The Study About A Reform Method Of Artificial Freezing Cement Soil To Inhibit Frost Heave

With the rapid development of subway construction，various urgent engineering issueshave come out. To enhance the end foundation is a big issue when subway tunnels shield enterand exit during construction.Cement-soil foundation reinforcement and artificial freezingfoundation reinforcement are in common use interiorly，which both have pros and cons.Theformer is always going wrong in control of the groundwater seepage。Frost heaving and thawcaused by the latter easily has an effect on the surrounding environment.This paper aims at howto improve combing these two methods and learn from the other’s strong points and close thegap.The paper puts forward reinforcement scheme and experimental scheme to measure andanalyse on artificial horizontal freezing engineering、freeze temperature field and groundfreezing，based on the lab test results and shield Lauching project of crossing-river tunnelconstruction of Nanjing Subway Line10.Then, ADINA, the large finite element analysissoftware was used to simulate the freezing temperature field and frost heave displacement fieldof the soil-cement before and after reinforcement in this engineering. Combined with themeasured data, the validity of the numerical simulation method was tested and the feasibility ofthe technology to inhibit frost heave with freezing soil-cement was studied. At last, ADINA wasused to research the specific parameters to put forward a complete construction method.Main conclusions are as follows:Strengthening and monitoring scheme was discussed and proposed to have a field researchon the freezing reinforcement project of the river-across tunnel which is at the eastern end ofthe Nan Jing subway line10, at the meantime, complete freezing temperature field and surfacefrost heave deformation were acquired and analysed. The study found that the back of thebehind frozen pipe was the most unfavorable place in frozen curtain development, after makinga judgment on the development form of freezing curtain.Numerical analysis found that: Cement-soil reinforcement method slightly decreased theextending speed and the final range of the frozen curtain, but it had no adverse effect onconstruction safety. The development speed of the frozen curtain in the front soil body washigher than that in the back soil body of frozen zone, which coincided with the conclusion thatthe back of the last row freezing tube was the most unfavourable position of the development ofthe frozen wall, which was made after analysis about the measured data according to thefreezing temperature field.After exploring the mechanism on the disturbance of artificial vertical frozen soil, thestudy found that if the last row of frozen tube was set as a boundry, the vertical deformation of soil frost heave area was divided into the front frozen area and rear elastic-plastic deformationarea and the two regional soil deformation characteristics were summarized. Cement soil frostheave susceptibility decreased significantly after reinforcement, the ability of resistance toelastic and plastic deformation was improved, and the vertical deformation of soil had smallerrange and, shallower depth. Soil-cement reinforcement had an obvious effect on inhibiting frostheave effect.After numerical analysis of artificial freezing design parameters and considering projectrequirements and related method, the best number of the frozen pipe group on the side of tunnelportal was4, the optimal distance from the frozen pipe to wall was40cm, and best row spacingof frozen pipe was0.8m~1.0m. Sand cement reinforcement of cement mixing ratio should be10%cement mixing ratio and clay reinforcement of cement mixing ratio should reach10%~20.This study proposed an artificial freezing cement reform method to seal water and amethod to inhibit frost heave. A lot of aspects, including technical background, constructionsteps and beneficial effects were improved.