Dynamic Centrifuge Model Research Articles

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.

地震履歴が砂の液状化強度およびコーン貫入抵抗に及ぼす影響に関する動的遠心模型実験

東北地方太平洋沖地震では、若齢の人工造成地盤に液状化被害が多く発生した。これは、堆積・造成年代の異なる地盤における液状化強度の「年代効果」が影響を及ぼした結果であると考えられている。砂の年代効果に関する具体的な作用としては様々なものが考えられるが、本研究では地震履歴に着目した動的遠心模型実験を行った。数多くの地震履歴を与えたケースと地震履歴を与えていないケースの過剰間隙水圧等の変化を分析・比較することにより、地震履歴が液状化強度に及ぼす影響を検討した。実験結果は地震履歴と液状化強度比の関係に加えて、液状化強度比と相対密度、コーン貫入抵抗の関係にも着目して整理した。その結果、地震履歴を受けることで砂の液状化強度が顕著に上昇する傾向と、コーン貫入抵抗とS波速度は砂の相対密度の違いとよく対応する傾向が認められたものの、地震履歴による液状化強度の上昇傾向はコーン貫入抵抗およびS波速度に表れにくいことを明らかにした。

Study of dynamic stability of unsaturated embankments with different water contents by centrifugal model tests

It has been pointed out that the damage to unsaturated embankments caused by earthquakes is attributed to the high water content brought about by the seepage of underground water and/or rainfall infiltration. It is important to study the effects of the water content on the dynamic stability and deformation mode of unsaturated embankments in order to develop a proper design scheme, including effective reinforcements, for preventing severe damage. This paper presents a series of dynamic centrifugal model tests with different water contents to investigate the effect of the water content on the deformation and failure behaviors of unsaturated embankments. By measuring the displacement, the pore water pressure and the acceleration during dynamic loading, as well as the initial suction level, the dynamic behavior of unsaturated embankments with an approximately optimum water content, a higher than optimum water content, and a lower than optimum water content, are discussed. In addition, an image analysis reveals the displacement field and the distribution of strain in the embankment, by which the deformation mode of the embankment with the higher water content is clarified. It is found that in the case of the higher water content, the settlement of the crown is large mainly due to the volume compression underneath the crown, while the small confining pressure at the toe and near the slope surface induces large shear deformation with volume expansion.

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.

Centrifuge modeling of the seismic responses of sand deposits with an intra-silt layer

Three dynamic centrifuge model tests were conducted at an acceleration of 80g to simulate the seismic responses of level sand deposits: an intra-silt layer was embedded in two of these sand deposits at different depths. The effects of a low-permeability intra-silt layer on the build-up and dissipation of excess pore-water pressure, surface settlement, and the related liquefaction mechanism were investigated. An intra-silt layer modifies the seismic response of the sand deposit, reduces the extent of liquefaction, and thus decreases surface settlement. The depth of the intra-silt layer is one of the factors influencing the seismic responses of the sand deposits. The magnitude of the surface settlement is proportional to the degree of liquefaction in the sand deposit. The high positive hydraulic gradients appearing in both the intra-silt layer and in the sand deposit lying on the intra-silt layer can break a thinner or weaker top layer and result in sand boiling. Our visual animation of the ratio of the excess pore-water pressure and the lateral displacement revealed that the liquefaction front travels upward during shaking and the solidification front travels upward after shaking.

Evaluation of the seismic response of stone pagodas using centrifuge model tests

This study attempts to propose dynamic centrifuge model tests as a method of seismic risk assessment in order to discover how stone architectural heritages with masonry structures have endured seismic load, and whether there is any possibility of future earthquake damage. Dynamic centrifuge tests have been conducted for one fifteenth scale models of Seok-ga-tap and the five-storey stone pagoda of Jeongnimsa temple site, which are Korean representative stone pagodas. In order to make input motions of the earthquake simulator, site investigation and site-specific response analysis have been performed. The models of two stone pagodas, which have the same number of pieces with the real structures, have been produced and the dynamic centrifuge tests have been conducted for the model pagodas. Accelerometers were attached at different heights of the pagoda. The measured acceleration records and frequency responses were analysed during dynamic centrifuge test. Two real earthquake records, Hachinohe and Ofunato earthquakes and a sweeping signal with ranged frequency were utilised for input motions of dynamic centrifuge tests to evaluate the behaviour of the stone pagodas. For Seok-ga-tap models, it was observed that acceleration tends to be amplified with height. The third floor body shows at most 2.5 amplification of acceleration in comparison to the surface ground. The amplification was at a frequency of 3.83 Hz and it was considered as the natural frequency of the pagoda. For the five-storey stone pagoda, the seismic wave energy significantly reduced while it passed the first body floor, and then the peak acceleration was gradually amplified upwards. It was found that the pagodas did not collapse when the peak acceleration of ground surface was raised to 0.4 g. Given that the maximum design seismic acceleration specified in Korean seismic design guide is 0.22 g and the amplification ratio of peak acceleration in the supporting ground of the pagodas ranges from 1.45 to 1.74, it can be shown that the two pagodas are stable against 2400-year return period earthquake level, and have excellent seismic performance.

格子状地盤改良による住宅沈下量抑制効果に着目した遠心模型振動実験

格子状地盤改良による住宅沈下量抑制効果に着目した遠心模型振動実験

Uplifting behavior of shallow buried pipe in liquefiable soil by dynamic centrifuge test.

Underground pipelines are widely applied in the so-called lifeline engineerings. It shows according to seismic surveys that the damage from soil liquefaction to underground pipelines was the most serious, whose failures were mainly in the form of pipeline uplifting. In the present study, dynamic centrifuge model tests were conducted to study the uplifting behaviors of shallow-buried pipeline subjected to seismic vibration in liquefied sites. The uplifting mechanism was discussed through the responses of the pore water pressure and earth pressure around the pipeline. Additionally, the analysis of force, which the pipeline was subjected to before and during vibration, was introduced and proved to be reasonable by the comparison of the measured and the calculated results. The uplifting behavior of pipe is the combination effects of multiple forces, and is highly dependent on the excess pore pressure.

Dynamic centrifuge model tests of seismic behavior of bridge abutment with the EPS backfill

Dynamic centrifuge model tests of seismic behavior of bridge abutment with the EPS backfill

Aftershocks and the whole-life seismic performance of granular slopes

Shallow embankment slopes are commonly used to support elements of transport infrastructure in seismic regions. In this paper, the seismic performance of such slopes in non-liquefiable granular soils is considered, focusing on permanent movement and dynamic motion at the crest, which would form key inputs into the aseismic design of supported infrastructure. In contrast to previous studies, the evolution of this behaviour under multiple sequential strong ground motions is studied through dynamic centrifuge, numerical (finite-element, FE) and analytical (sliding-block) modelling, the centrifuge tests being used to validate the two non-physical approaches. The FE models focus on the specification of model parameters for existing non-linear constitutive models using routine site investigation data, allowing them to be used routinely in design and analysis. Soil-specific constitutive parameters are derived from shearbox and oedometer test data, and are found to significantly outperform existing empirical correlations based on relative density, highlighting the importance of specifying a suitably detailed site investigation. An improved sliding-block (‘Newmark') approach is also developed for estimating permanent deformations during preliminary design, in which the formulation of the yield acceleration is fully strain-dependent, incorporating both material hardening/softening and geometric hardening (re-grading). The site-specific (improved) FE models and the new sliding-block approach are shown to outperform considerably existing FE parameters and sliding-block models in capturing the permanent deformations of the slope under virgin conditions, and further, only the improved FE and sliding-block models are found to capture correctly the behaviour of the ‘damaged' slope under subsequent earthquakes (e.g. strong aftershocks). The FE models can additionally accurately replicate the settlement profile at the crest and quantify the dynamic motions that would be input to supported structures, although these were generally overpredicted. The FE procedures and sliding-block models are therefore complementary, the latter being useful for preliminary design and the former for later detailed design and analysis.

Centrifuge model tests on liquefaction-induced settlement and pore water migration in non-homogeneous soil deposits

This paper presents the results of dynamic centrifuge model tests conducted to investigate the liquefaction mechanism in non-homogeneous soil deposits. Four types of model tests were conducted: one model test involved a uniform soil deposit; one involved continuous layered soil deposit; and two involved discontinuous layered soil deposits. Non-homogeneity in the tests was incorporated by including periodically distributed discontinuous silty sand patches. It was found that more excess pore water pressure (EPWP) remains for a longer period of time in the discontinuous region in non-homogeneous soil deposits compared with the continuous layered and uniform soil deposits. The generation of pore water pressure ceases the supply of a new mass of water after seismic excitation; therefore the dissipation of EPWP becomes the dominant factor for settlement after seismic excitation. The rapid dissipation of EPWP through the discontinuous part in the non-homogeneous soil deposits manifests as a larger settlement in the discontinuous part, causing non-uniform settlements.

Centrifuge Model Test and FEM Analysis of Dynamic Interactive Behavior between Embankments and Installed Culverts in Multiarch Culvert Embankments

A multiarch culvert embankment is a new type of filling structure for which several precast arch culverts are installed continuously in the direction of the road extension. The key points in the design are to estimate the practical, optimal spacing between installed arch culverts and to clarify the interactive seismic behavior of the filling material and the culvert structure. In the current study, first, dynamic centrifuge model tests and a numerical analysis were carried out to clarify the basal earthquake behavior of the structure and verify the numerical approach. Then, the full-scale numerical analysis was performed to investigate the influence of spacing between multiarch culverts and the mechanical behavior under seismic conditions. From the results, it is confirmed that when the unit spacing is narrow, the whole rigidity of the ground and the arch culvert increases relatively. This is because the volume in the fill part, where the rigidity is small, decreases comparatively. Hence, the section force and the deformation are controlled.

Centrifuge modelling for evaluation of seismic behaviour of stone masonry structure

Many surviving ancient monuments are freestanding stone masonry structures, which appear to be vulnerable to horizontal dynamic loads such as earthquakes. However, such structures have stood for thousands of years despite numerous historic earthquakes. This study proposes a scaled-down dynamic centrifuge modelling test to study how these masonry structures resist seismic loading. The test is proposed for seismic risk assessments to evaluate risk of damage from a future seismic event. The seismic behaviour of a 3-storey, freestanding stone block structure has been modelled and tested within a centrifuge. Models were made at 3 different scales and dynamic tests were conducted using different centrifugal acceleration fields so that the behaviours could be transformed to an equivalent full-scale prototype and compared. Data from 2 earthquakes and a sweeping signal were used to simulate the effects of earthquake ground motion within the centrifuge. The acceleration and frequency responses at each storey height of the model were recorded in different centrifugal acceleration fields. Similar behaviours appeared when the results of the small-scale models were transformed to a full-size prototype scale. This confirms that the seismic behaviour of stone masonry structures can be predicted using scaled-down models.

Seismic performances of dyke on liquefiable soils

Various field investigations of earthquake disaster cases have confirmed that earthquake-induced liquefaction is a main factor causing significant damage to dyke, research on seismic performances of dyke is thus of great importance. In this paper, seismic responses of dyke on liquefiable soils were investigated by means of dynamic centrifuge model tests and three-dimensional (3D) effective stress analysis method which is based on a multiple shear mechanism model and a liquefaction front. For the prototype scale centrifuge tests, sine wave input motions with peak accelerations 0.806m/s2, 1.790m/s2 and 3.133m/s2 of varied amplitudes were adopted to study the seismic performances of dyke on the saturated soil layer foundation with relative density of approximately 30%. Then, corresponding numerical simulations were conducted to investigate the distribution and variations of deformation, acceleration, excess pore-water pressure (EPWP), and behaviors of shear dilatancy in the dyke and the liquefiable soil foundation. Moreover, detailed discussions and comparisons between numerical simulations and centrifuge tests were also presented. It is concluded that the computed results have a good agreement with the measured results by centrifuge tests. The physical and numerical models both indicate that the dyke hosted on liquefiable soils subjected to earthquake motions has exhibited larger settlement and lateral spread: the stronger the motion is, the larger the dyke deformation is. Compared to soils in the deep ground under the dyke and the free field, the EPWP ratio is much smaller in the shallow liquefiable soil beneath the dyke in spite of large deformation produced. For the same overburden depth soil from free site and the liquefiable foundation beneath dyke, the characteristics of effective stress path and stress–strain relations are different. All these results may be of theoretical and practical significance for seismic design of the dyke on liquefiable soils.

Centrifuge shaking table tests on a single pile embedded in clay subjected to earthquake excitation

Pile foundations are extensively used to achieve the bearing capacity required to support heavy superstructure loading, especially under adverse soil conditions. In view of this, the behavior of pile foundations under earthquake loading is an important factor affecting the integrity of infrastructures. In this paper, the results from a series of dynamic centrifuge model tests carried out at the National University of Singapore are presented. The centrifuge experiments were performed to examine response of a single pile in soft clays subjected to earthquake, with special focus on the effect of superstructure loading on the seismic soil–pile interaction. The experimental observations were then compared with the results obtained from a simple theoretical analysis, based on lumped mass approach. The centrifuge test results suggest that the pile does not move in tandem with the ground. The results also indicate that the degree of soil–pile interaction depends on the presence of the superstructural load on the top of the pile.

Centrifuge model test study on pile reinforcement behavior of cohesive soil slopes under earthquake conditions

In this study, dynamic centrifuge model tests were conducted to investigate the dynamic response of cohesive soil slopes with the use of stabilizing piles during an earthquake. The behavior of the pile reinforcement was analyzed based on the obtained deformation over the entire slope through image-based measurement, and the behavior of the slope was compared to that of an unreinforced slope. The piles significantly increased the stability of the slope and reduced its deformation during an earthquake. The bending moment of the piles exhibited a nearly triangular distribution due to the earthquake. The acceleration response of the slope increased with increasing elevation, and the displacement accumulated apparently irreversibly over the course of the earthquake. The piles significantly affected the deformation of the slope in a certain area, the boundary of which was defined using a continuous surface. A strain analysis of the slope demonstrated that the piles had a significant effect on the reduction in the deformation of the slope in their vicinities, and this effect expanded upward along the slope and arrested the possible slip surface that would have occurred in an unreinforced slope. Several influencing factors were simulated in the tests, and observation of these factors demonstrated that the dynamic response of the pile-reinforced slope was affected by the pile spacing, pile location, slope gradient, and input earthquake to varying extent.

Centrifuge Model Tests and Finite Element Analyses on Seismic Behavior of Quay Walls Backfilled with Cement-Treated Granular Soils

Dynamic centrifuge model tests and finite element analyses (FEA) were conducted to investigate the seismic behavior of quay walls backfilled with cement-treated granular soils (CTGS). In particular, the effects of the CTGS fill depth and fill range on seismic behavior were investigated. The centrifuge model tests showed that no liquefaction was generated in the CTGS backfills. The quay wall’s horizontal displacement induced by the seismic loading decreased with increases in the CTGS fill depth because the earth pressure acting on the quay wall was reduced. In addition, a wedge-shaped CTGS fill was found to be effective at reducing the horizontal displacement of the quay wall. However, the results of the dynamic FEA indicate that the wedge angle of the CTGS fill should be carefully designed.

Development of Piled Geo-wall (A new type reinforced soil wall

This study aims to achieve a new type of independent reinforced soil wall (Piled Geo-wall) that can be substitute for one made up of concrete with similar scale, and to contribute to sustainable development. In order to confirm the practicability of the novel structure, three experimental studies with static and impact loading tests and a dynamic centrifuge model test were carried out in the past years. Simple design methods of the novel structure, which can reproduce the results of the experiments, are introduced in this paper

Experimental Analyses of Dynamic Damage of the Reinforced Concrete Pile

The earthquake often leads to the damage of stabilizing concrete pile. In order to analyze the damage mechanism of the reinforced concrete stabilizing pile, this article uses the developed concrete model piles, studies the seismic deformation of a slope reinforced with stabilizing piles and the dynamic broken damage phenomenon of pile by using the dynamic centrifuge model test without groundwater. The results show that the earthquake action leads to the obvious increase of dynamic excess bending moments, eventually results in the pile’s breaking damage.