End-bearing Capacity Research Articles

End bearing capacity of embedded pile with inclined base plate:Field dynamic and static tests

The objective of this study is to investigate the effects of incorporating inclined base plates on the end bearing capacities of embedded piles by conducting dynamic pile tests and static load tests. Two types of embedded piles were prepared – conventional piles with a 50-cm-diameter flat base plate and piles with a 56-cm-diameter inclined base plate. The dynamic pile tests were conducted during pile construction, and the static load tests were conducted after curing the cement paste to investigate the end bearing capacities of the test piles. Test results indicate that the base resistances of piles with inclined base plates are greater than those of conventional piles and that the base resistances increase with an increase in the inclination angle. The increased projected area, increased contact area, extended rupture surface, and enhanced slime discharge due to the inclined base plate may result in an increase in the end bearing capacity of the pile. This study demonstrates that the end bearing capacities of the embedded piles may be maximized by incorporating inclined plates to the pile base. Thus, the pile with the inclined base plate may be effectively used for the construction of embedded piles.

An Experimental Study on Bearing Capacity of Steel Open Ended Pipe Pile with Exterior Wings Under Compression Load

The present study investigates the increasing in ultimate pile capacity and studied the soil plugging phenomenon and the incremental filing ratio for a modified type of open-ended pipe pile. The modification performed by adding steel plates as wings with special dimensions and fixed on the exterior face of the pipe pile wall at a location near the pile tip with specified dimensions. Five wings have used for each new model of pipe pile. These wings distributed in equal spacing along with the circumstances of the exterior wall of the open-ended pipe piles. The efficiency of the proposed type studied by modelling and manufacturing twelve piles (40 mm diameter, L/D = 15 and L/D = 20). Complete setup manufactured for installing and loading the piles in a constant rate of penetration. The model piles installed in poorly graded loose dry sand. The obtained results show that the proposed type has a higher ultimate bearing capacity. The percentage of increase reaches more than 50%. The development of the load capacity is due to the three effects. The first is increases of the exterior shaft friction, and the second effect creates a new end-bearing capacity under the constrained soil between the exterior wings. And the third effect is developing the end-bearing capacity under the soil plug inside open-ended pipe pile due to the first and the second effects.

End-Bearing Capacity of Embedded Piles with Inclined-Base Plate: Laboratory Model Tests

AbstractThe objective of this study is to investigate the effects of an inclined base plate on the end bearing capacity of embedded piles and soil behavior below a pile base according to the vertic...

3D simulation for tunnelling effects on existing piles

Abstract Numerical simulation was performed to analyse the effects of two advancing open face tunnel excavations on existing piled foundations into London Clay stratum. As excavation advances, it is necessary to cut and remove piles in the tunnel face (‘cut’ piles). Piles outside the tunnel face remain in-situ and are referred to as ‘adjacent’ piles. A suitable end-bearing capacity had to be selected for the piles in order to guarantee an accurate distribution of the axial pile load. Negative skin friction increases with higher end-bearing capacities of the piles. Additionally, the stiffness of the building has a significant impact on the settlement of the piles. The stiffer the building, the lesser the settlement of the piles. The results of the model indicated a considerable zone of influence due to the tunnel: one tunnel diameter in advance of the excavation face; one tunnel diameter behind the excavation face; and transversally, five times the tunnel diameter either side from the centre point between the two tunnels. Due to the negative skin friction, the factor of safety for adjacent piles was 1.1 and for cut piles 1.0.

Axial Load Transfer Analyses of Energy Piles at a Rock Site

An axial load-transfer analysis for energy piles is presented in this study that incorporates empirical models for estimating the side shear resistance and end bearing capacity in rock along with associated normalized stress-displacement curves. The analysis was calibrated using results from field experiments involving monotonic heating of three 15.2 m-long energy piles in sandstone. Analyses of the field experiments indicates that poor cleanout of the excavations led to an end restraint smaller than that expected for a clean excavation in sandstone. Specifically, end bearing parameters representative of cohesionless sand were necessary to match the load-transfer analysis to the field experiment results. Parametric evaluations demonstrate the importance of using appropriate rock- or soil-specific empirical models when estimating the side shear resistance and end bearing capacity of energy piles. Specifically, the end bearing capacity and side shear resistance in rock are greater than in soils, leading to more restraint and greater thermal axial stresses. The stiffer side shear restraint in rock was also found to lead to a less nonlinear distribution in thermal axial stress along the length of the energy pile.

Experimental Study on the Bearing Mechanisms of Rock-socketed Piles in Soft Rock Based on Micro X-ray CT Analysis

Nondestructive imaging techniques enable the study of failure mechanisms within physical models for a wide range of geotechnical problems. This paper presented an innovative experiment that utilized micro X-ray computed tomography (CT) and an in-house experimental apparatus to study the bearing mechanisms of model piles embedded in synthetic soft sandstone rock with regular triangular asperities subjected to compressive loading. X-ray CT image analyses of the model pile-load tests revealed four stages of sliding and shearing between the rock asperities and piles and the interaction mechanisms in each stage were interpreted via schematic representations. Moreover, the compression zone distribution below the model pile tip was consistent with a spherical failure pattern, which is based on the spherical cavity expansion theory. Intuitively, this study supports the applicability of the spherical cavity expansion theory for calculating the end-bearing capacity of piles socketed in soft rock. Additionally, during sliding and initial local shearing, the deformation of the surrounding rock was dominated by the cylindrical cavity expansion, which generated radial cracks inside the rock. The cylindrical cavity expansion theory and Hoek–Brown failure criterion were used to discuss the stress paths of rock of the bore wall and crack formation in the surrounding rock. To date, the effects of these radial cracks on normal stiffness of the bore wall and the bearing behaviour of rock-socketed piles have received little attention. The qualitative analyses and discussion presented in this paper provide insights into the mechanisms governing pile–rock interfacial behaviour at larger scales.

Experimental Study on the End Bearing Capacity of the Pile in a Group Pile

Experimental Study on the End Bearing Capacity of the Pile in a Group Pile

Experiment on Improving Bearing Capacity of Pile Foundation in Loess Area by Postgrouting

Postgrouting technology is an inevitable trend in the development of bored piles in the loess area. To study the behavior of end resistance, lateral friction, and bearing capacity of postgrouting pile and conventional pile, the mechanism of improving the bearing capacity of postgrouting at the end of pile is analyzed by the static load failure test of pile foundation, combined with the principle of grout‐soil interaction and Bingham fluid model. The results show that the grout‐soil interaction enhances the strength of pile end soil and promotes the exertion of end resistance; the relative displacement of pile‐soil decreases, while the lateral friction increases with the change of the interface property of pile‐soil; simultaneously, the climb height of grouting is approximately the theoretical analysis value. In addition, postgrouting can obviously improve the bearing characteristics of the pile so that the settlement of the pile foundation is slowed down and the bearing capacity is increased.

A Study on Estimation of End Bearing Capacity of a PHC-W Pile in Building Underground Additional Wall Using the PHC-W Earth Retaining Wall

A Study on Estimation of End Bearing Capacity of a PHC-W Pile in Building Underground Additional Wall Using the PHC-W Earth Retaining Wall

嵌岩桩极限端阻力发挥性状研究

嵌岩桩极限端阻力发挥性状研究

Experimental and Simple Semiempirical Methods for Interpreting the Axial Load Versus Settlement Behaviors of Single Model Piles in Unsaturated Sands

Abstract Experimental studies were undertaken to investigate the vertical load versus displacement behavior of single model piles in sand (i.e., Unimin 7030 sand) under both saturated and unsaturated conditions. Stainless steel model piles with three different diameters (i.e., 19.25, 31.75, and 38.3 mm) with a length of 350 mm were used to conduct the pile load tests. Semiempirical methods were proposed to successfully predict the variation of end- and shaft-bearing capacities of single piles with respect to matric suction by modifying three conventional end-bearing capacity equations (Terzaghi 1943; Hansen 1970; Janbu 1976) and the β-method (Burland 1973), respectively. In addition, finite element analyses were also carried out to simulate vertical load versus settlement behaviors of model pile tests using a commercial finite element software, SIGMA/W (GeoStudio 2007).

Evaluation of pile capacity from CPT and pile setup phenomenon

Piles driven in cohesive soils usually experience a large increase in capacity over time, known as setup or freeze. This paper presents the field results of two test piles that were driven in two different locations of Louisiana to evaluate the pile setup behavior. Laboratory and in situ soil testings (cone penetration test, CPT) were conducted to characterize the subsurface soil properties. Several dynamic load tests (DLTs) and one static load test (SLT) were conducted on each test pile at different times after end of driving (EOD) to quantify the magnitude and rate of setup. The test pile in one site was instrumented with vibrating wire strain gages to calculate the load-distribution along the length of the pile during the static load test. With the aid of Case Pile Wave Analysis Program (CAPWAP®) analyses and load distribution plots from strain gages, skin friction and end-bearing capacities were measured separately. The load test results showed that the setup was mainly attributed to increase in skin friction with time and end-bearing capacity remained almost constant. The load test results also showed that setup behavior was more significant in soft cohesive soil. The pile capacity of one test pile was also evaluated using different CPT methods (such as Schmertmann, De Ruiter and Beringen, LCPC). The result showed that all the methods can estimate the pile capacity with good accuracy.

A full-scale field study for performance evaluation of axially loaded large-diameter cylinder piles with pipe piles and PSC piles

This paper presents the results from a pile load testing program for a bridge construction project in Louisiana. The testing includes two 54-in. open-ended spun cast concrete cylinder piles, one 30-in. open-ended steel pile and two (30- and 16-in.) square prestressed concrete (PSC) piles driven at two locations with very similar soil conditions. Both cone penetration tests (CPTs) and soil borings/laboratory testing were used to characterize the subsurface soil conditions. All the test piles were instrumented with vibrating wire strain gauges to measure the load distribution along the length of the test piles and measure the skin friction and end-bearing capacity, separately. Dynamic load tests were performed on all test piles at different times after pile installations to quantify the amount of setup with time. Static load tests were also performed on the PSC and open-ended steel piles. Due to expected large pile capacities, the statnamic test method was used on the two open-ended cylinder piles. The pile capacities of these piles were evaluated using various CPT methods (such as Schmertmann, De Ruiter and Beringen, LCPC, Lehane et al. methods). The result showed that all the methods can estimate the skin friction with good accuracy, but not the end-bearing capacity. The normalized cumulative blow counts during pile installation showed that the blow count was always higher for the PSC piles compared to the large-diameter open-ended cylinder pile, regardless of pile size and hammer size. Setup was observed for all the piles, which was mainly attributed to increase in skin frictions. The setup parameters “A” were back-calculated for all the test piles and the values were between 0.31 and 0.41.

End bearing capacity comparison of screw pile with straight pipe pile under similar ground conditions

In the present study, the end bearing capacity of screw and straight pipe pile under similar pile tip area and ground conditions were investigated. The effect of increasing overburden pressure was also considered in this research. Pile load tests on close-ended screw and straight pipe piles were conducted in the small scale. Dry Toyoura sand was used to develop the model ground. The sand was compacted at relative density of 70, 80 and 92 %. It was observed that in case of straight pipe pile, load settlement curve plunges downward without increase in load around settlement equals to 10 % of pile tip diameter, whereas in case of screw pile, the load settlement curve plunges around settlement equals to 15 % of pile tip diameter. Moreover, the screw piles having helix-to-shaft diameter ratio 2–4.1 showed 2–12 times higher end bearing capacity than straight pipe piles with similar pile shaft diameter. It was also observed from the test results that the end bearing capacity of single-helix screw pile was in average 16.25 % less than straight pipe pile with similar pile tip area and ground conditions irrespective of the effect of increasing overburden pressure.

Construction QA/QC Methods for Postgrouting Drilled Shafts

AbstractThe design and anticipated end-bearing capacity of postgrouted drilled shafts hinge on achieving sufficient grout pressure applied to the soils beneath the shaft tip. Implied, however, is that the grout is distributed reasonably well across the entire tip area. To this end, minimum grout pressure and volume thresholds are usually prescribed in an effort to address both concerns. Unfortunately, it is difficult to practically ascertain the actual area of the grout bulb during production grouting when manually-recorded values of pressure, volume, and uplift are the only available information. Therein, artificially-high grout pressure can be recorded, resulting from a blocked grout-distribution system that goes undetected and the shaft is accepted as both the minimum pressure and volume criteria were satisfied. This article outlines minimum monitoring practices and field quality-assurance/quality-control (QA/QC) measures that can and should be used to better ensure tip grouting is performed in conform...

사질토 지반에 설치된 버킷기초 및 얕은기초의 수직지지력 산정

The vertical bearing capacity of a bucket foundation installed in sand can be calculated as sum of the skin friction and end bearing capacity. However, the current design equations are not considering the non-associated flow characteristics of sand and the reduction in the skin friction and increase in the end bearing capacity when the vertical load is applied. In this study, we perform two-dimensional axisymmetric finite element analyses following non-associated flow rule and calculate the vertical bearing capacity of circular bucket foundation of various sizes installed in sand of different friction angles. After calculating the skin friction and end bearing force at the ultimate state, design equations are derived for each. The skin friction of bucket foundation is shown significantly small compared to the end bearing capacity. Considering the difference with the available design equation for piles, it is recommended that the equation for piles is used for the bucket foundation. A new shape-depth factor (s q ?d q ) for bucket foundation is recommended which also accounts for the increment of the end bearing capacity due to skin friction. Additionally, the shape and depth factor of embedded foundation proposed from the associated flow rule can overestimate the bearing capacity in sand, so it is more adequate to use the shape-depth factor proposed in this study.

Optimizing the Bearing Capacity of Tapered Piles in Realistic Scale Using 3D Finite Element Method

This study aims to investigate the behavior of tapered and their counterpart cylindrical piles using a commercially available 3D finite element software. Three series of tapered and cylindrical piles with the same volume are modeled. In each series, five single piles are modeled, one cylindrical and four tapered. Piles embedded in sandy soils with different internal friction and dilatancy angles are considered. After twice analysis of end and frictional bearing capacity of each pile, the load-settlement diagram is obtained. The end and skin bearings are then computed using various methods. The results are then compared to obtain the optimum taper angle for maximum bearing capacity of tapered piles. It is found that the optimal tapering angle reaches to 1.2° in dense sands. A parametric study is also performed. The results indicated that by increasing internal friction and dilatancy angles of soil, the bearing capacity of tapered piles in sand is utmost increased 11 % compared to that for the same volume cylindrical pile.

Numerical modelling of energy piles in saturated sand subjected to thermo-mechanical loads

This study investigates the impact that different magnitudes and combinations of thermal and axial mechanical loads have on the mechanical behaviour of energy piles in saturated sand. The work is based on the results of a series of thermo-hydro-mechanical finite element analyses, which are compared with centrifuge data, and parametric numerical runs. The analyses prove that an increase in heating loads induces a significant amount of stress and displacement in energy piles, with a remarkable mobilisation of their shaft and end-bearing capacity. Temperature variations up to ΔT= 50 °C induce axial stress up to σth=716kPa and pile heave up to dyth=−14.09mm. These temperature variations mobilise an average side shear resistance and an end-bearing load normalised with respect to those mobilised at failure up to qs,ave/qs,ULT,ave=−14.11% and Qb/Qb,ULT=27.35%, respectively. The magnitude of these phenomena depends on the significance of the applied temperature variation, the significance of the applied mechanical load to the foundation head prior to thermal loading with respect to the pile axial capacity and the soil response to additional loading/unloading processes. These aspects serve a major role in the evolution of the foundation constraint, which governs the mechanical performance of energy piles when subjected to thermo-mechanical loads.

An analytical study of tunnel–pile interaction

Tunnelling under the foundations of structures is becoming more common because of the lack of available space for infrastructure, both above and below ground. The interaction between newly constructed tunnels and existing piled foundations is an important issue. This paper presents results obtained using a computationally efficient analytical approach which aims to estimate the effect that constructing a new tunnel will have on an existing pile. The method uses a spherical cavity expansion analysis to evaluate the end-bearing capacity of the pile, and cylindrical cavity contraction to estimate the decrease in the confining pressure and resulting reduction in pile capacity caused by tunnel volume loss. The paper extends previously published work using this method by considering the effect of tunnel location on the tunnel–pile interactions, examining different possible assumptions of soil stiffness used in the analysis, and by considering the effect that tunnel cavity contraction has on the friction along the pile shaft.

Theoretical breakage mechanics and experimental assessment of stresses surrounding piles penetrating into dense silica sand

This letter extends an earlier theoretical and numerical analysis that aimed to improve predictions for the large-displacement end-bearing capacity of piles in sand by considering the boundary conditions applying to steady penetration and the effects of grain crushing via breakage mechanics. The earlier work led to good agreement with the end-bearing capacities, soil displacements and evolution of grain size distributions observed in experiments of penetrating model piles. The purpose of the current paper is to complement the previous evaluation through comparisons with more recently published calibration chamber measurements of the stresses surrounding instrumented model piles penetrating into dense silica sand. Encouraging agreement is demonstrated for the radial, circumferential and vertical stress components. Scope for further improvements is also identified.