The primary support is the main load-bearing structure in the tunnel construction stage,the response rule and safety control of the primary support under dynamic disturbance are of great significance to ensure the safe and rapid construction.Figuring out the dynamic response characteristics and the safety control of the primary support is an important issue for the blasting excavation of a soft rock tunnel with reserved core soil.A three-dimensional finite-element numerical model was established by ANSYS/LSDYNA for the Linchang tunnel blasting excavation,and the reliability of the numerical model was verified by the field vibration monitoring data.The stress distribution characteristics of the primary tunnel support under the simultaneous action of two blast sources was studied combined with the construction characters of the reserved core soil method.The attenuation law of blasting vibration was obtained by using Sadovsky empirical formula.The safety criterion of blasting vibration velocity for the primary tunnel support under the simultaneous blasting excavation of both sides of the lower bench was proposed by taking stress as the control standard.The results show that the maximum vibration velocity appears at the arch foot of the primary support rather than at the tunnel floor or vault,which is different from the full section method and bench blasting method.Meanwhile,the propagation path of the blasting stress wave is dramatically affected at the un-backfilled area of the tunnel invert.The vibration velocity of the primary tunnel support is larger and attenuates faster on the left arch foot versus right arch foot.The maximum tensile stress and shear stress appear on the left arch foot of the tunnel under simultaneous blasting with 7.544 MPa and 2.78 MPa,respectively,which exceed the allowable value of the specification.According to the established linear stress-vibration velocity relationship,a blasting vibration safety criterion of primary tunnel support is proposed based on the ultimate strength.In addition,the safety vibration velocity threshold of the primary support in Linchang tunnel is 10 cm/s.