Research On The Interactions Of Swelling Rock And Subway Shield Segments In Nanning

There are many swelling rock areas will be across by Nanning rail transit, which is mainly consist of the tertiary mudstone. This tertiary mudstone has the characteristics of short digenetic time, poor degree of consolidation and significantly in water swelling and water loss shrinking. The swell-shrink characteristics of the swelling rock will influence on the internal force and deformation of the shield segment. The research on the interaction of the swelling rock with the shield segments become a new engineering problem, which is worth in-depth study. Taking the swelling rock area across in Nanning rail transit line1as the target, through data collecting and comprehensive analyzing, using laboratory test, numerical calculation and comprehensive research methods, large-scale physical model test, the interaction research on the swelling rock and the subway tunnel structure was carried out.Through site investigation and data compilation, analyzes the engineering properties of the tertiary mudstone in Nanning, reveals the distribution and the structure characteristics of the swelling tertiary mudstone in Nanning, and the physical index, mechanical index and the swelling feature index were analyzed. Based on the regional geological conditions, the covering soil characteristics of the shield tunnel and hydrogeological conditions of Nanning rail transit line1where across the swelling rock area, the strata combination characteristics of swelling rock section were studied and the rock combination model was put forward. Through mechanism test, the calendar features of the swelling deformation and the expansion of swelling force influencing factors and their relationships were studied. Consideration both the dry density and the initial moisture content of double factors impact the swelling force, got the relationship between them:P(?,?b)=-265.012?d+21.453?+34.583e(23?b-01?)-142.294Then the experiment research on micro expansive force under the condition of deformation were taken, proposed the change law of the expansion forces as the micro deformation, that the ratio of the expansion force of micro deformation to the corresponding zero deformation lessen as the micro deformation rate increase. The equation of the ratio of the expansive force and the micro deformation rate was obtained as follow:P/P0(?)=C·eD·?, C, D for fitting constants. On the basis of this analysis, the representative rock combination model for load-structure method, and considering the applying range of the influence of shield segments expansive rock, the expansive force under the condition of the segment internal force and deformation law were studied. Research shows that the class ? as the most adverse combination model, which the bottom of the shield segment were swelling rock, the upper of non-swelling rock. The results show that the moment and deformation of the segment change along with the thickness of the bottom swelling rock, which increases at first then decreases with the angle ? increasing, When the contact angel ? between expansion force and segment equal45°, positive bending moment was max, the maximum negative bending moment and maximum deformation happened When the contact angel ? equal30°Considering expansion force as the contact deformation and the attenuation correction model for numerical calculation, the improved calculation model can more accurately reflect the expansive force influence law of internal force and deformation of the segments after considering expansion force reduction value of internal force and deformation were reduced.Based on the special and complex properties of the tertiary mudstone in Nanning, on the basis of both numerical and physical model research, the problem about how to consider the effect of swelling rock surrounding the shield in the design were solved. The swelling force applied range and exerting mode for shield segments of the swelling rock surrounding were given, and the design and calculation model was optimized which can be more accurately reflect the actual stress of the segment. The results could be used in Nanning where the swelling rock section of subway construction to provide theoretical guidance and may benefit to the subway construction for both the domestic and foreign similar swelling rock areas for reference.