CA FLAP LA CR2N40(1)_Site 5 Pavement Rehabilitation Memo.pdf

Jacobs Engineering Group 707 17th Street Suite 2400 24th Floor Denver, CO 80202

Memorandum

Jacobs Engineering Group Inc.

Date May 26, 2016

Subject CA FLAP LA CR 2N40(1) –Santa Anita Canyon Road

Site 5: Pavement Rehabilitation Approach

GENERAL. The Santa Anita Canyon Road (SACR) project includes improvements to five sites along the roadway corridor.

The focus of this memorandum is to discuss the pavement rehabilitation approach at Site 5. Site 5 is located in the center of the project area and is approximately 0.6 miles in length.

EXISTING STRUCTURAL SECTION. A visual inspection was conducted and subsurface borings have been obtained along Site

5. The pavement condition varies within the limits of Site 5. The most common distress observed consists of longitudinal cracks, transverse cracks, and alligator cracking. Longitudinal cracks were observed in approximately 25 to 50 percent of the length of the Site and transverse cracks at a 5 to 20-foot interval. Alligator cracking was noted in approximately 5 percent of the roadway. Approximately 25 to 50 percent of the cracks observed were sealed. The borings at Site 5 were drilled to a depth of five feet below ground surface. Six borings where taken within the Site 5 limits. The soils encountered typically consisted of loose to dense, silty sand. Layers of silt with sand and gravelly silt with sand were also encountered. Structural section thicknesses are presented below.

Boring Asphalt Concrete (in)

Untreated Aggregate Base

Course (in) B-01 5 0 B-02 5.5 0 B-03 5 0 B-04 4 0 B-06 4 0 B-07 5 0

Memorandum Site 5: Pavement Rehabilitation Approach May 26, 2016

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PROPOSED REHABILITATION APPROACH. During the FLAP Application and Scoping processes, the existing pavement thickness was thought to be 2 to 2 1/2 inches thick. Based on the anticipated thickness, a mill and fill approach was anticipated. Following geotechnical field investigations it became apparent that the existing pavement was considerably thicker (4.75 inches on average).

One of the primary benefits of a mill and fill approach is that the proposed roadway surface elevation remains essentially unchanged from the existing condition. This reduces the likelihood that existing drainage patterns along the roadway will be affected. However, milling to depths greater than about 2 inches becomes cost prohibitive. Partial depth reclamation is an option, but reflective cracking from the remaining un-milled asphalt mat may result in a short pavement surface life.

The existing guardrail along the entire outboard side of the rehabilitation segment poses problems regardless of the rehabilitation approach selected (especially due to the tight horizontal curvature and steep vertical grades). Removal and replacement of the guardrail would afford the contractor a better opportunity to provide a quality product.

The combination of concerns with reflective cracking with the mill and fill option and the realistic need to remove the guardrail result in a full depth reclamation/overlay approach being the preferred option. This approach includes pulverizing the existing asphalt mat full depth. The pulverized material would be shaped, compacted and overlaid with two lifts of new asphalt (3 inches total).

The full depth reclamation approach would effectively raise the existing roadway surface about 3 inches. However, with the guardrail posts removed, existing inverted shoulders would be overlaid and existing asphalt berms could be matched into. Thus, reducing the potential that existing drainage patterns would be affected.

Guardrail could then be replaced with all steel post to: 1) reduce the potential for heaving, provide better drivability in the rocky soils and 3) better resist future wildfires. As an added benefit, the increased elevation of the roadway elevation would allow for better establishment of inboard ditches and the introduction of inboard curb or paving directly up to existing rock cut faces. The proposed typical section for the Full Depth Reclamation option and the proposed treatment adjacent to guardrail are provided on the following pages.

COST COMPARISON. Rehabilitation using a mill and fill approach (two-inch mill and fill depth) is anticipated to cost about $5 per sy for milling and $20 per sy for the overlay. Full depth reclamation (6-inch FDR with a 3-inch overlay) is anticipated to cost about $8 per sy for pulverizing and $29 per sy for overlay. Site 5 is 0.617 miles in length and on average 22 feet wide. The resulting structural section costs for the two alternatives are:

Mill and Fill $160,000 FDR and Overlay $230,000

The mill and fill approach would require, at a minimum removal and resetting the existing guardrail rail. This cost is approximately $15 per lf, or $49,000. Removal and installation of new guardrail for the FDR approach would be about $45 per lf, or $147,000. The FDR approach would also require overlaying the existing inverted shoulder. This cost is estimated to be approximately $8,000.

Considering the above items the cost of each approach is estimated to be:

Mill and Fill $209,000 FDR and Overlay $385,000

INSERT A9 and Special 617-A