shaking table soil

large-scale shaking table tests on the seismic responses of soil slopes with various natural densities - sciencedirect

large-scale shaking table tests on the seismic responses of soil slopes with various natural densities - sciencedirect

Large-scale shaking table tests of soil slopes with different natural density distributions were carried out.The failure processes and mechanisms of slopes were summarized under earthquake.The effect of natural density on acceleration amplification effect of soil slopes was discussed.The influence of acceleration Fourier spectrum on slope damage law was clarified.The dynamic strain response and shear stress-strain behaviour of soil slopes were revealed.

To distinguish how the natural density of soil affects the seismic response of a soil slope, three large-scale shaking table tests are conducted on slopes of different densities under seismic excitations. The natural density of the homogeneous dense slope (HDS, case #1) is 1.65g/cm3; that of the heterogeneous graded slope (HGS, case #2) increases from 1.35g/cm3 to 1.65g/cm3 with depth; that of the homogeneous loose slope (HLS, case #3) is 1.35g/cm3. The failure processes, acceleration response laws, spectral characteristics, dynamic strain responses and shear stress-strain behaviours observed during the three tests are compared. The results show that the soil density distribution has a significant effect on the seismic response of a slope. The HGS and HLS fail suddenly under peak ground accelerations (PGAs) of 0.6g and 0.5g, respectively. The failure zone in the upper HLS is larger than that in the HGS. The acceleration amplification effect of the HDS is weak, while those of the HGS and HLS gradually increase with the PGA. The position and energy required to produce a nonlinear acceleration amplification factor effect are closely related to the natural density of the slope. The acceleration amplification factors of the HGS and HLS show nonlinear effects at 0.50 times and 0.357 times the slope height, respectively, and the corresponding PGAs are 0.4g and 0.3g. With an increasing natural density, the acceleration amplification factor decreases gradually, and more energy is required for the slope to fail under earthquake activity. The acceleration response law is related to the shape and amplitude of the peak in the fast Fourier transform (FFT) spectrum. The dominant frequency differences among the FFT spectra show that the lower the natural density of the slope is, the lower the location of damage in the slope. Combining the results of the peak micro-strain and shear stress-strain behaviour of the three slopes, the shear modulus of the HDS is the highest, and that of the HLS is the lowest.

shaking table modeling of mse/soil nail hybrid retaining walls - sciencedirect

shaking table modeling of mse/soil nail hybrid retaining walls - sciencedirect

A series of 1-g shaking table tests using variable-amplitude harmonic excitations was performed on 0.8-m-high MSE/soil nail hybrid retaining (MSE/SN) wall models to investigate the seismic behavior of this innovative retaining earth structure. The tests were conducted on physical wall models with strips having a constant length and different nail lengths under loading conditions with different peak accelerations and durations. It was found that the deformation mode and the horizontal displacements of the MSE/SN walls were highly dependent on the length of the nails, such that L/H=0.7 can be defined as the critical ratio in seismic conditions for MSE/SN walls which have been reinforced with strips having a constant length. Irrespective of the different nail lengths, the pattern of the observed failure mechanism included a moving block which was delineated by a two-part failure plane consisting of a concave curve and an inclined line with a certain point of intersection. Also, a consistent range of the normalized horizontal displacements (x/H), about 0.551.10%, corresponding to the formation of local shear bands, and a range of x/H=5.05.6%, corresponding to the development of active wedge failure, were determined.

seismic response of soil slopes in shaking table tests: effect of type and quantity of reinforcement | springerlink

seismic response of soil slopes in shaking table tests: effect of type and quantity of reinforcement | springerlink

To study the effect of reinforcement type and quantity on the response of model slopes in this study, a series of shaking table tests were carried out on model slopes reinforced with different quantities of geotextile and geogrid. Model slopes were constructed to an angle of 45 using poorly graded sand. Acceleration of base shaking and shaking frequency were varied in different tests. The response of model soil slopes is compared in terms of the acceleration amplifications and horizontal displacements of the slope measured at different elevations. Results from these model tests revealed that the acceleration amplifications were slightly lesser in case of geogrid reinforced slopes because of higher interfacial friction of cohesionless soil with the geogrid. Acceleration amplifications were not affected by varying the quantity of reinforcement. However, horizontal displacements reduced drastically with the inclusion of reinforcement. Though the difference was not substantial, geotextile reinforced slopes were more effective in reducing the deformations compared to geogrid reinforced slopes. With the increase in the quantity of reinforcement, deformations decreased linearly, until reinforcement saturation occurred, beyond which the rate of decrease of deformations was less.

Response of reinforced soil slopes to seismic loading conditions is governed by the properties of soil, properties of reinforcement and geometry of the slope apart from the ground motion parameters of the seismic event. Studies specific to seismic response of reinforced soil slopes mainly focused on the investigation of failure mechanisms, understanding the effect of reinforcement parameters and ground motion parameters on the seismic stability of the slopes. Researchers used experimental, field investigation and numerical techniques to understand the response of reinforced soil slopes under seismic loading conditions. Physical modelling using reduced scale models is often preferred by the researchers because of several advantages like reasonably large size models, facility to embed instrumentation and ability to carry out tests under controlled conditions. Researchers have successfully used shaking table tests [14] and centrifuge tests [5, 6] to understand the influence of various parameters on the seismic performance of reinforced soil slopes or walls. The test results generally showed that the permanent displacements increased with increasing input motion amplitude and decreased with increasing reinforcement stiffness, density, and decreasing slope angle.

Through shaking table studies on 1:2 reduced scale models of geotextile-reinforced soil retaining walls of 1.9m height subjected to E1 Centro earthquake and sinusoidal harmonic motion, Guler and Enunlu [7] demonstrated that geosynthetic reinforced retaining structures behave very successfully under earthquake loading conditions. Lin and Wang [8] performed large scale shaking table tests to study the dynamic response of sand slopes under earthquake conditions. It was observed that the response of the soil converted from linear to nonlinear at the acceleration amplitude of 0.5g. The failure surface appeared to be fairly shallow and confined to the slope surface, which was consistent with the field observations of earthquake-induced landslides. Huang et al. [9] performed a series of full-scale shaking table tests on reinforced soil slopes subjected to stepwise intensified sinusoidal pulse loads with various frequencies and reported that accelerations and displacements of the slopes showed frequency dependent behaviour. Transition from the state of amplification towards the state of deamplification at the crest of the slope consistently preceded the critical collapse state of the slopes. Wang et al. [10] investigated the earthquake triggered failure modes, failure mechanisms and failure surfaces of slopes by means of field investigations, large scale shaking table tests and numerical analysis. Large scale shaking table tests could reproduce the process of deformation and failure of slopes in field. Tension cracks emerged at the top and upper part of the model, while the bottom of the model remained intact, which was consistent with the field observations. Through shaking table tests on model slopes with different combinations of reinforcement length, strength/stiffness and vertical spacing, Perez [11] showed that the failure surface gets flatter with the increase in quantity of reinforcement. Lo Grasso et al. [12, 13] carried out shaking table tests on geogrid reinforced soil slopes and demonstrated that reducing the spacing of reinforcement near the top of the slope is beneficial for the stability of slopes. Shaking table model tests carried out by Sugimoto et al. [14] on geogrid reinforced soil slopes with sand bag facing showed that the slopes undergo large ductile deformations without any distinct failure surface under sinusoidal as well as scaled earthquake shaking. Lin et al. [15] performed large scale shaking table tests on three reinforced embankment slope models with Wenchuan earthquake motions. These studies showed a decreasing trend in horizontal acceleration response with the increase in peak input horizontal acceleration. Huang et al. [16] applied sinusoidal waves and actual seismic waves measured from the Wenchuan earthquake to the slope models in shaking table tests under 37 different loading configurations. The location of sliding plane in the model was consistent with the location of the maximum horizontal acceleration. The present study is focused towards understanding the difference in the seismic response of soil slope with geotextile and geogrid reinforcement and to study the effect of reinforcement quantity on the performance under different ground shaking conditions.

A computer controlled servo hydraulic uniaxial (horizontal) shaking table facility has been used in simulating horizontal seismic action, associated with seismic or any other vibration conditions. The shaking table has a loading platform of 1m1m size and the payload capacity is 1 ton. The shaking table can be operated within the acceleration range of 0.05g to 2g and frequency range of 0.05Hz to 50Hz with the amplitude of 200mm. The major problems associated with laboratory model studies are scaling and the boundary effects, especially in studies related to earthquake engineering. Models of soil slopes have been built in a laminar box to reduce the boundary effect to some extent. The laminar box used for the tests is rectangular in cross section with inside dimensions of 500mm1000mm and 800mm deep with fifteen rectangular hollow aluminum layers. These layers are separated by linear roller bearings arranged to permit relative movement between the layers with minimum friction. Details of the shaking table setup and laminar box were presented by Srilatha et al. [17].

Locally available sand was used to prepare the model slopes. The soil was classified as poorly graded sand (SP) according to the Unified soil classification system. Particle size distribution curve of the test soil is shown in Fig.1. Properties of the soil are listed in Table1.

A biaxial geogrid and a geotextile were used in the present study to reinforce the model soil slopes. Figure2 shows the dimensional details of the geogrid used in experiments. The ultimate tensile strength of the geogrid was determined from standard multi-rib tension tests as per ASTM: D 6637. The ultimate tensile strength of the geotextile was determined from the wide-width tensile strength test conducted as per ASTM D-4595. Results of the tensile strength tests on the geosynthetics are given in Fig.3. Properties of the geotextile and geogrid are listed in Table2.

Accelerometers and ultrosonic non-contact displacement transducers (USDT) were used to measure the response of the model slope during seismic shaking. Accelerometers are of analog voltage output type with a full-scale acceleration range of 2g along both the x and y axes, with sensitivity of 0.001g and these accelerometers were connected to the shaking table controller through a junction box for data acquisition [17]. Non-contact type ultrasonic displacement transducers were used to measure the horizontal displacements at different elevations. These sensors work on ultrasonic energy multiple pulses, which travel through the air at the same speed of sound. The sensing range of these sensors is 30 to 300mm with short dead zone of 30mm and output response time is 30ms.

To cover the gap between the each rectangular panel, polyethylene sheet was used inside of the laminar box and also to minimize the friction between the model and the laminar box. For compaction, a mass of 5kg was dropped from a height of 450mm on 150mm150mm square steel base plate with fixed guide rod at the centre of the base plate to achieve the desired unit weight for each layer. Three layered compaction was adopted for unreinforced and two layer reinforced slopes and four layered compaction was used for one layer and three layer reinforced slopes. Total number of blows used was 180 in all cases, 60 on each layer in case of three layered compaction and 45 on each layer in case of four layered compaction. This method ensured uniform unit weight of soil in all models, as verified from many trials. Schematic diagrams of typical reinforced single, two layer and three layer slopes with instrumentation are shown in Fig.4. Construction sequence of typical geotextile reinforced soil slope is shown in Fig.5. Reinforcement was placed at the interface of the compacted soil layers. Each model was constructed using poorly graded sand in three equal lifts, each of 200mm, to get a total slope height (H) of 600mm with a base width of 850mm. The remaining space in the laminar box (150mm500mm in plan) was kept empty for mounting the displacement transducers and that space was packed with concrete cubes enclosed in plywood panels during compaction. The unit weight and water content of the model slopes were in the range of 1717.1kN/m3 and 1010.1% respectively in all these model tests. The geogrid and geotextile reinforcement was provided at the interface of the compacted layers and was kept at a distance of 50mm from the face of the slope to the full width of the slope for all the reinforced model slopes. Then the slope of required angle is marked and the compacted soil was trimmed to the required slope geometry using a trowel. After finishing the model preparation the plywood and concrete cubes were removed one by one. During the process of compaction the accelerometers, A1, A2 and A3 were embedded in soil at elevations 170, 370 and 570mm from the base of the slope, where one accelerometer, A0, was fixed rigidly to the bottom of the shaking table to measure base acceleration. Three displacement transducers, U1, U2 and U3 were positioned along the face of the slope at elevations 200, 350 and 500mm from the base of the slope to measure the horizontal face displacements. The transducers are fitted in wooden planks which were bolted horizontally to the T-shape steel bracket which is in turn fitted to the steel frame. The response of the slope was recorded in terms of acceleration at different elevations and the displacement of the facing.

Shaking table tests in this study are 1-g model studies carried out on reduced scale models. The stresses and deformations measured in the experiments do not truly represent the stresses and deformations in field because of low confining pressures and boundary effects in model studies. Hence it is essential to apply proper similitude rules for the experiments in order to apply the results to actual field conditions. Many shaking table model studies on slopes in literature have used much smaller slope models in experiments. For example, Lo Grasso et al. [12] and Lin and Wang [8] used slopes of 0.5m height and Huang et al. [9] used model slopes of 0.48m height. Though scale effects cannot be completely eliminated in 1-g model studies, similitude laws to correlate the model and prototype scaling and response are effectively used by several researchers. In the present study, similitude relations derived by Iai [18] and later used by Meymand [19] and Lin and Wang [8] were used. A geometric scale factor, L, was defined as the proportionality constant between the model and prototype. The geometric scaling factor L used in the present study is 10. The slope height of 0.6m used in the study in order to simulate a 6m high prototype slope in the field. Accordingly the scaling parameters between prototype and model slope were derived are listed in Table3. Scaling of reinforcement tensile strength is not attempted in this study. Hence the geogrid used in the study simulate very strong prototype geogrid.

Sixteen different shaking table tests on unreinforced and reinforced soil slope models were performed in this study. These tests are devised to understand the effect of reinforcement parameters on acceleration, frequency of base shaking and reinforcement on the response of the slope during seismic excitation. The test parameters varied in different tests are given in Table4. The base acceleration was varied from 0.1 to 0.3g and frequency was varied from 1 to 7Hz in different tests. Test code for each test gives the reinforcement type, number of reinforcing layers, base acceleration and shaking frequency in sequence. Unreinforced, geogrid reinforced and geotextile reinforced model tests are represented with letter symbols U, G and T respectively. In case of tests on geotextile reinforced models, the number of geotextile layers used in the model follows the letter T. Base accelerations used were 0.1, 0.2 and 0.3g in different tests, which are represented as A1, A2 and A3 respectively. Various shaking frequencies used in the tests were 1, 2, 5 and 7Hz, which were represented by F1, F2, F5 and F7 respectively in the test code. For example, T3A3F2 represents the model test, where the slope is reinforced with 3 layers of geotextile, subjected to base shaking at an acceleration of 0.3g and frequency of 2Hz. The resonant frequencies of the slopes change significantly with the height of the slope.

where V S is the shear wave velocity of the model in m/s, e is the void ratio of soil in model slope and \(\sigma^{\prime}_{\text{o}}\) is the mean effective confining pressure in Pa. The void ratio of the compacted model slope was 0.68 and the mean effective confining stress at the bottom of the model slope was 10.2kPa. Shear wave velocity of the model was calculated as 94m/s as per Eq.(1). Kramer [21] gave an expression to calculate the natural frequency of the model from its shear wave velocity.

where f n is the natural frequency of the compacted model slope in Hz and H is the depth of compacted model slope in meters. According to Eq.(2), the natural frequency of the compacted model slope of height 600mm and shear wave velocity of 94m/s is calculated as 40Hz. The frequency range used in the present study is much less than the natural frequency and hence the models are not subjected to resonance. Each model slope is subjected to 40 cycles of base shaking with the corresponding frequency.

Response of geotextile and geogrid reinforced soil slopes constructed with single, two and three layers of reinforcement and subjected to the same base shaking of 0.3g acceleration and 2Hz frequency for 40 cycles is compared. To simplify the presentation of acceleration response at different elevations of the slope, Root mean square acceleration amplification factor (RMSA) is used. RMSA amplification factor is the ratio of response acceleration value in the soil to that of corresponding value of the base motion [21]. Acceleration amplification is observed to be the most at the top of the slope in all the tests.

Figure6 presents the effect of reinforcement type on acceleration response of soil slopes subjected to base shaking of 0.3g acceleration and 2Hz frequency. The elevation is normalized with respect to the height of the slope in all the plots. Comparison of RMSA amplification factors with elevation for single, two and three layer reinforced slopes with different types of reinforcement are shown in Fig.6a, b and c respectively. Acceleration amplification factors were close to unity at all the elevations along the height of the slopes, indicating that the reinforcement type has no effect on the acceleration amplifications at the specific base shaking conditions. The computed maximum RMSA amplification factor at a normalized height of 0.95 for unreinforced model slope was 1.074, whereas it was 1.046 for single layer geogrid reinforced slope and 1.064 for single layer geotextile reinforced slope. For two layer and three layer reinforced slopes, geogrid reinforcement has slightly reduced the acceleration amplifications at higher elevations, whereas the response of geotextile reinforced slopes was closely matching with the response of unreinforced slope. At lower elevations of the slope, there was no effect of reinforcement on the acceleration amplifications. Slight reduction in acceleration amplifications was observed in case of geogrid reinforced soil slopes. However, the difference in behaviour is not significant and hence it is evident from the model test results that the type of reinforcement has no significant influence on the acceleration response of the slopes at low frequencies.

Figure7 presents the effect of reinforcement type on the horizontal displacement response of soil slopes subjected to base shaking of 0.3g acceleration and 2Hz. Comparison of horizontal displacements with elevation for single, two and three layer reinforced slopes with different types of reinforcement are shown in Fig.7a, b and c respectively. The measured horizontal displacement at a normalized height of 0.84 was 146.35mm for unreinforced model slope and it reduced to 88.81mm with a single layer geogrid reinforcement and 71.33mm with a single layer geotextile reinforcement, as shown in Fig.7a. Similar behaviour was observed in case of two and three layers of reinforcement, as shown in Fig.7b and c. For a three layer reinforced slope, maximum displacement was 16.33 and 11.65mm with geogrid and geotextile reinforcement respectively. Geotextile reinforcement was proved to be better than the geogrid reinforcement in reducing deformations for this case. Several earlier researchers demonstrated the decrease in deformations of reinforced soil structures with the increase in reinforcement stiffness [22].

Tensile strength of the geotextile used in this study was 55.5 kN/m and that of the geogrid was 26 kN/m. However, tensile stiffness of geotextile and geogrid are almost the same at low strain levels, which represent the model test conditions. The reason for better displacement control with geotextile reinforcement is better mobilization of friction at the interface due to large area of contact between fine sand and geotextile compared to geogrid. Figure8 shows the photographs of model slope of soil before shaking (Fig.8a), unreinforced soil slope after shaking (Fig.8b), two layer geogrid soil slope (Fig.8c) and two layer geotextile soil slope (Fig.8d), respectively subjected to a base shaking frequency of 2Hz at the end of 40 cycles of base motion. As observed from the figures, unreinforced slope (Fig.8b) has shown extensive cracking at the end of the test. Reinforced soil slopes has not shown any cracks during and at the end of the tests, showing high benefit of reinforcement by the inclusion of two layer geogrid and geotextile reinforcement (Fig.8c, d).

Photographs of the model slopes: a slope before the test, b unreinforced slope after the test at a frequency of 2Hz, c Geogrid reinforced slope after the test at a frequency of 2Hz, d geotextile reinforced slope after the test at a frequency of 2Hz

To study the effect of reinforcement type on acceleration and horizontal displacement response of reinforced soil slopes subjected to different frequencies, model soil slopes reinforced with three layers of geogrid/geotextile were tested at 0.3g base acceleration and different frequencies. Geogrid reinforced model slopes were tested at frequencies of 2, 5 and 7Hz, while geotextile reinforced model slopes were tested at 1, 2, 5 and 7Hz frequencies. Figure9 presents the effect of reinforcement type on acceleration response of soil slopes subjected to two different frequencies 2 and 7Hz. When the three layer reinforced slope was subjected to base shaking of 2Hz, a slight deamplification was observed at higher elevations. At frequency of 7Hz, accelerations were amplified considerably for both the types of reinforcement. Compared to unreinforced soil slope, amplifications were less in reinforced slopes, the effect is more prominent at higher frequencies. Horizontal displacement response of these slopes at two different frequencies is plotted in Fig.10, which shows that both geogrid and geotextile were equally effective in reducing deformations to a large extent.

Figure11 presents the summary of effect of reinforcement type on the acceleration and displacement response of model slopes subjected to base shaking of different frequencies. Geogrid reinforced slope displayed lesser accelerations compared to geotextile reinforced slope, especially at higher frequencies because of higher interfacial friction, as shown in Fig.9a. Difference in displacement behaviour of slopes with different types of reinforcement is not substantial at all the frequencies (Fig.10).

The model slopes were subjected to different base accelerations with shaking frequency of 2Hz. Since the geotextile reinforcement was performed well in reducing displacements from the earlier study, to understand the effect of reinforcement at different base accelerations, tests were carried out on model slopes reinforced with geotextile subjected to 0.1, 0.2 and 0.3g base accelerations at 2Hz shaking frequency. Acceleration and horizontal displacement response from these model tests are presented in Figs.12 and 13 respectively along with results from unreinforced model tests subjected to similar ground motion. Figure12 clearly shows that the geotextile reinforcement does not have significant influence on the acceleration amplifications at all three base accelerations investigated. The measured horizontal displacement at a normalized height of 0.84 was 3.34, 4.66 and 146.35mm at 0.1, 0.2 and 0.3g accelerations, whereas the corresponding displacement in case of 3 layer geotextile reinforced slope reduced to 1.03, 3.01 and 11.65mm respectively. The catastrophic flowslide type of failure occurring in case of unreinforced soil slope at 0.3g acceleration and 2Hz frequency (Fig.8b) was arrested when the slope was reinforced with 3 layers of geotextile and the deformations were reduced by about 92% for that case. The efficiency of geosynthetics on the prevention of slope instabilities and the reduction of the anticipated stress levels on the geostructures was highlighted by Tsompanakis [23].

Figure14 presents the maximum acceleration amplification factors and horizontal displacements of unreinforced and 3 layer geotextile reinforced soil slopes with variation in base shaking acceleration. Reinforcement was effective in reducing horizontal deformations at all accelerations, the benefit being substantial at higher accelerations.

Effect of quantity of reinforcement on the seismic response of soil slopes was investigated through model tests on soil slopes reinforced with single, two and three layers of geogrid/geotextile. Figure15 presents the effect of quantity of reinforcement on the acceleration amplification response of both geogrid and geotextile reinforced slopes along with the unreinforced slope subjected to a base shaking of 0.3g acceleration and 2Hz frequency. As seen from Fig.15, acceleration amplifications were not influenced significantly with the inclusion of reinforcement.

Figure16 shows the effect of quantity of reinforcement on horizontal displacement response of geogrid and geotextile reinforced model slopes along with the response of unreinforced slope. It can be observed that displacements decreased with the increase in the reinforcement quantity. Figure17 presents the effect of quantity of reinforcement on the response of both geogrid and geotextile slopes subjected to base shaking of 0.3g acceleration and 2Hz frequency. The quantity of reinforcement is represented by normalized vertical spacing (S v /H) in this plot, S v representing the vertical spacing between the reinforcing layers. As observed from figure, quantity of reinforcement does not have considerable influence on the acceleration amplifications. With the increase in number of reinforcing layers or decrease in normalized vertical spacing of reinforcement layers, slight reduction in amplification factors is observed. The acceleration amplification factors are between 1.0 and 1.5, similar to the amplification factors reported by El-Emam and Bathurst [22] for model walls of 1m height tested at 0.3g acceleration. Drastic reduction in horizontal displacements with the increase in the quantity of reinforcement was observed for both geogrid and geotextile reinforced soil slopes. The reduction in displacement was substantial with the inclusion of single and two layers of reinforcement, showing linear decrease in deformations with the increase in the number of reinforcing layers and further increase in the quantity of reinforcement could reduce the deformations only to a certain extent, indicating reinforcement saturation. The reduction in lateral deformations with 50% reduction in vertical spacing (which means doubling the number of reinforcing layers) is about 67% in case of geogrid and 74% in case of geotextile. Sakaguchi et al. [24] reported a 40% reduction andBathurst and Hatami [25] reported a 32% reduction in lateral displacements of reinforced vertical walls tested at 0.3g acceleration with doubling up the number of reinforcement layers. The reductions in lateral deformations observed in the present study for 45 model slopes are much higher than these values.

It should be noted that the present study uses only one type of poorly graded sand and the results may not be equally applicable to other types of soils. Also, extrapolation of results from model tests to the field slopes using similitude laws has certain limitations because of boundary effects in model studies and the difficulties in scaling reinforcement properties.

Geotextile reinforcement was slightly better in decreasing the horizontal deformations, though the tensile stiffness of both these materials is almost same, because of better mobilization of friction at the interface in case of geotextile due to its large area of contact.

The catastrophic flowslide type of failure occurring in case of unreinforced soil slope at 0.3g acceleration and 2Hz frequency was arrested when the slope was reinforced even with a single layer of geotextile or geogrid, indicating the importance of soil reinforcement in mitigating seismic hazards.

Rate of decrease in deformations with increase in the quantity of reinforcement was drastic up to certain extend (2 layers in this study) and further increase in the quantity of reinforcement could reduce the deformations only to a certain extent, indicating reinforcement saturation.

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dynamic behavior of sawdust-mixed soil in shaking table test - sciencedirect

dynamic behavior of sawdust-mixed soil in shaking table test - sciencedirect

A scaled model soil mixture of clay and sawdust for shaking table test is developed.A series of scaled model shaking table tests were conducted.Dynamic behavior of sawdust-mixed soil are analyzed and the results are given.

In the shaking table tests of underground structures, the scale ratios of the soil and structure are inconsistent. To this end, a scaled model soil was developed in this study. Through a series of tests, the dynamic response of the model soil was investigated. A clay mixed with sawdust was designed for shaking table tests based on the predominant period similarity relationship between the structure and the foundation soil. The sawdust-mixed clay was subjected to a series of shaking table tests at Beijing University of Technology using a rigid prefabricated continuous model box (dimensions: 7.7m3.2m1.2m). Through the tests, the performance of the model box and the nonlinear seismic behavior of the model soil were studied. The results are as follows: (i) The boundary effect of the model box was negligible during the test. (ii) The predominant frequencies of the model soil shifted toward lower values with increasing shaking intensity. This indicated that the model soil became increasingly softer and that the nonlinear effect of the soil was more evident. (iii) With the increase in the shaking intensity, the peak acceleration of the model soil at the same measured points increased, whereas their amplification factors decreased. In addition, the amplification factors first decreased and then increased from the bottom to the top of the soil. This might have been due to the increase in the shear strain and decrease in the shear modulus of the soil with increasing shaking intensity. (iv) The shear modulus of the soil was closely related to the confining pressure. At the same shaking intensity, the shear stress increased, and the shear strain decreased from top to bottom of the model soil.

seismic response of subway station in soft soil: shaking table testing versus numerical analysis - sciencedirect

seismic response of subway station in soft soil: shaking table testing versus numerical analysis - sciencedirect

The seismic response of a station is studied combining experiments and analysis.Shaking table tests are conducted using synthetic model soil and granular concrete.A nonlinear FE model is calibrated and validated against the shaking table tests.The validated model is used to transfer the results from model to prototype scale.Insights on the seismic vulnerability of multi-storey metro stations are offered.

As revealed by the collapse of the Daikai Metro station during the 1995 Kobe earthquake, underground structures are not immune to seismic loading. Shanghai Metro operates 16 lines of 676km length, comprising 413 underground stations. An additional 1000km with 600 underground stations are planned for the next 20years, calling for improved understanding of their seismic response. This paper studies the seismic performance of a typical 2-storey, 3-span Shanghai Metro station in soft soil, combining shaking table testing and numerical modelling. Notwithstanding scale effects, shaking table testing is performed to allow detailed simulation of the complex structural system of the station. The structure is modelled using granular concrete and galvanized steel wires to simulate the RC prototype. To remedy the problem of scale effects, synthetic model soil (a mixture of sand and sawdust) is used, along with similitude relations derived considering dynamic equilibrium. The properties of the synthetic model soil are adjusted to satisfy similitude; target stiffness and density are attained by adjusting the mixture proportions. To quantify the transferability of the results to prototype scale, the experiments are simulated with nonlinear finite elements (FE), modelling the synthetic model soil with a kinematic hardening constitutive model, calibrated against resonant column and direct shear tests. The FE model is shown to compare adequately well with the shaking table tests. The validated FE model is used to predict the seismic response of the prototype, thus allowing indirect transfer of the results from model to prototype scale. The model in prototype scale is calibrated for the real soil layers against in situ (down-hole) and laboratory (resonant column) tests. Moving from model to prototype scale, the racking deformation remains qualitatively similar. The racking drift is reduced by 50% going from model to prototype scale, which is partly due to scale effects, but also related to differences between the idealized soil of the experiments and the multiple soil layers encountered in reality. The maximum bending moment also reduces by 30% going from model to prototype scale. The base of the lower-storey columns is proven to be the most vulnerable section, as was the case for Daikai.

seismic soil response of scaled geotechnical test model on small shaking table | springerlink

seismic soil response of scaled geotechnical test model on small shaking table | springerlink

This research comprises a series of shaking table tests and finite element analyses of scaled soil-foundation model to determine the dynamic interaction effects between the foundation and the underlying soil. The purpose of this work is to specify a realistic geometric scaling coefficient for test model to be used in a small-capacity shaking table. The scaling factor addressed in this study involves not only geometric similarity but also kinematic and dynamic similarity with the real system. The free-field soil response under different earthquake excitations for both real system and scaled test model was directly performed by using 2D finite element method under plane-strain conditions. The kinematic interaction of the shallow foundation slab on free-field motion was also examined. In this computational model, the behavior of the soil medium is idealized by linear elastic-perfectly plastic assumption with a yield surface according to Mohr-Coulomb failure criterion. Two different earthquake acceleration records as Chi-Chi (1999) and Loma Prieta (1989) have been carried out at the bedrock level of the soil-foundation system for this study. By comparing the results of the numerical analysis with data from the laboratory tests, the proposed geotechnical model can properly simulate the seismic response of the full-scale real system. It can be concluded that the kinematic interaction effects are negligible in the low frequencies. It should be noted that the local soil properties have considerably amplified the earthquake response of the free-field motions in comparison to the bedrock excitations.

Aldaikh H, Alexander NA, Ibraim E, Oddbjornsson O (2015) Two dimensional numerical and experimental models for the study of structuresoilstructure interaction involving three buildings. Comput Struct 150:7991

Brinkgreve RBJ, Al-khoury R, Bakker KJ, Bonier PG, Brand PJ, Broere W, Burd HJ, Solty G, Vermeer PA, Haag DD (2002) Plaxis finite element code for soil and rock analyses. Published and Distributed by AA. Balkema Publisher, The Netherlands

Hosseinzadeh NA, Nateghi F (2004) Shake table study of soil structure interaction effects on seismic response of single and adjacent buildings. In: 13th World Conference on Earthquake Engineering, Vancouver, B.C., Canada

Tabatabaiefar SHR, Fatahi B, Samali B (2016) Numerical and experimental investigations on seismic response of building frames under influence of soil-structure interaction. Adv Struct Eng 17(1):109130

elebi, E., Gktepe, F. & Omid, A.J. Seismic soil response of scaled geotechnical test model on small shaking table. Arab J Geosci 12, 44 (2019). https://doi.org/10.1007/s12517-018-4197-8

numerical simulation of dynamic soilstructure interaction in shaking table testing - sciencedirect

numerical simulation of dynamic soilstructure interaction in shaking table testing - sciencedirect

This paper provides an insight into the numerical simulation of soilstructure interaction (SSI) phenomena studied in a shaking table facility. The shaking table test is purposely designed to confirm the ability of the numerical substructure technique to simulate the SSI phenomenon. A model foundationstructure system with strong SSI potential is embedded in a dry bed of sand deposited within a purpose designed shaking-table soil container. The experimental system is subjected to a strong ground motion. The numerical simulation of the complete soilfoundationstructure system is conducted in the linear viscoelastic domain using the substructure approach. The matching of the experimental and numerical responses in both frequency and in time domain is satisfying. Many important aspects of SSI that are apparent in the experiment are captured by the numerical simulation. Furthermore, the numerical modelling is shown to be adequate for practical engineering design purposes.

shaking table test study on seismic performance of inclined pile foundations in liquefiable soil | springerlink

shaking table test study on seismic performance of inclined pile foundations in liquefiable soil | springerlink

Inclined pile foundations are widely used in civil engineering by virtue of sufficient horizontal stiffness, but few studies have touched upon the seismic performance of inclined piles in liquefiable soil. To better understand the performance of the inclined piles in liquefiable soil under earthquake conditions, a series of 1g shaking table tests of inclined and vertical piles in liquefiable soil were performed. Superstructure-pile-soil dynamic interaction was considered while three types of earthquake waves with different characteristics were selected as the applied earthquake motions. The horizontal acceleration of the superstructure and the pile cap, the rotational acceleration of the pile cap, the total base shear force, and the bending moment of two types of physical models were monitored and analyzed. The results show that inclined piles in liquefiable soil can effectively reduce the horizontal vibration of the superstructure and the pile cap, and the acceleration reduction of the pile cap is about 2.5 times larger than that of the superstructure. Meanwhile, inclined piles can also reduce the total base shear force, and the extent of reduction depends on the input earthquake wave. Besides, the results suggest that the maximum bending moment of inclined piles is located at the pile head, and its value is positively correlated with the amplitude of the earthquake wave, and is affected by the type of the input earthquake wave. Overall, inclined pile foundations show satisfactory seismic performance for a superstructure-foundation-liquefiable soil system, and this study, with a rich amount of data, can serve as an important reference for the seismic design of inclined piles in liquefiable soil.

Amiri AM, Ghanbari A, Derakhshandi M (2018) An analytical model for estimating the vibration frequency of structures located on the pile group in the case of floating piles and end-bearing pile. Civ Eng J 4:450468. https://doi.org/10.28991/cej-0309105

Gerolymos N, Giannakou A, Anastasopoulos I, Gazetas G (2008) Evidence of beneficial role of inclined piles: observations and summary of numerical analyses. Bull Earthq Eng 6:705722. https://doi.org/10.1007/s10518-008-9085-2

Giannakou A, Gerolymos N, Gazetas G, Tazoh T, Anastasopoulos I (2010) Seismic behavior of batter piles: elastic response. J Geotech Geoenviron Eng 136:11871199. https://doi.org/10.1061/(ASCE)GT.1943-5606.0000337

Harn RE (2004) Have batter piles gotten a bad rap in seismic zones (or everything you wanted to know about batter piles but were afraid to ask). In: Ports 2004: port development in the changing world, pp 110. https://doi.org/10.1061/40727(2004)13

Ling XZ, Wang C, Wang C (2004) Scaling modeling method of shaking table test of dynamic interaction of pile-soil-bridge structure in ground of soil liquefaction. Chin J Rock Mech Eng 23:450456. https://doi.org/10.3321/j.issn:1000-6915.2004.03.017

Lund LV (2003) Lifeline performance, El Salvador earthquakes, January 13 and February 13, 2001. In: Advancing mitigation technologies and disaster response for lifeline systems, pp 265273. https://doi.org/10.1061/40687(2003)28

Sitharam TG, Dash HK, Jakka RS (2013) Postliquefaction undrained shear behavior of sand-silt mixtures at constant void ratio. Int J Geomech 13:421429. https://doi.org/10.1061/(ASCE)GM.1943-5622.0000225

The research was supported by the National Key R & D Program of China (Grant no. 2016YFC0802203) and Science and Technology Research and Development Program of China Railway Corporation (Grant no. 2013G001-A-2).

Chen, W., Ma, J., Cao, S. et al. Shaking table test study on seismic performance of inclined pile foundations in liquefiable soil. Environ Earth Sci 79, 398 (2020). https://doi.org/10.1007/s12665-020-09139-4

shaking table tests on the seismic performance of a flexible wall retaining eps composite soil | springerlink

shaking table tests on the seismic performance of a flexible wall retaining eps composite soil | springerlink

A series of shaking table tests were designed and conducted to study the seismic performance of an inverted T-shape cantilever retaining wall with an anti-sliding tooth at the base using EPS composite soil as backfills. For comparison, the same wall model retaining Nanjing fine sand was simultaneously excited. The macro phenomena and seismic behaviors of two wallsoil systems are depicted in detail and analyzed. The displacement mode of the non-sliding flexible retaining wall and distribution characteristics of dynamic earth pressure acting on the wall back retaining two types of backfills are emphasized. The testing results show that, as a kind of backfill, Nanjing fine sand has a greater peak ground acceleration (PGA) than EPS composite soil under the kinematic interaction between wall and soil, while the difference in the inertial force of the retaining wall itself is not obvious. As the input peak base acceleration increases, Nanjing fine sand which possesses the compaction strength gradually transforms from the global shearing deformation to the wedge sliding deformation, while EPS composite soil with a cemented strength exhibits the block shearing deformation mode under all excitations. The tested retaining walls with the rotation displacement are non-sliding flexible walls. The dynamic deformation mode of backfills is closely related to the inertial interaction between wall and soil, which results in a significant difference in the dynamic earth pressure increment distribution between the walls retaining two types of backfills. The dynamic earth thrust in the retaining wall-Nanjing fine sand system (WSS) has a nonlinear relation with PGA, and the action position approximated 2/3 wall height. A linear relation is more suitable for retaining EPS composite soil and the corresponding action position is about 1/3 wall height. The retaining wall-EPS composite soil system is shown to have a better seismic performance in contrast to WSS. The Seed and Whitman method with 100% PGA is recommended to predict the dynamic earth thrust on the wall retaining EPS composite soil.

Alampalli S, Elgamal A (1990) Dynamic response of retaining walls including supported soil backfill: a computational model. In: The fourth U.S. national conference on earthquake engineering, vol 3. Palm Springs, CA, pp 623632

Anastasopoulos I, Georgarakos T, Georgiannou V et al (2010) Seismic performance of bar-mat reinforced-soil retaining wall: shaking table testing versus numerical analysis with modified kinematic hardening constitutive model. Soil Dyn Earthq Eng 30(10):10891105

Arias A, Sanchez-Sesma FJ, Ovando-Shelley E (1981) A simplified elastic model for seismic analysis of earth-retaining structures with limited displacements. In: Proceedings of the international conference on recent advances in geotechnical earthquake engineering and soil dynamics. St Louis, MO, pp 235240

National Cooperative Highway Research Program (1991) Manuals for design of bridge foundations. Barker RM, Duncan JM, Rojiani KB, Poi PSK, Tan CK, Kim SG (eds) Rep 343. Transportation Research Board, Washington

Seed HB, Whitman RV (1970) Design of earth retaining structures for dynamic loads. In: Proceedings of the ASCE specialty conference on lateral stresses in the ground and the design of earth retaining structures. Ithaca, New York, pp 103147

This study is funded by the National Natural Science Foundation of China (Grant No. 51578286) and China Postdoctoral Science Foundation (Grant No. 2013T60529). The authors are grateful to Dr. Chen Weiyun for providing his revision advice. The contributions of anonymous reviewers and editors are also acknowledged.

Gao, H., Hu, Y., Wang, Z. et al. Shaking table tests on the seismic performance of a flexible wall retaining EPS composite soil. Bull Earthquake Eng 15, 54815510 (2017). https://doi.org/10.1007/s10518-017-0189-4

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