Research On Anchoring Mechanism Of Reinforced Rammed Earthen Site In Arid Regions

Rammed earth site is historical building relic with soil as the main material left by ancient human activities.Among them,the ground sites are more concentrated in arid regions of Northwest China.However,under the long-term natural force and man-made influence,rammed earth site cracks due to tension and shearing,presenting failure modes of collapse,unstability etc..Under the protection concept of cultural relic?repair old as before?,it is generally subject to concealed mechanic stability control technology to treat stability of earthen site at present.Different from traditional rock-soil body anchoring,earthen sites are mostly subject to anchor bolt of which base materials are bamboo and wood coordinating modified mud as anchoring material,and failure modes for historical sites affected by diseases of undercutting,fracture etc.differ greatly.Therefore,research about anchoring mechanism and anchoring force demand is always the key problem of anchoring design.In view of this,mechanical behavior of bolt-slurry-soil and anchoring force demand under different load in anchoring system of earthen sites were provided with systematic research combining test research,theory analysis and numerical simulation method in the Thesis,and one set of anchoring design method suitable for earthen site was proposed based on this.Main work is shown as follows:Load transfer law in anchoring system for anchor bolt of Phyllostachys Pubescens was analyzed according to result of in-site pull-out test,where anchoring length,diameter for anchor bolt and influence of diameter for anchor hole on anti-pull and bonding performance of anchoring system were researched.Distribution law and change trend of slippage,stress and strain of anchoring interface along with the axial direction of anchor bolt were analyzed.The result shows:residual shearing stress of this kind of interface is very limited when slippage is relatively large,and there is effective anchoring length limit.Through research about interface bond-slip relation,improved tri-linear bond-slip model considering complete de-bonding phenomena was proposed.Friction section of this model is limited in length,and shearing stress in complete de-bonding section is zero.Based on improved tri-linear bond-slip model,the whole process for bond-slip in anchoring interface was divided into six stages:elastic stage,elastic-softening stage,elastic-softening-friction stage,elastic-softening-friction-debonding stage,softening-friction-debonding stage and friction-debonding stage,and distribution and evolution process for interface shearing stress in all stages were provided with theory analysis.Calibration method for bond-slip model characteristic parameter was given based on this,and analytical expressions for a series of parameters for axial deformation of anchor bolt u_p,interface slippage u_p,interface shearing stress?,interface shearing strain?,length for elastic section L_e,length for softening section L_s,1,length for friction section L_c,1 and limit for effective bond length L_effff etc.corresponding to all stages were deduced,and calculation result agreed well with test value.Finally,influence laws of parameters for length for anchor bolt,axial rigidity for anchor bolt,bond-slip model etc.to anchoring performance were systematically analyzed.Nonlinear spring element was used to simulate bond-slip behavior in anchoring interface to provide nonlinear finite element analysis for tension test.In order to verify the results of the test and theoretical analysis,the distribution law and change trend of interface slippage,shearing stress and shearing strain along with the axial direction for anchor bolt were studied.Stress transfer mechanism of modified mud-soil interface and load transfer law bttween two interfaces and stress distribution state inside modified mud and soil body for rammed earth site were supplemented and analyzed.Its main unstability and failure mode was classified into three kinds according to damaged current state for earthen sites?cracking-falling type,cracking-dumping type and slipping-the lower stagger type?.Dangerous body was simplified to cantilever beam model with equal section according to Timoshenko beam theory,and failure mechanism of historical site under the dynamic action was analyzed combining with failure criterion of the maximum tension stress and energy transformation principle.On this basis,total anchoring force demand for historical site under given environment condition was solved taking restricting the first cracking of dangerous section as the purpose.Change trend with factors of its anchoring angle,existing cracking depth and earthquake acceleration etc.was discussed.Taking anchoring system for single anchor bolt of earthen sites with longitudinal crack as the object,friction function of soil body to anchor bolt was simplified as one linear spring and one parallel mechanism for damper related to speed,and calculation model for wholly grouted anchoring system for single anchor bolt under seismic action was established.Based on dynamic balance theory for elastic body,dynamic balance equation for anchoring micro-section in dangerous body and stable body was established,and analytical expression for axial stress response of anchor bolt was deduced.Based on this,anchoring force demand for single anchor bolt system was provided with checking.Based on the equilibrium condition for anchoring force demand,one set of anchoring design method suitable for earthen sites was proposed,and the application for this design method taking the practical engineering as example was explained.Finally,safety for rammed earth site after anchoring was assessed.