Possible Causes of Surfside Condo Collapse

According to the author's hypothesis and opinion, 1- conditions of the site on which the Condo building located, 2- specific marine waterway form (right-angled form) on the western side of the Condo building and also 3- continuous tidal currents, causing water erosion (scouring) in the corridor where the condo building was located. The zone, between the west and east marine area, on which the Condo building is located, has an area of about ​​7.5 hectares (width, in the north to south direction, 150 meters, and length, east to west, 500 meters).

Due to the soil conditions and location-specific of this zone, the formation of subsurface cavities in this area was potentially expected. Furthermore, there is, also, the possibility of subsurface tunnel erosion, as well as, softening of fine-grained soil beneath the earth's surface, in this zone. Under such circumstances, presumably, there was a contingency of sudden subsidence of the land beneath the building. Sudden subsidence under one or more pillars in the middle part of the building eventually caused the collapse of Building 8777 Collins Street in Surfside, at about 1 a.m. on Thursday, June 24, 2021.

Site condition and Formation of cavities in the building site

According to the author, considering the performed evaluations on the possible causes of the collapse of the Condo building and reviewing of published reports of various news agencies (they listed in the reference part of this article), "the effect of site conditions and the specific landform around the event point in Surfside city are the main hypothetical reasons and causes of the Condo building collapse".

The soil type, on which the Condo building was built, is a "modified wetland", that has specific site qualifications. The landform of the Condo building and its southern neighbor building, surrounding area, include the marine waterways on the western side, is unique and special in Surfside city (right-angled form). 

The form of marine waterway on the west part of the Condo building in Surfside city is shown in fig1 and the location of two buildings, the Condo building, and its southern neighbor building, in the probable hazardous zone, is shown in fig. 2.

The unique and special form of the marine waterway on the western side of the Condo building shows that, during the construction and development of the city, with the human intervention, the marine water flow path has probably been manipulated and changed and has found an abnormal shape like right-angled form (fig. 1).

The ocean water flow tends to current from the west side to the east over time. The author hypothesizes is that such tendency of marine water flow, causes continuous underground water scouring as well as under the foundation of buildings located in the zone of a width of at least 150 meters and length about 500 meters, in the east side of the area where, the seawater path, shows an abnormal right angle sharp direction change. It should be emphasized that the continuous tidal marine current has also been effective as an aggravating factor in the formation of subsurface water flow from west to east and as a result, the intensification of the water scouring phenomenon. It is necessary to mention that, two buildings, Condo and its southern side neighbor building, are located right along this zone.

According to the author, it is probable that the continuous water scouring and water movement, provide a condition of sudden building subsidence and collapse. Subsurface water and water scouring (maybe named tunnel erosion), can perform very soft and saturated soil and provides longitudinal subsurface tunnels or localized cavities in this zone, especially under the "Champlain towers south Condo". Landfall in the subbase of the building, where the probable cavities and tunnels could be formed, at least, led to the sudden subsidence under one or more pillars in the middle part of the building, which eventually caused the collapse of the 8777 building in Collins Avenue in Surfside, at about 1 a.m. on Thursday, June 24, 2021.

It is emphasized that the above-mentioned hypothesis is based on technical report about the Condo building condition and the information obtained from the reports of news agencies and should be considered only as a "hypothesis". Expert field studies absolutely will be more definitive, especially after field measurements.

Suggestions

Considering the importance of the 150*500 meters zone from west to east (Figure 3), in which the Condo building, was located, it is suggested and recommended to do some below-mentioned studies and measurements:

• Geophysical studies, especially measuring the p and s wave velocity (to the understanding of bedrock form, detecting probable underground cavities, and tunnels, and the basement soil condition). 
• Geotechnical investigation includes boreholes drilling and soil parameters investigation. 
• It is strongly recommended that the southern neighbor building of the Condo building, be carefully evaluated and monitored (in the Author's opinion it is located in a hazard zone).