Influence of displacements determination accuracy of bored piles on analysis results of their response under lateral loads

An approach to improve of determination reliability of horizontal displacements (x), bending moments (M), shear forces (Q), horizontal soil reaction (R), which describes of soil reaction along surface, for large-diameter bored piles under lateral loads is proposed. in the article. As the research object a bored pile with 1.5 m diameter and 12.5 m length (hereinafter referred to as the TP15 pile), tested under lateral loads (P) with various intensity, was taken. The proposed approach provides for construction and comparison on depth (z) reaction diagrams x(z), M(z), Q(z), R(z), obtained using two following ways (methods). Method #1 based for classical differentiation of a rotation angles φ(z) curve for normal sections of the pile, method #2 - provides direct differentiation of a M(z)-diagram obtained from FEM-analysis results under a pile model, which involves using of lateral displacements on x(z)-curve, which were determined with the method #1 for assign of parameters for check points located at a depth (z) along of the pile length. The authors obtained distribution diagrams of K-coefficient and a subgrade-soil-resistance coefficient CZ (in a formulation of SP 24.13330) along length of the tested pile. The research was carried out using results of in-situ experiments conducted by G. Price and I.F. Wardle (1987), in particular using measurements of angular displacements (φ) of check points along length of the pile. The diagrams (curves) were plotted by the authors in MathCAD; computational estimations of M(z)-curves for method #2 are made in SAP2000 taking into account non-linear deformations of reinforced concrete members. For reliability assessments of M(z), Q(z), R(z) values obtained by these two methods, several assessment criteria were accepted. It has been established that slight deviations of a φ(z)-curve plotted using analytical function, when it envelopes discrete φ-values obtained during inclinometric measurements, these slight deviations have a significant influence on calculation reliability of M(z), Q(z), R(z). It is shown that at the slight deviations of a φ(z)-curve for the TP15 under P = 1200 kN a discrepancy between displacement values (x) determined 0.7%, discrepancies between maximum values of (M), (Q) and (R) are 30, 30 and 38% respectively. It has been established that K(z) and CZ(z) dependencies obtained for the pile at different load (P) at land-surface level have a radically different view. This feature should be explained by peculiarities of non-linear behavior of soil and inelastic reaction of the pile under high intensity lateral loads.