Shaking Table Model Test Research Articles

Quasi-static model test and numerical simulation of a single-story double-span underground subway station

The model test method is crucial for studying the seismic performance of underground structures. Presently, model tests for the seismic response of underground structures are primarily performed with 1-g and N-g centrifuge shaking table. The 1-g shaking table model test is limited by the stress similarity in the soil-structure interaction system and cannot reproduce the seismic damage process and extent of the underground structure. The small table size of the N-g centrifuge model test makes it difficult to reflect the spatial effects of the seismic response of large underground structures. Seeking a large-scale model test method that can directly simulate the seismic damage process is essential for investigating the seismic performance of underground structures. Herein, based on the seismic response characteristics of underground structures, a quasi-static pushover test device applicable to underground structures was designed, and the corresponding tests and numerical model calculations were executed using the Daikai subway station as a prototype. Based on the macroscopic phenomena of structural damage development of the subway station in the test, the damage mechanism of the station structure was analyzed and compared with the numerical model. The strain amplitudes, displacements, and digital scatter strain color maps were analyzed to verify the reliability of the cyclic pushover loading test simulating the seismic performance level and damage process of the underground structure. Simultaneously, the rationality of the proposed quantification system for classifying the seismic performance level of single-story underground structures was verified.

A new counterweight design method for shaking table test models of single-layer spherical latticed shells

Shaking table test is one of the effective methods to study the dynamic behaviors of single-layer latticed shells, and the dynamic behavior of a shaking table test model is significantly affected by the size and installation way of the counterweight. Considering the characteristics of the single-layer latticed shells and the requirement of the test model similarity design, the size of the counterweight needed is normally large. To accommodate the counterweight in the test model, one way is to install the counterweight on the nodes directly and the other way is to enlarge the node size directly to account for the counterweight. Both the methods change the size and configuration of the nodes significantly, which brings additional bending moment and torque forces to the bars or causes a non-negligible reduction of the effective length of the bars. Those problems caused by the counterweight will have considerable influence on the evaluation of the seismic behavior of the single-layer latticed shells. A new counterweight design method is proposed by using multiple layers of upper and lower paired spherical steel shells assembled around a node, which improves the shortcomings of the traditional counterweight in the shaking table test model of single-layer spherical latticed shell (SLSLS). Thin rubber cushions are adopted between two layers of steel counterweight layers to help accommodate the local defects of the counterweight layers when they are not manufactured perfectly so that the counterweight layers can be tightly fixed to the node. With the new method, the improved counterweigh is installed around the node to avoid producing additional forces and keep the satisfaction with the design of the effective length of the bars. The effectiveness of the proposed counterweight design method is verified through theoretical analysis and numerical simulation of the test models. To carry out the finite element (FE) analysis of the test models, the seismic waves input way and the FE model updating method are improved. The static stability capacity of the bars and SLSLSs, and dynamic characteristics and dynamic stability capacity of SLSLSs are discussed to compare the improved counterweight with the traditional counterweight. The applicability of the new counterweight design method to the similarity ratios of the dynamic behaviors of the test models and the prototypes of SLSLSs is also studied under different rise-span ratios and grid-making.

Analysis of Factors Affecting Railway Settlement of Embankment Section due to Liquefaction Using 1-g Shaking Table Model Tests

Herein, 1-g shaking table tests were performed under test by changing the embankment height and non-liquefiable layer thickness below the embankment for the same input seismic load. Accelerometers, pore water pressure transducers, and linear variable differential transformers were embedded inside the foundation ground or installed on the embankment surface to measure their responses to shaking. The testing procedure for analyzing the behavior of a two-dimensional embankment-ground system and well-documented experimental data are presented. The results show that the settlement of the railway embankment placed on the liquefiable sand ground due to ground liquefaction is greatly affected by the embankment height and non-liquefaction layer thickness, which determine the degree of liquefaction and lateral flow of the foundation ground. The embankment settlement increased with the embankment height due to the liquefaction of the ground and increased by twice the settlement of the ground without embankment when the embankment height was approximately 20% of the total liquefiable sand layer. Moreover, the settlement was reduced by over 20% compared to that without a layer when the layer thickness was 50% of the embankment height. Furthermore, the settlement decreased to a negligible level when it was approximately 1.5 times the height of the embankment.

Dynamic Response Law and Failure Mechanism of Slope with Weak Interlayer under Combined Action of Reservoir Water and Seismic Force

The southwestern region of China is close to the Eurasian earthquake zone. Many engineering areas in southwestern China are affected by earthquakes and are close to the epicenter of earthquakes that occur in this region. During earthquakes, slopes with weak interlayers are more likely to cause large-scale landslides. In response to the low stability of slopes with weak interlayers in reservoir dam areas, the dynamic response law and failure mechanism of weak interlayered slopes under the combined action of reservoir water and seismic forces were studied through shaking table model tests and finite element numerical simulation software. The height of the water level and the size of the seismic waves were changed during these tests. The research results indicate that seismic waves are influenced by weak interlayers and are repeatedly superimposed between the weak interlayers and the slope surface, resulting in an acceleration amplification effect that increases by approximately 1.8 times compared to homogeneous slopes. Vertical earthquakes have a significant impact on the dynamic response of slopes, and their peak acceleration amplification coefficient can reach 0.83 times the horizontal peak acceleration. The stability of weak interlayers during earthquakes is the worst within the range of the direct action of reservoir water. The failure mode of a slope is as follows: earthquake action causes cracking in the upper part of the slope, and as the earthquake increases in intensity, and the infiltration of reservoir water intensifies, the cracks expand. The soft and muddy interlayer in the front section of the slope forms a sliding surface, and ultimately, the sliding failure forms an accumulation body at the foot of the slope. In reservoir dam areas, the stability of a slope is closely related to the engineering safety of the reservoir dam. Therefore, when a strong earthquake and the water level in a reservoir jointly affect a weak-interlayer slope, the slope is in the stage of plastic deformation and instability. The stability of the slope may be overestimated, and the slope is likely vulnerable to sliding instability, which needs to be monitored and treated.

Shaking table test on the dynamic responses of shield tunnel in liquefiable stratum

Seismic liquefaction affects badly the safety of the underground structures. For the dynamic responses of the tunnel in liquefied watered sandy stratum in one of the rail transit projects in Shanghai, this paper proposes a tunnel-foundation shaking table model test and analyses the dynamic responses of electrolytic desaturation technology on surrounding soil, which provides some theoretical guidance for seismic designs of Shanghai rail transit projects. The test result shows that the excess pore pressure ratio of soil decreases gradually with the increase of buried depth; sand is easier to liquefy than silt so the tunnel liquefaction and uplift during the sandy section should be paid more attention to; electrolytic desaturation technology works significantly on improving the liquefaction resistance abilities of sand and silt which can effectively reduce the damage caused by tunnel uplift due to seismic liquefaction.

Model tests on static/seismic behavior of three-hinged multi-arch culvert constructed using different embankment processes

A three-hinged multi-arch (THMA) culvert is a new type of underground structure that is gradually being adopted in practical engineering in Japan as an alternative to elevated bridges. However, there exist reports that THMA culverts were seriously damaged by earthquakes in the past, and research on the behavior of THMA culverts during the embankment process and exposure to post-construction earthquakes is insufficient. Therefore, to carefully investigate the static/seismic mechanical behavior of the THMA culvert, systematic 1 g shaking table model tests were carried out in the current study. THMA culverts were constructed using different embankment procedures in dry/saturated sand ground, and then subjected to seismic loading. The results showed that the different embankment procedures significantly affect the deformation mode of the multi-arch culvert on both dry and wet sand grounds, and the construction sequence involving simultaneous backfilling on both sides of the culvert can reduce the generated bending moments during seismic vibration. Furthermore, in all cases, the bending moments generated during the earthquake were significant on both sidewalls of the culvert in the range of 30°–60° from the ground, and the bending moments in the region near the hinges were smaller, which provided basic data for the optimized design of the culvert.

Multiple earthquake-induced progressive failure of bedding slopes with a saturated weak layer: Shaking table model tests

The Longmenshan (LMS) orogenic belt located in the south-eastern Tibetan Plateau has suffered from frequent earthquakes. Despite the fact that multiple earthquakes can accelerate the catastrophic failure of deep-seated bedding landslides by causing rock mass damage accumulation, the seismic deformation evolution characteristics during the progressive failure have received limited attention. This study employs a physical model of deep-seated bedding landslides with a saturated weak layer as a slope prototype to conduct model tests that simulate the progressive failure induced by repeated earthquakes. Embedded sensors and digital image correlation (DIC) technology were used to monitor the seismic response and deformation evolution of the physical model. During the test, sensors embedded in the saturated weak layer recorded the excess pore water pressure (EPWP). The test results revealed that the EPWP responses are highly related to the input parameters of seismic waves and the seismic damage state of the weak layer. In addition, a deformation coefficient (Dc) was proposed to identify the deformation stages consisting of the release of steep tensile failure surface and the shear failure evolution from stable to accelerated deformation. Finally, the test results indicated that historical seismic damage accumulation will make an important contribution to later earthquake-induced coseismic instability, which provide new insight into the initiation of large landslides triggered by low magnitude earthquakes.

Liquefaction Potential of Saturated Sand Reinforced by Cement-Grouted Micropiles: An Evolutionary Approach Based on Shaking Table Tests

Cement-grouted injections are increasingly employed as a countermeasure material against liquefaction in active seismic areas; however, there is no methodology to thoroughly and directly evaluate the liquefaction potential of saturated sand materials reinforced by the cement grout-injected micropiles. To this end, first, a series of 1 g shaking table model tests are conducted. Time histories of pore water pressures, excess pore water pressure ratios (ru), and the number of required cycles (Npeak) to liquefy the soil are obtained and modified lower and upper boundaries are suggested for the potential of liquefaction of both pure and grout-reinforced sand. Next, adopting genetic programming and the least square method in the framework of the evolutionary polynomial regression technique, high-accuracy predictive equations are developed for the estimation of rumax. Based on the results of a three-dimensional, graphical, multiple-variable parametric (MVP) analysis, and introducing the concept of the critical, boundary inclination angle, the inclination of micropiles is shown to be more effective in view of liquefaction resistivity for loose sands. Due to a lower critical boundary inclination angle, the applicability range for inclining micropiles is narrower for the medium-dense sands. MVP analyses show that the effects of a decreasing spacing ratio on decreasing rumax are amplified while micropiles are inclined.

Influence analysis of overlying soil layer to seismic behavior of inclined liquefiable soil and pile interaction system

The statistical data of earthquake hazard indicate that the liquefaction and large lateral flow deformation of ground is one of the main reasons of pile foundation failure. It is significant to focus on the seismic dynamic behavior of pile foundation in inclined liquefiable soil. Based on the Opensees finite element platform, an integrated finite numerical model of inclined liquefiable soil-pile group-structure interaction is established in this study, according to the shaking table model test of inclined liquefiable soil. The nonlinearity of pile-soil contact and the shear localization of soil layer are considered in the numerical simulation. The comparison of the numerical simulation result with the shaking table test results are verified. In order to discuss the influence of different overlying soil layer on the seismic behavior of soil and pile system, a typical inclined liquefiable soil-pile group-structure interaction finite element model is established by the proposed numerical simulation method. The results show that the overlying soil layer has an obvious influence on the seismic dynamic behavior of the pore pressure, the horizontal displacement of soil and pile. The increase of the thickness of overlying soil can reduce the liquefaction degree of sand and improve the mechanical performance of pile foundation.

Experimental Study of Dynamic Responses of Special Tunnel Sections under Near-Fault Ground Motion

Data surveys show that near-fault ground motion does great damage to tunnel structures, especially the portal section and fault zone. In this paper, a series of shaking table model tests of near-fault tunnels were conducted and the surrounding-rock fault-zone-lining model of the near-fault tunnel was established. Accelerometers and strain gauges were arranged at specific locations, and the experimental process of earthquake occurrence was simulated by inputting seismic waves of different working conditions, which obtained the characteristics of stress, damage and deformation of the tunnel model. The tested results showed that the acceleration response of the tunnel portal section was close to the wave shape of the inputted seismic wave, and the acceleration response of the arch shoulder, arch waist and arch foot was more prominent. The internal force of lining at the arch shoulder and arch foot was greater than that at the arch crown, and the peak internal force appeared at the arch foot. The internal force and the maximum or minimum principal stress of the lining under impulse ground motion were larger than those under non-impulse ground motion. Additionally, the surrounding rock had a filtering effect on the high-frequency band of seismic waves. Meanwhile, when the geological characteristics of the fault zone were poor, and the tensile damage first appeared at the arch foot, the compressive damage appeared at the junction of the surrounding rock and fault zone. This study will offer a practical guidance for tunnel engineering earthquake damage.

Experimental Research on the Dynamic Characteristics of Several Model Soils in Small Strain Range and Application in Shaking Table Model Test

Reasonable model soil is very important in shaking table model tests to reduce the distortion of the soil structure stiffness ratio. Several model soils, such as sawdust soil, sawdust sand, rubber granular soil, rubber powder soil, and sawdust kaolin were prepared and a dynamic triaxial test proceeded to determine their dynamic characteristics. The experimental results showed that the variation of the dynamic shear modulus and dynamic damping ratio with dynamic shear strain was consistent with that of undisturbed soil. Finally, sawdust soil was adapted to a shaking table test of complex interaction systems and achieved good results. The results showed that sawdust soil is feasible as model soil. The research results can provide helpful references for the design of a similar shaking model test.

Design method of frequency similarity relation for shaking table model test

It is very important to determine the dynamic similarity relation in the shaking table model test. The accurate dynamic similarity relation can make the model reflect the dynamic characteristics of the prototype to the greatest extent. This paper describes the principle of similarity design for shaking table model test and reviews the related literature. According to the different research objects and purposes, four common similarity design methods including separation similarity method, artificial mass method, less artificial mass method and ignoring gravity method are summarized. Analysis of the shortcomings of the method of deriving frequency compression ratio from static factors in the design of seismic wave similarity relation. The Duhamel integral analytic expression of the structure motion equation under earthquake is analyzed. The seismic response of the structure is closely related to the natural vibration frequency of the structure. A design method using frequency as input seismic wave similarity design control quantity is proposed. The natural vibration frequencies of the prototype and the model are studied by means of the Gonza landslide field ground pulsation test and the model white noise excitation. A new frequency compression ratio design scheme is given from the perspective of dynamic similarity. It is of great reference significance to optimize the dynamic similarity design of shaking table model test and improve the accuracy of test results.

Liquefaction characteristics in triaxial tests under various gravity environments – DEM analyses

Liquefaction of sands occurs when the effective stress becomes zero during undrained loading, and the state of liquefaction is often considered that individual particles do not transmit contact forces. In shaking table model tests, seepage flows towards the surface occur during liquefaction; this potentially maintains individual particles floated as the gravitational forces can be cancelled out by the upward seepage forces. In laboratory element tests, however, undrained conditions induce no seepage flows during liquefaction. This raises a key question of how the individual particles behave during liquefaction in element tests, and how the macroscopic mechanical response is affected due to gravity. To answer these questions, this contribution conducts a series of triaxial loading simulations using the discrete element method (DEM) considering the effect of gravity on the mechanical response of spherical particle assemblies. The results reveal that the presence of gravity affects both packing properties and liquefaction characteristics. Inter-particle contacts are maintained during liquefaction under non-zero gravity conditions. Although the liquefaction resistance is merely affected due to gravity, the stress–strain relation and stress path are measurably altered. This contribution highlights the importance of considering the potential effect of gravity when laboratory or DEM results on liquefaction phenomena are interpreted.

Shaking table test study on dynamic performance of a base-isolated frame structure under an isolation bearing removal scenario

Studies on the progressive collapse of structures have been at the forefront in structural engineering domain recently. The progressive collapse of isolated structures is quite different from that of conventional fixed-base structures. Once an initial failure occurs in the isolation layer which is the most vulnerable to accidental events due to the low horizontal stiffness, progressive failures at other locations may lead to a large-scale collapse of isolated structures. This paper presents a 1:4 scale model shaking table test of a three-story irregular plane reinforced concrete (RC) frame isolated structure to investigate the progressive collapse resistance of isolated structures. An edge bearing was removed quickly by an electromagnetic failure excitation device during the first seismic input case. The dynamic responses such as the macroscopic crack distribution, acceleration responses, displacement responses, internal forces of the isolation bearings, and concrete and reinforcement strains of the failure span beams were evaluated. The results show that the significant vertical deformation with dynamic impact response was produced at the failure point under multi-directional dynamic coupling excitation, i.e., the combined effect of the vertical unbalanced load caused by sudden failure of a bearing and horizontal earthquakes. This sudden failure of the isolation bearing not only had an impact on the internal forces of bearings adjacent to the failure bearing, but also on other non-adjacent bearings. As the tensile and compressive stress of adjacent bearings were more likely to exceed design limits under earthquakes, the risk of overturning collapse for isolated structures markedly increased following the failure of a few bearings. In addition, vertical and low-frequency components of earthquakes could have a significant influence on dynamic responses and damages of isolated structures, especially in the area of bearing failure. The experimental results obtained in this study act as important references for the progressive collapse design of isolated structures.

Static and Dynamic Load Transfer Behaviors of the Composite Foundation Reinforced by the Geosynthetic-Encased Stone Column

An accurate description of the load transfer behaviors of the geosynthetic-encased stone column (GESC) is of great importance for revealing the bearing capacity of GESC. Static load tests and shake table model tests were performed to characterize the static and dynamic load transfer behaviors of the composite foundation reinforced by the GESC. Under static loading, static load tests were conducted on a fully geosynthetic-encased stone column (FGESC), partially geosynthetic-encased stone column (PGESC) and traditional stone column (TSC). The influence of length and stiffness of the encasement on the stone columns were investigated. Under seismic loading, the shake table model tests were performed to analyze the differences of the dynamic pile-soil stress responses between the composite foundations with the GESC and the TSC. The results show that the static pile-soil stress ratios of the composite foundation with the FGESC are about three to six times of those of the composite foundation with the TSC, and the difference increases with the increase in the stiffness or length of the encasement. The static vertical stress of 60% acting on the pile top can be transferred to the pile bottom for the FGESC, while only 27~45% for the TSC. The dynamic pile-soil stress ratios of the GESC and the TSC first decrease and then increase slightly with the increase of the input peak acceleration. The dynamic pile-soil stress ratio of the GESC is about three times that of the TSC under seismic excitation with the same type and peak acceleration. The attenuation rate of dynamic stress along the pile body under dynamic loading is much faster than that under the static loading. Under the static and dynamic conditions, the load transfer capacity and pile efficacy of the GESC are always better than those of the TSC.

Experimental study on horizontal pressure of column-supported concrete group silos under earthquake force

ABSTRACT The overpressure of silo wall caused by granular materials under earthquake is one of the main reasons of silo damage. Two shaking table model tests were carried out with column supported silos and independent single silos, respectively. The seismic response of silo granular materials was analyzed first, and then the dynamic lateral pressure of silo wall under different levels of earthquake and overpressure coefficient were obtained. The results showed that the interaction between the granular materials and the silo wall in the group silos is related to the position of the individual silo. The seismic response of granular materials is linked with the spectral characteristics of seismic waves. The overpressure coefficients of the corner silo and the side silo are greater than that of the independent single silo with a 7% and 9% higher value, respectively. Apparently, the seismic response characteristics of the independent single silo are totally different from that of the group silos. It was concluded that when designing the wall of the group bin, the position of the bin should also be considered.

Shaking Table Test and Numerical Simulation Study of the Reinforcement Strengthening of a Dam

This paper presents experimental and numerical investigations of the seismic failure of the reinforced and unreinforced monoliths of the Huangdeng concrete gravity dam. To verify the scale factors, we use suitable materials (emulation concrete material and fine alloy wire) to simulate the dam concrete and the steel reinforcement (SR) in a scaled experiment model that includes the water-retaining monolith and overflow monolith of the dam. We design shaking table model tests based on the similarity laws and perform nonlinear numerical simulations of damage to the dam. By comparing the numerical simulation with the experimental results, the intervals for peak acceleration, in which microcracks appear and macrocracks rapidly expand, are obtained. The modal and damage distribution results verify the proposed design method for the scaled experimental model with SR. By analyzing the results, we reveal the crack resistance mechanism of SR. This research provides a rational foundation for further study of the similarity laws for reinforced dams.

Evaluation indicators of saturation on partially saturated sand induced by microbial gas

The induced partial saturation (IPS) technique introduces a certain amount of air/gas into soil voids to mitigate sand liquefaction. The microbial desaturation method utilises biological metabolic processes which are good for environmental protection and disaster prevention. Real time monitoring and quantitative analysis of the saturation after microbial bubble generation are the first step in the field application of the IPS method. In this study, shear wave velocity measurements were taken using the pre-vibration technique through an array of accelerometers at different depths on the basis of shaking table model tests. The shear wave velocity was obtained during the desaturation of microbial gas production. The arrival time of the first wave peak increased and the shear wave velocity decreased with the decreasing saturation. The shear wave velocity decreased with the saturation, and the rate of shear wave velocity decreased when the degree of saturation reduced to 90 %. This result indicates that the shear wave speed is effective as an indicator of saturation in microbial gas production. The shear wave velocity decreases with the saturation, and the relationship between the two satisfies the exponential functions. A quantitative relationship was established between the saturation and shear wave velocity during microbial gas production. The maximum shear modulus decreases with the saturation during the gas production process. Meanwhile, the relationship between shear wave velocity and resistivity was established using resistivity meters. The resistivity value decreases with the degree of saturation. The power function relationship between resistivity and saturation was satisfied in this experiment. The explicit analysis of the saturation data at each point in the desaturation method has significant research value for field trials using high-density electrical resistivity tomography. The research results obtained in this experiment can help in the quantitatively analysis of the uniformity and effectiveness of bubble distribution in the field test application of the microbial desaturation method and provide a basis for the engineering application of the microbial desaturation method in field tests.

Seismic response analysis of slope reinforced by pile-anchor structures under near-fault pulse-like ground motions

Many post-earthquake investigations have found that natural slopes and geotechnical structures near the faults can be seriously damaged by earthquakes. Pile-anchor structure is one of slope reinforcement measure that widely used in earthquake-prone areas due to its flexible characteristic. To explore the seismic responses and behavior of slopes reinforced by this kind of retaining structure near faults, a series of shaking table model tests were performed. The effect of pule-like ground motions on the seismic responses of system are systematically analyzed by the results from the excitation of pulse-like and no-pulse ground motions in terms of acceleration responses, amplification effect, wave reflection effect and the soil-structure interaction effect. The results demonstrate that the pulse-like ground motions can seriously aggravate the seismic responses and reduce the stability of the system. To better reveal the effect from the pulse-like ground motions, a special shaking scenario, based on the semi-artificial ground motions generated by the wavelet analysis approach, was also conducted to study the effect from different components in the pulse-like ground motions on the seismic responses of system. The results obtained in present study can promote the understanding of the seismic behavior of slopes and slope retaining structures under the pulse-like ground motions, and provide a basis for the seismic design of pile-anchor structures near the faults in earthquake-prone regions.

Assessing uncertainty in fast Bayesian modal identification based on seismic structural responses

Modal identification is an important step to evaluate the basic modal properties of structures using measured data. In this process, the existence of modeling error and measurement noise will inevitably lead to uncertainty in modal identification. A Bayesian framework was established to determine the optimal values of modal parameters efficiently based on the structural response under earthquake excitations. In this paper, in the same framework, a new method is presented to determine the analytical formulation for carrying out uncertainty evaluation of modal parameters utilizing seismic structural responses. Based on Bayes’ Theorem, the covariance matrix can be calculated based on the Hessian matrix determined using the negative log-likelihood function (NLLF). In this work, for determining the Hessian matrix, a series of formulations were derived analytically. Simulated data of a six-story building were generated to investigate the new formulations. The noise effects on the posterior uncertainty were investigated. After the verification, applications were carried out using the data in a shaking table test model under laboratory conditions and a real building from a field test. The modal properties and their uncertainty obtained by the proposed method were studied under different earthquake excitations.