Research On Monitoring And Main Influence Factors Of Diseases For ZhuChang The 5^th Bridge And Railway Line Of Nanning-Kunming Railway Line

The 5th bridge of Nanning-Kunming railway line in Zhuchang, still according to the old 80's building design and construction specifications, was built in 1993 and completed in 1996. With the rapid development of society, six times of raising train speed have been carried out and heavy rail has also made tremendous growth and improvement, which impacted the using 5th birdge significantly, and the complex geological and hydrology environment, combined with various natural factors, increased the disease probability of the serving foundation-bridge-line system. Diseases as pier settlement, lateral displacement of the bridge structure, titled hinged movable support, subsidence and crack of the cone slope, concrete crack and abscisic, rail creep deformation and over cant of the line seriously affected the overall stability and lifetime of the serving 5th bridge, as well as the smooth running of vehicles and even the treaten traffic safety.Firstly, taking the diseases of 5th bridge as the background, the domestic and international situation of bridge railway line diseases were fully studied, the various causes of the 5th bridge railway line were comprehensively analyzed, according to the disease characteristics and geographical environment, based on high-precision measuring instruments and sensors, a scientific, systematic and economic system of railway line disease monitoring was formed, and the prism forced pluming pole greatly enhanced the accuracy and efficiency of the railway lin plate measurement. Through long-term monitoring of the 5th bridge railway line in Zhuchang, the development law of the line disease was obtained, the piers had the trend of settlement and tilt, the tilt angle of the hinged movable supports were large and parts of them had the trend of increasing; the average curve radius was less than the dedign value, the line smoother was poor and the line cant was over. Whatmore, the line segment system and the foundation structures were investigated, the within track wear was more serious than the outside, parts of the ties were loose, the steel plates crossing the beams were seriously corrosive and rusted, the longitudinal joints were leakage and subsidence and crack of the cone slope happened at the bridge head.Secondly, according to pecific disease conditions, additonal exploration of parts of the piers was carried out, the foundation geology of the full- bridge was extremely complex, the groundwater was rich and shallow, the rocks were crushing and the karst was developed. The additional exploration results were different with the preconstructing geological survey, whenas the bridges with caverns, cracks, settlement or displacement on the pier top were almost the same.Thirdly, Three-dimensional numerical simulation of the typical bridge pier with caverns or special geology was carried on, the upper structure, track and vehicle loadings was simplified and directly applied to the bearing sheet; the soil layers were supposed to be homogeneous isotropic plastic materials and Drucker-Prager model was adopted; Elastic Coulomb friction model was used for pile-soil contact model; the stability of the pile foundation without caverns or with different caverns and the settlement and differential settlement of the bridge foundation in different soil layers was analyzed. The results showed that the settlement and differential settlement of the pile cap plate with cavern was much larger than those without cavern and increased with the increasing cavern span, approximately a linear relationship; when the cavern was located at the side of the pile cap, the differential settlement and the stress concentration was more pronounced; when the pile substratum didn't reach the capacity requirement of the upper loading and the substratum mechanical properties were different, the differential settlement and the stress concentration appeared.Finally, based on the disease surveillance and additional foundation exploration results and combined the three-dimensional numerical simulation results, two main causes of the 5th bridge diseases in Zhuchang of Nanning-Kunming railway line were determined:①the geological problem of the bridge foundation;②the average circular curve radius of the line was less than the design value and the bad line geometry. Other minor factors should also be given due attention, avoiding its development from quantity to quality and ensuring long-term running safety.