HI_SR_200(3)_Saddle_Road_P M_Tech_Memo.pdf

CFLHD Pavement & Materials

Subject: Evaluation of Pavement Design & Material Recommendations, HI SR 200(3) Saddle Road – East Side MP 11 to 5.6

From: Mike Voth Pavement & Materials Engineer, CFLHD

To: Mike Will Project Manager, CFLHD

INTRODUCTION

The purpose of this memorandum is to evaluate the proposed pavement design and material recommendations and report the results.

A comprehensive pavement report was completed in July 2009 for the 200(2) project from MP 11 to 19. This report documents the meetings, supporting data, and presentations that were used to arrive at a decision for the pavement design. The report also documents correspondence from the Hawaii DOT indicating their concurrence with the design approach and recommendations. It was intended that the pavement design process, standards, and criteria included in this report would apply to the remaining Saddle Road projects, which were the 6(6) and 6(7) projects from MP 42 to 54 and this current project. However, with each project a soil subgrade investigation was to be completed to evaluate subgrade conditions. Traffic data was also to be monitored to evaluate our predictions/estimates. Adjustments, if necessary, were to be made to the pavement recommendations based on the most current and localized conditions.

Unlike most of the previous Saddle Road projects, this project is in a more heavily vegetated area with very high annual rainfall amounts. The elevations of the project will range from about 2850 feet at the west end of the project to about 1350 feet at the east end in Hilo. The annual rainfall within the project area is expected to be in the range of 160 to 240 inches. The average daytime air temperatures will range between 70 and 80 degrees. Overnight temperatures will average between 60 and 70 degrees. In regards to asphalt paving operations, it should be noted that frequent and almost daily rainfall should be expected. Low cloud conditions and/or fog will also be a common occurrence.

SUBGRADE EVALUATION

The Geotechnical Data Report completed by Geolabs (W.O. 4984-30 & 40) contains comprehensive information about the subgrade conditions and properties. This memo just provides a brief summary of the conditions and properties as related to pavement design; and

Technical Memorandum

Date: September 4, 2015 compares the properties to the targeted properties from the pavement report completed for the 200(2) project.

Summary of Subgrade Conditions Project Design R-Value Design MR Typical Soil

Class Geologic Materials

200(2) 60 15,000 GW, GM, SM

(A-1-a)

•Pahoehoe basalt rock •A’a basalt rock •Fill sands and gravels

200(3) GW, GM, SM,

MH-CH (ash).

•Same as above •Volcanic ash*

*Volcanic ash is generally a clayey silt material. It is difficult to work with due to very high liquid limits and plasticity index values. Stiffness of this material is often very sensitive to moisture content. For the purposes of pavement design evaluation, the volcanic ash is being ignored with the understanding that it will either be covered with deep embankment fill, or in cut sections it will be subexcavated to a depth of 30 inches (or more) and backfilled with geogrid reinforced granular backfill to establish a working platform.

Refer to the geotech report for additional information on the volcanic ash and how it will be addressed.

The table above indicates that the subgrade soil and rock materials are similar for both the 200(2) and 200(3) projects; with the exception that volcanic ash will be present on the 200(3) project.

As indicated above the volcanic ash will be addressed by either subexcavation or deep embankment fills and is not expected to impact the pavement structural design.

The 200(3) geotech report did not contain R-value testing, but subgrade soil classifications are very similar to the 200(2) project. On the previous Saddle Road projects we have not had issues with attaining R-values of 60. It is also important to note that embankment construction will use granular, non-plastic soil and cobbles, which will provide a strong foundation for the pavement structure. The design R-value of 60 is assumed to be applicable for the 200(3) project. During construction it is recommended that soil samples be routinely evaluated to verify that R-values of 60 are being achieved.

The soils investigation for the 200(2) project included 19 field permeability tests which indicated that percolation rates were adequate for draining water from the pavement and base structure.

Most locations had permeability rates that exceeded 10 ft/day. The 200(3) geotech report did not contain field permeability test results, but the geologic materials are similar to the 200(2) project.

As indicated in the 200(3) geotech report, the pahoehoe and a’a lavas will have good porosity through the numerous surface cracks that will readily permit water to percolate into the subsurface.

TRAFFIC EVALUATION

The ESAL used for design in the 200(2) report was 2,500,000. The following table estimates total ESAL for the 200(3) project using recent traffic data from the WIM site that has been installed on Saddle Road. It is important to note that the traffic data collected at this WIM site (mile post 33) may not be fully representative of the traffic between mile post 11 and 6, but it is the best information available and is expected to provide a reasonable estimate. The growth rates are rough, conservative estimates and were taken from the 2009 pavement report for the 200(2) project.

Traffic Count May, 2015 = 4094 ADT, 2-way, @ Mile Post 33

FHWA

Class

Average Daily Volume

Growth Rate (estimated)

Truck factor 20-year

ESAL

1 7 4 0 0 2 2233 4 0.0004 5202 3 1417 4 0.004 33004 4 9 5 2 120441 5 303 5 0.5 1010199 6 12 5 1 78932 7 1 5 1 3656 8 4 5 2.2 52521 9 60 5 2.2 874875 10 4 5 2.2 52994 11 1 5 3 18711 12 0 5 3 0 13 1 5 3 26454

Total ESAL = 2,276,988

The total ESAL for the 200(3) project from the table above is less than the 2,500,000 which was used for design in the 200(2) project. This is good validation of our previous traffic estimates and indicates that there should not be a reduction of service life based on traffic.

CONCLUSIONS

Based on the subgrade and traffic evaluation discussed above, the specified pavement design from the 200(2) project is verified and will be sufficient for this 200(3) project. This pavement design is as follows:

2” Superpave asphalt concrete pavement, ½” NMA, PG 64-14 binder 3” Marshall asphalt concrete pavement, ¾” NMA, PG 64-16 binder 6” Crushed aggregate base

The other material recommendations have been appropriately carried forward into this project including the use of lime at 1% for the antistrip additive and the inclusion of the PTA quarry as an optional source for embankment material, base, and asphalt concrete pavement aggregate.

Also carried forward with this project is the use of CFLHD staff and equipment to conduct all acceptance and verification testing of materials.

A copy of the 2009 pavement report is available upon request. It includes comprehensive information about the pavement design, Hawaii DOT concurrences, and HACP mix designs using the PTA quarry.