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What could have been the cause of this collapse?. Suggestions please.
Regards
Teddy

It is seen that the building into which the collapsed one fell into was able to withstand the impact (despite the dynamic loading). What a great difference between a good engineering and a bad one.
Regards
Teddy

Hi,

I guess, since the over ground structure itself is ok; the problem would be at its foundation. Forces have been transferred among beam and columns but the problem comes after that.

The other reason could be some uncalculated excavation at neighbor building without proper soil protection.

Whatever it is, it is relevant to sub-ground part of structure.

foundation soil

The collapsed building depicts what we should expect when we did not do our jobs well or when events outside our control come into play. Sincerely speaking, some of the problems encountered are as direct result of poor design—either simple carelessness or lack of engineering ability (incompetency); in other cases, the problems could be attributed to what I would like to describe as “the hands of the gods”
It would be observed that the superstructure failed as complete unit, without any of the parts destalking until the structure made impact with obstacles (the adjacent building and the ground). The observation of the mode of failure indicates that the problem was that of foundation. Foundation problem is one of the engineers’ most dreaded nightmares.
Due to the unpredictability/variability of soil coupled with several variables such as the unanticipated loads and/or soil movements, a situation could develop that could wreck lots of havoc. Such movement could be as result of e.g., earthquakes, soil subsidence, movement in the fault lines etc. These could result in settlement problems over which the designer may have none or little control over. Though engineering has made several grounds in understanding the materials that we use and or encounter in construction, yet we still have a lot of way to go. Engineering at its present stage or current state-of-the-art design methods may greatly reduce the likelihood (risk factor) of structural failure (including settlement and general foundation problems) but cannot provide a risk-free project.
One of the major factors that militates and complicates foundation design is that the soil parameters used
for the design are usually sourced/obtained before or at the design stage of the project. This may be a long time before the construction aspect of the project is started. On the completion of the project, the engineer may find himself face to face with a different soil from that on which he started. At that stage, the soil’s properties may nave been considerably modified as such greatly deviates from the original. The modification of the soil could have been as a result of either
the construction process or could have resulted from the installation of the foundation. In the construction process, the soil may be excavated, remixed, backfilled and/or replaced and compacted. In the interval between the excavations and the conclusion of the project, the supporting soil must have gone through lots of transformations e.g. the removal of soil-thus load tends to allow the underlying soil to expand. In pile foundation construction, the driving of piles usually makes some types of soil denser. On the other hand, some soil may lose part of their strength in the process. These events either directly alters the soil (replacement) or modifies the initially estimated soil strength
Parameters.
Another factor to keep not only an eye but three eyes on is the changes in the groundwater level. This could produce a much an unexpected and undesirable effects on any construction — be it an up-rise or lowering of the water level. Water has a buoyant effect on soil. So the change in its content, like any other materials, changes the soil matrix configuration. Lowering the ground water level reduces buoyancy effect and effectively increases the superimposed load on the supporting soil matrix by same amount. This could overstress the soil as such result in its settlement which if excessive could lead to failure. If the soil receives an inflow, it could become so wet that the natural attraction between the matrices becomes diluted. The soil may at a point, no longer be able to sustain the weight of the structure particularly if the strength lost is greater than the buoyancy weight gained. Seepage could also set in and erode the foundation thus resulting in settlements, for all the underlying soil as such on the structure. As a result of these weight movements, a phenomenon known as "sees" could develop (i.e. a stress increase from this weight
increase). The resultant settlements could be very large if the underlying soil has a large void ratio as such could lead to a catastrophe as witnessed. Example of these included: -
· The pumping of water from wells in Mexico City that produced aerial settlements of several meters.
· The pumping of water (and oil) in the vicinity of Houston, Texas, that also lead to aerial settlements
of more than 2 meters in places. Pumping to dewater a construction site can produce settlements
of 30 to 50 mm within short periods of time. In line with this, think of an adjacent buildings that cannot tolerate this
additional settlement. What will happen is a collapse. The aftermath will be a legal litigation that will certain to follow.
Regards
Teddy