Large-scale Shaking Table Model Test Research Articles

Seismic fragility analysis of slopes based on large-scale shaking table model tests

Seismic fragility analysis is one probabilistic method that represents the conditional probabilities of exceeding different predetermined damage states for various given earthquake hazard levels, which is the essential part of probabilistic seismic risk assessment. It has gained much popularity recently because much more comprehensive and richer results than traditional probabilistic methods can be provided. The classical seismic fragility analysis of slopes is always performed through analytical approaches. In the present study, a novel seismic fragility analysis framework combined with shaking table model test results is proposed for probabilistic seismic performance and risk assessment of slopes. The shaking table model tests of a rock slope reinforced by pile-anchor structures were firstly performed subjected to a suite of real earthquake records with different intensity levels. Subsequently, the seismic responses from shaking table model tests were then gathered for the optimal analysis to determine the optimal engineering demand parameter (EDP) and earthquake intensity measure (IM) for seismic fragility analysis of slopes. At last, the identified most appropriate IM and EDP were selected to construct the scalar-valued fragility curves, vector-valued fragility surfaces and fragility surfaces considering acceleration elevation amplification effect by the proposed framework. The results indicate that using single IM to construct scalar-valued fragility functions may result in different failure probabilities depending on the chosen earthquake IM. The vector-valued fragility surfaces provide more information than ordinary fragility curves, and lead to more proper and realistic evaluations of seismic hazard of slopes. The methods and results presented in this paper also provide the basis for the probabilistic seismic risk and loss assessment of earthquake-induced slope geological disaster.

Large-scale shaking table model tests and numerical simulation for composite reinforcement aseismic measure of high earth rockfill dam

<p indent="0mm">The aseismic safety of high earth rockfill dams is an important problem in engineering construction in the intensive earthquake area of West China. A composite reinforcement aseismic measure (CRAM) for high earth rockfill dams was developed. The CRAM’s effectiveness and reliability were validated using comparative model tests on a large-scale shaking table. Numerical simulation was used to examine the CRAM’s reinforcement mechanism. The results demonstrated that the CRAM had an inhibiting effect on the acceleration response; the CRAM can effectively inhibit the loosening and slipping of rockfill at the crest and reduce earthquake-induced permanent deformation. The numerical simulation also revealed that the shear strain amplitude and distribution were significantly altered. A slightly larger shear strain appeared at the front of the CRAM’s internal reinforcement materials, and the dam slope’s potential sliding surface was transformed from shallow sliding to deep sliding. As a result, the CRAM can improve the high earth rockfill dam’s seismic safety. The research results can provide a reference for the seismic design of the high rockfill dam in the intensive earthquake area.

A Method for Quantitative Evaluation of Seismic Stability of Loess Slope Based on the Shaking Table Model Test

The large-scale shaking table model test, which can directly reproduce the process of slope instability and failure, is an important technical means for the prediction and evaluation of slope seismic stability. However, up to now, the systematic slope stability evaluation method based on the shaking table slope model test has not been established, which limits the application of the expensive shaking table model test in slope seismic design. Therefore, the slope stability evaluation method based on the model test needs to be developed and innovated. In this research, through three loess slope model tests with different rainfall, according to the change law of the peak value of transfer function spectrum, combined with the macrodestructive characteristics of the slope model, an accurate calculation method of the critical instability acceleration of the slope is proposed. Based on the behavior similarity theory, for the shaking table model test of slope whose soil cohesion cannot meet the similarity ratio, the reduction method of applying the critical instability acceleration obtained from the model test to prototype slope is proposed. Based on first-order natural frequency and damping ratio extracted from the TF spectrum curve, a calculation method for the stability factor Fs of loess slope based on the shaking table model test is proposed, and the stability factors of loess slope under the action of different seismic ground motion would be quantitatively calculated. The above methods provide another effective way for qualitative prediction and evaluation of seismic stability of loess slope.

Dynamic response characteristics and failure mode of a bias loess tunnel using a shaking table model test

The shallow bias section at the tunnel portal is one of the most seriously damaged areas under earthquake conditions. The seismic responses of the loess slope and the tunnel structure interact in a bias tunnel-loess slope coupling system. In this study, a 1:25 large-scale shaking table model test on the bias loess tunnel is conducted, and the seismic responses and failure modes of the loess slope and bias tunnel are analyzed. Additionally, the interaction between the tunnel structure and loess slope is studied. The experimental results show: (1) Tunnel structure influences on the acceleration distribution characteristic of the slope. The closer the soil at the slope surface is to the tunnel, the higher the peak ground acceleration (PGA) amplification factor. (2) Slope also has an impact on the seismic response of the tunnel structure. The peak accelerations of the tunnel vault and the sidewall at the shallow-buried side are larger than those of the tunnel invert and the sidewall at the deep-buried side. (3) Under earthquake conditions, several tensile cracks appear in the slope top, and shear failure appear along the slope foot to the slope surface above the tunnel vault. (4) Hances and arch feet are easily damaged in an earthquake, and the seismic damage of lining at the deep-buried side is more severe than that at the shallow-buried side.

A large-scale shaking table model test for acceleration and deformation response of geosynthetic encased stone column composite ground

Effective mitigation of seismic-induced ground hazards requires an improved understanding of ground response in terms of earthquake wave propagation and ground deformation. Here, this paper examines the effects of geosynthetic-encased stone columns (ESCs) and ordinary stone columns (SCs) on the acceleration amplitude and frequency content responses of sand profiles, and the deformation of the ground using a large-scale shaking table model test. The model was excited by 15 shaking events including El Centro motion, Wenchuan Qingping motion and Kobe motion with peaks ranging from 0.1 to 0.9 g. The results indicate that the ESCs more significantly amplify surface accelerations compared to the SCs in the frequencies ranging from 10 to 17 Hz and from 2.5 to 9 Hz. The horizontal peak acceleration values in the ESCs composite ground are approximately twice those of the SCs composite ground. The acceleration response of the ground is influenced by the applied acceleration peak and frequency content, reinforced type, and structure. After the seismic excitation, the ESCs composite ground develops much narrower surface cracks distributed in a larger area compared to the SCs.

Experimental Study on Structure Water Support Interaction of Large Aqueduct

Based on the large-scale shaking table model test of aqueduct, the interaction and influence of large-scale aqueduct structure-water-damping bearing were studied. Through the dynamic detection of white noise, the free vibration characteristics of aqueduct model under different working conditions were obtained. Based on the comparison of seismic responses of aqueduct under three conditions of water, half water and normal water level and two states of locking and releasing damping bearing, the influence of water quality and damping bearing on natural frequency, dynamic water pressure and dynamic strain of aqueduct structure was studied. By inputting Ricker waves with different frequencies, the correlation among the input wave frequency, the fundamental frequency of aqueduct structure and the frequency of water sloshing and the influence on the aqueduct response were studied. The experimental results show that with the increase of water quality, the interaction between water and aqueduct structure enhanced, which had a great influence on the fundamental frequency of aqueduct structure, and the influence of water level presented an obvious nonlinear. The hydrodynamic pressure decreased along the middle section elevation of the aqueduct, and the acceleration increased with the increase of the tank elevation, which reflected the complexity of the interaction between water and aqueduct structure. The results provide support for the seismic design of aqueduct and the application of shock absorption bearing.

Study on Dynamic Response Characteristics of Slope with Double-Arch Tunnel Under Seismic Action

To study the seismic dynamic characteristics of the slope with double-arch tunnel, a large-scale shaking table model test of slope with double-arch tunnel whose scale is 1:20 was designed and finished. A series of tests were performed with different excitation direction seismic waves including WC, EI and Kobe seismic wave whose peak are 0.1 g, 0.2 g, 0.4 g, 0.6 g. The influence of seismic wave type and excitation intensity on the dynamic response of the slope with double-arch tunnel were discussed. The results show: (1) As the slope height increases, the acceleration amplification coefficient shows a non-linear trend. The acceleration response characteristics of the slope under WC-XZ excitation are different from those of K-XZ and EI-XZ. (2) Different types of rocks have different amplification effects on acceleration. At the rock mass interface, the acceleration amplification effect is more obvious. (3) The acceleration magnification factor at the top of the slope is relatively large, which is susceptible to earthquake damage, rock ejection and other damage phenomena. (4) The slope has a filtering effect on the high frequency band of seismic waves. (5) The peak value of the dynamic displacement response of the slope increases non-linearly with the increase of the slope height. The peak of the dynamic displacement response at the top of the slope is large, while the peak of the vertical displacement at the foot of the slope is large. (6) The response characteristics of slope acceleration and dynamic displacement under earthquake are related to the type of seismic wave, the location of the measuring point, and the nature of the rock mass. Significance guidance for seismic study on the slope with double-arch tunnel was provided.

Analysis of the stability and seismic behavior of the geosynthetic-reinforced embankments under earthquake

The stability and seismic behavior of geosynthetic-reinforced embankments during the earthquake is not well known. In this paper, the damage types of embankments were summarized, and the seismic stability of reinforced embankment were analyzed through an earthquake damage investigation in the Wenchuan earthquake region. Then, large-scale shaking table model tests were performed on the geosynthetic-reinforced embankment. The results show that the damage level of the reinforced embankment was almost less than that of the unreinforced embankment. The peak seismic earth pressure was nonlinear along the height of the embankment, the largest peak seismic earth pressure was roughly in the middle of the embankment slope. The peak ground accelerations (PGA) amplification factor first showed an increasing pattern and then a decreasing pattern with the increase of elevation, but there was a final increasing trend along the height of the reinforced embankment. The results can help to establish the proper design of the reinforcement embankments under earthquake conditions.

Shear Effects on the Anchorage Interfaces and Seismic Responses of a Rock Slope Containing a Weak Layer under Seismic Action

The shear effects on the anchorage interfaces under seismic action is a key problem requiring urgent investigation in the field of rock and soil anchorages. In this paper, the model of rock slope with a weak layer was constructed by pouring, and the large-scale shaking table model test was completed. The shear strain on the anchorage interfaces and the acceleration of the slope were collected using built measurement systems. The shear effects on the two anchorage interfaces (a bolt-grout interface and a grout-rock interface) and seismic responses of the slope under seismic action were investigated. The distribution laws of the shear stress on the two anchorage interfaces along the axial direction of the bolt under seismic action were gained. The variations of the peak acceleration amplification coefficient on the slope surface, the magnitude, and the growth rate of peak shear stress on the anchorage interfaces under seismic action with different excitation directions and intensities were obtained. Furthermore, the positive relationship between the shear effect on the anchorage interfaces and the seismic response of slope was revealed. This study provides support for theoretical research, numerical simulation analysis, and aseismic design of rock and soil anchorages under dynamic conditions.

Dynamic-response characteristics and deformation evolution of loess slopes under seismic loads

The Loess Plateau is one of the most seismically and geologically active regions in China. The related catastrophic earthquakes and geological disasters have caused more than 1.4 million deaths in the plateau. In this study, the slopes on the edge of the loess tableland in Pingliang City, Gansu Province—the core area of the Loess Plateau—are investigated. Based on large-scale shaking-table model tests and discrete-element numerical simulation—particle flow code (PFC 2D), the dynamic-response characteristics and deformation evolution process of fissured and non-fissured loess slopes under different seismic loads are studied. The test results show that with increasing seismic load input, the peak ground displacement (PGD) of the loess slopes increases gradually with increasing slope height. For the two types of slopes, the acceleration amplification effects in the slope with horizontal direction load are larger than those of the vertical direction load. The amplification factor of the peak ground acceleration (PGA) at the shoulder of the fissured slope is significantly larger than that of the non-fissured slope. According to the numerical simulation results of the fissured slope, when the seismic load is small, the bond-failures are distributed densely in the initial fissured structural plane and at the model bottom. Regarding the non-fissured slope, the bond-failures in the slope are mainly distributed at the bottom of the model. With increasing acceleration amplitude, the number of bond-failures in the slopes increases rapidly. When the input load increases to 0.40 g, two potential slip surfaces occur in the shallow surface of the fissured slope and a potential slip surface appears at the back edge of the non-fissured slope.

Large-scale shaking table model test on seismic performance of bridge-pile-foundation slope with anti-sliding piles: a case study

This study aimed to illustrate the seismic performances of anti-slide pile-reinforced bridge foundations in landslides. Based on the anti-slide reinforcement project at Yousuotun along the Chengdu-Lanzhou high-speed railway under construction, shaking table tests were performed on a double-row anti-slide pile-reinforced bridge foundation and landslide model with a 1:40 similitude ratio. Given that the similitude law was satisfied, seismic waves with different frequencies and acceleration amplitudes were input as base excitations to monitor the responses of dynamic parameters: slope acceleration, earth pressure, and pile strain. The amplification effect of peak ground acceleration (PGA) was analyzed. The landslide thrust distribution characteristics and slope response processes were further studied to verify the seismic design of such bridge foundations in landslide-prone areas. The response acceleration of the slope subjected to seismic loads showed a nonlinear amplification “elevation effect”, “surface effect”, and “geological structure effect”. When the distance between the bridge foundation and the back-row anti-slide pile was small, the pier maintained a relatively large PGA amplification factor and was subjected to strong seismic loads. The landslide thrust was mainly borne by the upper part of the back-row anti-slide piles as its distribution changed from spoon-shaped to bow-shaped. Under high-intensity earthquake events, the load-bearing section of the bridge foundation should be strengthened at the sliding surface. Anti-slide piles can effectively limit the dynamic response of the landslide and weaken the seismic response of the slope. The results of testing this reinforcement are the first results proving that the seismic design of reinforced bridge foundations with anti-slide piles can be reliable.

Shaking Table Test and Numerical Verification for Free Ground Seismic Response of Saturated Soft Soil

This paper investigates shaking table test (1g) and numerical simulation (fully coupled) of vertically propagating shear waves for saturated soft free field. A large-scale shaking table model test was performed to study seismic response characteristics of saturated soft soil free field. According to test results of seismic response features of free field system in saturated soft soil, the free field nonlinearity fully coupled numerical model of dynamical effective stress of saturated soft soil was established using OpenSEES, based on the u-p formulations of dynamic consolidation equation as well as effective stress solution method for saturated two-phase media. The numerical simulation of the free field seismic response of saturated soft soil under various test conditions was performed and the calculated results were compared with the shaking table test results. The results show the following. (1) With the increase of input ground motion intensity, the characteristic frequency of the saturated soft free ground decreases and the damping ratio increases gradually. (2) The saturated soft soil ground has short period filtering and long period amplification effect on the horizontal input seismic loads. The failure foundation takes on the isolation and shock absorption under strong ground motions. (3) The peak pore pressure ratio of the saturated soft soil ground is located in the shallow buried soil layer, and with the increase of the input ground motion intensity, the advantage of dynamic pore pressure ratio in this area is gradually weakened. (4) The numerical simulation results are consistent with the results of the shaking table test. This fully coupled effective stress numerical method can reasonably simulate the seismic response characteristics of free field in saturated soft soil, which lay the foundation for other more complex parameter extrapolation models of saturated soft soil sites. This research can provide the necessary technical experience for experimental study on non-free field.

Experimental Study on Seismic Dynamic Characteristics of Shallow-Bias Tunnel with a Small Space

In order to obtain the seismic dynamic characteristics of a shallow-bias tunnel with a small space, a series of large-scale shaking table model tests were carried out. The key technology of the test is introduced in detail, for example, similar ratios of model, test equipment, testing model box, testing model, sensor arrangement, seismic waves, and testing system. The results show that the first predominant frequency is similar between measuring points. However, the second predominant frequency is highly different between measuring points. The first and second predominant frequencies gradually decrease with the increasing of input PGA. The rock stratum can shield seismic wave in the high frequency band. The research results provide reference for similar tunnels.

Seismic responses of deep buried pipeline under non-uniform excitations from large scale shaking table test

The seismic response of long deep buried pipeline under non-uniform excitation is very important for suitable seismic design. However, due to restriction by excitation devices, few model tests have been carried out. In this study, a large-scale shaking table model test for a long deep buried pipeline was carried out, where two controlled-independent tables were used to excite two model containers and the excitations for the two tables are in the three directions and non-uniform. From the model test, the strains and deformations of the pipeline and the accelerations of the soil in containers were measured and evaluated. Some results were achieved: (1) non-uniform seismic excitation has great influence on the acceleration amplification in soil and the strain and displacement of the pipeline; (2) the deep buried pipe in ground has few impact on ground surface acceleration response, but has greater impact on the acceleration response of the soil surrounding the pipe; (3) the bending stain and permanent displacement under uniform excitation are negligible, but not neglected for non-uniform excitation; (4) the model test proves that there is obvious rotation of the pipeline in addition to horizontal and vertical displacements under non-uniform excitation.

Large-scale Shaking Table Model Test Research on Bai He Tan Hydropower Station Left Bank Slope

The large-scale shaking table model test for a large engineered slope was conducted in this paper to reveal the slope seismic failure mechanism and analyze the seismic motion magnification effect along the slope height, in which dynamic stability of the slope could be evaluated. The model design, seismic motion input method, test program and measuring point arrangements are introduced. The model slope dynamic properties are obtained. The test results indicated that the tested slope is stable under design earthquake, and there are large safety margin.

Seismic behaviors of soil slope in permafrost regions using a large-scale shaking table

Large-scale shaking table model tests were carried out to study the dynamic behaviors of slopes and failure mechanism of landslide in permafrost regions. The model slope was constituted of silty clay layer stacked on an ice layer with 8° surface slope. Acceleration, displacement, and pore pressure were measured subjected to vertical and horizontal seismic loadings. The horizontal wave has a stronger influence on the failure of the model than the vertical wave motion, and the natural frequency of vibration in the horizontal direction decreased obviously at the failure state. The model slope has three components of different nonlinear mechanical properties, which are the soil layer, soil-ice interface, and ice layer. The amplification factor of peak ground acceleration is obviously smaller at the soil-ice interface than that at the soil and ice layer. The acceleration responses are nonlinear because of the nonlinear soil properties and degradation of modulus with increasing horizontal acceleration. Especially, excess pore pressure generation was observed near the soil-ice interface of the slope subjected to higher input acceleration, which resulted in the decrease of the effective stress. Failure surface appeared to be the soil-ice interface, which was consistent with the field observations of landslides in permafrost regions. Slope failure could be defined based on the massive movement of the slope, characterized by integral sliding pattern along the soil-ice interface without the distinct deformation inside the sliding body. The results show that the sliding of the slope with soil layer at gentle gradient is mainly triggered by the combined action of horizontal seismic wave, existence of soil-ice interface, and pore pressure generation in permafrost regions.

The Large-Scale Shaking Table Model Test of the Shallow-Bias Tunnel with a Small Clear Distance

A physical shaking table test model of the shallow-bias tunnel with a small clear distance whose scale was 1:10 was performed to study the type, direction and acceleration peak of the seismic wave which have an immense influence on the dynamic response characteristics of the tunnel. In shaking table model test, the Wen Chuan wave (wc–xz), Da Rui wave (dr–xz) and Kobe wave (k–xz) were adopted as loading wave in x, z-direction (horizontal and vertical direction loading at the same time). The results show that under the action of seismic wave, the acceleration amplification factor of z-direction is generally larger than that of x-direction. Compared with the lining of the right hole, the acceleration amplification factor and variation trend of the lining of the left hole are highly different. The strain is less affected by the type of seismic wave, but that is greatly affected by acceleration peak. The tension strain increases with the increase of the acceleration peak of seismic wave, and is larger than the compression strain at each measuring point. The variation trend of tension strain is more intense than the compression strain.

Experimental study of motion characteristics of rock slopes with weak intercalation under seismic excitation

In order to investigate the effect of a weak intercalation on slope stability, a large-scale shaking table model test was conducted to study the dynamic response of rock slope models with weak intercalation. The dynamic response of the prototype slopes were studied in laboratory with the consideration of law of similitude. The initiation failure was observed in the rock slope model with a counter-tilt thin-weak intercalation firstly, not in the slope model with a horizontal thin-weak intercalation. Furthermore, it was interesting that the fracture site is shifted from crest top to the slope surface near the weak intercalation, which is different with the location of failure position in a normal layered slope. We also discussed the effect of the dip angle and the thickness of weak intercalation on the failure mechanism and instability mode of the layered rock slope. From the experimental result, it was noted that the stability of the slope with a counter-tilt weak intercalation could be worse than that of the other slopes under seismic excitation. The findings showed the difference of failure in slopes with a horizontal and counter weak intercalation, and implicated the further evaluation of failure of layered slopes caused by seismic loads.

Large-scale shaking table model tests on seismically induced failure of Concrete-Faced Rockfill Dams

An increasing number of high Concrete-Faced Rockfill Dams (CFRDs) have been and are being built in highly seismic hazardous regions. Because there are few examples, the failure mechanisms for each damaged CFRD still remain unclear, which prevents a rational evaluation of aseismic performance of a CFRD. In this paper, a series of large-scale shaking table tests are conducted to determine the dynamic failure modes of CFRDs, especially the failure mechanism of the face slab. A type of model slab material is developed according to similitude rules. Particle Image Velocimetry (PIV) is used and improved to track the motion of each grain and subsequently measure the entire velocity field of the deforming cross-sections of dam models. The failure processes of the dams, the failure mechanisms of the slab fractures and the slab dislocations are discussed based on the experimental results. The experiments indicate that large deformations of the uppermost part of the dam caused the face slab to curve upward and crack. Another important fracture morphology of the face slab is the dislocation of its joint. The change in the granular fabric caused the granular slope to slide down and thrust outward, eventually dragging the upper half of the face slab down against its lower half; this motion is accompanied by the formation of a joint dislocation. Therefore, the stability and anti-deformation ability of both the downstream slope and the crest region of the upstream slope should be improved to withstand earthquake. The results of the shaking table model tests are consistent with the numerical simulation, and both results support the prototype dam׳s seismically induced failure characteristics.

Large-scale shaking table model tests of aseismic measures for concrete faced rock-fill dams

The aseismic design of concrete faced rock-fill dams (CFRDs) has become vitally important in recent years. A series of 1-g large-scale shaking table model tests were conducted, applying similitude laws to evaluate the effectiveness of various aseismic measures. The following four reinforcing measures are discussed in this study: reinforcing the top zone with geogrid, protecting the downstream slope surface using stone block, replacing the top zone of the dam with cemented rock-fill material or concrete layers. The failure developments were visualised using the particle image velocimetry (PIV) technique. The mechanisms of these reinforcement measures were analysed in detail. The effectiveness of these measures was evaluated by comparing the crest settlement rates and key accelerations corresponding to surface grain yield, slab fracture and slab dislocation. Based on the model test results, a combination of reinforcement measures was proposed for the prototype CFRDs.