Study On The Field Test And Bearing Capacity Calculation Method Of The Capsule Type Of Underreamed Anchor

The capsule type of underreamed anchor is a new kind of underreamed anchor technology which adds rubber capsule at the end anchor basing on the the traditional anchor.The rubber capsule rubber owns the trait of good gas tightness,high bearing capacity,anti friction and corrosion resistance,which can form high quality anchor bolt by grouting anchor expansion,so that the new anchor can overcome the traditional anchor bolt of low strength,poor quality of construction defects.Since being developed,the new anchor has been successfully applied in many domestic engineering because of its high capacity,low cost,wide application range and convenient construction.However,the research on the new anchor is still relatively scarty and the theory cognition is far behind the engineering application so that it is very necessary to carry on the thorough research on the capsule type of underreamed anchor.This paper mainly adopts the method of field test monitoring combined with finite element analysis and researched the stress mechanism,axial force and side friction distribution of capsule type Underreamed anchor in different high injection pressure and bag grouting pressure.The essay also analysis the main factors influencing the capsule underreamed anchor bearing capacity by changing different parameters.Moreover,on the basis of field test and finite element simulation the article analysis the capsule type Underreamed anchor of different bearing capacity calculation model and its applicable conditions.The main research results and conclusions are as follows:(1)The capsule underreamed anchor bearing capacity increases linearly with improving Underreamed section of high injection pressure and bag grouting pressure.Besides,when the grouting pressure is over 1.5MPa with the same other parameters,it is not significant to improve more ultimate bearing capacity.Combining with the traditional Underreamed anchor without capsule,the limit bearing capacity of new anchor improve 27%~43%.(2)The final failure form of deep cystic type capsule underreamed anchor buriedin the silty clay soil show underreamed upper terminal soil of local shear failure.When the pull-out load is relatively smaller,the capsule anchor depends mainly on the friction pull resistance capacity and when it is more than 500 kN,the end bearing force begin to play a role.Then the end bearing effect is more and more obvious while the side friction resistance tends to be stable.When the load reach 625 kN,the soil of underreamed end begin to appeare plastic strain,and the plastic region is constant expanding around.With reaching the ultimate load,the plastic zone appears the shape of butterfly wing.(3)The expansion pressure of capsule has a limited effect on the soil around the anchor and the ultimate bearing capacity of the anchor does not change after the expansion pressure exceeds a certain value.Because of the action of expansion and extrusion,the capsule presents a large inverted cone and the shape of the irregular expansion section and the change of the soil characteristics have significant improvement on the bearing capacity.Moreover,through the analysis of different parameters influencing on the bearing capacity,the paper considers that capsule bag length,diameter and depth of underreamed section is the most significant parameters impacting on the ultimate bearing capacity and the second significant parameters is the soil feature and the bag grouting pressure.The underreamed length is relatively smaller impacting on the bearing capacity of the anchor.(4)Through the comparative analysis of the calculation model of the different bearing capacity of the capsule Underreamed anchor,it is concluded that the most realistic calculation of ultimate bearing capacity of the soil weight method,calculating is simple and has a larger safety factor,elastic theory method can be used in soil less parameters,the calculation results although conservative but can meet the safety requirements.Rock soil anchoring method and Boussinesq displacement method appropriate to the estimation of shallow buried Underreamed ground anchor ultimate bearing capacity.