Key Points in Road, Bridge, Rail and Metro Construction

India on the fast track

India is on an ambitious infrastructure project planning path with some very remarkable developments underway in the country. Did you know that the widest expressway being built is the Delhi-Meerut Expressway and has 14 lanes?  And that the Mumbai Trans Harbour Link when completed will be the longest sea bridge construction project in the country with a total stretch of 16.5 km above the sea and land length of about 5.5 km? The bridge will connect Central Mumbai with Navi Mumbai with a travel time of just 20 minutes. High speed rail expansions are underway connecting major cities of Mumbai, Ahmedabad, New Delhi, Chennai and Kolkata with the first trial run of the Mumbai – Ahmedabad Bullet Train project covering 63 kilometres scheduled for 2026. Apart from this, an impressive fact about the metro rail is that there are around 810 kilometres of metro lines operational in 20 cities across the nation and more than 980 kilometres of under -construction metro network currently in 27 cities.

Be it road and bridge construction, railroad track construction or building elevated or underground metro rails, quality of materials and superior workmanship will ensure safety and long life of the projects.

Common Key Points for all Infrastructure Works

According to our experts, the most salient aspect during construction of infrastructure, especially such mega projects is taking utmost care of materials used and the standard workmanship.

MATERIAL KNOWLEDGE

Ensuring Quality of Materials

Be it any kind of infrastructure construction project, ensuring quality of the material employed is of prime importance. Since concrete is the common material used, its components like cement, aggregate and steel have to be tested thoroughly and the quality must be in accordance to codes of the Bureau of Indian Standards (BIS). Another key component of building projects, sand also needs to be tested and verified against the applicable BIS codes for similar aspects like physical characteristics (shape, grain size percentages) and chemical requirements.  Also, construction materials should not get saturated or have excess water holding capacity, else the material will swell, leading to faults in the construction design.

Knowing the Source of Materials

There are times in the lifetime of projects where clients pressurize contractors and engineers to use any material at hand, when quality material is not available, just in order to keep the project work going on and completing it by hook or by crook. Unsuitable material shortens the life span of the project and results in poor quality of work. Therefore, as per our experts, knowing the source of material is a key point in ensuring the quality of the material. Nowadays tracing the source of material is not easy as it is transported from far flung places. There are also legal and environmental impacts of sand mining to be considered as one cannot extract sand and rocks for aggregate from anywhere except from earmarked areas for mining.

Following Standards and Codes

As per the codes laid down by BIS, there are numerous checkpoints like Specific Gravity and Water Absorption for cement, sand, water, steel and other materials. The codes are basically the averages arrived at by BIS scientists after many experiments involving materials and if followed diligently, the project should not have any issues. To illustrate the application of codes let’s take the case of an Expressway project where heavy cargo will be transported by trailers and trucks. If the specific gravity of the stones or aggregate used is lower than the stipulation in the BIS codes or the water absorption capacity of the stones or aggregate used is on a higher side than the average stated in the BIS codes then it means that the material is brittle and thus not suitable for road making.

Other issues

Construction industry projects have multi-dimensional dependencies, and are often plagued by various legal, commercial, technical, socio-economic obstacles. As such, project progress timelines and deadlines top the priority list while quality of materials, step by step technical checks and workmanship gets neglected in the process.

WORKMANSHIP

Quality of workmanship is the next factor, the importance of which cannot be underscored enough in construction.

Impact of Poor Workmanship

To give an everyday example – you might have seen dumpers carrying material to be used as a base for laying roads in the city. This material then is dumped on the road site and compacted by road rollers. The idea is to achieve a base which has minimum water absorption. More the compaction of the base, the lesser water it absorbs and hence better quality of the road laid on top of it. In a shoddy compaction job, water collects in voids that eventually ingress in the upper bitumen layer and cause disintegration of the road that is creation of potholes.

Now contractors don’t follow standards that limit the material particle size to a maximum of 75mm leading to poor compaction. Though one may have machines and equipment on site like rollers to make road, the finesse with which the site engineer executes the compaction job will ultimately decide the quality of the road.

Unfortunately in India, the workmanship is seriously compromised in roads meant for the general public and that is why we see frequent disintegration. These roads are in bad shape solely due to bad work.  Aspects of good workmanship apply to all infrastructure works and decide the performance of the project.

Importance of Codes for Superior Work

The stretches of roads with elevated portions are often constructed with Reinforced Soil (RS) walls that require infill soil and soil reinforcement (geosynthetics/steel) having material and usage properties compliant to relevant BIS, Indian Roads Congress (IRC) codes, Ministry of Road Transport and Highways (MORTH) guidelines. Improper infill soil usage and inferior workmanship (like insufficient compaction, using heavy rollers for compaction near Reinforced Earth block/panel edges, improper drainage or alignment) result in batter, bulging, facing wall cracks, excessive differential settlement, sliding, slip failures or even collapse of the entire RS structure.

Geotechnical Assessments

Regions having soft soil need to be assessed as per geotechnical report and suitable ground improvement solutions needs to be implemented before the construction of overlying structure for safety and quality of the construction.

Road Design and Construction

Classification

Roads are classified according to the load that they are going to bear. Roads are classified depending on the increasing load – city or arterial roads, State Highways, National Highways and Expressways. The finance, public convenience, technical aspects, social impact are other important factors to consider in road construction apart from using material as per BIS codes and ensuring good workmanship.

• Expressways are usually 6 to 8 or even more lane projects with very heavy traffic and hence it is always mandatory that they be constructed as concrete roads only. Concrete road construction uses PQC – Pavement Quality Concrete which is a rigid, top wearing layer of a concrete road with a thickness between 180 to 300 mm.
• National Highways are usually six laned in India and they can be laid with PQC or a flexible coat like bitumen or tar.
• State Highways have 4 lanes as they carry relatively lesser loads.
• Arterial roads in cities and district and village roads are managed by the respective municipal corporations and Zilla Parishads, whereas the Public Works Department looks after roads that feed state highways district roads.

Services Running under Roadways

Storm water Drainage – it is mandatory to have drains on the side of roads so that rainwater or water from other sources can be carried away thus preventing flooding of roads. When cities in India were just developing, rainwater was left to drain freely on the road sides as road widths were lesser than present day. As the roads got wider, with more cars populating them and parking alongside roads, town planners felt the need to provide underground drainage system for storm water.

Drains are made of concrete and the design differs as per the rainfall in the area – saucer shaped shallow drains for scanty rains or with trapezoidal, deep cross-sections in places with heavy precipitation. On national highways, drains are covered with steel grates to take the load of heavy trucks passing over them. 

Sewage System – Sewage system is strictly separate from storm water drainage as the latter is still clean and the idea is to direct it to the nearest stream that then drains into the water body in the town or city. Sewage goes into the Sewage Treatment Plant (STP) and the treated waste is discharged into the river.

Now, sewer lines are planned to go through the centre of the road with manholes placed in the middle. However when the roads were laid for the first time, they used to be on one of the side of the road. This had disadvantages like the entire right of way had to be excavated for maintenance work and thus they sewer pipes came to be located in the middle.

The sewage pipe that runs beneath the main roads is usually 1200 to 600 mm in diameter, depending on the area’s population. The whole pipe in not filled with sewage but there has to be adequate space for overflows.

Potable Water Supply – Drinking water pipelines are 1 foot, ductile iron (DI) pipes that run under roadways in the city. The use of cement pipes for potable water has been discontinued as concrete is permeable.  Oftentimes sewer lines run next to water pipes and the nature of concrete has caused mixing of the two and contamination of drinking water resulting in serious public health concerns like cholera outbreaks. Punctures are made in water pipes at various locations to for individual water connections.

HDP and LDP – high density and low density plastic pipes are employed to take individual water connections from the main waterline under the road. Canals are also an important infrastructure for water supply and have their own specialised building contractors. They are always designed in a trapezoidal shape only due to hydrostatic pressure.

Bridge Design and Construction

Aqueducts and Viaducts

Aqueducts and viaducts are also important parts of infrastructure. A Via duct is a specific type of bridge that has piers or arches supporting an elevated roadway or railway connecting two points over a valley. Aqueducts are similar bridge like structures for water transport.

Bridges

Bridges are of two types, namely major and minor and both types are constructed over water bodies, rivers, banks etc. Bridges with larger spans are called major bridges. Road over bridge (ROB), road under bridge (RUB), Foot over bridge (FOB) and flyover are all different types of bridges.

Key Points

• Key points that affect bridge construction are material strength and quality and the workmanship. Apart from this span of the bridge, the conditions of the site, the geotechnical analysis, and abutment plan where the bridge meets land and safety considerations are noteworthy aspects. 
• Vehicle underpasses are built where highways pass near villages and the width of the same depends on the village population. For example the underpass at Uran in Mumbai is very wide to allow heavy vehicle movement as it connects Jawaharlal Nehru Port Trust which is a major port and thus sees many trailers passing through.
• Bridges stand over the banks supported by abutments and centre is supported by piers.

Railways and Metro Rails

Railways

Now as the country is developing, the old infrastructural system is getting a fillip. The current railway system is designed for speeds not more than 80 kilometres per hour continuously but now high speed rails to carry bullet trains are being constructed.

• A traditional railway line consists of tracks laid on concrete beams called sleepers. This assembly is placed on embankments that have to be necessarily heavily compacted. This is required as the ground must be stabilized to take the weight and vibrations of the railway carriages that move swiftly on it. If compacting is not done well, the ground beneath the sleepers will sink and have a cup type depression causing a sag in the tracks and ultimate derailing of the train.
• Also, railways traditionally have aggregate called ballast between sleepers to take in the vibrations and reduce compressions in the ground. Over a period the stones settle in the gaps in the ground and they have to be replenished from time to time. Railway embankments are trapezoidal mounds that need nearly 100 % compaction as trains pass over them.
• Train tracks turn in a curved fashion as it is obvious that right angle turns will rupture the rail and sleepers. In recent times, railway tracks are being laid on rigid pavements of required thickness as per the increasing load of trains. In this case sleepers and ballast are not needed as the concrete pavement takes the vibrations of the train.

Metro Rails

A Metro is basically a railway where the ground it runs on is stabilised. Metrorail is not necessarily elevated but can be laid on the road as well. Now as our cities are over civilised there is no land available for the metro to pass and that is why elevated metro projects have been planned and underway in major Indian cites. The reason why the project is called a Metro is because it passes through metro cities that are highly dense. Sometimes the metro can run underground or in tunnels or on bridges.

• A metrorail on the road consists of a raft which is a concrete bed laid over ground that should not sink under the pressure of the railways weight and speed. Rails are laid on sleepers on which ensure the perfect alignment for the tracks.

• In an elevated metro, this entire assembly of the concrete raft and tracks is supported on piers.  All the elements are made in concrete in the Metrorail infrastructure like the piers or columns, slabs and stations. The required grade of concrete like M25 or M30 is employed as per the utility. M40 or M50 grade of concrete is generally used in piers of the metro as they must be strong to absorb the vibrations of the trains and no cracks must appear used in piers and be earthquake resistant.
• Another important aspect is the watering of the concrete in metro construction. Rapid hardening cement is employed as regular concrete takes more time to cure, requires large quantities of water that is unsustainable and costly and results in increasing the project time. This type of cement needs little water for curing. Steam curing is also done for curing of large elevated metro piers.
• The applications of Precast, Pre-stressed and Post-Tensioned Concrete have revolutionized the construction of metro projects.
• Indian cities also have Monorails. They consist of the same component of a regular Metrorail like piers and girders. However, here the railway is hanging from a channel on top and that is why it’s called monorail as it does not rest on the concrete raft.

Runways

Runways are a kind of a road but built at airports to cater to the movement of air planes that run at a speed of around 200 kilometres per hour.

• The rotations per minute of the plane wheel are so high that a regular road would be destroyed if a plane were to land on one. The purest form of asphalt was used in runways earlier but now it is constructed as a rigid pavement made of concrete.
• No type of imperfections like bumps and depressions are permissible on the runway. Runways cannot have curved roads as planes have a large turning radius.
• Turns of an airplane are taken at right angles and hence there are no transitional or gradient curves on a runway and all aspects are considered scientifically.