Study On Deformation Characteristics And Control Measures Of The Shallow Burried Excavation In The Loess Tunnel Of Xi’an Subway

Tunnel collapse and Surface subsidence & so on accidents were offen occurred during the shallow burried excavation in the loess tunnel of xi’an subway,which bringed greater bad impactance to the city traffic.So,how to ensure the Loess tunnel construction to be safe, quick and economical was one of engineering problems to be solved. Depended on the running tunnel of a interval of Xian metro, tunnel surrounding rock deformation and control technology in the loess was researched by using the method of combing the field monitoring,theoretical analysis with finite element numerical simulation.(1) With the method of field test, the formation response law induced by construction was researched in Loess tunnel. Through monitoring the reflection law of ground in the phase which were befor the monitoring section, during the monitoring section and after the monitoring section, the relationship between ground heterotaxy, supporting arguments and ground conditions. The deformation factor of overlying strata, which was regional induced by tunneling, was put forward. At the same time, the monitoring necessity of deep formation during the tunnel construction in loess was to be proved. Combined with the characteristics of surrounding rock deformation in construction site, the surrounding rock deformation was influenced on soil properties, groundwater, stress release rate,overlying strata span ratio and construction Management.(2) Used laboratory test methods, the physical and mechanical properties of loess tunnel face for the study of were analyzed.The result of research was that loess strength was greatly affected by moisture. Under the condition of wet and dry load, the damage stage of loess had two reasons, one was the function of wet and dry and another was the interaction of wet and dry in load(3) With the methord of phenomenological damage mechanics and none-quilibrium statistical, damage evolution equation was obtained. Combined triaxial compression test data and Moore stress circle, loess strength failure criteria of loess was established under moistureeffects.(4) Loess tunnel rock deformation characteristics were analyzed by FLAC numerical simulation, the results show that Loess rock stability was closely related to moisture content and formation of tunnel support, and the moisture of loess was higher, the strength of loess was lower. So, must the moisture content of loess Excavating Face must be control well during the construction process. In the condition of no advanced ground reinforcement, the surrounding rock deformation and surface deformation was to large to induce rock failture and road damage. Taking the strength measures, the surrounding rock deformation and surface deformation was controlled well and met the meet regulatory requirements.(5) With the numerical simulation, the surrounding rock deformation control measures was studied in loess tunnel and the influence factors of reinforcement parameters. At the same time, the internal relationship between reinforcement parameters with Formation parameters,support parameters and tunnel excavation was obtained. Combined the ground condition in Xi’an, the result of research gave the small catheter best parameters. After taking the sleeve-valve-pipe grouting, the impermeability, Shear Strength and compressive strength of ground was improved well, which was helpful to water stop and ensured the tunnel to be stable during the construction. Besides, the strength function of sleeve-valve-pipe grouting on loess ground was demonstrated, which could be used to deal with high water content loess.Based on the field observations, experience and numerical simulation, the reasonable grouting range was put forward.(6) Considered the problem of surrounding rock large deformation and surface subsidence induced by tunnel construction in Xi’an metro, the the original supporting program was improve by taking the surrounding rock deformation control measures that was put forward in the paper. The results of site monitoring and numerical simulation show that after taken the reinforcement measures, the surrounding rock deformation value was little and ground settlement was controlled effectively. It’s could ensured the surrounding rock to be stable and proved the control measures to be reasonable and reliable. At the same time, the deformation phase of loess tunnel had three parts, which were rapid deformation, slow deformation and stability.(7) Compared the FLAC numerical simulation value and site measured values, both was very close and the error is less than 5%, which showed that the method of FLAC numerical simulation rresearch was reliable and credible.