| The stability of anchoring structures directly affects the long-term safety of roadways under impact dynamic loads.Frequent low-to-medium energy impacts cause sustained fatigue damage to the surrounding rock and anchoring structures of the roadway,leading to reduced load-carrying capacity and posing great difficulties to roadway maintenance.Therefore,studying the cumulative damage and load-carrying capacity degradation of anchoring structures under high-frequency and low-energy disturbance caused by impact dynamic loads is of great significance for constructing a reasonable anchor support system and maintaining the stable load-carrying capacity of anchoring structures effectively.This thesis mainly takes a typical impact dynamic load roadway in Shandong Province as the engineering background and focuses on the scientific problem of failure and damage of anchoring structures under high-frequency and low-energy impacts.Using a combination of field investigations,theoretical analysis,laboratory experiments,numerical simulations,and field tests,the thesis analyzes the cumulative damage and load-carrying capacity degradation of anchoring structures under multiple working conditions and scales under impact loads.The thesis clarifies the key factors affecting the stress of anchoring structures under impact loads and reveals the dynamic response characteristics,crack evolution laws,damage,and fracture mechanisms,and instability failure criteria of anchoring structures.The thesis proposes control criteria and support technologies for impact dynamic load roadways,and completes field application,achieving the following main research results:(1)The mechanical relationship between the three-phase two-interface of anchor bolt-rock-anchor adhesive under different working conditions was analyzed.Theoretical analysis revealed that seismic source energy,impact distance,and impact angle all affect the debonding failure mode of the interface in the anchored structure.The three key factors that affect the bearing performance of the anchored structure are compressive stress,tensile stress,and oscillation effects resulting from rapid changes between tension and compression.The main cause of the oscillation effect is the reflection of the shock wave at the free segment,and the key parameters that determine whether the anchored structure will fail to include energy magnitude,mechanical properties of the anchored medium foundation,interface bonding stiffness,and the seismic resistance and anti-sliding capacity of the nut threads.(2)The cumulative damage and crack evolution of different anchoring interfaces under impact were elucidated based on the SHPB and NMR techniques.The dynamic compressive strength of the specimens showed a nearly linear increase with increasing shock pressure,but an overall decreasing trend with increasing shock numbers.The maximum strain and average strain rate were positively correlated with shock pressure and shock numbers.During the increase in shock numbers,the elastic potential energy of the specimen changed significantly,while the plastic potential energy changed only slightly.The fluctuation of internal pore and crack development in the specimen corresponded to the changing trends of dynamic stress-strain curves.The failure mode of the specimen could be divided into fragmentation,irregular longitudinal splitting,bending-type splitting-shear composite failure along the anchoring interface,and anchoring interface failure splitting.The anchoring interface mostly underwent stages of synergistic load-bearing,crack initiation,damage exacerbation,and non-coordinated deformation failure.The compressive strength of the medium and non-coordinated deformation were key factors affecting its failure.(3)The mechanical response and damage mechanism of anchor structures under triaxial cyclic loading and static loading were revealed.A small-scale triaxial loading experimental device for anchor structures that meets the field stress environment was designed.The peak bearing capacity of the anchor structure is positively correlated with the strength of the anchor matrix,anchor length,and lateral pressure strength.With the increase of loading rate,it shows a trend of first increase and then stability,and the bearing performance decreases significantly when the anchor direction is severely inclined.There are various failure modes in the damage of the face,including penetrating cracks,concave fragmentation,V-shaped slippage,and layer peeling.The intensity of the failure increases with the decrease of the strength and length of the anchor matrix,the increase of the lateral pressure strength and loading rate,and the inclination of the anchor angle.The instability condition of the anchor structure failure is when the tangent modulus of the displacement strength curve is negative or the deformation amount continues to rise against the trend during cyclic impact.Under the action of impact dynamic load,the normal expansion driving force of the rock mass and the stiffness of the anchor structure are the key factors determining the stability of the roadway.(4)It was discovered that under impact loading,the dynamic response and loadbearing performance of pre-stressed solid anchor rod anchorage structures decay in a certain pattern.A pre-stressed solid anchor rod anchorage structure drop hammer impact test device and supporting constraint device were designed and processed,and axial compression impact and lateral shear impact experiments were conducted.Under axial compression impact,the loss of pre-tension force in the anchorage structure decreases with the increase of impact times,which follows a third power function decay law,and the dominant factor is the oscillation effect.The speed of pre-tension force reduction and the speed of internal damage increase are positively correlated with the impact energy,and negatively correlated with the length of the anchorage structure.Under lateral shear impact,the loss of pre-tension force in the anchorage structure can be divided into four stages: oscillation descent,tension growth,slow descent,and destruction descent.The anchorage sample exhibits obvious cumulative-mutagenic effect,evolving gradually from oscillation effect to tension effect,and finally to compression failure effect.The increase in anchorage length can effectively increase the overall stiffness of the anchorage structure,weaken the oscillation effect,mobilize a larger range of rock mass co-bearings,and protect the anchorage interface,greatly enhancing its anti-dynamic load capacity.(5)The cumulative damage and failure evolution process of anchorage structures under high-frequency and low-energy impact loads were analyzed.Under impact loads,internal cracks of the anchorage structure developed simultaneously at three positions:the exposed end,the anchorage interface,and the top of the anchorage structure.The internal cracks of the anchorage structure were elongated and penetrated through the interface between the free and anchorage segments.One side of the anchorage interface debonded and failed,and the entire length of the anchorage crack penetrated into the interior of the anchorage matrix.The cracks in the anchorage interface developed intermittently to a small extent,with most of them being well-preserved.The internal cracks were mainly tensile cracks,accounting for about 85% of the total.The peak velocity and fluctuation frequency of particle vibration at the exposed end of the anchorage were significantly lower than those of the elongated anchorage.The overall stress transfer showed a fluctuating change until it approached a constant value,and the failure mode was basically consistent with the laboratory results.(6)A criterion for damage and failure of anchorage structures under highfrequency and low-energy impact,as well as a guideline for tunnel control,were proposed and field tests were completed.When the stress caused by ground pressure and impact dynamic loads exceeded the cracking strength of any anchoring medium,each impact would cause irreversible residual deformation.Compared with static loads,it was easier for large penetrating and splitting cracks to form rapidly inside the anchorage structure,accompanied by tensile-shear failure and prestress loss.After a vicious cycle,failure occurred at a relatively low energy level.The control criteria include building a far-field unloading and near-field strong support system,shallow broken grouting modification,strengthening pre-tensioning maintenance,and increasing the letting compression structure.A project verification of repairing and reinforcing a typical impact-loaded roadway was carried out in a mine,and an anchoring-grouting integrated device that can achieve grouting modification and fulllength anchoring without damaging the rod body was developed.The monitoring results under the new support scheme showed that the anchoring rod/cable support resistance was stable,the deformation rate of the roadway slowed down,and the deformation amount was controlled within 100 mm.The cracks developed in the thicklayered basic anchoring layer,and the control effect was good.This dissertation totally has 118 figures,19 tables,and 228 references. |
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