Stochastic Application on the Variability of Soil Deformation Models

Abstract

This study conducted a probabilistic evaluation of immediate settlement with foundation depths at the centre of raft foundation in Borokiri and Nwokekoro close, Old GRA, Port Harcourt, Rivers State, Nigeria. It utilized deterministic methods for immediate settlement analysis, specifically those developed by Meyerhof, Peck and Bazaraa, Steinbrenner and Fox, Mayne and Poulos, and Burland and Burbidge. The geotechnical and elastic parameters necessary for reliability estimation were derived from the geotechnical investigation of soil samples collected from the sites. Serviceability limit state functions were formulated based on the immediate settlement equations mentioned earlier. The uncertainties associated with the random variables for each limit state function were sourced from existing literature. Reliability estimates were performed using computer programs developed in MATLAB based on the First Order Reliability Method (FORM). The findings indicated that in the Borokiri area, the Steinbrenner and Fox method produced reliability index values ranging from 2.4 to 2.7, which are within the recommended target reliability index range (2.5 – 4.0) for geotechnical structures. In contrast, the Mayne and Poulos method yielded a higher reliability index (6.1 to 6.5). The other methods, such as Burland and Burbidge (-0.07 to 1.6), Meyerhof (-1.4 to 0.8), and Peck and Bazaraa (-2.5 to - 0.6), underestimated the target reliability index. For the Nwokekoro close, Old GRA area, Steinbrenner and Fox again provided reliability index values between 3.4 and 4.0, aligning with the recommended target reliability index, while Mayne and Poulos (6.3 to 7.2) overestimated. The other methods, such as Burland and Burbidge (-2.3 to 1.9), Meyerhof (-2.4 to 1.7), and Peck and Bazaraa (-3.3 to 0.5), underestimated the target reliability index. Consequently, the Steinbrenner and Fox method emerged as the most reliable for predicting the immediate settlement of raft foundations in both Borokiri and Nwokekoro close, Old GRA. These results corroborate the findings from deterministic methods, suggesting that as estimated settlement exceeds the maximum allowable limit, the reliability index is expected to decrease, and vice versa. The MATLAB program developed in this research is user-friendly and suitable for geotechnical applications.