Numerical Simulation And Analysis On Frost-heave Capacity Of Tunnel Surrounding Rock With The Pre-reinforcement Technique Of Combined Pipe-roofing And Freezing

The 21st century is the era of underground space. With the change of infrastructure construction strategy, China has transferred the main part of construction from overground to underground. Each province and city set off a wave of building underground tunnel, especially in the littoral developed area. However, the soil of littoral area is ill-suited for construction. The water content of the soil is high and the bearing capacity is low. In order to work out the construction item of this kind of soil, the artificial horizontal freezing technique comes into people’s eyes. The artificial horizontal freezing method means putting the freezing pipe into the soil along the periphery predetermine position of excavation surface of the tunnel, then let saline water in and proceed heat exchange with the soil which makes the water in soil interstice is frozen into ice around the freezing pipe and turns into frozen soil column, finally the frozen soil column enclosed and turn into frozen wall. As the pre-reinforcement technology of tunnel construction, the artificial horizontal freezing method has its obvious advantages, such as reliable sealing, strong applicability and innocuousness for environment. But the artificial horizontal freezing method still has limitation, that is, it accompanies frost heave phenomenon and damages the buried pipeline and surface buildings.This thesis studies the artificial horizontal freezing method in the project background of excavation section of Gongbei tunnel connecting Zhuhai in HZMB project. First of all, the author consults a large number of document information and investigation of related subject, then realizes the formation rules of frozen soil in freezing construction and the mechanism of the frost heave phenomenon. With the methods of theoretical analysis and ABAQUS numerical simulation, this thesis researches the variation of soil temperature field in the process of active freezing with the combination of artificial freezing method and pipe curtain method. Through comparing and analyzing the numerical simulation results of three kinds of freezing schemes(single-pipe freezing,double-pipes freezing and difform pipes delayed-opening freezing), this research obtains the best freezing scheme. Finally, the author puts forward some related advises to the key technology of practical engineering construction.As a result, the research shows that the frozen area of single freezing pipe frozen is basically a circular area circle with freezing pipe cross section. Plurality pipe freezing indicates that the round frozen columns formed by each freezing pipe will gradually merge and form a frozen wall with water stopping effect. In variety freezing scheme, opening the circular pipe and the shaped freezing pipe at the same time is beneficial to improve the efficiency of freezing, shorten the freezing time and makes the surface frost heave displacement smaller.