Zhijia Xue

The disposal of high-water-content bentonite slurry generated from underground construction presents prominent environmental and technical challenges, calling for low-carbon and efficient consolidation technologies. This study proposes an integrated flocculation–preloading–electro-osmosis (FPE) method using anionic polyacrylamide (APAM) combined with ground granulated blast furnace slag to strengthen dewatering and stabilization of bentonite slurry. Settlement column experiments were conducted to determine the optimal APAM dosages. A series of FPE consolidation experiments were performed to monitor drainage, settlement, electrical current, temperature and post-treatment soil properties, combined with microstructural analysis to reveal the synergistic mechanism. The results show that APAM creates abundant seepage channels via adsorption bridging and flocculation, significantly accelerating early-stage drainage and settlement rates without obviously increasing total drainage and final settlement. The polymer hydrogel homogenizes soil structure, leading to a gradual increase in moisture content and decrease in shear strength from anode to cathode, and effectively eliminates cracking during electro-osmosis. The temporary seepage channels induce a faster initial current rise, while the polymer coating increases apparent resistivity after free water discharge, thereby reducing current and temperature during the electro-osmotic consolidation stage. Appropriate APAM dosage thickens the electric double layer to raise the free swell ratio, whereas excessive dosage restricts swelling by particle coating. Microscopic observations confirm that chain-structured APAM and flocculent C-(A)-S-H hydration products cement soil particles and fill pores, improving soil integrity and shear strength. Overall, APAM improves early-stage efficiency and soil uniformity/integrity. In addtion, its combined effect with slag on bentonite shear strength increase is relatively higher than that of 0% slag condition. The integrated FPE technique realizes synchronous high-efficiency dewatering and low-carbon stabilization of high-water-content bentonite slurry, providing a novel and practical solution for engineering slurry disposal.

Geopolymer solidified soil has been extensively studied and however, knowledge gaps exist regarding the long-term influence of temperature and its modelling on the strength characteristics of geopolymer solidified soil. Fly ash (FA), calcium carbide residue (CCR) and NaOH are among the most widely investigated precursor and activator materials. Owing to their excellent performance, a CCR-FA-NaOH geopolymer is adopted as the binder in this research. An attempt is made to investigate the long-term influence (7, 14, 28, 60, 90, 150, 180, 240 days) of temperature (20 °C, 30 °C, 40 °C) on strength of solidified marine soft clay. Strength calculation model regarding long-term temperature influence is proposed, modified and established. The model accuracy is verified and deviation between true and predicted values is within approximately 10%. The 7-day strength of the specimen cured at 40 °C reaches 2352.5 kPa, which is 2.44 times that of the specimen cured at 20 °C. Strength improvement index (SI) of temperature is defined, indicating that higher curing temperatures correspond to greater SI values. Surface microgram is obtained by scanning electron microscope, and the stabilization and temperature influence mechanisms are discussed. Strength development is mainly attributed to pore filling, cementitious products and ion exchange. Higher curing temperatures enhance the chemical reaction rate, promoting the generation of more cementitious products. The experimental results can provide theoretical guidance for achieving the target strength of geopolymer solidified soil under long-term temperature influence in engineering applications.

Based on the demand of marine soft clay treatment, it is still urgent to seek green cementitious materials. Meanwhile, knowledge gaps exist regarding the application of waste tile powder (WTP)-calcium carbide residue (CCR) geopolymer into marine soft clay. This research explores the mechanical properties and freeze–thaw durability of WTP-clay-CCR system. Experimental results of unconfined compressive strength demonstrate that the strength is 1832.77 kPa after the incorporation of 13% CCR and 15% WTP. However, it is reduced to 474.69 kPa after 4 freeze–thaw cycles. The stability index (SI) is 0.422 after 2 freeze–thaw cycles but it is improved after the incorporation of CCR and WTP. The strength calculation model containing freeze–thaw cycles is proposed. The failure strain of sample is 1.0–2.0%. The peak strain energy and secant modulus are 18.53 kJ/m³ and 138.44 MPa after the incorporation of 13% CCR and 18% WTP. Finally, the pore characteristics and microstructure are revealed by scanning electron microscope and mercury intrusion porosimetry tests. The stabilization and freeze–thaw mechanism are analyzed. It reveals that the pore filling, gelling material and ion exchange are responsible for the mechanical property improvement. The micro-cracks formation and cracks development result in strength reduction of CCR-WTP-clay under freeze–thaw cycles.

The formation of collapse holes can adversely affect the efficacy of the lime soil compaction piles. This study employs a combination of field experiments, laboratory tests, microstructure observations, and theoretical analyses to elucidate the mechanisms underlying the improvement of soil compaction pile composite foundations in the Gansu region, particularly in the context of collapse hole problems. The conclusions are showed as following: (1) The implementation of lime soil compaction piles results in a gradual reduction of the void ratio of the loess between the piles due to horizontal extrusion effects. As the number of ramming times increases, the state of the pile transitions from loose to dense. This transformation is further enhanced by bridging and cementation within the pile body, leading to an enlarged particle structure and a reduction in pore size. (2) An increase in the number of ramming times correlates with a rise in both the average dry density and penetration resistance of the lime soil compaction piles. However, the presence of collapse holes can lead to the mixing of collapsed loess and lime soil filler, which significantly diminishes the penetration resistance of the pile body in the sections affected by collapse. Notably, after 16 ramming times, there is a marked increase in the dry density of the collapsed hole sections. (3) The issue of collapse holes contributes to an increase in the falling height of the rammer hammer, which in turn reduces the compressive stress within the hole and diminishes the extrusion of loess between the piles. Furthermore, the collapse effect negatively impacts the effectiveness of collapsibility elimination in the loess between the piles. This paper provide theoretical value and practical guidance for the enhancement of collapsible loess foundations.

Due to the influence of soil structure, structured soils exhibit significantly different mechanical behavior compared to the reconstituted soils having the same material. In this work, a theoretical analysis focusing on the mechanical behavior of structured soils is presented. Based on the mechanical behavior of the structured soil, a newly defined variable structural index was used as a measurement of the integrity of soil structure based on the concept of intrinsic compression line of intact structured soils. Furthermore, a novel correlation for the variation in volume of structured soils is established using effective stress and newly defined structural index as the constitutive variables. The novel correlation provided interpretation about the mechanism of compression behavior of the structured soils. Afterwards, the proposed correlation for the variation in volume was extended to triaxial stress state in the framework of subloading surface to include the effect of overconsolidation. Comparisons between the predictions and experimental results validated the proposed constitutive model for structured soils.

Electro-osmotic consolidation has been applied in several geotechnical engineering applications that contain a series of complex processes, including electrochemical processes, temperature changes, and mechanical evolution. To explore the combination of electrochemical–temperature–mechanical processes in marine clay, electro-osmotic consolidation experiments were conducted using a self-made electro-osmotic consolidation system under various durations and voltages. The following findings was obtained: (1) the change in the pH value increased during electro-osmotic consolidation and as the voltage rise; (2) the temperature increased with a rise in voltage in the initial stage of the experiments, which was induced by Joule heating; (3) the temperature rise promoted the electro-osmotic consolidation process, which included a rise in the coefficient of consolidation and a reduction in water content; (4) horizontal shrinkage occurred when the horizontal stress increment was greater than the critical stress condition. In addition, the volume difference reached a constant value, and was proportional to the voltage rise. After the discussion, a coupling analysis was conducted, which can help to better understand the mechanism of electro-osmotic consolidation and can provide reference for engineering applications.