On-Site Lab Drives Construction Quality for America's Tallest Asphalt Core Dam

Building America’s Tallest Asphalt Dam: The Chimney Hollow Reservoir Story

Client

Barnard Construction

Location

Loveland, Colorado

Challenge

As the tallest dam built in the United States since 2000, and only the second (and tallest) asphalt core dam in the country, the dam at Chimney Hollow Reservoir presented generational challenges. The project was completed in four years and at the height of construction, work continued around the clock for more than two years to keep this vital infrastructure project on schedule. Our dedicated materials testing team was at the heart of it all, working in concert with other contractors to keep pace with the project timeline. 

The construction of the 350-foot-tall primary dam and 40-foot saddle dam at Chimney Hollow Reservoir consists of approximately 12 million cubic yards of material. Terracon’s Fort Collins, Colorado, office was tasked with providing materials testing data for nearly all of that material. Their responsibilities included several different testing methods, including: 

• Soil, aggregates, and sand testing
• Sieve analysis
• Proctor analysis
• Plasticity
• Relative density
• Durability and soundness
• Dispersivity
• Water soluble sulfates
• Alkali silica reactivity
• Clay lumps
• Lightweight particles
• Specific gravity and absorption
• Concreate, shotcrete, and grout testing

The construction schedule depended on the data provided by our materials professionals. And the accelerated timeline meant that shuttling samples to and from the permanent laboratory in the Fort Collins office – more than 20 miles from the project site – was not an option.

Solution

Since the project team couldn’t operate from the Fort Collins office laboratory, the team instead set up a mobile laboratory at the site of the rising primary dam. For more than three years, our team used the mobile laboratory to deliver essential materials data for the project. At the peak of construction, Terracon had 10-12 employees on-site every day. With 24-hour operation, which halted only in inclement weather, the team coordinated to keep pace. Schedules were carefully monitored to support the project team’s physical and mental well-being.

With long hours in a small, cramped mobile laboratory, the team came together to look after each other and get the work done. 

Results

By the time our materials testing work ended in 2025, Terracon’s professionals performed more than 25,000 tests on more than 12 million cubic yards of material. Once completed and filled, it will provide water to nearly 1 million people throughout Colorado. In addition, the reservoir will host recreational activities for local residents and be an integral project in the region for years to come.