Load-settlement Relationship Research Articles

A Study of the Prediction of Load-Settlement Curves of Bored Piles with an Improved Grey Model

An improved grey system model GM(1,1) was proposed in this paper, considered that the large difference between predicted results and measured load-settlement relationship results of bored piles, in which the prediction results were given by the original theory. The complete and incomplete load-settlement curves from pile loading tests were fitted and predicated by the improved grey model. The results calculated with empirical equations or methods in technical code for building pile foundations were compared with those predicted with the improved grey model. Analysis of a case study showed that the results predicted by the improved grey theory model GM(1,1) had higher precision, which demostrated that this improved theory was of significance in engineering practice.

Stiffness of reinforced level sandy ground loaded by a footing

ABSTRACT: Previous studies on the characteristics of reinforced level sandy ground have focused on the bearing capacity or settlement of footings at ultimate states. The applicability of their conclusions may be limited, because in many cases ground reaction modulus values are required. Based on the load–settlement relationship obtained from model footing tests, increases of the stiffness of reinforced sandy ground, loaded by a footing, are closely related to deep-footing and wide-slab effects. That is, theoretical bearing capacity ratios BCRd and BCRs, representing deep-footing and wide-slab effects, respectively, at ultimate states of reinforced sandy ground, can be used to evaluate the stiffness increases of reinforced sandy ground. A stiffness ratio Rk, defined as the ratio between the stiffness of reinforced ground and that of unreinforced ground subjected to a specific footing load q, can be expressed using linear functions of BCRd and BCRs. Results of regression analyses suggest that BCRs has a larger contribution to Rk than BCRd for all values of q examined, and that the effect of the wide slab on the ground stiffness increase is more pertinent for a relatively large value of q.

Modelling load–settlement behaviour of piles using high-order neural network (HON-PILE model)

An accurate estimation of pile response to loading is a challenging task due to the complexity of the soil–pile interactions and uncertainties in the soil properties. Conventional methods of predicting pile load–settlement relationship either oversimplify the problem or require the parameters that are difficult to determine in the laboratory. In this study, a high-order neural network (HON) is developed to simulate the pile load–settlement curve using properties of the pile and SPT data along the depth of pile embedment as inputs. The results indicated a significant improvement in the quality of HON predictions over that of BPN, RBF and GRNN models. Based on the comparisons with the predictions of elastic and hyperbolic models, the proposed HON model provides better predictions than existing theoretical models.

INVESTIGATION ON GROUND EXTENT THAT INFLUENCES LOAD-SETTLEMENT RELATIONSHIP OF PILE END

To estimate the load-settlement relationship of the pile end, the extent of ground below the end which influences the relationship should be considered. The consideration is more important in case of layered ground. In the paper, the extent is investigated by FEM analysis and pile load test results. On investigation by FEM analysis, 24 models of layered ground and the results show that the extent of the influence is different between two cases of layered ground. In the one case, standard penetration test N-value of a layer is equal to or larger than one of the upper layer. In the other case is opposite. It tells us the point for estimating the bearing capacity that the different average N-value should be adopted between the two cases. And the point is explained by a proposing model that pile end settlement is accumulated compressive deformation of layers. The pile load test result also shows that the point is proper.

Numerical assessment of axial pile group response based on load test

Axial pile load tests are considered within the design procedure of most major construction projects that include pile foundations, aiming to determine both the ultimate bearing capacity and the pile stiffness at working load level. Commonly used pile spacings of 3–4 pile diameters between the test pile and the reaction piles cause significant interaction with drastic effect on to the load-settlement relationship. The objective of this paper is to evaluate the influence of this interaction on both bearing capacity and stiffness of single piles and pile groups. For this purpose, a back analysis of a pile load test was initially performed which facilitated the determination of the single pile response and the verification of the soil properties. Subsequently, a numerical analysis was carried out to establish load-displacement relationships for several different layouts of pile groups. Based on these non-linear analyses the effect of the interaction was quantified for both the pile load test and pile group layouts examined.

Prediction of load–settlement relationship for large‐diameter piles

AbstractAn analytical solution for the bearing capacity of a large‐diameter pile is proposed based on the load transfer function in this paper. The load–settlement relationship or the P–S curve of such a pile can be determined by the proposed method for practical application. Comparison is made between the results obtained by the proposed method and the test data, and close agreement has been found, thus verifying the accuracy of the proposed method. It is noted that the most reliable approach to the determination of the vertical load capacity of a pile is to use the ­P–S curve, which is usually obtained through on‐site load test. However, for a large‐diameter pile (e.g. a diameter over 3 m), this kind of test requires a thousand tons of test load, which sometimes is impossible to provide. It is expected that the proposed method can be used in this kind of situation. Copyright © 2002 John Wiley & Sons, Ltd.

Observed and calculated load-settlement relationship in a sandy gravel

The purpose of this research was to obtain a better understanding of the nonlinear stress-strain behavior of the typical gravel of Santiago, Chile, due to the increasing needs for construction of high-rise buildings, multilevel underground constructions, and new subway lines to be built under historical city landmarks. A finite-element computer program to perform incremental stress-strain analyses of soils was developed on the basis of a modified version of the hyperbolic elastic model. The changes herein proposed to this well-known constitutive model were based on triaxial tests carried out on 150 mm diameter specimens of compacted sandy gravels which involved various stress paths. A comparison was performed between the observed and calculated load-settlement relationship in a plate-load test that included unloading-reloading cycles. From the good agreement obtained it is concluded that the modified version of the hyperbolic model proposed represents reasonably well the behavior of the Santiago gravel.Key words: constitutive relations, finite-element model, laboratory tests, field tests, soil properties, case history.

Visco-elastic load transfer models for axially loaded piles

Viscoelastic or creep behaviour can have a significant influence on the load transfer (t–z) response at the pile–soil interface, and thus on the pile load settlement relationship. Many experimental and theoretical models for pile load transfer behaviour have been presented. However, none of these has led to a closed-form expression which captures both non-linearity and viscoelastic behaviour of the soil. In this paper, non-linear viscoelastic shaft and base load transfer (t–z) models are presented, based on integration of a generalized viscoelastic stress–strain model for the soil. The resulting shaft model is verified through published field and laboratory test data. With these models, the previous closed-form solutions evolved for a pile in a non-homogeneous media have been readily extended to account for visco-elastic response. For 1-step loading case, the closed-form predictions have been verified extensively with previous more rigorous numerical analysis, and with the new GASPILE program analysis. Parametric studies on two kinds of commonly encountered loading: step loading, ramp (linear increase followed by sustained) loading have been performed. Two examples of the prediction of the effects of creep on the load settlement relationship by the solutions and the program GASPILE, have been presented. Copyright © 2000 John Wiley & Sons, Ltd.

Observed and calculated load-settlement relationship in a sandy gravel

Observed and calculated load-settlement relationship in a sandy gravel

Numerical analysis of piled rafts

An approximate numerical method for the analysis of piled raft foundations is presented. The raft is modelled as a thin plate and the piles as interacting non-linear springs. Both the raft and the piles are interacting with the soil which is modelled as an elastic layer. Two sources of non-linearity are accounted for: (i) the unilateral contact at the raft–soil interface and (ii) the non-linear load–settlement relationship of the piles. Both theoretical solutions and experimental results are used to verify that, despite the approximations involved, the proposed method of analysis can provide satisfactory solutions in both linear and non-linear range. © 1998 John Wiley & Sons, Ltd.

Field testing to evaluate stone column performance in a seismic area

For construction of a 16 mgd sewage treatment plant on predominantly deep, soft, cohesive soils in an area of highest seismic susceptibility, soil improvement with stone columns was considered as one foundation solution. While the deformation behaviour of subsoil improved with stone columns, under static vertical load, has been documented, little if any information is available on the performance of such improved soils under seismic loading conditions. For this reason, large scale field tests were performed to demonstrate that (a) in the process of stone column installation, sand lenses in the predominantly cohesive subsoil are sufficiently densified with respect to liquefaction potential; (b) the combined mass of stone columns and native, intervening soil develops suficient shear strength to resist safely horizontal forces resulting from a ground acceleration of 0·25 g; (c) the stone column pattern which satisfied the shear and density requirements also provides an adequate load-settlement relationship. Pour construire une usine de traitement de résidus (ayant une capacitéde 16 millions de gallonspar jour) sur des sols cohérents mous sur une grande profondeur dans une zone à grande séismicité on a envisagé d'améliorer le sol avec des colonnes de Pierre. Alors que l'on connaît bien le comportement sous une charge statique et verticale d'un sol amélioré par des colonnes de Pierre, il y a peu d'information concernant le comportement de tels sols sous les actions sismiques. Pour cette raison, on a réalisé des essais de chantier, importants, afin de démontrer que (a) par la méthode d'installation de colonnes depierre, les lentilles de sable dans les sous-sols essentiellement cohésifs, sont sufisamment densifiées vis à vis de la possibilité de liquéfaction; (b) les colonnes de Pierre et le sol originel intervenant ensemble, peuvent développer sufisamment de résistance de cisaillement pour résister en sécurité aux forces horizontales résultant d'une accélération terrestre de 0·25 g; (c) le modèle de colonne en Pierre satisfaisant aux exigences de densité et de cisaillement présente aussi la relation charge–tassement correcte.

A field trial of the reinforcing effect of a stone column in soil

The load-settlement relationship for plate loading of an isolated stone column in soft clay was predicted prior to field testing. The column was constructed by vibro-replacement and, after the test, was excavated to check its dimensions. The theory used was proposed on the basis of laboratory model tests by Hughes and Withers (1974). The purpose was to verifv the theory on a field scale. A standard site investigation supplemented by Cambridge and Ménard pressuremeter tests provided basic soil parameters. The ultimate column load depends on the friction angle of the gravel used to form the column, the size of the column formed and the restraint of the clay on the uncemented gravel. To predict the load-settlement curve the essential radial stress-strain data for the clay were obtained from a Cambridge pressuremeter. The prediction is excellent if allowance is made for transfer of load from column to clay through side shear and correct column size. Accurate estimation of column diameter is the major factor influencing the calculation of ultimate load and settlement characteristics. The column improved substantially the bearing capacity of the natural soil. La relation charge-tassement pour un essai à la plaque d'une colonne en Pierre, isolée, dans l'argile molle, a été prévue avant l'essai in situ. Suite à l'essai, la colonne construite par la méthode de vibro-remplacement, a été excavée afin de vérifier ses dimensions La théorie utilisée est à la base d'essais sur modèle de laboratoire, d'après Hughes et Withers (1974). L'objectif a été de vérifier cette théorie à l'échelle du chantier. Une reconnaissance classique du terrain, complétée par des pressiomètres de Cambridge et Ménard, ont fourni les caractéristiques du sol. La charge limite de rupture d'une colonne, dépend de l'angle de frottement du gravier qui la forme, de sa taille et de la contrainte de l'argile sur le gravier non-cimenté. Afin de prévoir la courbe de charge-tassement, l'information essentielle de contrainte-déformation, a été obtenue à l'aide du pressiomètre de Cambridge. La prévision est excellente, si l'on tient compte du transfer de la charge, de la colonne à l'argile, grâce au cisaillement latéral et la taille exacte de la colonne. Une estimation précise du diamètre de la colonne, est le facteur principal pouvant influencer le calcul de la charge de rupture et du tassement. La colonne a considérablement amélioré la force portante du sol réel.