Sandpile Research Articles

Field and numerical study of the lateral response of rigid piles in sand

Large diameter, short monopiles are the preferred foundation type for offshore wind turbines. These piles demonstrate a rigid response with significant rotation of the pile base under ultimate lateral load. As traditional empirical p-y curves used in lateral loaded pile analysis have been derived from tests on small diameter onshore piles, there is some doubt about their applicability to rigid monopiles, particularly in view of the significant difference in the response of the pile base compared with a typical onshore pile. To address this issue, this paper reports on a unique series of field tests using instrumented driven pipe piles, complimented by numerical analysis, which was performed to examine explicitly the contribution of the pile base to the response under lateral load. The field tests, which included tests on pipe piles that had the sand plug removed to below pile tip level prior to testing, confirmed that the influence of the base on the lateral response for the tested 273- and 457-mm-diameter piles was negligible. Numerical analyses that were calibrated using the field test data showed that the contribution of the base to the lateral capacity of a monopile with a diameter as large as 10 m is negligible. Results also indicated that p-y curves are not affected by the length to diameter ratio and can be used to predict the response of monopiles in sand.

Thermally induced ratcheting of a thermo-active reinforced concrete pile in sand under sustained lateral load

Thermally induced ratcheting of a thermo-active pile is the accumulation of net and irreversible pile head displacement upon heating–cooling cycles. Although this kind of phenomenon has been observed in vertically loaded piles in sand, it is unknown whether this exists in laterally loaded cases, and also what underlying mechanisms occur under the thermomechanical flexural soil–pile interaction. This study presents a series of centrifuge tests and finite-element simulations of the thermomechanical behaviour of a laterally loaded thermo-active pile in sand. A new model reinforced concrete (RC) was used in the centrifuge tests to mimic the thermal and mechanical properties of a prototype RC pile realistically. Ratcheting was evident in laterally loaded piles and its extent was more significant when the working horizontal load was higher. The ratcheting phenomenon was attributed to the accumulation of soil plastic strain due to the cyclic mechanical loading induced by pile thermal horizontal expansion and contraction, soil dilation upon soil–pile interface shearing and creep. The additional bending moment induced by the thermal action did not induce yielding within the pile. A subsequent numerical sensitivity study suggested that ignoring the softening behaviour of the sand would lead to underestimation of the magnitude of the accumulative thermally induced pile head lateral displacement.

Axial Bearing Mechanism of Post-Grouted Piles in Calcareous Sand

Post-grouted piles, as a foundation form for large-span and large-scale structures on calcareous sand, are expected to provide a high bearing capacity, but research on the response of post-grouted piles subjected to axial load in calcareous sand is still in the exploratory stage. In this paper, a model test is constructed for static pressure piles in calcareous sand under axial loading. The response of axial compressive piles, with and without post-grouting, in calcareous sand were investigated, and the test results were compared with those of axial compressive piles, with and without post-grouting, in siliceous sand. The influence of post-side-grouting on the response of a single pile subjected to axial compressive load in calcareous sand and its bearing mechanism were further analyzed. The results show that the change in shaft resistance, caused by the lateral extrusion of calcareous sand, is less than the negative effect caused by particle breakage during pile driving, so single piles without post-grouting in calcareous sand exhibit weaker axial bearing behavior than that in siliceous sand. A single pile with post-side-grouting in calcareous sand can provide a higher bearing capacity by increasing the shaft resistance and tip resistance compared with a single pile without post-side-grouting, and the increased ratio of the bearing capacity of piles, after grouting in calcareous sand, is better than that of piles in siliceous sand. Post-side-grouting can not only strengthen the surrounding soil by the solidification effect of injected cement grout, but it can also have a strengthening effect on the tip resistance. In addition, ideal-geometry grouting has more obvious advantages in improving the bearing behavior of pile foundations than annular point grouting, and higher stability in improving the bearing properties of pile foundations is evident for ideal-geometry grouting. Therefore, it is suggested that a directional grouting device should be adopted in actual projects in the future to form a more stable pile-soil interaction system and to expand the application prospect of pile foundations in calcareous sand.

Numerical study on the installation effect of a jacked pile in sands on the pile vertical bearing capacities

The installation effect of a jacked pile in silica sand is investigated numerically. A simplified state-dependent dilatancy model is used to model the sand behavior and the sand grain crushing effect is considered by modifying the critical state line at large confining pressures. The Arbitrary Lagrangian-Eulerian (ALE) technique is adopted to model the pile penetration and the load-displacement behavior at the operational loading stage is simulated using standard finite element method with the initial states being the equilibrium of the pile-jacking-disturbed soil stress and void ratio fields and a free pile head. The numerical procedure has been verified against some calibration chamber tests and centrifuge tests. Simulations of wished-in-place piles are performed for the quantitative study of the installation effect. The results show that the capacity ratios between the jacked and wished-in-place piles become higher for long piles in dense sand. Linear fittings have been applied to obtain the capacity ratios as functions of the relative density and the penetration length-to-diameter ratio, which can be used for a quick estimation of the bearing capacity difference between jacked and wished-in-place piles.

Near universal values of social inequality indices in self-organized critical models

We have studied few social inequality measures associated with the sub-critical dynamical features (measured in terms of the avalanche size distributions) of four self-organized critical models while the corresponding systems approach their respective stationary critical states. It has been observed that these inequality measures (specifically the Gini and Kolkata indices) exhibit nearly universal values though the models studied here are widely different, namely the Bak–Tang–Wiesenfeld sandpile, the Manna sandpile and the quenched Edwards–Wilkinson interface, and the fiber bundle interface. These observations suggest that the self-organized critical systems have broad similarity in terms of these inequality measures. A comparison with similar earlier observations in the data of socio-economic systems with unrestricted competitions suggest the emergent inequality as a result of the possible proximity to the self-organized critical states.

Alternative method for measuring characteristic lengths in absorbing phase transitions.

We applied an alternative method for measuring characteristic lengths reported recently by one of us [J. M. Kim, J. Stat. Mech. (2021) 03321310.1088/1742-5468/abe599] to the models in the Manna universality class, i.e., the stochastic Manna sandpile and conserved lattice gas models in various dimensions. The universality of the Manna model has been under long debate particularly in one dimension since the work of M. Basu etal. [Phys. Rev. Lett. 109, 015702 (2012)10.1103/PhysRevLett.109.015702], who claimed that the Manna model belongs to the directed percolation (DP) universality class and that the independent Manna universality class does not exist. We carried out Monte Carlo simulations for the stochastic Manna sandpile model in one, two, and three dimensions and the conserved lattice gas model in three dimensions, using both the natural initial states (NISs) and uniform initial states (UISs). In two and three dimensions, the results for R(t), defined by R(t)=L[〈ρ_{a}^{2}〉/〈ρ_{a}〉^{2}-1]^{1/d},L and ρ_{a} being, respectively, the system size and activity density, yielded consistent results for the two initial states. R(t) is proportional to the correlation length following R(t)∼t^{1/z} at the critical point. In one dimension, the data of R(t) for the Manna model using NISs yielded anomalous behavior, suggesting that NISs require much longer prerun time steps to homogenize the distribution of particles and larger systems to eliminate the finite-size effect than those employed in the literature. On the other hand, data from UISs yielded a power-law behavior, and the estimated critical exponents differed from the values in the DP class.

Dynamic Dimensional Reduction in the Abelian Sandpile

We prove the dimensional reduction conjecture of Fey, Levine, and Peres (2010) on the hypercube. The proof shows that dimensional reduction, symmetry, and regularity of the Abelian sandpile persist during the parallel toppling process. This stronger result verifies empirical observations first documented by Liu, Kaplan, and Gray (1990).

Numerical investigation of the monotonic drained lateral behaviour of large-diameter rigid piles in medium-dense uniform sand

This paper presents a numerical investigation of the monotonic lateral response of large-diameter monopiles in drained sand with configurations typical of those employed to support offshore wind turbines. Results from new centrifuge tests using instrumented monopiles in uniform dry sand deposits are first presented and used to illustrate the suitability of an advanced hypoplastic constitutive model to represent the sand in finite-element analyses of the experiments. These analyses are then extended to examine the influence of pile diameter and loading eccentricity on the lateral response of rigid monopiles. The results show no dependency of suitably normalised lateral load transfer curves on the pile diameter and loading eccentricity. It is also shown that, in a given uniform sand, the profile with depth of net soil pressure at ultimate lateral capacity is independent of the pile diameter because of the insensitivity of the depth to the rotation centre for a rigid pile. A normalisation method is subsequently proposed which unifies the load–deflection responses of rigid piles with different diameters at a given load eccentricity.

Smartphone-Based Photogrammetry Assessment in Comparison with a Compact Camera for Construction Management Applications

Close-range photogrammetry (CRP) has proven to be a remarkable and affordable technique for data modeling and measurements extraction in construction management applications. Nevertheless, it is important to aim for making CRP more accessible by using smartphones on-site directly without a pre-calibration procedure. This study evaluated the potential of smartphones as data acquisition tools in comparison with compact cameras based on the quality and accuracy of their photogrammetric results in extracting geometrical measurements (i.e., surface area and volume). Two concrete specimens of regular shapes (i.e., beam and cylinder) along with an irregular-shaped sand pile were used to conduct this study. The datasets of both cameras were analyzed and compared based on lens distortions, image residuals, and projections multiplicity. Furthermore, the photogrammetric models were compared according to various quality criteria, processing time, and memory utilization. Though both cameras were not pre-calibrated, they both provided highly accurate geometrical estimations. The volumetric estimation error ranged from 0.37% to 2.33% for the compact camera and 0.67% to 3.19% for the smartphone. For surface area estimations, the error ranged from 0.44% to 0.91% for the compact camera and 0.50% to 1.89% for the smartphone. Additionally, the smartphone data required less processing time and memory usage with higher applicability compared with the compact camera. The implication of these findings is that they provide professionals in construction management with an assessment of a more direct and cost-effective 3D data acquisition tool with a good understanding of its reliability. Moreover, the assessment methodology and comparison criteria presented in this study can assist future research in conducting similar studies for different capturing devices in construction management applications. The findings of this study are limited to small quantification applications. Therefore, it is recommended to conduct further research that assesses smartphones as a photogrammetric data acquisition tool for larger construction elements or tracking ongoing construction activities that involve measurements estimation.

Settlement of a pile under cyclic lateral loads in dry sand

It is found through centrifuge model tests that the cyclic lateral load on a pile reduces the shaft friction and induces additional pile settlement. A theoretical model using the load-transfer method was proposed for the settlement prediction of cyclic laterally loaded piles in dry sand. A simple formula was established to quickly predict the pile settlement in practical engineering. The theoretical model provided a reasonable estimate of the pile settlement, while the predictions from the proposed quick prediction formula were relatively conservative. A new concept of ‘settlement-controlled design’ was proposed to advance the methodology for the design of a pile by considering potential settlement after many cycles of lateral loads. According to the design plane derived from this study, it was suggested that the design-state points should be limited to the convergent zone.

Super UWB Grooved and Corrugated Antenna for GPR Application

A novel super Ultra-Wideband (UWB) monopole antenna for Ground Penetrating Radar (GPR) application is investigated in this paper. The designed antenna is constructed by a grooved elliptical patch and a corrugated semi-elliptical ground plane. The designed antenna is fabricated on the FR4-substrate that has a compact size of 0.195 λ0 × 0.1625 λ0 × 0.00975 λ0 at 1.95 GHz. The measurements are performed by using a well calibrated R&S®ZNB Vector Network Analyzer. The measured results show that the fabricated prototype covers a super UWB extending from 1.95 GHz to upper than 20 GHz (>164.46 %). Additionally, the voltage standing wave ratio (VSWR) and the gain responses of the antenna are simulated in close proximity to a dry/wet sand box to verify the penetration ability of the antenna. The results are acceptable which guarantee the aptitude of this antenna to operate as a GPR antenna.

A collapsing sandpile problem with nonlocal boundary condition

In this work, we continue our study on the sandpile model proposed by Igbida. We are particularly interested in the study of avalanches that occur on the surface of a pile of sand following a drying out. The main novelty here is that we do a theoretical and numerical analysis in the case of local and non-local boundaries conditions. We also present some results of numerical simulations in 2D.

Stability and load-displacement behaviour of axially cyclic loaded displacement piles in sands

Uncertainties regarding the axial cyclic behaviour of piles driven into sands led to an extended programme of calibration chamber instrumented pile experiments. Broad trends are identified and interpreted with reference to normalised cyclic loading parameters Qcyclic/QT, Qmean/QT, and N. Cyclic damage is shown to be related to changes in the radial effective stress regime close to the shaft. While stable loading leads to little or no change as cycling continues in the sand masses’ effective stress regime, high-level cyclic loading can affect stresses far out into the sand mass. The ratio of the chamber diameter to pile diameter of the test system has a significant impact on outcomes. Piles installed in loose, fine sand are far more susceptible to cyclic loading than those installed in denser, coarser sand. Little or no change in pile stiffness was seen in tests that remained within the stable cyclic region, even over 10 000 or more cycles. Unstable tests lost their stiffness rapidly and metastable cases showed intermediate behaviours. The permanent deflections developed under cycling depend on the combined influence of Qcyclic/QT, Qmean/QT, and N. While model tests provide many valuable insights into the behaviour of piles driven into sand, they are unable to capture some key features observed in the field.

Emergence of oscillations in fixed-energy sandpile models on complex networks.

Fixed-energy sandpile (FES) models, introduced to understand the self-organized criticality, show a continuous phase transition between absorbing and active phases. In this work, we study the dynamics of the deterministic FES models on random networks. We observe that close to absorbing transition the density of active nodes oscillates and nodes topple in synchrony. The deterministic toppling rule and the small-world property of random networks lead to the emergence of sustained oscillations. The amplitude of oscillations becomes larger with increasing the value of network randomness. The bifurcation diagram for the density of active nodes is obtained. We use the activity-dependent rewiring rule and show that the interplay between the network structure and the FES dynamics leads to the emergence of a bistable region with a first-order transition between the absorbing and active states. Furthermore during the rewiring, the ordered activation pattern of the nodes is broken, which causes the oscillations to disappear.

Modeling a Weak Foundation in Interaction with Reinforced Sand Piles under a Low-Rise Building

One of the ways to increase the bearing capacity and stability of a water-saturated base by introducing a sand pile vertically reinforced along the contour with geosynthetic material (geogrid SSP 30 / 30-2.5) is experimentally substantiated. This constructive solution is used in low-rise construction. For the theoretical substantiation of the suggested method, it is proposed to model the interaction of a weak foundation and a reinforced sand pile on the basis of the linear theory of viscoelasticity. Calculation of vertical displacements of the pile and comparison with the results of in situ experiments is presented.

Settlement Behavior Evaluation of Soft-Clay Layer Reinforced with Sand Piles

In this study, the performances of the sand piles in Istanbul's Bağcılar and Zeytinburnu districts has been analyzed using Finite Element Method (FEM). Single and group (triple) piles with various length/diameter ratios (L/D) were placed in the water-saturated soft clay soil. Sand piles were modeled in various L/D ratios (10, 5.71, and 8.57). The distance between the piles was chosen as 2 meters and the group effect was also investigated. A uniformly distributed load of 162 kN/m2 is placed on the ground. In addition, the soil was modeled with the Soft-Soil soil model, the hardening soil model for the infill part, and the sand piles with the Mohr-Coulomb soil model. According to the results , the settlement of the soil decreases by 52.8% for a single pile with an L/D ratio of 8.57. However, the best L/D ratio for triple piles was found to be 5.71. In this case, the settlement decreases by 52.8% compared to the pileless situation. Finally it was concluded that the model with the L/D ratio of 8.57 reduced settlement in the best and the most efficient way.

Sand and fire: applying the sandpile model of self-organised criticality to wildfire mitigation

Background Prescribed burns have been increasingly utilised in forest management in the past few decades. However, their effectiveness in reducing the risk of destructive wildfires has been debated. The sandpile model of self-organised criticality, first proposed to model natural hazards, has been recently applied to wildfire research for describing a negative linear relationship between the logarithm of fire size, in area burned, and the logarithm of fire incidence number of that size. Aims We demonstrate the applicability of the sandpile model to an understanding of wildfire incidence and its trend with interested factors, such as prescribed burns. Methods We leverage the sandpile model to perform a series of simulations, along with comparisons to historical wildfire data in three American states: Florida, California, and Georgia. Key results Both simulated and historical data indicate that increased prescribed burning is associated with lowered incidence of large wildfires. Conclusions Our study justifies the application of the sandpile model to wildfire research and establishes a novel method for facilitating the investigation of potential risk factors of wildfires. Implications The sandpile model may be utilised for the development of optimal strategies for prescribed burning. An R-script for sandpile model simulation is available for further wildfire investigation.

Seismic analysis of extended piles in sand considering effect of scouring and effect of water as added mass

Scouring is one of the major causes of the failure of bridges and offshore wind turbines. Piles under extreme scouring and earthquake loads are vulnerable to failure and need to be investigated thoroughly. In this study, the seismic responses of an extended concrete pile with no scour and four scouring depths conditions are investigated under an input motion based on a Kobe earthquake record. The effect of water during an earthquake has a significant impact on the structure as hydrodynamic pressure; however, it is generally ignored in the seismic analysis of piles. The present study uses the concept of added mass to consider the effects of water. The combined soilstructure-interaction and shear beam model is used to simulate pile and soil using the beam-on-nonlinear-Winkler foundation (BNWF) method. Soil is divided into multiple layers with increasing shear modulus and the mass of each soil layer is lumped into two nodes of the layer. Modal analysis and nonlinear time history analysis are performed on different models. Results of the modal analysis show the decrease in fundamental frequencies of the pile with increasing scouring depths. The time history analysis results are reported in the form of Arias and Housner intensities, envelopes of acceleration, velocity, displacement of pile top, and envelopes of shear force and bending moment of the pile. Results show significant changes with scouring depth and the effect of water.

Determination of settlement parameters of highway embankment and base consolidation time depending on soil characteristics

The paper proposes and implements a calculation and forecasting principle for designing a subgrade of fast-speed and high-speed highways on a weak foundation, and it is also proposed, taking into account a significant increase in the predicted values ​​of total deformations, to consider embankments with a height of more than 6 m on high-speed highways as individual design areas. It has been proven that in case of strengthening the subgrade foundation with CFG piles, the deformation characteristics of the soft soil of the space between the piles do not affect the amount of settlement and the time of consolidation. It is shown that the theoretical positions are confirmed by the results of numerical simulation. The necessity of keeping the embankments up to the construction of the track superstructure, even with the strengthening of weak foundations with composite structures, has been proved. Based on the results of the performed calculations, the area of ​​effective application of composite base structures with CFG piles for sections with a ballastless superstructure of the track, which provide the minimum allowable residual deformation during operation, was determined. Sand piles and Jet-Grouting piles can be effectively applied in composite subgrade structures of fast-speed and high-speed highways with a ballasted track structure. The influence of physical and mechanical characteristics and filtration properties of weak soil of the inter-pile space on the total amount of settlement and consolidation time was determined.

Justification of the parameters of a flexible grillage to strengthen the soft foundations of the subgrade of high-speed highways

The paper analyzes the determination of the parameters of a flexible pile grillage according to the British standard BS 8006 and according to the methodology set out in the “Manual for the design of the subgrade of roads on soft soils”. The BS 8006 methodology does not take into account the characteristics of the soft soil of the inter-pile space, while the methodology for designing the subgrade of roads on soft soils does not take into account the change in the load on the pile grillage from the height of the embankment. At the same time, the maximum tensile forces for the considered cases, obtained by various methods, turned out to be similar. The results of modeling the operation of a flexible pile grillage by the finite element method are presented. To assess the forces arising in the geosynthetic material of a flexible grillage, numerical modeling of embankments reinforced with CFG piles, sand drain piles, and Jet-Grouting piles was performed in the Plaxis software package. Modeling was carried out for embankments with a height of 6, 8 and 10 m on a soft foundation. In the course of modeling, the values ​​of forces in the geosynthetic material were obtained. The obtained values ​​of tensile forces in a flexible grillage with concrete piles of the CFG type, determined by numerical simulation, turned out to be approximately 2 times less than those calculated by analytical methods. The values ​​of tensile forces in the flexible grillage for Jet-Grouting piles and sand piles in a geotextile shell are approximately 1.8 times higher than the forces arising from the reinforcement with CFG piles. The influence of the characteristics of the soft soil of the inter-pile space on the values ​​of tensile forces in the flexible grillage has been determined. The tensile forces that occur in geosynthetics, in all the cases considered, do not exceed the allowable values. Therefore, it can be recommended as a flexible pile grillage for the subgrade of high-speed highways.