Acta Geotechnica最新文献

In this study, a reduced-scale retaining wall specimen was subjected to laboratory testing to examine the strain localization phenomena behind an earth-retaining structure under passive conditions. The specimen was backfilled with two distinct soil materials—sand and fine gravels—in a medium dense state, while also retaining sloping ground surfaces with varying inclinations. The soil particle movement within the backfill was monitored and tracked through successive images captured at a consistent rate using a camera, as the wall progressively approached the backfill. By employing the digital image correlation technique, von Mises strain contours within the backfill were subsequently deduced from the recorded soil particle displacement field. This method unveiled the distribution and progression of strain concentration bands. Moreover, the laboratory tests documented the horizontal force–displacement curve of the wall, the earth pressure distribution across depth, and the wall’s uplift. These findings were verified against various analytical models and finite element simulations, illustrating good alignment. The von Mises strain maps disclosed the presence of a distinct boundary within the backfill, beyond which soil particles remained immobile during the pushover test. This boundary manifested during the early phases of the test when stress levels were relatively low. For specimens with positive slopes, this boundary evolved into the ultimate failure surface, characterized by a geometry resembling a log-spiral curve. Conversely, for specimens with negative slopes, the failure surface may not adhere to this log-spiral boundary; instead, it might follow a more direct route, resembling the straight line predicted by Rankine theory.

With the push toward global low-carbon and sustainable development goals, an urgent need exists to find building materials that can replace cement. Engineering muck (EM) produced by foundation pit engineering in subtropical areas is rich in clay minerals, which are suitable for the preparation of low-carbon geotechnical materials. In this study, the effects of SiO₂/Na₂O and the liquid–solid ratio on the performance of alkali-activated EM-based geopolymers were investigated. In addition, a life cycle assessment (LCA) was performed to evaluate the environmental impacts of EM-based geopolymers. The findings showed that the geopolymer with a SiO₂/Na₂O ratio of 1.5 achieved the highest 7-day compressive strength of 42 MPa, which was 47.46% and 56.49% greater than that of the geopolymer with SiO₂/Na₂O ratios of 0.9 and 1.8, respectively because of its densest structure and fewest cracks. Moreover, increasing the liquid–solid ratio from 0.75 to 0.90 slightly increased the 28-day compressive strength from 47 to 52 MPa because of the refined pore structure. However, this modification also increased carbonate formation and mass loss at elevated temperatures. Compared with those of concrete, the CO₂ and SO₂ emissions of EM-based geopolymers were reduced by 4–26% and 8–19%, respectively, owing to the considerable environmental impact of cement. The overall performance of the geopolymers was assessed via multiple influence indicator methods, and the optimal synthesis conditions for the geopolymers were a SiO₂/Na₂O ratio of 1.5 and a liquid–solid ratio of 0.75. This study suggests that using alkaline activation technology to transform EM into geopolymers has potential as a substitute for concrete, providing a new type of green material for geotechnical engineering.

Microbially induced calcium carbonate precipitation (MICP) is recognized as an eco-friendly approach in biological chemistry, offering significant potential for enhancing soil engineering properties. This study investigates the viability of MICP for stabilizing washed recycled sands (RS) sourced from construction and demolition wastes, offering significant potential for enhancing soil engineering properties and aligning this research study with sustainable waste management practices. Through meticulously designed laboratory experiments, this research examined the micro and macro biomineralization processes to assess the feasibility and factors influencing RS stabilization. The experimental setup evaluates the impact of cementation media concentration, ambient temperature, treatment cycles, and curing time on MICP-treated RS efficiency. The findings indicate that the optimal MICP conditions can be found at a cementation media concentration of 0.5 mol/L, an ambient temperature of 30 °C, and furthermore, up to 12 treatment cycles can significantly enhance the unconfined compressive strength (UCS) of RS to 724 kPa. In addition, extending the curing time results in a 28% increase in UCS compared to the initial strength of MICP-stabilized RS. Analyses via scanning electron microscopy and X-ray diffraction provide insights into the microstructural and mineralogical transformations that aid the biostabilization of RS. This research underscores the effectiveness of MICP-treated RS for usage as a geomaterial, emphasizing its environmental and practical benefits and furthermore advocates the sustainable usage of MICP for the biostabilization of RS for construction activities.

Deformation induced by finer particle loss is an important phenomenon during suffusion of gap-graded soils. This study focuses on the role of particle stress played in the particle loss-induced volumetric deformation. Discrete element simulations are performed to generate loss of finer particles with prescribed stress contribution, i.e. the contribution of particle stress to the macroscopic stress. Variations of volumetric strain, ε_v, with the stress contribution, C_σ^e, of eroded finer particles present two distinct patterns, that is, transition pattern, i.e. ε_v has extremely small values at relatively small C_σ^e and increases rapidly as C_σ^e exceeds the transition point near C_σ^e = 0.01%, and constant pattern, i.e. ε_v reaches a rather large value at extremely small C_σ^e and varies little with the increment of C_σ^e. A transformation from constant to transition pattern is observed for the ε_v–C_σ^e curves with the increment of the coordination number, Z_strong, of the load-carrying skeleton. The threshold of Z_strong for the transformation is around 3.71 for a relatively small eroded fraction (≤ 10%), while it is 3.96–4.09 for a relatively large eroded fraction (≥ 30%), in which the eroded fraction is the volume percentage of the eroded finer particles within the finer fraction.

Cracking of compacted clays during cyclic wetting–drying poses significant challenges to the stability of channel slopes. This study performed a series of unidirectional wet-dry tests to evaluate the cracking behavior of expansive soils collected from a channel slope in northern Xinjiang, China. Using computed tomography scanning and three-dimensional (3D) reconstruction, the internal crack characteristics of expansive soils were quantitatively described. The results indicate that the penetration depth of the cracks was stabilized after five cycles, reaching 31.4% of the initial specimen height. The morphologies of internal cracks revealed a transition in the cracking mode, form shallow and scattered cracks in the initial stage to deeper and more clustered cracks in the final stage. Centralized cracks were prominent in the first three wet-dry cycles, followed by a shift to crack deflection from the vertical plane in subsequent cycles. Four indices (i.e., slice crack ratio, crack length, branching number, and dead-end point) provided a satisfactory quantitative depiction of the evolution of the spatial distribution and connectivity of the cracks over the number of cycles. Additionally, the crack volume fraction and fractal dimension effectively evaluated the 3D cracking behavior of soil crack networks.

The “yield-resist” combined support measure is a widely employed control measure in soft rock tunnels for controlling large deformation, particularly in high geostress conditions. For strain-softening rock masses, the strength parameters in the plastic zone are coupled with the support reaction. Due to the complexity of the interaction mechanism between yielding support and strain-softening surrounding rock, the majority of current solutions are based on the plane–strain model. However, the advancement of the tunnel is a three-dimensional problem. Therefore, the longitudinal effect is worthy of discussion when analyzing the mechanical behaviors of strain-softening rock and yielding support. A new two-stage method is proposed to describe the interaction between strain-softening rock mass and yielding support based on the generalized Zhang–Zhu (GZZ) strength criterion. Firstly, a simplified mechanical model of the yielding support structure is suggested to describe the mechanical response of the surrounding rock and support. Subsequently, a semi-analytical solution to three-dimensional ground–support interaction is proposed, taking into account the longitudinal effect. The results of the proposed solution are compared with those of a finite element simulation, and a high degree of agreement is observed. Finally, the mechanical behaviors of different yielding supports are discussed. The findings indicate that postponing the support timing by means of yielding technologies is essential, as otherwise the support would bear a very large load. The second stage of support reaction can be significantly reduced by implementing the “control-yield-resist” (CYR) support. The research offers novel insights and methodologies for investigating the three-dimensional interaction between the surrounding rock and various tunnel supports in high geostress conditions.

This communication presents a critical discussion of the article “Undrained shear strength prediction of clays using liquidity index”, authored by Q. Wang, S. Qiu, H. Zheng, R. Zhang, and recently published in Acta Geotechnica (https://doi.org/10.1007/s11440-023-02107-9). Various inaccurate claims and flaws regarding the Authors’ newly developed three-parameter strength–liquidity index (S_u–I_L) models/correlations are highlighted and discussed herein. In particular, comparing existing two-parameter and their newly developed three-parameter S_u–I_L models, contrary to the Authors’ claims, no improvement in prediction accuracy is achieved over the two-parameter model by introducing a third model parameter. Rather, it is shown herein that the existing two-parameter and the Authors’ three-parameter S_u–I_L models are mathematically identical. Furthermore, two of the Authors’ newly developed S_u–I_L correlations, i.e., relating the triaxial-compression and shearbox derived strengths to the liquidity index, are shown to be inaccurate, forecasting gross under- and over-predictions of the measured strengths, respectively. This highlights the need for a reassessment of the proposed correlations, and emphasizes the importance of accurate and reliable correlations in geotechnical engineering.

Wang et al. (2024) proposed a new method to measure soil stiffness through triaxial tests. This discussion illustrates some limitations of the proposed method and details several modifications on the post-image analysis process to enhance its capability. These modifications include the introduction of true stereophotogrammetry for camera and triaxial cell wall orientation, optical ray tracing technique for optical ray reconstruction, and three-dimensional digital image correlation (3D-DIC) for full-field two-dimensional (2D) point cloud generation. With these modifications, the capability of the new method can be significantly improved from only local strain to full-field deformation measurement at a higher accuracy and resolution.

Ren et al. (Acta Geotech, 2023. https://doi.org/10.1007/s11440-023-01967-5) recently reported an interesting experimental investigation of the thixotropism, or thixotropy mechanism, of a deep-sea marine clay, conclusively claiming that the conversion of weakly and strongly bound waters to free water, in addition to microfabric change, contributes to the thixotropic hardening of the studied clay. While the microfabric evolution of the clay during the thixotropic hardening process was observed, in a speculative and qualitative fashion, using scanning electron microscopy, the interconversion of different types of waters (i.e., weakly bound water, strongly bound water, and free water) in the clay was quantitatively assessed using thermogravimetric analysis (TGA) and qualitatively judged by Fourier transform infrared spectroscopy (FTIR). However, some fundamental issues related to the viability and suitability of the employed experimental techniques and the interpretation of TGA and FTIR results arise and are worth re-examination and discussion. In this short communication, the TGA curves and FTIR spectra were re-interpreted, based on a mathematically more accurate and scientifically more rigorous analysis of the data, which appears to make the proposed model of evolution of different types of waters in clays invalid. Consequently, the attribution of thixotropy or one potential thixotropism to the conversion among different types of waters and the conclusions drawn based on the speculative interpretations are also worth further clarifying and commenting. Overall, the TGA and FTIR results probably fail to conclusively establish the conversion among the different types of waters occurring along with the thixotropic hardening process.