Design Method And Test Study Of Pile-column Bridge Foundation In Steep Slope

With the advance of west development, constructions of expressways andrailways in mountainous region are blooming. When these paths are passing throughmountain area, it should be avoided to cut and trench the mountains overly in order toprotect the existing ecological and culture environment. Structures like trestle andhalf road and half bridge along steep slopes are inevitably set in some specialsegments. Pile-column bridge foundation is a new foundation style widely used inconstructions of bridges in mountainous region of western China and has littleguidance of specifications and experience regarding to its design and calculation. It isan urgent problem in construction of bridges in mountainous region to give a deep andsystematic investigation of some involved issues of pile-column foundation in steepslopes such as bearing mechanism, calculations of internal forces and deformation,stability analysis and others. In order to solve the abovementioned issues, this workwas devoted into the establishment of a complete design and calculation method forpile-column bridge foundation in steep slopes by analytical methods and model tests,combining with Western Transportation Construction Project of TransportationMinistry “Design and Construction Technology for Bridge Pile-column Foundation inHigh and Steep Cross Slope” and Graduate Students Research Innovation Project“Design and Calculation Method of Bridge Double Pile Structure in High and SteepSlope”.The bearing mechanism of pile-column foundation subjected to vertical loads,lateral and lateral loads, axial loads and combined loads were analyzed respectively.Calculation formula for the sliding force of slope was derived by stability analysisbased on the limit equilibrium theory. Mechanical analysis of pile element wasperformed to establish the differential equations of flexible deformation for eachcharacteristic segment of pile shaft. Power series approach was employed to solve theequations to obtain the semi-analytical solution of internal force and displacement ofpile-column bridge foundation. On this basis, analysis for the influence factorsindicates that the internal force and displacement increase linearly with the increaseof lateral loads on the pile top, and the lateral loads affect more on the upper segmentof the shaft; and that with the reduction of ground resistance, the increments of theinternal force and displacement ascends and the location of maximum bending moment moves downwards; and that a rational selection of pile diameter benefits todecrease the values of internal force and displacement.An analytical calculation model for the bulking stability of pile-column bridgefoundation in steep slopes was constructed by energy theory considering the “steepslope effect”, and the corresponding total potential equation of pile-slope system wasderived. By solving this equation using energy approach and boundary conditions, thecomputational formulas for bulking critical loads and computed stability length wereobtained. The reliability of this technique was verified by laboratory model test.Influences of pier height, modulus of elasticity of pile-column and slope inclinationon the bulking stability were discussed systematically incorporating with practicalcases.By deep analysis on the structural properties and bearing characteristic of dualpile foundation of pile-column bridge double piles in steep slope, its simplecalculation model was established taking the pile-slope-pile interaction into account.The derived differential equation of flexible deformation for each characteristicsegment of pile shaft was solved for the semi-analytical solution involving themechanical and deformational analysis of dual pile foundation. The influence of thespace between front pile and back pile, the resultant remaining slide force andproportional coefficient of ground resistance coefficient on the internal force anddisplacement of dual pile foundation were explored. Thus the design and calculationmethod for pile-column bridge foundation in steep slope was proposed as well as itsdetailed design circuit.On the basis of similarity theory, the laboratory model test of double pilefoundation for pile-column bridge in steep slope was designed and accomplished.Most attention was paid on the influence of the pier height and slope inclination onthe bearing mechanism, failure modes, internal force and deformation of dual pilefoundation. The reliability and rationality of this theoretical calculation method wasevaluated and verified by comparing with the measured data.