Research On Load Bearing Charactertics Of Socketed-pile In Weak Rock

The difference rock strength combined stiff and weak often occurs in stretum by geological processes for millions of years and it also called the alternation of soft and hard bedrock.This is the reason for bearing capacity of rock socketed pile is difficult to get accurate value in weak strength rock mass.This paper,we are taking the foundation of a super high-rise building in Guangzhou as an example.Through the bearing mechanism of rock socketed pile,the calculation method of bearing capacity recommended by the code,theoretical calculation method of bearing capacity and the finite element numerical simulation analysis.We are already understand the bearing capacity characteristics of rock socketed piles in soft rock and some beneficial results are obtained.The main research results are as follows(1)After analysed the rock socketed pile of the mechanism and loading transfer characteristics,we found that rock socketed pile has the best effect in the soft rock.With the increase of rock socketed depth,the rock socketed ratio is improving.When hr verusu D are greater than 5,the pile end resistance will lose its effect completely.(2)The formula we know from the codes for estimate the ultimate bearing of single pile,pile-bottom-resistance,pile-side-friction and allowable stress of pile in the case enginnering.The Q-s obtained from a large number of static load experiments which is verified.The results show that when the pile body passes through the soft and hard interbedding.Bearing capacity of single pile is determined by the rock and the layers of ohysical and mechanical parameters of the pile and gradually changed into the control of the pile’s own conditions.The design value of the rock strength of the bearing layer at the pile end should be less than 25 MPa.The ultimate bearing capacity calculated by the foundation code is 1.2 times that of the pile code.(3)The governing differential equation of pile rock load transfer of rock socketed pile shows that the compressive stress σ(z)in the pile body is transformed into the pile body shear stress τ(z),and the rock and soil around the pile diffuse into the surrounding rock and soil in the form of-τ(z)or qs(z).The remaining force is transferred downward along the pile body in a decreasing manner until it is reduced to zero,and the residual force is transferred to the bearing layer at the pile bottom and diffuses into the 3D depth range below the pile bottom.(4)A simplified calculation model of rock socketed pile is established by using Midas software.The settlement deformation and stress of rock socketed piles with different sizes are calculated by using the model,and compared with the field monitoring values.The results show that the axial force in 2D depth below the top of the pile is similar to that of the pile in soft rock and the stress is mainly concentrated in the pile body and does not diffuse to the surrounding rock and soil.With the increase of the length of the pile into the soil,the axial force in the pile body decreases nonlinearly and rapidly,and the stress diffuses to the surrounding rock and soil which reaching 8% of the pile top load within 1D of the lower part of the pile.The axial stress of piles with different diameters converges with depth,while the internal stress of piles diverges at the top and converges at the bottom.(5)Through the calculation and measurement of rock socketed ratio of different size piles and the comprehensive analysis of MIDAS software,it can be concluded that the rock socketed ratio hr/D form 1 to 3 is more appropriate,and the rock socketed ratio of soft rock in this case is about 1.6.