.08 Mixing. The modifier, soil, and water shall be thoroughly mixed.
Mixing shall continue until a homogenous layer of the required thickness has been obtained and a minimum of 75 percent of the mixture is smaller than 1 in. (25 mm). The moisture content of the modified soil shall be above optimum moisture content with a maximum of three percent above optimum. For soil modification with fly ash, more than one pass of the rotary speed mixer may be necessary to obtain a homogenous mixture. If more than one pass of the rotary speed mixer is required, the application of the fly ash shall be modified such that 25 percent of the specified fly ash quantity is applied and mixed with a down-cut motion as a preparation for the final pass of the rotary speed mixer. The remaining specified quantity of fly ash shall be applied prior to the final pass of the rotary speed mixer. Mixing shall continue until a minimum 75 percent of the mixture is smaller than 1 in. (25 mm).
302.09 Compaction. Compaction of soil modified with portland cement, slag-
modified portland cement, or fly ash shall be completed no later than one hour after mixing begins. Compaction of soil modified with hydrated lime or by-product non-hydrated lime shall be completed within the same day. Compaction of soil modified with lime slurry shall begin within 24 hours. Compaction of soil modified with by-product hydrated lime shall be delayed a minimum of 24 hours. The Engineer may require additional water or further mixing prior to the final compaction of soil modified with by-product hydrated lime. In no case shall compaction be started later than three days after mixing, unless approved by the Engineer. If compaction is to be delayed, the surface of the soil shall be crown-graded and sealed from moisture loss by either blade dragging or light rolling immediately after mixing. The compacted, modified soil shall have a minimum dry density of 95 percent of the laboratory standard dry density. The in-place dry density will be determined according to Illinois Modified AASHTO T 191, or Illinois Modified AASHTO T 310 (Direct Transmission Density/Backscatter Moisture). The laboratory standard dry density will be determined according to Illinois Modified AASHTO T 99.
302.10 Finishing and Curing. When multiple lifts are used to construct the
modified soil layer, the top lift shall be a minimum of 6 in. (150 mm) thick when compacted. Construction of pipe underdrains shall follow the requirements of Article 407.07. The surface of the modified soil shall be kept drained according to Article 301.09 and Soil Modification Art. 302.12 shall maintain moisture content not exceeding three percent above optimum prior to pavement construction. When compaction of the modified soil is nearing completion, the surface shall be shaped to the required lines, grades, and cross section shown on the plans. For HMA base course and pavement (full-depth) and portland cement concrete base course and pavement, the surface of the modified soil shall be brought to true shape and correct elevation according to Article 301.07, except well compacted earth shall not be used to fill low areas. The modified soil shall be cured for a minimum of 24 hours. The ambient air temperature shall be above 45 F (7 C) during curing. During the curing period, the moisture content of the modified soil shall be maintained at optimum by sprinkling with water, use of plastic sheeting, or applying bituminous materials according to Article 352.13, except the method of moisture control for curing shall be applied as soon as possible after completion of final rolling. During this period, no equipment or traffic will be permitted on the completed work beyond that required for maintenance of curing. Equipment of such weight, or used in such a way as to cause a rut depth of 1/2 in. (13 mm) or more in the finished modified soil, shall be removed, or the rutting otherwise prevented, as directed by the Engineer.
302.11 Subgrade Stability. Following curing, the Engineer will determine the
stability of the modified soil in terms of the immediate bearing value (IBV), according to Illinois Test Procedure 501. The IBV shall be a minimum of 10.0 measured within 10 calendar days prior to pavement construction. No equipment or traffic shall be on the modified soil after compaction until the required IBV is attained.
302.12 Method of Measurement. This work will be measured for payment as
follows.
a.Contract Quantities. The requirements for the use of contract quantities shall conform to Article 202.07(a).
b.Measured Quantities. Processing modified soils will be measured for payment in place and the area computed in square yards (square meters). The width for measurement will be as shown on the plans. Modifier will be measured for payment in tons (metric tons). The modifier will be measured in trucks or freight cars. The Contractor shall furnish or arrange for use of scales of a type approved by the Engineer. When the modifier is shipped in trucks, it will be measured 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 freight bills in lieu of determining the weight (mass). Should the Contractor’s method of construction require extra earth excavation or embankment due to requiring more than one lift to construct Art. 302.12 Lime Stabilized Soil Mixture the modified soil layer as shown on the plans, this extra earth excavation and embankment will not be measured for payment.
302.13 Basis of Payment. This work will be paid for at the contract unit price
per square yard (square meter) for PROCESSING MODIFIED SOIL, of the thickness specified and per ton (metric ton) for LIME, FLY ASH, PORTLAND CEMENT, or SLAG-MODIFIED PORTLAND CEMENT. SUBBASE SECTION 310. LIME STABILIZED SOIL MIXTURE
310.01 Description. This work shall consist of the construction of a lime
stabilized soil mixture, composed of soil, lime, and water which shall be considered as subbase.
310.02 Materials. Materials shall be according to the following.
Item Article/Section
a.Water ....................................................................................................... 1002
b.Hydrated Lime .................................................................................... 1012.01
c.By-Product, Non-Hydrated Lime ........................................................ 1012.03
d.Lime Slurry ......................................................................................... 1012.04
e.Soil for Lime Stabilization .................................................................. 1009.02
f.Bituminous Materials (Note 1) ................................................................. 1032 Note 1. The bituminous materials used for curing shall be emulsified asphalt RS-2, CRS-2, HFE 90, or HFE 150; rapid curing liquid asphalt RC-70; or medium curing liquid asphalt MC-70 or MC-250.
310.03 Equipment. Equipment shall be according to Article 302.03, except a
disk harrow may be used when permitted by the Engineer. CONSTRUCTION REQUIREMENTS
310.04 General. The lime stabilized soil mixture shall be constructed when
the temperature of the soil measured 6 in. (150 mm) below the surface is above 50 F (10 C) and the ambient air temperature in the shade is above 45 F (7 C). The quantity of lime stabilized soil mixture constructed shall be limited to that which can be covered by the full thickness of PCC pavement or HMA binder during the same construction season.
310.05 Proportioning. Proportioning shall be as follows.
a.Samples. Samples of the lime and the project soil(s) shall be obtained and submitted to the Engineer at least 45 days prior to the construction of the lime stabilized soil mixture. Sample sizes shall be a minimum of 25 lb (11 kg) for the lime and 200 lb (90 kg) for the project soil(s).
Referenced in this section
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Source: Illinois Standard Specifications for Road and Bridge Construction, 2022 Edition. Pages 163–167 of 1,217. View official source ↗