Study On The Main Diseases And The Influence On Carrying Capacity Of Bridge In Collapsible Loess Area

Gansu province located in the loess plateau,most of the engineering properties of the loess give expression to wet sex, easy to wash, easy to corrosion and anisotropy. The gullies of the Loess Plateau landform determines the most bridges across the valley and river and substructure of bridge built in slope or channel. In recent years, with the development of highway construction in Gansu province, combined with the frequent extreme weather such as heavy rain, some new and old bridge located in the collapsible loess areas appear such as foundation settlement, lateral displacement of beam body, cone slope collapse and other diseases. For bridges located in the collapsible loess areas, these diseases not only make a year into the bridge maintenance cost increase, but also with the development of diseases will affect the safety, the stability and the comfort of driving of the bridge. So, it is very important to investigate and analyze the diseases of the bridge in loess areas and put forward the corresponding maintenance technology.This paper, selecting the highway bridge of the Western and Eastern Gansu province collapsible loess area as the engineering background. Based on the investigation of diseases, the method of numerical simulation and theoretical calculation is used. From three aspects analyze the influence of diseases to the lower part of bridge structure: the influence of part foundation scour for stability and the maximum compressive stress of the basement of rigid expanded foundation; the scouring effect on the mechanical behavior of pile foundation; the influence of sedimentation on the internal forces of the double column pier. From three indicators of the counteracting force, control section deflection and stress analyze the influence on the bearing capacity of the beam bridge upper structure by foundation settlement. The paper, combining with investigation disease types, disease mechanism and the analysis results of diseases to the bridge structure, puts forward corresponding preventive and maintenance technology.By the research results of this paper can be: the main causes of the foundation settlement and other bridge diseases are the loess soaking wet sinking and the water flow scouring. The base anti overturning coefficient of rigid expansion foundation is irrelevant with base erosion shape, which appears linear decrease with degree of scouring increase. With the erosion area increased, the maximum compressive stress of the base show a gentle trend curve start at the beginning of the curve. When one side of the erosion area begin in 10% and both sides of the erosion area begin in 20%, the curve becomes steep. With the increase of scour degree, the bending moment increases linearly and the maximum pile displacement shows a curve growth. The joint of pier and beam appears cracks on large inclined side in no tie beam of pier biprism. The influence of simple supported beam bridge reflects on 1/4 and 3/4 cross beam body under torsion becoming large by lateral inclination of abutment. Long span prestressed concrete continuous beam bridge should give priority to the middle span and lower deflection value. With the increase of the foundation settlement, the section stress of bridge pier's bearing place and middle span will increase and be beyond the allowable value at first in simply supported continuous girder bridge. Bridge prevention and maintenance should begin in four aspects: the bridge survey and design stage, the construction stage, the maintenance and management stage and the bridge disease stage.