Study of the behavior of mechanically stabilized earth (MSE) walls subjected to differential settlements

The limit equilibrium (LE) analysis has been used to design MSE walls. Presumably, the deflection of MSE walls can be limited to an acceptable range by ensuring sufficient factors of safety (FOSs) for both external and internal stabilities. However, unexpected ground movements, such as movements induced by excavations, volume changes of expansive soils, collapse of sinkholes, and consolidations of underlying soils, can induce excessive differential settlements that may influence both the stability and the serviceability of MSE walls. In this study, a numerical model, which was calibrated by triaxial tests and further by a specially-designed MSE wall tests, investigated the behavior of an MSE wall as well as the influence of various factors on the performance of the MSE wall when the wall facing settled relatively to the reinforced zone. The numerical results showed that the differential settlement would cause substantial vertical and horizontal movements for the MSE wall, as well as an increase in lateral earth pressure and geosynthetic reinforcement strain. The maximum horizontal movement and increase of the lateral earth pressure occurred at about 1.0 m above the toe. The differential settlement resulted in a critical plane that coincided with the plane of 45°+?/2. The maximum increase of the strain for each geogrid layer occurred in that plane, and the bottom layer had the greatest strain increase among all layers of reinforcement. The study further indicated that the surcharge, backfill friction angle, tensile stiffness of geogrid, reinforcement length and MSE wall height had noticeable influences on horizontal and vertical movements, and strain in geosynthetics. According to the results, the MSE wall that had a higher factor of safety would have less movements and geosynthetic strain increase. In contrast, only the friction angle, tensile stiffness and MSE wall height showed some degree of influence on the lateral earth pressure due to differential settlements.     

Shaking table performance of reinforced soil retaining walls with different facing configurations

In this paper, a new type of MSE wall facing, termed as hybrid facing, is introduced and studied, which is built using a combination of concrete modular blocks and cast-in-place concrete. Two shaking table tests were carried out to compare seismic performances of model reinforced soil retaining walls with full-height vs. hybrid facing configurations. Results of this study show that the stability and performance of the hybrid facing model were similar to those of the full-height panel wall for peak input acceleration magnitudes less than 0.40 g. The amplification factors along the height of the facing were more uniform and smaller in the hybrid facing model as compared to the full-height panel wall, especially at higher peak acceleration amplitudes. Dynamic increment of lateral earth loads acting on the facing in both cases were found to be only 20% of the values calculated using pseudo-static methods. Connection loads in the hybrid facing model were smaller than those in the full-height panel wall, which was attributed to its smaller facing displacements.     

Centrifuge modeling of geosynthetic-reinforced soil retaining walls subjected to the combined effect of earthquakes and rainfall

Local fine-grained soils were usually used as backfill for geosynthetic-reinforced soil retaining walls (GSRWs). However, there are few studies on the seismic response in this case, especially under the influence of rainfall. In this study, three centrifuge shaking table tests were performed at 30 gravities to investigate the performance of GSRWs subjected to the combined effect of earthquakes and rainfall. Two stages were designed in this study. In the first stage, three conditions were simulated, i.e., post-rainfall earthquake (Test-1), rainfall and earthquake occurring simultaneously (Test-2), and post-earthquake rainfall (Test-3). The results show that if there was enough time for rainwater seepage, the suction force generated in unsaturated GSRW enhanced the soil strength. When GSRW was subjected to heavy rainfall and no time for seepage, the deformation of the GSRW was largest due to the high excess pore water pressure of local saturated soil in GSRW. In the second stage, seismic failure models of GSRWs with different water contents were studied. Under the excitation of a series of continuous earthquakes, a large tensile crack was formed in the unsaturated GSRW, whereas no cracks were found in the saturated GSRW, but its panel demonstrated a large bulging deformation.     

一字形短肢剪力墙抗震性能的模型试验研究

为了研究一字形短肢剪力墙的抗震性能,对其进行了低周反复荷载试验研究。设计制作6片不同轴压比(0.3、0.5、0.7分别制作二组)和3片不同配筋方式的一字形短肢剪力墙模型及试验加载装置,对9片剪力墙进行了抗震性能试验。基于试验结果,对试件的破坏形态、滞回性能、位移延性、耗能能力、刚度退化等方面进行了分析,结果表明:轴压比对一字形短肢剪力墙的抗震性能影响较大,随着轴压比的增大,试件表现出明显的脆性破坏;配有X型交叉筋的短肢剪力墙的裂缝分布均匀,承载能力较高,延性较好。提出了一字形短肢剪力墙一般应采用带暗柱及X形交叉配筋形式并严格控制轴压比限值等建议。