Developing LRFD Side Shear and End Bearing Resistance Factors for Design of Axially Loaded Drilled Shafts in Soil Containing Caliche Layers Using the Monte Carlo Approach

Conventional design and construction procedures of the drilled shafts (bored piles) are mainly developed for homogenous soils in the absence of highly cemented layers. However, the presence of competent and cementitious layers such as caliche deposits in soil profile can affect the resistance and settlement of pile foundations. This study concerns with the uncertainties on the resistance estimation of axially loaded drilled shafts in interaction with caliche layers The prime objective is to calibrate the side shear and end bearing resistance factors of axially loaded drilled shafts based on the soil characteristics of Nevada. The load-settlement responses of axially loaded drilled shafts installed as single piles are evaluated based on the 40 available databases of full-scale bi-directional Osterberg static load tests performed in the Southern Nevada valley. The side shear and end bearing resistance of drilled shafts are separately determined by analyzing upward and downward load-displacement components of the bidirectional Osterberg tests. To measure the drilled shafts’ resistances up to their failure capacity, extrapolations are conducted by incorporating polynomial, cubic spline, and exponential functions to achieve the best extrapolation fit using MATLAB. Furthermore, finite element back analysis is incorporated for extrapolations to include the geotechnical properties of homogeneous soil along with characteristics of caliche and drilled shafts to achieve outcomes with more accuracy on the measured resistances. Additionally, the resistance values of drilled shafts are predicted using the SHAFT program. The design procedure is conducted following the strength I limit state criteria of the Load and Resistance Factor Design (LRFD) approach. Resistance factors of axially loaded drilled shafts in the soil containing caliche deposits is calibrated by performing Monte Carlo (MC) simulation. Side shear and end bearing resistance of drilled shafts are calibrated and categorized if the extrapolation on measured values was conducted by MATLAB and FEM back analysis prior to commencing the calibration. The calibrated side shear resistance factors by MC based on the type of the performed MATLAB and FEM extrapolations are ∅Side=0.318 and ∅Side=0.365, respectively. The developed end bearing resistance factors using MC approach according to the extrapolations by MATLAB and FEM are determined as ∅Tip=0.242 and ∅ Tip=0.225. The developed resistance factors in this research by conducting MC simulations concerns with the presence of competent caliche layers in LRFD design procedure of axially loaded drilled shafts in Nevada soil and can be applied to other soil profiles with comparable geotechnical characteristics