Piles In Dense Sand Research Articles

Discussion of “Field investigation of the axial resistance of helical piles in dense sand”

Discussion of “Field investigation of the axial resistance of helical piles in dense sand”

Effect of Sand Relative Density on Response of a Laterally Loaded Pile and Sand Deformation

Two scale-model tests were separately conducted in standard Toyoura sand with relative density of 50% and 80%. The effect of sand relative density on pile-soil interaction was investigated through the response of a laterally loaded pile and the sand movement around the pile. At a displacement of 3.6 mm of the loading point, the applied loads in loose and dense sand were 4.775 N and 21.025 N, respectively, and the maximum moment and soil resistance of the pile in dense sand were over 4 times those in loose sand. However, the deflection of the pile in dense sand was less than that in loose sand; additionally, the depth of zero deflection in dense sand was also less than that in loose sand. At the same time, the maximum displacements of loose sand in the vertical profile and ground surface were over 1.5 times those of dense sand. These characteristics occurred because the relative stiffness ratio of soil and pile increased as the relative density increased, which caused the behavior of the pile in dense sand to be elastic rather than rigid. In addition, the compacted sand particles did not move as easily as the loose sand particles.

Field investigation of the axial resistance of helical piles in dense sand

This paper presents the results of compression and tension load tests performed on a single helical pile installed in dense sand. The pile was instrumented using strain gauges that allowed the shaft and base load resistance to be separated and the distribution of shaft resistance along the pile during the test to be determined. The pile was loaded first in compression, with a maintained load test, followed by a constant rate of penetration load test being performed to assess the effects of creep on the pile’s response to compression loading. The pile was then loaded in tension using a maintained load test procedure. Finite element analyses were performed using Abaqus and these helped to provide additional insights to explain the response of the instrumented pile during loading. The test showed that during compression loading, substantial bearing pressures developed beneath the pile helix, which provided the majority of axial load resistance. During tension loading, uplift pressure mobilized on the helix again provided the majority of axial resistance. The strain gauges suggested that the pile load response to compression loading was ductile. During tension loading, the pile response was brittle. Whilst load tests performed on only one instrumented pile test are presented, the use of instrumentation and finite element analyses allowed important insights into the load–displacement response of helical piles.

A Driveability Study of Precast Concrete Piles in Dense Sand

AbstractA research study was recently completed by University College Dublin to examine the performance of various pile types including open steel tubular piles, concrete precast piles, and helical piers. At the outset of this project, one of the key risks identified was that the concrete piles could not be installed to the target depth due to (i) insufficient energy from the available hammer and (ii) the onset of pile material damage. In order to mitigate this risk a detailed pile driveability analysis was completed to predict the installation performance during driving. Selecting an appropriate model for predicting the Static Resistance to Driving (SRD) was seen as a critical component of the driveability process in order to predict reasonable stresses and blow counts. This paper describes the procedures adopted for a base case driveability analysis and the outcome of the pile installations. A comparison of the SRD using other models (including the API and IC-05 methods) was conducted and the results we...

Experimental investigation on seismic behavior of single piles in sandy soil

This paper describes a quasi-static test program featuring lateral cyclic loading on single piles in sandy soil. The tests were conducted on 18 aluminum model piles with different cross sections and lateral load eccentricity ratios, e/d, (e is the lateral load eccentricity and d is the diameter of pile) of 0, 4 and 8, embedded in sand with a relative density of 30% and 70%. The experimental results include lateral load-displacement hysteresis loops, skeleton curves and energy dissipation curves. Lateral capacity, ductility and energy dissipation capacity of single piles under seismic load were evaluated in detail. The lateral capacities and the energy dissipation capacity of piles in dense sand were much higher than in loose sand. When embedded in loose sand, the maximum lateral load and the maximum lateral displacement of piles increased as e/d increased. On the contrary, when embedded in dense sand, the maximum lateral load of piles decreased as e/d increased. Piles with a higher load eccentricity ratio experienced higher energy dissipation capacity than piles with e/d of 0 in both dense and loose sand. At a given level of displacement, piles with circular cross sections provided the best energy dissipation capacity in both loose and dense sand.

Uplift Capacity of Belled and Multi-Belled Piles in Dense Sand

This paper evaluates the uplift capacity of belled and multi-belled piles in dense sand. A two-dimensional distinct element (DE) analysis was applied in pullout tests on single piles to investigate the uplift resistance of the piles, the soil behavior around the piles, and the interaction between the soil and the pile surface. It was observed from the DE analysis that the soil mass adjacent to the projections of the belled and multi-belled piles moved vertically, and that the soil movements leaned slightly with the occurrence of relative displacement between the soil and the pile surface. A theoretical solution for predicting the uplift capacity of belled and multi-belled piles was derived from an upper bound limit analysis based on the soil movements in the DE analysis. The solution was able to reproduce the ultimate uplift resistance in the DE analysis using the friction angles in the aggregates and on the pile surface that were evaluated from a simulation of direct and simple shear tests. In addition, a continuity equation that satisfied the relationship between the displacement vector of the soil mass adjacent to the projections and the change in volume around the soil mass was proposed for predicting the uplift capacity of actual piles under axisymmetric conditions. The theoretical solution obtained with the continuity equation was in good agreement with the pullout resistance of the belled and multi-belled piles in centrifuge model tests and full-scale tests conducted in situ.

Development of dynamic p-y backbone curves for a single pile in dense sand by 1g shaking table tests

A series of 1 g shaking table model pile tests were carried out in dry and saturated dense sand to evaluate dynamic p-y curves for various conditions of the acceleration frequency, the acceleration amplitude of input loads, the flexural stiffness of the pile shaft and the mass at the pile head. The influence of each parameter on dynamic p-y curves was evaluated. Dynamic p-y backbone curves for pseudo static analysis of dense sand were proposed as hyperbolic functions by connecting the peak points of the experimental p-y curves, which correspond maximum soil resistances. In order to express the backbone curves as hyperbolic functions, empirical equations for the initial soil stiffness (kini) and the ultimate soil resistance (pu) were developed, respectively, as a function of the soil friction angle and the confining stress. The herein suggested backbone curves were also compared with the currently available p-y curves.

Experimental Arrangements for Investigation of Soil Stresses Developed Around a Displacement Pile

ABSTRACT Experimental arrangements are described that lead to reliable stress measurements in calibration chamber tests involving steel displacement piles in dense sand. The research required: developments with the chamber and pile testing equipment; novel approaches to the calibration and modelling of soil in-situ stress sensors; special arrangements for the sensors’ deployment; and development, calibration and operation of a miniature instrumented ICP pile. Preliminary results are reported from pilot tests to demonstrate the capabilities of the resulting measurement systems.

Wave equation analyses of tapered FRP–concrete piles in dense sand

Fiber-reinforced polymers (FRP)–concrete composites provide an attractive alternative to conventional pile materials such as steel, concrete and wood by improving the durability of deep foundations. In the current study, FRP tubes with different taper angles are filled with self-consolidating concrete (SCC) and driven into dense sand that is enclosed in a large pressurized soil chamber. Driving tests are conducted on FRP–SCC composite piles to determine how the pile material and geometric configuration affect its driving performance. Dynamic data is employed to determine the soil parameters in the TNO model (i.e., soil quake and damping constant) using the DLTWAVE signal-matching program. The driveability of FRP–SCC and traditional pile materials is compared using the wave equation analysis program PDPWAVE. The experimental data and the wave equation analyses indicate that the taper shape has a favourable effect on the driveability and static resistance of piles. It is also found that the driveability of FRP–SCC composite piles is similar to that of conventional prestressed concrete and steel piles. However, empty FRP tubes required a much higher driving energy. Their low flexural resistance along with risk of buckling can hinder their driveability in different soil conditions.

Lateral behaviour of composite tapered piles in dense sand

When used in harsh environments and offshore applications, conventional pile materials (such as steel, timber and concrete) are prone to costly durability problems, such as corrosion in reinforced/prestressed concrete and steel shell piles. Fibreglass-reinforced polymer (FRP) composites provide a corrosion-resistant construction material. FRP–concrete composite piles have been used successfully over the last decade in several projects for fendering applications. This paper investigates the behaviour under lateral loading of FRP composite tapered and cylindrical piles filled with self-consolidating concrete (SCC) and driven in dense sand enclosed in a pressure chamber. Seventeen pile installations were conducted using toe driving and conventional head driving. The piles were subsequently subjected to static lateral load tests. The results show that the pile taper increased its lateral capacity and enhanced its overall performance. A taper coefficient, Ktl, was introduced to account for the taper effect on the lateral response of piles. The experimental results were compared with two commonly used approaches for the analysis of the lateral response of piles: the p–y curves approach and the strain wedge model (SWM). The taper coefficient can be easily incorporated in both methods to account for the effect of pile taper. The comparison between the measured and computed responses showed that both the p–y curve approach and the SWM, modified using Ktl, can be used for the prediction of the lateral response of tapered piles.

Lateral behaviour of composite tapered piles in dense sand

When used in harsh environments and offshore applications, conventional pile materials (such as steel, timber and concrete) are prone to costly durability problems, such as corrosion in reinforced/prestressed concrete and steel shell piles. Fibreglass-reinforced polymer (FRP) composites provide a corrosion-resistant construction material. FRP–concrete composite piles have been used successfully over the last decade in several projects for fendering applications. This paper investigates the behaviour under lateral loading of FRP composite tapered and cylindrical piles filled with self-consolidating concrete (SCC) and driven in dense sand enclosed in a pressure chamber. Seventeen pile installations were conducted using toe driving and conventional head driving. The piles were subsequently subjected to static lateral load tests. The results show that the pile taper increased its lateral capacity and enhanced its overall performance. A taper coefficient, Ktl, was introduced to account for the taper effect on the lateral response of piles. The experimental results were compared with two commonly used approaches for the analysis of the lateral response of piles: the p–y curves approach and the strain wedge model (SWM). The taper coefficient can be easily incorporated in both methods to account for the effect of pile taper. The comparison between the measured and computed responses showed that both the p–y curve approach and the SWM, modified using Ktl, can be used for the prediction of the lateral response of tapered piles.

Uplift performance of FRP tapered piles in dense sand

The influence of taper angle on the uplift performance of FRP tapered piles in dense sand at various embedment ratios is investigated using a large-scale testing facility (pressure chamber). The current study evaluates the uplift performance of tapered piles relative to the uplift performance of straight-sided wall piles. Thirteen pile installations were performed in a pressure chamber using conventional head driving and a novel toe driving technique. Twenty­six uplift load tests were performed at different radial and vertical confining pressures in order to simulate pile segments at different depths. The results of uplift loading tests are presented and discussed. The results showed that the uplift capacity of tapered piles is slightly higher than that of cylindrical piles with similar average diameter and length. The taper effect on the pile uplift performance is evaluated using the uplift taper coefficient. A hyberbolic relationship is established between the uplift load and displacement that can be used to determine the soil stiffness for use in non­linear analysis. A simplified design approach for uplift capacity of tapered piles is discussed and evaluated.

Load transfer of fibre-reinforced polymer (FRP) composite tapered piles in dense sand

This paper describes an experimental study conducted using a large, laboratory-scale testing facility to test pile segments at different stress levels. The objectives of the study were twofold: to examine the load-transfer mechanism of tapered piles in compression, and to evaluate the effect of pile material on pile performance characteristics. The results of axial compressive loading tests on 26 pile load tests were presented using fibre-reinforced polymer (FRP) concrete composite tapered piles and steel piles. Two installation techniques were used, including conventional head driving and toe driving using a new technique. Piles were tested at different confining pressures to represent a pile segment at depths of 4.0 and 8.0 m. The load distribution along the pile shafts was measured and the results were compared with those from an analytical solution in terms of the taper coefficient Kt. The comparison showed reasonable agreement between Ktvalues established from the experiments and those obtained from the analytical solution. The measured toe resistance of tapered and cylindrical piles was compared with those from the analytical solution. A simple rational approach was proposed for the design of tapered piles.Key words: tapered piles, FRP, pile capacity, axial performance, centrifuge modeling, shaft resistance, toe resistance.

Time-related increases in the shaft capacities of driven piles in sand

Displacement piles can gain capacity with time through pore pressure dissipation and consolidation, not only in clay but also in sand. In recent tests on strain-gauged pipe piles in dense sand at Dunkirk, France, the shaft capacity increased by 85% between six months and five years after installation. This technical note describes the Dunkirk results and similar cases, involving steel, concrete, and timber piles in saturated, unsaturated, and carbonate-free sands. Possible mechanisms to explain the observations are reviewed. The most plausible explanation seems to be a change in the stress regime, created during pile driving. Creep may reduce arching effects around the pile shaft, increasing the radial effective stresses. Ageing may also result in stronger dilation during shearing, and larger increases in radial stress during pile loading. There are several important practical implications. The set-up time allowed in pile testing needs to be standardised, and should be at least 20 days. There could be substantial cost savings, if piles can be installed early and allowed to age before loading. Higher working loads on existing aged piles may be permissible. Capacities, assessed from pile driving, are unlikely to match those available in medium to long term. Some needs for further research are indicated.

Driving characteristics of open-toe piles in dense sand : Raines, R D; Ugaz, O G; O'Neill, W J Geotech Engng Div ASCE V118, N1, Jan 1992, P73–87

Driving characteristics of open-toe piles in dense sand : Raines, R D; Ugaz, O G; O'Neill, W J Geotech Engng Div ASCE V118, N1, Jan 1992, P73–87

Driving Characteristics of Open‐Toe Piles in Dense Sand

Driving tests are conducted on large‐scale steel model pipe piles with open toes to determine how geometric configurations of the toes affect driving performance. A further objective is to investigate a wave‐equation model for predicting driveability of open‐toe piles in dense, saturated sand. The tests are conducted in a large pressure chamber. Examination of the experimental data and of finite element analyses of the problem indicate that pipes with thickened and beveled toes require less energy for penetration than plain, cylindrical pipes, and that none of the piles plug solidly during driving up to penetrations of 21 diameters into the dense layer. It is found that the angle of wall friction on the interior of the pipe is a major factor in controlling the plug movement. One‐dimensional wave‐equation simulations of the tests are found to be adequate, but only with empirical adjustment of parameters related to static resistance.

Performance of piles with enlarged bases subject to uplift forces

The influence of embedment, base diameter, and backfill density on the uplift behaviour of piles with enlarged bases embedded in sand was investigated in a centrifuge. Comparitive tests on straight-shafted piles are also reported. For piles in dense sand, sensible agreement was found with earlier research on anchor plates and published field data. However, uplift capacities in loose sand were considerably lower than previously observed for anchor plates. A number of theories for anchors considerably overpredict the observed capacity for belled piers in both dense and loose sand, although in the case of dense sand, reasonable values are obtained using an empirical equation derived from centrifuge tests on anchor plates and a finite element based design approach. The normally conservative vertical slip-surface model is alone in providing reasonable agreement with the surprisingly low observations for piles in loose sand. Key words: piles, uplift capacity, centrifuge tests, sand.

Experimentally determined distribution of stress around a horizontally loaded model pile in dense sand : Williams, D J; Parry, R H G Proc 4th Australia-New Zealand Conference on Geomechanics, Perth, Western Australia, 14–18 May 1984V2, P578–P582. Publ Barton: Inst of Engineers, 1984

A model pile instrumented with miniature load cells has been jacked into a bed of dense sand and loaded horizontally in two directions. From the load cell readings taken and a consideration of force equilibrium, the approximate distribution of stress around the circumference of the pile on horizontal loading has been obtained. The stresses induced on horizontal loading were found to be confined essentially to the leading face of the pile and comprised components in the horizontal plane and a longitudinal shear component resulting from flexing of the pile. The resultant stress in the horizontal plane was non-uniform and directed approximately radially towards the pile around much of its circumference.

Uplift Behaviour of Short Piles In Uniform Sand

The results of laboratory studies on the uplift behaviour of short piles in uniform sands are presented. Smooth and rough mild steel piles (12.7 mm in diameter) in two uniform sands were used in the investigation. Tests were conducted for dry and submerged conditions of soil placed at either of the two densities (loose or dense). The uplift capacity was found to increase with L / D ratio, pile roughness, soil density and particle size. Pile movements of about 5% of pile diameter in loose sands and about 10% of pile diameter in dense sands were found to be necessary to mobilise the uplift capacity. These values are much more than 3 to 6% required for shaft loads during push-in tests. The unit skin frictions during pull-out tests are significantly less than during push-in tests, especially in case of rough piles for which it is as much as 80% less. Submergence resulted in reduction of uplift capacity in all cases, earth pressure coefficients, however, reduced only in case of piles in dense sand and remained almost unaffected for piles in loose sands.

H steel piles in dense sand : De Beer^E.; de Jonghe^A.;Carpentier R. Proc 10th International Conference on Soil Mechanics and Foundation Engineering, Stockholm, 15–19 June 1981, V2, P693–698. Publ Rotterdam: A.A. Balkma, 1981

H steel piles in dense sand : De Beer^E.; de Jonghe^A.;Carpentier R. Proc 10th International Conference on Soil Mechanics and Foundation Engineering, Stockholm, 15–19 June 1981, V2, P693–698. Publ Rotterdam: A.A. Balkma, 1981