Gassy clay, commonly encountered in coastal areas as overconsolidated deposits, demonstrates distinct mechanical properties posing risks for submarine geohazards and engineering stability. Consolidated undrained triaxial tests combined with cyclic simple shear tests were performed on specimens with varying overconsolidation ratios (OCRs) and initial pore pressures, supplemented by SEM microstructural analysis. Triaxial results indicate that OCR controls the transitions between shear contraction and dilatancy, which govern both stress-strain responses and excess pore pressure development. Higher OCR with lower initial pore pressure increases stress path slope, raises undrained shear strength (su), reduces pore pressure generation, and induces negative pore pressure at elevated OCR. These effects originate from compressed gas bubbles and limited bubble flooding under overconsolidation, intensifying dilatancy during shear. Cyclic tests reveal gassy clay's superior cyclic strength, slower pore pressure accumulation, reduced stiffness softening, and enhanced deformation resistance relative to saturated soils. Cyclic pore pressure amplitude increases with OCR, while peak cyclic strength and anti-softening capacity occur at OCR = 2, implying gas bubble interactions.

For the soils in sloping ground, the effect of static shear stress must be considered to evaluate the cyclic behaviors of soils when subjected to seismic loading. This study aims to reveal the effect of both static shear stress magnitude and direction on the cyclic behaviors of the medium-dense sand based on a series of multi-directional cyclic simple shear tests. It is found that the effect of static shear stress on the liquefaction resistance of the medium-dense sand is detrimental in both parallel and perpendicular loading modes. The detrimental effect is more pronounced in parallel loading mode. Under the perpendicular loading mode, the full liquefaction of the specimens cannot be reached. The deformation pattern of the specimens is cyclic mobility along the cyclic loading direction, and plastic strain accumulation along the static stress direction. A modified pore pressure prediction model with two fitting parameters is further proposed to incorporate the effect of static shear stress.

The mechanical properties and constitutive model of unsaturated soils under cyclic loading are crucial for understanding the behavior of foundations and slopes subjected to dynamic motions such as earthquakes and traffic loading. In this study, multilevel strain-controlled cyclic simple shear tests of unsaturated weathered red mudstone (WRM) were conducted. The detailed investigation focused on cyclic responses, including shear stressstrain behavior and volume change, strain-dependent secant shear modulus and damping ratio, and stress-dilatancy behavior. This study revealed the significant influences of the degree of saturation and vertical stress on these responses, with the initial static shear stress mainly affecting the shear stress-strain behavior and volume changes at the initial loading stage. Based on the experimental observations, a cyclic constitutive model was proposed for unsaturated WRM. The model incorporates a slightly revised Davidenkov model and Masing criterion to generate shear stress-strain hysteresis loops with or without initial static shear stress. Additionally, a stress-dilatancy equation was included to capture the volume changes during cyclic loading. The proposed model was verified by comparing representative test data and calculation results, demonstrating the excellent performance of the proposed model in modeling the main features of unsaturated WRM under cyclic loading.

Loess exhibits typical water sensitivity and dynamic vulnerability. The combination of rainfall and earthquakerelated issues presents a complex disaster process, posing a significant threat to the infrastructure in the loess region. A cyclic simple shear test was conducted on undisturbed loess under a constant vertical stress ranging from 50 to 300 kPa, comprising three stages(C-W-D): consolidation, pre -humidification, and cyclic loading. The deformation behavior under humidification and cyclic loading was analyzed. The microstructure evolution of loess during three stages was examined using scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP). Results indicated that: (1) Cyclic deformation increased with the rise in vertical stress sigma v , humidification parameters S w , and dynamic shear stress amplitude gamma d . The sensitivity of cyclic deformation to sigma v and gamma d gradually decreased as S w increases. (2) The total deformation in the three stages correlated positively with S w , sigma v , and gamma d . The proportion of humidification deformation and cyclic deformation in the total deformation was largely unaffected by sigma v , with cyclic deformation gradually dominating as gamma d increases. (3) The prehumidification stage promoted aggregates and the formation of numerous intergranular pores. Cyclic loading mainly leads to the change of pore structures, forming obvious seismic damage area. Based on the relationship between humidification deformation and cyclic deformation, a loess deformation prediction model was proposed, which can comprehensively consider S w , sigma v , and gamma d . This can provide a theoretical reference for earthquake disaster prediction in collapsible loess areas.

Liquefaction is a phenomenon marked by a rapid loss of soil strength and stiffness, which generally occurs in loose saturated sandy deposit during earthquake because of the generation of excess pore water pressure. Several experimental researches concluded that liquefied soil behaves as a fluid during ground movement, but after the earthquake motion ceases, due to the dissipation of excess pore water pressure, the liquefied soil recovers its initial stiffness and returns to behave as a solid. Liquefaction resistance of sandy soil can be studied by means of Cyclic Simple Shear (CSS) test or Cyclic Triaxial (CTX) tests. While CTX tests are widely used in liquefaction studies due to their simplicity, CSS tests are more representative of stress conditions produced during an earthquake by simulating the continuous rotation of the principal stress axes. In this research the preliminary results of CSS tests carried out with confining rings on the sandy samples retrieved in the South of Sicily are reported. The apparatus is described in detail. All samples used were obtained from the same type of Italian sand by using same preparation method to minimize the number of factors influencing the results. Moreover, all tests were conducted by a single operator. All experimental results are reported in the plane cyclic resistance ratio (CRR) and number of cycles where liquefaction occurs (N-liq) in order to assess the liquefaction phenomenon.