Experimental Study On Mechanical Properties Of Lining Concrete In Urban Drainage Deep Tunnel Under The Coupling Action Of Surrounding Rock Pressure And Dynamic Water Pressure

The contradiction between the continuous advancement of urbanization and the lagging development of urban infrastructure has become increasingly prominent.Under the condition of frequent extreme weather,urban waterlogging and other urban diseases are common.Urban shallow drainage system is difficult to bear the huge urban runoff caused by extreme weather.Urban deep drainage tunnel system has gradually become the choice to solve the above contradictions.At present,the buried depth of urban deep drainage tunnel system which has been built and operated at home and abroad is generally more than 30 m.The tunnel in operation has long been subjected to the pressure of external surrounding rock and the disturbance of internal variable flow.The surrounding rock pressure causes the creep deformation of lining segment concrete,and the disturbance caused by dynamic water pressure will deteriorate the mechanical properties of lining segment concrete,thereby affecting the durability and safety of the tunnel.Therefore,it is necessary to study the mechanical properties of lining concrete of urban drainage deep tunnel.In this thesis,the lining segment concrete of tunnel in operation is taken as the research object,and the existing urban deep drainage tunnel system engineering at home and abroad is taken as the background.Combined with the regional precipitation law,the mechanical properties of lining segment concrete are experimentally studied.Tests include: natural curing state and saturated state of concrete samples conventional compression test;cyclic loading and unloading tests of concrete specimens in natural curing state and saturated state;creep disturbance test of saturated concrete specimen.The results are as follows:The conventional compression test of concrete shows that pore water causes large-scale cracking of coarse aggregate and cement slurry surface in the interface transition zone of the sample,which not only weakens the cohesion between the components of the concrete sample,but also reduces the internal friction angle of the sample.Finally,the compressive strength and elastic modulus of the water saturated sample are reduced.The results of cyclic loading and unloading tests show that the ultimate failure strength of saturated specimens after cyclic loading and unloading creep process increases and first increases and then decreases with the increase of the upper limit stress level.Under the same number of cycles,the loading and unloading elastic modulus of the specimen increased with the increase of the upper limit stress level;when the upper limit stress level is the same,the loading elastic modulus of the specimen gradually increases with the increase of cycles.External water pressure increases the deterioration of compressive strength and elastic modulus of saturated samples.Under the same cycle times,the damage caused by loading process is larger than that of unloading process.The damage after each cycle decreases with the increase of cycles.The unit volume strain energy of the specimen decreases with the increase of cycles,and the average strain energy at loading is larger than that at unloading.The plastic property absorbed by natural curing sample is more than that of saturated sample.Creep disturbance test shows that the axial deformation curve of saturated specimen under creep disturbance can be divided into stable stage and unstable stage.The development process of creep is changed by disturbance.The strain increment caused by initial disturbance decreases with the increase of confining pressure.Under the same disturbance,the strain increases with the increase of confining pressure,and the test life of the sample is shortened.When the disturbance is large,the creep acceleration stage of the strain duration curve of the specimen is very short.Compared with the strain caused by the initial disturbance,the axial strain of the subsequent samples does not always increase with the increase in the number of disturbance groups.