| Large deformation in soft rock tunnel is always an important issue of tunnel engineering, especially in terms of deformation mechanism of soft rock tunnel. Due to surrounding rock’s deformation law and deformation mechanisms are unable to be mastered accurately via conventional theoretical analysis and empirical judgments, for which the effective control measures are put forward.In this paper, based on Xingyuan Tunnel of Capacity Expansion Revamping Project of Mudanjiang-Suifenhe Section of Haerbin-Suifenhe Railway, with large deformation of soft rock tunnel as background, large deformation mechanism of this tunnel was analyzed through combining stress, deformation’s monitoring measurement, theoretical analysis and finite element method. Besides, the optimacl control measures of deformation are selected by comparative analysis of numerical simulation method. Finally, catastrophe theory was used to analysis the limit displacement of tunnel during construction, and the three-level management mechanism which is generally used in engineering was used to classify control benchmark of tunnel surrounding rock’s deformation in different depth. The main results of this paper are as follows:The interactive relationship and characteristics between deformation and supporting force of Xingyuan Tunnel are analyzed in light of the site-monitored data. The result manifests that surrounding rock deformation lasts for a long time and embraces strong rheological property. Besides, the deformation of surrounding rock and the forces of supporting structures are obviously asymmetry under the influence of weak intercalation, strike and direction of rock stratum.It turned out to be that large deformation of Xingyuan Tunnel belongs to the lithological control type of surrounding rock after analyzing site-monitored data as well as engineering geological data. Stratigraphic lithological property, high stress, weak intercalation and groundwater are main factors triggering large deformation of surrounding rock, whose mechanics lies in the common influence of soft rock’s plastic flow under high geo-stress, surrounding rock’s bending deformation and layer’s weakness.According to the results of analyzing soft rock deformation mechanism, well-focused measures for controlling deformation have been put forward, and every control measure was screened through finite element method including different step length and height, excavating footage, locking anchor pipe as well as forms of vertical connections. At last, the optimal measures of deformation control were worked out by comparison and selection, that is, this tunnel was suggested to be excavated with step length of 5 m, footage of 0.5 m, step height of 3.5 m, 30°inclined anchor pipe used in top bench, 15°inclined anchor pipe used in middle bench and 14#U-bar for longitudinal connection.The plastic strain around tunnel at the diverse stress release rate have been calculated respectively by using cusp catastrophe theory. Then the catastrophe point of plastic strain was spotted via criterion of, so that stress release rate in corresponding to the catastrophe of surrounding rock deformation could be figured out, which is the limit state of surrounding rock deformation. The calculations show that surrounding rock became unstable suddenly and reached plastic rheological stage when the stress release rate hit 70%, and reached plastic development stage when the stress release rate ranged between 45% and 70%, less than which, surrounding rock was still in elastic stage.Based on 70% stress release rate, the calculation result of limit displacement, deformation control benchmarks of surrounding rock were graded on the basis of Three-level Management System which is commonly used in the field of engineering and deformation control benchmark of surrounding rock were brought up for different depths incccluding 50 m, 100 m, 150 m. |
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