This assignment will deliberate on how lack of standard procedure and precaution taken by engineers during the early years of 1950’s, when constructing the Banqiao dam in the city of Zhumadian, Henan Province located China, led to loss of over 200 000 lives, this included the people who drowned and also the people that contracted diseases in the aftermath of flooding . It is considered one of the worst “forgotten” structural failures in history.
The Banqiao dam along with 99 dams and reservoirs, were built within the Zhumandian city of the Henan province as a result of extreme flooding the area experienced during the 1950s. The purpose of these dams was to control flooding, store water for irrigation of crops and as a way to harness hydroelectricity . The Banqiao dam was constructed in a way that it can withstand weather extremes of 0.53 m of rain over a period of 3 days. It had a storage capacity of 492 million cubic meters, the 375 million cubic meters capacity was reserved for flood storage i.e. it can store 1000 years’ worth of flood and the dam had an overall height of 116m . The dam was had a clay core.
Engineers have a duty to fulfill which allows them to take command, these command includes ensuring that the design is safe and protected from the possible disruption that could put the public in danger. One of many ways that engineers can ensure public safety is to design structures that are able to withstand the extreme external forces that are about by natural/man-made disasters or incorporate signal that could warn the public when structures failed to withstand external forces, failure to do so could result in an engineering disaster. The failure of the Banqiao dam was classified as a natural disaster event but there was evidence to prove that human error played a role in the loss of lives. Factors such as poor planning, design and maintenance, unsafe construction and unclear evacuation procedures contributed to the failure of the dam.
The plan layout had based all 100 dams into one concentrated place, with the Banqiao dam being the biggest one, which raised concern according to the hydrologist Chen Xing, who expressed that having a large number of dams in one place can potentially raise the level below which the ground is saturated with water i.e. the water table . Raising the water table would mean that none of the water would be absorbed by the ground but instead, it will add more volume to the amount of water above the ground surface as shown in Figure 1. This will increase the quantity of water found in the dam.
Chen Xing also suggested that there should be an increase in the sluice gates which will help the drain the water faster in times of heavy rain, the number of sluice gates which the hydrologist proposed was 12. The concerns and the suggestions were turned down by engineers because the hydrologist was accused of being too ‘conservative’ and the number of sluice gates that were installed was reduced to 5 because it was more costly to install 12 sluice gates. The dam and the sluice gates showed numerous cracks after completion, this was due to many implications. Firstly, there were some design and construction flaws when the Banqiao dam was being built, secondly, the dam was highly under maintained after completion and thirdly the clay material used can be easily subjected to cracking due to high water pressure, it was therefore important to ensure that regular maintenance takes place or a better material, such as cement, could have been used. The engineers were able to repair, redesign and reinforce the dam, this new design was called the ‘Iron dam’ and it was considered ‘unbreakable’.
After more than 20 years of completion, in August of 1975, the city of Zhumandian experienced very heavy rains accompanied by a Typhoon. This was the heaviest rain recorded in the area, more than a year’s rain fell in 24 hours. The storm had damaged the telegraph wires which were unable to pass on the information near the dam so that people could evacuate, the under-designed walls of the sluice gates were unable to handle the water volume, and the material used could not handle the water pressure which caused the clay core to crack. The water was peaking higher than the height of the dam causing the Banqiao dam to fail, a huge wave engulfed the entire Zhumandian area which caused between 170 000 and 240 000 casualties. A number of people died because of drowning, others died after because they were trapped in the water, others from water contamination and others of starvation. Those that survived were feeding in off dead animals that were floating above the water. Proper evacuation procedures should have been implemented, these include sirens to alert people about the upcoming storm, safety measures they should take in the event where flooding might occur, this could have saved many lives. Figure 2 shows where the dam was destroyed, this can be identified where there are two embankment areas on either side of the river.
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