Dynamic Earth Pressure Research Articles

Dynamic response of different bridge piers

Throughout their construction period and service lifespan, the piers of bridges that built in earthquake zones are susceptible to abrupt earthquake. Thus, during their design period, all the possible circumstances must be taken into consideration because they are strategic infrastructures. Basically, the piers can be considered as the major part of the bridges. This paper presents an experimental work to investigate how the earthquakes influence on the seismic behavior of the selected concrete bridge piers. Physical modeling principals were applied to prepare three models of piers and table of shaking (1-g tests). The piers models were tested under 0.8g waveform for three cases, a rectangular pier constructed on a saturated cohesionless layer of soil, a hexagonal pier constructed over a saturated cohesionless layer and a circular pier installed on saturated cohesionless layer. The obtained results involved the time-acceleration measurement from the accelerometers throughout the shacking, the dynamic earth pressure, and the seismic displacement piers models. Basically, the obtained results of the experiments revealed that the acceleration amplification enhanced greatly at the pier top. The seismic displacement increased sharply because of the strong motion. The rectangular pier exhibited the highest values of the dynamic earth pressure.

Shaking Table Tests on a New Antislide Pile under Earthquakes

A retaining form of a shock-absorbing antislide pile is proposed for slope engineering. A flexible material (shock-absorption layer) is filled in front of an ordinary antislide pile, which is used to absorb a large amount of seismic energy, thereby decreasing the transmission of seismic energy to the antislide pile. The flexible material thus reduces the seismic response, hence improving the aseismic capacity of the antislide pile. To verify the seismic performance of the shock-absorbing antislide pile, a shaking table contrast test was conducted and the results were compared with those from an ordinary antislide pile. The test results show that the flexible material absorbs a portion of the seismic deformation of the slip mass, decreasing the final displacement of the shock-absorbing antislide pile compared to that of the ordinary antislide pile, thereby reducing the sensitivity of the pile body to the displacement. Under the same conditions, the acceleration response of the slope body at the same height is lower for the shock-absorbing antislide pile than that for the ordinary pile, with the seismic performance of the former being superior to that of the latter. Furthermore, the shock-absorbing antislide pile is similar to the ordinary pile in terms of the dynamic earth pressure distribution form of the pile shaft; however, its value is relatively smaller, and the former exhibits better dynamic stress performance than the latter. The test results should prove useful for aseismic design of slopes.

English

English

Dual row retaining walls in dry sand: influence of wall stiffness on seismic response

Dual row retaining walls can form efficient port and embankment structures, or even be used as coastal defence against tsunamis. The system of parallel sheet pile walls can have a large lateral capacity within serviceability limit states due to the combined strength and stiffness of the walls and confined soil. Optimising the design by reducing the wall section and ensuring greater utilisation of the soil capacity has economic and environmental benefits but requires a deeper understanding of the dynamic soil–structure interaction. Centrifuge modelling and numerical modelling are used to elucidate the mechanics of two systems with relatively flexible and stiff walls. Considering the fraction of the wall’s plastic moment capacity mobilised alongside the peak deflections illustrates the advantages of using relatively flexible retaining walls in these systems. More fundamentally, the importance of vertical variations of both the stress and strain during the horizontal dynamic loading is shown. The limiting horizontal stresses and phasing of the stress components around the walls are better understood by considering the mobilisation of earth pressure coefficients, reinforcing previous work that recommends a move away from conventionally defined limiting dynamic earth pressure coefficients.

Large-scale shaking table test on seismic behaviour of anti-slide pile-reinforced bridge foundation and gravel landslide: a case study

This study aimed to illustrate the seismic response and instability process of a double-row anti-slide pile-reinforced bridge foundation and gravel landslide. Selecting the gravel slope of Jiuzhai Valley along the under-construction Chengdu-Lanzhou high-speed railway as the site prototype, large-scale shaking table tests were first conducted at a similitude ratio of 1:70, with sine waves and El Centro waves as the seismic wave inputs. The amplitudes of the input seismic waves were increased, while the acceleration, dynamic earth pressure, and strain distribution were monitored in the gravel landslide. The dynamic response patterns of anti-slide pile-reinforced bridge foundations in gravel landslides were illustrated. The front-row and back-row anti-slide piles should be a reasonable distance from the bridge foundation. The response acceleration manifested an elevation amplification effect with an increasing elevation in the slope behind the anti-slide piles. Back-row anti-slide piles reinforcing the bridge foundation can reduce the effect of landslide thrust on the bridge foundation and maintain a uniform distribution of earth pressure behind the bridge foundation, mitigating seismic effects. The dynamic earth pressure peaked at the top of the bridge foundation and then decreased along the depth. The back-row anti-slide piles displayed greater resonance coupling and unloading effects before and after reaching the load-carrying limit, respectively. In seismic strengthening design involving bridge foundations and gravel landslides, when the earthquake-induced resonance coupling effect on inclined, loosely packed land masses is fully considered, pre-reinforcement measures (e.g., high-pressure grouting and anchor spraying) should be carried out on the gravel slopes.

Shaking table investigations on seismic performance of prefabricated corrugated steel utility tunnels

A series of shaking table model tests were performed to investigate dynamic responses and damage mechanisms of prefabricated corrugated steel utility tunnels holding various brackets and pipelines. Details of the shaking table experimental setup for this kind of new utility tunnel are presented in this paper for the first time. Multiple seismic responses are measured, including the displacement of the soil surface, acceleration and strain of the utility tunnel, pipelines and brackets, as well as the acceleration and dynamic earth pressure of the test soil. The results demonstrate that the model box designed by our lab did not impose an obvious boundary effect. Displacement of the overlying soil above two sides of the utility tunnel was larger than that of the center of the model in the field nearby. The acceleration response of the structure was perfectly consistent with the surrounding soil. Dynamic earth pressures acting against the tunnel sidewall were significantly affected by the tunnel’s mass distribution under strong excitations. Response acceleration varied with different kinds of pipelines and brackets. The peak strain obtained from the suspending bracket was larger than that of the standing bracket. Different types of brackets were suitable for different applications. Both of the utility tunnel and brackets were not yielded under strong ground motions. The results provide valuable insight into the seismic performance of the shallow-buried underground steel structure and the safe design of the prefabricated corrugated steel utility tunnel.

Shaking table study of the influence of facing on reinforced soil wall connection loads

Reinforcement plays an important role in seismic stability and performance of reinforced soil retaining walls, and accurate assessment of reinforcement connection loads is an essential step in internal stability analysis of reinforced soil retaining walls using pseudo-static methods. However, the influence that the choice of wall facing could have on reinforcement connection loads is not adequately addressed in the current pseudo-static methods of analysis. In this study, two shaking table tests were carried out on full-height panel and modular block reinforced soil retaining wall models in order to examine the influence of facing type on the connection loads in the two models. The magnitudes and distributions of measured connection loads in the two models are compared with each other and against predictions from two pseudo-static methods. Results of this study shows that reinforcement connection loads are primarily influenced by the outward inertial force of the facing rather than dynamic earth pressure. Predicted connection loads from the Bathurst and the FHWA method showed better agreements with the measured results on the modular block and full-height panel wall models, respectively.

Investigations of seismic response to an irregular-section subway station structure located in a soft clay site

In this study, shaking table tests were performed to investigate the dynamic interaction of a silty-clay soil with an irregular-section subway station. During the tests, a shape acceleration array (SAA) was used to measure the lateral deformation of the model soil, and a non-contact dynamic displacement testing method was applied to visualize and digitalize the seismic damage process of the station structure. Typical test results, including the dynamic earth pressure, seismic settlement, deformation, and acceleration of different levels of the structure, were interpreted. The results indicated that the movement of the subway station was more controlled by the surrounding silty-clay soil in terms of phase and amplitude. SAA can effectively measure the soil deformation, and the relationship between the relative lateral displacement and soil depth can be well fitted in a cosine function, especially when subjected to strong earthquakes. Seismic settlement is significantly linked to Arias intensity, and the subway station experienced significant uneven settlement, resulting in soil-structure separation in the vertical direction. The multi-story irregular-section subway station deforms in a shear mode. The maximum inter-story drift ratio was approximately 1/171. The components in the lower layers of the shallow-buried subway station structure, particularly in the central columns, underwent cumulative damage. Hence, more robust forms of structural members and the ductility of central columns should be carefully considered in the seismic design of subway station structures.

Study on seismic behaviors of a double box utility tunnel with joint connections using shaking table model tests

Shaking table model tests were carried out to study the seismic behaviors of double box utility tunnel with joint connections and the surrounding soil. The seismic wave obtained from 1952 Taft earthquake was employed as the input in this study, and its PGA has been adjusted to 0.2 g, 0.4 g, 0.8 g, and 1.2 g, respectively. In addition, a series of sine waves with PGA of 0.2 g and frequencies of 5 Hz, 10 Hz, 15 Hz, 20 Hz, 25 Hz, and 30 Hz were applied to study the effect of frequency characteristics on seismic behavior of the utility tunnel and the surrounding soil. The testing results show that the laminar soil container does not impose significant boundary effect, and the dynamic earth pressure response is significantly influenced due to existence of the joint connection. Besides, the effect of soil-structure interaction on seismic behaviors is becoming even more obvious as the input PGA increases. The acceleration response is also significantly influenced by the dynamic property of the soil. Greater bending moment occurs at the corners of the structure, and its increasing ratio will decrease with an increasing input PGA magnitude. Lastly, the effect of frequency is significant. Therefore, it is noteworthy that the possible effect of natural frequency is considered when the utility tunnel is under construction.

Experimental study on seismic response of soilbags-built retaining wall

The seismic performance of soilbags-built retaining wall model was studied experimentally. A series of small-scale shaking table tests with the input of different amplitude sinusoidal waves and a large-scale shaking table test in a designed laminar shear box with the input of the Wenchuan earthquake wave were carried out on soilbags' retaining wall models. For comparison, the small-scale shaking table tests were also conducted on horizontally reinforced retaining wall models. The horizontal acceleration responses, the Fourier spectra, the dynamic earth pressure and the lateral displacements of soilbags' retaining wall models were investigated in shaking table tests. The results show that the seismic response of the soilbags' retaining wall is equivalent to or even slightly better than that of the horizontally reinforced retaining wall. The fundamental frequency and the Fourier spectral characteristics of the soilbags’ retaining wall are similar to those of backfill sands. The dynamic earth pressure of the wall model fluctuates almost synchronously with the input Wenchuan wave and no residual earth pressure is induced by the seismic loading. The permanent lateral displacements are small when subjected to multiple shakings, providing a proof that the retaining wall of soilbags has a good seismic performance.

Dynamic response characteristics and failure mode of slopes on the loess tableland using a shaking-table model test

Loess tablelands are widely distributed in the center of the Loess Plateau. The percentage of the Loess Plateau area that experiences seismic intensities greater than or equal to level VII is 54.21%. Because of the gravity of the loess slope and a large number of vertical pores, the fissures are mostly developed in the Loess Plateau. The fissures can easily cause slope instability subjected to earthquakes. Considering the structural characteristics of loess tableland slopes and earthquakes, a shaking-table test on slope models with and without fissures is conducted to study the dynamic response characteristics and the law of deformation and instability of the slopes under seismic action. The results indicate that the amplification factors of peak ground acceleration (PGA) in the vicinity of the fissures in the loess slope are significantly higher than those in the non-fissure slope, which reaches a maximum value of 3.6 at the shoulder of slope (measuring point A15). Dynamic earth pressures have stress concentration in the middle and upper part (0.7 times slope height) near the fissure, which affects the variation law of slope earth pressure. The failure mode of the fissure slope is as follows: fissure development, fissure expansion, soil collapse at the slope shoulder, shear failure at high-position on the slope, shear failure at low-position on the slope, and formation of new fissures at the edge of the tableland.

EXPERIMENTAL STUDY OF SEISMIC RESPONSE OF THE SQUARE TUNNEL IN GRANULAR SOIL

In this study a series of shaking table tests were carried out to investigate the effect of tunnel model depth and direction of ground acceleration on the horizontal acceleration of tunnel model and soil beside it, ground surface settlement, and the dynamic earth pressure on the tunnel wall. Square tunnel model embedded in both dry and saturated soil (Karbala Sand). It subjected to three input sinusoidal motions 0.05g, 0.1g, and 0.2g. Two relative densities used, 30% for the upper layer and 70% for the lower layer. The results obtained indicate that the direction of seismic loading has significant effect on the horizontal acceleration of tunnel model. The increase of tunnel model depth lead to decrease the horizontal acceleration of tunnel model. While, the settlement of soil surface increases with an increase of tunnel model depth and ground acceleration especially at 0.2g earthquake loading. The change of direction of seismic loading leads to a small change in the settlement for dry soil. The results appear that dynamic earth pressure (DEP) was positive in dry soil and negative in saturated soil in all test. In saturated soil, the effect of direction of ground acceleration and depth of tunnel model on DEP in 0.2g is quite little.

A Pseudodynamic Approach of Seismic Active Pressure on Retaining Walls Based on a Curved Rupture Surface

Reasonable determination of the magnitude and distribution of dynamic earth pressure is one of the major challenges in the seismic design of retaining walls. Based on the principles of pseudodynamic method, the present study assumed that the critical rupture surface of backfill soil was a composite curved surface which was in combination with a logarithmic spiral and straight line. The equations for the calculation of seismic total active thrusts on retaining walls were derived using limit equilibrium theory, and earth pressure distribution was obtained by differentiating total active thrusts. The effects of initial phase, amplification factor, and soil friction angle on the distribution of seismic active earth pressure have also been discussed. Compared to pseudostatic and pseudodynamic methods for the determination of planar failure surface forms, the proposed method receives a bit lower value of seismic active earth pressures.

Seismic behavior of a single-form lattice anchoring structure and a combined retaining structure supporting soil slope: a comparison

The lattice anchoring structure is a widely used single-form retaining structure to enhance the stability of soil slope. Meanwhile, the lattice anchoring beam is commonly combined with a gravity wall, namely a combined retaining structure, to support the high slope in engineering practice. In this study, the numerical models for both a single-form lattice anchoring structure and a combined retaining structure were established using FLAC3D code. The Wenchuan ground motions with different amplitudes were applied to investigate and compare the seismic response of the single-form lattice anchoring structure and the combined retaining structure regarding the earth pressure response, the deformation response, the mechanical characteristic of anchor and the element state of structure during earthquake. The numerical results were verified by shaking table test in terms of the dynamic earth pressure response and the axial stress of anchor. Although an intense earth pressure response was observed behind the combined retaining wall, the combined retaining structure was recommended to support the high slope in high seismic intensity region instead of the single-form lattice anchoring structure in view of the deformation of structure, the axial stress of anchor and the failure state of element.

Seismic performances of three- and four-sided box culverts: A comparative study

Studying the critical response characteristics of box culverts with diverse geometrical configurations under seismic excitations is a necessary step to develop a reasonable design method. In this work, a numerical parametric study is conducted on various soil-culvert systems, aiming to highlight the critical difference in the seismic performances between three- and four-sided culverts. Two-dimensional numerical models consider a variety of burial depths, flexibility ratios and foundation widths, assuming a visco-elastic soil condition, which permits to compare with the analytical solutions and previous studies. The results show that flexible three-sided culverts at a shallow depth considerably amplify the spectral acceleration and Arias intensity. Larger racking deformation and rocking rotation are also predicted for the three-sided culverts, but the bottom slab influence decreases with increasing burial depth and foundation width. The bottom slab combined with the burial depth and structural stiffness also significantly influences the magnitude and distribution of the dynamic earth pressure. The findings of this work shed light on the critical role of the bottom slab in the seismic responses of box culverts and may have a certain reference value for the preliminary seismic design using R-F relation.

Sand–scrap tyre chip mixtures for improving the dynamic behaviour of retaining walls

ABSTRACT This paper presents the dynamic response of retaining wall models backfilled with different types of sand–tyre chips (STC) mixtures using shaking table tests. The STC mixtures with different tyre chips proportions, such as STC10, STC20, STC30, STC40, STC50 and STC0 (control test) were considered as backfill materials. A 600 mm retaining wall that is produced in a box this is certainly anchored on a shaking table that will produce dynamic excitations. According to the tyre chips content in sand, up to 50% to 65% reduction in wall displacements and 70% to 80% lowering of dynamic earth pressures were observed. The exploratory study reveals the seismic actions of a retaining wall with STC30 backfill over an retaining wall using conventional backfill.

Assessment of Soil Tunnel Interaction in Sand Soil

In this study, series of shaking table tests were carried out to investigate the effect of tunnel model depth and direction of ground acceleration on the ground surface settlement and the dynamic earth pressure on the tunnel wall. Box tunnel model is embedded in dry and saturated soil (Karbala Sand). It subjected to three input sinusoidal motions 0.05g, 0.1g, and 0.2g. Two relative densities were used, 30% for the upper layer and 70% for the lower layer. The results obtained indicate that the settlement of soil surface increases with an increase in ground acceleration. The increase in tunnel model depth leads to an increase in settlement especially at 0.2g earthquake loading (for saturated and dry soil). The change of direction of seismic loading leads to a small change in the settlement for dry soil. The results appear that dynamic earth pressure (DEP) was positive in dry soil and negative in saturated soil in all test. In saturated soil, the effect of direction of ground acceleration and depth of tunnel model on DEP in 0.2g is quite little.

Shaking table test on the seismic response of large-scale subway station in a loess site: A case study

More and more underground infrastructures have been built in special soil in recent years, especially in the loess area of western China. The loess, as a special soft soil, can have particular influence on the seismic characteristics of underground structures. Therefore, the seismic performance and safety evaluation of underground structures in loess area should be concerned. A series of large-scale shaking table tests were performed to investigate the damage mechanisms of a frame-type subway station structure in a loess site. The test results showed that the model soil softening and the stiffness degradation of the soil-structure system were more serious under stronger input motions. The acceleration response of the soil-structure interaction system in a loess site was more like that of a free-field when input PGA is lower. However, the soil-structure interaction phenomenon was more remarkable both in horizontal and vertical direction when higher PGA was input. The dominant frequency of the input motion had an inverse effect on the lateral soil deformation. The direct-force action mode of the dynamic earth pressure acting on underground structures presents a trumpet-type distribution. Meanwhile, the soil-structure interaction exhibited complex mechanical behavior, and slipping or gapping in test cases with higher PGA may occur. The strain measured in the center pillar and middle slab of the subway station was larger than that in other components. The results provide an insight into how strong ground motion might induce the influence and a possible way to describe quantitatively the damage of subway structure in loess ground.

Seismic responses of vertical-faced wrap-around reinforced soil walls

A series of shaking table tests on geosynthetic-reinforced walls with a height of H = 0.6 m is performed to investigate the seismic performance of prototype walls with H = 6 m. Ground-wall resonance occurs at small values of horizontal peak ground acceleration (HPGA), namely 0.1–0.5g, with an amplification factor of Am = 1.2–2.2 at the crest of the wall. This factor decreases with increasing HPGA. For walls that attain states of maximum horizontal displacement (Dmax)/H > 5%, the failure mechanism consists of a vertical failure surface at a distance from the facing of 0.3H for the upper half of the wall and a Rankine triangular wedge over the lower half of the wall. Mononobe-Okabe theory gives dynamic earth pressure coefficients that agree well with experimental results based on kh = η·HPGA/g, where khand η are the horizontal seismic coefficient and an empirical constant, respectively, with values of η ranging from 1/4 to 1/3. Furthermore, the maximum tensile forces induced by shaking increase as the depth of reinforcement increases, generating a trapezoidal shape rather than the inverted trapezoidal shape proposed in the literature.

Response of full-height frame integral abutments subjected to seismic motions

As a new type of bridge, integral bridges can significantly reduce long-term maintenance costs, and their application is encouraged in many countries. However, there is great uncertainty regarding the dynamic performance of full-height integral abutments during earthquakes. This paper presents the findings from a dynamic numerical simulation on a typical full-height frame integral bridge abutment. The influences of peak acceleration, bridge deck length, and abutment height are investigated. The effect of a mitigation method, i.e., installation of a compressible layer behind the abutment, is also discussed. The results highlight the effect of the rigid connection between the deck and the integral abutment, which will transfer the very large inertial force of the bridge deck to the abutment top and cause strong dynamic interaction between the abutment and the backfill. The traditional Mononobe-Okabe method adopted in current bridge abutment design codes cannot provide a reasonable prediction as to the dynamic earth pressure behind integral abutments, leading to unsafe designs. Although a compressible layer can reduce the dynamic earth pressure, the deformation and bending moments of the abutment will increase as a result of the much lower restraint provided by the compressible layer during earthquakes.