Assessing Earth-Covered Magazines in the Indo-Pacific

Ammunition and explosive storage facilities such as above-ground magazines as well as earth-covered magazines (ECMs) have been used by the U.S. military for decades. There are approximately 25,000 ECMs currently in place, with many approaching 70 to 80 years of age. These facilities have started to show signs of aging due to environmental factors, along with large-scale structural vulnerabilities arising from cracks and other forms of concrete structural degradation.

The Department of Defense Explosives Safety Board recently tasked the U.S. Army Corps of Engineers with performing visual inspections of the structural health of ECMs across nine U.S. Navy and U.S. Air Force installations throughout U.S. Indo-Pacific Command. These structures range across a wide variety of types, structural conditions, and dimensions.

Structural health ratings were provided for each inspected facility, along with laboratory testing results that gave a projected remaining service life for the magazines. The information gathered from this effort will aid decision-makers in properly prioritizing and funding maintenance efforts across their portfolios.

CONDUCTING INSPECTIONS

The initial effort of inspections at any installation begins with coordination to obtain data on the types and quantities of ECMs present. This information allows inspection teams to estimate the boots-on-ground time needed for inspections, concrete core extraction, and lab testing. Other desirable characteristics may include years of construction, structural designation, type, as-built drawings, and if any ECMs are empty or less than full for inspection. Once on the ground, personnel conduct a visual walk-through inspection of each magazine, noting any distresses in the structural health condition. Teams typically consist of three persons specialized in explosives safety, structural engineering, and materials science. Following a standardized checklist and procedure, inspections are undertaken for cracks, spalling, delamination, and any other structural deficiencies.

At the same time, visual data, structural health, and physical measurements are recoded using an offline tablet. Significant degradation often correlates to environmental conditions from the surrounding soil—this presents a consistent presence of moisture that can cause efflorescence and corrosion over time.

The locations of degradation relative to the primary blast components are considered in structural health ratings. For example, the wingwalls to the left and right of the front headwall are strictly used to hold the two feet of earth cover that is needed for ECMs to maintain their designation, as compared to above-ground magazines. These components are scrutinized to a slightly lesser degree than other structural components such as flat roofs and arches, which would impact internal munitions if failed.

LEVERAGING FINDINGS

Following completion of an assessment, a structural health rating is assigned based on the noted deficiencies that were observed during the inspection. These structural health ratings range from 0 to 9 and are assigned an Installation Status Rating. After the completion of laboratory testing, the structural health rating is revisited to determine if it should be altered based on data from the lab.

Ratings of 7 through 9 are considered adequate for assigned structural designation. Ratings of 5 and 6 are adequate for assigned structural designation (as long as the recommended repairs are incorporated). Ratings of 2 through 4 are considered not adequate for assigned structural designation and in need of significant repairs. Ratings of 0 to 1 are deemed unrepairable and should not be used. Typical repair recommendations include crack and spall repair, exposed reinforcement repair, overall degradation repair, and floor slab crack repairs.

COSTS TO CONSIDER

For the evaluations across Indo-Pacific Command, after results were captured in the field and laboratory test data, repair costs were estimated for each magazine, to aid in determining the funding needed for rehabilitation and maintaining the current explosives siting. This information allows installations to determine the necessary funds to maintain current ammunition storage as well as project the funds needed in the future for magazine replacement based on remaining service life of the current infrastructure.

With the cost to construct a standard ECM varying from $2 million to over $6 million based on type, the need for a realistic timeline for replacement is clear. Several of the largest Army installations in the United States, for instance, have thousands of ECMs. Total replacement cost would be in the tens of billions of dollars. A timed approach to repair and replacement, based on the data and recommendations provided, will save many installations up to hundreds of millions of dollars over the next 50 years.

EVALUATING RISK

Overall, the majority of the ECMs were found to be in fair to good condition with ratings of 5 to 7, despite their significant age. To date, none of the magazines assessed were deemed unrepairable. In fact, based on the overall ratings at each installation and laboratory testing, it was concluded that many of these structures could perform adequately for up to an additional 100 years as long as proper maintenance and repairs are performed.

However, as weapon systems used by the warfighter become more complex and technology-dependent, many current ECMs will not be suitable to store these munitions due to their structural deficiencies and noticeable areas of environmental factors such as moisture. The results from the structural assessments conducted in the Indo-Pacific can assist in requesting funding to rehabilitate these facilities so they can continue to serve their intended purpose and protect the munitions for the men and women who defend our nation every day.

Josh Umphrey, P.E., is Structural Engineer, Daniel Richey, P.E., is Structural/Blast Engineer, and Michael Pickett, P.E., is Structural/Blast Engineer, U.S. Army Engineering Support Center, Huntsville. They can be reached at joshua.m.umphrey@usace.army.mil; daniel.t.richey@usace.army.mil; and michael.c.pickett@usace.army.mil.

[This article first published in the September-October 2022 issue of The Military Engineer.]