Evaluation And Stability Analysis Of Karst Foundation Reinforcement In South Shandong High-speed Railway Subgrade Section

Karst geology is widely distributed in China,accounting for about 1/8 of China’s land area.In 2019,China plans to invest 800 billion yuan to vigorously develop the railway industry,ensuring that the new line will be put into operation 6800 kilometers,including 3,200 kilometers of high-speed railway.The karst problem is one of the most important problems in the construction of high-speed railways in karst areas,which has the impact of pre-construction construction and post-operation safety.In the high-speed railway construction in the karst area,the karst ground grouting reinforcement effect detection and stability analysis can assist the karst area engineering design and guide the site to rational construction,to ensure the karst ground reinforcement effect is good,to meet the stability of railway operation in the later period.Therefore,the study of the method of grouting reinforcement effect detection and stability analysis in karst area has important engineering practical significance to meet the needs of China’s vigorous development of high-speed railway environment.In this paper,the karst ground reinforcement area of LQTJ-2 section of Linyi to Qufu section of Southern Shandong high-speed railway is used as the engineering background to study the effect of grouting reinforcement,through geophysical test,coring test,water injection pressure test and flat load test.The test methods summarize the evaluation criteria for karst remediation in the Southern Shandong area.Through the method of numerical simulation analysis,the difference of foundation stability under different grouting materials is studied,and the grouting material which is more suitable for the karst area is obtained.The main work and research results are as follows:(1)By summarizing the results of karst grouting reinforcement at home and abroad,the research status and numerical simulation analysis methods of karst ground consolidation test are expounded,and the research content and technical route of this paper are put forward.(2)Based on the hydrogeological conditions of the karst ground reinforcement area in the LQTJ-2 section of the Southern Shandong high-speed railway from Linyi to Qufu,it is decided to use the grouting reinforcement method to carry out the Luji high-speed railway LQTJ-2 section.Reinforcement treatment.Refer to the railway design requirements for post-grouting quality inspection of the grouting reinforcement area,determine the arrangement of the inspection area of the inspection area,the position of the core hole,the depth of the water test hole and the selection of the plate load test,etc.Test plan.(3)Based on the comparative analysis between the test sequence of the test sequence I,II,and III grouting reinforcement test,the comprehensive evaluation of the test results including the combined geophysical test,borehole core test,water pressure test and plate load test is obtained.It can effectively judge the goodness of the grouting reinforcement effect.From the geophysical geological section,it is macroscopically understood whether the large cave is filled and squeezed by the slurry;the core condition is used to visually reveal the good condition of the cement and rock mass cementation;the P~Q curve type summarized from the water pressure test reflects the interior of the rock mass.The seepage coefficient q reflects the change of the crust or fissure opening of the rock mass under the action of hydraulic force;the results of the plate load test judge from the mechanical point of view,whether the bearing capacity of the foundation meets the design requirements after different grouting reinforcement stages.(4)Through the analysis and analysis of the test data of the regional test section,the criteria for evaluating the quality test of the karst grouting of the standard section are obtained.Firstly,the comprehensive geophysical method is used to eliminate the large karst caves in the stratum,and then the borehole core is used to verify whether the geophysical results are better.After the large-in and out,the P~Q curve and the permeability of the rock mass in the water pressure test are used to quantify the degree of compaction of the rock mass after grouting.Finally,the accuracy of the evaluation criteria is determined from the design bearing capacity by the plate load test.feasibility.The conclusion of the quality evaluation of grouting reinforcement saves the inspection period and speeds up the connection of the construction process before and after,thus shortening the construction period.(5)Based on the results of grouting reinforcement test,numerical simulation analysis of the study area.Through the MIDAS/GTS simulation of the train’s up and down loads,the grouting reinforcement material is changed,and the displacement and stress between the unreinforced karst foundation and the non-karst foundation are compared.It is concluded that changing the properties of the grouting material does not affect the stress transmission.Large,the displacement changes are relatively obvious,and the elastic modulus of the grouting material is closer to the elastic modulus of the rock mass,and its mechanical properties are more excellent.