Mahmoud N. Hussien

Soil–pile separation effect on the performance of a pile group under static and dynamic lateral loads

The effect of soil–pile separation is studied with respect to the performance of a laterally loaded pile group. Full-scale tests, which consist of a combination of a single and a 3 × 5 group pile under static and dynamic lateral loads, present a unique opportunity and allow a rigorous study without arbitrary parameter back-fitting. The coupled soil–pile system is idealized through two-dimensional finite elements with soil models idealized by a hyperbolic-type multiple shear mechanism. Nonlinear spring elements are used to idealize the soil–pile interaction through a hysteretic nonlinear load–displacement relationship. Joint elements with a separation–contact mechanism are used to idealize the separation effect at the soil–pile interface. Ignoring soil–pile separation in static tests overestimates the ultimate lateral load–carrying capacity by 43% for a single pile and 73% for the trailing pile in a closely spaced pile group. Moreover, neglecting soil–pile separation in dynamic tests overestimates the tota...

Vertical loads effect on the lateral pile group resistance in sand

Vertical loads effect on the lateral response of a 3×5 pile group embedded in sand is studied through a two-dimensional finite element analysis. The soil-pile interaction in three-dimensional type is idealized in the two-dimensional analysis using soil-pile interaction springs with a hysteretic nonlinear load displacement relationship. Vertical loads inducing a vertical pile head displacement of 0.1-pile diameter increase the lateral resistance of the single pile at a 60 mm lateral deflection by 8%. Vertical loads inducing the same vertical displacement applied to a pile group spaced at 3.92-pile diameter increase the overall lateral resistance by 9%. The effect on individual piles, however, depends on the pile position. The vertical load decreases the lateral resistance of the leading pile (pile 1) by 10% and increases the lateral resistances of piles 2, 3, 4, and 5 by 9%, 14%, 17%, and 35%, respectively. Vertical loads applied to the pile group increase the confining pressures in the sand deposit confined by the piles but the rate of increase in those outside the group is relatively small, resulting in the difference in a balance of lateral soil pressures acting at the back of and in front of the individual pile.

Prediction of axial capacity of piles driven in non-cohesive soils based on neural networks approach

AbstractThis paper presents an application of two advanced approaches, Artificial Neural Networks (ANN) and Principal Component Analysis (PCA) in predicting the axial pile capacity. The combination of these two approaches allowed the development of an ANN model that provides more accurate axial capacity predictions. The model makes use of Back-Propagation Multi-Layer Perceptron (BPMLP) with Bayesian Regularization (BR), and it is established through the incorporation of approximately 415 data sets obtained from data published in the literature for a wide range of un-cemented soils and pile configurations. The compiled database includes, respectively 247 and 168 loading tests on large- and low-displacement driven piles. The contributions of the soil above and below pile toe to the pile base resistance are pre-evaluated using separate finite element (FE) analyses. The assessment of the predictive performance of the new method against a number of traditional SPT-based approaches indicates that the developed ...

Ultimate Lateral Resistance of Piles in Cohesive Soil

Abstract The ultimate lateral resistance of piles in cohesive soil is studied using the well-known finite difference code, FLAC2D. The Modified Cam Clay (MCC) constitutive relation is adopted in the analyses to model the cohesive soil behavior, whereas the structural pile model with three degree of freedoms, available in FLAC2D library, is adopted to model the piles. The reliability of Bromss method, still used in the current design practice of piles under lateral loads, is verified. Comparisons between the ultimate lateral resistances of piles and those deduced from the graphs proposed by Broms (1964) are presented in graphs. Different factors thought to affect the lateral resistance of piles in cohesive soil, not adequately considered in Bromss method, such as clay stiffness, pile length, pile diameter and axial load are parametrically studied. A special concern is devoted to elucidate the effects of over-consolidation ratio (OCR) on the ultimate lateral resistance of piles in cohesive soil.

Numerical investigation of the lateral response of battered pile foundations

Three-dimensional finite difference parametric analyses have been carried out to investigate the influence of vertical loads on the lateral performance of battered piles in both sandy and clayey soils. Different batter angles and soil stiffness were considered to examine the salient features of this complex soil–structure interaction problem. Numerical results show that the lateral response of battered piles embedded in sands is influenced by the value and the direction of the pile inclination, the presence of vertical loads as well as the soil state of density. When the lateral load acts in the opposite direction of the pile inclination (negative batter angle), the lateral response of the piles increases substantially with the batter angle as well as the sand packing. The response of piles at positive batter angles, however, does not appear to vary considerably with the batter angle or the sand density. The effect of the vertical loads on lateral response of battered piles in sands is found to be very pronounced. On the other hand, the lateral response of piles embedded in a clayey soil at negative batter angles increases greatly with the inclination angle and does not vary with its undrained shear strength. The lateral response of the piles with positive inclination angles is independent of the batter angle and the soil stiffness. Moreover, the presence of a vertical load prior to the application of a lateral load to a battered pile does not alter its lateral capacity.

Load sharing ratio of pile-raft system in loose sand: an experimental investigation

This technical note presents the results of a series of tests carried out on instrumented model pile-raft foundation to investigate the load sharing ratios between the foundation’s components where a loose sand layer is encountered near the ground surface. Four different pile-raft models with two different pile numbers and lengths were considered. In each model, the settlement of the raft and the load of each pile were monitored during the load application process. The experiments showed the effectiveness of pile length on reducing the overall settlement of the pile-raft system. The results showed also that the proportion of load transferred to any pile in a closely spaced pile group increases with its distance from the centre of the group. Unlike some previous studies that classified soil profiles containing loose sands near the surface as unfavourable situations for piled rafts, the experimental results herein represent an evidence of the efficiency of piled rafts even in soil profiles with loose sands immediately beneath the raft. Indeed, ignoring the contribution of the raft would lead to unnecessary over-conservatism in the design of piled rafts.