Pile Groups In Clay Research Articles

Investigating the Efficiency Coefficient of Pile Group in Clay Under Two-Way Lateral Load

Investigating the Efficiency Coefficient of Pile Group in Clay Under Two-Way Lateral Load

Estimation of Settlement of Pile Group in Clay Using Soft Computing Techniques

Estimation of Settlement of Pile Group in Clay Using Soft Computing Techniques

Influence of a rigid cap on thermo-mechanical behavior of nonsymmetrical thermally loaded energy pile group in clay

This paper presents the results of a series of cyclic nonsymmetrical thermally loaded model-scale tests conducted on floating pile groups, with and without a rigid cap in saturated clay. The energy pile in each group was subjected to 10 two-way (heating–cooling) thermal cycles with an amplitude of 15 °C to investigate the potential effects of a rigid cap on the thermomechanical behavior of energy pile groups. It was found that the rigid cap restrained the expansion/contraction of the energy pile in response to temperature change and reduced its irreversible settlement, resulting in a lower differential settlement between the energy and nonenergy piles. Consequently, a lower tilting was observed in the pile group with a rigid cap. In addition, the thermally induced axial load was significantly increased (especially in cooling mode) due to the restriction of a rigid cap. The thermomechanical load transfer profile of the energy pile was also affected by it, resulting in the downward transmission of shaft resistance.

Combined loading of RC pile groups in clay accounting for N–M interaction

Motivated by the need for retrofit of existing bridges, this paper explores the nonlinear response of pile groups in clay under combined loading. The problem is analysed numerically, employing a kinematic hardening model for soil, and the Concrete Damaged Plasticity (CDP) model for the reinforced concrete (RC) piles. Using a reference 2 × 1 pile group, it is shown that three resistance mechanisms are mobilized: axial pile loading (Max), pile bending (Mb), and pilecap resistance (Mcap). While current design practice typically considers only the first mechanism, it is shown that allowing for strongly nonlinear soil response and full mobilization of all three mechanisms may lead to a significant increase of pile group moment capacity. The analysis also reveals the need to account for axial force–bending moment (N−M) interaction of the RC piles, which is feasible through the CDP model. Especially for existing pile groups, more realistic estimation of ultimate moment capacity may facilitate the development of rational retrofit strategies. A parametric study is subsequently conducted, exploring the effect of the safety factor against vertical loading (FSv), the moment to shear (M/H) ratio, interface modelling, and pilecap contribution. The results are generalized by analysing more complex 3 × 1 and 4 × 1 pile group typologies and by deriving 3D failure envelopes in the V – H – M space. Thanks to the contribution of the pilecap, the decrease of FSv leads to an expansion of the failure envelope, which can be of relevance for existing pile group assessment after bridge widening. Finally, the interaction diagrams are normalized, leading to a unique non-dimensional 3D failure envelope for all examined pile group typologies.

Numerical evaluation of scour effects on lateral behavior of pile groups in clay

Scour can cause the water-induced failure of fluvial and marine bridges and structures. Previous studies have focused on the scour mechanisms and their effects on the load capacity of single piles, although deep foundations consist mostly in pile groups. In this paper, scouring on pile groups embedded in soft clay is studied when piles are laterally loaded and affected by the formation of scour holes. This boundary problem is simulated using the three-dimensional finite element method. The scour depth, slope angle, and pile spacing are analyzed as main influence factors. Summary charts quantify how the dimensions of scour holes affect the lateral load capacity of 3x3 pile groups for varying pile spacing and their corresponding p-multipliers. Importantly, results indicate that it is unreasonable to design pile foundations by ignoring the influence of scour holes or directly removing the soil layer above the scour depth, as frequently assumed in practice.

Pile group in clay under cyclic lateral loading with emphasis on bending moment: Numerical modelling

Pile foundations supporting major structures are often founded in soft compressible clays. Apart from usual super-structural loading, these piles are subjected to cyclic lateral loads originating from actions of waves, ship impacts, winds or moving vehicles. Such repetitive loading induces stress reversal in adjacent soft clay initiating progressive degradation in soil strength and stiffness. This not only deteriorates the pile capacity with unacceptable displacements, the bending moments also increase. Although past studies investigated the response of single pile under lateral cyclic loading, a detailed study on pile group in clay under cyclic lateral loading with emphasis on bending moment is of immense practical interest. This paper focuses on detailed study of the response of pile group in clay under cyclic lateral loading, with emphasis on bending moment, through numerical modelling via a three-dimensional dynamic finite element (FE) approach and simplified boundary element modelling (BEM). Comparisons of computed results with available test data imply that the results obtained by 3 D dynamic FE model are better than the BEM. Extensive parametric studies with field data indicate that pile bending moment has been significantly influenced by cyclic loading parameters (number of cycles, frequency and amplitude). Relevant conclusions are drawn from the entire study.

Centrifuge Modeling of Cyclic Nonsymmetrical Thermally Loaded Energy Pile Groups in Clay

Heat transfer from/to energy piles can cause plastic contraction of soft clay with a low overconsolidation ratio (OCR) during heating and cooling. This can lead to thermally induced excess pore water pressure and changes in the lateral stress acting on a pile. These thermally induced phenomena cause additional plastic settlement of the soil and pile. Irreversible settlement may cause serviceability or ultimate limit state problems for floating energy piles whose capacity is mainly derived from shaft resistance. Due to intended operational needs or by accident, cyclic nonsymmetrical thermal loads may be applied to floating energy pile groups and piled rafts. The thermomechanical interaction among nonsymmetrical loaded piles is not well understood. In this study, a series of cyclic nonsymmetrical thermally loaded centrifuge model tests were conducted on floating pile groups and piled rafts in soft kaolin clay with an OCR of 1.7 at the pile toe. The performance of floating 2×2 elevated energy pile groups and energy piled rafts was investigated. Three piles in each group were subjected to 15 cycles of ±14°C in temperature change. The thermally induced irreversible settlement and tilting of the elevated pile groups exceeded serviceability and ultimate criteria. The piled rafts similarly settled but to a smaller extent than the elevated group. Their tilting, however, did not exceed the serviceability criterion. It is recommended that energy piled rafts be used in soft clay instead of elevated energy piles.

Reliability Analysis of Settlement of Pile Group in Clay Using LSSVM, GMDH, GPR

Robust and reliable design at certain levels of safety has earned lot of attention in recent. To build over the limitations of FOSM based reliability analysis, the paper proposes least square support vector machine (LSSVM), The Group Method of Data Handling (GMDH) and Gaussian process regression (GPR) based reliability analysis of pile group resting on cohesive soil. LSSVM is an improvement over support-vector machines (SVM) which uses linear systems instead of complex quadratic equations. GMDH is a self-organized neural network capable of solving complex non-linear problems. GPR is an effective Bayesian tool of machine learning the performance of the developed models is ascertained using various statistical parameters and Taylor curves. The reliability indices of the simulated values are compared to that of the actual values obtained from FOSM. The results show that all the models are applicable for reliability analysis of settlement of pile group.

Estimation of P-multipliers for laterally loaded pile groups in clay and sand

ABSTRACTPile-supported marine structures are generally subjected to lateral loads caused by earthquakes, waves, currents, etc. p–y curves are traditionally used to evaluate the response of a pile under lateral loading. For a group of piles, p–y curves need to be modified using a factor referred to as P-multiplier. In this study, two new models were developed to predict the P-multiplier for the pile groups in clay and sand using genetic programming. To this end, an extensive database was gathered from the previous experimental studies on the pile groups. In addition to input parameters used for P-multiplier estimation in design guidelines, several other governing parameters were considered in this study. The accuracy of the proposed formulas was investigated by various error measures and it was shown that the new models outperform the previous approaches. Moreover, the uncertainties incorporated in the new formulas were assessed and also a sensitivity analysis was performed.

Numerical modelling of perimeter pile groups in clay

The load distribution among piles in a group varies such that the inner piles often carry a smaller share of the total load compared to the outer piles, which is a result of increased soil–pile interaction. The main objective of this paper is to establish the relative effectiveness of pile groups with no inner piles (perimeter group), when compared to the more common grid configuration. The numerical investigation utilized the finite element programme ABAQUS and considered a range of variables that affect pile group behaviour including number of piles, pile spacing, length/diameter ratio, and soil strength. It was demonstrated that a complete grid group is less efficient than a perimeter group, where efficiency is defined as the load capacity of the whole group expressed as a ratio of the number of piles in the group multiplied by the load capacity of a single isolated pile. Efficiencies close to unity were observed for some perimeter groups. Perimeter groups also showed that a “block” type group failure could occur, where piles were placed at a spacing of less than 2.0 pile diameters,d, centre-to-centre. This often, but not always, led to a reduction in the efficiency of the pile group.

Dynamic Response of Laterally Loaded Pile Groups in Clay

The effects of pile spacing, number of piles, and configuration on displacement and bending response of pile groups in clay under dynamic lateral loading were investigated. The displacement response of pile group in clay is strongly nonlinear. Pile-soil-pile interaction is predominant for the groups with closer spacing and with greater number of piles. Group interaction causes reduction in the group stiffness and increase in damping of the pile group. Strong group interaction leads to significant differences in bending profiles of different row piles of the groups. Dynamic lateral loading increases the maximum bending moment and active pile length.

Experimental Investigations on the Behaviour of Pile Groups in Clay Under Lateral Cyclic Loading

This paper presents the results of two-way cyclic lateral load tests carried out on model pile groups embedded in soft marine clay. The tests are conducted on 1 × 2, 2 × 2 and 3 × 3 pile groups having length to diameter ratio (L/D) of 15, 30 and 40 with the spacing to diameter ratio (S/D) of 3, 5, 7 and 9. The experimental results are presented in the form of load–deflection curves and bending moment profiles. Cyclic group efficiency, critical spacing, critical cyclic load level and cyclic p-multipliers are evaluated. It is found that the lateral capacity of the 3 × 3 group reduces by about 42% after 50 cycles of loading. The cyclic p-multipliers of 3 × 3 pile group are found to be 0.41, 0.25 and 0.29 for leading, intermediate and rear rows respectively. The test results are compared with the numerical analysis carried out by p–y method using GROUP program. The analysis carried out with experimentally evaluated p-multipliers predicts load—deflection and bending profiles of pile groups reasonably well, but underestimates the depth to maximum bending moment by about 15%.

Discussion of “Centrifuge Model Study of Laterally Loaded Pile Groups in Clay” by T. Ilyas, C. F. Leung, Y. K. Chow, and S. S. Budi

Discussion of “Centrifuge Model Study of Laterally Loaded Pile Groups in Clay” by T. Ilyas, C. F. Leung, Y. K. Chow, and S. S. Budi

Discussion of “Centrifuge Model Study of Laterally Loaded Pile Groups in Clay” by T. Ilyas, C. F. Leung, Y. K. Chow, and S. S. Budi

Discussion of “Centrifuge Model Study of Laterally Loaded Pile Groups in Clay” by T. Ilyas, C. F. Leung, Y. K. Chow, and S. S. Budi

Closure to “Centrifuge Model Study of Laterally Loaded Pile Groups in Clay,” by T. Ilyas, C. F. Leung, Y. K. Chow, and S. S. Budi

Closure to “Centrifuge Model Study of Laterally Loaded Pile Groups in Clay,” by T. Ilyas, C. F. Leung, Y. K. Chow, and S. S. Budi

Centrifuge Model Study of Laterally Loaded Pile Groups in Clay

A series of centrifuge model tests has been conducted to examine the behavior of laterally loaded pile groups in normally consolidated and overconsolidated kaolin clay. The pile groups have a symmetrical plan layout consisting of 2, 2 32, 233, 333, and 434 piles with a center-to-center spacing of three or five times the pile width. The piles are connected by a solid aluminum pile cap placed just above the ground level. The pile load test results are expressed in terms of lateral load-pile head displacement response of the pile group, load experienced by individual piles in the group, and bending moment profile along individual pile shafts. It is established that the pile group efficiency reduces significantly with increasing number of piles in a group. The tests also reveal the shadowing effect phenomenon in which the front piles experience larger load and bending moment than that of the trailing piles. The shadowing effect is most significant for the lead row piles and considerably less significant for subsequent rows of trailing piles. The approach adopted by many researchers of taking the average performance of piles in the same row is found to be inappropriate for the middle rows, of piles for large pile groups as the outer piles in the row carry significantly more load and experience considerably higher bending moment than those of the inner piles.

Lateral Load Behavior of Full-Scale Pile Group in Clay

A static lateral load test was performed on a full-scale pile group to determine the resulting pile-soil-pile interaction effects. The 3 × 3 pile group at three-diameter spacing was driven into a profile consisting of soft to medium-stiff clays and silts underlain by sand. The piles were instrumented with inclinometers and strain gages. The load carried by each pile was measured. A single pile test was conducted for comparison. The pile group deflected over two times more than the single pile under the same average load. Group effects significantly reduced load capacity for all rows relative to single pile behavior. Trailing rows carried less than the leading row, and middle row piles carried the lowest loads. Maximum moments in the group piles were 50–100% higher than in the single pile. P-multipliers were 0.6, 0.38, and 0.43 for the front, middle, and back row piles, respectively. Good agreement between the measured and computed pile group responses was obtained using the p-multiplier approach. Design c...

Cyclic Response of Axially Loaded Pile Groups

This paper presents a total stress hybrid load‐transfer analysis for the response of pile groups in clay under either uniform or irregular cyclic loading. The soil mass may be arbitrarily layered and the nonlinear pile response is represented by a simple cyclic hyperbolic interface soil model. The reduction of shaft stress and accumulation of displacement are considered using the degradation of the soil secant modulus and shaft limiting stress. The shaft‐stress‐degradation factor is related to the cyclic strain in a hyperbolic form. The formulation of the analysis is relatively simple and the soil parameters required are relatively few and have physical meaning. The method is used to analyze the response of model pile‐group tests in soft clay under cyclic loading. In addition, a repeated monotonic loading on a full‐scale pile‐group field test in stiff overconsolidated clay is analyzed. The measured and computed results are in reasonably good agreement.

Pile-soil-pile interaction considering weakened zone of soil around piles

Under working conditions, the effect of high shear strains in the soil due to loads acting on the piles is simulated by a numerical model which considers a weakened zone of soil around each pile in a linear elastic pile group settlement analysis. Two reported case histories of field tests on pile groups in clay are analysed and the results show that the consideration of this weakened zone better models the behaviour of pile groups under vertical working loads.

Dynamic lateral response of a pile group in clay : Blaney, G W; O'Neill, M W Geotech Test JV12, N1, March 1989, P22-29

Dynamic lateral response of a pile group in clay : Blaney, G W; O'Neill, M W Geotech Test JV12, N1, March 1989, P22-29