Journal of Rock Mechanics and Geotechnical Engineering最新文献

The overall carbonation of MgO-admixed soil provides not only an efficient and environmentally friendly technique for improving soft ground but also a permanently safe solution for CO₂ sequestration. To evaluate the carbon sequestration potential and promote the carbonation application in soil improvement, a laboratory-scale model investigation is designed under pressurized carbonation considering the influences of MgO dosage and CO₂ ventilation mode (way). The temperature, dynamic resilience modulus, and dynamic cone penetration (DCP) were tested to assess the carbonation treatment effect. The physical, strength, and microscopic tests were also undertaken to reveal the evolution mechanisms of CO₂ migration in the MgO-carbonated foundation. The results indicate that the temperature peaks of MgO-treated foundation emerge at ∼20 h during hydration, but occur at a distance of 0–25 cm from the gas source within 6 h during carbonation. The dynamic resilience moduli of the model foundation increase by more than two times after carbonation and the DCP indices reduce dramatically. As the distance from the gas inlet increases, the bearing capacity, strength, and carbon sequestration decrease, whereas the moisture content increases. Compared to the end ventilation, the middle ventilation produces a higher carbonation degree and a wider carbonation area. The cementation and filling of nesquehonite and dypingite/hydromagnesite are verified to be critical factors for carbonation evolution and enhancing mechanical performances. Finally, the overall carbonation model is described schematically in three stages of CO₂ migration. The outcomes would help to facilitate the practical application of CO₂ sequestration in soil treatment.

The rubber-containing waste materials have been widely used to improve the engineering properties of soils in recent years. Among others, granular rubbers are utilized in various ways to increase the bearing capacity and shear strength and to reduce the settlement and liquefaction potential of soils. The granular rubbers have many advantages such as temperature resistance, flexibility, tear-resistance, non-slip, and thermal and electrical insulation. This study presents the distribution characteristics of five different types of clayey soils with different engineering properties containing waste rubber particles (WRPs). On the other hand, determining and controlling the dispersion characteristics of clayey soils is two significant engineering problems. The study aims to solve these two remarkable and problematic issues in an eco-friendly and safe way. The role of WRP treatment in the investigation of soil dispersion behavior, which can cause dangerous problems such as piping, erosion, and dispersion, reflects the original and different perspectives of this study. Within this scope, geotechnical parameters of the clayey soils were determined. Subsequently, pinhole test, crumb test, double hydrometer test, and scanning electron microscopy (SEM) analysis were performed on the Na-activated bentonite, refined ball clay, Ukrainian kaolin, Avanos kaolin, and Afyon clay samples with different percentages of WRPs (0%, 5%, 10%, and 15%). Consequently, Avanos and Ukrainian kaolin clays gave the most limited response to the dispersion behavior with the addition of WRP. Also, WRP treatment on the ball clay and bentonite samples showed limited efficiency. Afyon clay, which was defined as dispersive by the three tests that determined its dispersion potential, showed 3 level changes in the pinhole tests and 2 level changes in the crumb tests, and gave the most effective results in terms of WRP efficiency.

Investigation of mining-induced stress is essential for the safety of coal production. Although the field monitoring and numerical simulation play a significant role in obtaining the structural mechanical behaviors, the range of monitoring is not sufficient due to the limits of monitoring points and the associated numerical result is not accurate. In this study, we aim to present a spatial deduction model to characterize the mining-induced stress distribution using machine learning algorithm on limited monitoring data. First, the framework of the spatial deduction model is developed on the basis of non-negative matrix factorization (NMF) algorithm and optimized by mechanical mechanism. In this framework, the spatial correlation of stress response is captured from numerical results, and the learned correlation is employed in NMF as a mechanical constrain to augment the limited monitoring data and obtain the overall mechanical performances. Then, the developed model is applied to a coal mine in Shandong, China. Experimental results show the stress distribution in one plane is derived by several monitoring points, where mining induced stress release is observed in goaf and stress concentration in coal pillar, and the intersection point between goaf and coal seam is a sensitive area. The indicators used to evaluate the property of the presented model indicate that 83% mechanical performances have been captured and the deduction accuracy is about 92.9%. Therefore, it is likely that the presented deduction model is reliable.

This study aimed to reveal the influence of different free-iron-oxides contents on the strength and deformation characteristics of in situ lateritic soil. A test method that combined the selective chemical dissolution method and in situ Ménard pressuremeter test (PMT) was proposed. The soaking time in dithionite–citrate–bicarbonate (DCB) solution was used as a variable to control the free-iron-oxides content in lateritic soil. Then, the in situ lateritic soil boreholes with different soaking time were tested by PMT. The results showed that the in situ horizontal pressure $p_0$, critical edge pressure $p_f$, ultimate pressure prediction $p_l$, pressuremeter modulus $E_m$, shear modulus $G_m$, and foundation-bearing capacity $f_{0k}$ of lateritic soil decreased rapidly after immersing in DCB solution within 1–4 d. With increasing soaking time, the decrease rate reduced gradually. Moreover, the relationship curve between free-iron-oxides content and soaking time declined rapidly and then stabilized, and the free-iron-oxides content at the inflection point was 30.11 g/kg. When the free-iron-oxides content changed to the inflection point, the free-iron-oxides that played a cementing role was largely removed, indicating that the effective cementing iron-content of Miaoling lateritic soil was about 52.9%. This study demonstrated that the proposed test method can determine the influence of free-iron-oxides content on the strength and deformation characteristics of lateritic soil.

The scaling-dependent behaviors of rocks are significant to the stability and safe operation of the structures built in or on rock masses for practical engineering. Currently, many size effect models are employed to connect laboratory measurements at small scales and engineering applications at large scales. However, limited works consider the strain rate effect. In this study, an fractal-statistical scaling model incorporating strain rate is proposed based on a weakest-link approach, fractal theory and dynamic fracture mechanics. The proposed scaling model consists of 8 model parameters with physical meaning, i.e. rate-dependent parameter, intrinsic material parameter, dynamic strain rate, quasi-static strain rate, quasi-static fracture toughness, micro-crack size, micro-crack intensity and fractal dimension, enabling the proposed scaling model to model the scaling behaviors under different external conditions. Theoretical predictions are consistent with experimental data on red sandstone, proving the reliability and effectiveness of the proposed scaling model. Thus, the scaling behaviors of rocks under dynamic loading conditions can be captured by the proposed fractal-statistical scaling model. The sensitivity analysis indicates that the nominal strength difference becomes more obvious with a higher strain rate, larger fractal dimension, smaller micro-crack size or lower micro-crack intensity. Therefore, the proposed scaling model has the potential to capture the scaling behaviors considering the thermal effect, weathering effect, anisotropic characteristic etc., as the proposed scaling model incorporated model parameters with physical meaning. The findings of this study are of fundamental importance to understand the scaling behaviors of rock under dynamic loading condition, and thus would facilitate the appropriate design of rock engineering.

Engineering disasters (e.g. rock slabbing and rockburst) of the tunnel groups induced by the transient excavation of an adjacent tunnel threaten the stability of the existing tunnel, especially for those excavated by using the drill and blast tunneling (D&B). However, the dynamic response and failure mechanism of surrounding rocks of the existing tunnel caused by adjacent transient excavation are not clear due to the difficulty in conducting field tests and laboratory experiments. Therefore, a novel transient unloading experimental system for deep tunnel excavation was proposed in this study. The real stress path and the unloading rate can be reproduced by using this proposed system. The experiments were conducted for observing the dynamic response of the existing tunnel induced by adjacent transient excavation under different lateral pressure coefficients λ (= 0.4, 0.6, 0.8, 1, 1.2, 1.4, 1.6, 1.8) with a polymethyl methacrylate (PMMA) specimen. The propagation of the impact wave and unloading surface wave was detected through the digital image correlation (DIC) analysis. The reflection of the unloading surface wave on the incident side of the existing tunnel (tunnel-E) was observed and analyzed. Moreover, the dynamic characteristics of the stress redistribution, the particle displacement and vibration velocity of surrounding rocks of tunnel-E were analyzed and summarized. In addition, the Mohr-Coulomb (M–C) failure criterion with tension cut-off was adopted to evaluate the stability of the existing tunnel under adjacent transient excavation. The results indicate that the incident side of the existing tunnel under the dynamic disturbance of transient excavation of an adjacent tunnel was more prone to fail, followed by the shadow side and the top/bottom side.

Fault rupture propagation is more complex in the overlying soil with intercalation than in homogeneous soil, and it is challenging to simulate this phenomenon accurately using the finite element method. To address this issue, an improved nonlocal model that incorporates softening modulus modification is proposed. The methodology has the advantage that the solutions are independent of both mesh sizes and characteristic lengths, while maintaining objective softening rates of materials. Using the proposed methodology, a series of numerical simulations are conducted to investigate the effects of different mechanical parameters, such as elastic modulus, friction angle and dilation angle of the soil within the intercalation, as well as the impact of geometries, such as the depth and thickness of the intercalation, on the fault rupture progress. This study not only provides significant insights into the mechanisms of fault rupture propagation, specifically in relation to intercalations, but also shows a great value in promoting the current research on fault rupture.