Analysis Of Karst Grouting Foundation Settlement Characteristics In Qian Zhang Chang High Speed Railway

The karst develops strongly and it is also widely distributed in the southwest of China,this brings great inconvenience to the design,construction,operation and maintenance of high speed railway,especially the subgrade deformation and uneven settlement caused by a series of karst cavitation and karst collapse during the construction of high speed railway.Consequently,regarding to the issue of the settlement characteristics of the foundation,it is significant to carry out the research of karst grouting.Basing on the study on the grouting test of karst foundation of Qian Chang high speed railway,which is also an important part of the East and west east and west channel of the Shanghai Chongqing railway.this thesis investigates the mechanical properties of a new type of controlled grouting slurry with "less water analysis and rapid condensation".Based on the numerical model of karst foundation,the characteristics of karst development and grouting are studied.The influence of filling degree on the settlement and deformation of karst foundation are analyzed,and the reinforcement effect of karst grouting is calculated and analyzed.The main works and achievements in this paper are as follows:(1)On the basis of the research results at home and abroad,the research status of Karst Subgrade Deformation and the disease forms and treatment measures of Karst Subgrade are expounded,and the research content and technical route of this thesis are put forward.(2)Based on the compressive strength test of the grouting stone body,the mechanical properties of the conventional cement slurry stone body and the new controlled slurry stone in the laboratory were studied.The relationship between the dosage of speed coagulant,water retaining agent and water reducing agent and the uniaxial compression strength of the grouting stone body were compared and analyzed.The experimental results show that the superiority of the new controllable slurry filling effect and also provide reliable parameters for subsequent numerical modeling analysis.(3)Based on the geological survey data and the borehole survey results,the three-dimensional surface modeling method is used to simulate the karst cave in the test section,the solid model of the karst foundation is established,and the modeling method is optimized under the actual working condition.Finally,cylindrical karst caverns are selected to establish the numerical model of karst foundation.(4)Based on the numerical model of karst foundation,the influence of the span of karst cave,the thickness of the roof,the shape of the karst cave,the height of the karst cave and the bead type karst cave on the settlement of the karst foundation are studied,and the change of the settlement of the foundation before and after the karst grouting is compared and analyzed.The calculation results show that the span of karst cave and the thickness of the roof have great influence on the settlement of karst foundation,and the depth of karst cave,the shape of the karst cave section and the lower karst cave in the bead type cave have little influence on the settlement of the karst foundation.Grouting shows very good effect on the deformation and uneven settlement of karst foundation.(5)Based on the numerical model of karst grouting strengthening foundation,the influence of grouting filling degree and the change of physical properties of grouting stone on the subsidence of karst grouting strengthening foundation is studied.The calculation results show that when the grouting filling rate is within the range of 90%?98%,the vertical displacement of the karst foundation surface decreases with the increase of grouting filling degree.In the actual construction process,the larger the cavity length or the smaller the roof thickness,the higher the requirement for grouting.Based on the calculation results,the recommended values of grouting for different types of karst are put forward.