The rapid pace of urbanization has created a critical shortage of available land for urban construction, compelling many coastal cities to initiate projects for reclaiming land along their coastlines. These initiatives not only relieve the pressure on urban land usage but also promote vigorous and dynamic growth within the urban economy. For instance, the ongoing and extensive coastal reclamation project in the Binhai New Area of Tianjin provides a relevant example. However, these reclamation projects inevitably lead to the production of considerable quantities of waste soil and sewage. The combination of these waste materials creates a mixture characterized by high water content, low strength, notable compressibility, and restricted permeability, making it unsuitable for practical engineering purposes. At the same time, the substantial accumulation of sewage and waste soil leads to the diminishment of land resources and severe environmental pollution. Consequently, it is imperative to innovate with solidification materials for the treatment of wastewater and waste soil, addressing the vulnerabilities related to low strength, high water content, and structural instability within the waste soil–wastewater amalgam. In practical engineering scenarios, solidified soil experiences diverse loads, including fill soil and dynamic forces, resulting in an intricate three-dimensional stress condition. Traditional testing equipment encounters challenges in accurately and comprehensively replicating these loading conditions. Furthermore, the mechanical attributes of the soil exhibit significant complexity owing to various influencing factors, and simplistic elastoplastic models fail to provide an accurate depiction of its genuine stress state and mechanical traits. Consequently, there is a need for the ongoing enhancement of solidification techniques, resolution of the engineering challenges inherent in high-water-content fill locations, and extensive investigation into the associated mechanical evolution mechanisms. This endeavor bears substantial economic and social significance in facilitating the rational and effective utilization of high-water-content fill soil while expediting engineering construction.
Both domestic and international scholars have made significant progress in researching the solidification treatment of reclaimed land resulting from the accumulation of wastewater and waste soil. They have also investigated the three-dimensional stress–strain relationship of solidified soil and explored elastoplastic constitutive models. Shen et al. [
1] utilized slag as the primary constituent, complemented by activators like water glass and gypsum powder, to solidify and remediate hydraulic fill with a high water content. Yang et al. [
2] conducted an investigation into the correlation between the dosage of fly ash, a key constituent of solid waste-based solidifying agents, and the levels of cohesion and internal friction angle. They delved into the linear relationship between these factors. Additionally, they examined the connection between the pore structure of the solidified soil and the hydration products that ensued from the process [
3]. Lei et al. [
4] employed anionic polyacrylamide to treat solidified soil. Li et al. [
5] conducted an innovative investigation on soft soil stabilization in hydraulic fill using microbial-induced calcium carbonate precipitation. Soganci et al. [
6] utilized slag as a solidifying agent for soft clay and investigated the solidification effect when combined with marble dust. Jia et al. [
7] employed solid waste materials including steel slag and desulfurization ash in a cooperative solidification procedure to treat high-water-content soil. The optimum solidifying agent formulation was achieved with steel slag constituting seventy percent. Cui et al. [
8] investigated the enhancement of performance of high-water-content dredged slurry utilizing steel slag. Shi et al. [
9] collaborated on the use of steel slag and cement to mitigate the challenge posed by a high water content in dredged soft soil. Huang et al. [
10] developed a comprehensive understanding of the adverse mechanical effects concerning the moisture content and the ratio of intermediate principal stress through rigorous true triaxial testing. However, as this ratio and moisture content increased, the detrimental effect gradually became more pronounced. Rong et al. [
11] collaborated on a study investigating the mechanical properties of clay in frozen states within mining areas, employing orthogonal experiments and true triaxial tests. The results suggest that various factors, including temperature, moisture content, and confining pressure, significantly influence strength indicators. Zheng et al. [
12] enhanced the fundamental true triaxial apparatus by implementing multiple partitions to mitigate interference during loading. The apparatus underwent testing through a series of one hundred experiments, providing insights into the failure mode of loess. In their research, Gu et al. [
13] analyzed the coupling of different stresses, investigating scenarios where both compression and tension states coexist and lead to separation at a certain threshold. Zheng et al. [
14] carried out numerous isotropic consolidation tests on loess with the aim of exploring the failure envelope and mechanical properties of this material. Han et al. [
15] investigated the contact density and liquefaction properties of geomaterials at a critical state. Li et al. [
16] integrated the GDS apparatus with a true triaxial setup, revealing a critical point in the failure behavior of aeolian sand. Shao et al. [
17] employed a true triaxial apparatus to investigate the failure modes of shear bands under low confining pressure. Additionally, they modified the intermediate principal stress to establish a model. Zhang et al. [
18] developed anisotropic boundary conditions for the analysis of dams and subsequently compared them with conventional constitutive models. Cabrejos et al. [
19] conducted true triaxial tests, considering intricate factors like particle size distribution, to derive suitable models. Salimi et al. [
20] incorporated fluid coupling in their true triaxial experiments to investigate the mechanical characteristics of simulated soil particles. Ren et al. [
21] explored the impact of temperature factors on true triaxial tests and investigated the corresponding degradation conditions. Cao et al. [
22] studied the variation trend of deformation of high-calcium clay, considering the combined influence of various factors, including the salt content and temperature. Shao et al. [
23] conducted true triaxial experiments, taking into account the influence of matric suction factors, and subsequently analyzed the geostress. Shao et al. [
24] modified the true triaxial apparatus by incorporating a balance plate and a hydraulic chamber. They also designed algorithms for research. Andreghetto et al. [
25] incorporated a true triaxial apparatus into an automated program and verified its functionality by comparing it with conventional experimental instruments. Sun et al. [
26] performed a collaborative analysis of load tests utilizing true triaxial experiments and fractional plasticity models. Foroutan et al. [
27] developed a model that correlates confining pressure with porosity, investigating the significant influence of the intermediate principal stress ratio. Liu et al. [
28] developed a model that correlates confining pressure with porosity, investigating the significant influence of the intermediate principal stress ratio. Huang et al. [
29] employed a modified apparatus to investigate frozen soil under complex stress conditions. Shao et al. [
30] explored the strength variation of soil following natural structural failure and investigated the impact of microcracks on the strength pattern through the use of true triaxial tests. Liu et al. [
31] formulated a three-dimensional creep model and then optimized it specifically for accelerated creep conditions. Wang et al. [
32] refined an elastoplastic constitutive model to account for non-uniform deformation and fracture, enhancing its applicability in capturing the dynamic characteristics of soil. Yamada et al. [
33] introduced a novel approach to integrate cementation into the current elastoplastic constitutive model of soil. Zheng et al. [
34] introduced velocity parameters into the prediction model. This model demonstrated enhanced predictive performance, particularly for extended creep durations. Tachibana et al. [
35] incorporated parameters related to the compaction curve into the constitutive model, resulting in simulation results of higher accuracy. Zhao et al. [
36] conducted triaxial tests on soft soil, considering the coupling conditions of cyclic loading and the salt content. Zhang et al. [
37] formulated a binary medium computational model for samples, treating them as two-phase materials. They proceeded to validate and calibrate the model. Peng et al. [
38] formulated a constitutive model with the ability to accurately predict uncertain boundary values. Subsequently, they conducted validation to assess its performance. Mazzucco et al. [
39] examined the peak strength of nonlinear materials employing a model loaded via a novel procedure. Sternik et al. [
40] studied a constitutive model that integrated temperature and hardening parameters. They then compared experimental data with the predicted results across diverse loading conditions. In summary, enhancing soil engineering properties through the addition of solidifying materials is well acknowledged in both academic and engineering circles. The preceding research has established a robust foundation for more effective soil treatment. However, there has been insufficient research on soft soil reclamation with a high moisture content, especially in coastal areas, in the studies mentioned. Various materials are available for soil management, each differing in composition and properties, primarily emphasizing the strength of the solidified soil after the interaction between solidifying agents and the soil. However, research on the influence of factors like moisture content and foaming rate on the strength of the solidified soil is notably scarce in the studies mentioned. Hence, the development of stabilization technology for coastal, highly saturated reclaimed soils that simultaneously enhances the soil strength while reducing the bulk density is of significant engineering and academic value. In reviewing the research and experimental findings on diverse types of soil conducted by a multitude of scholars employing various methodologies globally and domestically, it becomes evident that true triaxial tests yield results that better depict the stress–strain characteristics of soils in practical engineering when contrasted with simplistic direct shear or unconfined compression strength tests. Until now, research on the three-dimensional mechanical properties of solidified lightweight soil has been limited. Hence, investigating the stress–strain characteristics of solidified lightweight soil under actual three-dimensional stress conditions holds paramount scientific and practical importance. Presently, scholars, both nationally and internationally, have conducted research to varying extents concerning the formulation of constitutive models for rock and soil materials, yielding relevant outcomes. Nonetheless, research regarding the constitutive model of solidified lightweight soil, a novel subgrade material, remains limited. Aligning with the national sustainable development strategy, the integration of novel geotechnical materials into subgrade construction represents a prevailing trend. Hence, given the stress attributes of subgrade fill materials, developing the three-dimensional Cambridge model for solidified lightweight soil carries noteworthy theoretical and practical importance within the realm of engineering.
In this study, we utilize solidification technology to address the suboptimal mechanical properties of soft and viscous clay in the Tianjin Binhai reclamation area. Our objective is to ensure that the solidified lightweight soil, after undergoing this treatment, meets the requisite strength standards for engineering applications. Furthermore, this study furnishes theoretical underpinnings for ensuring the safe operation of the site. Subsequently, in light of the actual stress characteristics and engineering challenges present at the reclamation site, we conducted a thorough analysis of the three-dimensional mechanical properties of solidified lightweight soil under diverse stress pathways. This involved a comprehensive investigation into the three-dimensional mechanical constitutive model of solidified lightweight soil operating under the conditions of three-dimensional stress. The insights derived from this research offer both theoretical and technical support for the efficient and secure utilization of solidified lightweight soil in engineering applications.