| The Gaoloushan Tunnel is a control project for Longnan City and Jiuzhaigou,Sichuan Province.With the characteristics of "three high and three large",etc.The project is a typical representative of deep buried long highway tunnel under complex geological conditions.Rockbursts of various grades have occurred in all the construction sections,which have caused serious problems to the safety and smooth penetration of the tunnel construction.In order to solve the above problems,by means of site survey,theoretical analysis,numerical simulation and interior experiment,this thesis reveals the rockburst mechanism of Gaoloushan Tunnel and puts forward its rockburst control countermeasures.The main research contents and results are as follows:(1)The research results of rockburst hazard zoning of Gaoloushan Tunnel based on in-situ stress analysis show that:1)The three principal stresses increase nearly linearly with the increase of depth.The pressure coefficients inside the depth of the measurement section are all greater than1,indicating that the stress in the test range is dominated by tectonic stress;2)It is determined that the distribution law of the in-situ stress field is based on horizontal tectonic stress.The whole line is basically dominated by high stress and extremely high stress,and the local stress can reach more than 77MPa;3)High crustal stress,metamorphic sandstone lithology and blasting disturbance are the main factors of rockburst in Gaoloushan Tunnel.The rockburst type of Gaoloushan Tunnel is established,which is dominated by impact rockburst and supplemented by slab buckling rockburst.The location of on-site rockburst disaster is consistent with the prediction results of rockburst hazard zones,which proves the reliability of them.(2)Through the experimental study on the mechanism of slab buckling rockburst and impact rockburst in Gaoloushan Tunnel,the following results and conclusions are obtained:1)Slab buckling rockburst has attenuation characteristics in the process of rockburst,and the intensity of rockburst shows the characteristics from strong to weak.The expansion of "slab buckling circle" has time effect,which is shown as time-delay failure behavior in engineering.The two rockbursts occurred in the process of the experiment formed a shallow rockburst pit.Rockburst fragments are dominated by medium-grained slaty fragments,which are more easily broken in the length direction.The impact rockburst has no attenuation characteristics in the process of rockburst,and the rockburst intensity shows the characteristics from weak to strong.The two rockbursts occurred in the process of the experiment formed a V-shaped rockburst pit,the flaky and V-shaped characteristic fragments are the unique fragments type of this rockburst.Due to the intervention of dynamic load,rockburst fragments are obviously sheared,so it is easier and more broken in the thickness direction,forming fragments dominated by coarsegrained flake fragments,which may be more harmful due to their large mass,large volume and long ejection distance in on-site rockburst;2)In terms of acoustic emission characteristics,the similarities between the two types of rockburst are that the original waveform characteristics of each key point are the same,and the two-dimensional spectrum characteristics of the key points are roughly the same.The absolute energy of acoustic emission of slab buckling rockburst has the characteristics of cluster distribution,the cumulative energy curve of acoustic emission shows the characteristics of gentle growth→stepwise growth→70° stepwise increase in the whole process of rockburst.The main frequency characteristic of the whole process is that frequency emission signal shows the conversion relationship from small to large,and then presents the characteristics of linear broadening of main frequency distribution band and linear increase of signal points.The 150 k Hz low frequency band can be used as its rockburst early warning band.The acoustic emission energy and cumulative energy of impact rockburst are less than those of slab buckling rockburst.The absolute energy of acoustic emission is sporadically distributed,and the cumulative energy curve of acoustic emission shows the characteristics of gentle growth→stepwise growth in the whole process of rockburst.The main frequency has obvious fluctuation at the key points and in the whole process.The bandwidth has experienced a process from narrow→wide→narrow→wide.When exceeding a certain disturbance amplitude,the main frequency band basically covers the 100-600 k Hz range.The frequency band is richer than slab buckling rockburst,while the main frequency span is large and presents the characteristics of bundle.The frequency band of 150-200 k Hz can be used as the early warning frequency band of this type of rockburst;3)In terms of inoculation mechanism and discrimination criteria,both slab buckling rockburst and impact rockburst are failure phenomena that occur only when the static load and dynamic load meet a special coupling effect.The difference lies in the different combination degree of dynamic and static load.According to the above conclusions,the discrimination criteria of two rockburst types are obtained.The slab buckling rockburst mechanism can be regarded as the result of the joint action of shear crack and tension crack(leading role),which reflects the characteristics of progressive fracture development.It is a typical rockburst mode of progressive fracture induced instability,which is a strain rockburst.The rockburst mechanism of impact rockburst can be regarded as the result of the joint action of shear crack and tension shear crack(leading role),which reflects the characteristics of sudden fracture development.It is dominated by sudden and highdensity energy release,which is a typical failure mode of instantaneous rockburst.(3)The experimental research on rockburst control about step method and "step method + NPR coupling support" was carried out.Two technologies on rockburst control were compared and expounded from the aspects of time-space evolution process(effect)and acoustic emission characteristics,the results of the study are as follows:1)The time-space evolution process of the deformation and fracture of the surrounding rock by step method is obtained.The surrounding rock resists the rockburst by forming "fracture zone" or "logarithmic spiral".Under the two experiments,the speed of fragments,depth and volume of pits,number of times are lower than rockburst mechanism experiments,and the range of the rockburst area is effectively reduced.The risk level,intensity of rockburst are effectively reduced,and the treatment and improvement of tunnel rockburst are realized;2)In terms of displacement characteristics and acoustic emission characteristics,the specimen of "step method+NPR coupling support" is far less than the step method.Different from the rockburst control technology of step method,which not only changing the way of energy release,but also increasing the absorption of rock masses energy caused by rockburst.Rockburst occurs only at a higher buried depth,so as to achieve the purpose of safe release of rock mass energy in rockburst disaster.After two disturbance stress shocks,there is no fracture failure,and the integrity of the inner wall of the tunnel is still maintained,it shows that NPR coupling support has special mechanical properties of constant resistance and basically constant,can meet the control requirements of large deformation of rockburst.In addition,the mechanical model based on the interaction relationship between rockburst disaster rock masses and NPR coupling support is established;3)It is suggested to use step method to control rockburst in high stress sections ZK53+500-ZK54+700 or non above sections with rockburst tendency below 1350 m buried depth.It is suggested to adopt "step method+NPR coupling support" to control rockburst in extremely high stress sections ZK47+700-ZK51+500 or non above sections with rockburst tendency with burial depth of more than 1350 m. |
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