Physical model tests on supporting performance of micro-pile and micro-pile with thread in natural gas pipe-landslide system in mountainous area

Natural gas pipeline projects in mountainous areas are inevitably affected by geological hazards such as landslides, which pose a serious threat to the safe operation of pipelines along the routes through landslide areas. Based on the engineering background of China-Guizhou natural gas pipeline K558 + 700 landslide, this paper studies and compares the supporting mechanism and applicability of two different support structures, namely, flower-tube micro-pile and threaded micro-pile, in pipeline landslide through indoor large-scale physical model tests. The results show that: (1) The distribution pattern of peak soil pressure along the mountain side and river side of flower tube micro-piles is basically similar along the pile depth, which is in the shape of "S" curve. The soil arching effect behind the pile is obvious, and the distribution pattern of soil pressure is generally consistent at all levels of load. In general, the distribution pattern of soil pressure on the side of the flower-pipe pile is the largest among piles, followed by the pile top, and the bottom of the pile. The soil pressure around the pile near the sliding zone is larger, so the optimization should be considered in the design of anti-slide pile. (2) The distribution diagram of the peak earth pressure along the pile depth of the threaded pile presents a double "S" curve. The distribution pattern of the peak earth pressure on the river side is significantly different from that of the mountain side, and the earth pressure at the bottom of the pile decreases greatly compared with that of the mountain side. With the increase of external load, the soil pressure around the pile increases greatly, indicating that the screw micro pile is deficient in lateral bearing capacity. (3) The bending moment of flowered pipe pile presents an "M" shape distribution along the depth direction, and the maximum positive bending moment occurs at the position 5 cm above the simulated slip surface. The pile body bending moment distribution along the depth direction is "S" shape, and the pile body positive and negative bending moment position near the simulated sliding surface roughly rotate symmetrical distribution, most of the region above the sliding surface is negative bending moment, the pile body below the sliding surface is positive bending moment. Under the same thrust load, the deformation degree of the screw micro pile is greater than that of the flower tube micro pile. (4) The load-bearing performance of the splined pipe pile is better than that of the threaded pile under thrust load, which effectively reduces the landslide thrust transferred to the pipeline; Under the large thrust load, the threaded pile can not effectively bear and offset the landslide thrust due to its insufficient flexural performance and serious deformation, and the stress transmitted to the pipe in front of the pile is large, causing more intense deformation of the pipe. Under the condition of this test, the flowered pipe micro-pile has outstanding protection benefit to the pipeline, and is more suitable for the retaining structure of the landslide area of the pipeline.