Main Types Of Analysis And Evaluation Of Loess Tunnel Engineering Geological Disasters

The loess is a special kind of soil which has been forming in the drought and partly drought climate in the Quaternary period. It is composed of particular material constitute and microstructure in particular region and piles up on the ancient physiognomy. The fundamental character depends on the grain series, contacting relationship, hole types and size, joint types, surrounding rock condition and feature. They give the loess special tectonic structure, such as lower strengths, weak bearing power, wet-collapsing partly. Therefore loess reveals special geology engineering character and maybe damages engineering building. The surrounding rock of loess tunnel is regarded as II,III,species . The natural stress are changed during the tunnel's features, and changed again with the timbering and interfacing, which makes surrounding rock complicated. Some transferred to neighbor, others were released during it collapsed. The prime problem is the up-growth of joint, weak microstructure strength and water-impairing.The engineering geology term of the tunnel is in charge of the tunnel's excavation method, lining structure forms and interfacing structure. The surrounding rock engineering geology is not only the material foundation of producing disasters in loess tunnel, but also the carrier of studying the geological disasters. The sources of the disasters in loess tunnel can be found out from the surrounding rock engineering geology condition except for the artificial factor. The special geology engineering character of the loess, such as physical mechanics, compressibility, wet-collapsing, shearing, water-impairing etc, which dominate the geology engineering character of surrounding rock of the loess tunnel. Based on the practice of the loess tunnels, this paper demonstrates and studies the effect mechanism of the disaster, then draw a conclusion of the main geological disaster types of the loess tunnels.Cave-ins are dominating within the tunnel disasters. This paper analyzes the main factors that influence the tunnel collapse (geology factor and project factor) and study the disasters-caused mechanism and regularity. Making use of mechanics, stereographic projection, numerical calculation, probability calculation, we can evaluate the danger of cave-ins. New behavioral traits of cave-ins of the loess tunnels engineering are extracted and summarized up. They are rapidity, no premonition, intermittence and direction .The scales of cave-ins also have close relationship with construction. Cave-ins would like to occur where the layer is the interface, the transformation between loess and bedrock, where the layer is threatened by the immerged underground water. Based on the FEM, numerical calculation have remarkable outlook to calculate and imitate the mechanics action and the...