Treatment Of Defects And Effects Asseessment Of The Piers Foundation In Karst Areas Of Nanning-Kunming Railway Line

In order to meet the needs of the rapid development of society, the railway has accelerated trains’speed for six times since1997and the heavy haul railway with the feature of heavy axle load and large density of trains has been developed greatly. After the speed acceleration, line and bridge system and subgrade foundation not only bear static load, but also experience the repeated impact and vibration of moving loads. The railway bridges which is designed and constructed according to original specifications can easily cause line deformation, vibration transfinite of bridge span structure, uneven settlement of pier foundation under poor geological condition. Besides, line diseases may influence the dynamic behavior of trains and exacerbate trains’vibration. Especially for the curved bridges, the influence is more serious.The hydrology-geological conditions of the Fifth Bridge in Pig Farm in Nanning-Kunming Railway are remarkably complex and affected by various natural factors throughout the year. The above factors are coupled with increase of axle load level and traffic density, which make the disease probability of foundation-bridge-line system during the period of their serves increase sharply.This paper takes the karst disease of pier foundation of the Fifth Bridge in Pig Farm in Nanning-Kunming Railway as background and does the survey about disease causes and improvement methods of karst at home and abroad. In addition, it collects disease status and geological exploration data of foundation of the Fifth Bridge in Pig Farm. According to the disease condition, research of cause analysis is carried out. Firstly, foundation problems include:The karst and cracks of foundation develop extremely; the stratum weathers seriously and the bedrock breaks; parts of piers’piles are too short and support on soft rock, extremely soft rock or sand layer est., which are special layers. Secondly, line geometric problems include:The mean radius of circular curves is less than that of designed and eccentric distance of line is abnormal; the excess cant and ride comfort are worse. Thirdly, lateral amplitude transfinite of pier top problems:The problems may be caused by:The lateral stiffness of pier is low and the foundation of pier is unstable; lateral load of upper structure is too large. The problem of lateral amplitude can be completely solved by foundation consolidation, pier reinforcement and upper structure adjustment and so on.This paper introduces the reinforcement measures of pier and abutment including the reinforcement method of enlarging foundation, the reinforcement method of pile supplement and high pressure revolving blast-grout method and analyses the range of application and points for attention of above methods. Aiming at disease deformation characteristics of the Fifth Bridge in Pig Farm, targeted repair programs are laid down as follows. The reinforcement method of enlarging foundation and the reinforcement method of pile supplement are used to reinforce such piers whose bearing capacity is poor and whose settlement deformation is too large. The post grouting is used to reinforce supplement piles of pier in poor geological conditions. According to construction site and personnel allocation, the technology roadmap of damage repair of the Fifth Bridge in Pig Farm is established. According to the damage repair scheme, bearing capacity and settlement deformation of piles are calculated under the most adverse load combination. Besides, in order to check the correctness of designed reinforcement scheme, punching shear of pile cap and contact action between concrete are checked.Aiming at the karst problem of pile end and taking the fifth pier foundation for example, the3-dimensional numerical analysis model is established. The situations including the pile end has karst and the pile end doesn’t have karst are contrasted with different longitudinal bridge stuffiness. The relationship between center settlement of bearing sheet and settlement differences of both sides and change of longitudinal bridge stuffiness is analyzed. In addition, the vertical settlement of piles and lateral amplitude of pier are analyzed. Outsourcing piers including3meters and5meters are simulated. The vertical settlement and stress of new and original piles foundation are obtained. Then, the vertical settlement and stress of original piles are contrasted with the ones before reinforcement. Combined results of theoretical calculation and numerical calculation, reinforcement effects of pier foundation after reinforcement are evaluated in order to insure upper safe driving.