Abstract: In order to ensure safe mining and smooth excavation, the technology of L mode borehole grouting was utilized to reinforce the direct limestone aquifer n umbered Lg under the I-1 coal seam in No.1 mine of Zhaogu first. Proper borehole structure was proposed by detailed analysis of geological information of I-1 coal s eam with thick alluvium layer and thin bedrock. Also, the corresponding construction technique was also taken to solving the difficulties in the borehole drilling and pipe driving. The technology of ground L mode borehole grouting indicate a good results for coal seam floor reinforcement with thick alluvium layer and thin bedrock.