Study On Anti-explosion Performances Of Surrounding Rock And Lining Structure Of Shallow-buried Large-span Underground Cavern

In the face of rapidly updating precision-guided weapons in various countries,the protection of large-scale military equipment and important strategic materials has become increasingly prominent.At present,the underground protection engineering is developing in the direction of large-span and high-strength,and its anti-explosion performances have become a hot issue to be explored.In recent years,the research direction of many scholars mainly focuses on the anchored and unanchored small-span caverns,while the research on the anti-explosion performances of large-span underground caverns is still less.Based on the research experience of previous scholars,this thesis uses a combination of laboratory model tests and numerical simulation to study the anti-explosion performances of surrounding rock and lining structure of shallow-buried large-span underground cavern.The main research contents and conclusions are as follows:（1）Firstly,according to the basic physical and mechanical parameters of surround ing rock and lining structure（mass density,elastic modulus,Poisson’s ratio,compressive strength and tensile strength,etc.）and Froude similarity theory,the physical and mechanical parameters of surrounding rock and lining of two models were determined.Then,through the preparation of similar material specimens and the corresponding physical and mechanical properties tests,the quality ratio of similar materials of surrounding rock and lining is finally determined.（2）The large-scale three-dimensional model test bed was used to carry out anti-explosion model tests on two kinds of large-span caverns,and a total of four models were made.Thin film pressure sensors,acceleration sensors,displacement sensors,resistance strain gauges,dynamic signal acquisition instrument and high-speed dynamic analysis system were used to monitor the dynamic responses and failure patterns of surrounding rock and lining structure of the cavern.The test results show that under the same explosive charge,the peak compressive stress of the measuring points decreases gradually with the increase of the vertical distance from the explosion center,the peak acceleration of the measuring points of the vault lining is much greater than that of the bottom lining,the peak displacement of the measuring points decreases as the horizontal distance from the explosion center increases.With the increase of explosive charge,the peak values of all measuring points show an increasing trend.The strain of all measuring points of the four models is compressive strain,and the maximum peak strain appears at the arch foot.In the failure pattern of the surrounding rock,there are obvious collapse zones above the blasting holes of the four models,which are in the form of“C hinese character eight”,and the fragmentation materials in the collapse zones are large.With the increase of explosive charge,the area of the collapse zone increases significantly,and the number,width and depth of horizontal cracks increase.In the failure pattern of the cavern,no cracks appear in the model M1-1 and M2-1 caverns,but obvious longitudinal cracks appear in the vault and arch foot of the model M1-2 cavern,and slight longitudinal cracks appear in the vault of the model M2-2 cavern.（3）Through the spectrum analysis of the measured stress waves,it can be seen that the main energy of the stress waves of the 4 model measuring points is concentrated in the low frequency band.With the increase of the vertical distance from the explosion center,the main frequency domain of the stress wave becomes narrower and narrower,and the high-frequency components are more and more obviously filtered out,that is,the energy contained in the stress wave is decreasing.As the explosive charge increases,the main frequency domain of the stress waves at the measuring points become wider,and the high-frequency and low-frequency components become more abundant.As the explosion stress wave propagates to the cavern,the main remaining components are low-frequency components,and the low-frequency components are rich in high energy,so it can be judged that the damage of the model caverns is mainly the result of low-frequency stress wave.（4）FLAC^3D finite difference software is used to establish numerical calculation models,and the model material parameters are calibrated based on the laboratory test results.Based on the secondary verification of the test results by numerical simulation with reference to the test conditions,the numerical research of multiple conditions was further carried out.The numerical simulation results show that the model M1-5 and M2-5 caverns suffer serious instability failure under the peak explosion pressure of 50 MPa and 90 MPa,respectively.In other words,in the real working conditions,the caverns with section sizes of 40 m×12 m and24 m×7 m will suffer serious instability failure and basic loss of bearing capacity when they are attacked by weapons with explosive equivalents of about 741 kg and 1202 kg TNT,respectively,and penetration depth of 11 m,under the condition of 30 m burial depth.（5）According to the statistics of the plastic zone volume of the surrounding rock and lining structure of the caverns under the action of different peak explosion pressure,it can be seen that when the plastic zone volume of the lining structure of the model M1 and M2caverns increases to 19.47%and 23.10%of the total volume of the lining structure,respectively,serious instability failure will occur in two caverns.When the plastic zone volume ratio of lining structure is less than this value,two caverns can maintain certain stability.There are 116 pictures,31 tables and 123 references in this thesis.