突水突泥是富水全强风化花岗岩隧道施工常见的地质灾害，地层颗粒的流失是导致突水通道扩展的关键因素，其中颗粒达到起动流速是其流失的临界条件。考虑水流冲刷和土体黏结作用，对突水通道断面颗粒进行三维受力分析，导出颗粒的临界起动条件，建立了考虑颗粒粒径、颗粒坡面位置、相对暴露度三因素的颗粒起动流速函数，并利用数值方法分析了上述三因素对起动流速的影响规律。计算分析表明：起动流速随粒径增大先减小后增大，通道断面不同坡面位置颗粒起动流速呈明显的对称性，总体上起动流速随相对暴露度的增大呈增大趋势。采用正交试验法研究了三因素对颗粒起动流速的敏感性，发现粒径对起动流速影响最为显著。同时根据断面颗粒起动最小流速标准及相对暴露度的随机性，简化颗粒坡面位置和相对暴露度两因素，导出颗粒起动流速的简化公式，最后利用室内试验和工程实例验证了该公式的合理性。

Water and mud inrush is a common geological disaster in the completely weathered granite tunnel during construction. The key factor leading to the expansion of water inrush channel is the loss of soil particles, where the starting velocity is the critical condition of its loss. By considering the water erosion and particles adhesion, the particle 3D force in the water inrush channel cross-section was analyzed, and the function of particles starting velocity was established. The function includes the following factors, namely, the particle diameter, the particle position of channel cross-section and relative exposure degree of the particle. Meanwhile, numerical simulation was conducted to analyze the effect of the above three factors on the starting velocity. Numerical results showed that the starting velocity decreased initially and then increased with the increase of particle diameter. Furthermore, the starting velocities of channel cross-section at different positions were symmetry, and they were increased with the increase of relative exposure degree generally. By combining with orthogonal tests to analyze the sensitivity to starting velocity for the above three factors, the results showed that the diameter was the most sensitive factor. Accordingly, by considering the minimum starting velocity standard of channel cross-section and the randomness of relative exposure degree, the factors of particle position of channel cross-section and relative degree of exposure were simplified, and a simplified theoretical formula of the starting velocity was developed. Finally, the rationality of the starting velocity formula was verified by the laboratory test and field investigation.