KeNHA to close Southern Bypass for repairs

Kenya National Highways Authority (KeNHA) will close the Southern Bypass for 10 days from December 24, 2024 for repairs.

The closure will enable the agency to install new expansion joints at Airtel and Ole Sereni Hotel Interchange, Kibera slum bridge and Ngong Road-Nairobi Interchange.

Speaking during a media briefing at Airtel-Ole Sereni Interchange Friday, KeNHA Director, Corridor A Dennis Odek,  said the project commenced in August 2022 for a 36-month period.

“It was being undertaken by Ebeneza Commercial Works Ltd at a cost of about Sh716 million. The main works on the project included surface dressing of the entire road which is about 29 kilometers, and it's a dual carriageway,” he said.

Other main works he said included construction of a rigid pavement of the way in motion, extension, and construction of a new crash barrier on the median.

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It will also include repairs of both of the carriageway and its structures and the performance-based component itself.

This takes care of the maintenance activities, including sweeping the road, clearing the bushes around the road, and landscaping on the median.

Eng Odek who said they selected this specific period when most of the traffic is expected to be reduced because most people may have traveled out of town for Christmas festivities.

“Now, these major works that we are talking about entail replacement of the expansion joints to three bridges along this road. The three bridges are Ole Sereni Bridge, the Kibera Overpass, and the interchange with Ngong Road,” said Odek.

According to KeNHA Deputy Director Infrastructure Jared Makori, the first importance of the expansion joints in a structure is to ensure that there is a smooth passage of traffic on top of the bridge.

“It also allows the expansion and contraction of the bridge due to environmental factors that includes the temperature, and as well as enable the structure to respond appropriately to the structural dynamics or the impact of the traffic,” said Eng Makori.

“The type of expansion joints which are provided during construction are the TST elasto-plastic solid devices of the crushed stone fill-up type, installed on both sides of the abutments and piers whose design life is between 10 and 15 years, depending on the exposure conditions and the kind of traffic,” he added.

The engineer said that affected roads are busy with on average 25,000 vehicles on use daily.

And about 60 percent are tracks because it's a transit route and other vehicles that will want to bypass the Nairobi’s Central Business District (CBD).

The road serves a dual purpose; providing mobility and access while alleviating traffic pressure on the main Nairobi-Nakuru Highway (A8).

“The reason why we are doing this is because the expansion joints, if not replaced, will affect the overall performance of the bridge. The bridge will not be able to function properly. That means we are going to affect the design life,” he explained.

Makori said on average, they design structures to last 120 years, but if the expansion joints are not functioning well, they might affect the overall duration or durability of the entire bridge.

“We understand the importance of bridges. If the bridges are not there, the infrastructure is affected, and the efficiency of the entire network will also be affected. And that's why Kenha feels that it's important for us to replace these things in good time,” he said.

He added: “It's a strategic intervention that we are doing, apart from the normal maintenance that we are undertaking. Now, during the routine inspection that was carried out by the team that is in charge of the corridor, they were able to identify the damages that are developing on the three bridges at Ole Sereni, Kibera Overpass and the Ngong Road interchange.

He said that the type that they are putting in place is called the finger-type expansion joints, which are robust, durable and are able to carry traffic for up to 60 years if properly maintained.

“If both expansion and drainage are not provided, there's a danger of internal stresses accumulating within the structure. And that will ultimately cause cracking and other structural failures to the entire bridge,” he explained.

At Ngong Interchange and Kibera Overpass, the damage of the expansion joints is evident.

The bridge decks have been overlaid with asphalt concrete, but the deterioration of the expansion joints remains evident, as shown by cracked asphalt layers exposing the joints.

"The uneven riding surface at the joints, combined with the impact of heavy vehicles, exacerbates vibrations in the structures, increasing the risk of further damage. If unaddressed, these intensified vibrations could lead to serviceability issues for road users and, eventually, structural failure of the bridges," said Makori.

The works, he said will entail cutting and removing the existing joints which are damaged already and replace with new joints which will cost Sh48 million.

He blamed overloading of the road as a problem that are also trying to take care of with a virtual weight station at Kibera, there's a waste station just to monitor the trends in terms of what they do.

He however said the cases of overloading are quite minimal and they have compliance rates of about 99 percent but are still concerned about the 1 percent that is overloading and that is not only affecting the road, but the bridges themselves.