Study On Heat Transfer Characteristics And Thermal Effect Of Tunnel Surrounding Rock In Swelling Rock Area

As the swelling rocks are widely distributing in the Nanning basin,the construction of the subway will surely pass through the swelling rock strata.As heat continuously generated in the swelling surrounding rock during the subway operation,the characteristics of the swelling rock surrounding rock will change.The components of the swelling rock change during the long-term change of temperature,and the material properties of the rock change accordingly.Base on this,the deformation,strength properties and water physical properties of the swelling rock are affected,the original internal and external forces increase or decrease,and there will be the heat and moisture transfer and volume changes of the swelling rock also can be observed.Based on the "thermal sensitivity" of swelling rock,it is great significance to study the heat transfer law and thermal effect of the expanded surrounding rock of subway.This paper study the thermophysical problem of the swelling surrounding rock which the metro tunnel through in Nanning,by using engineering field investigation,data collection and analysis,indoor mechanism test,model test and numerical simulation.The thermophysical index and the physical mechanics index of the tertiary mudstone of the 56 stations and intervals of Nanning metro line 1 and line 2 were statistically analyzing,and the sensitivity between the each factor sequence and other physical mechanical parameters were analyzed using the grey correlation analysis method.Comparison between remodeling swelling rock and original swelling rock by experiment,the result show that,the remodeling soil granule with a diameter of 0.25mm or less than 0.5mm can replace the original sample in the condition of the experiment heat transfer characteristic,expansion force test and triaxial test,the remodeling soil granule with a diameter of 1mm or less than 2mm can replace the original sample in the condition of the no load expansion test.Based on this,a series of indoor experiments on remodeling swelling rock were carried out to exploring the influence on the thermal conductivities of swelling rocks of some factors such as the ratio of three phases,the dry density,the moisture content,the temperature,and the expansion ratios.The test results show that the thermal conductivity of the swelling rock increase as the rise of the temperature,the moisture content and the dry density,and the decrease of deformation of the swelling rock after swelling.Moreover,two relationships were established by quantitative analysis of experimental data,one between the moisture,the dry density and the thermal conductivity of the swelling rock and the other between the temperature and the thermal conductivity of the swelling rock.To reveal the thermal effect of swelling rock expansibility and strength,the experiment of unloaded expansion rate,expansive force test and triaxial test were carried out in different temperature conditions.The results show that the expansion ratio and expansive force of the swelling rock increase with the rising of the temperature.Especially,there is a good correlation between swelling force and temperature and the relationship between them can be expressed with P=AeBt by fitting the test results.Another important finding is that the cohesion force of the swelling rock increase with the rising of temperature when the moisture content sample is low showing "thermos-hardening";while it shows the "thermal softening"when the moisture content of the swelling rock sample is high because the cohesion force decrease with the rising of temperature.According to the actual working condition of Nanning subway,the influence of the segment lining and surrounding rock affected by the heat generated by the subway operation are investigated by both laboratory tests and and numerical simulation.The heat transfer law of the swelling rock and the internal force and deformation characteristics of the shield affected by the thermal effect of the swelling rock are analyzed in different working conditions by both two methods and comparison between then shows greet agreement.The study shows that the temperature of the surrounding rock tends to be stable after 2.37years?5years operation,and the surrounding rock within the area of 4 times the diameter of the tunnel(4D)are affected.Moreover,the expansion force of tunnel surrounding rock increase with the increase of temperature,showing obvious thermal effect.The results of this paper can provide a reference for the subway design and construction in practical engineering,as well as the heat related issues of the swelling rock in the subway operation.