Sandpile Research Articles

Three-Dimensional Discrete Element Analysis of Bearing Characteristics of Concrete–Cored Sand–Gravel Pile Composite Foundation under Cyclic Dynamic Load

Concrete-cored sand–gravel piles are a kind of composite pile formed by wrapping a concrete-cored pile with a sand–gravel shell, which has the advantages of both a rigid pile and bulk-material pile. The bearing characteristics of the concrete-cored sand–gravel pile composite foundation were investigated by establishing a three-dimensional discrete element numerical model for a cyclic dynamic loading test. The results show that the vertical stress of the core pile body fluctuates greatly at the beginning of loading, and the fluctuation amplitude decreases with the depth, and gradually tends to be stable in the middle and late stages, and the vertical-stress distribution is relatively uniform. The radial stress in the upper part of the core pile body fluctuates greatly, the fluctuation in the lower part is small, and the radial stress in each part of the core pile body gradually tends to be stable in the late-loading period. The radial stress factor of the core pile body reaches the stable speed with the foundation depth decreasing; the fluctuation amplitude of the pile-soil stress ratio decreases with the foundation depth and gradually tends to be stable with the increase in loading. The results of this study can provide a reference for the design and construction of a core sand pile composite foundation.

An approach to complex network analysis on pp collisions at LHC energies

We have introduced the complex network analysis techniques such as Visibility Graph (VG), Horizontal Visibility Graph (HVG) and Sandbox (SB) algorithm as a mapping between complex network and time series measurements. This study explores the application of complex network-based analysis techniques to proton–proton [Formula: see text] collisions data at [Formula: see text], 7, 5.02 and 2.76[Formula: see text][Formula: see text]TeV to unravel the underlying dynamics of the particles and their interactions. To ensure the robustness and comprehensive analysis, we have incorporated UrQMD-, PYTHIA- and AMPT-simulated data sets of [Formula: see text] interactions at LHC energies that enable a thorough investigation of the underlying phenomena of the interactions. We have analyzed the fluctuations in pseudorapidity densities of singly charged particles created in [Formula: see text] interactions at LHC energies. We have also investigated some properties like symmetry scaling, correlation, clustering and scale-freeness among the produced particles. The findings from this study contribute to our understanding of the complex dynamics within [Formula: see text] collisions and have implications for the field of high-energy physics and particle phenomenology.

Influence of Installation Method on the Axial Capacity of Piles in Very Dense Sand

Influence of Installation Method on the Axial Capacity of Piles in Very Dense Sand

Load cascades in spatial networks: A sandpile model approach

In the real world, the construction of infrastructure networks is influenced by spatial factors. For such complex networks, We refer to them as spatial networks. This study investigates, based on the Bak–Tang–Wiesenfeld sandpile model, the impact of spatial factors on sandpile cascading avalanches. Through simulations, we discover that spatial factors not only facilitate the occurrence of moderate-scale avalanches in the system but also have a suppressing effect on the occurrence of the largest cascading avalanches. Using a multiplicative branching process, we analyze the influence of triangular structures composed of nodes on sandpile avalanches and find that nodes within triangular structures are relatively resistant to topples. Because of the relatively stable nature within triangular structures, more load tends to stay within this kind of structures. Once a cascading avalanche occurs in the system, the avalanche scale is often larger than that in the non-spatial counterpart. This increase in avalanche scale results in more load being released by the system, making the spatial networks more relaxed. And their probability of very-large-scale cascading avalanches is lower than that of non-spatial networks.

Life-cycle-based considerations in design of driven piles in sand

This study conducts a life-cycle assessment to evaluate the environmental impacts of driven shafts across 12 different siliceous sand sites, selected from a database of static load pile tests. Through parametric studies, this paper investigates the influence of soil properties, pile geometry and on-site activities on environmental impacts. For a single pile, the findings demonstrate that material production is the most impactful phase, contributing 88.4% of global warming potential (GWP) per unit capacity, while on-site operations contribute minimally at 1%. Sensitivity analyses show that variations in fuel consumption by ±25% and linear interpolations of blow counts result in negligible difference in GWP (less than 0.1 and 1%, respectively). On average, the total GWPs for steel and concrete piles are approximately 4.3 and 0.92 kg carbon dioxide (CO2) equivalent per kilonewton capacity, respectively. Although various factors influence pile design and installation, the results presented herein provide a foundational framework for geotechnical engineers to integrate environmental impacts into project planning, design and construction considerations.

Ultimate Lateral Resistance of Single Piles in Sand

The p-y curve method is currently the most widely utilized analytical approach for horizontally loaded piles. Precisely determining the ultimate soil resistance is essential to enhance the accuracy of the p-y curve. Despite various scholars proposing methods to establish the law governing ultimate soil resistance with soil depth in the sand, significant discrepancies exist among these approaches. This paper posits that the three-dimensional failure mode of the shallow soil in front of the pile manifests as a cone when it reaches the limit state. The expression for the ultimate soil resistance of a single pile in shallow soil is derived through limit equilibrium theory, and subsequently, the modified p-y curve is obtained. The accuracy was validated through a comparison between the corrected p-y curve and results obtained from centrifugation experiments and field studies. In contrast to the API specification method, the refined hyperbolic function p-y curve demonstrates enhanced precision, facilitating precise predictions of pile head displacement and pile bending moments under horizontal loads.

Field testing performance of prebored precast piles with enlarged base in soft ground

Prebored precast piles with an enlarged base (PPEB piles) are constructed using an innovative and environmentally sustainable method, which notably reduces noise, soil squeezing, and mud discharge. Although PPEB piles have been widely applied in many cities in China, their bearing performance, including side friction and end resistances, on soft ground remains relatively unelucidated. This paper focuses on case studies of vertical-bearing PPEB piles based on a group of vertical static load field tests in Shanghai. The following conclusions are drawn: (1) Compared with traditional hammered-driven piles, PPEB piles exhibit better construction quality and load-bearing performance, as well as a relatively slow increment of settlement even under ultimate loading. (2) The resistance of the enlarged base section of the PPEB pile was approximately 16.3% of the total resistance under ultimate loading. (3) Compared with the values proposed in the Shanghai Foundation Design Code, the side friction resistance of the PPEB pile in deep silty sand (34.5–39 m) exhibited a considerable increase of approximately 156%. Additionally, the side friction in the soft ground was close to the values proposed in code. The case studies provide practical guidelines for the application of PPEB piles in soft ground.

Influences of the Decomposition Atmosphere and Heating Rate on the Pyrolysis Behaviors of Resin Sand

The pouring of sand casting is accompanied by severe heat conduction, and there is an urgent need to investigate the pyrolysis properties of foundry sand. The main purpose of this study was to investigate the pyrolysis behaviors of resin sand, including precoated sand (PCS), hot box sand (HBS), and warm box sand (WBS), at heating rates of 20 °C/min, 30 °C/min, and 40 °C/min in nitrogen and air atmospheres. The mass loss of the resin sand was monitored continuously with a simultaneous thermal analyzer, and the kinetic parameters of the resin sand were calculated based on the Coats–Redfern method and thermal data. The average mass loss of the resin sand during pyrolysis was 3.03%, which was much smaller than that of the other sands. The volatile release characteristic index of resin sand could not be calculated based on this concept. To solve this issue, the term Tstv/mloss was established, and its value was determined. With increasing heating rates from 20 °C/min to 30 °C/min and from 30 °C/min to 40 °C/min, the mass losses of the resin sand increased by 0.79% and 0.64%, respectively, and the volatile release characteristic indices of the resin sand increased by 3.8 × 10−10 and 1.06 × 10−9, respectively. In addition, the mass losses and volatile release characteristic indices of resin sand in an air atmosphere were greater than those in a nitrogen atmosphere. With increasing heating rate, the activation energy of the resin sand decreased in a nitrogen atmosphere. The findings concerning the thermal decomposition behaviors of resin sand provided a theoretical basis for the pouring step of the sand casting process.

An experimental study on factors affecting the ageing of shaft friction on steel displacement piles in sand

Ageing of shaft friction is now an accepted characteristic of displacement piles in sand. However, there is little guidance available on how the associated gains in pile capacity can be incorporated in design. This paper provides an overview of findings from a number of previous high-quality investigations before presenting results from a recent pile testing campaign in the field that targeted aspects of pile ageing to improve understanding of the ageing mechanism. The field testing involved 52 tension tests on pipe piles and specifically examined the influence of installation method (driving, vibration, vibration + driving), pile diameter, steel type and loading history (static and cyclic). These results, taken together with other experimental investigations, show that the development of a welded crust on the pile shaft is a necessary part of the ageing process for steel piles and that the increase with time in the level of constrained dilation under shear on this crust is a primary contributor to ageing of shaft friction. Creep within the sand mass following the disturbance induced by installation can explain the increase in the level of this constraint, while stress redistribution and breakdown of arching may also contribute to the phenomenon. Ageing leads to the inference of instances of long-term aged shaft friction (in tension) of 500 mm and 2 m dia. pipe piles that are, respectively, at least 50% and 30% higher than given by the design method in ISO 19901-4 (2024). Additional observations relating to the effect of the installation method, steel type and load history on the ageing of shaft friction, which could assist designers.

Eigen microstates in self-organized criticality.

We employ the eigen microstates approach to explore the self-organized criticality (SOC) in two celebrated sandpile models, namely the BTW model and the Manna model. In both models, phase transitions from the absorbing state to the critical state can be understood by the emergence of dominant eigen microstates with significantly increased weights. Spatial eigen microstates of avalanches can be uniformly characterized by a linear system size rescaling. The first temporal eigen microstates reveal scaling relations in both models. Furthermore, by finite-size scaling analysis of the first eigen microstates, we numerically estimate critical exponents, i.e., sqrt[σ_{0}w_{1}]/v[over ̃]_{1}∝L^{D} and v[over ̃]_{1}∝L^{D(1-τ_{s})/2}. Our findings could provide profound insights into eigen microstates of the universality and phase transition in nonequilibrium complex systems governed by self-organized criticality.

A geometric proof for the root-independence of the greedoid polynomial of Eulerian branching greedoids

We define the root polytope of a regular oriented matroid, and show that the greedoid polynomial of an Eulerian branching greedoid rooted at vertex v0 is equivalent to the h⁎-polynomial of the root polytope of the dual of the graphic matroid.As the definition of the root polytope is independent of the vertex v0, this gives a geometric proof for the root-independence of the greedoid polynomial for Eulerian branching greedoids, a fact which was first proved by Swee Hong Chan, Kévin Perrot and Trung Van Pham using sandpile models. We also obtain that the greedoid polynomial does not change if we reverse every edge of an Eulerian digraph.

Hysteretic Damping of Piles in Sands for Offshore Wind Jacket Structures

Hysteretic Damping of Piles in Sands for Offshore Wind Jacket Structures

MPM Simulation of the Installation of an Impact-Driven Pile in Dry Sand and Subsequent Axial Bearing Capacity

MPM Simulation of the Installation of an Impact-Driven Pile in Dry Sand and Subsequent Axial Bearing Capacity

Optimization of retrofit strategies for urban bridge networks before earthquake via dynamic-static integration

Addressing earthquake resistance in urban areas, the intervention and retrofit of bridge networks are crucial considerations. While previous studies have predominantly focused on the importance and retrofit aspects of bridges, there has been limited exploration of optimization issues. This study introduces a method for assessing node importance and optimizing retrofit strategies for bridge networks before earthquake. Combining the Personal PageRank (PPR) approach with the technique of ideal solution similarity order preference (TOPSIS) yields static importance evaluation results for nodes, reducing the subjectivity of their weights in multi-metric evaluation works. Employing a sandpile model to simulate post-earthquake traffic congestion, the static results are then refined based on the model. The study establishes a dynamic-static integration approach to assess bridge importance, and genetic algorithms are applied to optimize the retrofit strategy. The practicality of the dynamic and static integration evaluation methods is verified through a numerical example, demonstrating that the optimized strategy effectively improves retrofit performance.

New hybrid foundation solutions for offshore wind turbines

This paper reviews latest developments of substructures for offshore wind turbines focusing on investigations and applications of hybrid foundations. Model tests and numerical analyses were used to simulate the loading of hybrid piles in sand. The results of pile-soil interaction were investigated to confirm the changes in soil stiffness around the hybrid monopile head. The mechanism and factors affecting the change in lateral stiffness of the hybrid foundation were explained by analysing p–y curves for M+H loading conditions in sand. Based on this research, a new shape of p–y curves for hybrid monopiles was established and a method for determining key parameters was proposed. The effectiveness of new p–y curves was verified by comparing back-calculated results with those from numerical simulations. The conducted tests confirmed that the hybrid monopile displacement is 30–50% smaller when compared to a standard monopile with similar dimensions. The gained experiences can be useful for designers and researchers to enhance the design of foundations for offshore wind turbines.

Pipe pile with internal diaphragm as effective bearing element of deep-water structures

One of the ways to reduce piling expenses is decreasing volume of piling works. It can be provided by shortening either the piles length or the number of pipes. These results may be achieved if each short-cut pile is improved and bears the same loading as a pile of normal length or if each pile of normal length is improved and bears larger axial force in comparison with its initially designed capacity. Presented study clarified possibilities to regulate the pipe pile’s bearing capacity using an internal rigid diaphragm (closure) placed inside the pile’s shaft. It increases the bearing capacity of the tubular pile due to additional soil reaction under the closure. Pressing the pipe pile’s model into sand box was assumed as the most gentle and precise method to study considered driving process. Besides results of such approach may be good adapted to predict pipe behavior in case of Press-in method of the pile installation. Some conclusions were made clarifying the diaphragm’s positive contribution to pile bearing capacity, the effect of the closure’s location along the pipe shaft, and the influence of the diaphragm’s design (flat, conical, and cylindrical closures). Numerical analysis of the gained experimental data gave the possibility to apply approximating functions with good correlation indexes

Analysis of influencing factors of penetration mechanism and vertical bearing characteristics of monopile in calcareous sand: Laboratory model testing and in-situ testing

The construction of islands and reef engineering structures in marine environments has been a hot topic in recent years, and calcareous sand, which possesses unique physical properties, is widely distributed on islands and reefs. Due to the properties of calcareous sand, engineering problems such as pile slipping while driving and a low bearing capacity during service can occur. To address the key problem of pile‒soil interactions in calcareous sand foundations, laboratory model and in situ tests were conducted, accounting for factors such as impact energy, relative density, pile-forming method, and pile aspect ratio. First, the penetration mechanism of hammered piles in calcareous sand was studied. Then, the differences in vertical bearing characteristics between hammered and pre-embedded piles under different conditions were explored. The pile driving test results showed that a higher impact energy and lower relative density are more conducive to pile sinking. Moreover, as the number of hammer drops and dynamic penetration resistance increase with increasing burial depth, the pile tip resistance is the main factor limiting pile penetration in calcareous sand. The vertical static loading test revealed that particle breakage accelerates soil redistribution around the pile and that compaction enhances the bearing capacity of the pile. The pile aspect ratio, relative density and pile-forming method also play major roles in the vertical bearing capacity of piles in calcareous sand. In addition, the skin friction of a pile rapidly increases to the ultimate value along a multisegment trend of polyline functions. Similarly, the pile tip resistance rapidly increases at the initial loading stage, exhibiting the behavior of an end-bearing pile. The in situ test results indicated that the pile penetration depth in coral calcareous sand is an important factor affecting the bearing capacity.

“All-or-none” dynamics and local-range dominated interaction leading to criticality in neural systems

Since the first observation of criticality in neural systems, many researchers have thought that the nervous system can operate in a critical state, and an increasing number of models equipped with different mechanisms have been proposed. We believe that there are simple mechanisms underlying the criticality in neural systems. We constructed a neural network model to investigate the mechanism underlying criticality in neural systems. We found that a neural system consisting of neurons with all-or-none dynamics and local-range dominated interaction exhibits critical behavior when properly driven. The all-or-none dynamics of single neuron and local-range dominated interaction are the identical mechanisms of criticality in the BTW sandpile model, so we concluded that whatever mechanism causes the neural system to evolve to the state where short-range dominated interaction and appropriate input is received, critical behavior can be observed.

The role of intervention mechanisms on a self-organized system: dynamics of a sandpile with site reinforcement

We revisit the sandpile model and examine the effect of introducing site-dependent thresholds that increase over time based on the generated avalanche size. This is inspired by the simplest means of introducing stability into a self-organized system: the locations of collapse are repaired and reinforced. Statistically, for the case of finite driving times, we observe that the site-dependent reinforcements decrease the occurrence of very large avalanches, leading to an effective global stabilization. Interestingly, however, long simulation runs indicate that the system will persist in a state of self-organized criticality (SOC), recovering the power-law distributions with a different exponent as the original sandpile. These results suggest that tipping the heavy-tailed power-laws into more equitable and normal statistics may require unrealistic scales of intervention for real-world systems, and that, in the long run, SOC mechanisms still emerge. This may help explain the robustness of power-law statistics for many complex systems.

Stress effects due to different installation methods for pipe piles in sand

Impact-driven pipe piles are commonly used in offshore structures, but vibratory driving is becoming more popular due to advantages regarding noise emissions, material fatigue and installation time. In offshore practice, crane-guided vibratory driving is used for maximum control over the installation process. Regarding the load-bearing behaviour of piles, the influence of the installation method is currently subject to research. To contribute to this question, comparative scale model investigations were carried out on impact-driven, jacked and vibratory-driven piles in dense sand. The tests focused on variations of vibratory installation parameters, including crane-guided and free vibratory driving. Based on measurements at the pile and in the soil, the influence of dynamic pile motions on the soil stress development could be analysed. The well-known increase of radial effective soil stresses due to impact driving could be reproduced. The tests showed that the same effects could be evoked by free vibratory driving if certain vibration parameters were met. Increased soil stresses may be beneficial for the lateral or axial pile behaviour, but can cause problems regarding drivability. A sequential application of crane-guided and free vibratory driving may optimise both the installation process and the bearing behaviour.