B12_Rock_Fall_and_Road_Surfacing_Description_0004.pdf

Hart Mountain NAR Grade Road Restoration Project

Rockfall

The rockfall at this location is primarily a nuisance and/or maintenance concern, and generally consists of small to moderate sized rock (< 12 inches). The upgradient cut slopes are generally between 20 and 45 feet high and have slope faces between 55° and 65° to horizontal. No evidence of controlled blast lines was observed, indicating that these slopes were excavated using aggressive blasting methods which likely damaged the exposed rock face. Observation of the upgradient rock face revealed lava flows between 10 and 30 feet thick separated by flow breccias that are generally less than 10 feet thick.

In order to address the concern with rockfall, the final design includes scaling of the upgradient rock face between approximate Stations 0+00 and 11+00. This would entail a qualified scaling contractor dislodging and disposing of loose rock, by either manual or mechanical means, which would otherwise have eventually fallen with time. This will not ultimately solve any rockfall issues but is expected to significantly reduce any risk of hazard and reduce the maintenance concerns over the next 10 – 20 years.

In addition, it is proposed that the existing ditch be cleared of all accumulated rock fall and sediment as a measure of protecting the road from rockfall. The existing ditch will serve as a point of accumulation for rockfall, that will have an intermittent cleanout schedule as required to maintain a positive drainage path for runoff and snowmelt. Material produced by the scaling and ditch cleaning may be hauled to the Rattlesnake Rock Pit and processed with the quarry rock for producing road base and riprap material.

Figure 1-1. Upgradient Rock Face

Road Resurfacing / Material Sourcing

In the AOI it is expected that the road will be resurfaced, with particular attention given to locations where the road is experiencing corrugation (“washboarding”), potholes, or other road surface deficiencies.

Outside of the AOI, it is expected that USFWS will perform any road maintenance needed with its available road grading equipment. The construction contractor, as part of the construction contract, will develop a stockpile of crushed aggregate road surfacing material for use by USFWS in quantities dictated by the overall project budget. The road surfacing material shall be according to the ODOT Dense Graded 1”-0 aggregate specification, as summarized in the following tables. Aggregate should be free from organic material and free from lumps or balls of clay.

Table 1-1. Road Surfacing Specifications

Material Property

Test Method

Value

Abrasion AASHTO T104 35% max

Degradation passing No. 20 sieve ODOT TM 208 30% max

Sediment Height ODOT TM 208 3” max

Material Property

Test Method

Value

Sand Equivalent AASHTO T 176 30 min.

Fracture of Rounded Rock AASHTO T 335 50% min for 1 ½” and larger

70% min for ¼” to 1 ½”

Table 1-2. Road Surfacing Gradations (AASHTO T27)

Sieve Size

Percent

1-1/2” 100

1” 90 – 100

½” 55 – 75

¼” 40 – 55

No. 10 40 – 60 of material passing ¼” sieve

Based on preliminary site observations and testing of existing material collected at the site (see Figure 1-2), it is expected that material developed at the existing Rattlesnake Rock Pit will be capable of supplying adequate material for the roadway aggregate for regrading of the Grade Road. The rock material is discussed at greater length in an Appendix. It is recommended, however, that the construction contractor verify the suitability of the rock with an independent testing program.

Figure 1-2. Existing, Stockpiled Road Surfacing Material

(Pen – 5-1/2” for scale)

The preliminarily expectation is that development of the aggregate source material from the Rattlesnake Rock Pit can be performed according to the following methods, though the development of quarry will ultimately be the responsibility of the construction contractor:

The existing access road down to the bottom of the Snake Pit (see Figure 3-5) will need to be cleared and developed to gain vehicular access to the bottom of the pit, for hauling of materials.

Conventional blasting (could) or (will) be performed on an approximate 6-ft x 6-ft or 8-ft x 8-ft section of the pit wall, for development of source material.

Rock would then be crushed by a mobile crusher unit to the desired size, as required by the above specifications.

Material would then be screened on-site and would be mixed to form the AASHTO T27 gradation specifications given above.

Material would then be stockpiled in separate stockpiles at the top of the Rattlesnake Rock Pit for future use in road grading activities.

Figure 1-3. Rattlesnake Rock Pit Existing Access Route