Deformatiom Time-space Effect And Supporting Parameters Optimization Of Surrounding Rock In A Tunnel Of Chenglan Railway

With the rapid development of China’s economy,the development of tunnel engineering has made a breakthrough.Recently,tunnel in soft rock with high ground-stress appear frequently among the railway and road tunnel engineerings under construction in our country.Problems,such as large deformation,supporting damage,etc seriously affect the normal construction of these tunnels.The long tunnel built in Chenglan Railway has the characteristics of deep buried,large cross-section.It is a typical high ground stress soft rock tunnel,which has a Partial deformation of surrounding rock beyond reserved deformation inflict initial support Intrusion limit,shotcrete support cracking,desquamate,steel arch distortion and other issues during the construction process.In this paper,the D5K219+080～D5K219+140 For engineering background,Study on the Time-space Effect and Support Parameters of Tunnel Weak Rock Deformation,Using a combination of domestic and foreign literature research,field investigations,on-site monitoring,theoretical analysis,and numerical calculations.the main results are as follows:(1)The study of the ground stress field in the tunnel area shows that Stress field dominated by NW～SE extrusion of the tunnel area;The maximum horizontal principal stress near the tunnel is about 15 MPa,and the minimum horizontal principal stress is about 10 MPa.It is divided by the absolute magnitude of the ground stress and belongs to the area of high stress;The main stress relationship in the three directions near the tunnel is S_H>S_V>S_h,and the ground stress is dominated by horizontal tectonic stress.(2)Through the analysis of the surrounding rock deformation monitoring data,it is found that the exponential function can be well fitted with the deformation monitoring data to reflect the change law of the surrounding rock deformation;the deformation of the surrounding rock is obvious:the step rock excavation conditions,the surrounding rock Deformation has obvious stage characteristics,and the deformation curve shows a"step-type"change rule.During the excavation of the upper step,the deformation rate of the surrounding rock is obviously increased,and the deformation time curve is expressed as a“rapid deformation stage”,and the deformation of the surrounding rock is relatively slow before the excavation of the step to the next step,and the surrounding rock is slowed down.The deformation is in the“slow deformation stage”;with the excavation of the lower steps,the deformation of the surrounding rock has a shorter deformation acceleration process than the previous stage,that is,“relative acceleration deformation stage”,after which the deformation is slow and gradually tends to be stable.Generally,the settlement deformation of the vault from 35m to 40m(about 2.5 to 2.8 times of the span)is generally stable;the convergence around the face of 25 to 30m(about 1.8 to 2.5 times the span)is basically stable.(3)The simulation results show that the deformation of tunnel dome subsidence and sidewalls in the horizontal direction shows obvious spatial effect,and the spatial effect of the face area is 2.5 times the rear of the excavation surface,and the dome is about 16 meters in front of the excavation surface.Settlement has already begun and the dome deformation accounts for 31%of the total vertical displacement of the dome.After the initial support is closed,the surrounding rock tends to converge.(4)The force deformation of the lock foot anchor tube mainly occurs in the very small range of the force end of the anchor tube;the stress extreme value occurs at about 0.2 m from the end,and the strength of the surrounding rock has a great influence on the bearing capacity of the lock foot anchor tube.In the geometric parameters of the anchor pipe,after increasing the length of the anchor pipe,the bearing capacity cannot be increased by increasing the length of the anchor pipe.The locking foot anchor pipe should be opened and grouted in full length,and the strength of the surrounding rock of the anchor pipe near the inside of the hole should be strengthened as much as possible;With the increase of the lower insertion angle of the anchor pipe,the ability of the anchor pipe to resist vertical deformation has been improved.(5)Taking into account the effect of the length of the locking foot anchor pipe on the horizontal converging deformation of the surrounding rock wall and the effect on the axial limit resistance of the anchor pipe,it is recommended that the length of the locking anchor pipe should be maintained at the original design length of 6 m and the down angle is 30°.Steel arches use HW175 steel instead of the original design of I20b steel,increasing the initial spray thickness from 25cm to 27cm.(6)The premature application of the secondary lining leads to excessive compressive stress on the outside of the secondary lining at the foot of the arch,which is unfavorable for the safety of the secondary lining support structure;if the secondary lining is applied too late,the initial support bears the load of the surrounding rock.Entering the plastic stage,it is easy to cause damage to the primary support structure.It is recommended that the displacements generated when the displacement has reached 85%to 90%of the total predicted displacement should be applied to the second liner,preferably no later than 90%of the limit displacement,and the initial support strength should be appropriately reinforced.