Study on the characteristics of surface thaw settlement of subway tunnel reinforced by grouting-freezing combined construction method
Artificial freezing method and grouting reinforcement method are two commonly used methods in sub-way tunnel construction. However,in the process of subway tunnel construction,if a complex bad geology with high water content,low soil strength and high compressibility is encountered,a single construction method sometimes cannot achieve the expected effect. Some experts and scholars have proposed to combine the two con-struction methods to reinforce the soil by grouting first and then freezing for complex strata. However,there is a lack of theoretical research and engineering experience in the field of subway tunnel construction. Based on this,this paper relies on a turn-back line tunnel project of Guangzhou Metro Line 3,and adopts the research method of numerical simulation. The thermal parameters and mechanical parameters measured in the laboratory test are substituted into the finite element numerical analysis software. Based on the basic theory of hydrothermal cou-pling,a two-dimensional finite element model is established,and the reliability of the model is verified by the measured data of the project. The development of the thaw settlement temperature field in the actual construction process of the subway tunnel is analyzed,and the development law of the surface thaw settlement displacement field is obtained,and then the best construction scheme to suppress the surface thaw settlement displacement is obtained,the main conclusions of this paper are as follows:The development of natural thawing freeze-thaw set-tlement displacement field gradually changes with the passage of natural thawing time. In the early stage of natu-ral thawing,the soil began to gradually thaw. At this time,the maximum vertical displacement of thaw settle-ment is located on both sides of the central line above the tunnel,while the maximum displacement of soil thaw settlement below the tunnel is-39 mm,which is located below the waist of both sides of the tunnel. This dis-placement is much smaller than the thaw displacement above the tunnel. After 200 days of natural thawing,the growth rate of surface thaw displacement has slowed down. At the end of natural thawing,the maximum thaw settlement displacement of soil reached 340 mm,especially on both sides of the surface. The surface thaw settle-ment displacement gradually decreases with the increase of the grouting radius,but the effect of continuously in-creasing the grouting radius on the surface thaw settlement decreases sharply after the grouting radius exceeds 4 m,and when the grouting radius exceeds 5 m,the surface vertical thaw settlement displacement almost does not change with the increase of the grouting radius. Therefore,the grouting radius between 4～5 m has the best con-trol effect on thaw settlement. The incorporation of cement is beneficial to improve the surface thaw settlement phenomenon. When the cement content exceeds 12％,the effect of cement on improving the surface thaw settle-ment displacement is gradually weakened. Considering the economic and environmental effects,when the grout-ing-freezing combined reinforcement method is adopted for this project,the cement content is set to 12％,which is the most reasonable for the control of the vertical thaw settlement displacement of the surface. When the pre-grouting-freezing combined reinforcement is adopted in this project,12％ cement content is selected,and the grouting radius is selected as 4～5 m,which can ensure that the project has high safety and economy. Compared with the original construction scheme,the surface thaw settlement can be reduced by 71％. The research shows that the natural thawing temperature field is divided into three stages rapid thawing,phase change stage and sta-ble temperature rise. In the early stage of natural thawing,the soil is in the stage of rapid thawing,and the tem-perature difference between different positions in the soil is large. Then,with the passage of time,the average temperature of the frozen curtain continues to rise to-2 ℃. At this time,the frozen soil curtain enters the stage of ice-water phase change. At the end of the natural thawing period,the soil enters the stage of stable tempera-ture rise,and the positive temperature is basically restored,and the pore ice in the soil is converted into liquid water.
combined construction methodthaw settlementcement contentgrouting radiusnumerical simulationsandy clay
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维普
