| The paper took the the construction of Dayong tunnel of Anliu Railway as the research background,finite element simulation and field measurement were combined to study the mechanical characteristics and deformation law of the tunnel through filled clay karst cave.From the aspects of support structure and displacement,stress state and plastic zone change of surrounding rock,the common construction mechanical behaviour of karst tunnel treatment scheme were compared and analyzed,and a safe construction technology suitable for tunnel through filled clay karst cave was formed.The main research work and achievements were as follows:(1)In view of the stability problem of the tunnel face when the tunnel through filled clay karst cave,the numerical simulation analysis method was used to study the stress of structural unit,extrusion deformation of tunnel face,stress and deformation characteristics of supporting structure when the pipe shed and small pipe supporting prereinforcement measures were adopted.Based on numerical simulation analysis,the prereinforcement measure for pipe shed reinforcement were determined.(2)Aiming at the problem of initial support cracking and large deformation of tunnel through filled clay karst cave,a refined numerical analysis model was constructed,the stress and displacement changes of the surrounding rock-support structure system caused by three initial support reinforcement schemes of the “anchor cable + ?76mm feet-lock pipe”,“rotary jet pile” and “rotary jet pile + horizontal anchor cable” were studied in detail.Results showed that the minimum principal stress caused by “rotary jet pile + horizontal anchor cable” was the smallest,the range of tensile failure of the supporting structure was the smallest,and the effect of controlling the deformation instability of the cave was better,and the shear strain of filled cave was the smallest.Overall consideration,it was recommended to use the “rotary jet pile + horizontal anchor cable” initial support reinforcement program for the construction.The field monitoring analysis of the tracking construction verified the economic,rational and feasible of the recommended scheme.(3)To solve the problem of operation safety of the tunnel through clay karst cave,the vibration load function was used to calculate the train vibration load to approximate the vibration of high-speed train.Through the time-history analysis(non-linear integration method),the displacement,vibration velocity,additional stress of the lining floor and the string-beaded caves displacement caused by the three tunnel bottom reinforcement schemes of “sleeve valve tube”,“sleeve valve tube + rotary jet pile” and “pile raft structure” were compared.The results showed that the additional tension and compressive stress caused by the “sleeve valve tube + jet grouting pile” and “pile raft structure” tunnel bottom reinforcement scheme were small,the lining structure had a large safety reserve,less damage under tension and compression,the displacement and vibration velocity met the specification requirements.According to the field construction environment,it was determined that the string-beaded cave area at the bottom of the tunnel was reinforced with the “sleeve valve + rotary jetting pile”,and the non-stringbeaded cave area at the tunnel bottom was reinforced with the “pile raft structure”.Light aggregate backfilling and drainage treatment should be adopted for the upper cavity karst cave.For the treatment of the bottom string-beaded cave,the No.1 karst cave should be strengthened to ensure the stability.No.2,No.3,and No.4 cavities didn't need to be treated or filled with grouting. |
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