Array Of Piles Research Articles

Load Transfer in Geosynthetic-Reinforced Piled Embankments with a Triangular Arrangement of Piles

A geosynthetic-reinforced piled embankment situated along a newly constructed high-speed rail line was fully instrumented and monitored to explore soil arching in an equilateral-triangular arrangement of piles with circular cap configuration. During construction, the settlement and vertical stress on the pile caps and subsurface at ground level and the tensile strain in the geogrid were recorded. A modified analytical arching model is derived from the established concentric arches (CA) model to elucidate the load transfer mechanism, specifically for a triangular array of piles. The general framework assumes that the embankment load, not resting on the subsurface beneath the arches, is transferred outward along the arches and distributed uniformly over the improved ground. Compared to the conventional CA model, the proposed model gives a lower proportion of load carried by piles, more in line with field measurements. Given the friction and adhesion between soil and geosynthetics, a novel quartic equation is applied to characterize the tensioned membrane effect of geosynthetic reinforcement based on Pham’s circular and parabolic models. The stiffness variation of the biaxial geogrid was critically assessed for the triangular pile arrangement, and its implications for the design were revealed. Finally, the pile efficacy and critical arch height were determined from different analytical methods and checked against field observations, demonstrating the potential of the proposed model.

Using a Bed Sill as a Countermeasure for Clear-Water Scour at a Complex Pier with Inclined Columns Footed on Capped Piles

River bridge piers may collapse due to the local scour around their foundations. It is known that local scour is an effect of the three-dimensional flow field that develops near the pier and that the geometric complexity of a non-cylindrical pier may, correspondingly, increase the complexity of the process. It is also known that various devices may be used as scour countermeasures. This manuscript explores the use of a bed sill as a countermeasure for local scour at a complex bridge pier compound of an array of piles, a pile cap, and two inclined columns with the rectangular sections above the cap. This pier geometry, never studied before in combination with a scour countermeasure, was stimulated by an existing bridge. Different sill placements were tested (at the upstream or downstream edges of the pier, or in an intermediate position) for various values of the pile diameter and number, cap thickness and cap elevation. The results of a wide experimental campaign consistently showed that the most effective placement of the transverse sill was at the upstream edge of the pier, for which scour reductions of up to 30–40% could be obtained for the long-term scour depth. The countermeasure performance decreased to about 10% when the sill was placed at the downstream edge of the pier. Furthermore, the installation of a transverse sill upstream of the pier also changed the shape of the scour hole because the pier was then located in an area prone to sill scour; however, for the present experiments, the combination of the effects was beneficial in terms of the resulting scour depth. Although the investigation of a single hydro-dynamic condition prevents the experimental findings from being generalized, the promising results stimulate further consideration of a transverse sill as a countermeasure for local scour at a complex pier.

Experimental Investigation of Piezoelectric Energy Harvesters Applied in Concrete Pavement

This paper proposes the application and manufacturing of piezoelectric devices based on pile and arc-bridge transducers to harvest mechanical energy from concrete pavement. Multi-scale experiments are conducted to clarify the influence of electrical connection, load resistance, traffic speed, and loading times on the electrical properties of the harvesters. The reduced-scale test shows that the transducers should be connected to rectifiers before being connected as an array. Moreover, the output power of the arc-bridge transducer with resistance variations is unstable compared with that of the pile transducer. Accelerated pavement testing illustrates that the output power of the half pile array device increases to 1.7 mW with an optimal resistance of 10.0 MΩ; reducing the internal equivalent resistance is a potential way to increase the energy output. The results also show that the load speeds significantly influence the profile of the voltage and have a minor effect on the generated electric energy in the tested conditions. Furthermore, the electrical properties of the piezoelectric device exhibit no statistical degradation after the electrical fatigue test of 100,000 tire loads, indicating a novel electrical fatigue performance. The findings in this paper can further guide the application of such piezoelectric devices in concrete pavement.

The influence of geometry on the performance of a helical steel pile as a geo-exchange system

Foundation piles have the potential to improve the economic and technical feasibility of ground source heat pump (GSHP) systems. They simultaneously provide structural support and energy for space heating and cooling. In this study, a thoroughly verified and validated numerical model of a novel in-ground heat exchanger for GSHP systems is developed and used to simulate and optimize performance. Commercially available helical steel casings with nominal sizes according to the American Petroleum Institute (API) of API 13.5, API 23, API 29, API 53, API 60, and API 68 were considered. The flow rates considered were 1 L/min, 2 L/min and 4 L/min for laminar flow and lower pressure drops. Results show the performance to increase with increasing pile size owing to improved heat transfer and longer residence times. Optimizing performance with an API 68 steel casing, (with a 2” nominal plastic pipe) gives a capacity increase of 0.01 ton/pile (or 8.3%), which would reduce the approximate pile array required for a 3 ton cooling system from 13 to 12. Doubling the size of this pile while keeping other parameters constant gives an 18.5% capacity improvement with an output capacity of 0.28 ton/pile, and an 11, 20 m pile array requirement to meet a 3 ton cooling load. With a maximum heat exchange rate of 58.6 W per meter depth, this shallow in-ground heat exchanger has the potential to minimize energy and costs for small-scale implementation. In addition, the possible low flow rates help reduce pumping power requirements. This study provides a foundation for sizing and design of helical steel piles. Moreover, the study also gives insights into pile performance in multi-layered soils where the thermal conductivity varies with depth.

EXPERIMENTAL TESTS OF THE BASIS OF “FUNDEX” PILES AFTER THE LONG “RELAXATION” IN CLAY SOILS

In the soil conditions, typical for the city of Saratov, piles on Fundex technology with a loss screw tip of DPOS-4E are executed. After the long «relaxation» of piles without loading guaranteeing completion generally of processes of compaction, consolidation, restitution of the water and colloid communications additional engineering-geological researches are executed and the complex of laboratory researches of parameters of the near pile array of a soil is conducted. Physicomechanical characteristics of the basis immediately at a lateral area and at the lower end of a pile, apart by 1 m are received from its side and in a soil of natural addition. Results are compared in a tabular and graphic form. Conclusions are drawn on the nature of changes of physical, strength and deformation characteristics of the near pile array of a soil at various distance from a lateral area of a pile. The essential differences in formation of the condensed soil zones around Fundex piles from the traditional displacing drive and pressed piles influencing a carrying capacity (the extreme resistance) of the basis of stuffed piles are noted. Comparison of the obtained datas of laboratory with results of field tests of similar piles in identical soil conditions after long “relaxation” (3 months) in accordance with static indenting and pull out loads. Conclusions are drawn on need of additional pilot studies of the basis of Fundex piles for the wide range of soil conditions by laboratory and field methods with parallel tests by the dead pressing and pulling-out loads.

Estimation of the Load Sharing Ratio of Pre-installed Columns in Top-Down Buildings on Korean Rock

The estimation of the load sharing ratio of the pre-installed column in typical top-down method building was carried out using three dimensional finite element analysis. The main focus was on quantifying the apparent load sharing ratio of the prebored and precast pile–which is the common form of a pre-installed column – throughout the construction process. Additional parametric study was conducted based on series of numerical analysis with special attention given to the pile load sharing ratio under different pile array, pile embedded length, structure height and rock type. Moreover, the load sharing ratio of a single pile was investigated based on the relative location of the pile in the raft (footing). The numerical model was verified based on the field data of two actual construction site using the prebored and precast pile and the top-down method. Based on the analysis results, it was shown that the pre-installed columns of top-down method building is capable of supporting a notable portion of the structural load throughout the construction process. Furthermore, it was also shown that the pile near the center of the raft carried more structure load compared to the piles in the side and the corner.

LABORATORY EXPERIMENTAL RESEARCH OF LOADING FORCES DEVELOPMENT ACTING ON THE SIDE SURFACE OF THE PILES

The forces of negative friction or loading forces of friction on the piles develop due to additional deformations of near pile array and they cannot be more force of resistance on the side of pile in rest, that is formed due to own weight of the ground founding. The paper presents the results of laboratory experimental research of loading forces of friction acting on the lateral surface of the piles without taking into account the vertical load (being relatively at rest) and provided an analysis of methods for detection of negative friction forces (loading forces) acting on the lateral surface of the pile, with the appointment of their load-bearing capacity. The researches have confirmed the theoretical statement about the equality of the loading forces of friction to ground resistance forces under the action of the torque load but not the pulling load, as it is suggested in the modern standards.

Evaluation of Harmony Search Optimization to Predict Local Scour Depth around Complex Bridge Piers

One of the main causes of bridge collapse may be flood flow scour near piers. Several experimental and local field investigations were carried out to study scour depth. However, existing empirical equations do not commonly provide accurate scour prediction due to the complexity of the scour process. Physical and economic considerations often lead to bridge foundation constructs which included a pier column based on a pile cap supported by an array of piles. Piers with this configuration are referred to as complex piers. A few studies have been done on complex bridge pier scour depth estimation. Such efforts may be classified into theoretical and empirical equations. This paper investigates local scour around complex bridge piers by using harmony search algorithm under clear water conditions. Statistical indices such as the coefficient of determination (R2), root mean square error (RMSE), mean absolute error (MAE), mean absolute percentage error (MAPE), and bias were used to evaluate the performance of these methods. By designing laboratory tests, 82 experimental data points were measured by authors. Also 615 experimental data sets with the same measured experimental conditions were collected from published literature and used for optimization. The results show that the developed HS model can predict scour depth better than other equations according to statistical indices.

Scattering of periodic surface waves by pile-group supported platform

A semi-analytical approach is proposed to solve the scattering of free surface waves around a platform supported by a pile array. Assuming periodic lattice configuration and strong contrast between cylinder spacing and typical wavelength, the multi-scale perturbation theory of homogenization is employed to derive the effective equations governing the macro-scale wave dynamics and the boundary-value problem of micro-scale flows within a unit cell. The constitutive coefficient in the macro-scale effective equations are computed from the solution of the micro-scale boundary-value problem, which is driven by the macro-scale pressure gradient. Flow separation is treated by the eddy viscosity model where the bulk eddy viscosity is determined by balancing the time-averaged rate of dissipation and the rate of work done by wave forces on the cylinders integrated over the entire platform region. The proposed semi-analytical approach is validated by comparisons with laboratory experiments for a pile-group supported platform in a wave flume. In addition field-scale wave scattering by a pile-group supported circular platform is investigated. For long waves, the maximum vertical force exerted on pile-group supported platform may reach 1.2 times of the value without piles. The maximum increase of the torque in transverse direction occurs for intermediate waves, which may reach 40% for the parameters discussed.

Experimental and numerical investigations on the performance of sacrificial piles in reducing local scour around pile groups

This paper presents both experimental study and numerical simulation to investigate the effects of an innovative sacrificial piles concept to reduce local scour surrounding service piles. These sacrificial piles are placed upstream of the pile groups, which serves to change the flow field and reduce the erosive force before it reaches the service piles. Four types of pile group arrangements were considered in the experimental and simulation analyses, including single pile, double pile in tandem arrangements, double pile with side-by-side arrangements, and pile array of 2 × 2 arrangements. Scaled experiments were conducted in flume for each group of design, and local scour around piles with and without sacrificial piles was monitored. It was found that the sacrificial piles effectively reduced the development of local scour surrounding the service piles, especially at their heels. The results also showed that the use of sacrificial piles reduced the time required for the scour depth to reach the equilibrium conditions than those without the sacrificial piles. To corroborate the experimental observation, numerical simulation with three-dimensional computational fluid dynamics model has also been carried out with commercial code with verified erosion model. The development of dynamic scour process and maximum scour depth were obtained by the computational simulations. Comparison of experimental and computational results both indicates that the use of sacrificial pile is effective in reducing the scour depth. The extent of reduction in the maximum scour depth varied with the arrangement of sacrificial piles.

Prediction of Equilibrium Local Scour Depth at Complex Bridge Piers

At present, bridges are frequently built with geometries that consist of a column founded on a pile cap and supported by an array of piles, referred to as common complex piers or most often (as also in this paper), briefly, as complex piers. This paper addresses prediction of local scour depth at those complex piers. An experimental campaign of 48 long-duration tests was performed with seven complex pier models under steady clear-water flow conditions to quantify the influence of the relative column width, Dc/Dpc (Dc = column width, Dpc = pile cap width), the relative pile cap thickness, T/h (T = pile cap thickness, h = approach flow depth), and the pile-group configuration on the equilibrium scour depth, dse. Several tests were carried out for the possible range of variations in the pile cap position relatively to the initial bed level. The values of dse were estimated by extrapolation of the experimental data series. The performance of three methods, i.e., Auckland, HEC-18, and Florida Department of Transportation (FDOT), to predict dse is analyzed and discussed. Based on the experimental results of the present study and on the conceptual approaches of Auckland and FDOT methods, an alternative formulation for a predictor of dse at (common) complex piers is suggested and validated.

The settlement behavior of piled raft in clay soils

The settlement behavior of a square piled raft in clay soil was investigated using numerical analysis. The emphasis was on quantifying the reduction of the average and differential settlements in soft and stiff clay soils. To obtain the detailed information on the piled raft, a nonlinear three-dimensional finite element analysis with pile–soil slip interface model was performed for various pile positions, pile numbers, pile lengths under the raft and different loading types. Based on the results obtained, the settlement aspects for an efficient design of piled rafts subjected to vertical loading are discussed for soft and stiff clay soils. It is found that the variation of reduction ratio (sPR,avg/sUR,avg) of soft clay was relatively greater than that of stiff clay, whereas the reduction ratio of soft clay was relatively smaller than that of stiff clays. It is also found that the required pile group-raft area ratio (Ag/Ar) for minimizing differential settlement in soft clay was slightly larger than that of stiff clay in the same pile array.

Viscous effects on Bragg scattering of water waves by an array of piles

We examine the effects of viscous damping in the boundary layers on the Bragg resonance of surface water waves by a two-dimensional array of vertical cylinders. For cylinders of small radius relative to the wavelength, we first derive an effective boundary condition for the radial derivative of the velocity potential to account for the viscous forces. Coupled-mode equations are then rederived by an asymptotic method for the envelopes of multiply resonated waves inside the array. Effects of viscosity on band gaps and scattering coefficients due to a plane incident wave are examined analytically for an infinitely long array of finite width surrounded by open water. For normal incidence the envelope physics is one dimensional. The transmission and reflection properties are studied first. Oblique incidence can in principle excite several wave trains in different directions. Explicit solutions are given and discussed when there are only two wave trains inside the array. Results are compared with recent theories where viscosity is not taken into account. The asymptotic theory can be modified for two-dimensional sound scattering by a cylinder array.

Vibration isolation by an array of piles : Boroomand, B; Kaynia, A M Proc Fifth International Conference on Soil Dynamics and Earthquake Engineering, Karlsruhe, 23–26 September 1991P683–691. Publ Southampton: Computational Mechanics Publications, 1991

Vibration isolation by an array of piles : Boroomand, B; Kaynia, A M Proc Fifth International Conference on Soil Dynamics and Earthquake Engineering, Karlsruhe, 23–26 September 1991P683–691. Publ Southampton: Computational Mechanics Publications, 1991

The Effect of Staggared Array of Piles on Equilibrium Bed Form in Sandy Rivers

Laboratory experiment and theoretical analisys are performed focusing on the two effect of pile-array or tall vegetations on sediment transport in sandy rivers. The one is additional resistance which reduces velocity and bed shear force, making erosion and bed load decrease. The other is increase of diffusivity of the flow field by means of the wake behind them. In the experiment, it is shown that the bank region is made shifted toward the center of the river with those two effects. And, taking account of them into the theoretical analysis, the general features of equilibrium bed form are well explained.

WAVE TRANSMISSION THROUGH A DOUBLE-ROW PILE BREAKWATER

Several previous investigators have conducted experiments leading to expressions for predicting the transformation of waves passing through closely-spaced pile or large cylinder breakwaters. The present study extends the earlier experiments which used a single row of piles instead of a double row of piles forming a breakwater. The experiments using the double-pile breakwater were performed in the same facility as the experiments conducted on a single-pile breakwater and employed the same method of analysis for a more meaningful comparison. The experiments consisted of allowing waves to pass through a pile array and measuring the incident and transmitted wave heights. The variables were: depth, period, diameter, monochromatic and random waves. The experimental matrix was three water depths, four wave periods, two pile diameters, two gap dimensions between piles and four random wave spectra: Darbyshire, I.T.T.C., Pierson- Moskowitz and JONSWAP, two pile diameters and two gap dimensions between piles. The two-row breakwater had less wave transmission than the single-row breakwater, as expected. For a gap to a pile diameter ratio, or b/D = 0.2 (where b = gap spacing, D - pile diameter), the wave transmission was reduced by 15 percent, as compared with a single-row breakwater; for a gap ratio of b/D - 0.1, the wave transmission was reduced by 5 to 10 percent.

WAVE FORCES ON PILES OF VARIABLE DIAMETER

A method of calculating nonlinear wave induced forces and moments on piles of variable diameter is presented. The method is based on the Morrison equation and the linear wave theory with correction parameters to account for convective inertial effects in the wave field. These corrections are based on the stream function wave theory by Dean (1974). The method permits one to take into account the added wave force due to marine growth in the intertidal zone or due to a protective jacket, and can also be used to calculate forces on braces and an array of piles.