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It is important to be fully aware of the dynamic characteristics of saturated soft clays under complex loading conditions in practice. In this paper, a series of undrained tests for soft clay consolidated with different initial major principal stress direction ξ were conducted by a hollow cylinder apparatus (HCA). The clay samples were subjected to pure principal stress rotation as the magnitudes of the mean total stress p, intermediate principal stress coefficient b, and deviator stress q were all maintained constant. The influences of intermediate principal stress coefficient and initial major principal stress direction on the variation of strain components, generation of pore water pressure, cyclic degradation and non-coaxiality were investigated. The experimental observations indicated that the strain components of specimen were affected by both intermediate principal stress coefficient and initial major principal stress direction. The generation of the pore water pressure was significantly influenced by intermediate principal stress coefficient. However, the generation of pore water pressure was merely influenced by initial major principal stress direction when b = 0.5. It was also noted that the torsional stress–strain relationships were affected by the number of cycles, and the effect of intermediate principal stress coefficient and initial major principal stress direction on the torsional stress–strain loops were also significant. Stiffness degradation occur under pure principal stress rotation. Anisotropic behavior resulting from the process of inclined consolidation have considerable effects on the strain components and non-coaxial behavior of soft clay.

Solid wastes are increasingly used to stabilize marine soft clay. Disposals of alkali slag and steel slag cause serious problems in Lianyungang City. These two waste materials are used to produce the compound cementitious material by mixing with GGBS, replacing the cement to treat the soft clay in Xuwei Port. The raw materials are collected from fields. The orthogonal test is performed to investigate the unconfined compressive strength (UCS) of the treated soil. The influence of alkali slag-soft soil (SR-S) ratio, the steel slag-GGBS (SS-GGBS) ratio, the curing agent, and the curing time are considered, followed by the investigation of reaction mechanisms. The optimal mixing ratio is recommended when the SR-S ratio is 1:1 and the curing agent content equals 10%. A well-documented dataset is developed by summarizing 1069 data of UCS from the literature. A PSO-BP-NN model is developed using the collected data and the experimental data so that generalization is guaranteed. The model is feasible to predict the UCS of treated soil by considering characters of the material properties and experimental techniques. This study aims to provide a reference for initially determining the mixing ratio of cementitious materials at field treatments.

Coastal regions are typically characterized by extensive deposits of soft clay, which are notable for their high water content, high compressibility, high organic matter content, low bearing capacity, low permeability, and prolonged stabilization time, collectively referred to as “three highs, two lows, and one long”. Solidification treatment stands out as a prevalent and effective method for enhancing the properties of this soft clay. An in-depth understanding of the static and dynamic characteristics of cement-solidified soft clay is essential to ensure the long-term safety and stability of coastal foundations. This paper reviews the static and dynamic properties and durability of cement-solidified coastal soft clay, elucidates the multi-scale coupling mechanism of cement solidification in coastal soft clay, addresses the existing research gaps, and proposes future research directions. The findings of this study offer valuable insights for the advancement of both scientific research and practical engineering applications.

The study aimed to elucidate the curing mechanism and establish an empirical model for the stabilization of marine organic soft clay (MOSC) using a combination of calcium carbide residue (CCR) and silica fume (SF) at the optimal proportion, employing response surface methodology (RSM) in conjunction with multi-scale characterization techniques. Initial investigations involved a series of unconfined compression strength (UCS) tests conducted on CCR and SF to ascertain the most effective dosage of each material for the stabilization of MOSC. Notably, it was observed that CCR exerted a more pronounced influence on enhancing MOSC properties when compared to SF. Further refinement of the optimal CCR-SF ratio was undertaken utilizing RSM, culminating in the establishment of a novel binder, denominated as PZ-2, with a composition ratio of 56% CCR and 44% SF. Characterization through X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), Energy-Dispersive X-ray Spectrometry (EDS) identified the primary products formed within the stabilized MOSC matrix with PZ-2 as comprising C–S–H, calcite, and dolomite. SEM analyses unveiled a substantially improved microstructure characterized by the presence of flocculent and agglomerate products in MOSC stabilized with PZ-2. Moreover, Mercury Intrusion Porosimetry (MIP) results indicated reduced pore volume in cured MOSC as opposed to its raw counterpart, indicative of a stronger microstructural configuration post-stabilization. The salutary effects of PZ-2 on MOSC stabilization were attributed to mechanisms encompassing pozzolanic reactions, neutralization, carbonation, and ion exchange. Additionally, it was noted that PZ-2 offered cost and environmental advantages over conventional Portland cement (PO 32.5). To facilitate practical applications, empirical models predicting the UCS strength of cured MOSC were developed incorporating key parameters such as initial water content ( w i ), organic matter content ( w o ), and binder content ( w b, ) with the optimal mixing ratio. These models demonstrated reliability and utility in guiding effective strategies for strengthening MOSC.

Purpose Deep excavation in soft clay often causes additional deformations to surroundings. Then, if deformations cannot be predicted reasonably, the adjacent buildings may be threatened by the deep excavation. Based on the good field observations from ten deep excavations in Hangzhou, this paper aims to thoroughly investigate the characteristics of wall deflections and ground settlements induced by deep excavations. Design/methodology/approach On the basis of good field observation of ten deep excavations, the performances of excavations, supported by contiguous pile in Hangzhou, were studied, and also compared with other case histories. Findings The maximum wall deflections (dhm) rang mostly from 0.7 to 1.2 per cent He, where He is the final excavation depth, larger than those in Taipei and Shanghai. The observed maximum ground settlement in the Hangzhou cases generally ranges from 0.2 to 0.8 per cent He. Then, the settlement influence zone extends to a distance of 2.0-4.0 He from the excavation. The relatively large movements and influence zones in Hangzhou may be attributed to low stability numbers, large excavation widths and the creep effect. The excavation width is justified to have a significant influence on the wall deflection. Therefore, to establish a semi-empirical formula for predicting the maximum wall deflection, it is necessary to include the factor of excavation width. Originality/value The relevant literature concentrated on the characteristics of deep excavations supported by the contiguous pile wall in Hangzhou soft clay can rarely be found. Based on the ten deep excavations with good field observation in Hangzhou, the characteristics of wall deflection and ground settlements were comprehensively studied for the first time, which can provide some theoretical support for similar projects.

During the service life of marine structures, environmental loads, such as earthquakes and ocean wave storms, may exert dynamic shear stresses of different amplitudes and orientations in the foundation soil. To investigate the undrained cyclic behavior of marine soft clay under a complex shear stress state, a laboratory study was performed on remolded clay specimens using a variable-direction dynamic cyclic simple shear system, through which two mutually perpendicular shear stresses can be simultaneously applied to the specimen within the horizontal x–y plane. Stress paths of linear, circular, and elliptical patterns were obtained by adjusting the amplitude ratio (η) between the two cyclic shear stresses and applied to investigate the undrained behavior of soft clay. The undrained cyclic responses of the clay specimens were presented and then analyzed from the viewpoint of energy dissipation. A strain-softening phenomenon was observed when the cyclic effective stress path reached the failure line determined by the monotonic test. The cyclic strength of clay subjected to multidirectional cyclic shear stresses (i.e., circular and elliptical stress paths) was 0.775η times that under unidirectional shear stress (i.e., linear stress path). The coupling effects of CSR and η on the cyclic strength and accumulation of residual pore water pressure can be uniformly correlated to energy dissipation.

Soft clay generally cannot be directly used as subgrade material due to its poor engineering characteristics. The application of rice husk ash (RHA) for the solidification of problematic soil contributes to the recycling of waste and reduces carbon emissions. A series of mechanical, chemical, and microscopic tests were conducted to assess the early effectiveness of RHA in stabilizing soft clay. The pH and conductivity Ec also were measured to evaluate the effect of active ions. The results show that the use of RHA alone can only improve the compressive strength qu of soft clay to a certain extent. However, it cannot improve the soaked strength of the solidified soil. Carbide slag (CS) and metakaolin (MK) as activators were used to modify RHA, which significantly improved the compressive strength, shear properties, and soaked strength of soft clay. During initial curing, the compressive strength qu and cohesion c showed a marked correlation with pH and Ec. This is closely related to the dissolution and consumption behaviors of more abundant active ions contributed by the active oxides in the modified RHA. Finally, combined with XRD, SEM, EDS, and MIP tests indicated that the mechanical properties and microstructure improvement of soft clay can be attributed to the early physical reinforcement and meshing effect due to the porous granular structure of RHA. Subsequently generated CaCO3 crystals and C–S–H/C–A–S–H cementitious hydrates played a crucial role through carbonization and pozzolanic reactions supported by more abundant active ions.

In order to overcome the problems of the high economic and environmental costs of a traditional ordinary portland cement-based binder, this study used self-combusted coal gangue (SCCG), granulated blast furnace slag (GBFS) and phosphorous slag (PS) to prepare a novel SCCG-GBFS-PS (SGP) ternary alkali-activated binder for solidifying silty soft clay (SC). Firstly, the parameters of the SGP ternary binder were optimized using orthogonal experiments. Then the effects of the SGP ternary binder content (mass ratio of the SGP ternary binder and the SGP-solidified soil), initial water content of SC (mass ratio of SC’ water and SC) and types of additives on the unconfined compressive strength (UCS) of the SGP-solidified soil were analyzed. Finally, the hydration products and microstructure of the SGP-solidified soil were analyzed to investigate the solidification mechanism of the SGP ternary binder. The results showed that the optimal mass ratio of GBFS and PS is 2:1, and the optimal alkali activator content (mass ratio of Na2O and the SGP ternary binder) and modulus of alkali activator (molar ratio of SiO2 and Na2O of alkali activator) were 13% and 1.3, respectively. When the SGP ternary binder content was 16% and the initial water content of SC was 35%, the SGP-solidified soil met the requirement of UCS for tertiary cured soil. The incorporation of triethanolamine and polyvinyl alcohol improved the UCS, while the incorporation of Na2SO4 significantly deteriorated the UCS of the SGP-solidified soil. The C-S-H gels and C(N)-A-S-H gels generated by hydration of the SGP-solidified soil were interspersed, interwoven and adhered to each other to form a network-like space structure that played the roles of skeleton, bonding soil particles and filling pores, which improved the macroscopic properties of the SGP-solidified soil. The results of this study provide a reference for the design and development of a solid waste-based binder for solidifying SC.

In practical engineering projects, surcharge preloading is used to reduce secondary compression settlement. A soft clay can become over-consolidated after surcharge preloading, and its secondary compression behavior is different from normally consolidated soft clay. In this paper, based on a series of systematic secondary compression tests conducted on reconstituted soft clays, the effects of consolidation pressure, surcharge preloading pressure, and over-consolidation ratio (OCR) on the secondary compression coefficient (Cα) are presented. This study is made for reconstituted soft clay and as such, the conclusions are not relevant for intact soft clay. For normally consolidated reconstituted clay, Cα increases with an increase in the consolidation pressure and decreases slightly tends to stabilize when the consolidation pressure exceeds the pre-consolidation pressure. For over-consolidated reconstituted clay, Cα decreases after surcharge preloading: the higher the surcharge preloading pressure, the lower the value of Cα. With the increase in the OCR from 2 to 16, Cα decreases in different degrees. Based on the results, an exponential relationship between Cα and OCR considering the effect of surcharge preloading is established.

To promote the sustainable utilization of agricultural solid waste, this study proposes a novel approach for reinforcing soft clay using a peanut ash (PA)–cement composite stabilizer. The unconfined compressive strength (UCS) of pure cement and PA–cement composite systems was tested at curing ages of 3, 7, and 28 days, while the durability of the stabilized clay was evaluated through dry–wet cycling. Given that PA is rich in pozzolanic components, its addition may influence the hydration process of cement. Therefore, hydration heat analysis was conducted to examine the early hydration behavior, and XRD and TG analyses were employed to identify the composition and quantity of hydration products. SEM observations were further used to characterize the microstructural evolution of the stabilized matrix. By integrating mechanical and microstructural analyses, the solidification mechanism of the PA–cement stabilizer was elucidated. Mechanical test results indicate that the reinforcing effect increases with the stabilizer dosage. Pure cement exhibited superior strength at 3 days; however, after 7 days, specimens incorporating 5% PA showed higher strength than those stabilized solely with cement. At 28 days, the UCS of the 15% cement + 5% PA specimen reached 3.12 MPa, 11.03% higher than that of the 20% cement specimen and comparable to the 25% cement specimen (3.15 MPa). After five dry–wet cycles, the strength reduction of the 15% cement + 5% PA specimen was 22.76%, compared to 31.31% for the 20% cement specimen, indicating improved durability. Microscopic analyses reveal that PA reduces hydration heat and does not participate in early hydration, leading to lower early strength. However, its pozzolanic reactivity contributes to secondary hydration at later stages, promoting the formation of additional C-S-H gel and ettringite. These hydration products fill the inter-lamellar pores of the clay and increase matrix density. Conversely, excessive PA content (≥10%) exerts a dilution effect, reducing the amount of hydration products and weakening the mechanical performance. Overall, the use of an appropriate PA dosage in combination with cement enhances both strength and durability while reducing cement consumption, providing an effective pathway for the high-value utilization of agricultural solid waste resources.