Although piezocone penetration test (CPTU) is widely used in engineering geological exploration

it has undeniable deficiencies in detection accuracy of shallow gas-bearing strata. Based on CPTU penetration principle

the shear deformation characteristics of soil at cone shoulder during penetration are analyzed. Furthermore

using the consolidated undrained triaxial shear test of dense gassy sand with different initial saturations

the response law and difference of excess pore pressure in soil at cone shoulder are discussed when CPTU probe penetrates into saturated and gas-bearing strata. The results show that

the presence of gas can significantly affect the shear deformation characteristics of sand

and with the increase of gas content

the shear volumetric strain increases

and transitions from shear dilatancy to shrinkage; however

the sensitivity of pore pressure response in soil decreases

leading to a non-negative characteristic phenomenon

which can be regarded as an important symbol of gas-bearing strata identification. According to the characteristics of shallow gas reservoir distributed in Jiangsu and Zhejiang coastal plain in China

a fine identification method of gas-bearing strata based on in situ multi-function piezocone penetration test is developed. In this method

the “dual control” index composed of silt or fine sand soil property identification and non-negative characteristics of excess pore pressure is used for preliminary judgment

and then combined with multi-functional auxiliary parameters for further inspection and correction. The validity of identification method is preliminarily verified in a practical engineering

and the identification accuracy of multi-layer gas-bearing strata is thereby improved.