SS305-002020-02.docx
DOCX document 36 KB Posted
- Attached to
- Construction, University Drive Bike Lanes
- Solicitation number
- IFB-114424
- Issued by
- Fairfax County, Virginia
About this file
This is a supplemental specifications document issued by the Virginia Department of Transportation (VDOT) on December 20, 2023, establishing technical requirements for subgrade and shoulder construction work under Section 305 of the 2020 Road and Bridge Specifications. The document outlines detailed specifications for subgrade preparation, including scarification to a depth of 6 inches extending 2 feet beyond proposed pavement edges, moisture content management, and compaction density requirements that vary based on material composition (0-50% retained on No. 4 sieve requires 100% density; 51-60% requires 95% density; 61-70% requires 90% density). Field density determination shall be performed using a portable nuclear density gauge per VTM-10 or other Engineer-approved methods. The contractor must shape and check the subgrade for proper cross section and uniform grade prior to subsequent course placement, and must scarify, reshape, and recompact any eroded or distorted subgrade areas.
The shoulders specification requires aggregate shoulder material to be placed and compacted at optimum moisture within 2 percentage points, with similar density requirements as the subgrade except when aggregate material No. 18 is used, which requires density between 90-95 percent. The portable nuclear density gauge may allow a 5% density reduction when used in direct transmission mode. For layers less than 4 inches thick, compaction with three or more passes of a heavy-duty vibratory roller is permitted as an alternative. Special requirements apply to guardrail sections, which must achieve 90% density and have asphalt mixture sealed immediately after spreading. Stabilized and paved shoulders must be constructed simultaneously with base or surface courses, with the 12-inch shoulder area adjacent to pavement rolled during course deposition, and shoulder material placed within 72 hours when base or surface courses exceed 1 inch in depth.
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Text version
SS305-002020-02 December 20,2023
VIRGINIA DEPARTMENT OF TRANSPORTATION
2020 ROAD AND BRIDGE SUPPLEMENTAL SPECIFICATIONS
SECTION 305 – SUBGRADE AND SHOULDERS
Section 305.03(a)1 – Subgrade consisting of material in place is replaced with the following:
1. Subgrade consisting of material in place: The subgrade area shall be scarified to a depth of 6 inches for a distance of 2 feet beyond the proposed edges of the pavement on each side. If sandy or other soil is encountered that will not compact readily, clay or other suitable material may be added or water applied in such quantity and within the allowable moisture content specified herein as will permit compaction of the subgrade. Subgrade material shall be compacted at optimum moisture, within ±20 percent of optimum. The density of the subgrade when compared to the theoretical maximum density as determined in accordance with VTM-1 or VTM-12 shall conform to the following:
| % Retained on No. 4 Sieve |
| Min. % Density |
| 0-50 |
| 100 |
| 51-60 |
| 95 |
| 61-70 |
| 90 |
Percentages of material shall be reported to the nearest whole number.
Field density determination will be performed with a portable nuclear density gauge as specified in VTM-10, or by other approved methods as directed by the Engineer.
The Contractor shall then shape and check the subgrade to ensure a typical cross section and uniform grade prior to placement of any subsequent courses. If the subgrade becomes eroded or distorted prior to placement of material for subsequent courses, the Contractor shall scarify, reshape, and recompact it in accordance with the original requirements.
At the time of placing material for subsequent courses, the Contractor shall compact the subgrade to the required density, free from mud and frost, and to a condition that will permit compaction of subsequent courses without distortion.
The Contractor shall remove material from the unstable area and contaminated aggregate if the approved subgrade becomes unstable after placement of the subbase or base course and becomes mixed with the aggregate therein. The area shall then be backfilled and compacted, and the subsequent course thereon reconstructed.
Section 305.03(e) – Shoulders is replaced with the following:
Shoulders: Aggregate shoulder material shall be placed in accordance with the applicable specifications governing the type of material or construction being used and shall be compacted at optimum moisture, within ±2 percentage points of optimum. Except when aggregate material No. 18 is used, the density of the aggregate shoulder material, when compared to the theoretical maximum density as determined in accordance with VTM-1, shall conform to the following:
| % Retained on No. 4 Sieve |
| Min. % Density |
| 0-50 |
| 100 |
| 51-60 |
| 95 |
| 61-70 |
| 90 |
Percentages of material will be reported to the nearest whole number. The above density requirements may be reduced by 5% per VTM-10 when using the portable nuclear density gauge in direct transmission mode.
When aggregate material No. 18 is used, the density, when compared to the theoretical maximum density, shall be not less than 90 percent or more than 95 percent.
Field density determination will be performed with a portable nuclear density gauge as specified in VTM-10, or by other approved methods as directed by the Engineer. When the total thickness of the layer for aggregate shoulder material being constructed is less than 4 inches, the minimum density requirement may not be enforced. For such cases, the aggregate shoulder should be compacted with three or more passes of a heavy-duty vibratory roller (e.g., a 10-ton smooth drum roller) or as approved by the Engineer. The aggregate shoulder should be compacted until it is apparent that no further densification can be obtained.
When it is determined by the Engineer that operating a roller/compactor on the shoulder material is a rollover hazard, the compaction requirements can be waived by the Engineer.
Aggregate in the guardrail section of fills, 1 foot from the roadway side of the guardrail face to the outside of the shoulder, shall be compacted until a density of at least 90 percent of the theoretical maximum density has been obtained. The asphalt mixture in this area shall be sealed immediately after the hot mixture is spread. Rolling of the asphalt mixture shall continue until roller marks are eliminated.
Stabilized and paved shoulders shall be constructed in accordance with the applicable specifications for pavement stabilization. If the aggregate shoulder material becomes overconsolidated prior to final finishing, it shall be scarified for the approximate depth, reshaped, and recompacted to conform to the specified grade and cross section.
Shoulders shall be constructed simultaneously with nonrigid types of base or surface courses other than asphalt concrete or in advance of the base or surface course so as to prevent spreading of base or surface materials. The area of shoulders 12 inches adjacent to the pavement shall be rolled simultaneously with the course being deposited.
Where base or surface courses are being constructed under traffic and are more than 1 inch in depth, shoulder material adjacent thereto shall be placed within 72 hours after placement of the base or surface course.
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