The Shenzhen landslide that buried nearly three dozen buildings underscores the challenges China faces managing construction waste as it digs and builds subway networks and underground facilities, experts say.

The disaster has been blamed on the illegal dumping of construction soil that locals say has gone on for two years behind the city's Hengtaiyu industrial park.

Chinese media reports have highlighted that finding places to dump construction waste soil in coastal Shenzhen has been a challenge since 2008, when the city began constructing a network of subway lines.

While the problem is more acute for Shenzhen, which has limited land compared to Beijing or Shanghai, construction waste is a problem for all of China, noted Professor Yuan Hongping of Southwest Jiaotong University who does research in waste disposal methods .

"We always read reports all over China about how trucks dump waste quietly at night, in places they're not supposed to," he told The Straits Times. "There are regulations but companies are more concerned about the bottom line."

The situation is worsened by Chinese cities' rush to build subway lines, which produces more soil waste than regular buildings. It has been estimated that at least 38 cities will have one subway line by 2020.

Cities are also looking to go underground as land becomes scarce. Central Wuhan has begun construction of China's largest "underground city", Xinhua news agency reported yesterday. When completed in 2018, it will have a floor area the size of 72 football fields.

In northern Jinan, only nine in 44 waste dumps have enough room to take in construction waste, according to one Chinese media report.

It said that as the cost of running a proper dump was high, illegal ones flourished.

Shenzhen has stepped up inspection of other dump sites following the disaster.

"Unfortunately, it sometimes takes a disaster before people sit up," said Prof Yuan.

Teo Cheng Wee