Dynamic Centrifuge Model Tests Research Articles

Dynamic centrifuge model tests and material point method analysis of the impact force of a sliding soil mass caused by earthquake-induced slope failure

Dynamic centrifuge model tests and associated analyses are carried out to develop a procedure for simulating the slope failure process during earthquakes and to evaluate the force of a sliding soil mass impacting a structure. This impact force is successfully measured in the dynamic centrifuge model tests using a slope height of 50 m in the prototype scale. The results of a pseudo-static limit equilibrium analysis, assuming a circular failure plane, show that a stability analysis can be an effective tool for evaluating the critical acceleration under which the slope failure starts, although it is not applicable for evaluating the runout distance or the impact force of the sliding soil mass to the structure. Therefore, an attempt is also made in this study to examine the applicability of empirical equations for evaluating the impact force by comparing the evaluated impact force using Hertz’s equation and an empirical equation based on fluid mechanics with the measured ones. The comparison reveals that these simple equations would not be able to estimate the impact force well, even though parameter setting is required for applying the equations. On the other hand, it is also found from a relevant analysis that the material point method (MPM) is an effective tool for simulating the failure behavior of a slope and for evaluating the impact force of a sliding soil mass induced by a slope failure.

Effect of Partial Drainage on Cyclic Strengths of Saturated Sands in Dynamic Centrifuge Tests

AbstractThe effects of partial drainage on the cyclic strength of saturated sand in a set of dynamic centrifuge model tests were evaluated. Three models of level profiles of saturated Ottawa F-65 s...

Evaluation of performance-based seismic coefficient for gravity-type quay wall via centrifuge tests

Conventional simplified analysis methods for seismic design of gravity-type quay wall are based on providing capacity to resist a design seismic force, but they do not provide information on the performance of a structure when the limit of the force-balance is exceeded. In order to overcome the limitation of conventional seismic design methods, a performance-based seismic coefficient (khk) concept which can verify the performance of port structures exceeding the limit of force-balance was proposed in the technical standards and commentaries for port and harbour facilities in Japan, published in 2007. The khk concept considers the deformation of the quay wall, the wall height, the effect of frequency characteristics and duration of the ground motions, and the natural period of the ground. This paper proposes a performance verification method for the gravity-type quay wall during earthquakes through dynamic centrifuge model tests. The centrifuge tests were used in the present study to validate the proposed khk concept for evaluating the seismic performance of the quay wall under various conditions. The reliability of the khk concept was evaluated for different wall heights, earthquake motions and the thickness of subsoil, which are the primary variables in the khk equation. In addition, some improvements that should be considered in the future revision of the khk equation are discussed in this research.

Mechanical role of reinforcement in seismic behavior of steel-strip reinforced earth wall

In the current design practices of steel-strip reinforced earth walls (SSREWs), the length of the reinforcing material is determined based on the equilibrium between the reinforcement tension and the earth pressure acting on the wall. Here, the resistance of the reinforcing material laid in the active failure zone (AFZ) is not considered. Moreover, the mechanical role of the reinforcing material against the integrity of the SSREW has not been sufficiently verified. Regarding the seismic stability of SSREW, although it is investigated by treating the entire reinforced earth wall as a rigid body, this inspection method is for gravity-retaining walls, and the difference in the seismic behavior between the SSREW and the rigid body is not clear. In this study, therefore, dynamic centrifuge model tests on 6 types of SSREWs were conducted to clarify the following items: (1) the basic earthquake behavior of a SSREW, (2) the mechanical role of the reinforcing material laid in the AFZ and (3) the mechanical role of the reinforcing material against the integrity of the SSREW. The results indicated that the reinforcing material laid in the AFZ can restrain the amount of deformation of the wall during earthquakes. Furthermore, the more stable the AFZ is, the smaller the maximum wall displacement will be.

Dynamic centrifuge model tests on embankment with different upstream conditions

Dynamic centrifuge model tests on embankment with different upstream conditions

Seismic Performance of Ancient Masonry Structures in Korea Rediscovered in 2016 M 5.8 Gyeongju Earthquake

The Gyeongju Historic Areas, which include the millennium-old capital of the Silla Kingdom, are located in the region most frequently affected by seismic events in the Korean peninsula. Despite the numerous earthquakes documented, most of the stone architectural heritage has retained their original forms. This study systematically reviews and categorises studies dealing with the seismic risk assessment of the architectural heritage of the historic areas. It applies research methodologies, such as the evaluation of the engineering characteristics of subsoil in architectural heritage sites, site-specific analysis of the ground motions in response to earthquake scenarios, geographic information system (GIS)-based seismic microzonation according to the geotechnical engineering parameters, reliability assessment of dynamic centrifuge model testing for stone masonry structures and evaluation of seismic behaviour of architectural heritage. The M 5.8 earthquake that hit Gyeongju on September 12, 2016 is analysed from an engineering point of view and the resulting damage to the stone architectural heritage is reported. The study focuses on Cheomseongdae, an astronomical observatory in Gyeongju, whose structural engineering received considerable attention since its seismic resistance was reported after the last earthquake. Dynamic centrifuge model tests applying the Gyeongju Earthquake motions are performed to prove that it is not a coincidence that Cheomseongdae, a masonry structure composed of nearly 400 stone members, survived numerous seismic events for over 1300 years. The structural characteristics of Cheomseongdae, such as the well-compacted filler materials in its lower part, rough inside wall in contrast to the smooth exterior, intersecting stone beams and interlocking headstones are proven to contribute to its overall seismic performance, demonstrating outstanding seismic design technology.

Influence of inherent anisotropy on the seismic behavior of liquefiable sandy level ground

Inherent anisotropy is a crucial aspect to consider for an improved understanding of the strength and deformation characteristics of granular materials. It has been the focus of intense investigation since the mid-1960s. However, inherent anisotropy’s influence on ground seismic responses, such as liquefaction, has not been extensively studied. In this paper, inherent anisotropy’s influence on ground seismic responses is examined through a series of dynamic centrifuge model tests on liquefiable level sand deposits. During the model setup, five different deposition angles (0, 30, 45, 60, and 90 degrees) were achieved using a specially designed rigid container. The models were exposed to tapered sinusoidal input accelerations and the recorded results were fully investigated. It was found that deposition angle-caused inherent anisotropy significantly influenced the excess pore pressure responses during the shaking and dissipation phases. The amount of excess pore pressure build-up and the high excess pore pressure duration increased with the deposition angle, while the dissipation rate decreased as the deposition angle increased. The inherent anisotropy also influenced liquefaction-induced ground settlement, with volumetric strain increasing along with the deposition angle. With respect to response acceleration, inherent anisotropy’s effects depended on the amount of excess pore pressure build-up (i.e., degree of liquefaction). In view of these results, it was concluded that a sandy ground, deposited at a higher angle (i.e., closer to 90 degrees), is more susceptible to liquefaction and that inherent anisotropy’s influence should be considered when evaluating the liquefaction potential and performing effective stress analyses.

Dynamic Centrifuge Model Tests on Pile Foundation of Plate-shape Building in Soft Clayey Ground and its Numerical Analyses

Dynamic Centrifuge Model Tests on Pile Foundation of Plate-shape Building in Soft Clayey Ground and its Numerical Analyses

Investigation of seismic performances of unconnected pile foundations using dynamic centrifuge tests

An unconnected pile foundation allows separation between the lower pile and the pile cap, and it has been proposed as an effective foundation type for reducing the seismic load during strong earthquakes. However, previous quantitative evaluations of unconnected piles with various foundation types and earthquake intensities are inadequate. In this study, the influence of base shaking level and the material of the interposed layer between pile and pile cap on the seismic behaviour of unconnected piles were evaluated using a centrifuge model test to reproduce the field stress conditions. A dynamic centrifuge model test was completed on an experimental model consisting of dry sandy soil, a foundation and a single degree-of-freedom structure. The acceleration of the structure and the settlement of the foundation system were measured during base shaking. For the unconnected pile system, the structural seismic load reduction effect due to rocking behaviour was confirmed, and the unconnected pile foundation with the interposed layer with large stiffness had less vertical settlement than the conventional shallow foundation. Finally, the rotational stiffness and damping ratio for the foundation system used in the centrifuge model tests were derived and discussed.

Earthquake loading response of a slope with an inclined weak intercalated layer using centrifuge modeling

Seismic performance and the dynamic deformation mode of a slope with a weak intercalated layer (WIL) under earthquake excitations are very important for suitable seismic design of certain structures. In southwestern China, near the Longmenshan Fault, the dynamic response of slopes triggered by earthquakes is still not well understood. In this study, a series of dynamic centrifuge model tests under a 50-g hypergravity treatment with different input seismic motions were performed to investigate the effect of the input motion on the dynamic behavior of the WIL slope. The test results indicate that the amplification factors of the acceleration response increased with increasing height of the slope, reaching maximum values at the crest and the top surface, but abrupt changes in amplification with increasing height occurred at the WIL. The acceleration amplification at the WIL was related to the peak of the input motion. The amplification factor at the intercalated layer was weakened when the peak of input acceleration was equal to or less than 0.15 g, but it increased when the input peak was greater than 0.15 g. Acceleration amplification at the WIL was affected by the slope structure effect.

Seismic behaviour of reinforced embankments in dynamic centrifuge model tests

A series of dynamic centrifuge model tests was conducted to investigate the effects of reinforcement on the seismic behaviour of hillside embankments consisting of sandy soils and resting on stiff base slopes. In total, three types of seismic reinforcements, namely, large-scale gabions, drainage-reinforcing piles, and ground anchors with pressure plates, were employed in the tests. The test results showed that: (1) the seismic performance of both lower and higher embankments was remarkably improved by installing large-scale gabions at the toe as they restrained the completion of the formation of sliding planes; (2) the installation of drainage-reinforcing piles at the embankment toe was rather effective in reducing the overall earthquake-induced deformation due to their high permeability and restraint effect against sliding displacement at the reinforced region; and (3) the embankments improved by ground anchors with pressure plates were not vulnerable to earthquake-induced damage due to their constraint effects even under high water table conditions. The improvement effects by the above-mentioned three types of reinforcements were presented by evaluating the global safety factors based on the results of a series of triaxial compression tests.

Effects of nails and facing plates on seismic slope response and failure

A rock bolt with a facing plate is one of the soil nailing methods against relatively shallow sliding failure, which can be applied to natural slopes without cutting trees. In this research, dynamic centrifuge model tests were conducted to study the reinforcement mechanism of the nailing with individual facing plates and the effects of facing plate width, bolt spacing and bolt inclination angle on the seismic stability of reinforced slope. From the test results, it was confirmed that the facing plate resistance works well against the seismic load, which suppresses the slope deformation during shaking, and the mobilised resistance increases with increasing plate size. Plate bearing failure and local surface failure are critical failure mechanisms. The bearing failure could occur for small plates, while for relatively large plates, the local failure causes reduction of plate resistance and triggers large deformation and slip failure of the slope. These failures could be controlled by slope acceleration and uncovered width. Downward inclined installation of the nailing from the normal to the slope surface can effectively prevent the movement and secure the slope stability with less mobilised resistance.

Investigation of the dynamic behaviour of a storage tank with different foundation types focusing on the soil‐foundation‐structure interactions using centrifuge model tests

SummaryThis paper proposes a dynamic centrifuge model test method for the accurate simulation of the behaviours of a liquid storage tank with different types of foundations during earthquakes. The method can be used to determine the actual stress conditions of a prototype storage‐tank structure. It was used in the present study to investigate the soil‐foundation‐structure interactions of a simplified storage tank under two different earthquake motions, which were simulated using a shaking table installed in a centrifuge basket. Three different types of foundations were considered, namely, a shallow foundation, a slab on the surface of the ground connected to piles and a slab with disconnected piles. The test results were organised to compare the ground surface and foundation motions, the slab of foundation and top of structure motions and the horizontal and vertical motions of the slab, respectively. These were used to establish the complex dynamic behaviours of tank models with different foundations. The effects of soil–foundation–structure interaction with three foundation conditions and two different earthquake motions are focused and some important factors, that should be considered for future designs are also discussed in this research. Copyright © 2017 John Wiley & Sons, Ltd.

Zhejiang University benchmark centrifuge test for LEAP-GWU-2015 and liquefaction responses of a sloping ground

A dynamic centrifuge model test of mildly sloping ground was conducted at Zhejiang University according to the LEAP-GWU-2015 experiment specifications. A 5-degree slope consisting of a saturated medium dense Ottawa F-65 sand was prepared by air pluviation method in rigid container, which simulated a prototype with a 20m length and 4m depth under 26g centrifugal acceleration. The model was subjected to three smaller and two destructive motions. Test data and preliminary analyses of model responses during multiple shakings are presented. In-flight measurement of shear wave velocity by bender elements was used to characterize the evolution of soil state. Acceleration response spectra were presented and site amplification effects were observed. Shear stress-strain loops were calculated from acceleration records, and asymmetric dilatancy in the sloping ground was observed during liquefaction. Generation and dissipation of excess pore pressure were depicted. Large liquefaction-induced ground displacements were measured and analyzed. This study provides valuable data and delivers some important observations of liquefaction responses of a sloping ground.

Numerical Predictions for Centrifuge Model Tests of a Liquefiable Sloping Ground Using a Strain Space Multiple Mechanism Model Based on the Finite Strain Theory

This paper presents the results of numerical simulations for dynamic centrifuge model tests of a liquefiable sloping ground performed by various institutions within a framework of Class A, B, and C prediction phases of the LEAP (Liquefaction Experiments and Analysis Project). The simulations are performed by using a strain space multiple mechanism model based on the finite strain theory (including both total and updated Lagrangian formulations), in which both material and geometrical nonlinearity are considered. In the simulation, dynamic response analyses are carried out following self-weight analyses with gravity. The soil parameters of the constitutive model are determined based on the results of laboratory soil tests (e.g., cyclic triaxial tests) and some empirical formulae. The identification process of the parameters is explained in details besides the computational conditions (e.g., geometric modeling, initial and boundary conditions, numerical schemes such as time integration technique). In addition to the numerical results of the Class A prediction using a target input motion, those of the Class B and C predictions using recorded motions in the centrifuge model tests are also presented. Comparison between these predictions and measured results has revealed that the constitutive model parameters for effective stress analyses should be calibrated to well capture the shape and trend of liquefaction resistance curves, and subsequently estimate the damage of soil systems due to liquefaction with higher accuracy.

Observation of post-liquefaction progressive failure of shallow foundation in centrifuge model tests

Liquefaction-induced large deformations of shallow foundations were widely observed during strong earthquakes, and one important feature of these is that they occur relatively slowly compared to the duration of earthquake shaking. As most previous model tests used clean sands with high permeability, this type of “delayed” failure mode has not been observed or reproduced realistically in the laboratory to date. In this study, a dynamic centrifuge model test was performed under 30g to study the mechanism of post-liquefaction progressive failure of buildings with shallow foundation on relatively thick deposits of liquefiable sandy soils. A two-dimensionally asymmetrical model structure was used to simulate the eccentric loads at the interface between the foundation and the subsoil. A clayey sand model with a relative density of 35% was prepared to have the relatively low permeability and coefficient of consolidation comparable to those of in-situ sandy soils. A prototype 2Hz, 80s long sine sweep with peak amplitude of 300gal was used to simulate an earthquake strong enough to trigger a typical liquefaction state. Seismic responses in the liquefiable deposits and deformations of the structure were monitored during and after shaking. The main finding of this study is that the post-liquefaction progressive failure of shallow foundation was due to the large ground deformation of subsoil where significant shear strain localization had developed during liquefaction. Progressive settlement and tilting of shallow foundation will continue as long as the liquefaction state maintains, and longer durations of liquefaction lead to larger deformations.

Several factors affecting seismic behaviour of embankments in dynamic centrifuge model tests

A series of dynamic centrifuge model tests was conducted in order to evaluate some factors affecting the seismic performance of hillside embankments consisting of sandy or silty soils and resting on stiff base slope. The effects of seepage water elevation in embankments, toe drain, embankment height, base slope inclination, soil compaction, and fill materials on the seismic behaviour of embankments were investigated. The test results showed that: (1) the seepage water was one of the most important factors for earthquake-induced embankment failure; (2) the seismic performance of both the smaller and higher embankments was remarkably improved by installing the toe drain; (3) larger base slope inclination produced larger earthquake-induced deformation of embankments; (4) well-compacted embankments were not vulnerable to earthquake-induced damage; and (5) the seismic performance of well-compacted embankments consisting of well-graded silty soils with large fines content was higher than that of poorly graded sands under otherwise the same condition. In some tests, as observed during past strong earthquakes, delayed flow failure occurred due possibly to the multiple effects of upward seepage associated with the redistribution of excess pore water pressures generated during main shaking, continued small vibration after main shaking, and driving static shear stresses caused by the embankment weight. A series of triaxial compression and cyclic triaxial liquefaction tests was also conducted to evaluate undrained behaviour of the fill materials. The correlation between the model and laboratory element test results was presented.

Correlation between liquefaction resistance and shear wave velocity of granular soils: a micromechanical perspective

The shear wave velocity method has become an increasingly popular means to evaluate the liquefaction potential of granular soils. Understanding the fundamental mechanism underlying existing empirical or semi-empirical relationships is important for better assessing their reliability. This paper presents a particle-scale study of the correlation between cyclic resistance ratio (CRR) and the shear wave velocity corrected for overburden stress (Vs1). The discrete-element method was used to simulate a series of undrained stress-controlled cyclic triaxial tests together with shear wave velocity (Vs) measurements. Discrete-element method modelling with various relative densities, confining pressures and micro-parameters was performed under various cyclic stress ratios (CSRs), and the onset of liquefaction was illustrated through both macroscopic and microscopic responses, for example, inferred excess pore-water pressure, mechanical coordination number and redundancy index. The inter-particle friction was identified as the key micro-parameter that governs the liquefaction resistance of granular soils. A micro-scale CRR–Vs1correlation considering two independent micro-parameters, inter-particle friction and particle shear modulus, was then obtained and further validated with the outcomes from three dynamic centrifuge model tests performed on silica sand no. 8. This study demonstrates that the CRR–Vs1correlation is particle specific, thus soil specific, and the particle mechanical properties should be included in the Vs-based method for future liquefaction evaluation of granular soils.

Centrifuge modeling of seismic response of normally consolidated deep silt deposit

Observations from recent earthquakes in Taiwan and Turkey have shown that current methodology to determine the liquefaction susceptibility of fine-grained soils is no longer sufficient to quantify seismic hazard, and that low plasticity fine-grained soils such as silts could also cause adverse effects on the performance of civil infrastructures. It is very important to understand the dynamic behavior of silt deposit because most of coastal areas, where there are many ongoing construction activities, consist mainly of silts, which might be vulnerable to earthquake loadings. This paper presents the experimental results of centrifuge tests on reconstituted specimen to investigate the dynamic response of normally consolidated deep silt deposit in Seattle area. The experimental sequence and preparation of the artificial silt deposit are described in detail. The recorded downhole accelerations are utilized to identify variation of shear modulus and damping ratio with shear strain amplitude via inverse analysis techniques applied to dense instrumentation arrays in a dynamic centrifuge model test.

Evaluation of seismic behaviour of Cheomseongdae using dynamic centrifuge model test

SummaryCheomseongdae is known to be the oldest astronomical observatory in Asia. According to historical records, the Gyeongju area, where Cheomseongdae is located, suffered from numerous medium‐scale earthquakes. Cheomseongdae has a masonry structure, which is apparently vulnerable to horizontal dynamic loads such as earthquakes. However, despite its appearance, features such as the filler of the lower half, inner irregular‐shaped stones which can induce high frictional resistance, eight long horizontal tie stones inside the artefact, and a grid of interlocking headstones increase its resistance to horizontal dynamic loads. Dynamic centrifuge model tests were performed on Cheomseongdae in order to evaluate the seismic response characteristics of this architectural heritage structure. Model tests were executed on two 1/15‐scale models: one which was an exact duplicate of the original Cheomseongdae and the other without the long horizontal tie stones and grid of interlocking headstones. On the basis of the amplification patterns in the time and frequency domains, the differences in seismic behaviour between the two Cheomseongdae models, and a broken stone at the 19th layer during tests, the long horizontal tie stones and headstones were found to increase the seismic resistance within Cheomseongdae and provide a glimpse of the ‘seismic design’ of our ancestors. Copyright © 2014 John Wiley & Sons, Ltd.