Shaking Table Test of Geogrid Reinforced Soil Slope with Gabion Surface Protection

The southwestern mountainous region of China is tectonically active and characterized by high, steep anti-dip rock slopes with weak intercalations. Under seismic action, the dynamic response characteristics of these slopes are complex, and the mechanisms of deformation and damage remain unclear, hindering effective disaster risk prevention and control. Based on extensive investigations of high and steep slopes in the upper reaches of the Jinsha River, a conceptual geological model is developed. It examines the dynamic response characteristics and deformation failure of the slopes under varying conditions of peak ground acceleration(<italic>PGA</italic>), seismic wave frequency, and loading direction through large-scale shaking table model tests. The results indicate pronounced nonlinear dynamic response characteristics of weak interlayer anti-dip rock slopes under seismic action, exhibiting significant height and surface effects. As the<italic> PGA</italic> increases, these two dynamic amplification effects become more prominent. The vertical dynamic response of slopes within the range of 1/3<italic>h</italic> to 2/3<italic>h</italic> demonstrates a surface effect when subjected to sinusoidal waves. As the frequency of sinusoidal waves increases, the region exhibiting a greater dynamic response gradually shifts from 1/3<italic>h</italic> to 2/3<italic>h</italic> towards the foot of the slope. When <italic>PGA</italic>≥0.4 <italic>g</italic>, under the action of a 2 Hz sinusoidal wave, the dynamic response in the damage area at the top of the slope shows signs of decay. Under the influence of the Wenchuan wave, the horizontal dynamic response at the slope<italic>'</italic>s top and surface is significantly weaker than the vertical dynamic response. However, under the effect of high peak ground acceleration(<italic>PGA</italic>≥0.4 <italic>g</italic>) seismic waves, an opposing pattern is observed. The vertical dynamic response in the upper range of 1/2<italic>h</italic> to 5/6<italic>h</italic> of the slope is stronger when loading occurs simultaneously in the <italic>x</italic> and <italic>z</italic> directions compared to loading the Wenchuan wave solely in the <italic>x</italic> direction. The deformation and failure process of the slope model can be categorized into five stages: the tiny damage stage, the cracking stage at the slope top, the failure stage at the slope shoulder, the evolution stage of the sliding surface, and the instability stage of the sliding surface.

Examining dynamic soil pressures and the effectiveness of different pile structures inside reinforced slopes using shaking table tests

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.

Geogrid reinforced soil slope is a new type of slope supporting structure, which is of great significance for improving the slope stability, saving construction land and preserving the ecological environment. In order to provide the optimal design solution of the reinforced soil slope for high fill slopes, a case study is conducted on the No.6 slope at the northwest corner of the airport runway. Three design schemes with different slope ratios are carried out firstly based on the geological conditions of the slope and the field situation of the high fill slope. Secondly, the simplified Bishop method, Spencer wedge method and Morgenstern price method are used to calculate the stability factors of the reinforced slopes under the natural, rainstorm and earthquake conditions. Finally, the deformation characteristics of the slope and tensile force in reinforcements are investigated based on the finite element method under the natural conditions. The results show that all the proposed design schemes can meet the requirements of slope stability under different working conditions. A zigzag distribution of the tensile force in reinforcements in the multi-stage reinforced soil slope is observed along the slope height, and the maximum axial force of reinforcement increases abruptly at the toe of each slope. Compared with the design scheme of the gentle reinforced soil slope with the slope ratio of 1∶1.5, the reinforced retaining wall with the slope ratio of 1∶0.25 shows obvious advantages in reducing the slope height, consumption of geosynthetics, filling and excavation amount as well as slope protection area. The key issues including the slope stability, construction cost and duration are comprehensively considered, and the design scheme of the reinforced earth wall is reasonable.

Based on the similarity theory, two physical testing models (double-hole tunnel and single-hole tunnel) with a scale of 1:10 were designed and manufactured. A series of shaking table tests followed by numerical simulations was carried out to obtain the dynamic response characteristics of shallow-buried tunnels with asymmetrical pressure distributions. The similarities and differences in the dynamic response laws between double-hole tunnel and single-hole tunnel were studied. The effects of types of seismic wave (Wenchuan wave, Darui artificial wave, and Kobe wave), peaks acceleration excitation (0.1 g, 0.2 g, 0.4 g, and 0.6 g), excitation directions (horizontal and vertical directions), and excitation modes (unidirection and bidirection) on dynamic response laws of the tunnels were studied. The results show that the variation of acceleration multiplying factor (AMF) shows a nonlinear trend. The AMFs are different at different monitoring points. The type of seismic wave has a significant effect on the acceleration response, with Kobe wave being the most serious, followed by the Darui artificial wave and the Wenchuan wave. In bidirectional excitation, the AMFs are relatively larger than those of unidirectional excitation. A comparison between the numerical simulation and the shaking table tests in both acceleration time history and peaks acceleration shows that the results of the shaking table tests and numerical simulations are credible. The acceleration response of monitoring points near the existing slope is generally magnified. The residual strains are generated at the monitoring points. The variation trends of both tensile strain and compressive strain are opposite. The tensile strains are generally larger than the compressive strains. Many factors, such as the type of seismic wave, peaks of acceleration excitation, excitation direction, and excitation mode, have a significant influence on the dynamic strain response and acceleration response of the tunnels. The research results could promote the understanding of dynamic response characteristics of the tunnels.

In order to study the seismic response of the embankment slopes with different reinforcing measures, shaking table tests were performed on three embankment slope models (i.e., unreinforced embankment slope, 2-layer reinforced embankment slope and 4-layer reinforced embankment slope). Wenchuan earthquake motions and white noise excitations were performed to investigate the change of the model parameters, the horizontal acceleration response, the vertical acceleration response and the dynamic earth pressure response of embankment slopes. A comparison was made on the seismic response among the embankment slopes with different reinforcing measures. The results show that the natural frequency of reinforced embankment slope is larger than that of unreinforced embankment slope, and the reinforced embankment slope is less sensitive to seismic excitation. Horizontal acceleration response is obviously amplified by embankment slope. Horizontal acceleration magnification presents a decreasing trend with the increase of the peak value of input horizontal acceleration, and the decreasing ratio is higher for reinforced embankment slope. The vertical acceleration magnification of reinforced embankment slope is much smaller than that of unreinforced embankment slope, and the nonlinear characteristic of embankment slope in vertical direction is not as obvious as that in horizontal direction. Residual earth pressure is mainly induced at the upper part of embankment slope.

Based on the similarity theory, a physical testing model with scale of 1:10 was designed and fabricated. The Wenchuan wave (WC-XZ), Darui artificial wave (DR-XZ) and Kobe wave (K-XZ) were adopted as excitation waves which was XZ directions (horizontal and vertical loading at the same time). A series of shaking table tests were carried out to study the effect of the types, directions and peaks acceleration of the seismic waves on the acceleration response laws of the shallow-buried bias tunnels with small distance. The results show that: (1) in the horizontal direction, the types of the seismic waves have a little effect on the acceleration response, but the law is opposite with Kobe wave being the most serious, followed by Darui artificial wave and Wenchuan wave in the vertical direction. (2) The existing slope has a significant effect on the acceleration response of the right hole which is different from that of the left hole. (3) The acceleration response of the tunnel in the vertical direction is more severe than that of the horizontal direction and the acceleration amplification factors in vertical direction are is generally 1.02-3.94 times that of the horizontal direction. (4) in the seismic design of tunnel, different seismic measures should be adopted in different directions. The results have a significant reference for the anti-seismic design of the tunnel.

Effect of frequency on seismic response of reinforced soil slopes in shaking table tests

Slope stability analysis is one of the most intricate problems of geotechnical engineering because it is mathematically difficult to search the critical slip surface of earth slopes with complex strata owing to the involved multimodal function optimization problem. At present, a minimum factor of safety for a non-circular slip surface in a uniform and unreinforced earth slope can be calculated using several methods; however, for a reinforced soil slope, it cannot be easily calculated because of the additional effect of the reinforcement. One efficient method to search the critical slip surface is particle swarm optimization (PSO). PSO can solve complex non-differentiable problems, and its increasing ease of use has facilitated its application to multimodal function optimization problems in a variety of fields. However, the recommended PSO parameters to calculate the safety factors of unreinforced and reinforced soil slopes, namely the inertia and local and global best solution weighting coefficients, have not been sufficiently investigated. Moreover, the computational efficiency of PSO for safety factor calculation, including computational accuracy and time, has not been clarified. To calculate the unreinforced and reinforced soil slope safety factors, this study considers force and moment equilibriums, including the tensile force of the reinforcement. Firstly, the computational efficiency of the calculation process by PSO was shown to increase the maximum number of slip surface nodes in the calculation of the safety factor. Then, an analysis was carried out to investigate the safety factor sensitivity to the PSO parameters. Based on this analysis, appropriate PSO parameters for the safety factor calculation of unreinforced and reinforced soil slopes were proposed.

In this study, the failure mode of flexible reinforced soil slopes under earthquake action was investigated by shaking table tests. The distribution law of a potential failure surface of a flexible no‐faceplate reinforced soil slope under earthquake action was obtained based on the analysis results. A simplified trilinear failure surface suitable for flexible reinforced soil slopes without faceplate was proposed. Subsequently, based on the upper‐bound theorem of limit analysis, we derived the formula for calculating the yield seismic acceleration coefficient of a flexible no‐faceplate reinforced soil slope under a seismic load. The main parameters that affect its seismic performance were determined. The flexible geogrid reverse‐packed reinforced earth structure can effectively limit the fracture of a slope body and improve the stability of the slope. This provides a theoretical basis for facilitating the engineering of flexible reinforced soil slopes.

This paper studies the effect of slope angle on the seismic response of unreinforced and reinforced soil slopes through a series of laboratory shaking table tests. Slopes were constructed using clayey sand and geogrids were used for reinforcing the slopes. The slope angle varies from 45°, 60° and 75° in different tests and the quantity and location of reinforcement is varied in different tests. Acceleration of base shaking varies from 0.1 to 0.3 g in the model tests and the frequency of base shaking was 2–10 Hz in different tests. The slope is instrumented with ultrasonic displacement sensors and accelerometers at different elevations. The response of different slopes is compared in terms of the horizontal displacements of the slope and acceleration amplifications measured at different elevations. At all frequency levels and base acceleration conditions, unreinforced slopes showed higher acceleration amplifications and increased displacements with the increase in steepness It was also observed from the test results that increase in steepness of the slope has detrimental effects on both acceleration amplifications and displacement response of unreinforced as well as reinforced model soil slopes.

Full-scale shaking table tests of cross-laminated timber structures adopting dissipative angle brackets and hold-downs with soft-steel and rubber

In order to get the seismic active earth pressure with the mode of translation, adopting some related assumptions of the M-O theory, this paper establishes the first-order differential equation of the Seismic active earth pressure by horizontal slices analysis method and gets the solution of the seismic active earth pressure by boundary conditions. This formula can solve the distribution of the seismic active earth pressure is nonlinear along the wall, the point of application of the dynamic active thrust which is the advantage of this formula and announces the decreasing process of the filling’s rupture angle with the increase of the horizontal peak ground acceleration (PGA) , as well. The rationality and validity of the formula is confirmed by the comparison between the results of the shaking table tests and the formula, respectively. If the retaining wall takes place the mode of translation, the point of application of the seismic active thrust ranges between 0.4 and 0.5 times wall’s height at the horizontal seismic peak ground acceleration (PGA)&lt;0.4g.At the same time, the computational accuracy of the dynamic active thrust, their points of application and the angle of rupture increases with the increase of the horizontal peak ground acceleration at the horizontal PGA&lt;1.0g, as the astigmatic of the retaining wall in highly seismic intensity region supplying the valuable reference.

Load transformation from the yielding part of the soil to the adjacent part is known as the soil arching effect, which plays an important role in the design of various geotechnical infrastructures. Terzaghi’s trapdoor test was an important milestone in the development of theories on soil arching. The research on earth pressure of the trapdoor problem is presented in this paper using the three-dimensional (3D) discrete element method (DEM). Five 3D trapdoor models with different heights are established by 3D DEM software PFC 3D. The variation of earth pressure on the trapdoor with the downward movement of the trapdoor, the distribution of vertical earth pressure along the horizontal direction, the distribution of vertical earth pressure along the vertical direction, the distribution of lateral earth pressure coefficient along the depth direction, the magnitude and direction of contact force chain are studied, respectively. Related research results show that the earth pressure on the trapdoor decreases rapidly after the downward movement of the trapdoor, and then reaches the minimum earth pressure. After that, the earth’s pressure will rise slightly, and whether this phenomenon occurs depends on the depth ratio. For the bottom soil, due to the stress transfer caused by the soil arching effect, the ratio of earth pressure in the loose area decreases, while the ratio of earth pressure in the stable area increases. With the trapdoor moving down, the vertical earth pressure along the depth in the stable zone is basically consistent with the initial state, which shows an approximate linear distribution. After the trapdoor moves down, the distribution of earth pressure along with the depth in the loose area changes, which is far less than the theoretical value of vertical earth pressure of its self-weight. Because of the compression of the soil on both sides, the lateral earth pressure coefficient of most areas on the central axis of the loose zone is close to the passive earth pressure coefficient Kp. The existence of a ‘soil arch’ can be observed intuitively from the distribution diagram of the contact force chain in the loose zone.

By means of installing sloped rolling-type seismic isolators (SRI), the horizontal acceleration transmitted to the to-be-protected object above can be effectively and significantly reduced under external disturbance. To prevent the maximum horizontal displacement response of SRI from reaching a threshold, designing large and conservative damping force for SRI might be required, which will also enlarge the transmitted acceleration response. In a word, when adopting seismic isolation, minimizing acceleration or displacement responses is always a trade-off. Therefore, this paper proposes that by exploiting the possible information provided by an earthquake early warning system, the damping force applied to SRI which can better control both acceleration and displacement responses might be determined in advance and accordingly adjusted in a semi-active control manner. By using a large number of ground motion records with peak ground acceleration not less than 80 gal, the numerical results present that the maximum horizontal displacement response of SRI is highly correlated with and proportional to some important parameters of input excitations, the velocity pulse energy rate and peak velocity in particular. A control law employing the basic form of hyperbolic tangent function and two objective functions are considered in this study for conceptually developing suitable control algorithms. Compared with the numerical results of simply designing a constant, large damping factor to prevent SRI from pounding, adopting the recommended control algorithms can have more than 60% reduction of acceleration responses in average under the excitations. More importantly, it is effective in reducing acceleration responses under approximately 98% of the excitations.