Study on Mechanisms of Pull-Out Bearing Capacity of Expandable Capsule Type Anchor Rods and Field Tests

Compared with the traditional constant-diameter fully-bonded bolt with single friction resistance， the end-expanded bolt provides resistance by the combined action of support and friction resistance， which greatly improves the force transmission mechanism of the bolt under load， and the pull-out bearing capacity of the bolt can be significantly increased. The main feature of the expanded-body bolt is that the cement grouting is carried out in the capsule， which can make most of the volume of cement soil formed by high-pressure jetting into the expanded-body anchoring section be squeezed around by the bag filled with cement slurry. Because the strength of the cement-stone body is much greater than that of the cement-soil body in the expansion section of the high-pressure jetting technology， compared with the ordinary rotary jetting expansion head anchor. The capsule expansion anchor can not only significantly improve the friction strength of the expansion section and the surrounding soil， but also improve the friction strength of the expansion section and the surrounding soil. The supporting force of the extended head in contact with the formation can be ensured. Therefore， as one of the main anchoring components in the anti-floating structure design， the bolting with expanded capsule is increasingly favored by engineers and technicians. Based on the theoretical analysis and the field test results， the paper introduces the load-transfer mechanism and deformation characteristics of the expansion bolting which can significantly improve the pullout bearing capacity when the anchorage body is limited in length， through the analysis of the mechanical properties of the basic test results， the feasibility of not applying prestressing based on ensuring the anchoring effect is discussed， to reduce the difficulty of waterproof node and reduce the cost of the project.