Development of road networks and bridges in Nepal started around sixty years back through different donor agency and departments of government. During the initial years, most of the major works were completed through the technical and financial assistance of Russia, UK, India, China and other countries. Later, Department of Roads (DoR) and other departments like DoLIDAR took up the task. In the present scenario, around 250-300 bridges are built annually by DoR alone (as per 2019 data) and in a similar range by provincial and local governments. Some of those constructions fail at different stages before their design life span. However, if we analyze the failure rate of a bridge in Nepal, it has tremendously increased in the last five years. In 2017-2021, at least 50 bridge failures have been highlighted in national media.

 This year alone, national newspapers have reported 21 motorable bridges failed till now in different parts of the country. Most of the bridges have collapsed during construction or just after completion of works. Among the 21 bridges collapsed, 11 bridges failed during construction period and rest after completion of structural works. The cost of these bridge failures is around two billion rupees as per DoR. More importantly though, the series of bridge failures has created an environment of fear among the users whose livelihood (both social movement and business) may be affected.

The probable cause of failure of such bridges can be broadly categorized into improper construction methodology, inferior quality of works, faulty design and poor maintenance. Some bridges failed during construction due to a washout of shuttering support like at Mahesh Khola, Dhading. In failure of some completed bridges, supports settled during flood like at Kamala and Jabdighat. Some bridges were overflooded  i.e. flow over the deck level, like at Bhoteodar and Melamchi. At the same time, some bridges in Chure region are affected by excessive deposition, impending flood damage like at Dolalghat.

There are different considerations to ensure the safety of a bridge at three distinct stages, namely design, construction and maintenance. We discuss aspects of the design stage in this article, while the next stages will be considered in subsequent articles.

Before starting detailed design, the bridge site must be studied thoroughly, considering topography, hydrology and geomorphology of the river, geotechnical condition, roadway alignment, and ecological concerns. Bridge site selection is one of the most important step towards bridge safety. A bridge constructed at a bend of the river has different considerations than at a straight reach. Our design approach is mostly based on straight flow assumption in Nepalese practice, which can be risky for a bridge at river bend. Most of the bridges are built without analysing the possible extreme morphology of the river. Likewise, the study on extreme hydrology of streams is quite preliminary. An ample amount of good quality data is the biggest challenge to hydrologists in Nepal.

Some bridges suffer from poor hydraulic design. There is no practice for consideration of sedimentation under bridges in Nepal, which is commonly observed at bridges in Chure foothills.  Moreover Bridges in Nepal is designed for 100 years floods whereas in developed country, it is designed for 150 years flood. Additionally, to minimize the cost of bridge, there is a practice to reduce water way from normal channel width. It may cause changes in the morphology of rivers such as bed and bank erosion and upstream deposition, shifting of thalweg from initial position towards left or right bank in upstream. Reduction in waterway requires proper analysis of changes in river morphology. It can be simulated through physical hydraulic modelling or numerical modelling, which have been limited to research topics yet, while the bridges in field suffer.

Another major challenge to bridge design in Nepal has been the quality of geotechnical investigation. While scientific knowledge and equipment have become more accurate, poor planning and greed are pushing us further behind. A number of soil test service providers are willing to take shortcuts due to short deadlines and underbudgeting from the Client or due to greed and malpractice. This is not just a problem in Nepal, but even the past president of the American Society of Civil Engineers highlighted it as a major challenge to the engineering community in his country. Hasty and poor quality of soil test leads to extremely expensive failures and lengthy delays in bridge construction, as highlighted by the cases of Jabdighat and Thimura.

At the same time, structural design of bridge components has been on the over-safe side in most of the recent bridges in Nepal. Whether it is due to poor construction supervision and quality control practice in Nepal or plain lack of knowledge in design, designers often adopt over-safe size of bridge parts. Nonetheless, it is a problem that needs to be addressed. Additional concrete poured without need is a waste of valuable resources on the one hand and poor economics on the other. Rather than employing labor to extract and exploit more resources (striking axe to our own feet), we should increase construction quality through improved supervision. This way, less money will be spent on lifeless concrete and more on enhancing the life standard of construction professionals who will give back to the economy.

Unnecessary conservatism in design also leads to uncomfortable approach roads joining bridges, as seen in several bridge in urban areas as well as Terai. In order to tackle the lack of knowledge in design, a two-pronged approach is proposed. One is capacity building of design professionals through trainings and workshops. Another is vetting all designs through capable third-party checkers. Design costs are generally 1-2% of construction cost. So small addition of proof-checking cost (like 0.5%) can result in substantial savings from out of proportion sizing of bridge elements, and additional safety from some factors overlooked by the design team.

Lastly, another design issue that leads to failure of bridges during construction is the failure of temporary supports or “scaffolding”. Design of temporary works used to support the bridge during construction is on the contractor’s part as per contract documents, but it is rarely requested by the client and submitted by the contractor. Even when the design is presented, it is limited to structural design of the props. However, the major issue with temporary supports in Nepal is not its structural strength, but its stability inside the river. Where diversion of the river is not possible, sufficient waterway must be ensured between/under the prop supports.  Problem of the insufficient waterway under the supports was aptly highlighted by the failure of Badigad bridge in Gulmi twice in two years due to the same reason. Design of temporary supports requires input from not only the structure engineer, but also hydraulics and geotechnical engineer. There are several problems in implementation of temporary supports as well, but it is a topic for the next part of this article that discusses construction issues of bridges in Nepal.

Summing up, the design stage is undoubtedly the most important stage of bridge management. More the time spent and considerations made during design, less will be the issues faced during the subsequent stages of bridge management, which will be discussed in subsequent articles.