Centrifuge Tests Research Articles

A novel torsional test system for centrifugal modelling of interaction between finned suction caisson and soil

Suction caissons have been used in floating offshore wind farms worldwide with new types of finned suction caissons emerging to resist torque-loading. The additional fins attached to the caisson are expected to improve the torque-bearing performance, but the mechanism is yet to be clarified. Therefore, a novel torsional centrifugal modelling test system is developed to investigate the interaction between finned caisson and soil. The system is composed of the interacting chamber, the loading module, the transmitting module, and the measuring module. It allows precise control of the suction caisson penetration and pure torsional loading, which is validated by two torsion tests on a traditional caisson and a finned caisson. The results show that the torque-bearing capacity of the finned caisson is about 9.7 times that of the traditional caisson. The existence of the fins changes the failure mode from the interfacial friction failure between the caisson and the soil to the global soil-soil shear failure. The development of pore water pressure in soil was significantly changed by fins during torsional loading. The sudden change in the pore water pressure and soil pressure on the rear side of the fins indicates that tension gaps can be produced. The test results indicate that the developed test system is capable of evaluating the torsional performance considering foundation-soil interaction effectively.

Centrifugal model test of deep covered karst collapse induced by static overloading of dense building groups

Centrifugal model test of deep covered karst collapse induced by static overloading of dense building groups

The truncation effect of soil slope acceleration responses

A dynamic centrifugal model test was conducted for a homogeneous sandy slope under an impulsive ground motion to investigate the relationship between seismic response and slope deformation. Firstly, the deformation characteristics and dynamic responses of the slope were analyzed. Then, the main features associated with the response truncation effect were expounded. Subsequently, the Sliding block theory was introduced to explain the mechanism of the acceleration response truncation effect. At last, an approximate calculation method for the sliding mass dynamic response was developed, considering the influence of the truncation effect. The results show the variation pattern of response differs inside the slope and near the slope surface, and the dynamic amplification coefficients calculated by different methods also exhibit significant variations. The truncation of horizontal response acceleration results from the relative sliding in slope, and the truncated response fluctuates around a limited value related to the yield acceleration.

Lateral behavior of large-diameter monopiles in clay using transparent soil and centrifuge tests

Lateral behavior of large-diameter monopiles in clay using transparent soil and centrifuge tests

Centrifugal Test Study on the Vertical Uplift Capacity of Single-Cylinder Foundation in High-Sensitivity Marine Soil

Offshore wind power is a new type of clean energy with broad development prospects. Accurate analysis of the uplift capacity of offshore wind turbine foundations is a crucial prerequisite for ensuring the safe operation of wind turbines under complex hydrodynamic conditions. However, current research on the uplift capacity of suction caissons often neglects the high-sensitivity characteristics of marine soils. Therefore, this paper first employs the freeze–thaw cycling procedure to prepare high-sensitivity saturated clay. Subsequently, a single−tube foundation for wind turbines is constructed within a centrifuge through a penetration approach. Ten sets of centrifuge model tests with vertical cyclic pullout are conducted. Through comparative analysis, this study explores the pullout capacity and its variation patterns of suction caisson foundations in clay with different sensitivities under cyclic loading. This research indicates the following: (1) The preparation of high-sensitivity soil through the freeze−thaw procedure is reliable; (2) the uplift capacity of suction caissons in high−sensitivity soil rapidly decreases with increasing numbers of cyclic loads and then tends to stabilize. The cumulative displacement rate of suction caissons in high-sensitivity soil is fast, and the total number of pressure–pullout cycles required to reach non-cumulative displacement is significantly smaller than that in low-sensitivity soil; (3) the vertical cyclic loading times and stiffness evolution patterns of single-tube foundations, considering the influence of sensitivity, have been analyzed. It was found that the secant stiffness exhibits a logarithmic function relationship with both the number of cycles and sensitivity. The findings of this study provide assistance and support for the design of suction caissons in high-sensitivity soils.

Centrifuge model tests on pile groups under oblique pullout load for single point mooring system through transparent sand

Single point mooring systems anchored by pile groups have been widely applied to support floating offshore platforms. Centrifuge model tests on the pile group performance and soil displacement field were conducted using transparent sand. The pile group consisted of six piles connected by steel wires and divided into two groups. The two groups were symmetric in the x-direction, and the three piles in each group were symmetric in the y-direction. The influences of pile group arrangement and loading direction were investigated. With the increasing angle between adjacent piles in the same group (β), the pile group resistance for a given displacement increased under the x-direction load but decreased under the y-direction load. The difference in the pile load distribution increased with β, and the pile group resistance reduced significantly once one pile failed at β = 60°. The soil displacement field indicated that the overlap effect of the influence zone increased with the decreasing β, leading to a reduction in the pile group resistance at β = 30°. Therefore, the pile group arrangement with β equal to 45° was optimal in this study. Additionally, the pile group resistance improved as the loading direction changed from the x-direction to the y-direction.

Numerical assessment of ship anchor penetration depth in Baltic Sea Sand: Implications for subsea cable burial

As renewable energy demand increases, protecting subsea cables from ship anchor damage has become essential. This research comprises numerical simulations of the anchor penetration process in Baltic Sea sand (for an AC-14, a Hall and a Spek anchor). We apply a coupled Eulerian–Lagrangian (CEL) framework and a hypoplasticity constitutive model to analyze the influence of different anchor characteristics on penetration depth and seabed stress distributions. We conducted investigations under high velocities (v≥1m/s) with focus on inertial effects only. Furthermore, this study introduces stress circles to visualize a simplified anchor-induced spatial stress distribution in the seabed. Findings show that heavier anchors and slower drag velocities generally result in deeper anchor penetrations. Fluke geometry significantly affects penetration depth, with pointed designs penetrating more deeply. The observed trends align with previous results from centrifuge tests and numerical modeling of ship anchors. This research improves understanding of soil–structure interaction in maritime environments, offering insights for the protection of subsea installations in the Baltic Sea and similar regions.

Study on the Application of Foamed Lightweight Soil in Road Widening Project: A Numerical Insight.

This paper introduces a novel retaining wall structure that integrates a traditional mechanically stabilized earth (MSE) retaining wall with foamed lightweight soil (FLS) as the fill material. To evaluate the performance of the structure, a numerical approach based on the finite difference method was employed. Firstly, numerical models were developed based on a centrifuge test model designed by previous researchers, and the results were compared with the measured data. The close agreement between the experimental values and simulations demonstrates the reliability and validity of the proposed numerical models. Subsequently, a series of parametric studies were conducted to reveal the effect of key parameters on the performance of the newly proposed retaining wall. Furthermore, this paper proposes a modified harmonic search algorithm (MHSA), which is based on the original harmonic search algorithm (OHSA), to optimize the design of the proposed retaining wall structure. The results indicate that the proposed retaining wall structure can effectively reduce the differential settlement between the existing road and the newly constructed road at a relatively lower cost. The MHSA can serve as a practical design guidebook for engineers and potential users, enabling rapid and efficient design.

Prediction of impulse waves generated by the potential failure of large deposits in the Rumei Reservoir, Lancang River, China

The impulse wave generated by the reservoir landslide seriously endangers the surrounding safety. In this paper, the failure mode of a large deposit in Rumei Reservoir, China was first explored by centrifuge test. Thereafter, a physical model based on Froude similarity (scale 1:200) and a numerical model based on fluid‒solid coupling were constructed. The failure motion process and the generated impulse waves of the deposits at high (2895 m) and low (2750 m) water levels are studied in detail. The results of the two models are similar. The velocity and wave height of the deposits at the 2750 m water level are greater than those at the 2895 m water level. The maximum wave heights generated in the river under both conditions exceed 46 m and 22 m, respectively, and the maximum run-ups formed on the opposite bank are 71 m and 30 m, respectively. This also suggests that landslides in the near field area are dangerous. Waves at both water levels will not overtop the dam, but attention should be given to the effect of the first wave at the 2895 m water level on the dynamic water pressure in the key area of the dam.

Centrifugal test on the mechanical characteristics of existing prestressed anchor bolts in highway widening

To study the stress characteristics of existing prestressed bolts and slope stability during secondary excavation in a slope reconstruction and expansion project, five slope centrifugal tests were conducted. Tests focused on prestressed bolt-reinforced bedding slope with anchoring angles of 10°, 20°, 30°, 45°, and 60° during the excavation phase. The test results showed that the horizontal displacement at slope top increased slightly during the excavation of rock and soil masses in the upper slope part, while during the excavation of slope foot, such displacement increased rapidly. The bolt axial force in the anchorage section decreased along the anchoring depth. The peak axial force in the free section decreased significantly with the progress of excavation, and the axial force distribution in the free section presented a monotonically decreasing pattern. The anchoring angle significantly impacted the attenuation amplitude of axial forces in the anchorage section, while having insignificant effect on the distribution of axial forces. With the increase of anchoring angle, the cumulative horizontal displacement at slope top first decreased and then increased, while the earth pressure in slope first increased and then decreased, suggesting the presence of an optimal anchoring angle for the prestressed bolt.It is suggested that graded excavation should be adopted for the secondary excavation of slope engineering. Moreover, it is recommended to appropriately reduce the rate of excavation when working on the top and foot of the slope. Additionally, the design of the anchoring angle should consider various factors, including slope slope, rock formation, and the dip angle of the weak surface.

Exploring failure evolution of anti-dip slate slope using centrifuge test and discrete element method

Toppling failure commonly occurs in anti-dip slate slopes due to foliation splitting and gravitational deformation. The study uses centrifuge tests and the discrete element method (DEM) to investigate the influence of foliation and existing fractures on the toppling failure evolution of anti-dip slopes. Six centrifuge tests with slate blocks obtained from an actual slope were carried out. Then, a proposed foliation model was implemented in the DEM software 3DEC to simulate the failure evolution of anti-dip slopes. The 3DEC analysis was validated by the actual failure pattern of slopes in centrifuge tests. The results indicate that the toppling failure of the anti-dip slope was initiated by existing fractures rather than the original cohesive foliation. Though the slate foliation is regarded as a weak plane in the rock mass, it retains a higher strength than the existing fracture, so the toppling failure is difficult to initiate from the cohesive foliation. The closer the fracture is to the free surface, the more pronounced the damage. In addition, the simulation indicates that the existing fracture's position also affects the anti-dip slope's failure degree. The fractures on the top propagate more easily than those on the bottom.

Centrifuge tests on the consolidation behaviour of foundations under alternating loads

This paper presents the results from centrifuge tests on raft foundations and piled rafts in overconsolidated kaolin clay carried out in a beam centrifuge at the University of Pretoria. The foundations were subjected to unloading and reloading phases as well as to multiple consecutive groundwater drawdowns, simulating typical loading scenarios of structures in an urban environment. In order to investigate the time-dependent load-deformation behaviour of foundations, the settlement of the foundations, the pore water pressures at different depths and the axial strains in the piles, from which pile resistances were then derived, were measured continuously. In the tests, repeated groundwater drawdowns resulted in a settlement accumulation, with the increase in settlements decreasing with each repetition. The pile position within the pile group was found to have a major impact on the mobilised pile resistance. The position, however, became less significant as the load level increased. Furthermore, insights were gained concerning the load distribution within piled rafts during consolidation.

Study of the influence of rheological parameters on the behavior of a submarine debris flow

Submarine debris flows are events that occur with great frequency on a geological scale and can cause major damage to offshore structures or even loss of human life. Understanding the mechanisms involved in the development of a debris flow requires not only knowledge of soil mechanics, but also knowledge of fluid mechanics, since the incorporation of water during the flow causes changes in shear strength. Unlike soils, the shear strength of fluids is represented by mathematical models called rheological models. The objective of this paper is to propose a new rheological model capable of representing the changes caused by water entrainment into a submarine debris flow, by correlating it with the Liquidity Index of the soil. A rheological analysis of marine clay samples from the pre-salt layer has made it possible to represent the variation in strength due to water content. The influence of water content and velocity on flow behavior has also been studied through the analysis of centrifuge tests performed in a previous study.

Experimental and numerical study on the force transmission in granular packings under the hypergravity

Granular materials are ubiquitous in our environment, and their mechanical behavior is determined by particle-scale properties. The contact forces under hypergravity, which are crucial to planetary geology, remain underexplored, while extensive research has focused on behavior under surface pressure. We measured the contact forces between granular particles using a novel matrix film sensor under both hypergravity and surface pressure conditions, which were achieved in centrifugal and servo-hydraulic tests. Additionally, computations using the discrete element method were conducted to investigate the different patterns of force transmission from a microscopic perspective. We found an intriguing invariance in the contact force distribution under increased surface pressure. However, hypergravity enhances the contact forces between unjammed fine particles, causing contact forces converge to the distribution observed under surface pressure. Finally, a power-law fitted correlation was proposed to estimate the difference in contact force distributions between conditions of hypergravity and equivalent surface pressure.

Numerical analysis of relative density effects on shallow TBM tunnel excavation: Ground behavior and principal strains at surface in greenfield conditions

Tunnel construction in urban areas may result in ground deformations that pose a risk to existing buildings and infrastructure; thus, accurate prediction of these induced ground deformations during the design phase is crucial. The paper focuses on the effects of sandy soil relative density on the ground deformations induced by tunnels excavated with Tunnel Boring Machines (TBMs). The study utilizes the Finite Element Method (FEM) and the NorSand model to simulate the behavior of a sandy ground. The validity of the FEM modeling approach is established by comparing predictions with results from six centrifuge tunnel tests from the literature. The centrifuge tests were performed on sand at different relative densities, tunnel diameters, and tunnel depths. The parameters for the NorSand model were determined based on laboratory tests. Only the state parameter was modified to achieve the desired relative density in the numerical simulations. The effects of relative density observed in centrifuge tests (Franza et al., 2019) have been numerically reproduced with no further adjustments of the model parameters. The rich outputs from the numerical models enabled an in-depth investigation of tunnel behavior, yielding new insights into how tunnels respond under varying relative densities, depths, and diameters. A comprehensive analysis of the induced ground deformations caused by shallow tunnels in sandy ground and the potential to damage buildings is included.

Seismic behavior of soil-tunnel-building system considering earthquake frequency contents

Rapid urbanization has led to limited land availability, prompting the construction of residential and underground utility facilities in close proximity, forming an interconnected system with the surrounding soil. However, studies on the seismic behavior of such integrated systems are scarce due to their complex soil-structure interaction (SSI) mechanism. Furthermore, the dynamic behavior of these coupled structures depends heavily on earthquake characteristics like frequency content, an aspect that remains largely unexplored. This study aims to investigate the effects of earthquake frequency on the dynamic behavior of soil-underground structure-aboveground structure coupled systems. Using a novel experimental-numerical approach, two centrifuge tests were used to validate the numerical modeling framework. Three cases (soil-building, soil-tunnel, and soil-tunnel-building coupled systems) are then analyzed under earthquakes with varying frequency content. Results demonstrate how seismic response and SSI indicators of the structures evolve with changing seismic frequencies, offering valuable insights for enhancing safety measures in urban megacities.

Estimation of breakout force of spudcan footing in structured clay

For a jack-up rig installed in cohesive soil, assessing the extraction force is critical to ensure the safe and successful retrieval of each spudcan footing. The extraction force depends on the preceding stages, including installation and operation of the rig, due to soil strength changes around the spudcan. To investigate the entire ‘penetration - operation - extraction’ process of spudcan, an effective stress large deformation finite element analysis is conducted, with a Structured Cam-Clay model being incorporated to describe the behaviour of structured soil. The large deformation approach is validated against existing centrifuge tests. Parametric studies are then carried out to explore the influential factors on breakout force, including operation period, vertical load ratio, penetration depth, destructuring rate and soil sensitivity. A unique curve is formulated to predict the evolution of the recovery degree of breakout force over the operation period in structured cohesive soil. The soil sensitivity is identified as the dominant factor that affects the ultimate net resistance ratio, which is the key parameter required in applying the prediction curve. A simple method is proposed to estimate the ultimate net resistance ratio and a procedure to predict the breakout force is suggested.

Centrifuge tests for earthquake response of shallow soil with locally raised bedrock

ABSTRACT Centrifuge tests were performed to study the dynamic properties of shallow soil with locally raised bedrock (i.e. variable soil depth). The test parameter was the slope of bedrock: 0° (S0), 35° (S35), and 45° (S45). In each test, accelerations were measured along the soil depth, and the results of acceleration, displacement, Fourier transform, and response spectrum were compared. Based on the results, the transfer function (TF), the ratio of response spectrum (RRS), and the site period were estimated. The ground motion and site period of specimens with raised bedrock were smaller than those of the specimen without raised bedrock (i.e. with deeper soil). Further, parametric studies using 2-dimensional finite element (FE) analysis were performed to investigate the effect of design parameters on the response of shallow soil with variable soil depths. For design parameters, the length of raised bedrock and the length of foundation slab were considered. Parametric study results indicated that when the shallow soil region is wide, the results are similar to those of a 1-dimensional soil column. However, when the shallow soil region is narrow, the 2-dimensional response is smaller than the 1-dimensional soil column response. This was also observed in the actual site model.

Macro-element modelling for lateral response of monopiles with local scour hole via hyperbolic hardening relation

Monopile is a popular choice in the foundation supporting offshore wind turbines (OWTs), with local scour significantly impacting their lateral responses. Macro-element model, which encapsulates the response between the monopile and the surrounding seabed soils into a force-displacement relation, has been extensively developed to describe offshore foundations. However, such kind of models specifically targeting monopiles subjected to lateral loading in local scour remain underdeveloped. This work proposes a macro-element model with a succinct hyperbolic hardening relation for laterally loaded monopiles in local scour conditions, using the evolutionary polynomial regression (EPR) machine learning technique for easy and optimal design. First, the finite element model is verified and extended to generate force-displacement responses considering the monopile geometries, soil characteristics, and local scour geometries. These results are then utilised to determine the optimal hyperbolic hardening relation of the macro-element model. Next, the EPR technique is employed to determine the relationship between the hyperbolic hardening relation parameters and the influencing factors. Finally, the macro-element model is successfully evaluated by comparing with measurements from centrifuge tests and numerical solutions by finite element analysis, demonstrating its applicability in practical design and the ability to reproduce FEA results with a significant reduction in computational cost.

Research progress and prospects of seismic performance on underground structure embedded in soft soil foundation

For the complexity and difficulty of seismic research on subway station structure system embedded in soft soil foundation, the seismic research method is quite different from the ground structure. The methods of seismic research on subway station structures in soft soil were summarized, and relevant literature on this field in recent years were sorted out. The advanced progress of theoretical analysis and quasi-static simplification analysis, model test (shaking table test, centrifuge test), numerical simulation (the total stress method, the effective stress method), and dynamic reliability of underground structures were mainly introduced for seismic analysis of subway station embedded in the soft foundation. The advantages and disadvantages of each method and the development direction of this field were proposed briefly in order to better understand seismic analysis of underground structure engineering in soft soil.