A group of earthquakes typically consists of a mainshock followed by multiple aftershocks. Exploration of the dynamic behaviors of soil subjected to sequential earthquake loading is crucial. In this paper, a series of cyclic simple shear tests were performed on the undisturbed soft clay under different cyclic stress amplitudes and reconsolidation degrees. The equivalent seismic shear stress was calculated based on the seismic intensity and soil buried depth. Furthermore, reconsolidation was conducted at the loading interval to investigate the influence of seismic history. An empirical model for predicting the variation of the accumulative dissipated energy with the number of cycles was established. The energy dissipation principle was employed to investigate the evolution of cyclic shear strain and equivalent pore pressure. The findings suggested that as the cyclic stress amplitude increased, incremental damage caused by the aftershock loading to the soil skeleton structure became more severe. This was manifested as the progressive increase in deformation and the rapid accumulation of dissipated energy. Concurrently, the reconsolidation process reduced the extent of the energy dissipation by inhibiting misalignment and slippage among soil particles, thereby enhancing the resistance of the soft clay to subsequent dynamic loading.

In this study, impact compression tests on low-temperature concrete were conducted using a split Hopkinson pressure bar. The impacts of low temperatures on the strength, fractal, and energy characteristics of concrete were analyzed. The damage evolution mechanism of the microcrack density was discussed based on microscopic damage theory and microscopic tests. The results demonstrated that the impact fractal dimension and energy dissipation density of low-temperature concrete were positively correlated with the strain rate. The strain rate sensitivity of the impact fractal dimension was significantly affected by low temperature at low strain rates; however, low temperature had little effect at high strain rates. The pore water transformed into ice at negative temperatures, the fracture energy of the concrete increased, and the energy dissipation density increased. More than 50 % of the capillary and free water inside the concrete was frozen at -10 degrees C; approximately 30 % of the capillary and free water and 65 % of bound water did not freeze when the temperature was -30 degrees C. The macropores did not collapse under the action of ice filling at high strain rates; however, microcracks were generated around them. With a decreasing temperature, the threshold stress for microcrack propagation increased, crack propagation required more energy, and the microcrack density decreased.

Calcareous sands provide the foundational support for various marine infrastructures. In the harsh marine environment, earthquake or wave loads apply multidirectional cyclic shear stresses to the foundation soil. To explore the undrained multidirectional cyclic response of sand, a series of simple shear tests were performed on reconstituted sand specimens considering the effect of phase difference (theta). By comparing the results with those of siliceous sand under similar conditions, the behavior of calcareous sand under multidirectional cyclic loading became clear. The results demonstrated that calcareous sand shows a lower degree of cyclic instability compared to siliceous sand, corresponding to the weaker strain-softening observed in calcareous sand during monotonic shear tests. The trend in normalized pore water pressure evolution in siliceous sand exceeds that in calcareous sand. Furthermore, under multidirectional cyclic shear conditions, the liquefaction resistance decreases by 30 % in extreme cases, irrespective of sand type. The liquefaction resistance of calcareous sand surpasses that of siliceous sand. However, as the cyclic stress ratio decreases, the reverse trend is observed, regardless of the impact of theta. Subsequently, the possible causes of the above experimental phenomena are explored from the perspectives of shear modulus and energy dissipation.

The objective of this study is to develop and evaluate a new type of energy dissipation box damper, designed for use in seismic-resistant structures. This damper utilizes natural granular materials, primarily sand, as the key damping mechanism. The research was conducted through a series of experiments to investigate the mechanical properties of the damper under different operational conditions. The study focused on the effectiveness of sand as a damping agent, the examination of various damper configurations including both single and dual silhouette models, and the assessment of damper performance under variable testing rates. It was found that sand, with its fine and smooth particles, offers excellent damping properties. The single silhouette model, in particular, demonstrated improvements in stability, load distribution, and energy dissipation efficiency when used with sand. The damper showed robust hysteresis behavior, proving its reliability under high-load scenarios. Additionally, the influence of testing rates on the damping behavior was significant, with higher rates improving the damping ratio in sand-based systems. The LuGre model was applied to provide a mathematical representation of the experimental findings; however, some discrepancies were noted, attributed to the model's limitations and the experimental uncertainties. The results highlight the damper's potential as an economical alternative for seismic resistance, leveraging the low cost and simplicity of natural materials. The design of the damper focuses on simplicity and ease of maintenance, making a significant contribution to the progress in earthquake mitigation technologies.

Evaluating cyclic liquefaction of soil from the perspective of energy dissipation provides a more comprehensive insight into its liquefaction mechanism. This study conducted a series of undrained cyclic triaxial tests using discrete element method to investigate the influence of plastic fines content (FC) on the dynamic characteristics of sand-clay mixtures. A new evaluation index, the Viscous Energy Dissipation Ratio (VEDR), is introduced to assess the energy dissipation performance of sand-clay mixtures. Macroscopically, it is shown that when FC 30 %, the trend reverses. In terms of energy dissipation, as the fines content increases, VEDR gradually transitions from the sand-like to the clay-like mode, exhibiting a unique transitional mode when FC = 50 %. Microscopically, the development of bond breakage is highly similar to that of VEDR. The bond breakage facilitates particle sliding and rolling, which is the fundamental factor causing the differences of energy dissipation between pure sand and sand-clay mixtures. This paper contributes to the mechanistic study of liquefaction criteria based on energy theory by establishing the connection between microscopic particle behavior and macroscopic energy dissipation during the cyclic liquefaction process.

In recent years, researchers have taken advantage of the nonlinear characteristics of the underlying soil to mitigate the excessive seismic force demands on the superstructure under earthquake excitation. For this purpose, the conventionally designed foundation can be replaced with rocking foundation. This is achieved by under proportioning the shallow foundation. Although the mechanism of rocking foundations has been well documented, there remains a gap in developing a methodology for reduction of foundation sizes in multi storey Reinforced Concrete (RC) shear wall framed structure. Therefore, this study focuses on the seismic responses of a shallow foundations supporting a multistorey RC shear wall framed structure. The foundation for RC shear wall is proportioned by gradually reducing the earthquake load considered for the foundations to enhance the increased rocking effect and to mitigate seismic force demands. Thereafter, key parameters responsible for seismic behavior of sub-structure are being compared with conventionally designed foundation with increasing foundation rocking, by varying type of underlying soil and with increasing height. Seismic behavior obtained by implementing a series of nonlinear time history analyses indicates that the foundation rocking greatly influences the dynamic properties. With increasing degree of foundation rocking, natural fundamental period of the overall structure gets lengthened, with decreasing peak roof acceleration, thereby mitigating the peak base moment and base shear experienced at the shear wall compared to conventionally designed foundation. On the other hand, it is observed that there is an increase in roof displacement and shear wall settlement at the foundation level. It is found that the foundation of shear wall can be designed by considering 40%, 60% of earthquake loads for zone V and zone II structural designs, respectively without encountering excessive settlements. From the sensitivity analysis it is highlighted that the foundation size and design seismicity impact the base shear contribution ratios between shear wall and column members, fundamental natural period and foundation settlement.

In cold region engineering, the impact of coupled compression-shear loading on frozen soil foundations is a critical issue that urgently needs to be addressed, as it often significantly reduces bearing capacity and can cause structural failures. Accurately characterizing the mechanical behavior of frozen soil under dynamic coupled compression-shear loading is essential for enhancing the safety and stability of cold region engineering projects. This study prepared four frozen-soil specimens with varying tilting angles to investigate failure mechanisms and energy evolution under coupled compression-shear impact loading. The impact-compression experiments were conducted on the specimens under different loading strain rates and temperature conditions using a split Hopkinson pressure bar. The results indicated that the strength of frozen soil was effectively enhanced by higher strain rates and lower temperatures, while it was reduced by increased tilting angle. The fracturing morphology of frozen soil was analyzed from both microscopic and macroscopic perspectives to reveal its failure mechanisms. To quantify the strength characteristics of the frozen soil under various loading conditions, damage variables were defined from an energy-based perspective and incorporated into the Zhu-Wang-Tang viscoelastic constitutive model. Hence, a dynamic constitutive model for frozen soil under coupled compression-shear loading was developed. The model's predictive capability was validated through comparisons with the experimental data, which revealed a high level of agreement. The results of this study provide practical insights into the failure mechanisms and construction design of frozen soil foundations under coupled compression-shear impact loading in cold region engineering.

Acoustic emission (AE) offers the potential to monitor and interpret soil-pipe interaction behavior by sensing particle-scale interactions. However, application of AE is limited by gaps in understanding related to how particle-scale interactions influence AE activity. Discrete element method (DEM) simulations of buried pipe uplift with energy tracking were performed and compared with experimental mechanical, displacement, and AE measurements, to ensure realistic behavior was captured by the modeling approach. A parametric investigation was then performed to evaluate the influence of pipe displacement direction and pipe diameter on plastic energy dissipation, and hence AE. Trends of dissipated plastic energy and measured AE with stress level (via burial depth) and pipe velocity were analogous. Relationships were quantified (R2 ranging from 0.74 to 0.98) between AE, dissipated plastic energy, and pipe velocity. Measured AE and dissipated plastic energy were linked with a general expression, comprising increments of friction (sliding and rolling), damping, and damage energies. Sliding friction energy accounted for >80% of the total dissipated energy on average during buried pipe deformation. Exemplar relationships were established between dissipated energy, pipe movement direction, embedment ratio, and mobilized soil volume (R2 values ranging from 0.92 to 0.97). A conceptual framework for interpreting buried pipe behavior using AE monitoring was presented.

Energy dissipation can macroscopically synthesize the evolutions in the microstructure of the marine clay during cyclic loading. Hence an energy-based method was employed to investigate the failure criterion and cyclic resistance of marine clay. A series of constant-volume cyclic direct simple shear tests was conducted on undisturbed saturated marine clay from the Yangtze Estuary considering the effects of the plasticity index (IP) and cyclic stress ratio (CSR). The results indicated that a threshold CSR (CSRth) exhibiting a power function relationship with IP exists in marine clay, which divides the cyclic response into non-failure and failure states. For failed specimens, the development of energy dissipation per cycle (Wi) with the number of cycles (N) exhibited an inflection point owing to the onset of serious damage to the soil structure. In this regard, the energy-based failure criterion was proposed by considering the inflection point as the failure point. Consequently, a model was proposed to quantify the relationships between failure energy dissipation per cycle (Wf) [or failure accumulative energy dissipation (Waf)], initial vertical effective stress, IP, and the number of cycles to failure (Nf,E). An evaluation model capturing the correlation among CSR, IP, and Nf,E was then established to predict the cyclic resistance, and its applicability was verified. Compared with the strain-based cyclic failure criterion, the energybased failure criterion provides a more robust and rational approach. Finally, a failure double-amplitude shear strain (gamma DA,f) evaluation method applicable to marine clay in different seas was presented for use in practical geotechnical engineering.

At least 32 case histories have shown that liquefaction can occur in gravelly soils (both natural deposits and manmade reclamations) during severe earthquakes, causing large ground deformations and severe damage to civil infrastructures. Gravelly soils, however, pose major challenges in geotechnical earthquake engineering in terms of assessing their deformation characteristics and potential for liquefaction. In this study, aimed at providing valuable insights into this important topic, a series of isotropically consolidated undrained cyclic triaxial tests were carried out on selected sand-gravel mixtures (SGMs) with varying degrees of gravel content (Gc) and relative density (Dr). The pore water pressure generation and liquefaction resistance were examined and then further scrutinized using an energy-based method (EBM) for liquefaction assessment. It is shown that the rate of pore water pressure development is influenced by the cyclic resistance ratio (CSR), Gc and Dr of SGMs. However, a unique correlation exists between the pore water pressure ratio and cumulative normalized dissipated energy during liquefaction. Furthermore, the cumulative normalized energy is a promising parameter to describe the cyclic resistance ratio (CRR) of gravelly soils at various post-liquefaction axial strain levels, considering the combined effects of Gc and Dr on the liquefaction resistance.