Numerical Simulation And Physical Experiment Of Submerged Floating Tunnel Key Parameters Under Wave-current Coupling

With the development and practice of cross-sea tunnel engineering,traditional tunneling methods are facing enormous challenges in crossing deep-sea and trench-developed straits.Therefore,combined construction methods such as "drilling blasting and immersion method","shield and suspension method" or "shield and immersion method" may be adopted in future projects,especially in the case of Submerged floating tunnel.Especially,the Submerged floating tunnel which is a special ocean traffic structure that maintains dynamic balance by buoyancy and anchor tension,will emerge as the times require.At present.There are still many theoretical and engineering problems to overcome in the application of SFT.Supported by the Ministry of Transport’s project "Preliminary Study on Key Technologies of Submerged floating tunnel(2013318740050)",by means of theoretical analysis,numerical simulation and physical test,the SFT section type,cooperative anchorage parameters and suspension depth are studied in this paper.(1)Two physical model test systems of SFT are designed.One is a wave flume test system based on pressure characteristics,and the other is a wave-current coupled tank test system.The pool test system includes the design of similar simulation and data acquisition system.Among them,similar simulation design includes wave,current,SFT pipe and anchor cable.The design of data acquisition system includes pressure acquisition system,anchor tension acquisition system and pipeline motion displacement acquisition system.(2)With the increase of wave height and the decrease of wave period,the surface pressure amplitude and pressure difference of the three sections increase correspondingly,and the wave force on the three sections is estimated by the pressure distribution of the SFT section.From the uniformity of pressure distribution,the circle is the best,from the absolute value of pressure amplitude,the circle is the largest,and from the pressure difference,the ellipse is the largest.When the water depth is large,the circular section with uniform pressure distribution can be selected,the elliptical section with better hydraulic performance can be selected for medium water depth,and the elliptical section can be selected by controlling the pre-tension of anchor cable when the water depth is medium to large.When the water depth is small,the octagonal section with the optimal section layout space can be selected.(3)The variation rule of SFT collaborative anchorage parameters under different anchor spacing is obtained.Buoyancy weight ratio and cable inclination have obvious effects on the relaxation of SFT cable.Buoyancy weight ratio determines the degree of influence of cable inclination.When the distance between anchor cables is 40 m,the influence range of inclination angle is mainly around 10 degrees when the Buoyancy weight ratio is large.When the Buoyancy weight ratio decreases,the influence range of the inclination angle of the anchor cable increases gradually.When the Buoyancy weight ratio is small to 1.1,all the inclination angles of anchor cables will be relaxed.Finally,the influence diagrams of the parameters of the cooperative anchorage with the distance of 30 m and 60 m are given respectively.(4)Different structural responses of SFT under different wave-current loads are compared,and a method for analyzing the appropriate suspended depth of SFT is proposed.Comparing the effects of different wave and current loads on the SFT pipe section,the maximum test value of SFT pressure under wave-current coupling is smaller than under pure wave action.The cable tension of SFT under wave-current coupling is greater than pure wave,but less than linear superposition of pure wave and pure current.The maximum test values of transverse displacement,longitudinal displacement and heave displacement of pipe section under wave-current coupling are always smaller than those under pure wave interaction.The extreme pressure difference,the extreme tension difference of anchor cables and the maximum displacement of pipeline segment are taken as the control indexes of structural safety and driving comfort.The regression function of the above control indexes is obtained by linear regression method,and the recommended suspension water depth corresponding to the specific control index values is obtained.It provides a reference method for the analysis of reasonable buried depth of SFT under different wave and current conditions,and gives the recommended table of suspended depth corresponding to different control indexes.(5)Based on the above research results,we discussed the preliminary SFT project scheme of Qiongzhou Strait,which provided a new solution for the traffic across the deep sea.We did some theoretical support work to conceive SFT from engineering to engineering reality.The layout scheme of vertical section,recommended minimum depth of water,layout pattern of cross section,floating weight ratio of structural anchorage system and inclination angle of anchor cable of Qiongzhou Strait are given.