Flooding to trigger building collapse in major cities

Except there is a reorientation on locations, design and foundation methodology in flood prone areas, many buildings still risk collapse in view of the incessant rainfall across the country, professionals have warned.

There have been weeks of pounding rains, which swamped major cities, leaving homes and facilities isolated by flood water. As the floods stay weeks even months to recede, some buildings become weakened and exposed to the weather. Most of the buildings that had collapsed recently in some locations in states are multi-storey, which could suggest problems of soil structure and weak foundations.

For instance, a two-storey building recently caved in and collapsed at number 22, Nkisi Aroli street, Onitsha, Anambra state amidst the heavy rainfall, while four persons were confirmed dead after a house built on a hill and collapsed on another in the Otun Araromi area of Isheri-Magodo, Lagos State.

Similar circumstances were recorded in Abuja, when one storey building under construction behind the Apo mechanic village reportedly collapsed with about four people trapped, Also, there were reports of such instances in Ondo, Kogi and others that were not reported across the country.

The Guardian investigations revealed that most of the existing building structures and those under construction are hardly designed to withstand flooding conditions such as scour and erosion due to floods, quick rise and drawdown of floodwater and prolonged inundation.

Insufficient anchorages for storage tanks, sealed conduits and pipes, and other structures that may suffer from lateral movement and floatation during flood condition are also some of the current realities. Essentially anchorages and connections in the structures need to be designed and executed to withstand the influence of vertical loads, uplift forces, and lateral loads.

Building beams needs to be well connected to piles, columns, piers and foundation walls using suitable means such as bolts and welds. While moisture-resistant building products are also the first line of defense against rotting and mold, especially in tackling problems that could devalue homes and cause serious health issues and even death of occupiers.

The immediate past president of the Nigerian Institution of Structural Engineers (NIStructE), Mr. Oreoluwa Fadayomi told The Guardian that many Nigerians are building on flood prone locations, thus, making them more susceptible to flood effects and building collapse aside other factors that could trigger building collapse. He said government shouldn’t grant license to residents to embark on construction projects in flood prone areas.

“When you have a flood prone location, the number one thing is never to allow people to illegally build there because it’s supposed to be under government acquisition and a place that should be within the setback. The moment you allow them to build, they would continue to multiply and it would become a community and when government wants to enforce the law, an entire community would be displaced and it becomes a social problem.”

On the type of foundation required, should people build in such locations, he explained, “It is not a matter of what type of foundation, but the size of the building in terms of whether it’s a Bungalow, High-rise building and others and knowing the volume of load that would be transmitted to the foundation? If you want to do your foundation, it has to be based on scientific test.

“If you have bad soil area, you should do soil investigation to know the type of material that is in the ground and that would determine what type of foundation to use. For example, Lagos has different varieties of materials in the ground, Victoria Island is sandy, Maroko is muddy, there are Islands that are hard. So soil test is number one thing.”

Fadayomi regretted that buildings are collapsing at alarming rate and more would still give way if slums and flood prone areas were not transformed into estates for the people by government.

“You don’t need a soothsayer to say that. More buildings would still collapse because the existing buildings are not strong enough, water percolate into them. More collapse would still happen for as long as we didn’t do anything about it. What to do about it is to disallow this kind of development . We have being telling government that all the places that looks like slums. They should get the people together, talk to them and make them know that the whole –place could be demolished and be re-built into a community where law and order would reign.”

The President, Nigerian Institute of Building (NIOB), Mr. Kunle Awobodu explained that buildings collapse, because, “you have the contractor that is not thorough, artisans that are not properly trained and on this we should ask why do people yearn for artisans from Benin Republic, Ghana, it is because of the pattern of training”.

Other factors, he said include, the use of substandard building materials, uncertified building managers/poor workmanship, faulty building architectural designs and lack of comprehensive soil investigation, among others.

According to him, before any construction project takes place the importance of comprehensive soil investigation in the area can’t be over-emphasized before determining the type of foundation desirable.

While foundations provide support for structures, transferring their load to layers of soil or rock that have sufficient bearing capacity and suitable settlement characteristics to support them, he said there are ranges of foundation types suitable for different applications, depending on considerations such as, the nature of the load requiring support, ground conditions, the presence of water, space availability, accessibility and sensitivity to noise and vibration in buildings.

Awobodu said many buildings are collapsing and many more would still fall due to faulty foundation and incursion of quacks into piling profession in Nigeria. He said: “Government doesn’t have control on the piling works in Nigeria and drillers don’t have any training institution and so they embark on ‘trier and error’. So many landlords are falling victim of poor building foundation in locations such as, Arowojobe, Maryland, Medinah estate, Oke-Alo, Lekki and Ilubirin and others. Government should register capable companies that could handle comprehensive sub-soil investigation and piling projects because most of the building foundation in Nigeria are being handled by incompetent people.”

On the role of town planning, a past president of the Nigerian Institute of Town Planners, Bunmi Ajayi said some areas are classified as undevelopable for reasons which include, the presence of dam streams and the different degrees of slopes.

“When the slope in an area is beyond certain degrees or gradients, it shouldn’t be developed at all because what is involved is complicated and residents might not be able to handle it given the under developed nature of our technology. That is the case you find in the Magodo building collapse.

“With the slope, government opts not to have allowed development there because the slope was too sharp and so the building collapsed on another. It is part of the town planners’ business to determine at what point, development should stop based on the gradient of the land, make provision/advise on other uses that won’t cause damage and to demarcate areas that shouldn’t be developed and enforced it.

“If you look at the expired Lagos master plan, there are large areas of land that were not to be developed. For instance, the Iju road because of the Iju water works that was situated there at that time. Also, you have the water works at Iba road but some of these places are already been developed.”

He said the issue of flooding is a governance issue because “there was a drainage master plan that was commissioned for Lagos since the regime of Mobolaji Johnson but the issues remained that the primary, secondary and tertiary drains in the master plan are no where to be found today to take water out of the premises.”

“When you refused to implement the drainage master plan of Lagos, we would continue to face a flooding situation because at the end of the day, water will finds its level. The ideal thing is to provide a root for water. As far as there is an increase in rainfall, a lot of houses will still come down, especially in sloppy areas.

“Living in floodable areas portends that once there is flood for too long a time, because of the level of our technology and the fact that a lot of people use substandard products as well as because of the age of some of the buildings too, there’s going to be very high risk that some of the buildings might still collapse”, he said.

Source: Kunle Awodbodu

https://guardian.ng/property/flooding-to-trigger-building-collapse-in-major-cities/