In view of geological origin

the formation of shallow gas in Hangzhou area was analyzed; and the original occurrence zonation characteristic of reservoir soil is investigated. It is shown that matric suction variation range of the gassy sand in enriched zone of scale gas reservoirs is not large

and its initial occurrence water content is close to its residual water content that means it is usually at the state of residual water content. Based on soil-water characteristic curve of the gassy sand described by Van Genuchten (VG) model

the indirectly engineering predictive methods to obtain unsaturated parameters of gassy soil are proposed. Results compared between the prediction and the experiment show that using Van Genuchten and Mualeum (VGM) model

Parker model and strength formula described by the power function

it is effective to predict the unsaturated parameters such as water and gas permeability coefficients

and shear strength of the reservoir soil

which can meet the need of preventive measures taken before metro construction to eliminate the shallow gas geological hazards