CO_FLAP_CHA_CR300(1) Pavement Memo.pdf

Memorandum

Subject:

CO FLAP CHA CR300(1)

Browns Canyon Access Road Final Pavement Recommendations

Date: September 7, 2022

From: Robert Norick

Through:

Pavement & Materials Engineer

Mike Voth Pavement & Materials Team Lead

To: Tammy Eggers, PM Ryan Owen, Lead Designer

Project Description:

This memorandum provides the pavement structural section recommendations for the CO FLAP CHA CR300(1) Browns Canyon National Monument Access Road (Chaffee County Road 300) in Colorado. Chaffee County Road 300 provides access to the Arkansas River, the Browns Canyon National Monument, and Colorado State Park’s Ruby Mountain Campground (including RVs). Commercial rafting companies use this road for a boat launch during the three month white water rafting season (using passenger vans and school buses). The project consists of the reconstruction and widening of a 0.10 mile section of the existing gravel road immediately north of the Ruby Mountain Campground. Additionally, Blue Triton Brands operates a spring just north of this section of road for its Arrowhead Spring Water brand.

This section of road includes a short, narrow, 12-foot wide road segment (the “Narrows”) located at the crest of a vertical curve and in the middle of a horizontal curve. The “Narrows” is bordered by a rock cut on the north and the Arkansas River on the south with inadequate sight distance and geometry for traffic to pass safely. A traffic signal was installed by the County to facilitate one-way traffic but it has been vandalized and is currently inoperable. The scope of the project is to widen this section of road to a consistent 22-foot wide gravel surface, provide the required geometry and site distance, and improve drainage. The road has a low traffic level with a two-way annual average daily traffic (AADT) of only 100 (based upon FLAP application) and 95% of the vehicles being FHWA Class 2-3 cars, pickups, vans, and SUVs.

Pavement Investigation:

On September 8, 2021, a pavement investigation was conducted for the project consisting of two backhoe test pits (see attached test pit location map, as well as, photos from the pavement investigation). The Chaffee County Road & Bridge Department provided the traffic control (signs and two flag personnel), as well as, a rubber tired backhoe with operator. CFL personnel logged the findings including depth of surface aggregate and subgrade soils, visual soil classification, groundwater depth, and areas of distress. The existing gravel surfacing through the project site is in fair condition. Two bulk samples of the surface aggregate and one bulk sample of the TP-2 subgrade material were collected and submitted to the CFLHD lab for testing to determine the soil classifications (see attached lab reports). At the “Narrows” (TP-1), the investigation found a 6 inch depth of surface aggregate over fractured granite. The backhoe excavated into the fractured granite to a depth of 18 inches. Adjacent to the “Arrowhead Spring” site (TP-2), the investigation found a 6 inch depth of surface aggregate over a sand with silt, gravel, and cobbles (8” minus), a very good AASHTO A-1-b soil. TP-2 was excavated to a depth of 36 inches. The TP-2 subgrade sample was also tested for R-Value (resistance values on a scale of 0 to 100 per AASHTO T 190). The TP-2 sand with silt and gravel was found to have an R-Value of 80; similar to the performance of aggregate base. Groundwater was not encountered at either of the test pits.

Pavement Recommendations:

Based upon the pavement investigation, a 6 inch depth of surface course aggregate (item 30202-2100 in tons) is recommended for the proposed road reconstruction;

constructed using FP-14. The existing gravel surfacing may be used for unclassified borrow or topping. The subgrade material from TP-2 (sand with silt and gravel) may be reused as unclassified borrow. The subgrade material at TP-1 (fractured granite) will require crushing and processing to be reused. CFLHD standard SCRs related to pavements and materials are expected to be used. Any additional SCRs may be developed as needed.

CO FLAP CHA CR300(1) Browns Canyon Access Road

Looking Southeast to Test Pit TP-1 at the “Narrows” & Survey Point 4003

Looking Northwest to Test Pit TP-1 at the “Narrows” & Survey Point 4003

CO FLAP CHA CR300(1) Browns Canyon Access Road

Looking West to Test Pit TP-2 & Adjacent Spring Site & Survey Point 4005

Test Pit TP-2’s Sandy Subgrade with Silt, Gravel, & Cobbles to 3 Foot Depth