What is the direction of future underground space development?

At present, the coastal areas, north and south of Guangzhou has been related to underground space planning guidelines, and a large number of underground large-scale complex is also under construction, can be said to be in a rapid development stage, relative to foreign countries, such as Tokyo, Japan, in the underground rail transportation is still far from the shallow foreign countries have been developed almost, the domestic is still a bit of a distance. The future direction of development is certainly to diversification, large-scale, deep underground space development, the current application of roughly 40m above the stratum, deep development requires more advanced construction means and methods.