Acta Geotechnica最新文献

Naturally deposited sand in its undisturbed intact state exhibits distinct mechanical properties compared to reconstituted sand owing to the initial fabric generated during sedimentation. In this study, hollow cylinder torsional shear (HCTS) tests were conducted on an intact sand obtained from a river–lake sedimentation area and its air-pluviated reconstituted counterpart to compare their macro-scale mechanical behavior. In parallel, X-ray tomography scans were performed on corresponding mini-samples at an initial state to compare their fabric characteristics. The results indicate that, at the macro-scale, intact sand exhibits greater initial shear modulus and more pronounced dilation, with these differences gradually diminishing as loading progresses. At the micro-scale, the particle orientation of intact sand exhibits concentration within an inclined plane, whereas reconstituted sand particles tend to orient in the horizontal plane. Intact sand displays a more uniform contact normal orientation distribution, greater coordination number, and especially, greater contact area and volume compared to reconstituted sand. These disparities are more pronounced in the coarse particles within the samples. Based on the microstructure characteristics, an interlocking variable I is proposed. I is hypothesized to evolve during shearing and ultimately converge to a unique critical state and is introduced in a dilatancy state parameter to form the Critical State Theory incorporating Interlocking (CST-I). The simulation results highlight that with the incorporation of I in CST-I, the greater shear modulus and more pronounced dilation of intact sand can be well captured. CST-I provides a framework to unify the modeling of uncemented structured and reconstituted sand.

Under the coupling effect of effective stress and temperature, the permeability characteristics of rock under thermo-hydro-mechanical (THM) conditions are complicated. The complexity of permeability under THM conditions is mainly characterized by the non-monotonic variation with effective stress and temperature. The permeability variation under THM condition is mainly controlled by four different mechanisms, including compaction effect of mean effective stress, expansion effect of temperature, damage effect of effective shear stress, and damage effect of temperature. The former two mechanisms cause permeability to decrease, the latter two mechanisms cause permeability to increase. Therefore, based on the cubic model, a novel permeability model considering the four mechanisms described above is proposed in this study. The proposed permeability model is the function of effective stress and temperature. Besides, the permeability impact factor is defined based on the proposed model, which can directly reflect the contribution of effective stress and temperature to permeability. Four sets of permeability data under THM conditions were selected from existing literature to validate the proposed model. The fitted surface accurately describes the variation in the permeability data, which validates the accuracy and applicability of proposed model. Subsequently, the variation of permeability impact factor with effective stress and temperature is discussed.

The occurrence of landslides is often a complex dynamic evolution process, characterized by multiple slide-stop-slide cycles. Each state transition may be associated with changes in the mechanical state and structure of the sliding zone soil, significantly influencing the overall stability of the landslide. Taking the sliding zone soil of Ertaizi gully landslide as test material, a series of repeated ring shear tests were conducted under different moisture contents (Mc), normal stresses (σ_n), and the number of shear cycles (NSC) to investigate the mechanical strength characteristics of the sliding zone soil during the process of repetitive motion landslides movement. The results indicate: (1) Mc critically influences the soil shear strength in the deep sliding zone, while increasing NSC diminishes the strain-softening phenomenon of soil. Additionally, the attenuation effect of NSC against shear strength actually weakens the cohesion of the soil. (2) An increase in Mc reduces soil looseness near the shear plane, while an increase in σ_n expands relatively flat region adjacent to the shear plane. Under shearing, soil particles align along the shearing direction, exhibiting a preferred orientation within 0~30°. (3) Although there is a healing mechanism at the shear plane, repetitive motion landslides remain highly hazardous. This research offers a theoretical basis for comprehending the effects of Mc, σ_n, and NSC on the mechanical strength and microstructural deformation properties of soil. Additionally, it provides guidance for predicting the stability of repetitive motion landslides.

Particle shape plays a pivotal, yet poorly understood role, in the response of granular materials. Previous studies have shown a clear dependence between their bulk response and the morphology of the constituent particles. However, due to the intrinsic variability of natural materials, the effect of shape cannot be fully isolated in physical experiments, limiting the studies to an overall comparison between the bulk responses of granular assemblies with different particle shapes. In this study, plastic ellipsoids with different aspect ratios and surface frictions are employed to study both their micro- and the macro-scale effect under controlled and repeatable conditions. Six specimens of more than 20-thousand monodispersed particles are subjected to triaxial compression, while in operando X-ray tomography is used to characterise the material response at multiple scales. For the first time, each individual particle is identified and followed throughout the test, which is in itself a major technical achievement, which allows the reliable measurement of the full evolution of inter-particle contacts. We show that the development of contact fabric anisotropy is driven by the geometry of the particles, independently from both local and global strains. Additionally, we observe that the role of inter-particle friction is strongly related to the degree of induced anisometry of the particles, affecting mostly the development of inherent anisotropy during the deposition process, which translates into higher macroscopic shear strength.

The limit failure modes and earth pressure distribution of excavation retaining structures under rotating about the top (RT) displacement mode were systematically investigated. Finite element limit analysis incorporating the HMC constitutive model was employed, leading to the establishment of a logarithmic spiral failure surface model that accurately characterizes curved slip surfaces, overcoming the limitations of conventional Coulomb failure surface assumptions. An asymmetric soil arching effect characterized by a distinctive arch feet difference (Δh) was identified. An optimized arch-shaped differential element method was developed, in which asymmetric arch-shaped differential elements were established along the principal stress rotation trajectory at the soil's limit state. Analytical expressions for earth pressure were subsequently derived based on their mechanical equilibrium equations. Systematic parametric studies were conducted to quantitatively analyze the influence of soil properties, interface friction angle, and surface surcharge on earth pressure distribution, resultant force, and its point of application. These combined advances establish a refined theoretical framework for earth pressure calculation, offering engineers improved design accuracy for excavation retaining structures.

Vacuum preloading-airbag pressurization (VP-AP) technology is an emerging and proven effective method in dredged sludge treatment. To explore the mechanism of VP-AP and guide engineering applications, this paper proposes two axisymmetric consolidation prediction models that account for different distributions of prefabricated vertical drains and airbags. These models consider variations in vacuum pressure with depth and the effects of clogging. Analytical solutions derived from the models were compared with experimental data and analytical solutions from the literature under simplified conditions. Additionally, laboratory model tests were conducted to validate the proposed theoretical models and emphasize the necessity of considering clogging effect. Analysis under various influencing factors indicates that, at equivalent pressure levels, the VP-AP method outperforms vacuum-surcharge preloading. As the clogging factor or well resistance factor increases, the dissipation rate of excess pore water pressure slows down; however, the variability in well resistance has less effect on consolidation completion time when clogging effects are significant. Furthermore, accurate prediction of final ground settlement considering the attenuation of vacuum pressure with depth can effectively reduce project duration and costs.

Using biocement represents an innovative approach for controlling permeability. However, achieving the desired effects in coarse sand necessitates multiple treatment cycles. This study aims to enhance the efficiency of permeability reduction by introducing kitchen waste-derived powdered shellfish and modifying precipitation patterns. Experimental findings indicate that the control group, devoid of powdered shellfish, achieved a reduction of approximately 44%, whereas the experimental groups, supplemented with powdered shellfish, experienced reductions of over 91% within the same treatment period. The significance of biocement’s precipitation patterns in ameliorating permeability was substantiated through a series of experiments. These discoveries provide novel insights into optimizing biocement technology, with significant implications for potential applications, including hydraulic barrier pollution remediation schemes.

Intelligent compaction employs intelligent compaction measurement values (ICMVs) to assess the compaction quality in real time. Current engineering practices rely on a single harmonic ratio ICMV to evaluate the entire compaction process, overlooking variations in construction conditions. This paper introduces a hybrid-driven optimization approach to select the appropriate ICMV for subgrade compaction, based on the proposed multi-domain ICMV system. A series of heterogeneous scenario compaction tests are performed. The ICMV is refined by considering the compaction stage, filling soil gradation, and roller control parameters using mathematics and AI correlation model. The frequency-domain ICMVs are sensitive to roller vibration forces and are not recommended for construction sites with multiple or aged rollers. The influence of particle size is less pronounced. Considering the dynamic variation mechanism of the subgrade, it is recommended that the ICMV be changed for the third rolling pass. The proposed method effectively enhances the evaluation accuracy and efficiency in field validations.

In order to mitigate the coupling effect of bacterial organic matter and gravity on the heterogeneous distribution of calcium carbonate during MICP process, a bacterial organic matter control method for freeze–thaw resistance of MICP bio-cement was proposed. A series of laboratory tests were conducted on MICP bio-cement with varying bacterial organic matter contents and freeze–thaw cycles. A ternary precipitation structure induced by bacterial organic matter and gravity was identified, and the freeze–thaw resistance mechanism was analyzed. The main conclusions are as follows: (1) Adjusting the bacterial organic matter content during the MICP process to optimize freeze–thaw resistance performance is feasible, attributed to improved physicomechanical properties. Shear strength increased by 1.3 times (from 1386 to 1803 kPa) and P-wave velocity by 1.1 times (from 3020 m/s to 3439 m/s) with bacterial organic matter content increasing from 100 to 300%. (2) The ternary precipitation structure consists of small crystal layer, big crystal layer, and interlaminar gap. Higher organic matter content resulted in smaller crystals in both layers and a larger interlaminar gap. (3) The interlaminar gap is the main weak layer during freeze–thaw cycles. Sample S1 with 200% bacterial organic matter content exhibited better freeze–thaw resistance than the control sample after 10 freeze–thaw cycles, with a 15% increase in shear strength (from 1270 to 1463 kPa).

Microbially induced calcite precipitation (MICP)-based biocementation methods for soil improvement have drawn a substantial amount of attention in recent years. However, this method still suffers from several shortcomings. One of them is the need for multiple treatments. This paper presents a new method to enable a shear strength gain of more than 1 MPa to be achieved from a single MICP treatment. The key challenge is to use a cementation solution having a high calcium ion concentration. It is known that an excessively high calcium ion concentration will cause a retarding effect to impede the MICP process. In this study, a buffer solution and milk were used to enable a high calcium conversion efficiency of 95.5% for an all-in treatment solution with 2 M calcium ion concentration. By controlling the pH of the solution and using full cream milk, we could obtain an unconfined compressive strength of 1049 kPa from a single MICP treatment in 1 day. It was also discovered that the type of milk used could affect the strength of the soil treated and the use of full cream milk resulted in a higher strength than that of skim milk.