The Microscopic And Model Test Study Of Reasonable Distance Based On The Synergistic Effect Of Anchor Composite Soil Nailing

City construction has developed rapidly in China since the Reform and Opening to the Outside Word. The development of underground space is large, also the excavation’s depth and area is increasing, which makes Foundation Pit become a hot and difficult problems of current research. Composite soil nailing technology has the characteristics of safety and reliability, low cost, short construction period, wide range of application, suit one’s measures to local conditions, flexible, which is widely accepted in engineering application. Among them, the pre-stressed anchor can effectively limit the foundation’s displacement and increase the stability of the foundation pit, which makes it develop rapidly.The current study focus on the macro level, and the theoretical research is also not out of continuum mechanics category, also the study on the propagation of meso-level media is stagnant, which makes the micro mechanisms revealed synergistic effect become difficult. The reasonable spacing which is based on simple design method by 1+1 and considering the synergistic effect have a big difference.This paper is based on the Granular Medium theory, and a model test is carried out based on particle image technology. This paper has simple pullout test of soil nail, the simple anchor’s pullout test, different additional load, different anchor slenderness ratio, different anchor’s diameter, and different anchor spacing pullout test. Research on the reasonable spacing of anchor and soil nailing from macro and micro angle based on the synergistic effect, which is using the visual tracking technology and no punctuation measurement technology. The test results showed that:1. Single anchor’s drawing fracture plane shows a horn, but soil nail’s involvement makes fracture surface shrink, so there is a synergy between them. There is a synergistic effect of making the soil nailing and anchors around the lower porosity sand, and forming a compaction zone, so anchor’s ultimate pullout force is increased.2. Additional load and anchor’s ultimate pullout force, vertical influence scope showed a linearly increasing relationship.3. In sandy soil conditions of the experiment, when the length of anchor’s free section and soil nail is approximately equal, the synergy effect of anchor and soil nailing is remarkable.4. Vertical scope of the anchor is drawing with the anchor end diameter increases. Synergy region is sand between soil nail and anchor.5. The vertical spacing of soil nailing and anchor has significant effect on their synergistic effect.The reasonable distance of soil nail and anchor based on synergy effect according to indoor model test has significance to explain the synergistic effect mechanism of anchor composite soil nailing and improve the design theory and methods...