Koohyar Faizi

Developing a hybrid PSO---ANN model for estimating the ultimate bearing capacity of rock-socketed piles

Rock-socketed piles are commonly used in foundations built in soft ground, and thus, their bearing capacity is a key issue of universal concern in research, design and construction. The accurate prediction of the ultimate bearing capacity (Qu) of rock-socketed piles is a difficult task due to the uncertainty surrounding the various factors that affect this capacity. This study was aimed at developing an artificial neural network (ANN) model, as well as a hybrid model based on both particle swarm optimisation (PSO) and ANN, with which to predict the Qu of rock-socketed piles. PSO, a powerful population-based algorithm used in solving continuous and discrete optimisation problems, was here employed as a robust global search algorithm to determine ANN weights and biases and thereby improve model performance. To achieve the study aims, 132 piles socketed in various rock types as part of the Klang Valley Mass Rapid Transit project, Malaysia, were investigated. Based on previous related investigations, parameters with the most influence on Qu were identified and utilised in the modelling procedure of the intelligent systems. After constructing and modelling these systems, selected performance indices including the coefficient of determination (R2), root-mean-square error, variance account for and total ranking were used to identify the best models and compare the obtained results. This analysis revealed that the hybrid PSO–ANN model offers a higher degree of accuracy compared to conventional ANN for predicting the Qu of rock-socketed piles. However, the developed model would be most useful in the preliminary stages of pile design and should be used with caution.

Uplift Resistance of Buried Pipelines Enhanced by Geogrid

Failure of an oil or gas pipeline due to low uplift resistance of soil has serious economic and environmental consequences; hence, increasing the uplift resistance through soil reinforcement is of interest. The main purpose of this paper is to investigate the possible use of geogrid to enhance the uplift resistance of buried pipelines. For this reason, 11 small-scale laboratory tests were performed. The tests were conducted to investigate the effect of pipe diameter, burial depth, as well as length and number of geogrid layers on the uplift resistance of sandy soils. The experimental results suggest that although pipe diameter and burial depth are directly related to uplift resistance, the direct effect of geogrid incorporation is more pronounced. While Peak Uplift Resistance (PUR) is of interest, findings indicate that the number of geogrid layers does not have a pivotal influence on PUR. In addition, for verification purpose, the PUR of 11 laboratory tests were back analyzed numerically using finite element software PLAXIS 3D TUNNEL. The findings show that numerical and experimental results are in good agreement.

Various effective factors on peak uplift resistance of pipelines in sand: a comparative study

ABSTRACT A considerable attention to failure of pipelines should be paid to increase the uplift resistance of pipelines and it can be achieved by increasing the burial depth or utilizing soil improvement methods. The purpose of this study is to investigate the uplift resistance of buried pipelines in various conditions. In this regard, 17 small-scale laboratory tests were conducted to survey the roles of pipeline diameter, burial depth, geogrid length, and the number of geogrid layers, on the peak uplift resistance (PUR) in loose sand. Results of experimental tests clearly showed that burial depth and pipeline diameter affect the uplift resistance results directly and also revealed that the number of geogrid layers does not affect the PUR results, noticeably. However, when the residual PUR values are considered, the use of two geogrid layers instead of one geogrid layer for the same length is of advantage. On the other hand, ‘PLAXIS 3D TUNNEL’ and ‘ABAQUS’ programmes were used to analyse and verify 17 experimental results. As a result, average error values of 11.56 and 18.43 were obtained for ABAQUS and PLAXIS 3D TUNNEL programmes, respectively, which show that ABAQUS programme can simulate PUR results of pipeline with a higher degree of accuracy.

The Influence of Bituminous Coating on Uplift Resistance of Short Pile Foundations in Sand

Bituminous coatings can be used to reduce negative skin friction on pile. The present study investigates the other applications and the effectiveness of heated coating withelastic and visco-elastic-plastic behavior on the skin friction at soil-pile interface. Aseries of small scale physical modeling tests of short pile foundations under pullout load was carried out to study the effects of adhesive coating materials on the short pile foundation interaction. The results indicated that heated bituminous materials can significantly affect the pull-out capacity of short pile foundations.