Non-destructive ultrasonic testing has attained popularity due to its robustness and cost-effectiveness in monitoring the structural health and performance evaluation of pavements, thus replacing traditional methods. This paper presents the application of an explicit finite element method for the modeling of ultrasonic wave propagation through asphalt concrete. Prior to modeling, non-destructive ultrasonic testing was conducted on four different types of asphalt concrete (AC-13, SMA-13, AC-20, and AM-20). Based on acoustic information (wave velocity) obtained in non-destructive testing (NDT) and density, the dynamic moduli of these asphalt concretes were evaluated and used in numerical modeling of ultrasonic wave propagation using the commercial software package ABAQUS. The ultrasonic wave results obtained by numerical modeling were compared with experimental results. This comparison showed a good fit between the finite element (FE) results and the experimental results and confirmed a good FE approach for ultrasonic wave propagation. In addition, the influence of varying dynamic moduli, density, varying location, and crack size/depth on ultrasonic wave propagation was analyzed.

The contributions of this study, which include enhanced predictive precision and the integration of supplementary admixtures, may be effectively used in real-world scenarios to optimize self-compacting concrete (SCC) mixes for particular applications. This technology exhibits the capacity to improve construction productivity, minimize material wastage, and foster the development of resilient and environmentally friendly infrastructures. This research examined radial basis function (RBF) network and extreme gradient boosting (XGB-based models for predicting the compressive strength (C_s) of SCC. A dataset was generated through the collection of experimental samples, which encompassed supplementary admixtures in addition to the conventional constituents of concrete comprised of lime powders, fly ash, granulated blast furnace slag, silica fume, steel slag powder, super-plasticizer, and viscosity-modifying admixtures. In the present study, two optimization algorithms named the northern Goshawk optimization algorithm (NGOA), and Henry gas solubility optimization (HGSO) were linked with RBF and XGB models (abbreviated as XGB_NG, XGB_HG, RBF_NG, and RBF_HG). The results indicate that each of the four models exhibits a notable degree of precision in their prediction methodologies for C_s. A considered comprehensive metric named OBJ showed that the XGB_NG simulation received the slightest value at 0.8062, followed by XGB_HG at 1.657, then RBF_NG at 2.4891, and last RBF_HG by 3.9131.

Numerical simulation is an effective way to study the mechanical response of asphalt pavement, which is very important for the pavement structural design. In this study, a three-dimensional meso-structure discrete element model of asphalt pavement was generated with the FISH programming language and its meso-mechanical response under vehicle load was analyzed. The contact forces within the asphalt pavement, in asphalt mastic, in coarse aggregates and between asphalt mastic and coarse aggregates were studied. The results of the study show that the contact forces within the asphalt mixture are highly uneven. The number of contact points in coarse aggregates account only for about 10% of all contact points while the sum of the contact forces in coarse aggregates contributes to over 50% of all contact forces. This demonstrates that the coarse aggregates bear most of the vehicle load. The average normal contact force in coarse aggregates is about 5 N and the average tangential contact force in coarse aggregates is about 2 N. The modeling results provide a quantitative understanding of the distribution of loading in asphalt pavement.

To study the small strain shear modulus (G_max) of saturated sand-silt mixed soil materials, a series of tests were conducted using the bender element apparatus, and the influences of fines content (FC), relative density (D_r), and effective confining pressure (${{\sigma }^{\prime }}_{3\mathrm{c}}$) were taken into consideration. The test results indicate that the G_max of the mixed soil materials decreases first and then increases with the FC up to 100% with D_r = 35% and 50%, while the G_max decreases with the increasing FC when D_r = 60%. Moreover, for a given D_r, the G_max increases with the increasing ${{\sigma }^{\prime }}_{3\mathrm{c}}$, and the increase rate keeps constant under various FCs. The G_max of specimens under various FCs decreases with the increase of the void ratio (e). The decrease rate between the G_max and e differs when the ${{\sigma }^{\prime }}_{3\mathrm{c}}$ is given, which is influenced by the FC. The G_max of the mixed soil materials can be evaluated by the Hardin model when the FC is determined. The best-fitting parameter A of the Hardin model first decreases and then increases as FC increases. The revised Hardin model, considering the influence of FC, ${{\sigma }^{\prime }}_{3\mathrm{c}}$, and e, can be used to evaluate the G_max for different types of sand-silt mixed soil materials. The error between the evaluated and tested G_max is less than 10%.

As an indispensable part of the lifeline for the offshore gas and oil industry, submarine pipelines under long-term marine environmental loadings have historically been susceptible to earthquakes. This study investigates the impact of trench backfilling on the residual liquefaction around a pipeline and the induced uplift of a pipeline under the combined action of an earthquake, ocean wave and current loading. A fully coupled nonlinear effective stress analysis method, which can consider the nonlinear hysteresis and the large deformation after liquefaction of the seabed soil, is adopted to describe the interaction between the seabed soil and the submarine pipeline. Taking a typical borehole in the Bohai strait as the site condition, the nonlinear seismic response analysis of the submarine pipeline under the combined action of seismic loading and ocean wave and current is carried out. The numerical results show that trench backfilling has a significant impact on the seismic response of the pipeline. The existence of trench backfilling reduces the accumulation of the residual excess pore water pressure, so that the seabed liquefaction around the pipeline is mitigated and the uplift of the pipeline is also decreased.