Study On Deformation Control Of Three-hole Small Net Distance Tunnel Passing Through Water Tank Culvert

With the rapid development of urbanization in China,there are more and more cases of construction of underground rail transit.In the construction of rail transit projects,more and more new tunnels pass through the existing underground structures due to the complex construction environment,crisscross lines and different construction sequences.In order to alleviate the pressure of traffic,more three hole and more small clear distance tunnels will be built.However,due to the complexity and particularity of the form of three hole small clear distance tunnel,the influence between tunnels and in the process of tunnel underpass is great.The tunnel construction will inevitably cause the disturbance of the surrounding environment and itself,and then affect the normal use and safety of the three hole tunnel.Therefore,it is of great significance to study the mechanical response and deformation control during the construction of the existing underground structure under the three hole small clear distance tunnel.In this paper,based on the construction project of passing through the water tank culvert near the three hole small clear distance tunnel in R3 line of Jinan metro,the control differential equation of Timoshenko beam of the water tank culvert on the Winkler elastic foundation is established and solved by the two-stage analysis method.The maximum allowable deflection of the water tank culvert is obtained by the knowledge of material mechanics,and the deformation control index of the water tank culvert is proposed.Midas /GTS software is used to study the influence of different construction procedures of three hole tunnel and the distance h between the three hole tunnel and the water culvert on the deformation of the water culvert,and to discuss whether reinforcement is needed in the construction process.(1)The governing differential equation of Timoshenko beam is obtained by the energy method,and the differential equation is derived.The bending moment and shear force acting on the water tank culvert can be further obtained.Under the joint action of bending moment and shear force,the deflection of the beam is the total deflection of the beam,in which the bending moment is the main factor.In general,only the influence of bending moment is considered.Timoshenko beam theory is equivalent to Euler Bernoulli beam theory under thecondition of no shear force.(2)Based on the knowledge of material mechanics,the allowable maximum deflection of the culvert is calculated by simplifying the culvert to a simply supported beam under uniform load.The final calculation shows that the maximum allowable deflection of the beam structure is related to the ultimate tensile strain of the material,the calculated height and span length of the beam structure.The maximum allowable deflection is inversely proportional to the span length of the beam and inversely proportional to the calculated height of the beam.(3)The three-dimensional finite element method is used to calculate and analyze the actual project,study the deformation of three hole tunnel and its influence on the rock stress around the tunnel in different construction sequence,compare the different results,and select the optimal construction scheme.(4)The ratio of the distance h between the new three hole tunnel and the culvert through the water tank to the net distance b between the tunnels,i.e.the depth diameter ratio H / B is0.4,0.7,1.0 and 1.5 respectively.The influence of four kinds of Underpass construction conditions on the settlement displacement of the culvert through the water tank is analyzed.When the ratio of depth to diameter is less than one number,the effect of three hole tunnel on the settlement of water tank culvert tends to the case of single hole tunnel.When the depth to diameter ratio is less than a certain range,the settlement of the culvert increases with the increase of the spacing;when the depth to diameter ratio is more than a certain range,the settlement of the culvert decreases with the increase of the spacing h,which is similar to the deformation of the double hole tunnel,which is the result of the joint action of plastic deformation and superposition.(5)During the construction of the three hole tunnel,when the left line shield tunnel is completed,the settlement curve of the culvert passing through the water tank conforms to peck The settlement value assumed by the formula and its distribution characteristics show the basic distribution form of "single peak(U type)".When the right line shield tunnel construction is completed,the settlement curve of water tank culvert presents the distribution form of "double peak(W type)" because the clear distance between the two tunnels is larger than the diameter of the tunnel.When the mining method tunnel is constructed,the settlement of each tunnel can not be ignored under the condition of close construction The settlementcurve of the three hole tunnel presents a "double W" distribution pattern,and the settlement curve of the culvert passing through the water tank conforms to the law of superposition of the multi hole tunnel during the construction of the three hole tunnel.(6)(6)After the reinforcement of the culvert,the deformation control effect is obvious.The control effect is grouting + large pipe shed reinforcement > grouting reinforcement >large pipe shed reinforcement > no reinforcement measures.The grouting + large pipe shed reinforcement measures can control the deformation of the culvert within the allowable range.(7)In order to master the deformation trend of the culvert,the settlement of the tunnel crown and the ground surface was monitored,and the culvert was analyzed indirectly.The monitoring data and the simulation data can confirm each other.In the simulation process,the deformation of the culvert meets the requirements,and the simulation results can better reflect the project The real situation of Cheng.