Mourad Karray

A two-dimensional explicit FD program FLAC 2D (Itasca Consulting Group Inc., 2011) model was developed to simulate the seepage flow and evaluate the static performance of the Plovdivtsi ACRD dam. Plate load tests conducted on site during construction were modelled in this study to establish the Duncan-Chang parameters. The calibration of Duncan–Chang parameters is based on the experimental oedometric curves carried out for the Romaine-2 ACRD dam (Lashin et al., 2021). The distribution of stresses and deformations during and at the end of the construction phase, as well as following the first reservoir impoundment, were calculated with numerical analyses. Results expose that the core, the adjacent fill zones and the base of the ACRD dam appear to behave in a similar way, as a retaining wall. Based on these calibrated parameters, the pressure induced by the reservoir displaces the core downstream, favouring the formation of a Vshaped section immediately behind the core on the upstream side with larger vertical displacements in comparison with the whole of the embankment. This contrast in vertical displacements leads to notable differential displacements, which could likely lead to the formation of cracks in the upper part of the upstream dam fill. Although this behaviour is consistent with literature, instrumental data from this dam tends to support that deformations during the first reservoir impoundment would be lower than those calculated with the calibrated model. A sensitivity analysis was carried out to study two scenarios that could result in less deformation during the first reservoir impoundment. One scenario involves doubling rockfill stiffness while the second one is to study the effect of very rapid impoundment, as was the case for this dam, also considering the upstream rockfill shell could possibly be slightly less permeable. This scenario simulates the effects of rapid reservoir impoundment while considering calibrated stiffness parameters in line with the results of plate load tests carried out during construction appear to be the most realistic based on construction data, the first reservoir impoundment conditions and instrumental data.

The characterization of cold recycled bituminous materials (CRMs) at a very young age, shortly after compaction, is inherently challenging due to the nature of the material. The granular aspect of CRM at this stage and its high-water content render the use of conventional mechanical techniques impractical. Following previous work, the use of a nondestructive technique based on the frequency analysis of mechanical elastic shear waves, piezoelectric ring actuator technique (P-RAT), has enabled assessment of the behavior of cold in-place recycled material treated with bitumen emulsion from 10 min after compaction to 30 days of curing. Emphasis on shear wave velocity (Vs) measurements during the early age confirmed the rapid stiffening of the mix along with the departure of water present in the mix. A 6 °C drop of the surface temperature is observed along with this rapid increase of Vs and water loss. The initial and final Vs values range from 287 to 330 m s−1 and from 461 to 578 m s−1, respectively. To assess the capabilities of P-RAT, specimens with different void contents were tested, mainly 12, 15, and 17 %. It was observed that in each tested specimens, a similar behavior was exhibited during the first few hours of curing. Based on these observations, hypotheses are put forth regarding the phenomena governing the increase in stiffness during this period. Finally, the influence of the compaction of the specimens on the Vs values is consistent and comparable with the information available in the literature for such CRM.

Pavement materials like hot mix asphalt (HMA) and cold recycled mixes (CRMs) are typically considered isotropic. This study evaluates the anisotropy of a cold in-place recycled (CIR) material using the shear wave velocity (V_s) parameter. The piezoelectric ring actuator technique (P-RAT) is utilized to assess the V_s parameter in three directions in CIR slabs. Similarly, the ultrasonic pulse velocity (UPV) technique is employed to measure P-wave velocities. Both methods evaluate mechanical properties in multiple directions. Complex modulus tests are conducted to link velocities results to |E*| modulus. Finally, computed tomography (CT) scans are performed on the specimens in order to evaluate anisotropy resulting from aggregate alignment. The V_s obtained using P-RAT and the V_p from UPV indicate anisotropy, as the wave velocities differ across the three directions. Differences range from 0.6 to 11.6% in V_s, influenced by measurement location. UPV results are analysed in relation to the |E*| modulus master curves, demonstrating that the first peak arrival time for the P-wave corresponds with the master curve. CT scan analysis reveals that the aggregates tend to be more aligned in the direction of the compacting wheel’s displacement, which also highlights anisotropy.

For reliable seismic design of earth-retaining structures, it is critical to accurately assess the magnitude and distribution of dynamic earth pressures. Over the years, numerous experimental and numerical studies have sought to clarify the complex soil–structure interactions in backfill–wall systems under seismic loads. This article expands on an earlier review by the authors of analytical and field performance studies addressing the seismic behavior of retaining walls. Despite extensive research, there is still no consensus on a standardized seismic evaluation method or on the necessity of including seismic loads in the design of retaining structures. This review critically examines notable experimental and numerical findings on dynamic lateral earth pressure, highlighting that the current design practices cannot be generally applied to all types of retaining structures. More importantly, these practices often rely on experimental data extrapolated beyond their original applicability.

This paper investigates the anisotropic characteristics of Champlain marine clay soil using a combination of laboratory techniques. A modified oedometer cell with a piezoelectric ring actuator technique was used to measure shear wave velocity during consolidation stages. The axisymmetric design of the oedometer allowed for the determination of shear wave velocity in both the vertical and horizontal planes. The preliminary findings reveal that the sensitive marine clay is inherently anisotropic, with lower preconsolidation pressure for horizontally consolidated specimens and faster propagation of shear waves in the plane parallel to the bedding layer. High-precision strain gauges integrated into the consolidation ring were used to evaluate horizontal stress during the one-dimensional consolidation test. The ability to determine mean effective stress enables the normalization of shear wave velocities using this stress, providing more coherent empirical correlations in terms of shear wave velocity. Scanning electron microscopy was used to examine the microstructure of clay specimens, providing qualitative and quantitative insight into the restructuring and reorientation of clay platelets under consolidation stress. The consistency of the results through both micro and macro-scale analyses confirms the reliability of the experimental approach, highlighting its potential for future studies on the anisotropy of Champlain marine clay fabrics.

Upon dynamic loading, saturated soils lose their strengths and undergo deformations resulting in volumetric-induced settlements that vary according to the excess pore pressure generation and dissipation variations. Traditionally, these settlements have been evaluated using standard charts based on one soil type and its relative density (RD). To assess these settlements, this study established a unique experimental methodology based on two laboratory testings: triaxial simple shear and piezoelectric ring actuator technique. Fifty-seven tests were performed on Ottawa F65 sand under strain-controlled cyclic and post-cyclic conditions. A chart was generated, revealing a relationship between the dissipated energy from cyclic loading and volumetric strain ( ε_v ), based on the shear wave velocity as a controlling factor. This study was compared with previous studies to verify the compatibility of the proposed approach. Another novelty was revealed by studying ε_v variation with the dissipated pressure. This variation is presented in a post-seismic chart in which deformations are tracked based on the initial soil state and maximum excess pore pressure generation ratio ( Ru_max) at the end of the loading phase. For each RD, the soil is divided between liquefied and non-liquefied states according to a specific Ru_max ( Ru_max-_{trigger point}). The calculation of the volume compressibility coefficient is proven to serve as a liquefaction-triggering criterion identifying the liquefied state.