This paper presents an experimental study of shaking table tests on two back-to-back mechanical stabilized earth (MSE) walls with different width-to-height ratios (R_WH) of R_WH = 1.6 and 1.1, to investigate the influence of R_WH on the dynamic response. The reduced-scale MSE wall models were designed according to the similitude relationships considering model geometry, reinforcement stiffness, and input motions. The back-to-back MSE wall models were constructed using poorly graded backfill soil and geogrid reinforcement, and then were excited using a series of sinusoidal input motions with increasing acceleration. Results indicate that the incremental facing displacements and residual facing displacements of the two back-to-back MSE walls increase significantly with increasing input acceleration. For the back-to-back MSE walls with R_WH = 1.6, the predominant facing deformation mode is rotation for smaller input acceleration. However, the deformation mode becomes bulging with the highest displacement near the mid-height for higher accelerations. For the back-to-back MSE walls with R_WH = 1.1, the predominant facing deformation mode is rotation during shaking. Back-to-back MSE walls with small R_WH exhibited better seismic performance under the same input motions.

Ground improvement by rigid inclusions (RI) utilizes rigid columns to support foundations and embankments. Unlike conventional piles, the foundation and the RIs are separated by a granular compacted load transfer platform (LTP). The inclusions, the LTP and the surrounding soil act together to create a versatile and effective ground improvement system. Rigid inclusions are being introduced into new markets such as the Middle East or Asia, where their advantages and limitations are not yet well known, and where there is no official guidance nor codes of practice locally available. The design principles under static loading are straightforward and generally consistent in the industry, even in new markets. However, for seismic performance and liquefaction, there is far less consensus and without careful consideration, this can sometimes lead to unsafe design. Therefore, this paper provides a brief review of the critical factors to consider when designing rigid inclusions in seismic conditions, namely assessment of liquefaction and a realistic assessment of the liquefaction mitigation effect of rigid inclusions, consideration of lateral forces (both kinematic and inertial), and finally stability and settlement verification. A logical design procedure, consistent with international norms, is proposed for use in both liquefiable and non-liquefiable soil conditions. The procedure is summarized in a flow chart and demonstrated on an illustrative example based on sample site from the Middle East.

The sand boil damage suppression (SBDS) method using artificial drainage material (ADM) is a new concept-based countermeasure against sand boil damage such as uneven and undulated ground surface caused by liquefaction during earthquakes. The principle of this method is to rapidly absorb the upward seepage flow generated by propagating excess pore water pressure from the liquified sand layers, through the ADM system installed in the unsaturated soil layers and at the shallow depth of saturated soil layers. However, since there are still many points that have not been elucidated about the detail mechanism of sand boil, it is necessary to verify the method to suppress sand boil by ADM system. In this paper, through the numerical simulations on the mechanism of sand boil and the previous model tests, a new index by which to suppress sand boil by ADM in homogeneous unsaturated sandy soils has been proposed.

Geocell-reinforced slopes have proven to be one of the most efficient techniques of slope stabilization. However, the efficacy of utilizing geocell layers as fascia or reinforcement in slopes against seismic loading is yet to be intricately ventured. In this paper, numerical plane-strain modelling of geocell-reinforced slopes is carried out to study their response against seismic loading. Both pseudostatic analysis and non-linear time-history analysis are carried out considering a chosen strong motion history. Equivalent Composite Approach (ECA) is employed in modelling the 3-dimensional geocell layer as an equivalent 2-dimensional soil-geocell composite by introducing improved strength and stiffness imparted by the geocells. The improved strength is obtained from the additional confining pressure induced by the geocell pocket boundaries. The improved stiffness of the soil-geocell composite is calculated from the stiffness of the unreinforced slope material and the tensile modulus of the geocell material. Three different configurations of the placement of geocell layers are implemented to evaluate the response, where the geocell layers are introduced in the form of fascia, reinforcement, or a combination of both. The global stability of the reinforced slope sections is analysed using pseudostatic seismic coefficients assessed through different techniques, while the acceleration response and deformation of the slope face are analysed using an acceleration-time history input. The influence of geocell layers on the hysteresis behaviour of the slope face and on the development of potential slip surfaces is also investigated to yield motion specific observations.

This paper presents the kinematic interaction that exists between an over-consolidated cohesive soft soil and a group of rigid inclusions by performing two centrifuge tests using the dynamic centrifuge at Gustave Eiffel University in Bouguenais – France. Dynamic centrifuge tests were conducted at a macro-gravity of 50g and were subjected to the same predetermined sequence of seismic events constituted of sinusoidal motions and multi-frequency earthquakes of different peak ground accelerations. Kinematic interaction was studied by analyzing the soil's response in terms of acceleration and displacement at separate locations throughout the soil profile. Boundary effects were verified, and a frequency analysis was conducted in order to study the variation of the soil’s predominant frequency. Results indicate that signal transmissions were observed through the inclusions, leading to a larger response at the inclusions’ head compared the free field where attenuation was observed during the same ground motion.

Soil-nailed walls are retaining structures often used for their economic efficiency and ease of implementation. Moreover, post-earthquake surveys, and after the Loma Prieta earthquake, have demonstrated their exceptional seismic resilience, leading researchers to further investigate their seismic behavior and design. Among possible explanations, the repeated dynamic mobilization of friction at the interface between the soil and the nails is considered to be a major source of energy dissipation during an earthquake. Nevertheless, overdesigning soil-nailed walls to resist earthquakes increases their stiffness and, consequently, the amount of seismic energy transmitted to the supported structures. Inspecting an improvement of these walls seismic geotechnical design, the local dynamic soil-nail interface behavior appears to be of major concern. However, in the literature, only few studies have so far been devoted to this topic. With that specific purpose in mind, the RRO laboratory, Gustave Eiffel University, has recently designed and developed a new impulsive pullout tests device. This device, presented in this paper, allows applying at the nail’s head, about a static tension force, a series of dynamic load pulses up to 50% of the applied force at specified frequencies ranging from 0.1 to 5 Hz. In addition to the usual tension force and displacement measurements at the head of the nail, micro-deformations along entire length of the steel bar are observed at a millimeter longitudinal resolution based on optical fiber technique. The new device and the high-resolution monitoring of strain along the bar allows to investigate the local seismic behavior of the soil-nail interface, in order to propose a model to account for this behavior in soil-nailed walls design methods.