Workers use advanced mining equipment to extract coal from an open pit at the Pingshuo Antaibao Coal Mine. [Photo by Zhang Yi for China Daily]

Open-pit mining might be the safest and simplest way of coal mining. However, there are still challenges for operators to overcome.

Industry insiders say one of the challenges is to refill the pit after the coal resource is depleted to repair the damage to the environment.

But the depletion of resources doesn't mean all the coal in the mines is extracted. For the stability of the coal mine, a certain amount of coal should be kept to form terrace slopes to prevent the collapse of pit walls.

But the latest results of a pit-slope coal mining research program conducted by Zhongmei Kegong Energy Technology Development, a Shanxi-based subsidiary of China Coal Technology Engineering Group, are expected to offer a solution to this problem.

The company implemented the research program at the Pingshuo Antaibao Coal Mine in the Shanxi city of Shuozhou, one of the largest among the 400-plus open-pit coal mines in China.

The company's executives said the technological solutions it offers include geomechanics-based tests and appraisals, unmanned tunnel boring and reinforced coal column supporting.

The solution also features intelligent and fully automated coal stripping, which can substantially improve operational safety while increasing efficiency.

To prevent the pollution of air from coal dust and coal-bed methane, automated gas recovery and air-cleaning techniques are also part of the company's solutions.

The company's research report shows that, the pit-slope coal extraction volume at the various mining sites in Pingshuo Antaibao can reach 800,000 metric tons a year.

Company executives said these new solutions are made in response to the requirement of Shanxi's energy revolution strategy, which features increasing the ratio of new energy resources, improving efficiency and reducing the environmental footprint of the conventional coal-mining industry through technological innovations.

Statistics from the Shanxi Energy Administration show that a total of 157 million tons of outdated coal-mining capacity was phased out during the past five years, while more than 68 percent of the remaining capacity has been upgraded to advanced levels.

Zhang Yi contributed to this story.