Research On Pressure Distribution Characteristics Of Surrounding Rock Of Ventilation Shaft Of Tiantaishan Tunnel In Qinling Mountains

With the rapid development of highway tunnel,tunnel ventilation shaft,as its auxiliary structure,is advancing towards the deep direction.The distribution of the surrounding rock pressure of the shaft is a very important parameter for the design and construction of the ventilation shaft,and it is very important for the overall safety,rationality and economy of the shaft project.Shaft surrounding rock pressure,however,still used design specification of vertical shaft of coal mine in our country,in the case of deep,need to increase the wall thickness in response to the horizontal lateral impact of stress on the shaft,and the actual engineering construction and use process still did not use normal,from the point of view of both at home and abroad related research existing shaft confining pressure is contrary to the actual distribution form.In order to make the shaft wall rock stress distribution tends to be reasonable,based on the engineering background of qinling are green 2 # tunnel ventilation shaft,according to the measured data,through theoretical analysis,experiment research and numerical simulation of 2 # ventilation shaft surrounding rock stress distribution and the stability of shaft wall rock and supporting structure has carried on the systematic study.The main research contents and results are as follows:(1)Through the field measured data,it is found that the shaft side pressure will increase with the increase of depth,but the increase rate will become smaller and smaller,and finally tend to a stable value.Through theoretical analysis and comparison,combined with model test,the limitation of the current calculation formula of shaft ground pressure is verified again,and a more suitable calculation method of shaft surrounding rock pressure is put forward.that is,the surrounding rock pressure of the shallow rock and soil mass of the shaft is calculated by Bereztsev’s theory of active earth pressure of conical retaining wall,and the surrounding rock pressure of deep rock and soil layer is calculated by the theory of sandwich wall.That is,the spatial shape of the sliding body of the soil layer near the shaft is a hollow cone-cylinder.(1)Firstly,through theoretical analysis methods,it is studied that in the shallow soil layer,the loose and cohesive force of the rock is small,and the shear resistance around the sliding soil is small,and the soil may slide along the slip surface at the angle of intersection with the horizontal plane;However,in the deep part,the cohesive force of the soil layer is greater,and the shear resistance around the sliding body is also increasing.Only the soil near the shaft can enter the limit equilibrium state,so the sliding body is basically a cylindrical shape.That is,the spatial shape of the soil sliding body near the shaft shaft is a hollow cone-cylinder.(2)Through density test,uniaxial compression test and direct shear test,various mechanical properties such as bulk density,elastic modulus of compressive strength,cohesion and internal friction angle of granite are obtained.On this basis,the similarity ratio of this test is determined by using cement gypsum as cementing agent,barite powder and quartz sand as aggregate,and borax as additive.The similar material of surrounding rock is made up of cement gypsum as cementing agent,barite powder and quartz sand as aggregate,borax as additive,etc.on the basis of this,the similarity ratio of this test is determined by using cement gypsum as cementing agent,barite powder and quartz sand as aggregate and borax as additive.And the proportion test of the similar material in which the reinforced concrete structure layer is the supporting structure,and the prepared material has a good match with the field material.(3)In order to test the distribution characteristics of shaft surrounding rock pressure and restore the real stress state of the site,the shaft surrounding rock loading equipment was specially invented.The vertical force is provided by the Jack and the load sensor is recorded in real time;the confining pressure is uniformly arranged around the surrounding rock through the high-pressure airbag and recorded in real time by the precision pressure gauge after stabilizing the pressure.The miniature earth pressure box is uniformly buried in three layers around the shaft through the strain gauge to collect data,and then the pressure distribution characteristics of the ventilation shaft of Qinling Tiantaishan tunnel are studied by controlling the lateral pressure coefficient.comparative analysis and test results show that the shaft side pressure will increase with the increase of depth,but the increase is getting smaller and smaller,and shows an obvious non-linear relationship.(4)The construction process is simulated,and the stress of shaft wall and surrounding rock is calculated and analyzed by using Midas/GTS finite element numerical simulation software and stratum-structure method.The changes of stress and displacement of shaft surrounding rock are described according to the facts.The results show that the variation of surrounding rock pressure of tunnel shaft with depth also increases nonlinearly,but the increasing rate decreases gradually and finally tends to be stable.The paper has 90 figures,17 tables and 63 references.