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Written by: Wang Jie'en Kong Fanxu
2020-06-07 20:31
Date of last update: 2020-06-07 20:31In the early morning of Saturday (6th) in Hong Kong, severe weather and thunderstorms combined. The Observatory issued a black rainstorm warning signal since 2017. On that day, many areas were flooded to change the country, and the water level was deeper and lower. The incident also found that many bricks on the pedestrian road were washed away, and a number of floor tiles were connected to "float".
It has been pointed out that the flooding in many areas was caused by the government digging bricks for demonstrators earlier, and sticking glue between the floor tiles in many areas, which caused the rain to fail to channel. Chen Jianshuo, the former president of the Institute of Engineers and the former director of geotechnical engineering, explained that the main cause of flooding is that the water inlet is blocked by garbage and has little to do with floor tiles. However, he also pointed out that the glue on the local bricks may cause water pressure under the bricks, and then the bricks above the "valley" will be washed away. In addition, some experts pointed out that the design of stone tiles should not be glued at all.
After the heavy rain, the pedestrian road in Ngau Tau Kok was in a state of wolf, the bricks were uneven, and the washed bricks were temporarily covered with black plastic bags. (Photo by Kong Fanxu)
Uneven bricks in Kwun Tong area still to be repaired
In the early hours of June 6th, there was constant lightning in Hong Kong. Thunderstorms were added all night, and the number of cloud-to-ground lightning in Hong Kong exceeded 14,000 times. At 2:55 in the morning, the Observatory issued a black rainstorm warning signal, flooding many areas of Hong Kong. In the evening, Kwun Tong and Wong Tai Sin Districts were the hardest hit areas. Between 2:45 and 3:45 am, the rainfall amounted to 54 to 105 mm and 80 to 105 mm, respectively.
A reporter visited Kwun Tong District today. The bricks on the sidewalk became uneven, and the washed bricks were covered with black plastic bags. There were also fences nearby. As for the traffic tunnel on Kwun Tong Road, which was seriously flooded that night, it has returned to normal so far, and a cleaner has cleaned the sludge nearby.
Black rain in the early morning of June 6
Former Director of Geotechnical Engineering: Brick glue is difficult to cause flooding
The flooding situation was serious this time. Chen Jianshuo, former president of the Institute of Engineers and former director of geotechnical engineering, said that the drainage system in Hong Kong has been carefully designed and the capacity is absolutely sufficient to cope with heavy rain. The problem is that the drainage channel on the road surface is blocked by garbage. , The leaves may be washed away, but the plastic bag is the most troublesome."
Will the sticky glue on the bricks worsen the flooding? Chen Jianshuo said that the sand under the bricks can indeed guide the rainwater, but the proportion in the rainwater is not large. He explained that in general cities, more than 90% of rainwater can be drained off the ground through drains, and only less than 10% of the infiltration into the mud layer. Therefore, even if the bricks do not have glue glue, the sand can only seep a small part of the water, which has no effect on flooding. The problem is that the drains are clogged. When encountering heavy rainfall, the rain cannot be drained away.
Floating bricks due to brick glue
But he also pointed out that when the bricks are glued, it may be the cause of "floating bricks". He said that if rainwater enters the sand under the brick, it may cause water pressure, and then the brick above the "valley". "If it is not a glue, the water pressure can spread through the gap."
Water pressure caused "floating bricks". The brick floor should not be added with glue
Huang Jing, the former president of the Hong Kong Pipeline Professional Association, said that recently government departments have glued water between bricks, but some parts may not be glued. When the rain enters, there is no space to run off, forming water pressure, "the water itself has Buoyancy...When you reach a certain strength, you can turn the ground up." He emphasized that in the design of the brick floor, there should be no glue.
As for the concrete road, it is also sealed. Why is there no relevant situation? Huang Jing explained that before laying concrete, workers would place large tapes, and then put iron nets and concrete, "the water will not go up to the concrete level normally, and it will go under the tape."
One day later, there was still water left in the channel of Kwun Tong. (Photo by Kong Fanxu)
Flooding due to incomplete cleaning
Lu Jueqiang, a former engineer in the Department of Mechanical Engineering at the University of Science and Technology, also believes that due to the incomplete cleaning of the canal, the dewatering channel will be blocked, and then it will be flooded. There may even be a chance to loosen the sand under the brick and make the brick float. Washed out.
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Road Administration Department: Reinforcement of bricks does not affect public road drainage
The Highways Department responded to the enquiry that the reinforced brick pavement will not affect the drainage of public roads. Rainwater flows through the sloped road to the roadside catchment ditch and is discharged through the underground drainage channel. The spokesman also pointed out that since the early morning heavy rain yesterday (6th), personnel have been dispatched to follow up the damage to public roads. For several locations in Kwun Tong District, contractors have been arranged to clean up and temporarily enclose the affected locations as soon as possible. Repair damaged roads.
Flooding Drainage Services Department Highways Department Local Area Heavy Rain Black Rain (Black Rainstorm Warning) (Black Rain)