CA NP MOJA Morning Star Mine Rd Pavement Memo.pdf

Memorandum

Subject:

CA NP MOJA 11(2) 10(2)

Morning Star Mine Road Final Surfacing Recommendations

Date: June 4, 2025

From: Robert Norick

Through:

Pavement & Materials Engineer, CFLHD

Mike Voth Supervisory Materials Engineer, CFLHD

To: Neil Ogden, PM, CFLHD

Project Description:

This memorandum provides the gravel surfacing recommendations for the rehabilitation of the paved Morning Star Mine Road within the Mojave National Preserve in San Bernardino County, California (see attached site map). The Preserve is located south of Interstate Highway 15 and north of Interstate Highway 40 between the cities of Barstow, California and Las Vegas, Nevada. The Preserve became a unit of the National Park Service (NPS) in 1994. Prior to 2013, the roads within the Preserve were under the jurisdiction of the county. In 2015, NPS applied a single course chip seal to the paved Morning Star Mine Road. The road’s pavement has aged and is beyond its design life.

The project consists of the rehabilitation of the 15.0 mile length of Morning Star Mine Road from its intersection with Cima Road and Kelso-Cima Road (at Milepost 0) northeast to its terminus with Ivanpah Road (at Milepost 15). The road lies within critical desert tortoise habitat with a high tortoise mortality rate. With the completion of the Cima Road rehabilitation, the primary route for traffic through the Preserve is the combination of Cima Road, Kelso-Cima Road, and South Kelbaker Road. Morning Star Mine Road will become a secondary route within the Preserve with its primary use being sightseeing. The National Park Service has requested that this paved road be converted to a gravel road in order to reduce the road’s traffic and high speeds, and thereby, the tortoise mortality rate.

Pavement Assessment:

Geologically, the Preserve encompasses broad alluvium-filled valleys separated by mountain ranges, dry river beds, mesas, sand dunes, cinder cones, domes, and lava flows. Soils within the project vicinity generally consist of alluvial (sand and gravel) and eolian (silt and sand) deposits from volcanic and sedimentary sources.

On November 12-14, 2019, FHWA-CFL conducted a visual pavement assessment for Morning Star Mine Road (see attached photos). The existing asphalt was found to be approximately 22 feet wide with shoulders of the native silty sands. In a few locations, the shoulders consisted of clean “beach sand” (non-cohesive and unstable). The road’s existing asphalt pavement is highly oxidized with transverse, longitudinal, block, and fatigue cracking that comes with an old age hardened road. It is no longer cost effective to extend the pavement life with pavement preservation methods (e.g. chip seals). No coring or subsurface investigation was completed for Morning Star Mine Road. The following information from recent investigations on other routes in the area is presented for information only and the referenced conditions may not be representative of the conditions on Morning Star Mine Road.

Subsequent to the 2019 pavement assessment, pavement and subgrade investigations were conducted for Cima Road and Kelso-Cima Road in 2020 and 2023, respectively.

Both of these investigations found 3 to 5 inches of pavement lying directly on a sandy subgrade with average R-Values (resistance values on a scale of 0 to 100) of 54. The existing pavement was found to consist of a layer of hot mix asphalt over a layer of asphalt road mix (asphalt cold-mixed by blade with the native sands directly on-grade and compacted). Additional details from these two investigations follow.

Investigation for CA FTNP MOJA 12(1) Cima Road:

On July 29-31, 2020, FHWA-CFL conducted a pavement and subgrade investigation for Cima Road consisting of 55 shallow borings at 0.30 mile increments (5’ and 10’ depths) with associated subgrade sampling. The subgrade soils consisted of silty and clayey sands (ASTM SM, SC, and SC-SM soils). R-Values were determined for 11 of the subgrade samples and ranged between 21 and 76 with an average of 54.

Investigation for CA FTNP MOJA 11(2) 10(2) Kelso-Cima and Kelbaker Roads:

On June 9-12, 2023, GeoEngineers (San Diego, CA), conducted a pavement and subgrade investigation for Kelso-Cima Road consisting of 39 shallow borings at

0.50 mile increments (6.5’ depths) with associated subgrade sampling. The subgrade soils consisted of silty sands (ASTM SM soils). R-Values were determined for 6 of the subgrade samples and ranged between 27 and 76 with an average of 54. Additionally, GeoEngineers cored the road in 20 additional locations and used a Dynamic Cone Penetrometer (DCP) for California Bearing Ratio (CBR) correlations. All locations had CBRs greater than 22%.

Surfacing Recommendations:

The proposed gravel surfacing is designed in accordance with the South Dakota Catalog Method for a “high” subgrade support condition (CBR > 10%) with less than 5 trucks per day (see tables on the following page). The recommended gravel surfacing rehabilitation for Morning Star Mine Road is:

6 inches of Aggregate Base over Full Depth Reclamation (FDR) of Existing Asphalt (pulverize to 1-inch below the bottom of existing pavement)

If the existing asphalt is found to be less than 2 inches thick or if the subgrade is found to be clean “beach sand”, the 6 inches of aggregate base may be placed on top of the existing asphalt prior to completing FDR operations to promote greater stability for grading and compaction operations. The following pavement related pay items are recommended for the project.

Item Number Item Description Unit 30110-0300 Aggregate Surface Course Grading H TON 30401-5000 Full Depth Reclamation, Method 2 MILE

CFLHD standard SCRs related to pavements and materials are expected to be used with the exception of an SCR for Section 304 to specify the depth of pulverization as provided below.

SECTION 304. – FULL DEPTH RECLAMATION

304.05 Pulverizing. Delete the last paragraph and substitute the following:

Use the reclaimer to pulverize the existing roadway material to 1-inch below the bottom of the existing pavement, in-place until 100 percent passes the 1½-inch sieve. Reprocess or remove larger particles and dispose of them according to Subsection 203.07.

Attachments:

South Dakota Catalog Method with CBR Values (1 page) Site Map (1 page) Photos from Pavement Assessment (5 pages)

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CA NP MOJA Morning Star Mine Road – November 2019 Photos

Morning Star Mine Road at MP 0.05 just North of Cima Road Intx, Looking North

MP 1.35 – Looking North at Longitudinal Cracking & Vegetated Shoulders

MP 3.00 – Looking North at Transverse Cracking & Silty Sand Shoulder

MP 5.00 – Looking North at Transverse & Long. Cracking & Silty Sand Shoulder

MP 7.40 – Looking North at Transverse & Longitudinal Cracking

MP 8.30 – Looking North at Transverse Cracking & Clean “Beach Sand” Shoulder

MP 9.30 – Rental Car Stuck in Clean “Beach Sand” Roadway Shoulder

MP 10.00 – Looking South at Transverse, Longitudinal, & Block Cracking

MP 12.00 – Looking South at Transverse, Longitudinal, & Block Cracking

MP 14.60 North of Ivanpah Road – Looking South at Block Cracking

CA NP MOJA Morning Star Mine Rd Pavement Memo