Torrential rains over the weekend have wreaked havoc on several parts of Taiwan. On Saturday, video of a 300-tonne rock tumbling down a hill and just missing a car near Bisha Port (碧砂港) in Keelung grabbed worldwide attention.
Now public safety is being threatened by an even bigger boulder resting perilously at the top of the same hill.
Lee Tung-cheng (李銅城), head of Keelung’s Department of Public Works who led a group to inspect the rock on Monday, said the object — measuring 8m long, 10m wide and 10m high — was “bigger than imagined,” and weighed about 2,000 tonnes.
City officials had considered different ways to eliminate the danger, including pushing the rock down the hill, securing it with a net, hoisting it with cranes, and using explosives, but decided against these options because of safety considerations.
They finally decided to use non-explosive demolition agents to break the rock apart gradually, and estimated that this process would take 12 days to complete.
Lu Chien-kai, head of a company that has experience with major mudslide rescues, said non-explosive demolition agents are expensive and are mainly used in areas that are difficult or dangerous for humans to reach.
Another expert estimated that the city government would have to spend at least NT$10 million (US$335,880) to deal with this “most expensive” and yet completely worthless rock.
That figure is based on a labor cost of NT$60,000 per cubic meter of the target object. The rock is estimated to have a volume of 800m3. If the object is really hard and solid, more demolition agents might be needed.
Moreover, since the rock is perched on top of a hill, a makeshift 500m road has to be built to give workers and machines access to the site. The additional materials and transportation will add to the project’s costs.
The Ministry of National Defense said that there would be no problem sending military personnel to use dynamite to destroy the rock, but it could not predict the outcome of using such a method because of the residents and other facilities on the hillside.
This method would involve drilling holes into the rock and filling them with a demolition agent that expands and cracks the rock into smaller pieces. The sections that break off will be transported down the hill.
The process will be repeated until workers break up the entire boulder.
Military personnel said using dynamite could be the easiest and quickest way to destroy the boulder, but they were worried that the smaller rocks could turn into flying “projectiles,” threatening neighboring areas.
At least 10 yachts worth more than NT$30 million each are anchored at Bisha Port, they said.
They are also worried that the flying rocks could damage houses, hotels and shops located on or near the hillside.