The foundation soil below the structure usually bears the combined action of initial static and cyclic shear loading. This experimental investigation focused on the cyclic properties of saturated soft clay in the initial static shear stress state. A range of constant volume cyclic simple shear tests were performed on Shanghai soft clay at different initial static shear stress ratios (SSR) and cyclic shear stress ratios (CSR). The cyclic behavior of soft clay with SSR was compared with that without SSR. An empirical model for predicting cyclic strength of soft clay under various SSR and CSR combinations was proposed and validated. Research results indicated that an increase of shear loading level, including SSR and CSR, results in a larger magnitude of shear strain. The response of pore water pressure is simultaneously dominated by the amplitude and the duration of shear loading. The maximum pore water pressure induced by smaller loading over a long duration may be greater than that under larger loading over a short duration. The initial static shear stress does not necessarily have a negative impact on cyclic strength. At least, compared to cases without SSR, the low-level SSR can improve the deformation resistance of soft clay under the cyclic loading. For the higher SSR level, the cyclic strength decreases with the increase of SSR.

Freeze-thaw cycles in seasonally frozen soil affect the boundary conditions of aqueducts with pile foundations, consequently impacting their seismic performance. To explore the damage characteristics and seismic behaviour of aqueduct bent frames in such regions, a custom testing apparatus with an integrated cooling system was developed. Two 1/15 scale models of reinforced concrete aqueduct bent frames with pile foundations were constructed and subjected to pseudo-static testing under both unfrozen and frozen soil conditions. The findings revealed that ground soil freezing has minimal impact on the ultimate bearing capacity and energy dissipation of the bent frame-pile-soil system, but significantly enhances its initial stiffness. Additionally, the frozen soil layer exerts a stronger embedding effect on the pile cap, ensuring the stability of the pile foundation during earthquakes. However, under large seismic loads, aqueduct bent frames experience greater damage and residual deformation in frozen soil compared to unfrozen soil conditions. Therefore, the presence of a seasonally frozen soil layer somewhat compromises the seismic performance of aqueduct bent frames. Subsequently, a finite element model considering pile-soil interaction (PSI) and frozen soil hydro-thermal effects was developed for aqueduct bent frames and validated against experimental results. This provides an effective method for predicting their seismic behaviors in seasonally frozen soil regions. Furthermore, based on the seismic damage characteristics of aqueduct bent frame with pile foundations observed in pseudo-static tests, a novel selfadaptive aqueduct bent frame system was designed to mitigate the adverse effects of seasonally frozen soil layer on seismic performance. This system is rooted in the principle of balancing resistance with adaptability, rather than solely depending on resistance. The seismic performance of this innovative system was then discussed, providing valuable insights for future seismic design of reinforced concrete aqueduct bent frames with pile foundations in seasonally frozen soil regions.

Bucket foundations are considered to be environmentally friendly foundations. Their stiffness determines the resonant frequencies and fatigue life of the supported offshore wind turbines. This study proposes a rigorous three-dimensional (3D) elastic solution for the stiffness of laterally loaded bucket foundations in different soil profiles. The lumped spring stiffness acting on the top of the bucket and the exact distribution of the distributed soil spring stiffness along the bucket are first obtained from the analytical model. Closed-form formulae for the lumped spring stiffness are then fitted and verified with the existing studies. To facilitate the engineering application, the distributed soil spring stiffness is then averaged to a uniform distribution using the equivalent work method. Two types of simplified Winkler models are finally proposed and calibrated: one in which the spring stiffness is uniformly distributed along the bucket, and the other in which the distributed Winkler springs are divided into two parts bounded by the centre of rotation. The non-dimensional Winkler springs are mainly related to the bucket aspect ratio, the soil Poisson's ratio and the loading height. It is shown that the lateral soil springs alone, asp-y springs for piles, are not sufficient for bucket foundations. The combined two-part p-y springs and uniform rotational springs are suggested to obtain accurate bucket foundation responses.

Frozen soils exhibit unique mechanical behavior due to the coexistence of ice and unfrozen water, making experimental studies essential for engineering applications in cold regions. This review comprehensively examines laboratory investigations on frozen soils under static and dynamic loadings, including uniaxial and triaxial compression, creep, direct shear, and freeze-thaw (F-T) cycle tests. Key findings on stress-strain characteristics, failure mechanisms, and the effects of temperature and time are synthesized. Advancements in microstructural analysis techniques, such as computed tomography (CT), scanning electron microscopy (SEM), nuclear magnetic resonance (NMR), and mercury intrusion porosimetry (MIP), are also summarized to elucidate the internal structural evolution of frozen soils. While significant progress has been made, further efforts are needed to better replicate complex environmental and loading conditions and to fully understand the interactions between multiple influencing factors. Future research should focus on developing novel experimental techniques, establishing standardized testing protocols, and creating a comprehensive database to enhance data accessibility and advance frozen soil research. This review provides critical insights into frozen soil mechanics and supports validating constitutive models and numerical simulations, aiding infrastructure design and construction in cold regions.

Waves can cause significant accumulation of pore water pressure and liquefaction in seabed soils, leading to instability of foundations of marine hydrokinetic devices (MHKs). Geostatic shear stresses (existing around foundations, within slopes, etc.) can substantially alter the rate of pore pressure buildup, further complicating the liquefaction susceptibility assessments. In this study, the development of wave-induced residual pore water pressure and liquefaction within sandy seabed slopes supporting MHK structures is evaluated. Unlike most earlier studies that excluded the impact of shear stress ratios (SSR) on the residual pore pressure response of sloping seabeds, asymmetrical cyclic loadings are considered herein for a range of SSRs. To obtain wave-induced loading in the seabed (and cyclic shear stress ratios, CSRs), the poroelasticity equations governing the seabed response, coupled with those for fluid and structure domains, are solved simultaneously. Utilizing an experimental model based on anisotropic cyclic triaxial test data that includes CSR and SSR impacts, an equation for the rate of pore pressure buildup is developed and added as a source term to the 2D consolidation equation. Numerical investigations were performed by developing finite element models in time domain. The models were calibrated using particle swarm optimization method and validated against wave flume experimental data. The results indicate that the consideration of static shear stresses has led to sudden rise in residual pore pressures followed by fast dissipations at early and late time steps, respectively, beneath the structure. The exclusion of SSR is shown to cause significant overestimation of pore pressure accumulations at late cycles, potentially causing significant overdesign of MHK foundations. The impact of proximity to the free drainage boundary, CSR amplitude, and loading frequency on the accumulation of residual pore pressure is illustrated. The residual liquefaction susceptibility of the seabed is shown to decline by increase of the seabed slope angle.

Deep soil mixing (DSM) is a widely used ground improvement method to enhance the properties of soft soils by blending them with cementitious materials to reduce settlement and form a load-bearing column within the soil. However, using cement as a binding material significantly contributes to global warming and climatic change. Moreover, there is a need to understand the dynamic behavior of the DSM-stabilized soil under traffic loading conditions. In order to address both of the difficulties, a set of 1-g physical model tests have been conducted to examine the behavior of a single geopolymer-stabilized soil column (GPSC) as a DSM column in soft soil ground treatment under static and cyclic loading. Static loading model tests were performed on the end-bearing (l/h = 1) GPSC stabilized ground with Ar of 9 %, 16 %, 25 %, and 36 % and floating GPSC stabilized ground with l/h ratio of 0.35, 0.5, and 0.75 to understand the load settlement behavior of the model ground. Under cyclic loading, the effect of Ar in end-bearing conditions and cyclic loading amplitude with different CSR was performed. Earth pressure cells were used to measure the stress distribution in the GPSC and the surrounding soil in terms of stress concentration ratio, and pore pressure transducers were used to monitor the excess pore water pressure dissipated in the surrounding soil of the GPSC during static and cyclic loading. The experimental results show that the bearing improvement ratio was 2.28, 3.74, 7.67, and 9.24 for Ar of 9 %, 16 %, 25 %, and 36 %, respectively, and was 1.49, 1.82, and 2.82 for l/h ratios of 0.35, 0.5, and 0.75 respectively. Also, the settlement induced due to cyclic loading was high under the same static and cyclic stress for all the area replacement ratios. Furthermore, the impact of cyclic loading is reduced with an increase in the area replacement ratio. Excess pore water pressure generated from static and cyclic loads was effectively decreased by installing GPSC.

Post-grouted shafts (PGDS) and stiffened deep cement mixed (SDCM) shafts reinforce the surrounding soils with cement to enhance the bearing capacity of shaft foundations, and their applications are becoming increasingly widespread. Field tests involving two post-grouted shafts and two stiffened deep cement mixing shafts were conducted at the bridge foundations projects, analyzing the vertical bearing performance of the shafts with cement-stabilized soil enhancement. Additionally, numerical simulations were performed to establish calculation models for single shaft and groups of drilled shafts, PGDS, and SDCM shafts, enabling a comparative analysis of their bearing capacity performance within the identical strata. The results indicate that the post- grouted shaft demonstrated significant bearing deformation capacity, as confirmed by field tests. After grouting, the ultimate bearing capacities of DS1 and DS2 improved by 124.5 % and 110.9 %, respectively. In both single and group modeling shaft foundations, the post-grouted shafts demonstrated the highest bearing deformation characteristics, followed by the identical- size stiffened deep cement mixed shaft, while the long-core SDCM shafts and the ungrouted shafts exhibited the weakest performance. Due to interaction effects among group shafts, the total bearing capacity of the group shafts is not simply the sum of the individual shafts. Specifically, the reduction factor for group shaft capacity ranges from 0.68 to 0.79 at the Baoying Large Bridge site, while at the Yangkou Canal Bridge site, it varies from 0.66 to 0.85. The findings of this study provide valuable insights for practical engineering applications.

Polypropylene fiber and cement were used to modify iron tailings and applying it to roadbed engineering is an important way to promote the sustainable development of the mining industry. However, the existing studies are mostly concerned with the static mechanical properties, and lack the deformation characteristics of cyclic loading under different loading modes. The effects of fiber content, dynamic-static ratio (Rcr) and curing age on the deformation characteristics of fiber cement modified iron tailing (FCIT) under different cyclic loading modes were explored through dynamic triaxial tests. The research results show that: (1) Polypropylene fibers significantly reduced the cumulative strain of FCIT. Under intermittent loading, the cumulative strain decreased by 36 similar to 43 %, and under continuous loading, the cumulative strain decreased by 48 similar to 55 %. (2) The deformation behavior of FCIT under both intermittent and progressive loading was in a plastic steady state with cumulative strain <= 1 %. (3) The cumulative strain variation of FCIT with intermittent loading of 0.316 % was significantly lower than that with continuous loading of 0.417 %, and the resilience modulus was higher with intermittent loading. (4) The stress history effect of step-by-step loading can be eliminated by the translational superposition method, and the strain evolution law under continuous loading is predicted based on the progressive loading data, and the minimum error between the expected and actual results is 6.5 % when Rcr is 0.1.

The lateral cyclic bearing characteristics of pile foundations in coastal soft soil treated by vacuum preloading method (VPM) are not well understood. To investigate, static lateral cyclic loading tests were conducted to assess the impact of treatment durations and sealing conditions on pile performance. Results indicated that vacuum preloading significantly improved soil properties, with undrained shear strength (S-u) increasing by up to 36.5 times, especially in shallow layers. Longer treatment durations boosted the ultimate lateral bearing capacity by up to 125%, although the effect decreased with depth, suggesting an optimal duration. Sealing conditions had minimal impact on capacity but affected S-u distribution and pile behaviour. Analysis of p-y curves revealed that longer durations improved soil resistance in shallow layers, while shorter durations provided consistent resistance across depths. Sealed conditions enhanced displacement capacity. The API specification predicted soil resistance accurately for lateral displacements under 0.1D but showed errors for larger displacements. These findings emphasise the need for optimising VPM parameters to enhance pile-soil interaction and lateral cyclic performance. The study offers guidance for applying VPM in soft soil foundation engineering and balancing performance with cost efficiency.

Fracture toughness and cohesive fracturing properties of two classes of sandy-clay soils, (A) with fine and (B) coarse grains and stabilized with low (2%) and high (10%) cement (as soil stabilizer), were investigated using a chevron-notched semicircular bend (CN-SCB) sample under static and cyclic loads. The samples with coarser grains and higher amounts of cement stabilizer showed higher KIc compared to the soils containing low cement and fine grains. A noticeable reduction in KIc was also observed under cyclic loading compared to the monotonic loading. Load-crack opening displacement (COD) graphs obtained during cyclic loading showed high plastic deformation accumulation before the final fracture. The cycles required for the fatigue crack growth of the Class A soil were noticeably (three to six times) higher than the Class B. The FRANC2D nonlinear simulations, cohesive fracture analyses, and maximum stress theory were utilized for estimating the critical crack length and the onset of cohesive unstable crack propagation.