Engineering Geological Characteristics Of High-speed Railway Tunnels In The Loess Plateau And Geophysical Exploration

Dong Zhiyuan loess is the most representative loess sedimentary area in China.Its loess accumulation thickness is large.Loess is the accumulation formed in the Quaternary period.Its structure affects the mechanical properties of loess,and then affects the engineering properties.Among them,water content is the most important factor affecting the change of loess saturation and physical state,thus affecting the change of mechanical properties of loess.The whole section of Shanggecun tunnel and Yima No.1 Tunnel is located in Q2 loess stratum,which is easy to collapse and roof fall due to high water content(26.4-34.4%)and self weight collapsibility.In addition,the slope at the exit of the tunnel is steep and straight.Loess caves on both sides and gully slope are developed.the terrain is broken.Close to the landslide body.Prone to instability.so the engineering geological conditions are poor.In order to make sure that construction was going normally,the water content,liquid index,plastic index in the soft plastic belt and the water seepage in the tunnel have been significantly reduced through long-term surface de-watering measures.Thus,it improves the self stability ability of surrounding rock and effectively controls the falling and collapse of surrounding rock.Transient electromagnetic is a relatively effective geophysical exploration method for deeply buried loess tunnels,which has the characteristics of large depth,high resolution to stratum,high efficiency and low cost etc..It can accurately reflect the tendency of geological structure and the physical characteristics of the fault zone,and can qualitatively judge the water content of the stratum.As a high-resolution detection technology,ground penetrating radar is a common tunnel detection method.Therefore,in this paper,transient electromagnetic and ground penetrating radar are used to analyze the stratum of Shanggecun tunnel and Yima No.1 Tunnel,so as to provide a reliable basis for the determination of the fault zone and water content of the stratum in which the tunnel is located.After taking de-watering measures,they provide reliable prediction for the change of water content,joint development and self stability of surrounding rock in front of the face of the tunnel.Dynamically guide the construction,determine the reasonable excavation and support parameters,and take measures in advance to ensure the construction safety and controllability.It has profound political and economic significance to guide the safety management and quality control of tunnel construction,reasonably promote the construction and ensure the performance of the construction period.