Yu-liang Lin

Seismic response of embankment slopes with different reinforcing measures in shaking table tests

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.

Dynamic behavior of railway embankment slope subjected to seismic excitation

To reveal the dynamic behavior of a railway embankment slope subjected to seismic excitation, a shaking table model test was performed on a 1:8 scale embankment slope. Different types of seismic wave of differing amplitudes were applied to study the dynamic behavior of the embankment slope, and white noise excitations were interspersed among the seismic waves to observe the changes of dynamic characteristics of the embankment slope. Residual deformation behaviors of the embankment slope were also investigated. The results of the tests show that the natural frequency of the embankment slope exhibits a decreasing trend and that the damping ratio exhibits an increasing trend. The embankment slope exhibits a significant amplification effect on the input acceleration, and the acceleration response differs greatly when subjected to different seismic excitations of differing spectrum characteristics. The filler of the embankment slope affects the changes of the spectrum characteristics of the seismic wave. The filler performs a filtering effect on high-frequency seismic waves and amplifies the energy of low-frequency seismic waves, especially when the frequency is close to the natural frequency of the embankment slope. A bidirectional excitation creates a greater acceleration response than a unidirectional excitation does. The seismic residual deformation of the embankment slope occurs under the seismic subsidence mode.

Reliability back analysis of shear strength parameters of landslide with three-dimensional upper bound limit analysis theory

It is essential to determine the shear strength parameters c and φ on the sliding surface for stability evaluation and engineering design of a landslide. In this study, a new parameter back analysis method is proposed by combining the 2D/3D upper bound method of limit analysis and reliability theory to accurately determine the shear strength parameters for a 3D slope with a single failure surface. The proposed reliability back analysis method overcomes the shortcomings of the traditional deterministic analysis method of slope stability that cannot take into account the randomness and uncertainty of geotechnical parameters. Based on the reliability theory, two methods were studied: first-order reliability method (implemented by spreadsheet and Matlab, called spreadsheet method and constrained optimization method, respectively, in this paper) and Monte Carlo simulation. The optimized values of c and φ were obtained by establishing only one balance equation with the consideration of the pore water pressure or other complex conditions, which can solve the problem of the back analysis of strength parameters for a single 3D sliding surface condition. The correlation research showed that the negative correlation between c and φ greatly affected the back analysis results, and the reliability index values were conservative without considering such a negative correlation. A case study for the back analysis of shear strength parameters is conducted based on a practical landslide model with a broken line slip surface slope in Zhuquedong village, Luxi town, Xiangxi County, Hunan Province, China, and a suggestion for the selection of landslide cross section is presented. The results show that the back analysis results determined by the reliability theory coincide well with the survey and experimental results. The proposed method is found to be more accurate and effective in determining the values of shear parameters than that of the traditional deterministic inversion method.

Test Study on Engineering Properties of Gabion Structures

In order to study mechanical characteristic of gabion meshes, engineering properties of reinforced gabion retaining wall and green reinforced gabion retaining wall, tests including air tensile tests of gabion meshes, fatigue and aseismatic tests on gabion structures were carried out. The main tensile mechanical indexes of gabion meshes, fatigue property and seismic behavior of these two gabion structures were obtained. Test results showed: Air tensile curves of gabion mesh showed a zigzag shape; Main factors influencing the dynamic deformation behavior of gabion structures were amplitude of dynamic load, vibration times and so on, and vibration frequency had no significant influence; In fatigue tests, the maximum accumulated lateral deformation occurred in the third layer for reinforced gabion retaining wall, and the fifth layer for green reinforced gabion retaining wall; Accumulated deformation ratios of gabion structures were less than 1% under fatigue load; Both of these two gabion structures were excellent aseismatic structures, and they could bear earthquake action with seismic intensity of eight.

Pullout Test Study on Interface Friction Characteristics of Reinforcements with Red Sandstone as Filler

In order to study interface friction characteristics between reinforcements and red sandstone, pullout tests were carried out. Three reinforcements were chosen: 2.2 mm gabion mesh, 2.7 mm gabion mesh and 70RE geogrid. The pullout coefficient, cohesion and friction angle of these three reinforcements were obtained. The curves of pullout friction coefficient and normal stress, shear stress and pullout displacement were established. Test results showed: Pullout friction coefficient decreased nonlinearly with the increase of normal stress; When the pullout displacement reached a certain value, shear stress tended to be stable, and most of which presented a peak value; Pullout coefficients of different reinforcements differed greatly; Double twisted hexagonal gabion mesh had better interface friction characteristic than geogrid; The smaller the diameter of gabion mesh was, the better the interface friction characteristic would be; In general, the pulling-out process of reinforcements could be divided into three stages: initial stage, developing stage and yield stage. During the test, special clamping system was installed to limit lateral deformation of specimen.

Deformation Behavior and Dynamic Stress Response of High Railway Embankment under Cyclic Load

The deformation of railway embankment is strictly controlled to ensure the safety of train running. In order to study the engineering behavior of railway embankment, simulation analysis on railway embankment with height of 8 m was carried out. Dynamic loads with amplitudes of 0~50 kPa and 0~100 kPa were imposed. The deformation behavior and dynamic stress response of embankment were studied. The results show that the embankment presents attenuation effect on dynamic stress. The static earth pressure near the top of embankment is enhanced, and the static earth pressure at the bottom of embankment is released. The increase of train load will change the failure mode of embankment. The deformation mode of embankment is in subsidence mode when the amplitude of dynamic load is 0~50 kPa, and deformation mode turns sliding mode when amplitude is 0~100 kPa.

Settlement Behavior of New Reinforced Earth Retaining Walls under Loading-Unloading Cycles

Three new types of reinforced earth structures were introduced including reinforced gabion retaining wall, green reinforced gabion retaining wall and flexible wall face geogrid reinforced earth retaining wall. In order to study settlement behavior of these three retaining walls, lab tests were carried out. Cyclic loading-unloading of different levels (0~50kPa, 0~100kPa, 0~150kPa, 0~200kPa, 0~250kPa, 0~300kPa, 0~350kPa) were imposed. The settlement behaviors of retaining walls were analyzed, and secant modulus when loading and unloading was obtained. Results show that retaining walls present great elastic and plastic deformation, and plastic deformation is greater than elastic deformation. Secant modulus decreases with the increase of loading-unloading cycles under the same loading level. Unloading secant modulus is bigger than loading secant modulus in the same cycle. With the increase of loading level, both elastic and plastic deformation increase, and plastic deformation increases more quickly than elastic deformation.

Dynamic Deformation Behavior and Life Analysis of Green Reinforced Gabion Retaining Wall

In order to study dynamic deformation behavior of green reinforced gabion retaining wall, lab test was carried out and the dynamic loads of 4 frequencies and 4 amplitudes were imposed. The total cycles of dynamic load reached 2 million. Lateral and vertical deformation behaviors of green reinforced gabion retaining wall were investigated, and the main factors which influenced the dynamic deformation behavior and their significance were obtained. Meanwhile, fatigue life analysis on green reinforced gabion retaining wall was made. The results show that dynamic deformation is greatly affected by amplitude and the cycles of dynamic load, not significantly affected by frequency. The maximum lateral and vertical deformation occur in the fifth layer of green reinforced gabion wall. With the increase of train load and train speed, fatigue damage and fatigue life of green reinforced gabion retaining wall can be estimated based on accumulative fatigue damage theory.