Centrifuge Model Research Articles

Robustness of remediation measures against liquefaction induced manhole uplift under mainshock-aftershock sequence

Earthquakes generally consist of one mainshock and subsequent aftershocks. Although effects of aftershocks following the mainshock on surface structures has been studied extensively, similar studies on underground structures are rarely reported in the literature. With the fast advances in underground space development, robustness of remediation measures against underground structures uplift induced by soil liquefaction shall be examined to ensure their functioning subject to not only the mainshock but also the subsequent aftershocks. This paper studies the uplift behaviour of a conventional manhole subjected to the mainshock-aftershock sequence. It was found that, in the ground that becomes liquefied during the mainshock, manholes become more vulnerable when faced with aftershocks. Due to this reason, some of the previously proposed remediation measures, such as increasing the manholes’ self-weight, roughening the sidewalls, were examined using centrifuge modeling in this study. It was found that such measures had little effect in the aftershocks despite their effectiveness in the precedent mainshock. In contrast, the methods that mitigates manhole uplift by enhancing the manhole’s base permeability, demonstrated better performance in the aftershock than in the mainshock, indicating its promising application potential in future mitigation design.

Investigation of granular flow run-out behavior under dilative and compressive Coriolis conditions using DEM simulation

Centrifuge modeling allows granular flows to be simulated under stresses characteristic of full-scale flows, while maintaining repeatability. However, the impact of the Coriolis effect on the run-out behavior of dry granular flows is not fully understood. In this study, using the discrete element method (DEM), we conducted simulations of dry granular flow both with and without Coriolis (dilative and compressive) conditions to analyze the impact of the Coriolis effect on granular run-out mobility, flow structure, and granular interaction. For unsteady flows, the dilative Coriolis force increased the moving distance of the flow centroid by 60%–70% and increased the maximum kinetic energy by 5%–17%, whereas those parameters were reduced by 30% and 2%–9%, respectively, under compressive Coriolis conditions. Results showed that selecting a lower centrifugal acceleration by reducing the rotational angular velocity in physical modeling is ineffective for realizing a weaker Coriolis effect. This study established that using a larger centrifuge could mitigate the Coriolis effect, but that this outcome became less notable as the centrifugal radius increased. Additionally, we suggest a preliminary relation that could be used to correct the results of experimental granular flow final run-out distance obtained using a geotechnical centrifuge.

Centrifuge Modeling of the Performance of Suction Anchor in Soft Clay

Abstract Suction anchors are large cylindrical anchors and well suited for both catenary and taut mooring systems. The determination of horizontal and vertical load components hinges upon factors such as the inclined loading angle and the padeye position, significantly influencing its failure mechanism. This study undertook a series of geotechnical centrifuge tests to scrutinize the behavior of suction anchor under lateral loading. Precise measurements were taken for variables including the pore pressure at the anchor tip, soil pressure along the anchor, anchor capacity, as well as the displacement and rotation around X-, Y-, and Z-axes. The anchor failure mechanisms and interaction coefficients within a dissipation function were determined from the experimental results. The failure angle β serves as an indicator of anchor rotation in the translational failure mechanism, and αr describes anchor rotation in backward and forward movements. Under the inclined loading angle (θm) of 35 deg, the anchor failed in the translational mechanism, with its ultimate bearing capacity surpassing that of the anchor failing through backward and forward mechanisms. Upon elevating the padeye location moved upward to 4L/7 to 2L/3, the anchor failed in a forward mechanism, accompanied by a significant decrease in soil pressure on the passive side. This separation of the soil plug from the anchor, driven by accumulated displacement and rotation, resulted in 25% decrease in ultimate bearing capacity. Conversely, when the inclined loading reduced from 35 deg to 20 deg at the padeye location, the anchor failed in a backward mechanism, with no observed separation of the soil plug from the anchor.

CHARACTERIZATION OF PHYSICAL AND CELLULAR PROPERTIES OF MEMBRANES OF L-PRF PRODUCED BY DIFFERENT CENTRIFUGES/ CENTRIFUGATION PROTOCOLS.

Leukocyte and platelet-rich fibrin (L-PRF), an essential source of cytokines and growth factors, has been widely used to regulate the healing process. The quality of the L-PRF obtained is dependent on technical factors and the centrifugation protocol used. Thus, the present study aimed to macro and microscopically evaluate the formation of the L-PRF membrane/clot in two centrifuge models and protocols recommended by manufacturers. Four blood samples from 8 healthy volunteers undergoing rehabilitation surgery with dental implants were used. In group 1 of the Montserrat centrifuge (model 80-2B 15mL) 400g of centrifugal force were used for 10 minutes, 27ºC, and 2700 rpm, while in group 2 of the Intra Spin-Intra-Lock centrifuge (IntraSpin™, Intra-Lock Iberia) 400g of centrifugal force were used for 12 minutes, 27ºC and 2700 rpm. After obtaining 32 L-PRF clots/membranes, the pieces were recorded, measured, and weighed, separating the L-PRF from the supernatant/clot of red blood cells, remaining in the tubes. The specimens were then histologically processed for Hematoxylin/Eosin (H/E) staining and each slide was divided into three called areas: proximal, center, and distal. The presence of leukocytes was analyzed semi-quantitatively in each area. The results revealed no significant macroscopic differences in L-PRF between the two groups. However, the central areas of the L-PRF membranes produced in group 2 showed higher intensity of leukocytes (p=0.012), as well as the presence of concomitant leukocytes in at least 2 of the evaluated areas (p=0.003). In the proximal area, no significant differences were observed between the two groups. The results allow us to postulate that technical protocol factors influence the presence and distribution of leukocytes between the L-PRF membranes, obtained in different centrifuges.

Performance evaluation of prefabricated retaining wall systems based on centrifuge tests

Prefabricated and assembled retaining wall systems are gradually becoming the preferred choice for slope stabilization and earth retaining structures. However, current prefabricated retaining wall systems are often difficult to apply in complex and variable construction sites due to issues such as inconsistent production dimensions and transportation difficulties. This paper presents a novel prefabricated retaining wall system and reports centrifuge model tests performed to analyze its overall performance. The influence of different infill materials on the performance of the prefabricated retaining wall system was studied. The research findings reveal that the retaining wall system provides significant slope stabilization effects, and can withstand up to 4 times the stress level of natural slope. Moreover, the stability of the retaining wall system is more than twice better when infill with frictional soil, compared to clay infill. Due to its unique structure, it can not only reduce material consumption and carbon dioxide emissions around 63.94%, but also plant green plants in the gaps of components, thereby providing a more sustainable alternative to conventional concrete gravity wall systems.

Studies on the performance of water retention type tailings dams subjected to filling and inertial loading in a geotechnical centrifuge

The past decade has witnessed the failure of numerous tailing storage facilities and earthen dams. The most common factors causing failure include seepage and slope instability, apart from seismic activities. In the present study, a series of centrifuge model tests have been conducted to study the performance of water retention type (WRT) tailings dams impounded with fine tailings material (and water) on the upstream side. A custom-designed test setup to simulate upstream reservoir filling and inertial loading is employed in a 4.5 m radius large beam geotechnical centrifuge facility available at the Indian Institute of Technology Bombay, India. The centrifuge models were instrumented with pore pressure and displacement transducers to record porewater pressure (PWP) and surface settlement, respectively, and to ensure long-term safety and integrity of tailings dam. Additionally, an onboard digital camera was used to capture the front elevations of the centrifuge models to perform digital image analysis (DIA) for deducing slope face movements, surface settlements, and failure patterns. The results effectively demonstrate the performance of the WRT dam, delineate the slip surface and failure pattern, and quantify the critical design parameter related to inertial loading, which is the horizontal seismic coefficient (i.e. KHyield and KHmax). Based on these physically observed results, the analytical equations were also deduced for the WRT dams to quantify the stability (in terms of factor of safety, FS) and deformation response. The analytically obtained results agree reasonably well with the performance of WRT tailings dam models in the geotechnical centrifuge.

Centrifuge and analytical modeling of counterweight retaining walls under translation mode

Counterweight retaining walls (CRWs) are a variant of gravity-retaining walls that feature a pressure relief platform (RP) on the backfill side to reduce total earth pressure, offering a cost-effective option compared to traditional forms. However, the intricate interactions between CRWs and backfill, coupled with the lack of clear design guidelines, have restricted their use. This study examines the behavior of CRWs in translation mode using three different centrifuge model tests, each with varying fill heights. Observations show a slightly concave slip surface through the wall heel and a nearly planar slip surface extending from the edge of the RP to the back of the wall in an active limit state. Backfill movement can be classified into translation, sliding, and stable zones. Earth pressure distribution on the upper wall follows a trapezoidal pattern, whereas the pressure on the lower wall exhibits a triangular distribution. Earth pressure on the RP is approximately linear, peaking near the RP’s edge. Introducing a friction angle mobilization factor for the potential first slip surface improves accuracy in calculating earth pressure. The tests were replicated to validate the analytical model for earth pressure calculations, using the adaptive finite-element limit analysis method.

Predictions of seismic response for sheet-pile wall in liquefiable deposit within LEAP 2022 using the CycLiq constitutive model

The Liquefaction Experiments and Analysis Projects (LEAP) organized centrifuge tests and corresponding numerical predictions for the seismic response of sheet-pile wall in liquefiable deposits in 2022. Within LEAP 2022, two versions of the CycLiq constitutive model, i.e., the original (CycLiq) and modified (CycLiq-M) versions, were calibrated and used for numerical predictions. CycLiq-M was first calibrated using cyclic direct simple shear (CDSS) element tests on the test material, Ottawa F65 sand, and then used for Type-A predictions of another set of CDSS tests for which the results were priorly unknown, validating the model's performance at the element level. Type-B predictions of centrifuge shaking table model tests on sheet-pile wall in liquefiable deposit was then performed using both versions of the calibrated model, without prior knowledge of test results. The results show that the properly calibrated CycLiq model can make reasonable predictions for soil acceleration, excess pore pressure, settlement, and especially sheet-pile wall displacement. In particular, the CycLiq-M version with enhanced cyclic resistance simulation capability exhibits significant improvement in prediction accuracy. Using numerical simulation, the influence of soil-container friction in centrifuge model tests was assessed.

Geotechnical seismic isolation based on high-damping polyurethane: centrifuge modelling

Geotechnical seismic isolation (GSI) is a new category of low-damage resilient design methods that are in direct contact with geomaterials and of which the isolation mechanism primarily involves geotechnics. Various materials have been explored for placing around the foundation system in layer form to facilitate the beneficial effects of dynamic soil-foundation-structure interaction, as one of the GSI mechanisms. To reduce the thickness of the GSI foundation layer and to ensure uniformity of its material properties, the use of a thin and homogeneous layer of high-damping polyurethane (HDPU) was investigated in this study via centrifuge modelling. HDPU sheets were installed in three different configurations at the interface between the structural foundation and surrounding soils for realising GSI. It was found that using HDPU for GSI can provide excellent seismic isolation effects in all three configurations. The average rates of structural demand reduction amongst the eight earthquake events ranged from 35 to 80%. A clear correlation between the period-lengthening ratio and the demand reduction percentage can be observed amongst the three GSI configurations. One of the configurations with HDPU around the periphery of the foundation only is particularly suitable for retrofitting existing structures and does not require making changes to the structural systems or architectural features.

Centrifuge modeling of pile-supported embankment on soft soil base for highway widening

The pile-supported embankment has been widely adopted in highway widening projects. There is often significant differential settlement between the new and old embankments. Previous studies have not clarified the interaction mechanisms between different parts of the widening subgrade. In this research, a series of centrifuge model tests were carried out on the subgrades widened by pile-supported embankment on the soft soil base. The effect of the old embankment and piles on the subgrade deformation subject to new embankment is analyzed based on the full-field measurement results of displacement. The embankment displacement is mainly vertically downward and basically caused by the deformation of the soft soil base. The old embankment redistributes the vertical deformation of soft soil base by increasing and decreasing the vertical displacement in turn along the direction towards the slope surface. The piles exhibit supporting effect on the embankment above and restrict the vertical movement of the soil base. The piles influence the deformation of soft soil base within a certain area which expands with the increasing number of piles. The boundary of the pile influential area moves towards the subgrade axis with increasing depth. The vertical deformation of soft soil base shows peaks that are nearly linearly distributed along depth in the pile influential area. As the number of piles increases, the verticality degree of such linear distribution changes from the vertical to the slope firstly and then reverts to the vertical.

Evaluating stability of rigid-column-supported and geosynthetic-reinforced embankments

Field observations and centrifuge tests indicate that progressive column bending failure accompanies most instabilities of rigid-column-supported and geosynthetic-reinforced (RCGR) embankments. However, recognized guidelines specifically for evaluating the overall stability of such systems featuring bending failure remain limited. A general methodology to calculate the factor of safety (FS) for RCGR embankments using the limit equilibrium method is presented in this article. The focus is on deep-seated slope failures, wherein rigid columns progressively fracture due to subsoil overstressing. The concentric arches model, along with tensioned geosynthetic analysis, informs the determination of vertical and horizontal loads on the column heads. The column's resisting moment stems from its flexural and compression resistance. A mobilization factor for the net thrust on each column is defined to capture the progressive failure. The methodology involves an iterative computational procedure to identify the critical slip surface and the FS using the Fellenius' method. The solution was validated using three case studies, including both centrifuge models and field tests, as well as finite-element analysis. The results indicate that the soil mass contributes the most to resisting sliding and overall stability, followed by columns and geosynthetics. In addition, axial force mainly provides the resisting moment of columns.

Effect of model container on dynamic shear stresses in a centrifuge model

Effect of model container on dynamic shear stresses in a centrifuge model

Evaluating the Optimal Performance of skirted footing: A review study

Geotechnical engineers are currently confronted with the challenge of identifying innovative and efficient approaches to increase bearing capacity and minimize foundation settling. As a result, the skirt is regarded as one technique for enhancing the shallow foundation's carrying capability on various soil types. The skirt work mechanism involves the confining of soil beneath the foundation, resulting in a reduction of settling for the foundation. Soil engineers have endeavored to develop this approach as a substitute for pile foundations in normal structures. These foundations exhibit versatility in their applicability, as they may be useful in diverse settings, including marine environments, coastal areas, and arid terrains. This study provides a comprehensive evaluation of various research conducted on skirted foundations in different soil conditions. The objective is to assess the increase of bearing capacity and decrease in a settlement achieved via the utilization of skirted foundations. This assessment is based on laboratory testing, field tests, centrifuge models, numerical methods, and theoretical analysis; These investigations are employed to examine the behaviors skirted footing.

Assessment of seismic stability of centrifugal benched slope models subjected to lateral confinement

Assessment of seismic stability of centrifugal benched slope models subjected to lateral confinement

Centrifugal and Numerical Modeling of Seismic Behavior of Pile Foundation in Layered Ground of Dense and Cemented Sand

Centrifugal and Numerical Modeling of Seismic Behavior of Pile Foundation in Layered Ground of Dense and Cemented Sand

Centrifuge modeling of liquefiable sand supported by sheet pile wall: LEAP tests at Ehime University

Centrifuge modeling of liquefiable sand supported by sheet pile wall: LEAP tests at Ehime University

Centrifuge modeling of slope and embankment subjected to post-shaking rainfall

Centrifuge modeling of slope and embankment subjected to post-shaking rainfall

Dynamic centrifuge model tests on piled raft foundation and evaluation of sectional forces of piles

Dynamic centrifuge model tests on piled raft foundation and evaluation of sectional forces of piles

A Precise Analysis of the Behavior of Pit Side Tunnels Caused by Deep Excavation

As urbanization gathers pace, projects involving adjacent subway tunnels are increasing, thereby amplifying the need for robust tunnel protection measures. Currently, there exists a notable lack of precise analyses on the three‐dimensional (3D) deformation laws and mechanisms of tunnels affected by adjacent deep excavation. Moreover, the influence patterns of retaining wall stiffness and deep excavation depth on the 3D deformation of pit‐side tunnels remain unclear. The purpose of this research is to bridge the existing disparity by adopting the hypoplastic model, which effectively captures soil stiffness that is dependent on soil state, strain, and stress path, even at small strains, as well as soil strength, based on reported centrifuge model tests. This approach facilitates a comprehensive, precise numerical analysis of the interaction between deep excavation and preexisting tunnels located outside the retaining wall. The analysis sheds light on the deformation mechanisms and trends of pit‐side tunnels not solely confined to the longitudinal axis but extending to the transverse plane as well, while systematically examining the influence of varying excavation depths and retaining wall stiffness on key tunnel parameters, including longitudinal deformation, diameter changes, bending strains, and soil pressure distributions around the tunnels. The study reveals that if the tunnel situated outside the retaining structure lies beneath the foundation pit’s base, deep excavation only slightly deforms the tunnel. However, when the tunnel outside the retaining structure is positioned above the pit’s base, its deformation progressively intensifies with deeper excavation, but the growth rate has a decreasing trend. An enhancement in the stiffness of the retaining wall results in a notable decrease in the deformation exhibited by the adjacent tunnels. The findings contribute to a deeper understanding of the complex responses of pit‐side tunnels to excavation activities, ultimately facilitating the design and construction of safer and more resilient urban subway infrastructure.

An innovative experimental device for characterizing the responses of monopiles subjected to complex lateral loading

Offshore wind turbines are usually founded on monopiles. During the operation period, the structure is subjected to complex lateral loading from wind, wave and current. The soils surrounding those monopiles may deform with increasing the number of loading cycles, leading to tilting of the whole structure; hence, it is vital to carry out physical model tests to examine the long-term performance of monopiles. This study proposes an innovative experimental setup for centrifuge modelling of the response of monopiles under complex lateral loading. Hydraulic actuators are adopted to apply lateral loads on model pile, and electrohydraulic servo-valves and associated controllers are used to achieve a closed loop position or load control. A carefully designed spherical hinge and load bars are used to connect the model pile and actuator shafts. This enables that the pile can rotate freely and can move vertically freely. A centrifuge test on a winged monopole subjected to perpendicular lateral loading was carried out at 100g. The experimental results shed light on pile responses in the cyclic loading and constant loading directions.