Cone Penetration Based Probabilistic Assessment of Shallow Foundation Settlement

Abstract

Probabilistic (Reliability or safety) analysis, as a measure of structural performance, was expressed in terms of reliability indices which were calculated for a total settlement of shallow foundations in a Site in Abuja, the Federal Capital of the Federal Republic of Nigeria based on the Burland and Burbidge settlement prediction method. Reliability indices were calculated with the objective of developing a risk analysis procedure specifically for prediction of the settlement of foundations lying on soils. This research was aimed at the development of a method that will assist in the process of calibration of load and resistance factors (reliability-based design (RBD)) for service limit state based on cone penetration test (CPT) results. The CPT data were obtained from four test holes (CPT1 - 4) at three foundation embedment depths of 0.6, 1.2 and 1.8 m and analysis was done using applied foundation pressures of 50, 100, 200, 300 and 500 kN/m2. Reliability analysis, expressed in the form of reliability index (β) and the probability of failure (p f) was performed for foundation settlement using the First Order Reliability Method (FORM) in MATLAB. The footings were designed for a 25 mm allowable settlement value as recommended in Eurocode 7 for serviceability limit state (SLS) design which is a conventional approach. Sensitivity study indicated that the applied foundation pressure and coefficient of variation (COV) of CPT tip resistance significantly affected the magnitude of foundation settlements and the variability of the geotechnical parameters is highly influenced and has a significant effect on the settlement and safety of any structure. The use of COV value of 30 % of CPT tip resistance which corresponds to target reliability index (βT) of 4.52 and target probability of failure (p fT) of 0.000677% based on the Burland and Burbidge method for SLS design is recommended for RBD of footings total settlement on soils in Abuja, Nigeria.