A staff member from Guiyang high-speed railway maintenance division deals with dilapidated stones over a tunnel for Shanghai-Kunming high-speed train in southwest China's Guizhou Province, Feb. 21, 2019. The division's main task is to check and repair the facilities on the railway for high-speed trains threading through Guizhou Province where karst landform poses a threat to the security to the passing trains. (Xinhua/Liu Xu)

　　Staff members from Guiyang high-speed railway maintenance division thread through a stone gap towards their working point in southwest China's Guizhou Province, Feb. 21, 2019. The division's main task is to check and repair the facilities on the railway for high-speed trains threading through Guizhou Province where karst landform poses a threat to the security to the passing trains. (Xinhua/Liu Xu)

　　Staff members from Guiyang high-speed railway maintenance division walk towards their working point in southwest China's Guizhou Province, Feb. 21, 2019. The division's main task is to check and repair the facilities on the railway for high-speed trains threading through Guizhou Province where karst landform poses a threat to the security to the passing trains. (Xinhua/Liu Xu)

　　Staff members from Guiyang high-speed railway maintenance division thread through a stone gap towards their working point in southwest China's Guizhou Province, Feb. 21, 2019. The division's main task is to check and repair the facilities on the railway for high-speed trains threading through Guizhou Province where karst landform poses a threat to the security to the passing trains. (Xinhua/Liu Xu)

　　A staff member from Guiyang high-speed railway maintenance division has lunch during break in southwest China's Guizhou Province, Feb. 21, 2019. The division's main task is to check and repair the facilities on the railway for high-speed trains threading through Guizhou Province where karst landform poses a threat to the security to the passing trains. (Xinhua/Liu Xu)

　　Staff members from Guiyang high-speed railway maintenance division walk towards their working point in southwest China's Guizhou Province, Feb. 21, 2019. The division's main task is to check and repair the facilities on the railway for high-speed trains threading through Guizhou Province where karst landform poses a threat to the security to the passing trains. (Xinhua/Liu Xu)

　　Staff members from Guiyang high-speed railway maintenance division deal with dilapidated stones over a tunnel for Shanghai-Kunming high-speed train in southwest China's Guizhou Province, Feb. 21, 2019. The division's main task is to check and repair the facilities on the railway for high-speed trains threading through Guizhou Province where karst landform poses a threat to the security to the passing trains. (Xinhua/Liu Xu)