Research On Bearing Capacity And Group Effect Of Capsule-type Under-reamed Ground Anchor

As a new type of anchoring technology,capsule-type under-reamed ground anchor is widely used in engineering,and has obvious economic benefit and social benefit.However,the theoretical and experimental that research on capsule-type under-reamed ground anchor are still relatively few.Especially,the research on the bearing characteristics and failure mechanism of capsule-type under-reamed ground anchor has not kept pace with the engineering application.In this paper,bearing characteristics and failure mechanism of capsule-type under-reamed ground anchor was studied with the combination of theoretical analysis and numerical simulation.Also,group effect and engineering design method of capsule-type under-reamed ground anchor was analyzed,which could provide reference for engineering practice.The studies of this dissertation consist of following parts:1)Through analysis of bearing characteristics of capsule-type under-reamed ground anchor,failure modes under different loads was studied,and calculation method of ultimate bearing capacity of was researched according to the stress state of the soil element at the top of the expansion bolt section.2)Numerical analysis model of single anchor of capsule-type under-reamed ground anchor was established with the consideration of elastic and plastic characteristics of soil and contact relationship between anchor solid and surrounding rock mass.The load-displacement curve of capsule-type under-reamed ground anchor under tensile load is obtained by adding displacement on the rebar.By changing the parameters of the model,the variation of the ultimate bearing capacity of capsule-type under-reamed ground anchor under different structure parameters and different soil properties was obtained which showed that the bearing performance could be improved with increasing diameter and buried depth of under-reamed anchor section and the better soil properties.3)Numerical analysis model of group anchor was established to analyze the change of ultimate bearing capacity and displacement and plastic zone of surrounding rock mass under different anchor spacing.On this foundation,design method and points for attention were summarized and analyzed for stability of anchorage structure,bearing capacity,diameter and buried depth of under-reamed anchor section of capsule-type under-reamed ground anchor.4)The field pull-out test proved that the ultimate bearing capacity of capsule-type under-reamed ground anchor can reach the results calculated by the method in project practice.With comparison of three different construction schemes of the grouting pile,the common anchor and capsule-type under-reamed ground anchor,capsule-type under-reamed ground anchor has obvious advantages in engineering application.