Feb 11, 2020

Halting Highway Collapse

When a highway started to collapse in Colorado, an erosion control solution was needed

erosion control

Three hundred feet of highway between Denver and Boulder, Colorado, began to collapse during heavy rain and snow. As a solution, a trackout control system was needed to prevent sediment from leaving site and contaminating nearby storm water drainage paths.

The Colorado Department of Transportation (CDOT) tried to stabilize the soil with dirt from the nearby Central 70 project, but the crack soon expanded to more than 300 feet long and 60 feet wide.

Background

On Colorado’s western front range, there are two types of problematic soils: expansive and collapsible soil. A group of soils that rapidly settles or collapses the ground is known as collapsible soil. According to the U.S. Geological Survey website, collapsible soil has been an issue since the 1890s and was first discovered when lands were irrigated by early farmers and ranchers. 

Collapsible soil continues to be a geologic hazard and common cause to structural damage in housing, business and infrastructural developments, including a main section of the US 36 Colorado Highway that links Denver to Boulder. US 36 is a heavily traveled highway by commuters between Denver and Boulder. According to the 2018 Denver Regional Council of Governments, more than 107,000 vehicles travel on US 36 between Denver and Boulder daily.

The Problem

This stretch of US 36 was newly constructed five years ago and was built on top of a drained lake, but soil composition and additional dipping bedrock underneath the highway were not taken into account when the highway was constructed. Furthermore, deep foundation systems had not been installed to prevent collapse of this stretch from shifting and collapsible soils. 

Three hundred feet of the US 36 highway (almost the length of a football field) began to collapse during a series of heavy spring rain and snow. In July of 2019, there were no advanced warnings of the impending collapse except for a few major cracks in the highway pavement surface that only were noticed a week prior. CDOT tried to stabilize the soil with dirt from the nearby Central 70 project but was unsuccessful. The crack soon expanded to more than 300 feet long and 60 feet wide. The soil under the highway continued to settle and shift, causing the highway to buckle. Large chunks of concrete broke away from the concrete retaining wall under the highway, and the highway section collapsed due to collapsible soil under this section of the US 36 Highway containing clay that had become saturated from heavy rains. 

The collapsible soil under US 36 is also known as hydrocompactive soil. As the name hydrocompactive soil implies, the introduction of water into unconsolidated sediments is the driving mechanism behind the resulting compaction of soils. Hydrocompactive soils are found in specific depositional environments with semi-arid to arid climates in the substantial sections of Colorado and western U.S. Hydrocompactive soils have low density and moisture content and are not tightly packed together. Instead, the soil granules are stacked on each other in a loose skeletal array. The loose skeletal array of soil granules is preserved due to clay and silt buttresses, soil suction pressures and other sensitive binding agents but are all erodible by water. 

While these bonds are strong in dry meta-stable conditions, once water is introduced, the array of soil granules quickly break, soften, disperse or dissolve. Larger soil grains shift and shear against each other to reorient into a denser arrangement. This rapid densification of the soil results in a net volume loss of the soil deposit, which in turn manifests as ground surface settlement.

The Project

Kraemer North America was chosen by CDOT to handle the $20.4 million emergency repairs of sinking eastbound US 36 between Wadsworth Boulevard and 104th/Church Ranch Boulevard. Since 1911, Kraemer has been a distinguished full service heavy civil contractor serving three primary markets: transportation, rail and marine. Kraemer North America, along with David Evans and RJ Engineering, redesigned, reconstructed and stabilized the highway using geofoam cement and repaired the retaining wall on the stretch of US 36 that collapsed under an accelerated schedule to get the highway back into operation. The project was completed in October 2019.

sediment control
The stretch of highway encompassing the project was constructed five years ago and built on top of a drained lake. 

The Challenge

Due to the expedited nature of the project, Kraemer North America needed a stabilized construction entrance that was fast, easy to install and would not disturb the ground underneath. Instead of using a traditional aggregate stabilized construction entrance that would take a long time to install and could not be reused on future projects, Kraemer chose FODS Reusable Rockless Construction Entrance for the US 36 Emergency Rebuild Project site entrance. FODS Trackout Control Mats can be placed on top of any substrate and could be installed in about 30 minutes.

The US 36 Emergency Rebuild Project required priority attention. Labor and equipment was reassigned to the project from other job sites. Rebuilding the failed slope involved moving and shaping the dirt and sediment through existing highways and nearby roads, which were still in use.

The Solution

A prompt and effective trackout control system was needed to prevent sediment from leaving the job site and contaminating nearby storm water drainage paths. Having more than a century of experience, Kraemer North America was quick to implement a strategy that would prevent storm water pollution and sediment track out.

Kraemer installed and anchored five FODS Mats directly onto the gravel road entrance to the US 36 Emergency Rebuild Project meeting construction entrance detail plans. Kraemer had been using FODS Reusable Trackout Control Mats to comply with erosion prevention regulations on the I-25 Gap Project in northern Colorado, and five mats were transported and installed at the failed highway construction entrance. 

FODS Reusable Trackout mats provided an immediate erosion control system, which allowed for rapid delivery of aggregate and material to the job site. The quick deployment of these erosion control mats enabled construction to begin in less time and at a lower cost than would be possible using gravel or other traditional erosion control measures. 

Multiple heavy equipment vehicles entered and exited the site during the rebuild projects. FODS mats helped to mitigate dust, erosion and track out to nearby Old Wadsworth Boulevard and prevented sediment and erosion from additional rains from entering storm water runoff during the duration of the project.

erosion control
Five FODS Mats were anchored to gravel road.

Installation Specifications

FODS Trackout Control System is installed using FODS 12-foot-wide by 7-foot-long mats (in the direction of travel), which link together to create a uniform composite track out control system. The Reusable Construction Entrances are interconnected using steel strap hardware. The mats consist of staggered pyramid structures that flex open tire lugs, causing debris to fall out, cleaning the entirety of the tires. Once the debris is removed from the tires, it falls to the base of the mats where it remains undisturbed by subsequent vehicles. These mats prevent track out from leaving a worksite because they effectively trap dirt and prevent it from entering the roadway. A maintenance crew can then periodically clean the mats using a skid-steer broom attachment or a FODS shovel designed specifically to fit between pyramids on the mat.  

About the author

Amy Austin is digital marketing & operations manager for FODS. Austin can be reached at [email protected]

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