| The new method of combining pipe roof method with artificial ground freezing method is adopted at the port section of Gongbei tunnel of Hong Kong-Zhuhai-Macao Bridge,namely "freeze-sealing pipe roof method".During the freeze-sealing pipe roof construction of the Gongbei tunnel,if the frost heaving and thawing settlement of the ground is not effectively controlled,it will inevitably have a bad impact on the surrounding environment of the tunnel.For this reason,this paper takes the freeze-sealing pipe roof construction project of Gongbei Tunnel as the research object,and uses the combination of laboratory test and numerical simulation to study the ground frost heave and thaw settlement law during the construction period of the shallow-buried large-section tunnel freeze-sealing pipe roof method.On this basis,the control technology of frost heave and thaw settlement is proposed.The main research contents and results of this paper are as follows:(1)The laboratory tests were carried out to test the thermophysical and mechanical properties of artificial frozen soil.The specific heat,freezing temperature,thermal conductivity and uniaxial compressive strength of frozen soil and thawed soil were obtained.Especially,the frost heave rate and thaw settlement coefficient of different soil layers are determined,which provide basic parameters for numerical simulation of frost heave and thaw settlement.(2)Considering the orthotropic deformation characteristics of frozen soil,the formation process of frozen soil curtain and the variation law of frost heave in the ground during the freeze-sealing pipe roof construction of Gongbei tunnel are predicted by thermo-mechanical coupled numerical simulation method.The results show that during the tunnel freezing period,the frost heave displacement of the ground at the top center of the tunnel is relatively large.After 90 days of active freezing,the maximum ground frost heave displacement is 164.47 mm and the maximum surface heave is 154.6 mm,which results in large ground frost heave phenomenon.Therefore,it is necessary to take appropriate measures to control frost heave.(3)The thawing process of frozen soil curtain and the variation law of thawing settlement in the ground during the freeze-sealing pipe roof construction of Gongbei tunnel are predicted by thermo-mechanical coupled numerical simulation method.The results show that during the natural thawing period of the tunnel,the settlement of the soil layer at the top of the tunnel is obvious.After the frozen curtain is completely thawed,the maximum settlement of the ground is-69.53 mm,and the maximum settlement of the surface is-63 mm.Therefore,it is necessary to take appropriate measures to control thawing settlement.(4)In view of the large frost heaving and thawing settlement phenomenon in the ground of the Gongbei tunnel during the freeze-sealing pipe roof construction period,to this end,the comprehensive control technology of ground layer frost heaving,such as soil grouting improvement,salt water flow control,salt water temperature control,limit tube regulation and special-shaped freezing tube partition switch control,is proposed to reduce the frost heaving of the ground.According to the melting rate of the frozen soil curtain and the influence of the settlement on the surface and the tunnel,the method,time and parameters of the thaw settlement grouting were determined,and the technical measures of the thaw settlement grouting of the ground were proposed.The research results in this paper can provide reference for the control of ground frost heave and thaw settlement during the freeze-sealing pipe roof construction period of shallow large cross-section tunnel under similar conditions.Figure[41]table[18]reference[81]... |
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