Pile-soil Relative Displacement Research Articles

Field and Theoretical Study of the Response of Super-Long Bored Pile Subjected to Compressive Load

In this article, two full-scale pile loading tests were conducted to observe the field performance of the super-long bored piles, and a simplified approach for nonlinear analysis of the load-displacement behavior of a single pile was presented. The field tests on piles indicates that, under the maximum test load, more than 70% of the pile top settlement is caused by the compression of pile shaft. For practical purposes, the pile top settlement can be reduced through improving the pile shaft strength. When the load reaches the maximum test load, the proportion of the load carried by the pile tip is approximately 30%. The super-long pile is functioning as an end-bearing friction pile. The skin friction at shallow depth is fully mobilized and decreases from a peak value with increasing load. However, the skin friction of deeper soil is not fully developed due to less relative displacement. Furthermore, a BoxLucas1 model is used to capture the relationship between unit skin friction and pile-soil relative displacement, whereas a hyperbolic model is used to describe the relationship between toe stress and pile base displacement. Based on the BoxLucas1 model and the hyperbolic model, a load transfer method is used to clarify the response of a single pile, and a computational flow chart is developed. The efficiency and accuracy of the present method is verified using the field tests on piles. The proposed simple analytical approach is economical and efficient, resulting in savings in time and cost.

Field and Theoretical Analysis on the Response of Destructive Pile Subjected to Tension Load

Most field tests are carried out using working piles for verification purposes in China, and loading tests are terminated before achieving true pile capacity. In this work, two full-scale destructive loading tests on tension piles instrumented with strain gauges were conducted to capture true pile capacity. The load-displacement response, load transfer, and threshold of the pile-soil relative displacement for fully mobilizing skin resistance in the uplift case were discussed. It was found that the shaft resistance degradation is observed to be along the pile depth with a reduction factor of 0.905 to 0.931, and the thresholds of pile-soil relative displacement for fully mobilizing skin resistance of the tension pile in different soils are found to be in the range 0.67% to 1.34% of the pile diameter. Based on the field test results, a simple softening model was proposed to describe the degradation behavior of skin friction along the pile-soil interface. Further study was conducted to assess the influence of the threshold of pile-soil relative displacement for fully mobilizing skin friction and the reduction factor on the skin friction. As to the analysis of the response of single pile subjected to tension load, a highly effective iterative computer program was developed using the proposed skin friction softening model. Comparisons of the load-settlement response for the well-instrumented tests were given to demonstrate the effectiveness and accuracy of the proposed simple method.

Model Test on Negative Skin Friction for Super-Long Pile under Surcharge Load Considering Time Effect

Super-long pile bridges and high-rise buildings are commonly used in the form of pile foundation. In the flood area, due mainly silt stratum, as well as the decline in groundwater mound pile under the conditions set out in the consolidation, there will be a negative pile skin friction and negative friction obvious time effect, which bearing capacity of the pile has a great influence. Current research on negative friction for super-long pile considering time effect is relatively little. In the model box, on the base of the super-long pile silt model test, set out in a pile mound under consolidation, soil testing flour gradually over time preloading consolidation settlement, pile-soil relative displacement, so as to arrive negative friction pile variation with time, tip resistance variation with time from the pile-axial force curve deduce the location of the neutral point and changes in circumstances, the pile foundation engineering practice has a certain significance.

Field Study on the Behavior of Destructive and Non-Destructive Piles Under Compression

This paper presents a series of full-scale load tests on long bored piles instrumented with strain gauges along the shafts, including eight field tests of piles loaded to failure and one non-destructive pile load test. The load-displacement response, skin friction, end resistance, and the threshold of the pile-soil relative displacement for fully mobilizing skin resistance were discussed. A simple softening model was proposed to describe the degradation behavior of the skin friction along the pile-soil interface and the load-displacement relationship developed at the pile base. It is found that the shaft resistance degradation investigated in the non-destructive load test only occurs at a shallow depth, and the skin friction of deeper soil is not fully developed. However, unlike the results of the non-destructive load tests, the softening is accompanied by a reduction in skin friction and observed to be along the whole pile depth. The thresholds of pile-soil relative displacement for fully mobilizing skin resistances in different soils have been found to be in the range 0.6% to 2.4% of the pile diameter. Moreover, in practical applications, a bilinear model is assumed to be feasible in analyzing the load-settlement relationship developed at the end of non-destructive pile, whereas the load transmission curve of the soils below the pile base corresponds to a softening model in the field tests of piles loaded to failure.

Analysis of Compression Pile Response Using a Softening Model, a Hyperbolic Model of Skin Friction, and a Bilinear Model of End Resistance

AbstractFor a single pile subjected to compressive load, a softening model and a hyperbolic model are adopted in this work to simulate the relationship between pile-soil relative displacement and unit skin friction developed along the pile-soil interface, whereas a bilinear model is used to describe the unit end resistance–displacement response developed at the pile tip soil. Based on the proposed three models, two simple analytical approaches for nonlinear analysis of the load-displacement response of a single pile are presented. One method uses a softening model of skin friction and a bilinear model of end resistance to capture the pile response, and the other approach is based on a hyperbolic model of skin friction and a bilinear model of end resistance to describe the pile load-displacement response. As for the analysis of the response of a single pile subjected to a compression load, a highly effective iterative computer program is developed using the two proposed approaches and the load-transfer cur...

A simplified nonlinear approach for single pile settlement analysis

A simple analytical approach for nonlinear analysis of the load–displacement response of a single pile is presented. Two models are adopted in the proposed approach. One model uses a softening nonlinear relationship to simulate the degradation behavior between the unit skin friction and the pile–soil relative displacement developed in the pile–soil interface, and the other model adopts a bilinear load–displacement relationship to capture the pile-end response. Based on the two proposed models, a highly effective computer program has been developed for nonlinear analysis of the load–settlement behavior of a single pile. Comparisons are made between the present method, other analytical methods, and a well-documented field experimental pile loading case. The results of the comparisons indicate that the proposed method is generally in good agreement with field-observed behavior and the calculated results derived from other approaches. A parametric study is conducted to assess the influence of the parameters related to the proposed model on the load–displacement response of a single pile.

A Numerical Analysis of Soil Arching in Piled Embankments

Soil arching has important influence on the behavior of piled embankments. How to calculate stress concentration ratio is of great concern when designing embankment over soft soils reinforced by rigid concrete piles. A numerical analysis by using a commercial FEM program was conducted to reveal the mechanism of soil arching in piled embankments. And also, the influence of embankment height, pile-soil relative displacement, cohesion and internal friction angle on the equal settlement plane was evaluated. The results indicate that the stress concentration ratio varies with the pile-subsoil relative displacement and has upper and lower bound value. The effect of pile-soil displacement and the strength parameters of embankment material on the equal settlement plane can be neglected. It was also found that the equal settlement plane height is equal to 1.6 times the pile-cap clear spacing. When the ratio of embankment height to the pile-cap clear spacing is greater than 1.6, no apparent differential settlement will occur on the embankment surface.

Analysis on the Characteristics of Pile Skin Friction under the Displacement Interactions between Pile and Soil around

On the basis of analyzing the occurring mechanism of pile skin friction, pile-soil relative displacement difference function is introduced, and the differential equation which depicts the relationship between pile skin friction and depth is derived, then the calculating model of pile skin friction with depth is established under considering the displacement-interaction process. Field monitoring data are employed to verify the rationality and validity of the model proposed. Through the established model, influences, exerted by pile-soil relative displacement difference, on the pile skin friction distribution are discussed and divided into three stages: I. stage of linear increase; II. stage of nonlinear increase; III. stage of convergence. Filed testing data comparing and theoretical analysis results indicate that the method proposed can describe the transferring process as well as the distribution law of pile skin friction under taking the pile-soil interaction into account, the parameters related and needed can be easily obtained, and the model suggested in this paper is of value in pile theory and engineering.

Calculation of Settlement of Composite Foundation with Rigid Piles under Flexible Ground

According to the character of the interaction of the pile, soil and cushion in composite foundation by fitting the vertical relative displacement distribution function of pile-soil element and introducing an elastic-plastic load transfer model, and deformation form of the pile-soil relative displacement, friction variation of pile, and pile-side soil reaction force model were simplified to a certain degree, and a basic differential equation of settlement calculation of the rigid pile composite foundation was established with consideration of both upward and downward penetration displacements of piles and the coordination of deformation of neutral point and the pile-soil interface. Then, a new method of calculating the settlement of the rigid pile composite foundation considering the interaction of pile-soil-cushion system was developed. At last, this new method was applied to the analysis of a model experiment and a project example, and the results show that (1) there exist great difference between the deformation mode and pile-soil stress ratio of rigid pile composite foundation under flexible ground and those under rigid ground; (2) the calculated results are close to the measured values. This method can reduce the calculation and provide a reference for the settlement calculation of rigid pile composite foundation.

Evaluation of group effect of pile group under dragload embedded in clay

A simple semi-empirical analysis method for predicting the group effect of pile group under dragload embedded in clay was described assuming an effective influence area around various locations of pile group. Various pile and soil parameters such as the array of pile group, spacing of the piles (S), embedment length to diameter ratio of piles (L/D) and the soil properties such as density (γ), angle of internal friction (φ) and pile-soil interface friction coefficient (μ) were considered in the analysis. Model test for dragload of pile group on viscosity soil layer under surface load consolidation conditions was studied. The variations of dragload of pile, resistance of pile tip and the layered settlement of soil with consolidation time were measured. In order to perform comparative analysis, single pile was tested in the same conditions. The predicted group effect values of pile group under dragload were then compared with model test results carried out as a part of the present investigation and also with the values reported in literatures. The predicted values were found to be in good agreement with the measured values, validating the developed analysis method. The model test results show that negative skin friction of pile shaft will reach 80%-90% of its maximum value, when pile-soil relative displacement reaches 2 mm.