Evaluation of the pile bearing capacity in rock interbedded by cohesion soils under vertical loading

Introduction. The current regulatory calculation procedure for piles in rocks provides a means to determine the bearing capacity of a pile embedded in a solid rock mass containing no weak interlayers. However, it is not uncommon in actual design practice for rocky soils to be interbedded with softer and less stiff dispersive soils, whose presence affects pile performance. In this case, a summation of estimated resistances along the pile length and at its foot overestimates its estimated bearing capacity, which does not correspond to the actual work due to the different rates of friction force generation in soils of varying formations.
Aim. To develop a procedure for determining the bearing capacity of a single bored cast in place pile interacting with rock mass interbedded with cohision soils under vertical indentation loading.
Materials and Methods. The procedure for estimating the skin friction resistance of a pile penetrating rocky and dispersive soils is based on the analysis of static pile tests and numerical simulation, taking into account tabulated and analytical solutions given in regulatory literature.
Results. A procedure for determining the bearing capacity of a single pile interacting with a rock mass interbedded with cohision soils was developed using tabulated solutions given in regulatory literature, empirical dependencies, and numerical simulation. As a criterion for the ultimate shear resistance of bearing soil, a formula for reference settlement S_ref is proposed, which factors in pile dimensions and the characteristics of the pile shaft material. The extent to which the pile bearing capacity is sensitive to the parameters of the model and computational assumptions of numerical modeling is analyzed. The presented examples of determining the design pile bearing capacity via the proposed procedure show results similar to experimental data obtained in the field tests.
Conclusions. The presented method allows engineers to factor in the skin friction resistance of cohision soil interbedding in the rock mass to increase its design bearing capacity.

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