Why was there no stop on faulty rail tunnel work?

CHINA RAILWAY CORP has found that some of the tunnels along the Shanghai-Kunming high-speed railway have some serious quality problems, which may pose safety risks. China Central Television comments:

The sound construction of any high-speed railway is of the utmost importance because any flaw might cause an accident. That is especially true of the high-speed railway linking Shanghai and Kunming which passes through Southwest China's Guizhou and Yunnan provinces where the geological conditions are complex and require safety standards that are higher than normal.

In order to prevent quality problems, there is a supervision mechanism throughout the whole process of constructing a high-speed railway, from design to construction to acceptance of the final product. Yet those companies that used substandard materials and compromised safety by not doing their work to the required standards were not caught in their misdeeds by the supervisors.