CA_FLAP_PLU_CR411(1)_Buck's_Lake_Rd_V1_P&M_memo_6-22-16.pdf

Subject: Pavement & Materials Recommendations (V1) CA FLAP PLU CR411(1) Bucks Lake Road

From: Mike Voth Senior Pavement & Materials Engineer, CFLHD

To: Bob Bowden, Project Manager, CFLHD Leslie DeWitt, Lead Designer, CFLHD

INTRODUCTION

This memorandum provides final pavement and material recommendations for the 0.329 mile slope stabilization project on Bucks Lake Road in northern California in Plumas County.

The primary purpose of this project is to address the hazardous rockfall that occurs regularly along the project segment. The scope will include shifting the alignment, adding a reinforced soil slope, and replacing the pavement structural section. The planned roadway geometric section is two 12-foot driving lanes and 4-foot shoulders for a total width of 32 feet. In general this matches the existing typical section of the roadway.

CFLHD standards and guidelines were used to complete the pavement and materials recommendations.

FIELD INVESTIGATION

Given the small project size and scope, pavement & materials staff from CFLHD did not conduct a field investigation. Data gathered from the geotechnical investigation and traffic information provided by Plumas County was used to develop inputs for the pavement design. This approach typically leads to more conservative designs.

The geotechnical investigation took place from October 6 to 8, 2016. For pavement design purposes, one shallow boring was completed in the roadway to a depth of 4 feet and a bulk sample was gathered for soil classification and R-value testing. 3 other deep bores/cores were completed for analysis of other geotechnical elements of the project.

See table below for a summary of data gathered and test results. For more complete and detailed results, refer to the boring logs and lab test reports.

Summary of Sampling & Test Results

Technical Memorandum

Date: June 22, 2016

Location Pavement Depth

Soil Classification

Plasticity Index

R-value for Subgrade Comments

STA 356+50

(B-4)

~5”

A-1-b

(SC-SM) 5 55

R-Value is representative of the material from 0 to 4 feet in depth.

Scoping report indicated that longitudinal crack was present in wheelpaths. Divots in pavement from rockfall were also noted.

STA 369+40

(B-3) ~3.5” A-1-a

(GC-GM) 6 n/a Boring was completed in shoulder.

Pavement thickness may not be representative of mainline.

The as-builts indicate that the original pavement section consisted of 3 inches of asphalt pavement over 12 inches of aggregate base. The county staff indicated that numerous chip seals and at least one overlay has taken place since the original construction.

TRAFFIC:

Bucks Lake Road has two primary generators of traffic: 1) tourist / recreational traffic (trucks towing boats, campers, RVs, etc.), and 2) logging traffic from local timber sales. The following is a summary of traffic data provided by Plumas County:

• 2016 ADT = 1261

• 2041 ADT = 1617 (1% growth rate)

• Assumed 10% trucks; including heavy logging trucks (70-30 ratio assumed for single unit trucks to logging trailer trucks)

• Used 0.50 truck factor for single unit trucks and 2.2 truck factor for the logging trucks

• Directional factor = 60%

• Design Lane ESAL’s = 794,000

The 25-year 18-kip equivalent single axle load (ESAL) used for design was 794,000.

DESIGN RECOMMENDATIONS

MAIN LINE:

The pavement design and material recommendations are included below.

In developing the pavement structural recommendations the following criteria was used:

Design Criteria Initial Serviceability 4.2 Terminal Serviceability 2.5 Design Reliability Level 75% Overall Standard Deviation 0.49 Soil Resilient Modulus (average R-value = 55) 16,000 psi Performance Period (4R) 25 years

25-year ESAL 794,000 Calculated Structural Number 2.35

The following table includes the minimum pavement structural section required to meet the structural number, and the pavement structural section that will be included in the plan set for construction.

Main Line Roadway Layer Thickness

Minimum Pavement Structural Section Asphalt Concrete Pavement 4 inches (two equal lifts) Crushed Aggregate Base 7 inches

SN = 2.44

Pavement Structural Section to be Constructed*

Asphalt Concrete Pavement 4 inches (two equal lifts) Crushed Aggregate Base 9 inches

SN = 2.68

*This pavement structural section matches what was estimated during scoping. The CFT decided it was not worth the time and cost to change the plan set for a relatively minor change to the structure (only 2 inches of the aggregate base).

PULLOUTS:

Per the scoping report, no pavement or gravel surfacing will be applied to the pullouts. They will remain as is with their current native soil surfacing.

ADDITIONAL RECOMMENDATIONS:

• Per CalTrans climate and PG grade maps, the use of a PG 64-28 asphalt binder is appropriate for this region. LTPPBind does not have a weather site near Buck’s Lake Road.

• It was noted that moisture weeping from the rock cut and from snow melt may have been a factor in some of the pavement distress. Drainage improvement recommendations are included in the geotechnical report to address this concern.

• Recommend the following bid items (given size and scope of this project fog seal is optional).

Item Number Item Description Unit 30202-2000 Roadway Aggregate, Method 2 TON 40301-0100 Asphalt concrete pavement, Type 1 TON 41102-1000 Prime Coat, Method 1 SQYD 41105-0000 Blotter TON 41201-0000 Tack Coat TON

CONSTRUCTION CONSIDERATIONS & SPECIAL CONTRACT PROVISIONS

The standard SCRs as related to pavements & materials will be used.

Based on the borings weak and poor soils are not expected to be encountered. Other than saturated conditions during the snow melt, difficult or unique construction concerns with the aggregate base and pavement are not expected.

Attachments:

Lab Test Report AASHTO DARWin pavement design summary

Technical Memorandum