Research On Deformation Characteristics And Lining Technology Of The Tunnel Surrounding Wall Rock With Soil-Rock Interface Under Loess

The strata including soil and rock often appear in mountain of loess zone which often covers with four Era. When the tunnel passes through the loess mountain, there are the shallow-buried broken wall rock with soil-rock interface, Such as Shenyan railway Yangma river tunnel, Xinsongshuwan tunnel in Longxi county of Gansu province and Lijun speedway tunnel in Shanxi and Baotian speedway heiling tunnel and so on. This kind of geological strata not only affacts the mechanical properties of tunnel evidently, but also hydro-geological conditions taking place change significantly, which resultes in the water content significantly increasing on the interface. Because the complex stratum with soil-rock interface doesn't arouse a wide range of people's attention, a number of incidents include landslides, and too large rock deformation occure in the past practice. It also prompts to study the necessity and urgency of the soil and rock contacted stratum tunnel wall rock.Firstly, this paper studies physical index and mechanics index of loess, standstone and soil and rock's interface-by indoor test; Secondly,establishing a describe mean of soil and rock contected stratum, and qualitative and quantification evaluating the deformation of soil and rock marched with stratum tunnel wall rock and the internal force changing features of lining structure by numerical simulation; Thirdly,creating a numerical analysis mean of the locked anchor tube, anaslysing mechanism of action of steel rib locked feet and determining the rational length and infiltrate angle of the locked anchor tube; Finally,determining deep or shallow burial critical depth by coefficient of earth pressure and inter and outer ratio of wall rock deformation.Enduce mostly conclusion as follows:1) The soil and rock interface forms shear failure surface easily. The shear strength of interface depends mainly on the strength characteristics of weak loess. With the loess water content increasing on the soil and rock interface, cohesive strength on the interface decreases significantly; Angle of friction attenuate little,but smaller than loess's.2) The deformation features of soil and rock contected stratum tunnel wall rock manifest mainly on wall rock settlement displacement too big and settlement not equality.The maximum settlement displacement is not in the biggest dome and is in the dome away from the soil tend to the location of about 30°. This differential settlement caused internal forces changes large in the structure of the tunnel lining,it manifests mainly that lining structure axial force and bending moment are larger near the rock in the soil and rock interface.3) For the sake of convenience study and achievement application,putting forward a new mean that it describe quantificatively the soil and rock contected stratum with obliquity,area ratio,rigidity ratio and burial depth of the soil and rock interface.Analysising separate the influences of obliquity, area ratio, rigidity ratio, burial depth and excavate ways to the deformation rule of the soil and rock stratum tunnel wall rock and changed rule of lining structure internal force. Of these, the greatest impact is the depth and excavation methods, followed by the area ratio, angle and stiffness ratio.4) The locked anchor tube should be bound by its rotation along the z-axis degree of freedom to consider. Anchor tube length and angle have a greater influence to the internal forces of the supporting structure.Appropriate length and angle is not only conducive to limit the deformation of rock,but also help to play the internal force of supporting structure.Determining the locked anchor tube effective or not and reasonable should consider it's influence to the deformation of wall rock and the internal force of supporting structure.Study results indicate that general soil tunnel the locked anchor tube should be 3.0m and lock pin into the anchor tube should be 30°.5) Determining deep or shallow burial critical depth by coefficient of earth pressure is 2 times of hole diameter. Determining deep or shallow burial critical depth by inter and outer ratio of wall rock deformation is 1.7 to 3.0 times of hole diameter.6) Through the above numerical simulation, we consider that excavating tunnel in the soil and rock stratum, it's supporting approach of the soil surrounding the hole should be appropriate to strengthen,especially in spandrel so as to ensure the unity and uniform deformation of supporting structure;We should make a reasonable layout in excavation approaches and reduce the disturbance of the soil. We also put forward to reduce the disturbance of the soil:"Preventing disturbance, and soil is emphases; Soil side strengthens to support,and spandrel is strengthen".