通过对爆破试验中处于不同自由面条件下的炮孔爆破产生的振动信号进行频谱分析，并结合爆破振动数值模拟，研究了地下洞室全断面毫秒延迟爆破过程中产生的自由面对振动频率的影响机理及变化规律。结果表明：爆炸荷载产生的压应力波传播至自由面时发生反射，反射稀疏波与原应力波叠加致使远区荷载压力的上升时间和持续作用时间变短，造成荷载的频率变大，从而导致有自由面条件下其振动频率增大、高频振动能量占总能量的比重增加；爆源与自由面之间的距离越小，爆破振动频率越高；从振动频率的角度来看，较好的自由面条件可以减小爆破振动对结构的破坏。试验监测结果验证了分析结论的可靠性。

With the methods of spectral analysis of vibration signals and numerical simulation of blasting vibration, influence of the blast-created free surfaces on vibration frequency during underground full-face excavation were investigated in the present study. The vibration signals were measured from a specially designed small-scale blast test, where blastholes were detonated under different free surface conditions. The results show that the presence of free surfaces results in higher vibration frequency and an increased proportion of high-frequency vibration energy to total energy. As distances between blasting sources and the free surfaces decrease, the vibration frequency increases. This is since the rarefaction waves reflected on the free surfaces are superimposed onto the blast-induced initial compressive stress waves, and it causes the rising time and duration of the far-field blast loading pressure becomes shorter, thereby leading to an increased frequency of the loading. From the view of vibration frequency, the damage of blasting vibration to structures can be mitigated by a better free surface condition. Reliability of the results is demonstrated by the vibration monitoring in the blast test.