Elevate’s consulting services were requested by the City of Arlington (Client) and Arlington Baptist University (ABU) to assist with a historical preservation and campus renovation project at ABU. The focus of this project was the Top O’ Hill Terrace building, located in the central portion of the campus. This building was the site of a tea garden and social club in the 1920s-1930s that was used as an illicit, subsurface casino and host to other illegal activities at the time. A number of well-known historic figures from the time period were reported to have visited the site. The building was renovated in the 1950s into the ABU administration building and cafeteria, which is its current state. As part of the building’s illicit past, an “escape tunnel” is located in the subsurface on the western side of the building, leading from what was the casino (now the cafeteria kitchen) to a wooded area adjacent to the building. It is speculated that additional, un-documented escape tunnels exist as well. The City of Arlington and ABU have planned to renovate this building as part of a larger campus expansion. The goal is to turn the building into a museum and excavate the casino for preservation. The Client requested that Elevate assist with determining the possible existence and location of additional escape tunnels as well as documenting the conditions of the historic site and known escape tunnel.
Image of the ABC site.
Combined sUAS surface LiDAR and terrestrial subsurface LiDAR showing the underground tunnel and a portion of the casino floor. Note the surface LiDAR has been disseminated to allow the viewer to “see through the surface”.
Elevate used a combination of small unoccupied aerial system (sUAS or “drone”) based LiDAR, ortho-photographic imaging, terrestrial LiDAR, and magnetic field geophysics to accomplish the scope of work. The focus of the sUAS imaging was to serve as a record of current site conditions, provide spatial modeling of the site and analysis of surface variations. Spatial data collected from the terrestrial LiDAR system was incorporated into the overall point cloud of the site. This was used to correlate site variations to the exact position of the escape tunnel and serve as a historical record of the tunnel, the lower building interior that housed the casino and the portion of the excavated casino in the building. Geophysical imaging using magnetic field measurements was used to detect variations that could indicate the presence of potential subsurface historical structures. This imaging included the existing escape tunnel to provide a baseline of magnetic variation characteristics that could be used for analysis of the remaining site.
The sUAS orthophotography and LiDAR provided a complete model of the area of interest. Control points allowed for the terrestrial LiDAR data of the escape tunnel and lower portion of the building to be incorporated to accurately reflect real conditions on site. No surface variations were noted over the existing tunnel and this data will serve as a baseline for future investigations. Results of the geophysical imaging shows a variation in the total local magnetic field that correlates to the position of the known escape tunnel. A total local magnetic field variation with characteristics similar to those associated with the known tunnel was measured to the north of the existing tunnel. This variation is adjacent to the known tunnel and follows the same trend to the northwest. The variation originates on the northern side of the building (near the exposed portion of the casino floor) and is not as linearly continuous as the known tunnel signal, suggesting that this variation is not as consistent.
The use of multiple method of investigation allowed for more complete insight into the site conditions by correlation of variations seen in the data. It allows for physical objects to be related to geophysical or subsurface objects and provide better spatial context for the sites users.
sUAS magnetometer data combined with the spatial model. This allows for spatial correlation of magnetic field variations to known surface and sub-surface objects. Variations not correlated to know objects could be targeted for further investigation.