Axial Bearing Capacity Of Piles Socketed In Weak Rock In Plateau Reservoir

The port of Funing is located in plateau, in which the terrain is complex. On thesurface there are a lot weaker rocks with developing cracks and poor stability. With thecyclic water level’s fluctuation in reservoir, the mechanic properties of soft rock mayvary significantly so as to affect the long-term bearing capacity of rock-socketed piles.Based upon the characteristics of degradation concluded by taking sample of soft rocksand test of “water saturating and air drying”, this paper chooses four different workingconditions, researching on the axial bearing capacity in weak rocks based on thefoundation model. The parameters of foundation model and pile are determined bysimilarity analysis, test planning, field sampling, mixture ratio test, and optimizationdesign. The method of low speed maintenance has been applied to test piles with ahydraulic jack. The axial strain along the pile shaft is measured by strain gages, and theend resistance is measured by load sensors. On the basis of test data, this paper alsoconductes3D elasto-plastic finite element analysis of the axial bearing capacity, shaftfriction, and end resistance of the piles with different lengths and diameters under threeworking conditions. Lastly, this paper discusses four regulated rock-socketed pilecalculation methods. So this paper has come to the following conclusions:First, with the reduction of rock strength, the axial bearing capacity of thefoundation pile is gradually reducing. But the range of the reduction turns from small tobig, which is contrary to the range of degradation of soft rock (from big to small). Theultra-resistance of shaft is decreasing with the degradation of soft rock. When the shaftfriction reaches its limit, the model pile has only small displacement. After the shaftfriction reaches its limit the end bearing begins to play but its play degree will beinfluenced by the sand below the pile base. This paper carries out a method that whenthe end resistance takes up to nearly some percentage of the pile top load, then take theload on pile top as the ultimate bearing capacity of rock-socketed pile.The results of rock-socketed pile numerical modeling show that the pile shaftfriction distribution is changing when the rock-socketed depth varies. Increasingrock-socketed pile depth has little effect on increasing ultimate vertical bearing capacitywhen the depth reaches some value. Increasing soft rock rock-socketed pile diametercan be a significant advantage in improving the bearing capacity and reducing the pile top displacement, but the development of unit shaft friction level will reduce while thepile diameter increases.Different rock types and parameters influence the calculation results significantly.Therefore this paper advises standard method should be used to choose reasonable andcoefficient pile shaft friction and end resistance by various kinds of rocks and differentunconfined compressive strength. Finally this paper puts forward the soft rock-socketedpile design requirements in plateau’s underwater area and adapts a method to determinevertical bearing capacity of a single pile to assess Long-term bearing performance.