Jet Grouting Pile Reinforcement Parameter in Shallow-buried Bias Loess Tunnel
During the loess tunnel construction,the tunnel portal usually needs to be reinforced due to shallow-buried bias pressure and weak and broken surrounding rock.The surface jet grouting pile method has the advantages of wide range of application and good reinforcement effect,and is widely used in the surface reinforcement of weak surrounding rocks in shallow-buried bias section of tunnels.In this study,the initial support encroachment of shallow-buried bias loess tunnel inlet section was taken as the background.The construction process of surface jet grouting pile reinforcement on site was introduced.The three-dimensional reinforcement model of encroaching section was established.The deformation control effect before and after surface jet grouting pile reinforcement was analyzed to illustrate the reasonableness of treatment measures.The field monitoring and measurement results were compared and analyzed to verify the numerical simulation accuracy.Optimization analysis of process design parameters for surface jet grouting pile was carried out.The result indicates that due to the bias pressure,and the maximum surface settlement deviates from the tunnel centerline,the settlement at vault centerline>settlement at right arch shoulder>settlement at left arch shoulder.The application of surface jet grouting pile is very effective in reducing surface settlement with the maximum surface settlement value reduced by 45.5％.After the reinforcement treatment with surface jet grouting piles,the most significant reinforcement effect achieves at the vault,reducing the settlement by 57.9％ compared with the pre-strengthening settlement.While the difference in settlement between the left and right arch shoulders is reduced by 17.4％ after reinforcement.It is suggested that the design parameters of surface jet grouting pile reinforcement process for the shallow-buried bias section of tunnel are as follows:the diameter of piles is 0.4-0.6 m,the spacing of piles is 1.2 m,the range of horizontal reinforcement is 1.5-2 times of hole diameter,and the range of vertical reinforcement is the flush of jet grouting pile and the bottom of tunnel arches on the two sides of tunnel.
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