Cologne+City+Archives+Collapse

Cologne City Archives Collapse //Hannah Valentine, BAE/MAE Penn State, Fall 2015 // toc
 * Cologne, Germany - March 3, 2009 **

Introduction
When Cologne City Archives employees returned early from their lunch break on March 3, 2009, they were surprised by an alarm alerting them to evacuate the building. Within minutes, the six-story office building and archival documents dating back as early as 922 AD had collapsed into a pile of rubble. Two nearby buildings were also destroyed in the collapse, ultimately killing two people and injuring several. Recovery of salvageable documents and rescue efforts took several days and utilized everything from search dogs to robotics. The process for restoring damaged archival documents is still ongoing. Ultimately, the document restoration process following the collapse is expected to last 30 years and will not be able to recover all of the historical documents that were lost ( Stiftung Stadtgedächtnis).

Investigation into the Cologne City Archives collapse has taken several years and is surrounded by controversy and corruption. Foundation problems caused by the construction of a new underground public transportation along the same street as the City Archives was the suspected cause of the collapse. Speculation regarding how the construction caused the collapse uncovered a range of problems from theft during construction to improper engineering practices.


 * Keywords: Foundations, Geotechnical, Germany, Cologne, Ground Anchor, Diaphragm Wall **

Events Leading to Collapse
Constructed in the 1970s, signs of possible structural problems began to show in the 1970s Cologne City Archives building prior to its collapse. An investigation of the Cologne Archives before the collapse found cracks in basement flooring and a crack the size of a hand in a basement ceiling expansion joint. These cracks were deemed "harmless" but further expert investigation was advised to prevent further structural damage (Staff, 2009). The lead structural engineer on the project claims they were not notified of these construction issues, and nothing was investigated further before the collapse of the Archives (Goebel, 2010). Additionally, excessive water was beginning to accumulate in the construction pit underneath the archive’s basement floor (Goebel, 2010). Signs of structural issues caused by the underground rail go back to fall 2004, when the church steeple of the tower of the nearby St. Johann Baptist Church began to tilt. The report found that church structural problems were due to "loosening of the ground and cavity formations," although it was determined that the church was not in danger of collapse. The excessive tilting of the church steeple was attributed both to the soil in Cologne and a lack of sufficient reinforcement of the church with bentonite rings during construction (Staff, 2009).

Near the time of the Cologne Archives collapse, deep excavation of the nearby light rail on the Nord-Sud Stadtbahn Koln was near its full depth of 28m. Recent snow melts had raised the groundwater level to 12m below the surface at a location that is already only 300m from the Rhine river. As groundwater removal activities began for the light rail, measuring devices on-site did not indicate any unusual movement of the rail’s diaphragm wall (Rowson, Mar 19, 2009).

The collapse of the Cologne Archives occurred on March 3rd, 2009 and lasted only a couple of seconds (Goebel, 2010). The Archives and two adjacent buildings fell into the 25m deep pit currently being used for the construction of a new switch facility for the underground light rail (Stiftung Stadtgedächtnis). Witness reports describe the collapse as "bursting into a big, brown cloud." 20 people were in the Archives building at the time, and all of them made it outside before the collapse. The two fatalities were living in the adjacent housing that collapsed with the Archives building (Schmidt-Czaia, 2009). Rubble from the collapse was dense due to the amount of documents stored in the building.
 * Collapse **

Investigation & Cause of Failure
Document recovery efforts took priority over investigation into the cause of collapse in the years following the incident. In February 2015, six years after the collapse, the Cologne's Public Transit Authority (KVB) reported to City Council members that the assumed cause of collapse is “a construction defect” in the underground diaphragm walls (Damm, 2015). The evidence of this construction defect creation of a sinkhole behind the Cologne City Archives, which the building fell into during the events of the collapse. Legal proceedings for the investigation are reported to begin as late as summer 2017 (Damm, 2015). Until this time, some details regarding the collapse are obscured by the legal system. Overall, the cause of the collapse may be traced to missing diaphragm wall reinforcement and groundwater over-pumping during excavation, leading to an eventual ground anchor failure. Alternatively, it is proposed by project contractors that sudden, explosive flooding at the base of excavation caused the collapse of the City Archives (Damm, 2015). Details supporting this second theory are not readily available to the public .

Diaphragm Wall Reinforcement
At the time of the City Archives collapse, the construction of the 1-meter thick and 37-meter deep reinforced concrete diaphragm walls had been completed for the nearby railway (Rowson, Mar 19, 2009). During investigation of the collapse, it came to light that some workers on the nearby railway had sold some of the rebar intended for these diaphragm walls as scrap metal (Goebel, 2010). Reports state that up to one-third of the steel ties and rods on the railway project were sold to scrap metal dealers (Turner, 2010) and diaphragm walls on a nearby site in Cologne had only 17% of its required reinforcing (Staff, 2010). Lack of proper reinforcement would impact the capacity of the diaphragm walls to withstand soil pressures and forces due to construction activities such as groundwater removal. Disagreement on the (Rosie, 2010). An overall lack of supervision on the project was also evident when it was also revealed that site inspections were documented that had not occurred (Rosie, 2010).

Groundwater Over-Pumping[[image:8-Cologne-collapse.jpg width="363" height="363" align="right" caption="Broken Dewatering Pipes at Construction Site (Courtesy of Tunnel Talk)"]]
The volume of groundwater removed for deep excavation construction activities for the railway exceeded limits set by city officials. Nine extra extraction wells were built than allowed, which resulting in doubling the rate at which water was pumped (Rowson, Mar 19, 2009). Over-pumping at a rate faster than the maximum rate can remove fine silt and sand in addition to water and cause internal erosion. This internal erosion likely created a sinkhole behind the railway diaphragm walls and the Cologne City Archives. Another possible result of groundwater over-pumping is the liquification of soil due to an increased hydraulic gradient under excavation activities, creating an underground landslide (Rowson, Mar 19, 2009). Internal erosion would decrease the strength of the soil and weaken the anchor connection to the wall. Assessing soil strength in Cologne is difficult due to the high water table and variable soil conditions (Rowson, Mar 12, 2009). Depending on the location of anchors and dewatering points, weaker soil would reduce the strength capacity of the diaphragm wall anchors (Rowson, Mar 19, 2009). This possibility will be explored further in the following section.

**Wall Anchorage Failure**
Diaphragm walls were connected to the surrounding soil with ground anchors. Geotechnical engineers state that diaphragm wall failure could occur if the anchors hit gravel or soil that was weaker than expected. If one ground anchor hit weaker soil, the other ground anchors along the wall would take on greater load to compensate. If this load is too high, ground anchors will begin to fail (Rowson, March 12, 2009). Soil strength in Cologne is already considered weaker due to the presence of river gravel from the Rhine, which contains river sediment and groundwater. Failure of anchor bolts is indicated by the formation of a hole, such as the one behind the diaphragm walls. It is unknown from current information if the failure of ground anchors was progressive due to failure at the toe of the wall, or if the anchors were the first to fail (Rowson, March 12, 2009).

Prevention
Some activities discussed as potential causes for collapse were preventable. Standard procedure was followed for soil testing of the rail construction site, which does not require testing of spot tests of soil once construction begins (Staff, 2009). Senior research investigator John Burland indicated that the type of variable soil conditions in Cologne are difficult to excavate and therefore have no standard method. In such instances, Burland states that careful oversight is required in case a pocket of poor soil is discovered during construction (Rowson, Mar 12, 2009). Cologne legislators are pushing for laws that would require commissioning on major transportation projects to be performed by third-party inspectors (Goebel, 2010).

Foundations for the buildings adjacent to the excavation site could also have been better protected. No compensation grouting was applied to the foundations of the Cologne Archives or surrounding buildings (WIllis, 2009). Compensation grouting helps prevent building settlement due to soil loss during excavation Additionally, bored piles and ground freezing have successfully been used in the past to stabilize the water table along the Rhine river in Cologne (Willis, 2009). If such measures were implemented during the excavation of the underground rail, the water table might have risen as high or as quickly.

Further Investigations
The collapse of the Cologne City Archives prompted further investigation into the diaphragm walls of other Bilfinger Berger projects by the company itself. Its scope of investigation included all projects with permanent diaphragm walls of structural significance where the company was a contractor or subcontractor. The Nuremberg-Ingolstadt railway was one project in which issues with the anchoring of diaphragm walls were investigated. There was suspicion that documentation for this project’s ground anchors were manipulated in 2005, similar to the railway in Cologne. However, no conclusions from this investigation were provided by Bilfinger Berger (Bilfinger Berger, 2010). Cities such as Amsterdam and Copenhagen with similar soil conditions have begun to look into vulnerability to construction activities for historic buildings as a result of the collapse in Cologne ( Staff, 2010).

=== Document Recovery === Document recovery efforts began as soon as human rescue and recovery efforts had concluded. Due to the monolithic concrete structure, creative document recovery methods were required by firemen and others. Robotics were considered for document recovery methods, but never implemented. The formation of Stiftung Stadtgedächtnis or "Foundation of Memory" began to fund document recovery and document restoration efforts. 95% of the documents lost in the collapse have been salvaged since September 2010, including the manuscripts of 800 prominent German authors, 65,000 public records, 500,000 photos, videos, and maps, and 100,000 architectural drawings and artifacts ( Stiftung Stadtgedächtnis). Over $400 million euros will go into the restoration of the Cologne City Archives building and its historically significant contents (Goebel 2010).

Conclusion
The Cologne City Archives collapsed when the building fell into a construction pit for the nearby rail switch station. Investigation of the collapse by the Cologne Public Transit Authority (KVB) has identified several sources of concern at the construction site, and litigation is expected to begin as late as summer 2017. Improper ground anchorage for the underground diaphragm walls of the light rail, as well as higher levels of the water than expected, both contributed to the Archives collapse. Illegal selling of the rebar intended for the diaphragm walls of the light rail was discovered during the investigation process, and prompted review of related underground rail projects. Thousands of documents of historic significance were lost in the collapse, and restoration of damaged and lost documents continues to this day.

Additional References

 * Linder, T.; Tretyakov, V.; Blumenthal, S.; Molitor, P.; Holz, D.; Murphy, R.; Tadokoro, S.; Surmann, H. (July 2010). "Rescue robots at the Collapse of the municipal archive of Cologne City: A field report." Safety Security and Rescue Robotics (SSRR), 2010 IEEE International Workshop, 1-6, 26-30. <**[]**> (September 29, 2015)**
 * The recovery attempts for documents and human life after the collapse of the municipal archives in Cologne are detailed in this report released by the Institute of Electrical and Electronics Engineers. Reasons for the methods of recovery chosen and the effectiveness of these methods are explained, and a brief summary of the causes of the collapse is given.