Shaft Resistance Research Articles

Thermo-hydro-mechanical behavior of energy foundations in saturated glacial tills

This study focuses on the effect of temperature- and –stress dependent hydraulic conductivities on the thermo-hydro-mechanical behavior of energy foundations installed in saturated glacial tills. A thermo-poroelastic model based on finite element method was developed and validated against field measurements from a case study in the literature, then was used to simulate four different energy foundations installed on the Urbana-Champaign campus of University of Illinois. Coupled thermo-hydro-mechanical properties were integrated into the numerical analyses based on laboratory characterization of the hydraulic conductivities of several soil samples at different temperatures and confining stresses. The results indicate that the transient evolution of pore water pressure, axial stress, and shaft resistance are significantly influenced by temperature- and stress- dependent hydraulic conductivity. Changes in axial stress and shaft resistance peak at early times when excess pore water pressures are highest. Long-term changes in axial stress and shaft resistance were less than the short-term peak values, highlighting the importance of considering the evolution of coupled soil properties to capture the peak response. This study demonstrates that consideration of coupled material properties is required to capture the coupled response of energy foundations in saturated glacial tills.

Effect of a constrictor plate on behavior of a model steel pipe pile driven in dense sand

This study investigates the effect of a constrictor plate on the drivability and load-carrying capacity of open-ended pipe piles via a series of model pile tests. The model pile had an outer diameter of 88.9 mm and was driven in a dense sand to a depth of 670 mm using an impact hammer. Soil plug lengths were measured using a laser distance meter for the entire process of the pile driving. The model pile further employed a double-wall system to separately measure the annulus resistance, soil plug resistance, and outer shaft resistance. Two tests with a constrictor plate located at 98.4 mm and 200 mm above the pile base and one test without a constrictor plate were performed. The piles with a constrictor plate required about 15–20% more pile driving energy than the pile without a constrictor plate. Results from static load tests showed that the piles with a constrictor plate were able to resist more axial loads than the pile without a constrictor plate by about 25–38%.

Concrete Pile Defect Identification: Insights from Cross-Hole Sonic Logging and High Strain Dynamic Pile Test

This paper aims to identify the types of defects, location of defects, size of defects, and capacity of five concrete piles using a High strain dynamic pile test and Cross-hole sonic logging test. In this study, Cross-Hole Sonic Logging method (CSL) is a potent quality-control tool that exclusively detects much smaller flaws with high accuracy with utilizing velocity and first arrival time (FAT) from ultrasonic waves to find out the integrity of the drill shaft. From CSL test, the bearing capacity needs to be calculated manually using a waterfall diagram and soil profile. Moreover, the high strain dynamic pile test is used to identify integrity and bearing capacity of concrete pile via resistance analysis down to the pile and split of the base to shaft resistance when only pile head measurements are taken then using Case Method and CAPWAP analysis. Through this analysis, the bearing capacity can be interpreted; the Belta (damage factor) is applied to estimate location and size of the defect in the concrete pile. Based on the result of CLS test for three concrete piles, P01, P04, and P10, indicated that P01 and P04 are “Good” pile integrity with the bearing capacity of 4583kN and 6600kN, while P10 showed as “Potential defect at depth 9.25m to 10.25m” of pile integrity with bearing capacity of 6600kN. Furthermore, High strain dynamic pile test of two concrete piles, P2E and P2P, showed that the integrity category is “Ok” with bearing capacity 9896kN.

An elasto-plastic numerical analysis of THM responses of floating energy pile foundations subjected to asymmetrical thermal cycles

Although end-bearing energy pile foundations subjected to symmetrical thermal cycles have been extensively studied in the laboratory and in the field, the mechanisms underlying the thermo-hydro-mechanical (THM) interactions in floating energy pile groups and rafts, especially when subjected to asymmetrical thermal loads, are not well understood. In this study, an advanced thermo-mechanical bounding surface model was implemented in finite-element (FE) code to investigate the THM interactions of a two-by-two floating energy pile group and pile raft, focusing on asymmetrical thermal cycles. Computed results are compared with published centrifuge model test results in soft clay. It is revealed that the irreversible volumetric contraction of the soil adjacent to the energy piles accumulates with each thermal cycle, resulting in a decrease in the horizontal stress and hence shaft resistance of the floating piles. During thermal cycles, the stress states of the soil around the energy pile shaft and the soil beneath the pile toe approach the critical state line along different paths. The induced temperature in the soil adjacent to the non-energy pile (NEP) is 5°C lower than that in the soil at the energy pile EP1, which is flanked by the other two energy piles EP2 and EP3. Consequently, the induced excess pore pressure in the soil at the NEP is approximately 20% smaller than that in the soil at EP1. The irreversible volumetric soil contraction at the NEP is about half that at EP1, resulting in approximately 45% less toe settlement. The thermally induced ratcheting settlements of the head and toe of the NEP are less than those of the energy piles, resulting in unacceptable ratcheting tilting of the floating energy pile group. However, the excessive tilting can be reduced by the use of a pile raft.

Interpreting CAPWAP results for driven piles with corrections for setup and residual loads

Evaluation of pile capacity using dynamic testing and Case Pile Wave Analysis Program (CAPWAP) analysis has been shown to provide reasonable measurements of capacity and separates the shaft and tip resistance. It is a common method for verifying pile capacities; however, consideration of setup and presence of residual loads at the time of testing are necessary for interpreting the resistance distribution. A test pile program was conducted that included dynamic testing of piles at the end of initial driving and early restrikes to measure the rate of setup. The piles were instrumented to measure residual stresses. The shaft resistance and tip stiffness were interpreted from analyzing multiple blows and corrected for residual stresses. The results from CAPWAP were compared to measurements from static load tests. It was found that correcting CAPWAP results for residual loads resulted in better interpretation of the rate of setup and resistance distribution. Analyzing successive blows with CAPWAP provided an improved estimate of the tip load–movement curve by extrapolating the increase in tip capacity with penetration. The results demonstrate the importance of correcting CAPWAP results for residual stresses to gain a better understanding of the pile capacity, resistance distribution, and tip stiffness for design purposes.

A three-dimensional (3D) analytical solution for the ultimate side shear resistance of rock-socketed shafts

This paper presents a new analytical solution to the ultimate side shear resistance τsf of rock socketed shafts with consideration of three-dimensional (3D) strength and shaft sidewall roughness. Specifically, the shaft sidewall profile is simplified as triangular asperities and micro-mechanical analysis is performed on the shear behavior of one representative asperity. A 3D version of the Hoek-Brown (HB) criterion for rock mass and the equilibrium equations in a cylindrical coordinate system are first utilized to derive the governing equations. Then the governing equations are solved by using the method of characteristics. Finally, the τsf is obtained by considering the constant normal stiffness condition and the relative displacement of the rock mass due to sliding along the shaft-rock mass interface. Twenty-four (24) model and field test shafts with measured τsf are collected for analysis to verify the proposed solution. The results indicate that the predicted τsf values are in good agreement with the measured τsf values. Extensive parametric studies are also conducted to investigate the effects of rock mass properties, shaft dimensions, and sidewall roughness parameters on the ultimate side shear resistance factor αf (the ratio of τsf to the unconfined compressive strength of intact rock σc) of rock socketed shafts. The results indicate that the αf increases with rock constant mi, geological strength index (GSI) and asperity half chord length λ, but decreases with shaft diameter B, σc and disturbance D. Furthermore, the αf first increases and then decreases with the asperity inclination angle δ, resulting in an optimum asperity inclination angle δOp. Therefore, it is important to reduce the disturbance of rock mass from construction and select a proper asperity inclination angle when designing a rock socketed shaft.

Short-term axial loading of continuous-flight pile segment in frozen soil

Research on the performance of continuous-flight piles for the use in permafrost is rare. In the present laboratory research, continuous-flight pile segments with 89 mm diameter and 300 mm length were installed in frozen soils and loaded under a constant displacement rate. The objectives were to investigate the load-transfer mechanism and the failure modes associated with the shaft resistance of the piles. Pile segments were screwed into a chamber filled with frozen soil and then loaded in the axial direction; installation torques and pile load resistance were measured, respectively, during the installation and loading stages. The effects of soil temperature, salinity, and water content on the short-term performance of these piles were examined. Results show that the pile capacities decreased with warming temperatures. The installation torque increased significantly as the soil temperature and salinity decreased. Cylindrical shearing mode (CSM) and individual bearing mode (IBM) of pile failure were observed at soil temperatures of −1 and −5 °C, respectively. Adfreeze and plate bearing resistance were determined under these failure modes. The global failure surface occurred at the edge of the threads under the CSM, and the shear resistance was increased along this surface. The existence of plate (i.e., flights) bearing resistance under the IBM suggests a potential advantage of continuous-flight piles over conventional smooth piles, because the plate bearing resistance is mobilized during loading.

Three-dimensional numerical analyses of pile responses to tunneling-induced ground movements in bilayer soil

PurposeThis paper aims to investigate the responses of single piles and pile groups due to tunneling-induced ground movements in a two-layered soil system. The analyses mainly focus on the additional single pile responses in terms of bending moment, lateral deflection, axial force, shaft resistance and pile settlement. Subsequently, a series of parametric studies were carried out to better understand the responses of single piles induced by tunneling. To give further understanding regarding the pile groups, a 2 × 2 pile group with two different pile head conditions, namely, free and capped, was considered.Design/methodology/approachUsing the PLAXIS three-dimensional (3D) software, a full 3D numerical modeling is performed to investigate the effects of ground movements caused by tunneling on adjacent pile foundations. The numerical model was validated using centrifuge test data found in the literature. The relevance of the 3D model is also judged by comparison with the 2D plane strain model using the PLAXIS 2D code.FindingsThe numerical test results reveal that tunneling induces significant displacements and internal forces in nearby piles. The magnitude and distribution of internal forces depend mainly on the position of the pile toe relative to the tunnel depth and the distance between the pile and the vertical axis of the tunnel. As the volume loss increases from 1% to 3%, the apparent loss of pile capacity increases from 11% to 20%. By increasing the pile length from 0.5 to 1.5 times, the tunnel depth, the maximum pile settlement and lateral deflection decrease by about 63% and 18%, respectively. On the other hand, the maximum bending moment and axial load increase by about 7 and 13 times, respectively. When the pile is located at a distance of 2.5 times the tunnel diameter (Dt), the additional pile responses become insignificant. It was found that an increase in tunnel depth from 1.5Dt to 2.5Dt (with a pile length of 3Dt) increases the maximum lateral deflection by about 420%. Regarding the interaction between tunneling and group of piles, a positive group effect was observed with a significant reduction of the internal forces in rear piles. The maximum bending moment of the front piles was found to be higher than that of the rear piles by about 47%.Originality/valueSoil is a complex material that shows differently in primary loading, unloading and reloading with stress-dependent stiffness. This general behavior was not possibly being accounted for in simple elastic perfectly plastic Mohr–Coulomb model which is often used to predict the behavior of soils. Thus, in the present study, the more advanced hardening soil model with small-strain stiffness (HSsmall) is used to model the non-linear stress–strain soil behavior. Moreover, unlike previous studies THAT are usually based on the assumption that the soil is homogeneous and using numerical methods by decoupled loadings under plane strain conditions; in this study, the pile responses have been exhaustively investigated in a two-layered soil system using a fully coupled 3D numerical analysis that takes into account the real interactions between tunneling and pile foundations. The paper presents a distinctive set of findings and insights that provide valuable guidance for the design and construction of shield tunnels passing through pile foundations.

Energy pile skin friction at interface in clays under temperature cycles

In energy geostructures, the long-term shaft resistance is affected by cyclic thermo-mechanical loads associated with structural loads and cyclic thermal solicitations. This study aims to investigate the effect of monotonic and cyclic thermal loads on normally consolidated (NC) and overconsolidated (OC) kaolin clay–rough steel interface. The peak shear stress of interface increased with temperature while the critical state shear strength remained unchanged. For cyclic temperature tests, with applying ten temperature cycles (5–60°C) to NC kaolin–clay interface, significant thermal contraction was observed but the shear strength increased as much as one single heating test. NC interface contracted on heating whereas OC samples dilated. These results highlighted the impact of thermal cycles on clayey interface which was stress history dependent.

Nonlinear fictitious-soil pile model for pile high-strain dynamic analysis

Existing numerical models for simulating the pile behaviours in high-strain dynamic load tests (DLTs) cannot account for the wave propagation in base soil. This paper proposes a nonlinear fictitious-soil pile (FSP) model to better simulate the base soil. The proposed model regards the base soil as a FSP with a cone angle extending from pile toe to bedrock, and simulates shaft resistance by improved Randolph model. The pile-soil system is discretized into a series of mass-nonlinear springs, and was solved based on the Newmark’s β method. The proposed model was validated by comparing its predictions with those obtained from Randolph model and Smith model, as well as field measurements of driven and bored piles in different sites. Parametric study demonstrated that the calculated results were significantly affected by the discretization degree, FSP dimensions and soil nonlinearity. The displacement attenuation in base soil is nonlinear, and the impact energy is consumed rapidly near pile toe. Besides, large-diameter piles tend to have a larger affected zone, in which the wave phenomenon in base soil should be considered. Empirical formulas for soil affected zone and required pile displacements in DLTs were proposed to facilitate the practical application of FSP model.

A Lateral-Response Analyzed Model for Piles in Sloping Ground Considering Vertical Resistance Based on Transfer Matrix Method

In order to analyze the lateral response of piles subjected to combinational loads located at sloping ground, a simplified physical model is proposed and developed based on the Timoshenko beam theory and tri-parameter elastic foundation beam model. In this model, the effects of vertical resistance, shear deformation and initial inclination of pile shafts are taken into account, and the semi-analytical solution to the lateral behavior of pile is obtained by utilizing the transfer matrix approach. Specifically, the relative transfer matrix coefficients in the free, passive, and active segment of the pile are analytically determined through Laplace transformation. In addition, the validation of this model is conducted by comparing with field observations and predictions obtained from other existing methods. Moreover, the influences of initial inclination angle, vertical resistance in passive segments and the vertical load on the lateral response of the pile are also discussed in depth. The results indicate that, although there is a significant reduction effect emerged in both the lateral displacement and bending moment with the increase in the vertical resistance, a growth trend for those responses can be obtained with an increase in the initial inclination angle and vertical load.

Behavior Investigation of Necking Pile with Caps Assisted with Transparent Soil Technology

Pile easily develops necking defects during construction, which can limit the exertion of shaft resistance, resulting in reducing ultimate bearing capacity and creating potential safety hazards to projects. Based on transparent soil technology, this paper took the necking located in the middle part of pile shafts as an example and carried out vertical loading experiments on one intact pile and nine necking piles with caps. Then, the influences of necking length and diameter on the vertical bearing capacity were studied. The speckle field of the soil around piles was processed using the MatPIV program to investigate soil displacement. Through comparison and analysis with the intact pile, the reasons for the reduction in bearing capacity were obtained. The results show that the bearing capacity of the piles is seriously damaged by the necking. When the necking diameter is 4 mm and the necking length is 20 mm, the loss of vertical bearing capacity was 26.6%. The vertical bearing capacity decreases with the increase in necking length or the decrease in necking diameter. Pile necking makes a significant contribution to the displacement of soil around the cap. Inclined downward displacement of soil occurs near necking, which reduces the relative displacement between pile and soil and leads to the loss of pile resistance. For the necking with a large size, the soil displacement at the necking and around the pile cap is connected, which causes the displacement range of the soil under the pile cap to increase, resulting in a weakening of the exertion of shaft resistance. Subsequently, the vertical bearing capacity of piles is reduced.

Discussion of “Centrifuge Tests on Rock-Socketed Piles: Effect of Socket Roughness on Shaft Resistance’’ by J. G. Gutiérrez-Ch, G. Song, C. M. Heron, A. Marshall, and R. Jimenez

Discussion of “Centrifuge Tests on Rock-Socketed Piles: Effect of Socket Roughness on Shaft Resistance’’ by J. G. Gutiérrez-Ch, G. Song, C. M. Heron, A. Marshall, and R. Jimenez

Discussion of “Centrifuge Tests on Rock-Socketed Piles: Effect of Socket Roughness on Shaft Resistance” by J. G. Gutiérrez-Ch, G. Song, C. M. Heron, A. Marshall, and R. Jimenez

Discussion of “Centrifuge Tests on Rock-Socketed Piles: Effect of Socket Roughness on Shaft Resistance” by J. G. Gutiérrez-Ch, G. Song, C. M. Heron, A. Marshall, and R. Jimenez

Closure to “Centrifuge Tests on Rock-Socketed Piles: Effect of Socket Roughness on Shaft Resistance” by J. G. Gutierrez-Ch, G. Song, C. M. Heron, A. Marshall, and R. Jimenez

Closure to “Centrifuge Tests on Rock-Socketed Piles: Effect of Socket Roughness on Shaft Resistance” by J. G. Gutierrez-Ch, G. Song, C. M. Heron, A. Marshall, and R. Jimenez

Experimental and Numerical Investigation of the Load-Bearing Mechanisms of Piles Socketed in Soft Rocks

Rock-socket pile design predominantly depends on the shaft resistance to support the load at the serviceability state. However, due to limited understanding of the pile–rock interactions, the pile capacity is normally calculated using empirical correlations. In this study, the load-bearing mechanisms of rock-socketed piles were investigated through a miniaturised pile–load test setup in a soft synthetic rock. X-ray CT imaging and numerical discrete element modelling were used to investigate the micro-mechanics influencing the load-bearing mechanisms at the pile–rock interface. The numerical pile model was established based on suitable constitutive models capable of simulating the soft rock behaviour. The analysis of X-ray CT images at various displacements revealed three different interface mechanisms, namely sliding, local shearing and progressive shearing. The numerical model validated this observed micro-mechanics in the rock asperities through the evolution of damage and micro-cracks. Insights from the experimental and numerical results indicated that the height of the rock asperities significantly dictates the failure mode. Results also illustrated that the shaft load–displacement response primarily depends on the forces acting on the leading edges of the pile asperity. In particular, it was observed that the bottom leading edge carried a predominant portion of the shaft loads due to its connectivity with the rock at the base of the pile. Though negligible, the forces on the trailing edges provided valuable information on the contribution of residual shaft resistance by the debris at the interface. Moreover, the numerical studies revealed the different failure modes at the pile–rock interface. The discussions presented in this study provide novel insights into the load-bearing mechanisms of piles socketed in soft rocks, which will help to improve design guidelines in the future.

Method for Calculating Vertical Compression Bearing Capacity of the Static Drill Rooted Nodular Pile

The static drill rooted nodular (SDRN) pile is a new kind of composite pile foundation made by inserting a precast nodular pile into the cemented soil. Based on the tests and analysis on the mechanism characteristics of these two kinds of interfaces, which are between the pile and cemented soil, and between the cemented soil and soil, this paper proposes a calculation method for the ultimate vertical bearing capability of the SDRN pile considering two failure modes. When the precast pile and surrounding cemented soil fails as a whole, the diameter of the cemented soil pile is taken to calculate the ultimate shaft resistance, and the shaft resistance of the SDRN pile is about 1.05∼1.10 times that of the bored pile in the same soil layer. When the core precast pile fails in penetration mode, the diameter of the core pile is taken. The pile shaft resistance takes that of displacement piles in the same soil layer. The lower nodular pile shaft resistance should consider the squeezing effect of nodular joints. Besides, the improvement of pile tip resistance due to the expanded cemented soil should also be taken into consideration. The result is the smaller value calculated according to these two failure modes. The ultimate bearing capacity of a SDRN pile calculated by the theoretical method is not only compared with the field test result, but also the simulation result of a 2D model pile built by PLAXIS finite element software. In addition, the finite element simulation is also confirmed to be an effective way to investigate the mechanism characteristics of SDRN piles more thoroughly.

A Nonlinear Softening Load-Transfer Approach for the Thermomechanical Analysis of Energy Piles

Energy piles are a profitable solution for extracting shallow geothermal energy and have recently attracted increasing attention. However, the thermomechanical response of energy piles considering shaft resistance softening has not been sufficiently studied, which hinders the perfection of design methods for energy piles. To this end, an improved generalized nonlinear softening model was first developed to describe the thermomechanical loading–unloading–reloading response of energy piles. The parameters of the improved model can be easily calibrated using an interface direct shear test. We then proposed a nonlinear load-transfer approach for the thermomechanical analysis of energy piles considering the softening behavior of skin resistance by continuously describing the nonlinear load-transfer regime. The proposed approach was validated by comparing it with experimental measurements and other numerical methods. Finally, a parametric study was performed to assess the effects of various related parameters on the thermomechanical response of the energy pile. The results indicate that the proposed approach enriches the current methods for energy pile design and provides a helpful tool for obtaining the thermomechanical behavior of energy piles in the case of softening.

Prediction of driven pile resistances in shales considering weathering and time effects

The difficulty with shale sampling and testing and the lack of pile load tests in shales have created challenges with shale classification, pile resistance prediction, and understanding time-dependent pile responses. Treating shale as soil can yield a conservative pile design. Shales were classified into soil-based and rock-based depending on their weathering conditions, mechanical properties, and measured pile resistances. Failure behaviors of soil- and rock-based shales are discussed. Prediction equations were developed to account for predicting shale properties. Properties of rock-based shales decrease with the increase in weathering. New static analysis (SA) methods were proposed to predict unit shaft resistance ( qs) and unit end bearing ( qb) of piles in shales and validated. Our study yields higher resistance and efficiency factors for the proposed SA methods and piles in shales than existing SA methods developed for piles in soils. The qs in the soil-based shale exhibits pile setup, while the qs in rock-based shales experience both setup and relaxation. The qb in both soil-based and highly weathered shales is likely to experience pile setup. However, the qb in the moderately and slightly weathered shales experience both setup and relaxation.

Response of vertically-loaded pile in spatially-variable cement-treated soil.

Despite the extensive application prospects of piles in cement-treated soil, few studies have explored the ultimate bearing capacity especially in consideration of the spatial variability of cement-treated soil. This study examines the performance of driven piles which were installed inside the cement-treated ground, considering the inherent spatial variability of the cemented soil and the positioning error during piles installation through finite element analyses. The deterministic and random finite element analysis results have shown that the shaft resistance mainly provided the ultimate bearing resistance of piles in cement-treated soil. The spatial variability reduced the global performance of pile installed through a cement-treated soil. The ultimate bearing resistance of the pile inserted in cement-treated soil was controlled by drained condition. Drained ultimate bearing resistance should be used to determine the design working compression load of pile in cement-treated soil.