| The pipe-curtain frozen-soil composite structure formed by the combination of pipe jacking and freezing method can provide good maintenance for the excavation construction of large-section tunnels,and is more and more used in the construction of tunnels crossing rivers.The freezing effect of the freezing pipes arranged in the jacking pipe during construction will be affected by construction parameters and surrounding environmental conditions,especially the influence of groundwater flow on the freezing process and effect is more obvious.For the tunnel engineering that crosses the river,the underground dynamic water that is consistent with the flow direction of the river interacts with the pipe curtain structure,especially the interaction process between the multiple jacking pipes on the top of the pipe-curtain permafrost composite structure and the underground dynamic water is more complicated.Moreover,the shape of the frozen wall formed by the frozen pipes in the horizontally arranged jacking pipes will also be affected by the crossing moving water.Considering the impact of crossing moving water,mastering the process and shape of the frozen soil formed outside the horizontal pipe jacking at the top of the pipe-curtain frozen soil composite structure,and obtaining the distribution characteristics of the temperature field in the frozen wall are the basis for determining the design parameters of the freezing project and judging the freezing effect during construction.First of all,relying on the freezing project of the underground excavation section of the Nanjing South Station Tunnel on the Ningwu Railway that passes through the Qinhuai New River Section,the influence of crossing moving water on the formation process and shape of the frozen wall was studied through numerical simulation,and a method for characterizing the difference in the shape of the upstream and downstream frozen walls was proposed.Based on the index of offset coefficient,the rule of mutual influence between underground dynamic water and frozen wall is obtained.Studies have shown that the horizontally arranged pipe curtain and the formed frozen soil can reduce the velocity of moving water from the initial 4m/d to 3.68m/d,and the downstream freezing effect of the horizontal pipe curtain is the best when the freezing ends.The outward expansion range of the frozen soil outside the horizontal pipe curtain presents the characteristics of first increasing and then decreasing along the lateral direction.The temperature distribution at the middle and downstream pipe curtain positions is relatively uniform,while the upstream position is most affected by the moving water,and the frozen wall is the largest during the freezing process.The offset factor appears when freezing 44 d.Then,based on the established finite element calculation model,the effects of factors such as steel pipe diameter,steel pipe spacing,moving water velocity,brine temperature,and filling different media on the freezing process of the horizontal pipe curtain were analyzed,and the formation characteristic point temperature,freezing The variation rules of wall thickness,temperature gradient and frozen wall deflection coefficient established the significance level of different influencing factors.The research results show that the increase of the diameter and spacing of jacking pipes will directly affect the range and temperature gradient of the frozen wall,while the expansion of the diameter of the frozen pipe will reduce the deflection coefficient of the frozen wall.The offset of the wall.When the flow rate of moving water exceeds5m/d,the outward development effect of the upstream permafrost is weak,and the reduction of brine temperature and the improvement of filling material performance will improve the development range of the outer frozen wall of the steel pipe and increase the degree of deflection of the frozen wall.Finally,according to the similarity criterion,a physical model test of the freezing engineering of the tunnel under the Nanjing South Railway Station tunnel passing through the Qinhuai New River section was designed and carried out,and the development process of the frozen wall during the freezing process of the pipe curtain under the influence of crossing moving water was studied.,analyzed the law of the influence of moving water on the temperature of characteristic points,the thickness of the frozen wall,and the temperature gradient of typical sections,and found that the position where the frozen soil expands the most outward is located between the four and five jacking pipes.The comparison between the experimental data of the physical model and the calculation results of the numerical simulation verifies the reliability of the numerical calculation model.The dissertation research obtained the distribution characteristics of the freezing temperature field of the horizontal pipe curtain affected by the crossing moving water,mastered the basic shape of the freezing wall formed outside the horizontally arranged pipe jacking,and established the influence law of different influencing factors on the temperature field distribution characteristics in the freezing wall,the research results can be used as the basis for determining the basic parameters in the freezing design,and can also be used as a reference for determining the location of the temperature measuring holes and judging the quality of the freezing wall during the freezing construction.There are 122 figures,19 tables,and 103 references in the thesis. |
