Research On The Mechanism Of Recoverable Deformation Energy Absorption Bolt Action And Its Blast Resistance Performance Testing

Since the early 19th century,bolting support has been developed as a proactive support method,and it has rapidly spread worldwide and found wide applications in various fields such as mining,civil defense,and national defense.Nowadays,with the continuous achievements of science and technology,new technical issues and practical demands have been raised concerning traditional bolting support methods.For civil side,due to the depletion of shallow resources,the mining depth of mines has gradually increased,leading to a threat of deep dynamic disasters such as rock burst in the mining field.For military defense,protective engineering faces the potential threats of damage from new types of weaponry mostly.In this context Under these situation,both domestic and international research on new types of anchor bolt has mainly focused on energy-absorbing anchor bolts.However,during the instant of dynamic loading,the vibrations in protective engineering could cause the anchor head of the anchor bolt（or cable）to detach from the borehole wall when moving from the borehole wall towards the outside of the chamber.This phenomenon results in a reduction in the anchoring effect.Nevertheless,the energy-absorbing anchor bolts have struggled to address this issue.Therefore,there is a need to develop an energy-absorbing anchor bolt capable of maintaining tight contact with the borehole wall during dynamic loading and continuing to function even after experiencing multiple dynamic loads.In light of this research status,this paper has presented the development of a Recoverable Deformation Energy Absorption bolt（RDEA bolt）,and conducted relevant research on it,including static load performance testing,field blast tests,numerical simulation analysis,and theoretical analysis.It provides an in-depth analysis of the working mechanism and related characteristics of RDEA bolts.By solving the practical problems faced by protective engineering,this paper has offered a novel reinforcement technology and provided essential support for the subsequent promotion and utilization of RDEA bolts.The main research contents of this paper are as follows:1.Development and Static Load Performance Testing of RDEA Bolts.Starting from the practical problems and demands faced by protective engineering and underground chambers,RDEA bolts were developed.The preparation materials and structural forms of RDEA bolts were determined through static load performance testing.The RDEA bolt consists of two main parts:the free section and the anchoring section.The bolt body runs through both the free section and the anchoring section,with the free section being the part of the bolt body near the borehole wall.The direct anchoring element for the anchoring section is a sleeve with internal threads near one end of the free section.The extrusion slider is welded to the bolt body as a single unit,and an elastic element is placed between the extrusion slider and the shearing slider.Therefore,under external forces,the movement of the bolt body can be divided into 3 stages:the linear elastic motion stage,the shearing friction motion stage（constant resistance stage）,and the displacement recovery stage.The first stage is a linear elastic motion stage,during which the extrusion slider inside the RDEA bolt sleeve compresses the elastic element until it reaches the ultimate shearing force of the internal threads.Subsequently,it enters the shearing friction motion stage（constant resistance stage）,where the shearing slider shears the internal threads under the action of the extrusion slider,dissipating energy until the energy-absorbing segment fails.After the energy-absorbing segment failure,it enters the second stage of linear elastic motion.At this point,the shearing slider has moved to the limit valve,providing a linear elastic reinforcement effect similar to conventional rebar anchor bolts.Throughout the entire movement process,once the external force decreases to a level lower than the rebound force of the elastic element,the elastic element will drive the bolt body to undergo displacement recovery until a new force balance is achieved.This process constitutes the displacement recovery stage.Research findings indicate that the energy consumption in the energy-absorbing segment of RDEA bolts and the ultimate shearing force of the internal threads are directly related to the outer diameter of the shearing slider.In the case of constant pitch,the absorbed energy of the bolt and the ultimate shearing force of the internal threads increases with the increase in the outer diameter of the shear slider,but they are not in a proportional relationship.A two-dimensional plane strain assumption was used to establish an analytical model for the elastic-plastic mechanics of the RDEA anchor bolt’s energy dissipation segment.After calculation,the theoretical value of constant resistance was within a reasonable range of the experimental value,demonstrating that this elastic-plastic mechanical analytical model was reasonable.2.Comparative Field Blast Testing of RDEA Bolt Reinforced Chambers.From a field test perspective,blast resistance performance tests were conducted on both the RDEA bolt reinforced test section and the conventional steel bolt reinforced test section.The measured results indicated that after all tests were completed,the conventional steel bolt reinforced test section suffered more severe damage,with through-cracks appearing in the arch roof,significant circumferential cracks at the projection of the blast center,severe shear and peel-off damage on both sides of the 1/2 arch waist positions.In contrast,the RDEA bolt reinforced test section exhibited milder damage,with no circumferential cracks at the projection of the blast center,and less severe shear and peel-off damage on both sides of the 1/2 arch waist positions.When the scaled distance was 0.93 m/kg^1/3,the total residual displacement of the arch roof in the conventional steel bolt reinforced test section was 56.2%larger than that in the RDEA bolt reinforced test section,indicating that RDEA bolts possess certain displacement recovery characteristics.The peak acceleration values at identical measuring points on the arch roof of the conventional steel bolt reinforced test section were all greater than those in the RDEA bolt reinforced test section under the same loading conditions.This indicated that the full-length bonded conventional steel bolts are less effective in reducing accelerations compared to RDEA bolts.Field measurements from various aspects,including macroscopic deformations of the chamber,blast pressures,borehole wall displacements,and accelerations,all suggest the superiority of RDEA bolts over conventional steel bolts.This superiority is not only evident in their superior blast reinforcement effect on chamber structures but also in their energy-absorbing characteristics and partial deformation recovery characteristics.The RDEA anchor bolt has promising prospects for application.3.Research on a Numerical Simulation New Method for RDEA Bolts and Reinforced Chambers.Using the FLAC3D numerical simulation software,a computational model for RDEA bolt reinforced chambers was established,and modifications were made to the software’s built-in cable structural elements.Numerical simulation methods specific to RDEA bolts were proposed,considering the energy dissipation segment,free segment,and elastic components of the RDEA bolt.Failure criteria were incorporated for both conventional steel bolts and RDEA bolts during the simulation,allowing for an assessment of their respective performance during field tests.The calculated results closely matched the field measurements and followed the observed trends,indicating the reliability of the simulation results.The simulation results revealed that when the scaled blast distance was 0.93 m/kg^1/3,the conventional steel bolt experienced plastic deformation in its front half but did not reach failure criteria,while the RDEA bolt remained in the constant resistance phase and did not meet the overall plastic failure criteria.This suggests that the chambers respectively reinforced by both types of bolts retained load-bearing capacity in the test with a scaled blast distance of 0.93m/kg^1/3,but the RDEA bolt exhibited significantly superior blast resistance compared to the conventional steel bolt.Through numerical simulations with elastic elements placed at both the anchoring end and the chamber wall end of the RDEA bolt,it was found that the displacements at the arch tops were essentially the same.This indicated that placing the elastic elements at the anchoring end or the chamber wall end serves a similar purpose in mitigating chamber damage.However,the chamber wall was the first region to experience damage,particularly when subjected to multiple blast loads,making it more prone to failure when the elastic elements were placed at the chamber wall end.In contrast,there were no such issues when the elastic elements were embedded within the anchoring section of the RDEA bolt.Therefore,placing the elastic elements within the anchoring section of the RDEA bolt is a more rational approach.4.Study on the Anchoring Mechanism of RDEA Bolts.In terms of theoretical analysis,the stress distribution of the anchoring section of RDEA bolts was derived using the Kelvin displacement solution,obtaining the general form of the stress distribution.The research revealed that the stress distribution in the anchoring section of RDEA bolts is fundamentally similar to the stress distribution in fully bonded bolts,with differences in the expression of relevant parameters.Based on earlier investigations into the energy absorption,large deformation,and rebound characteristics exhibited by RDEA bolts in different motion phases,physical models for RDEA bolts in various motion phases were established.The physical models for the linear elastic motion in the first and second stages were both represented by equivalent Hookean model.The physical model for the constant resistance phase is described using a Maxwell model in series with elastic and viscous elements,and its constitutive equations were mechanically derived.The generalized Kelvin model was adopted as the physical model for the surrounding rock mass,and it was combined with the physical model for RDEA bolts in parallel to establish the physical model for the support rock mass of RDEA bolts.Constitutive equations for the support rock mass of RDEA bolts in different motion phases were derived,providing theoretical support for the practical engineering application of RDEA bolts.This study addresses practical issues in protective engineering by developing RDEA bolts to resolve the problem of anchor head detachment from the chamber wall during dynamic loading,which can reduce the anchoring effectiveness.RDEA bolts effectively enhance the load-bearing capacity of chambers in protective engineering.It has significant reference value for the construction and support of protective engineering and provides crucial experimental and theoretical support for the promotion and use of RDEA bolts.