Abstract: In view of the “eight” shaped micro-pile composite structure with a roof connection, relying on the upgrading project of the Guangtong-Dali railway, in-situ test of micro-pile combined structure to reinforce stage excavation landslide was carried out to study the anti-siding mechanism. The results show that under the action of sliding thrust, the axial force distribution of each row of piles was different, and the distribution law of anti “S”, “double bow” and “S” was successively presented along the thrust direction. The peak axial force of each row of piles was tension, and the proportion of the side piles of the mountain: the middle piles: the roadside piles was 2.5:4.1:3.2. The maximum axial force of the side piles of the mountain was at the lower part of the piles, the middle piles appeared at the middle and upper part, and the roadside piles appeared at the upper part of the pile body. The coordination effect of the top cap on the inclined pile group was more significant than that of the general vertical pile group. The pile group under horizontal load was prone to large flexure deformation. Under the combined influence of pile group effect and slip surface, the transfer of tension and pressure forms of pile body were generated. The force mechanism of the composite structure is that: the first two rows of piles are subjected to tension, the bottom embedded section of the third row piles is compressed, and the compression zone demonstrates upward trend with the continuous load. Our results also show that the axial force of the single pile is dominated by the tension force, which is beneficial to the exertion of the internal steel in tension.

Key words: micro-pile combined structure, in-situ experiment, axial force monitoring, anti-siding mechanism