Art. 311.01 Granular Subbase SECTION 311. GRANULAR SUBBASE
311.01 Description. This work shall consist of furnishing, placing, and
compacting granular material on the prepared subgrade as shown on the plans.
311.02 Materials. Materials shall be according to the following.
Item Article/Section
a.Coarse Aggregate .............................................................................. 1004.04
311.03 Equipment. Equipment shall be according to the following.
Item Article/Section
a.Steel Wheel Rollers ....................................................................... 1101.01(e)
b.Pneumatic-Tired Rollers .................................................................... 1101.01
c.Vibratory Machine (Note 1)
d.Subgrade Planer ................................................................................ 1103.08
e.Subgrade Machine ............................................................................. 1103.09 Note 1. The vibratory machine shall meet the approval of the Engineer. CONSTRUCTION REQUIREMENTS
311.04 Subgrade. The subgrade shall be prepared according to Section 301,
except Articles 301.05 and 301.06 will not apply, or according to Section 302 when soil modification is used.
311.05 Placing and Compacting Subbase Materials. The granular material
shall be placed and compacted as specified for the particular type of granular subbase. If any earth is worked into the granular material during the compacting or finishing operations, all granular material within the affected area shall be removed and replaced with new granular material. The Engineer may restrict hauling over the completed or partially completed work after inclement weather or at any time when the earth subgrade is soft and there is a tendency for the earth to work into the granular material. The granular material shall be placed and compacted at least three days prior to the placement of pavement or base course. Except where required for temporary access, the quantity of subbase granular material Types A or B to be placed shall be limited to that which can be covered by the full thickness of PCC pavement or HMA binder during the same construction season. If the moisture content is insufficient to maintain satisfactory compaction or to prevent segregation or raveling when hauling is permitted over the granular material, water shall be added as directed by the Engineer. When construction of the granular subbase has been completed at a location, or when directed by the Engineer, the Contractor shall salvage the excess granular material outside the construction limits of the granular subbase. The salvaged granular material shall be carried forward and utilized in the construction of the Granular Subbase Art. 311.05 granular subbase. The Contractor shall salvage the granular material in such a manner as to prevent segregation and the incorporation of earth. Placing and compacting of the different subbase granular material types shall be as follows.
a.Subbase Granular Material, Type A. The granular material shall be uniform in gradation. Before the material is deposited on the roadway, it shall contain the amount of moisture required for compaction. The amount of moisture required shall be that determined by the Engineer for the material and the compaction methods being used. The water and granular material shall be mixed through a controlled aggregate mixing system. The system shall consist of a mechanical mixing device and aggregate and water measuring devices meeting the approval of the Engineer. Wetting the aggregate by jetting in cars, bins, stockpiles, or trucks will not be permitted. Moisture shall be added to the material during compaction only when it is necessary to increase the percentage of moisture to obtain satisfactory compaction. The subbase shall be constructed in lifts not more than 4 in. (100 mm) thick when compacted, except that if tests indicate that the desired results are being obtained, the compacted thickness of any lift may be increased to a maximum of 8 in. (200 mm). The granular material shall be deposited full-lane width with a mechanical spreader or spreader box of a type approved by the Engineer, in a manner that shall not cause segregation and that shall require minimum blading or manipulation. The equipment and the method used shall be approved by the Engineer. Each lift shall be compacted immediately after placing. The granular material shall be compacted to not less than 95 percent of the standard laboratory density. The standard laboratory density shall be the maximum dry density determined according to Illinois Modified AASHTO T 99 (Method C). A coarse particle correction according to Illinois Modified AASHTO T 99 (Annex A1) shall be used. The dry density of the compacted subbase will be determined by the Engineer at regular intervals according to Illinois Modified AASHTO T 191, Illinois Modified AASHTO T 310 (Direct Transmission Density/Backscatter Moisture), or by other methods approved by the Engineer.
b.Subbase Granular Material, Type B. The subbase shall be constructed in lifts not more than 6 in. (150 mm) thick when compacted, except that if tests indicate that the desired results are being obtained, the compacted thickness of any lift may be increased to a maximum of 8 in. (200 mm). Each lift of material shall be compacted in a manner approved by the Engineer. If the moisture content of the material is such that compaction satisfactory to the Engineer cannot be obtained, sufficient water shall be added so that satisfactory compaction can be obtained. Art. 311.05 Granular Subbase
c.Subbase Granular Material, Type C. The subbase shall be compacted to the satisfaction of the Engineer. The manner of placing and compacting the material shall be approved by the Engineer prior to starting this work.
311.06 Finishing of Subbase for Base Course and Pavement. The
subbase shall be brought to true shape according to Article 301.07, except for the following. The compacted subbase shall be placed above the plan elevation and the excess trimmed or cut with the subgrade machine. The Contractor shall determine the amount of excess subbase material necessary to meet this requirement. After the subbase has been brought to its true shape and correct elevation, the surface shall be wetted and rolled as directed by the Engineer with a steel wheel roller meeting the weight requirements specified in Article 301.07. The surface of the subbase shall then be tested for crown and elevation. The Contractor shall have at all times a minimum of one day’s production of subbase prepared ahead of the paving. When portland cement concrete base course or pavement is being placed, the subbase shall be moist at the time of placement. If required by the Engineer, the prepared subbase shall be saturated with water the previous night, or not less than six nor more than 20 hours prior to the placing of the concrete. If the subbase subsequently becomes too dry, it shall be sprinkled again ahead of placing the concrete, in such a manner as not to form puddles of water.
311.07 Tolerance in Thickness. The subbase shall be constructed to the
thickness shown on the plans. Thickness determinations shall be made at such points as the Engineer may select. When the constructed thickness is less than 90 percent of the thickness shown on the plans, aggregate shall be added to obtain the specified thickness; however, the surface elevation of the completed subbase shall not exceed by more than 3/16 in. (5 mm) the surface elevation shown on the plans or authorized by the Engineer.
311.08 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. Granular subbase will be measured for payment in tons (metric tons), cubic yards (cubic meters), or square yards (square meters). When the unit of measurement for the aggregate is tons (metric tons), the aggregate may be weighed in trucks or freight cars. The Contractor shall furnish or arrange for the use of scales of a type approved by the Engineer. If, at the time the Type A aggregate is weighed, it contains more than six percent of absorbed and free moisture by weight, a deduction for the amount of moisture in excess of this amount will be made in determining the pay Granular Subbase Art. 311.09 quantity. Any aggregate that has been stockpiled will be weighed at the time it is incorporated into the work. If the material 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. If the material is shipped in freight cars, the Engineer will accept the freight car weights, instead of scale weights, provided the Engineer is satisfied that the car weights are sufficiently accurate. In order to verify the car weights, the Contractor will be required to weigh the contents of at least ten percent of the freight cars received each day, with a minimum of one car weight each day, over truck scales. If the truck weights do not verify the freight car weights, additional cars shall be weighed. In addition to this verification, the Contractor will be required to weigh the contents of any freight car that appears deficient in material. The Contractor shall furnish the original signed freight bill for each car. When the unit of measurement for the aggregate is tons (metric tons), payment will not be made for aggregate in excess of 108 percent of the amount specified by the Engineer nor for aggregate placed outside the design width plus 6 in. (150 mm). When the unit of measurement for the aggregate is cubic yards (cubic meters), the aggregate will be measured in place and the volume computed in cubic yards (cubic meters). The width and depth for measurement will be as shown on the plans. When the unit of measurement for the aggregate is square yards (square meters), the aggregate will be measured in place and the area computed in square yards (square meters). The width for measurement will be as shown on the plans. If the granular material removed during the subgrading operation is not carried forward and incorporated in the granular subbase, a deduction will be made for the quantity not salvaged, except that no deduction will be made where the quantity not salvaged is less than 2 cu yd/station (5 cu m/100 m) or where cubic yards (cubic meters) or square yards (square meters) is the basis of payment.
311.09 Basis of Payment. Subbase Granular Material, Type A, Subbase
Granular Material, Type B, and Subbase Granular Material, Type C will be paid for at the contract unit price per ton (metric ton) for SUBBASE GRANULAR MATERIAL, TYPE A, SUBBASE GRANULAR MATERIAL, TYPE B, or SUBBASE GRANULAR MATERIAL, TYPE C; at the contract unit price per cubic yard (cubic meter) for SUBBASE GRANULAR MATERIAL, TYPE A, SUBBASE GRANULAR MATERIAL, TYPE B or SUBBASE GRANULAR MATERIAL, TYPE C; or at the contract unit price per square yard (square meter) of the thickness specified for SUBBASE GRANULAR MATERIAL, TYPE A, SUBBASE GRANULAR MATERIAL, TYPE B, or SUBBASE GRANULAR MATERIAL, TYPE C. Art. 312.01 Stabilized Subbase SECTION 312. STABILIZED SUBBASE
312.01 Description. This work shall consist of furnishing, placing, and
compacting a stabilized subbase composed of hot-mix asphalt (HMA) or cement aggregate mixture II (CAM II) on a prepared subgrade.
312.02 General. When a particular material is not specified, the Contractor
shall have the option of selecting the type of stabilized subbase. Prior to placing the stabilized subbase, the subgrade shall be prepared according to Section 301, except Articles 301.05 and 301.06 will not apply, or according to Section 302 when soil modification is used. Stabilized subbase shall not be placed on frozen or muddy subgrade. The amount of stabilized subbase constructed will be limited to that which can be surfaced during the current construction season. The Contractor shall have at all times one day’s production of stabilized subbase prepared ahead of the paving location. HOT-MIX ASPHALT
312.03 Materials. Materials shall be according to Section 1030.
312.04 Equipment. Equipment shall be according to the following.
Item Article/Section
a.Steel Wheel Rollers .................................................................................. 406
b.Self-Propelled Pneumatic-Tired Roller ...................................................... 406
c.Vibratory Roller ......................................................................................... 406
d.Spreading and Finishing Machine ...................................................... 1102.03
e.Trench Roller ..................................................................................... 1101.01
f.Subgrade Machine ............................................................................. 1103.09 CONSTRUCTION REQUIREMENTS
312.05 Placing and Compacting. Prior to placing the initial lift of the HMA
stabilized subbase, trimmings and other loose material shall be removed from the prepared subgrade. HMA stabilized subbase shall be placed according to
Article 406 — 06 and compacted according to Article 406.07. The maximum compacted
thickness of each lift shall be 4 in. (100 mm), provided the required density is obtained.
312.06 Finishing. The compacted subbase shall meet the lines and grades
shown on the plans.
Referenced in this section
GRANULAR SUBBASE in other states
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Source: Illinois Standard Specifications for Road and Bridge Construction, 2022 Edition. Pages 171–175 of 1,217. View official source ↗