Bulletin of Engineering Geology and the Environment最新文献

The generation of negative excess pore water pressure (u₂) during cone penetration test (CPT) in a given environment represents a deviation from the actual situation, thereby affecting the accuracy of the parameter inversion. Dissipation tests have been conducted to ascertain the dissipation of the u₂ over time, which in turn allows for the parameters to be corrected. However, the tip resistance (q_c) and sleeve friction resistance (f_s) in dissipation process also vary with time, despite its potential impact on the inversion process. In this paper, the evolution of q_c and negative u₂ with time is successfully obtained through the utilization of indoor CPTs on silt soils. In conjunction with a viscoelastic model, the existence of stress relaxation of q_c is demonstrated and the causes of q_c decay are analyzed. The detailed conclusions are as follows: (1) The CPT parameters obtained from the dissipation test can be employed to rectify the discrepancy in negative u₂ that arises during soil classification. (2) The q_c undergoes a gradual decrease, reaching a final equilibrium state during the dissipation process. The stress-time relationship is consistent with the Three-element viscoelasticity model, which represents a stress relaxation phenomenon. The relaxation process can be divided into three distinct phases: fast relaxation, decelerating relaxation, and residual relaxation. The residual stress is found to be correlated with the depth of the soil layer. (3) During residual phase, the loss rate of q_c is observed to decrease in a linear fashion with the rate of u₂, prior to which the relationship is exponential. As the penetration rate increases, the rate of u₂ also increases.

In underground engineering, understanding rock strength parameters is fundamental for rock classification and evaluation, significantly influencing the design and optimization of support systems. Present research emphasizes real-time assessment methods for rock conditions during drilling operations. Employing the dimensionless rock drillability index (I_d) proposed in connection with Measurement While Drilling (MWD), it allows real-time evaluation of geological conditions in the surrounding rock through in-situ drilling tests. This study conducted in-situ drilling tests using both the MWD system and a drilling camera detection system. The results indicate a power function relationship (negative correlation) between I_d and rock strength (uniaxial compressive strength). Furthermore, under various drilling conditions, including the use of Polycrystalline Diamond Compact (PDC) bits and core bits, I_d continues to be a reliable method for assessing rock strength. A comparison of results from the two evaluation methods, I_d and specific energy, demonstrates that the application scope and stability of using I_d to assess rock strength superiors that of specific energy. Significant fluctuations in I_d within rock fracture zones suggest that I_d can accurately predict the presence of such zones. These findings affirm that I_d is stable and widely applicable for assessing the strength of the surrounding rock and predicting the presence of fracture zones.

The optimization and quantitative evaluation of tunnel support systems under complex geological conditions remains challenging. Therefore, a definition ‘deformation control contribution’ is put forward to quantitatively evaluate the effect of initial support on controlling the rock deformation. And a new optimization method of initial support is proposed for TBM tunnel crossing fault zone based on deformation control contribution. Firstly, the deformation characteristics of surrounding rock were explored. Subsequently, a series of numerical tests were conducted to investigate the deformation control effect of shotcrete, bolt, and steel arch parameters. Finally, the deformation control contribution of different support systems in fault-controlled section is quantitatively evaluated. The results show that: (1) The influence of support parameters on surrounding rock deformation is different. In terms of influence degree, the thickness of shotcrete is greater than stiffness, The spacing of bolts has greater influence than length, and the cross-sectional area, moment of inertia and spacing of steel arches are similar. (2) The deformation control contribution of the support systems in fault-controlled section is different. In bed rock zone, the contribution of shotcrete is highest (59.9%~67.6%). In fault damaged zone, the contribution of steel arch is highest (46.3%~56.2%). In fault core, the contribution of steel arch is also the highest (47.5%~62.2%). (3) The optimal support systems and support parameters for fault-controlled section are proposed, and the synergistic mechanism among support systems is revealed by stress analysis. The research results provide effective guidance for the dynamic design and optimization of the tunnel support systems.

Variations in reservoir water level and seasonal precipitation have reactivated or accelerated numerous reservoir landslides in the Three Gorges Reservoir (TGR) area in China since its impoundment in 2003. Majiagou landslide, a typical reservoir landslide with stabilizing piles, is affected by the coupling effect of rainfall and reservoir level fluctuations. Monitoring data of nearly 11 years show continuous movement of Majiagou landslide, in contrast to the step-like movements of many landslides in this region. Displacements of the landslide surface and sliding zone are accelerated in rainy seasons accompanied by rapid fluctuations in reservoir water level. A SHAP-XGBoost-based interpretable machine learning method was proposed to identify the key triggering factors of the deformation of Majiagou landslide. The crucial triggering factors vary among different monitoring sites, monitoring periods (e.g., before and after the replacement of monitoring sites), and monitoring intervals. Rainfall makes the most prominent contribution to the displacements of the landslide surface and slip zone. From the front to the rear of Majiagou landslide, the response period of surface deformation to reservoir water level fluctuation gradually lengthens, and the middle and rear parts are more sensitive to the average reservoir water level in the short term. The proposed SHAP-XGBoost method will facilitate deformation prediction, stability evaluation, and the calibration of early warning systems for reservoir landslides.

The morphology characteristics are key factors affecting the mechanical properties of structural plane. In this study, a systematic study is carried out to explore the actual roughness characteristics of standard profiles, the sensitivity of morphology parameters and the roughness prediction method with multi-parameter characterization. According to the statistical analysis of 552 pieces of literature on structural plane roughness, eight morphology parameters that are most representative are proposed and in-depth analysis is made on the relationship between each parameter and roughness coefficient. By smoothing the standard profiles and preparing structural plane specimens, the morphology characteristics and mechanical properties of structural plane smoothed for different times are put into scrutiny. A comprehensive analysis is conducted to investigate the correlation between morphology parameters and first and second-order roughness, as well as the relationship between first and second-order roughness and shear mechanical properties. The specimens of structural plane were manufactured via 10 standard profiles. Detailed discussion is made to analyze the deformation, failure and strength characteristics of standard structural plane. Based on the morphology parameters of standard profiles and the peak strengths of standard structural planes, the entropy weight-TOPSIS method is adopted to determine the actual rough characteristics of standard profiles. 86 sets of profile data were collected to establish the profile-morphology parameter-JRC database. The overlapping information between the eight morphology parameters is extracted by factor analysis. A stacked regression model incorporating multiple representative morphology parameters is proposed to predict the roughness characteristics of the structural plane.

The Baihetan hydropower station began impounding water on April 6, 2021, and its water level rose from 660 (m) to 817m by September 30, 2021. It is of great significance to catalog the landslides dynamically in the reservoir area and analyze the landslides deformation characteristics after impounding water. Stacking InSAR technology with ascending and descending Sentinel-1A data is applied to detect the potential active landslides on the upstream and downstream of Baihetan hydropower station from January 1, 2020 to April 6, 2022. Results show that a total of 76 active landslides were detected, and 21 landslides underwent significant deformation after impounding water. We analyze the relationship between slope stability and triggering factors, such as reservoir water level and rainfall to Mianshawan landslide, to which the displacement time series was obtained by small baseline subset (SBAS) InSAR technique. Results showed that the landslide was stable before impounding water, but increased to 15 cm/a after impounding water. Pearson correlation analysis revealed a 72-day lag between the displacement trend term of the landslide and the reservoir water level fluctuation. Wavelet analysis revealed a 60–90-day time lag between displacement trend term and precipitation, with common power on an interannual scale. The first impoundment of the Baihetan reservoir significantly enhanced the common power of precipitation and periodic term displacement on a quarterly scale. This research provides a reference for landslides detection and kinematics analysis in the reservoir regions.

Pakistan, a country blessed with diverse mineral wealth, has witnessed a rapid expansion of open pit mining operations in recent decades. Open pit mining has long been a cornerstone of the mineral extraction industry of Pakistan, allowing for the extraction of abundant natural resources critical for economic growth of the country. However, the pursuit of these valuable minerals often comes at a steep price, with slope stability issues posing significant challenges to mining operations across the country. This research paper investigates the challenges of slope instability in open-pit mining operations in Pakistan, focusing on the Muhammad Khel Copper Mining Project (MKCMP), using an integrated approach of geophysical and geotechnical investigations. The study first utilizes electrical resistivity tomography (ERT) technique, to comprehend subsurface dynamics critical for mining safety and efficiency. Through strategic ERT profile deployment, the research delineates strata types, traces water seepage patterns, and identifies potential causes of mass sliding. Analysis of four sets of ERT profiles reveals the complex interplay of geological, hydrological, and anthropogenic factors influencing subsurface dynamics. Findings underline the significance of moisture-induced destabilization, directional seepage flow, weak matrices, and cultural changes in driving slope instability within the study area. In addition to geophysical analysis, the paper also incorporates geotechnical investigations to enhance the understanding of slope behavior. The stability of the open-pit mine slopes was assessed using Limit Equilibrium Methods and Generalized Hoek & Brown (GHB) failure criteria in Slide 2D software. The western slope (Unit-I) was found to be more prone to circular failure due to weak rock mass properties and water infiltration, while the southern slope (Unit-II) exhibited lesser instability, with tension cracks and weak upper layers behaving like soil. Two stabilization methods — slope geometry modifications and soil nailing systems — were evaluated for both units. This comprehensive approach, combining geophysical and geotechnical techniques, provides valuable insights into slope instability mechanisms and effective stabilization strategies. The findings emphasize the importance of integrating subsurface analysis with engineering solutions to ensure long-term stability in open-pit mining operations, offering practical recommendations for improving safety and sustainability in Pakistan’s mining industry.

As the primary foundation material for island and reef structures, the long-term creep characteristics of coral sand can significantly impact the settlement and deformation of buildings. In this study, uniaxial creep experiments were conducted on coral sand from the South China Sea, and the creep characteristics of coral sand under different stress levels were analyzed. Five traditional component models were initially used to describe the creep behavior of coral sand, but significant errors were found when comparing the model's results to the experimental data. Therefore, the model was improved by introducing a time function and connecting an elastic body, a nonlinear H-M body, and a Kelvin body in series, to establish a nonlinear creep model that accurately describes the different creep stages of coral sand. Combined with a homotopy method to improve the inversion calculation, the required calculation parameters were obtained, and the accuracy of the model was verified through uniaxial and triaxial creep tests under different stress levels. The results showed that the experimental curve and the model results had a high degree of fit, with an average error of less than 1.5%, and can reflect the various stages of creep of coral sand well. Based on this, by comparing with field monitoring data, the combined average error of the two monitoring points is less than 5%. Therefore, this creep model has good engineering applicability.