Full-scale Pile Groups Research Articles

BEHAVIOR OF PILE GROUPS UNDER LATERAL LOADS IN SAND SOIL CONSIDERING MOHR-COULOMB AND MODIFIED MOHR-COULOMB CRITERIONS: COMPARATIVE ANALYSIS

The behavior of pile groups under lateral loads depends on the soil-structure interaction which is governed by the soil properties and behavior. In the three-dimensional finite element analysis, the prediction of the realistic soil behavior is a complex step in order to capture the realistic pile-soil interaction. In the analysis programs, the soil behavior can be defined using constitutive models like the Mohr-Coulomb constitutive model which is widely used in representing the soil layers in the analysis, but a new modified constitutive model called the Modified Mohr-Coulomb model also used in the analysis along with other constitutive models. The goal of this research is to compare the two constitutive models' capacity to capture the behavior of a full-scale pile group case study and validate the results to field measurements. A good agreement is found between the measured and the computed behavior of pile groups under lateral loads using the Modified Mohr-Coulomb constitutive model. يعتمد سلوک مجموعات الخوازيق تحت تأثير الأحمال الجانبية على التفاعل بينها وبين التربة والذي تحکمه خصائص التربة وسلوکها. في تحليل العناصر المحدودة ثلاثي الأبعاد ، يعد التنبؤ بسلوک التربة الواقعي خطوة معقدة لالتقاط تفاعل واقعي بين التربة و الخوازيق. فعادة يستخدم نموذج مور- کولومب على نطاق واسع في تمثيل طبقات التربة وسلوکها في التحليل العددي، ولکن يتم أيضا استخدام نموذج جديد معدل يسمى نموذج مور- کولومب المعدل في التحليل العددي جنبا إلى جنب مع النماذج الأخرى. الهدف من هذه الدراسة هو مقارنة قدرة النموذجين سالفي الذکر في التقاط سلوک مجموعة الخوازيق تحت تأثير الحمل الجانبي ومقارنة النتائج مع القياسات الميدانية. لوحظ اتفاق جيد بين السلوک المقاس والمحسوب لمجموعات الخوازيق تحت تأثير الأحمال الجانبية باستخدام نموذج مور- کولومب المعدل في تمثيل التربة.

Equivalent pier analysis of full-scale pile groups subjected to mechanical and thermal loads

Abstract This study presents an equivalent pier analysis of the vertical deformation and displacement of full-scale pile groups subjected to mechanical and thermal loads that are associated with a structural support and a geothermal heat exchanger operation, respectively. Based on the simulation of the behavior of a single representative pile, the investigation addresses pile groups characterized by different end-restraint and site conditions through the equivalent pier method. Loading levels of varying significance, which can be associated to a reversible response of the piles in the group as well as to an irreversible response due to the occurrence of plastic strains in the ground, are considered. Provided that appropriate modeling assumptions are made, the considered formulation of the equivalent pier method can effectively capture the vertical deformation and displacement of pile groups subjected to mechanical and thermal loads. The previous result provides further evidence on the capability of the equivalent pier method to appropriately and effectively serve the analysis and design of pile groups subjected to loading.

Effect of non-linear soil deformation on the interaction among energy piles

This study investigates the effect of non-linear soil deformation on the displacement interaction among energy piles. The work is based on interaction factor analyses of full-scale pile group tests, whose results are compared with experimental evidence. The results presented highlight the tendency of interaction factor analyses that ignore non-linear soil deformation to overestimate the interaction and the displacement of energy pile groups. This outcome, in accordance with previous studies for conventional pile groups subjected to mechanical loads, may be considered in the analysis and design of energy pile groups subjected to thermal (and mechanical) loads through the interaction factor method.

Numerical modelling of pile foundation angular distortion

In this paper, the PLAXIS 3-D Foundation finite element (FE) software package, in conjunction with the nonlinear Hardening Soil (HS) constitutive model, is employed in an extensive parametric study of the angular distortion of piled foundations. Angular distortion has been documented as the most influential settlement characteristic in the cracking of buildings. Numerical results are appraised in the context of the acceptable limits for angular distortion, recommended in the literature and set down in geotechnical building codes, since there is currently no guidance in the literature on appropriate pile cap rigidities for remaining safely within these limits. The results of the parametric study were validated by a comparison to the measured differential settlement characteristics from buildings and full-scale pile groups documented in the literature for which a good agreement was obtained. In addition, the numerical data has been formulated into a set of fully-normalised trends. Although a relatively wide range of variables are considered in the parametric study, a consistent trend between the average settlement performance and angular distortion for corresponding pile cap rigidities was evident. These trends present design engineers with a useful resource for estimating the angular distortion of piled foundations.

Discussion of “Lateral Resistance of a Full-Scale Pile Group in Liquefied Sand” by Kyle M. Rollins, Travis M. Gerber, J. Dusty Lane, and Scott A. Ashford

The discussers have used the Strain Wedge Model (SWM) developed by Ashour and Norris (2003) to compare the test program results based on field test data the authors compiled (but without the authors' adjustment factors) for laterally loaded pile and pile group response in liquefied soil. The discussers observed that the SWM predicts limited group effect of the p-y curves for CISS single and individual pile (in a 3 X 3 group at 0.3 m, 1.3 m, and 2.3 m depths) under fully liquefaction conditions. In partial liquefaction conditions, though, the SWM predicts a greater group effect at the same depths.

Lateral Resistance of a Full-Scale Pile Group in Liquefied Sand

Lateral load test was performed on a full-scale pile group following blast-induced liquefaction to evaluate pile–soil–pile interaction effects. The 3×3 pile group at 3.3 pile diameter spacing was driven into loose to medium dense sand. A single pile test was conducted for comparison. In contrast to preliquefaction tests, group interaction effects were insignificant after liquefaction. The lateral resistance of each pile in the group was similar and about the same as that for the single pile test. p–y curves were developed based on the bending moment versus depth data for Ru values of 95%. While the slope of p–y curves for nonliquefied sand typically decreases with continued deflection, the slope of the backcalculated p–y curves for liquefied sand increases with deflection. This phenomenon appears to be connected with load-induced dilation and a decrease in excess pore pressure locally around the pile. The p–y curves stiffened with depth and as the excess pore pressure ratio decreased. Equations were developed for p–y curves in liquefied sand which also account for the effect of variations in pile diameter.

Measured and Computed Lateral Response of a Pile Group in Sand

A lateral load test was performed on a full-scale pile group to evaluate pile–soil–pile interaction effects. The 3×3 pile group at 3.3 pile diameter spacing was driven opened ended into a profile consisting of loose to medium dense sand underlain by clay. The load carried by each pile was measured and strain gages were attached to determine bending moment. A single pile test was conducted for comparison. Group effects significantly reduced lateral resistance for all rows relative to single pile behavior. Trailing rows carried less load than the leading row. In contrast to tests in clay, lateral resistance was also consistently lower for middle piles within each row. Backcalculated p -multipliers were 0.8 for the front row and 0.4 for the trailing row piles which is consistent with results from previous centrifuge tests and full-scale tests where different installation methods were used. Good agreement between measured and computed pile group response was obtained using the p -multiplier approach. Based on...

Prediction of the horizontal load-displacement curves of pile groups based on the results of single pile tests

This paper presents the prediction of horizontal load-displacement curves of pile groups based on the results of single pile tests. Although the same basic model is employed, two different approaches are taken: one assumes soil to be linear elastic-plastic, and the other assumes it to be elastic nonlinear. The model is calibrated on the basis of the results of a full-scale single pile test. Special emphasis is placed on model calibrations, since the success of any prediction method depends on a careful characterization of the soil. Some new approaches for determining the soil parameters are presented. Two methods for predicting load-displacement curves, one from each model approach, are then proposed and discussed. Special emphasis is placed on group efficiency in the elastic-plastic method and on the boundary conditions of the single pile and the pile group in the elastic nonlinear method. Using the soil characteristics from the model calibrations, the load-displacement curves for a given pile group are then predicted. These predictions are compared with the results of a full-scale pile group test carried out at the same site as that of the single pile test. Agreement between the predictions and the test results tends to validate the methods proposed.Key words: displacement predictions, pile groups, model calibration, pile tests.

Lateral Load Capacity and Passive Resistance of Full-Scale Pile Group and Cap

Static and dynamic (statnamic) lateral load tests were performed on a full-scale 3 × 3 pile group driven in saturated low-plasticity silts and clays. The 324-mm outside diameter steel pipe piles were attached to a reinforced concrete pile cap (2.74 m square in plan and 1.21 m high), which created an essentially fixed-head end constraint. A gravel backfill was compacted in place on the back side of the cap. Lateral resistance was therefore provided by pile-soil-pile interaction as well as by base friction and passive pressure on the cap. In this case, passive resistance contributed about 40 percent of the measured static capacity. The measured resistance was compared with that computed by several techniques. The log-spiral method provided the best agreement with measured resistance. Estimates of passive pressure computed using the Rankine or GROUP p-y curve methods significantly underestimated the resistance, whereas the Coulomb method overestimated resistance. The wall movement required to fully mobilize passive resistance in the dense gravel backfill was approximately 0.06 times the wall height, which is in good agreement with design recommendations. The p-multipliers developed for the free-head pile group provided reasonable estimates of the pile-soil-pile resistance for the fixed-head pile group. Default p-multipliers in the program GROUP led to a 35 percent overestimate of pile capacity. Overall dynamic resistance was typically 100 to 125 percent higher than static; however, dynamic passive pressure resistance was over 200 percent higher than static.

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...

Dynamic response of pile groups under lateral loading

Dynamic experiments on full-scale pile groups subjected to lateral loading were conducted in the field, first during winter when the surface was covered by a frozen soil layer and then in the summer under a completely unfrozen state. The results of the experiments are compared with theoretical predictions based on the approach of the dynamic interaction factors. Using frequency response curves of stiffness, damping and displacement amplitude of the pile group, the influence of pile-soil-pile interaction and the frozen soil layer on the dynamic behaviour of the pile group were studied. It is shown that by allowing for the boundary zone and free-pile length effects, close agreement can be achieved between the theoretical predictions and the measured response curves.

Micro-computer analysis of pile group settlement using independent point and shaft loads

A FORTRAN-77 micro-computer program to predict pile group settlements is presented. The program incorporates concepts described in a recent publication (J. M. Polo and J. L. M. Clemente, J. Geotech. Engng, ASCE, to appear), where the pile cap is considered rigid and point and shaft loads are treated independently. Pile settlements are considered to consist of three components: settlement of pile point due to point load, settlement of pile point due to shaft load and elastic shortening of the pile due to axial load. Each of these components is evaluated taking into account appropriate pile and soil deformation parameters and numerically generated settlement influence factors. Group settlements are evaluated by incorporating settlement interaction factors which are also numerically generated. The program design is such that it can be used with minimum effort. The few input parameters needed can be provided in a user friendly interactive environment. Program use is illustrated with the prediction of the load-settlement behavior of a full scale pile group load test reported in the literature. A typical program output is shown for this example. Results obtained are excellent, indicating the soundness of the previously proposed method when properly used. Results also show the adequacy of the present micro-computer program.

Lateral load tests on full-scale pile groups : Kim, JB Brungraber, RJ Kindig, CH In Performance of earth and earth supported structures, Vol. 2. Proc. Speciality Conference, Purdue Univ. 1972. 20F, 3T. ASCE, New York, 1972, P1105–1133

Lateral load tests on full-scale pile groups : Kim, JB Brungraber, RJ Kindig, CH In Performance of earth and earth supported structures, Vol. 2. Proc. Speciality Conference, Purdue Univ. 1972. 20F, 3T. ASCE, New York, 1972, P1105–1133