| The Yinxi high speed railway encountered soft plastic loess when passing through Dongzhiyuan of Gansu Province.Soft plastic loess is Q2 loess with special engineering properties.It has high water content,high saturation,low strength and is in a soft plastic state.When the tunnel passes through the soft plastic loess stratum,the tunnel support deformation exceeds the design range,and engineering problems such as tunnel face collapse and excessive surrounding rock deformation occur in the construction area.However,at present,there are few studies on the reinforcement scheme of the tunnel crossing the soft plastic loess stratum,which is difficult to solve the problems in the construction process.It is necessary to study the reinforcement effect of different reinforcement schemes on soft plastic loess surrounding rock.The influence of surface precipitation on tunnel surrounding rock is not clear,and it is still doubtful whether it can effectively solve the engineering problems faced by soft plastic loess.After the surface dewatering in Shanggecun,the engineering problems faced by Shanggecun are still not completely eliminated.In view of the failure of the dewatering project of Shanggecun soft plastic loess tunnel,it is decided to adopt the surface grouting method to reinforce the surrounding rock of the tunnel.The application of grouting technology in soft plastic loess is still in the exploratory stage.Therefore,it is very necessary to study the grouting reinforcement technology in soft plastic loess.Based on the research project of Yinxi high speed railway,this paper studies the applicability of different reinforcement schemes to the soft plastic loess tunnel project,taking Yima and Shanggecun tunnels crossing the soft plastic loess stratum as the research objects.Firstly,the basic physicochemical properties of soft plastic loess are tested.Considering the special engineering properties of soft plastic loess,the conventional tunnel reinforcement scheme is difficult to meet the engineering requirements.Firstly,the method of surface precipitation is selected to improve the stability of surrounding rock.Through the field monitoring data,it is found that the surface precipitation can reduce the water content of surrounding rock before the excavation of Yima tunnel,from 30.0%to 27%,thus improving the stability of surrounding rock.The liquid index decreased from about 0.9 to 0.65,the self stabilization ability of surrounding rock was significantly strengthened,and the water inflow in the tunnel decreased from about 187m~3/d at the beginning to 50m~3/d.However,for Shanggecun with sufficient water sources around,the surface precipitation is still difficult to meet the engineering requirements.In view of the special situation of Shanggecun tunnel,it is decided to adopt the surface grouting method which has not been used in the loess stratum to reinforce the surrounding rock of the tunnel.According to the field monitoring data,this paper analyzes the changes of loess physical properties before and after grouting,and studies the dominant effect of surface grouting on loess tunnel reinforcement.At the same time,the deformation of Shanggecun tunnel is simulated based on FLAC3D software to verify the effect of grouting control on tunnel support deformation,and provide data for tunnel design in Loess Plateau.It is found that the grouting will lead to shear failure of the soil around the grout vein,resulting in a decrease in the dry density of the soil and a small increase in the water content,but the overall change is not obvious.The grout vein formed by grouting is filled in the stratum fissure in strip or cone shape,mainly developed vertically,but there is no connection between the grout vein and the grout vein,and no obvious network structure is formed.At the same time,the monitoring data of Shanggecun tunnel section support deformation show that the effect of grouting on controlling tunnel support deformation is verified.Compared with the non grouting section,the average settlement of the arch crown（33mm）in the grouting section is less than that in the non grouting section（45.9mm）,with a decrease of about 28%;The average deformation of the bench on the excavation section of the tunnel decreases by 28%;The average deformation of the middle step decreases by 24.2%;The average deformation of the lower step decreased by 19.8%.The results show that grouting can effectively reinforce the tunnel,improve the stability of surrounding rock and reduce the deformation of tunnel support.The numerical simulation results show that the calculated data of the model are consistent with the measured data.After grouting reinforcement,the ground settlement is reduced,the deformation of each position in the tunnel is reduced,and the stress on the tunnel lining is reduced. |
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