为提高隧道勘察围岩分级的准确性，减小施工阶段围岩变更率，对云桂线富宁隧道围岩分级变更进行分析，主要结论与建议如下： 1）造成该隧道围岩分级变更的主要原因是物探解译不准、岩溶发育、岩体层间挤压破碎和地下水发育，其中物探解译不准的原因有异常段飘移、断层破碎带解译过宽及解译错误等； 2）岩溶发育造成的变更量也较大，应重视可溶岩段围岩分级的确定，避免出现长段高围岩分级； 3）因岩体层间挤压破碎及地下水发育造成的围岩变更率一般较小，需在施工阶段结合超前地质预报进行变更； 4）地质条件复杂的长大深埋隧道采用可控源音频大地电磁法是适宜的，但应解决物探解译过程中存在的问题，布置钻孔对物探异常区进行验证，提高解译精度； 5）目前采用的综合勘察手段仍是确定铁路隧道围岩分级的主要方法，施工中应重视超前地质预报及施工地质工作。

In order to improve the accuracy of the surrounding rock classification in tunnel survey work and reduce the alteration rate of surrounding rock classification during tunnel construction, the analysis of alteration of surrounding rock classification of Funing Tunnel on YunGui Railway is carried out. Some conclusions and suggestions are drawn as follows. (1) The main reasons for the alteration of surrounding rock classification of the tunnel are inaccurate interpretation of geophysical prospecting results caused by abnormal drift, overwide interpretation of broken fault and interpretation errors, the karst development, the interlayer crushing of the rock mass, and the groundwater development. (2) The alteration amount of surrounding rock classification caused by karst development is large; hence attention should be paid to surrounding rock classification determination of karst section to avoid long section of high grade of surrounding rock. (3) Due to the interlayer crushing of the rock mass and groundwater development, the alternation rate of surrounding rock classification is generally small, which needs to be alternated combining with advance geological prediction. (4) The geomagnetic method is suitable for the long and deep tunnel with complex geological conditions; however, problems in geophysical interpretation process should be solved; and drilling should be arranged to verify the geophysical anomaly area and improve interpretation accuracy. (5) The comprehensive survey method is still the main method to determine the surrounding rock classification in railway tunnels; and the advance geological prediction and geological work in construction should be paid attention to.