- 154 - SECTION 302 -- SUBGRADE PREPARATION, SHOULDER SUBGRADE PREPARATION, AND PREPARATION OF INTERSECTIONS AND DRIVEWAYS
302.01 Description
1.The Contractor shall complete the following requirements under the "Subgrade Preparation" or “Preparation of Intersections and Driveways” bid item:
a.(1) Furnish and place subgrade materials as shown in the contract.
2.Bring the roadbed to the plan profile when the following conditions are met:
i.The roadbed was graded under a separate contract or an existing grade. (ii) The grade is less than 0.20 foot (60 mm) low. (iii) The material is available on the right-of-way within the minimum free haul distance specified in Section 209.
b.Adjust grade lines to meet intersections, pavements, bridge ends, railroad crossings, or any other physical features designated by the Engineer.
c.Lower the grade, if necessa ry, to provide adequate width.
d.Dispose of surplus, excavated material within the right-of-way or the free haul distance.
e.Scarify, mix, adjust the moisture content, shape, and compact the soils as necessary to conform to the contract.
2.Under the bid item "Should er Subgrade Preparation", the Contractor shall complete, the adjustmen t of the shoulder elevations and the construction of the earth portion of the shoulder outside the surfaced shoulder width to conform to the typical cross sections shown in the contract, in addition to the above requirements for "Subgrade Preparation".
302.02 Material Requirements
1.Soils shall meet the requireme nts described in Subsection 205.02.
302.03 Construction Methods
1.The Contractor shall shape t he subgrade to the typical cross sections shown in the contract. In t he event the subgrade width is less than the width shown on the typical cross sections, the widening shall be accomplished by either:
a.Lowering the grade. b. Placing additional embankment on the shoulder slopes. 2. Embankments will be constructed in accordance with Section 205.
a.Widening by placement of additional embankment material on the shoulder slopes to provide the minimum width will be allowed only if the existing slope is 1 vertical to 4 horizontal or flatter.
b.After placing, shaping, and compacting the material, the slope shall be no steeper than the slope shown in the contract. Subgrade Preparation, Shoulder Subgrade Preparation, and Preparation of Intersections and Driveways 302.03 - 155 - 3. After stepping and shaping the slopes, the Contractor shall scarify the upper 6 inches (150 mm) of the s ubgrade in all areas to be surfaced.
a.The scarified material shall be completely mixed vertically and horizontally to ensure a uniform material throughout the area to be surfaced.
b.Immediately before placing material on the subgrade, all areas to be surfaced shall be shaped and compacted. The upper 6 inches (150 mm) of the subgrade in these sect ions shall conform to the cross section requirements shown in the contract.
4.If, after the upper 6 inches (150 mm) of the subgrade has been thoroughly mixed, sections of the subgrade are too sandy to provide a firm and stable foundation for the subseq uent construction operations, these sections shall be stabilized, in accordance with the requirements of Section 303, using cohesive soil from sources approved by the Engineer.
5.“Preparation of Intersections and Driveways” shall also include salvaging, stockpiling, and reapplying the salvaged aggregate beyond the surfaced area.
6.Excess excavated material may be wasted, used for filling eroded shoulder slopes, flattening embankment slopes, or temporarily stored for use in shoulder construction. Material st ored for shoulder construction shall be placed so that it will always be adequ ately drained. Ditch drainage in cut sections shall be maintained.
7.In sandy regions, the Contra ctor shall compact the shoulder subgrade and then place the surface mate rial with a shoulder widener which rides on the traveled way.
8.The Contractor shall profile a ll subgrades after they are properly compacted.
a.Profiling for Flexible and Rigid Pavement:
1.Subgrades shall be profiled with an automated, electronically controlled machine. The machine must provide accurate vertical and horizontal control. Pr ofiling is done before placement of:
i.Flexible pavement. (ii) Rigid pavement. (iii) Foundation and base courses. (2) The described elevation for any point shall be based on the specified line, grade, and cross se ction information. The Contractor shall dispose of excess material removed in profiling.
3.When profiling the subgrade of a mainline roadway, a reference line shall be located along both outer edges of the section being profiled. The reference line shall be ma intained until the specified tolerances have been attained, except when stringless profiling is used.
b.Profiling for Shoulders: (1) A motorgrader with auto matic blade control may be used for profiling shoulders and medians.
2.The existing roadway surface may be used as a reference when profiling shoulders. Subgrade Preparation, Shoulder Subgrade Preparation, and
302.03 Preparation of Intersections and Driveways
- 156 - (3) When the traveled way does receive an overlay or an entirely new surface, then at least one lift of the surface course shall be placed and used as the reference for profiling the shoulder.
c.Profiling for driveways, intersections and irregular areas:
1.A motorgrader with auto matic blade control may be used for profiling driveways, intersections and irregular areas.
d.Automated profiling equipment will not be required for intersections, driveways, irregular areas, narrow areas or roadway grading of 1/2 mile (0.8 km) or less.
9.The final profile shall match t he plan profile with a tolerance of ±0.05 foot (15 mm) for each point, and the distance between any two points when measured perpendicular to the plan profile shall not exceed 0.05 foot (15 mm).
302.04 Method of Measurement
1.When the unit for payment is the square yard (square meter):
a.The quantity for payment of Subgrade Preparation will be the number of overlying square yards (square meters) of rigid or flexible pavement, including intersections and driveways.
b.Deductions will be made for all areas not prepared.
2.When the unit of payment is t he station, "Subgrade Preparation" and "Shoulder Subgrade Preparation" are measured as follows:
a.Stations shall be measured horizontally along the project centerline between the beginning and ending points.
b.Full length stations will be 100 feet (100 m).
c.Deductions will be made for all areas not prepared. d. The areas outside the plan typical cross sections, except intersections and driveways, will not be measured for payment but shall be considered subsidiary to "Subgrade Preparation" or "Shoulder Subgrade Preparation".
e.Each shoulder will be me asured separately in stations of 100 feet (100 m) without regard to wi dth. Stations will be measured horizontally along the project center line between the beginning and ending points. Areas where no shoulder is required are deducted from the total measured length of shoulder.
3.Preparation of Intersections and Driveways: a. Preparation of intersections and driveways, including compacting the subgrade and adjusting grade lines for intersections and driveways, will be measured by the square yard (square meter) for the areas outside the surfaced traveled way roadbed.
b.The work of salvaging, stoc kpiling, and replacing the existing aggregate surfacing on intersections and driveways will not be measured for payment but will be considered subsid iary to “Preparation of Intersections and Driveways". Subgrade Preparation, Shoulder Subgrade Preparation, and Preparation of Intersections and Driveways 302.05 - 157 - 4. Water will be measured by the gallon (liter), applied in increments of 1,000 gallons (MGAL) [Kiloliter]. Excess or wasted water will be estimated by the Engineer and deducted from the volume applied.
302.05 Basis of Payment
1.Pay Item Pay Unit Subgrade Preparation Station (Sta) [StaM] Subgrade Preparation Square Yard (SY) [Square Meter (m2)] Preparation of Intersections and Driveways Square Yard (SY) [Square Meter (m2)] Shoulder Subgrade Preparation Station (Sta) [StaM] Shoulder Subgrade Preparation Square Yard (SY) [Square Meter (m 2)] Water 1,000 Gallons (MGAL) [ K i l o l i t e r ( k L ) ]
2.When subgrade stabilization is necessary but not shown in the contract, furnishing cohesive soil for subgrade stabilization will be considered "extra work".
3.The work of adjusting shoulder subgrade elevations and constructing the earth portion of the shoulders will not be paid for directly but shall be considered to be subsidiary to shoulder subgrade preparation.
4.The disposal of surplus excavated material will be paid for as "extra work" when the following conditions exist:
a.The roadbed was graded under a separate contract.
b.The required excavation exceeds 0.20 foot (60 mm). c. Suitable disposal areas ar e not located within the minimum free haul distance specified in Section 209.
5.In all cut areas, those fill areas graded under a separate contract, and under existing approach slabs, the work of correcting faulty subgrade conditions below 6 inches (150 mm) in depth will be done as "extra work" unless such conditions are caused by the Contractor's operations.
6.Payment is full compensation for all work described in this Section. - 158 - SECTION 303 -- SUBGRADE STABILIZATION
303.01 Description
1.The Contractor shall complete the following requirements under the "Subgrade Stabilization" bid item:
a.Provide and place soil binder (cohesive soil). b. Mix soil binder into non-cohesive sand in the upper subgrade. c. Adjust grade lines to meet intersections, pavements, bridge ends, railroad crossings, or any other physical features.
d.Dispose of surplus excavated or profiled material. e. Scarify, adjust the moisture , shape, and compact soils as is necessary to conform to the contract.
303.02 Material Requirements
1.Soil binder shall conform to the requirements of Section 1034.
2.Soil binder shall be obtained according to the requirements of Subsection 205.02.
303.03 Construction Methods
1.The Contractor shall number, l abel, tally, and prepare a report of quantities and distribution of the materi als delivered. A copy of the report shall be given to the Engineer at the end of each day when hauling materials.
2.When the grading is complete, the Engineer will determine the quantity of soil binder the Contractor shall provide to stabilize subgrade sand.
3.Soil binder shall be pulverized to the extent that at least 90% will pass a 1/2 inch (12.5 mm) sieve and at least 60% will pass a No. 10 (2 mm) sieve. The binder shall be pulverized be fore it is mixed with the subgrade sand.
4.After the Contractor has thoroug hly mixed the soil binder with the subgrade sand, the upper 6 inches (150 mm) of the subgrade shall be compacted to the optimal stiffness as defined by a deflection target value established by the Engineer. Moisture may be added as necessary to obtain proper compaction. The moisture target value for granular materials shall be established in the field by the Contractor during the compaction process and may be adjusted at the discretion of the Engineer. Once established the target moisture shall not vary by more than +2%.
5.After the Contractor attains t he required stiffness, the stabilized subgrade shall be profiled in accordan ce with the requirements of Subsection 302.03.
6.In all cut areas and those fill areas graded under a separate contract, correcting faulty subgrade conditions below the 6 inch (150 mm) depth will be performed as "extra work " unless such conditions are caused by the Contractor's operations.
303.04 Method of Measurement
1.Water will be measured as described in Subsection 302.04.
Source: Nebraska Standard Specifications for Highway Construction, 2017 Edition. Pages 188–191 of 1,048.