GPRS Helps Discover the Cause of Persistent Pavement Failures at Denver’s Mile High Complex
25 year-old satellite data and Subsurface Investigation Methodology helped Mile High & Empower Field facilities managers to get to the bottom of a persistent and expensive problem.
GPRS Project Manager Matthew Pudimott and Area Manager Ryan Shannon used ground penetrating radar and electromagnetic (EM) locators to map out the “once in a lifetime” level of historical data.
25-Year-Old Satellite Data Meets GPRS Subsurface Investigation Methodology to Determine Why a Parking Lot at Mile High Keeps Breaking
GPRS recently assisted a client in Denver, Colorado in addressing a long-standing subsurface issue affecting the seven-acre parking lot adjacent to Empower Field at Mile High, home of the NFL’s Denver Broncos. Despite repeated surface-level repairs, the pavement continued to crack and deteriorate, prompting a deeper investigation into the underlying cause.
Project Manager Matthew Pudimott and Area Manager Ryan Shannon were assigned to lead the subsurface investigation. The site, formerly occupied by McNichols Sports Arena, presented unique challenges. Constructed in 1975, McNichols hosted numerous concerts and served as the home venue for both the Denver Nuggets and the Colorado Avalanche before its demolition in January 2000 to make way for Empower Field.
The primary objective of the investigation was to determine whether remnants of the demolished arena – such as buried foundations or underground tunnels – were contributing to the structural instability of the parking lot. Initial scans were conducted using ground penetrating radar (GPR), a non-invasive technology that identifies subsurface anomalies by transmitting high-frequency radio waves into the ground and analyzing the reflected signals.
However, the GPR data yielded inconclusive results. In accordance with Subsurface Investigation Methodology (SIM) best practices, the team employed a complementary technology: electromagnetic induction (EM/EMI) locators. This dual-technology approach is a core principle of SIM, which emphasizes the importance of corroborating findings through multiple geophysical methods.
“We initially were searching for voids, so we ran the GPR cart, took a whole day to get all the data together, and there was just no evidence of voids,” Pudimott said. “We started to get worried that we actually weren't going to have meaningful results for the client, but the next day we ran EMI and that was kind of interesting. Same thing, collected the whole result, took a full day, and I was hoping we'd have something for him. And when the post processing data came back, I mean, it blew up.”
Electromagnetic locators function by detecting signals emitted from conductive materials such as metallic pipes and cables. These signals are generated through several mechanisms:
• Direct current applied to a conductive pipe via the EM transmitter
• Active current flow in live electrical cables
• Passive re-radiation of stray electrical fields by conductive materials acting as antennas
Shannon and Pudimott overlaid GPRS’ captured data with Google Earth’s satellite data to demonstrate the alignment of their findings and help the facilities and operations teams to mitigate future parking lot damages.
The EMI scan revealed anomalous conductive reactions across the site. Shannon, recognizing the historical significance of the location, hypothesized that the anomalies might correspond to remnants of McNichols Arena. He consulted archived aerial imagery to validate this theory.
“We definitely found a huge reaction and I knew that [McNichols] stadium was built there and that's probably the reason why we were scanning out there. So, I just figured I would look at the old Google Earth data,” Shannon explained. “Sure enough, that popped up there, and then I thought to overlay that data over the historical data. It was most likely old foundations or possibly different backfill. The red, white, and orange reactions on the EMI typically indicate conductive reactions.”
By overlaying EMI data with satellite imagery from October 1999, Shannon confirmed that the conductive anomalies aligned precisely with the footprint of the former arena. This correlation strongly suggests that residual subsurface structures—such as reinforced concrete foundations or non-native backfill—are contributing to the pavement failures observed at the surface.
Shannon, a veteran of GPRS with over a decade of experience, acknowledged the rarity and significance of the findings.
“This is definitely once-in-a-lifetime data, for sure,” Shannon said. “It’s not a common example, but a great example of what the EMI can do to get this data consistently. To find a building footprint like this? Yeah, I've never heard of this before or seen it before.”
Armed with this data, the client is now positioned to make informed decisions regarding future remediation efforts. Rather than continuing to invest in surface-level repairs that fail to address the root cause, they can develop a targeted strategy that accounts for the subsurface conditions and legacy infrastructure.
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