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Study On Deformation And Failure Mechanism Of Deeply-buried Cavern Under Explosive Ground Shock And Anti-explosion Measures

Posted on:2021-10-20Degree:MasterType:Thesis
Country:ChinaCandidate:Q YangFull Text:PDF
GTID:2530307109475424Subject:Geotechnical engineering
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With the development of economy and a building boom,underground caverns are used more and more widely in our country.Urban subways,highway tunnels,water conveyance tunnels and protection projects are mostly designed and constructed in the form of underground caverns.The explosion impact caused by engineering blasting,terrorist attacks and natural causes will threaten the stability of that.If the support measures of the underground cavern are unreasonable,it will cause serious casualties and national economic losses.In this study,we simulate the deformation and failure process of underground cavern impacted by explosive ground shock from the influence of multiple factors,as well as the study of support mode.The main research results are as follows:(1)We analyze the attenuation characteristic of explosion stress wave by using LS-DYNA software.The functional relationship between explosion pressure peak value and proportional explosion distance is established then.Combining with the empirical law about Hao Baotian underground nuclear explosion load,we put forward a method of determining far region explosion load.Meanwhile,a model for mechanical responses of the deeply-buried cavern under static-dynamic load is modeled by ABAQUS.(2)We study the deformation and failure mechanism of unlined tunnel under the static-dynamic load.The effects of the characteristics of the explosive load,the initial stress state,surrounding rock grade and the type of the cavern in explosion resistance are analyzed by numerical simulation.We find that the lateral pressure coefficient not only has a certain influence on the failure degree of the cavern,but also changes the distribution pattern of the plastic zone of the cavern.The buried depth and the peak value of dynamic load only affect the failure degree and range of the cavern.There is an obvious difference in the failure degree and plastic zone distribution of the cavern under top blasting and side blasting.The explosion resistance of straight wall vaulted cavern is slightly better than that of circular and rectangular caverns.With the increase of the rise-span ratio of straight-wall-round cavern,horizontal displacement of the side wall will increase,and the vertical displacement of the arch and the bottom of the wall will decrease.The worse the grade of surrounding rock is,the weaker the vibration response of cavern is and the greater the degree of deformation and damage is.(3)Taking the straight-wall-round vaulted cavern with good anti-explosion performance as the supporting object,the anti-explosion performance of lining and prestressed anchor cable for deep-buried underground cavern is studied.The design concept of anti-explosion supporting structure under static-dynamic load is clarified.The difference between the anti-explosion characteristics of lining and prestressed anchor cable is that the former is more conducive to limiting the vibration response of the cavern,while the latter is more conducive to limiting the deformation of the cavern.Through sensitivity analysis,furthermore,it is found that when the axial force 1000~4000k N of prestressed anchor cable and the thickness of lining are increased.The degree of reduction of surrounding rock deformation is 7.88%~11.85% and6.57%~9.40% respectively.And the vibration velocity is reduced by 11.23%~12.96% and16.07%~24.54% respectively.The dynamic response capacity of the support limited cavern will be weakened in a certain range.And under the combination of cavern excavation unloading and ground shock,only the prestressed anchor cable can work within the range of strength.So the prestressed anchor cable can be used as the support structure to undertake the unloading effect of cavern excavation.(4)We carry out a study for the anti-explosion performance of cavern with a combined support of prestressed anchor cable and lining.The results show that the support can take the respective advantages of the two kinds of the support under static-dynamic load.It can also be guaranteed to work within the range of strength,and the anti-explosion efficiency of the cavern has been improved.Then we analyze the influence of the characteristics from new kinds of composite lining combined with different materials on the cavern anti-explosion efficiency.The results show that,the impact resistance of EPS foam sandwich material is better than that of aluminum foam sandwich material because of smaller modulus.The protective effect of EPS sandwich material on the second lining structure is more obvious.Considering that the concrete support used in the internal side of composite lining is easy to crack at the foot of the wall and the vault,the “steel arch-EPS foam-concrete” composite lining support scheme is put forward on the basis of the research of EPS sandwich composite lining.The support efficiency is superior to concrete sandwich composite lining.And it also has the advantages of EPS foam with protection for second lining structure.So,it is an optimal support scheme.Our research provides a reference basis for the study of the deformation and failure mechanism of the underground cavern under the explosive ground impact load.That can be used as a valuable design scheme for the anti-explosion support design of the underground cavern as well.
Keywords/Search Tags:Explosive ground impact load, initial stress field, CDP model, foam material, sandwich support structure
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