ENGINEERING BEHIND THIKA ROAD CONSTRUCTION

 

"the research of which this disquisition forms a record, however, broke new grounds which it aimed deliberately at unravelling and illustrating the steps and the reckoned eventuality. Rarely do you meet this kind of exposition, so read on...

In a city where most traffic rules are either non-existent or are flouted left, write and centre, the roads become a perfect battle field. Swapping between lanes, hooting for vehicles in front to move away yet the jam is 20 metres long ahead...

 

The Design AND Engineering

Sneak peek

• Cash on each segment
• Extreme construction
• Muthaiga Roundabout
• Highway or Boulevard
• Regimental Highways (Autobahns)
• Muthaiga--KU
• The Engineering beneath the Surface
• KU—Thika
• Priority control and Restraints
• Plastics for Road Construction(future)

It’s argued and even confirmed that if you can survive in Nairobi roads as a driver, you definitely deserve NFS licence primarily because all other odds have been eliminated. In a city where most traffic rules are either non-existent or are flouted left, write and centre, the roads become a perfect battle field. Swapping between lanes, hooting for vehicles in front to move away yet the jam is 20 metres long ahead, drivers who join the main road haphazardly without checking for the oncoming traffic, or squeezing in front to force their ways, these are just few examples of common madness in our daily roads.

The long snarl-ups caused by ministerial motorcade are not spared too. Matatus too, love them or otherwise, they are here to stay. Their lunacy, mindless driving will continue existing all in scramble for “space.” But all these will become a thing of the past given that the ministry of Roads has fully embarked on changing the faces of our roads into super-highways and flyovers to decongest the city of Nairobi.

EXTREME CONSTRUCTION

I am not yet acquainted with the engineers on the site and the strategies laid in store for the effectual action, but the research of which this disquisition forms a record, however, broke new grounds which it aimed deliberately at unravelling and illustrating the steps and the reckoned eventuality. Rarely do you meet this kind of exposition, so read on.

Roads and motor vehicles are correlative, and one without the other will simply be sending bright minds back to the dark ages to search for the other lost “sheep.” Good vehicles need good roads, and vice versa. It’s been argued that one important quality of a road is accessibility. This, technically, describes how vehicles are allowed to enter and exit a rad. By controlling access to a road, the road can support, in a given time, move traffic at higher speeds i.e. reduced traffic snarl-ups.

The Ksh. 26 billion project involves construction of two major types of roads:

(1) highways, and (2) boulevard or urban streets. Each of the two types control access to different levels, differ in location, the amount of traffic it can safely support, and the speed at which traffic can safely travel. These parameters shall be fully employed in the three demarcated segments, namely:

• Muthaiga Roundabout— Uhuru Highway Section

• Muthaiga Roundabout –KU Section
• KU – Thika Section

[A] Muthaiga Roundabout –

For this section, the contract bid was deservedly procured by China Wu Yi Company with a cheque of Ksh. 8, 030, 386, 596 dangling in their able hands. The contract narrative clearly laid the action and it involved construction of four-lane flyover across Globe Roundabout then widening the linking to 8-lanes from the current 6-lanes which shall meet a flyover on Muthaiga Roundabout. Wu Yi shall then set up an underpass at Pangani. Eventually, footpaths shall crown all the roads as a sign of pedestrian precincts.

Together, –

Museum Road

– Museum Hill Roundabout will be worked on, turning

Forest Road

into 6-lanes from the current 4-lanes, with a median (divider in the middle of the road). Similarly Museum Hill Roads will become 6-lanes as they erect a forked flyover on

Limuru Road

.

The construction of this section shall be much biased to erection of urban street rather than superhighway. To understand which one, it’s prudent of us to distinguish between the two primarily.

HIGHWAY OR BOULVARD DESIGN

As boulevards endeavour to cover cities, towns and suburbs, highways on the other hand strive to connect to or more major cities. Despite the fact that both are constructed using similar principles, boulevards are contrived to accommodate underground public facilities, such as electrical wiring, water and sewage pipes, and telecommunication lines. Besides, they are built around existing buildings and other barriers like rivers. The boulevards, which often control vehicle movements by use of traffic light and signs, can be classified into two on the basis of the amount of traffic designed to carry: collector streets and arterial streets. Collector streets convey traffic from residential streets to the main roads called the arterials. In cities like Nairobi, the arterials are often similar to highway in construction even though they are located within city limits. For the highways, the contrast lies in the amount of access control they have (i.e. the amount of traffic they are designed to carry). We have:

REGIMENTAL Highways aka Motorway/ Autobahns

The autobahns can handle the most traffic with the lustre of having three, four or more lanes for each direction of travel and often include medians to separate traffic moving in opposite directions of travel and often include medians to separate traffic moving in opposite directions. Vehicles that enter or exit the autobahns can do so only at incontestable points usually by using a special entrance and exit ramps (slope that join two parts of a road when one is laid higher than the other). The ramps grant vehicles access to the road without disturbing the flow of traffic. Incoming vehicles must merge with the flowing traffic, and vehicles leaving the highway use exit ramps that guide them off the highway without blocking the traffic behind. The burden of intersection with other roads is eliminated by use of special bridges called overpasses or tunnel-like structures called underpasses.

NON-REGIMENTAL Pass ways handle less traffic comparatively, and they intersect other roads at-grade (at the same level), rather than using overpasses or underpasses. This kind usually encourages traffic jam as vehicles scrample to find through way.

Now we know...

[B] Muthaiga Roundabout—KU

With the above design technique in mind, this segment must be designed as a high-speed autobahn with very limited access and exit. Sinohydro Corporation, the concerned contractor, pledges to widen the carriageway from Muthaiga—Kasarani into 8-lanes, and from Kasarani – KU into 6-lanes with a cheque of Ksh. 8, 690, 568, 489 the budget entails construction of three underpasses, at Kahawa, KU and at the former Nakumatt Building; three flyovers, at Kasarani Roundabout, Githurai Roundabout and Interchange at GSU Roundabout.

To support vehicles (light and heavy) moving at high speeds and to ensure durability, the road is made up according to standing civil conventions. Lets see what Sinohydro Corporation is devising...

The Engineering beneath the Surface

Basically a road has at least three distinct layers but the number often depends on the intended use of the road, number of vehicles and the budget constraints. From the bottom upwards, the layers are:

• the Topmost (pavement)
• the Base Course
• the Roadbed

The Roadbed is the base of a road. Natural soil is the most common roadbed material, but in case of wet-land, stones do better. Roadbed is shaped (consolidated) to make a smooth, level surface that will support the layers built over it. Engineers use bulldozers, compressors and other equipments to distribute soil evenly and firmly along the roadbed. The soil can be stabilized by adding or mixing materials such as calcium chloride, lime or Portland cement to the soil.

The Base Course is often made up of compacted gravel and it rests on top of the roadbed. Mostly, without adequate drainage, roads may buckle as water distends the ground underneath. To disengage this inconvenience, drainpipes are usually installed within the base course to control rain and moisture drainage. For very busy autobahns or motorways, a second layer is included to the base course for extra support.

The Topmost is made of wearing solid layer of pavement and is designed to be smooth and to withstand corrosion from traffic or weather. The pavements are of two main types:

• Bituminous (or flexible) pavement
• Concrete (or rigid) pavement

Bituminous Pavements is cheaper and easier to construct, but it requires more maintenance. The bituminous material, which maybe a by-product of petroleum like asphalt (or mixture with plastic waste), softens when heated and can be prepared and applied in a wide range of concentration. Asphalt, a thick bituminous material can be used directly as a pavement, or commonly mixed with aggregate for added strength and traction. Then thin overlays less than 2cm deep or in layers several centimetres deep is applied accordingly.

[The asphalt and aggregate are usually mixed and heated at their base station. The material is then transported to the construction site, where it is spread directly over the base course and compacted using a roller-dozer.]

Concrete Pavement, on the other hand, lasts for a very long time with minimal upkeep but is much more expensive. The concrete, which has been used once in , is generally laid as a single thick layer directly over the base course. With a thickness of about 30—35 cm, the concrete is usually laid in long sections or slabs of varying length. The metal bars or dowels are inserted between the slabs to help connect the joints, holding the slab firmly. Concrete despite it renowned for being strong material with a high compression tolerance, it has poor tensile strength. So when the ground underneath expands and contract unequally due to seasonal or weather changes, the concrete become prone to cracking. Cracks can occur at or near the joints where concrete slabs meet or on the slabs themselves. Deep cracks can allow the broken concrete slab to move upward or downward creating an uneven road surface. To eliminate this, reinforced concrete is preferred. This one contain steel bars or mesh imbedded within the concrete layer which help hold the concrete together over time, even if cracks occur. But cost is the deciding factor.

[C] KU—Thika

To be continued in Part 2...  

Mbagathi Way

Forest Road

University Way

Uhuru Highway

THE ENGINEERING BEHIND THIKA ROAD CONSTRUCTION