Effect And Control Of Deformation Of Adjacent Existing High-speed Railway During Karst Region Reinforce

The high standard of high-speed railway operation has strict requirements for the deformation control of railway roadbed.The stratum deformation induced by the construction must be controlled when the karst foundation is constructed adjacent to the existing high-speed railway to avoid its influence on the existing high-speed railway.It is one of the technical challenges in engineering practice to ensure the safe operation of existing high-speed railway and the construction quality of karst foundation grouting reinforcement.This study relies on the karst foundation grouting renovation project adjacent to the existing high-speed railway in the expansion project of Xuzhou east station of Beijing-shanghai high-speed railway.Firstly,the joint control grouting equipment based on the existing high-speed railway subgrade deformation control and karst grouting treatment is developed.Then the measured grouting amount and velocity,grouting pressure and surface deformation in karst grouting process are studied based on free site grouting test.On this basis,the grouting treatment technology and effect evaluation method of karst foundation suitable for deformation control of adjacent high-speed railway are put forward.The main contents and conclusions were drawn as follows,(1)The joint control grouting equipment of the adjacent high-speed railway roadbed displacement control and karst foundation grouting treatment is developed.The equipment can actively control and adjust karst grouting parameters according to predetermined deformation warning value of existing high-speed railway base and combined with real-time deformation monitoring data of existing railway roadbed.(2)The distribution characteristics of grouting pressure-grouting flux-time(P-Q-t),grouting amount and surface deformation in karst foundation grouting were studied based on free site grouting field test.Using three sequence grouting Ⅰ,Ⅱ,average Ⅲ sequence hole grouting volume proportion of total quantity of grouting were 40% ~ 60%,25% ~ 35% and 15% ~ 25%;P-Q-t curve type rise and an A-line shape can reflect the karst grouting filling effect,in Ⅰ,Ⅱ,Ⅲ sequence hole grouting is completed accounted for 37%,52% and 82%,respectively.When the pressure of the grouting end hole is less than 0.3mpa,the maximum surface displacement caused by grouting shall not exceed 1.5mm,and attenuate to 0.5mm at a distance of 8m from the grouting point.Seismic imaging,CT between holes and core drilling can be used to investigate karst distribution and evaluate grouting effect.(3)The numerical analysis model of karst grouting is established,and the influence of karst grouting on adjacent existing high-speed railway subgrade is studied.Based on the results of numerical analysis,a simplified practical empirical formula for surface displacement caused by karst grouting is proposed.Based on the field test and numerical analysis results of karst foundation grouting in the free site,it is clear that the project can realize the cooperative control of deformation of adjacent existing high-speed railway and grouting treatment of karst foundation with a final pore pressure of 0.3 MPa.(4)A field test study on karst grouting near the existing high-speed railway subgrade was carried out.The site adopts a two-sequence hole grouting scheme.The grouting amount of the front sequence hole accounts for about 80% of the total grouting amount,and the grouting amount of the back sequence hole accounts for about 20% of the total grouting amount.In the process of grouting from the front sequence hole to the back sequence hole,the proportion of ascending grouting curve is gradually increasing.Inter-hole CT and core drilling results show that the grouting effect is good.The maximum monitored vertical displacement of shoulder and toe of existing high-speed railway is 0.6 mm and 0.2 mm respectively.The measured results of the field test section verify the effectiveness of the joint control grouting equipment and grouting construction cooperative control technology developed by the project.