Field Test Research On The Vertical Load-bearing Characteristics Of Bridge Pile Foundation In Steep-slope Area Of Qinba Mountain Region

In order to meet the alignment and protect the natural environment,it is inevitable to use elevated viaducts in the steep-slope. The load-bearing characteristics of bridge pile foundations in mountainous steep-slope is quite different from that of flat slopes, the differences of site test results are limited, so that the calculation of bridge pile foundations in mountainous steep-slope is same as the calculation formula of load-bearing characteristics of bridge pile foundations in flat slopes, errors caused by this reason made much technique errors and potential safety hazards.To this end, the paper works with the field tests and theoretical analysis, research and analysis of the steep bridge foundation characteristics and working mechanism of the bearing. Field tests to study the steep-slope of the load transfer mechanism of bridge foundation, the results show that:mountain slopes and plains pile pile load transfer of transmission of load is very different, vertical load, the steep-slope and plains pile load transfer pile load transfer is very different from the law, steep pile load transfer process has obvious regional, the first area is the medial axis of the pile is greater than a certain range of lateral, axial force, a certain depth range pile inside a larger skin friction, pile axial force decrease was larger than the inside of the outer pile axial force reduced rate; second region outside the central axis of the pile is greater than the inside of the axial force, lateral friction pile resistance inside the pile to play bigger than magnitude of skin friction, pile inside the pile axial force reduces the lateral force amplitude less than amplitude; The third area is the lower end of a range of pile balance and harmony, both sides of the pile similar range of skin friction, balance and harmony axial force passed down. Based on field test results, combined with the existing norms "Highway Bridge Design Code and Foundation" (JTG D63-2007), proposed for steep vertical bearing capacity of bridge foundation locations formula, and clearly the corresponding values of calculated parameters. Based on theoretical analysis, in-depth analysis of the steep-slope of the load characteristics of the bridge piles, the pile top force summary of vertical load for the top of the pile, pile lateral load and lateral soil pressure, and several other areas, in the calculation model used by our current theories m-law on the basis of assumptions, from the differential equations of elastic deflection of the pile is derived steep pile under vertical load, lateral load and the pile is not balanced medial and lateral earth pressure of internal forces in the formula. Steep topographic features of the pressure change Pile greater impact pile hole excavation or construction of access roads built to the original stress field to balance the stress field of the new process, a stress state change and high stress concentration, and in with the pile base contact with the process, the formation of the load on the pile, that pile of earth pressure, over time the growth, lateral earth pressure is gradually increasing. And proposed steep bridge pile foundation construction technology, the bridge is located in steep mountain slopes from the top of the pile in the pile the following three times the pile diameter depth range, influenced by the slope-shaped. Therefore, the design calculation should take full account of the reduced capacity, and in the construction process should pay special attention to the slope protection to prevent the loss of soil lateral resistance of pile to play. Need to strengthen protective slope design and selection of reasonable construction technology.Combined with the simulation theoretical and analysis result, from the aspect of theoretical calculation, design and construction, this paper complements and improves the existing norms for the characteristics of bridge pile foundation steep sections.Thesis results provide a scientific basis for the steep-slope area of the bridge foundation design and construction technology. The project has a certain practical value and theoretical significance.