Minard+Hall+Facade+Collapse

= Minard Hall Facade Collapse (2009) =

// Jennifer Thiede, M.S. Architectural Engineering, Penn Statetoc //

Keywords
Minard Hall, NDSU, Facade Collapse, Foundation Failure, Adjacent Excavation, Geotechnical Investigation

Introduction
Minard Hall, originally named Science Hall, is located on the campus of North Dakota State University (NDSU). Minard Hall was constructed in three stages as the funds became available. The first stage, built in 1902, was 68x80 feet of ground plan and consisted of three stories (NDSU University Archives, 1930 p1). The building was designed to accommodate the departments of biology, geology, horticulture, and mathematics. The second stage of the construction project, built in 1918, was a four story structure, which became the central portion of the hall. This portion encompassed 92x66 feet of ground space, and was designed to include class room facilities and a museum on the fourth floor (NDSU University Archives, 1930 p1). The third stage was built in 1929 and was meant to mirror the construction of the first building. When the three stages were completed (see Figure 1), the building was 80 feet deep and 224 feet long, making it one of the most artistic buildings on campus (NDSU University Archives, 1930 p1). Subsequent additions have been added to Minard Hall. In 2003, a wing connecting the now historic Minard Hall and Music Education building was completed. In 2009, another renovation to Minard Hall was started. The project included building additions to the north and west side of the 1918 and 1929 sections, as well as, rebuilding the roof of the 1918 facility, a new main building entrance, and site improvements (NDSU Facilities Management, September 1, 2011 p1).

In the early morning hours of December 27, 2009 the northwest wall of Minard Hall, the largest building on NDSU's campus, collapsed (see Figure 2). Rescue crews reported to the scene at 3:17 am. After searching the premises, rescuers determined that no one had been injured in the collapse. The failure occurred in the portion of the building where the renovation was taking place. Crews from Meinecke-Johnson, the general construction company for the project, had been excavating the site adjacent to Minard Hall (see Figure 1). The excavation extended 25 feet into the ground along the northwest corner of the building, leaving the foundation exposed (Nowatzki, 2009 p1). Near the excavation site, piles were being driven into the ground to protect a steam tunnel and stair tower at the building's north entrance (Nowatzki, 2009 p1). The collapse resulted in a gaping hole in the building and cracks in the concrete foundation walls and brick facade. After the collapse, steps were taken to shore up the floors and roof to prevent any further collapse. The shoring system also allowed for safe demolition of the failed section of the building. To cover building damages associated with the collapse, NDSU filed a $500,000 insurance claim, even though the damage event has accrued additional costs into the millions of dollars. North Dakota State University was denied the insurance claim, and in response NDSU sued the State Fire and Tornado Fund.

Cause of Failure
The most recent phase of renovation on Minard Hall required excavating along the north wall and northwest corner of the building. Meinicke-Johnson Construction was performing the excavation work. The excavation went down about 25 feet into the ground, and remained open for several weeks before the collapse occurred. Even though the buildings foundation was exposed, a number of sources, including Heyer Engineering, the structural engineering firm on the project, concluded that the building was stable (Nowatzki, 2009 p1). In addition to the adjacent excavation, pilings were being driven into the ground nearby to protect a steam tunnel and the stair tower at the buildings north entrance (Nowatzki, 2009 p1). As a result of the piling driving, Minard Hall was subjected to vibrations in the ground. The combination of the adjacent deep excavation and the soil vibrations caused one of the exposed structural pillars to fail, thus leading to the facade collapse along the northwest wall of Minard Hall.

Explanation of the Failure
The foundation is the structural element of the building that supports the vertical loads (dead and live loads) and horizontal loads (wind and earthquake loads) acting on the structure. The foundation provides a means for the structural loads to be transferred to soil. The soil supports the building, and prevents it from settling and overturning. Minard Hall was constructed using a spread footing; a foundation type that transfers loads to the soil through bearing. Minard Hall was built on soil called Fargo Silty Clay (Web Soil Survey). Fargo Silty Clay is comprised of 50% clay, 44.7% silt, and 5.3% sand (Web Soil Survey). Based on the soil composition (falling into the poorly drained soil class and soil group D), the soil would conservatively have a bearing capacity of 1500 psf. The two primary types of foundation failures that can occur are a failure of the foundation element (footing or pilings), or a failure of the soil (Kaminetzky, 2001 p8.4). A soil failure can result from a loss of bearing or a disturbance from adjacent work, as was the case in the Minard Hall collapse.

Failure occurred near the center of the wall where one of the pillars was located. Based on photographs of the collapse, the building had a wood floor system, and interior and exterior wood stud bearing walls with a brick masonry facade. Dead and live loads from the building were being transferred to the pillar, which were then transferred to the foundation (see Figure 3). In the location of the excavation along the wall, the central pillar was the source of greatest load on the foundation, hence being the point of failure. The foundation transfers the loads radially away from the foundation and into the soil. The shape of the load distribution is referred to as a pressure bulb (see Figure 4). The excavation occurring adjacent to the building removed some of the soil that was distributing load from the structure. As a result, there was a loss of lateral restraint which decreased the amount of vertical support from the soil acting on the foundation. Small vertical settlements could have resulted from the excavation leading to some of the cracking that was observed in the concrete foundation walls. However, since no visible signs of damage were reported that would have indicated a collapse was imminent, the facade collapse could not solely be attributed to the excavation that took place.

Vibrations in the soil from the pile driving on the site was the second factor that contributed to the collapse. As stated earlier, Minard Hall was built on a silty clay soil. Liquefaction is a phenomena that can occur when certain soil types are subjected to vibrations. In liquefaction, the soil behaves like a liquid and any bearing support being provided to the structure is lost. While liquefaction did not occur at the site, because an immediate failure would have occurred during pile driving, it does elude to the ease at which soft soils, like silts and clays, can move in the ground. The piling driving would have caused some horizontal movements in the soil below the foundation, since the lateral restraint was removed. Lateral movement of a foundation will cause more damage than an equivalent amount of vertical movement (Kaminetzky, 2001 p8.23). Thus, in the opinion of the author, the combination of the potential for vertical settlement from the excavation and horizontal settlement from the pile driving vibrations resulted in the soil failure that caused the facade collapse along the northwest wall of Minard Hall.

Similar Failures
A case study was performed on a three story school in Chicago, Illinois that was located adjacent to a 12.2 meter excavation in soft clay. The school was built in the early 1960s and consisted of a reinforced concrete frame structure with a basement. The reinforced concrete foundation was supported by a 1.2 meter wide strip footing at a depth of 4 meters below the ground surface. The adjacent excavation was being performed as part of a subway renovation project, and took place as close as 1.2 meters to the strip footing of the school. An excavation support system consisting of a secant pile wall with three levels of support was used on the project. Ground movements were observed (before any excavation took place) during the installation of the secant wall due to the nature of the soft clay. Sensors were placed along the side of the school facing the excavation site to record any movements in the structure. The results show that the building did settle as a result of the excavation, however, no lateral movement (rotation of the building) was observed. Additionally, the settlement was greater toward the center of the building wall than at the building corners. Damage to the building included interior cracks to the infill walls concentrated in the second and third floors, cracks in the mortar and limestone facade, cracks in the first floor wall panels, hairline cracks in the foundation wall, cracks in the marble facade on the entryway floor, and interior cracks in floor tiles. While the level of damage observed in the school was within expected levels, the case study shows the potential for extensive damage when all proper precautions are not taken. (For more information pertaining to this study see Finno 2001)

Other failures have also been reported as a result of excavation work near existing structures. In New York City, excavation work was being done for a new high rise building near the foundation of an old existing five story building on 34th Street. The existing five story building completely collapsed when the vertical support was lost as a result of loss of lateral restraint during the excavation process (Kaminetzky, 2001 p8.8). Construction for a new sewer main project in Brooklyn required deep excavation adjacent to old residential buildings. The sewer lines were designed to run too close to the existing buildings. The excavation not only cut into the influence lines of the existing footings, but the contractor used vibratory pile drivers to install the piles, which caused the nearby buildings to settle, crack, tilt, and shift laterally (Kaminetzky, 2001 p8.10). Many of the buildings were saved with additional lateral bracing, but one collapsed due to soil support being lost below the footing level.

Prevention
The collapse of Minard Hall could have been prevented if the proper precautions had been taken. When an excavation is being done adjacent to an existing structure, especially in this case where the excavation was directly exposing the building foundation, proper shoring measures need to be taken. The most common reason foundation failures occur is from undermining of safe support (Kaminetzky, 2001 p8.7). A well designed bracing and shoring system is often needed to prevent a lateral shift, and a permanent support structure should be installed in places where new construction will undermine an existing support system (Kaminetzky, 2001 p8.8). Therefore, the foundation of Minard Hall should have been underpinned. The foundation should have been supported and permanent underpinning supports should have been installed. This is important because the foundation was originally constructed on undisturbed soil, meaning the soil retains full bearing capacity. Now that the excavation has taken place, the soil no longer qualifies as undisturbed, and in order to maintain the original bearing conditions extra support needs to be added. Additionally, the excavation cut off the pressure distribution path through the soil, which removed the lateral restraint. The presence of a bracing system would have provided the lateral support needed to prevent movement of the foundation.

The collapse could also have been prevented if a more thorough geotechnical investigation had been conducted prior to construction. Soil conditions had been looked at prior to the start of construction on Minard Hall. However, as soil data from the forensic study of the failed area became available, concerns arose about the soil conditions surrounding the north addition (North Dakota State University, 2011 p3). Therefore, the redesign of the collapsed portion and addition of Minard Hall no longer included a basement mechanical room, but rather a crawl space (North Dakota State University, 2011 p3). A more in depth study would have highlighted the concerns, and could have prevented the collapse.

Reconstruction
After the collapse of the northwest wall of Minard Hall, a shoring system was designed and installed to prevent any further collapse of the building. Once the building was stabilized, the collapsed portion could be demolished, and testing and evaluations took place. While removing the collapsed section, asbestos contaminated soils were discovered in the area, which needed to be contained and removed (North Dakota State University, 2011 p2). During the redesign of the collapsed section, concerns arose about continuing with the basement plan for the addition. Based on soil conditions, the basement mechanical space would be moved to a fifth floor or penthouse area, and a crawl space would be used instead (North Dakota State University, 2011 p3). While the new plans were being approved, the priority was to remove the loose sandy fill from the area and replace it with compacted engineered fill (North Dakota State University, 2011 p3). After this was completed, work could begin on the collapsed area and footings for the north addition. The north addition footings and foundation wall were completed in October 2011 and the steel frame installations for the collapsed portions and addition are currently underway (North Dakota State University, 2011 p4). It is estimated the project will be completed late 2012.

Insurance Claim
The damage associated with the façade collapse along the northwest wall was initially being assessed at over $1.3 million. The University filed a $500,000 notice with the State Fire and Tornado Fund to cover costs primarily related to the building failure. However, now the University estimates that collapse of Minard Hall will cost nearly $4.5 million (North Dakota State University, 2011 p5). The State Fire and Tornado Fund denied the claim submitted by NDSU stating that “the fundamental cause of [the] building failure was a deep and unsupported excavation with a steep slope next to the foundation of existing Minard Hall. This resulted in loss of adequate soil support that caused the foundation to fail.” (Roepke, 2011 p1). The insurance fund also contended that coverage was precluded because the building did not completely collapse and no “defective materials or methods” were used during construction (Roepke, 2011 p2). As a result, NDSU decided to sue the State Fire and Tornado Fund for coverage. Information has not been released pertaining to NDSU's decision to pursue litigation against other involved parties, including, general contractor Meinecke-Johnson, JLG Architect, and geotechnical firm Northern Technologies.

Conclusion
The Minard Hall facade collapse that occurred in 2009, is another example highlighting the potentially disastrous effects adjacent excavations can have on existing structures. The soil strength that near by foundations rely on becomes compromised, so vertical and lateral movement of the of soil and footings can occur. In this case, the disturbed soil was clayey, which is highly susceptible to in ground movement, especially from the vibrations that resulted from the pile driving activity on site. The collapse prompted an in depth forensic investigation by all parties involved. Reports led to concern with the north area of the building, which should have been identified before construction began.

Lessons can be learned from the partial collapse of Minard Hall and the similar failures that have occurred as a result of excavating adjacent to an existing foundation. First, a thorough geotechnical study of the excavation area should be conducted, so that the soil conditions at the site are known. Using this information, a shoring and underpinning system should be designed to account for the loss of soil strength surrounding the foundation. Finally, the method of retaining soil around the excavation needs to be addressed. If, piles are being used, precaution should be taken to prevent excessive vibration of the soil, or a different means of installing the piles should be implemented. Taking the time and money to insure proper investigation, design, and construction methods, is essential for preventing excessive damage and potential failure of structures located next to an excavation project.

Additional Resources
Becker, Troy. "Theories of the Minard Hall collapse." The Forum. <[]> (September 30, 2011.) Allan Ashworth, a professor at NDSU, provides a schematic detailing the theory behind the collapse of Minard Hall.

Dalrymple, Amy (January 22, 2010). "Minard Hall costs estimated at $1M." Sun Tribune. <[]> (October 3, 2011.)

Dalrymple, Amy (December 31, 2009). "Meinecke-Johnson's bid for NDSU's Minard Hall project was $1 million lower - Northwest wall of classroom building collapsed Sunday." Grand Forks Herald (ND). <[]> (October 14, 2011.)

Dalrymple, Amy (November 8, 2011). "Minard Hall collapse estimated at $4.5 million." INFORUM. <[]> (November 10, 2011.)

Kiyosumi, Makoto. et. al. (2007). "Yielding Pressure of Spread Footing about Multiple Voids." J. Geotech. Geoenviron. Eng., ASCE, 133(12), 1522-1531.

Roepke, Dave (August 16, 2011). "NDSU suing insurance provider after denying Minard Hall claim." INFORUM. <[]> (October 12, 2011.)

Tran, Tu-Uyen (January 22, 2010). "Portion of NDSU's Minard Hall will have to be demolished after collapse." Grand Forks Herald (ND). <[]> (October 13, 2011.)