Study On Mechanical Properties And Vertical Bearing Mechanism Of Pile-Rock Interface For Deep Socketed Piles In Complex Strata Under Heavy Load

Large diameter deep socketed pile because of deep socketed rock,rock socketed pile lateral resistance to bear most of the load from the upper part.Among them,the traditional method of research on pile side friction resistance often thinks that the pile-rock interface is a plane in structure.In fact,for large-diameter deep rock-socketed piles,due to factors such as differences in construction methods,rock properties,and concrete pouring-The rock interface will form a rough surface with large geometrical differences,and the traditional assumption cannot accurately characterize the lateral resistance of the pile body;in addition,most of the static load tests are used to determine the bearing capacity of the pile foundation,but the large-diameter deep rock-socketed piles only The bearing capacity of the pile is extremely high,and the traditional static load test cannot be carried out because it is difficult to achieve damage,so the bearing capacity of the pile can only be determined by methods such as pile foundation specifications and numerical analysis.For this reason,this paper takes the large-diameter deep rock-socketed pile foundation project of a bridge as the background.The mechanical properties of the pile-rock interface,the vertical bearing mechanism and the ultimate resistance of the pile body of the deep rock-socketed piles are studied.The main research contents and results are as follows:（1）Based on the 3D laser scanning point cloud data and the statistical roughness characterization method,the 3D digital geometry reconstruction and quantitative analysis of the roughness of the surrounding rock were carried out.The characteristics can also reflect the spatial characteristics and the comprehensive parameter characterization method suitable for the roughness of the rock around the pile corresponding to the shear direction of the actual pile-rock interface.The theoretical function of the three-dimensional roughness coefficient JRC^3D realizes a more scientific and accurate quantification and evaluation of the rock roughness around the pile.（2）Collect rock samples from the bridge site to carry out basic rock physical and mechanical tests to obtain basic physical and mechanical parameters of sandstone;at the same time,based on the quantitative analysis of surrounding rock roughness JRC^3D,the pile-rock interface compression shear samples independently developed by the author are used to prepare The device prepared concrete-（mud）-sandstone interface compression shear samples under different concrete and surrounding rock sidewall pressure P_hi,carried out indoor shear tests,and obtained the shear shear of the pile-rock interface at different pile depths in the same sandstone stratum.The shear failure form,the change of the three-dimensional roughness coefficient JRC^3D before and after the interface shear failure,and the shear stress-shear displacement curve.After that,the Morhr-Coulomb strength criterion and the modified Barton structural plane shear strength formula were respectively used to fit the shear strength index of the pile-rock interface.The concrete is proportional to the pressure P_hi on the sidewall of the surrounding rock.（3）Numerical simulation of vertical bearing of large-diameter deep rock-socketed piles in complex strata with and without consideration of P_hi was carried out,and the load-settlement curves under each working condition were obtained.The load-settlement curve under each working condition,the evolution law of the axial force and lateral resistance of the pile body along the pile body,and the sharing ratio of the pile tip resistance and the lateral resistance of the pile body to the pile top load are obtained.The research results show that the bearing capacity of the pile foundation is increased by 30.47%compared with the case without P_hi,and the lateral resistance of the pile body varies along the depth of the pile in the same sandstone stratum,which is different from the pile foundation code that considers the same It is assumed that the lateral friction resistance of the formation piles is constant.（4）Based on the indoor interface shear test and numerical simulation analysis,the formula for the shear strength of the structural plane proposed by Barton scholars was revised,and the calculation formula for the ultimate lateral resistance of the large-diameter deep rock-socketed pile in the sandstone stratum was established.Consider the effects of interface roughness(JRC^3D),interface uniaxial compressive strength（JCS）,interface cohesion（c_m）,normal stress（σ_n）,and the interaction force P_hi between concrete and surrounding rock before initial setting on the side friction resistance of the pile body.