Engineering Geology最新文献

Regional scale seismic hazard assessment including the effect of local seismo-stratigraphical conditions is a basic tool for seismic risk estimates. A novel physically based procedure is proposed for using geological maps to extensively estimate expected seismic amplification effects relative to spectral ordinates of main engineering interest (<0.8 s). Automatic GIS based analysis of geological maps, statistical data relative to the seismic/geotechnical properties of geological units and numerical modelling are combined to determine the probability distribution of expected amplification effects by accounting for uncertainty affecting the relevant parameters. To evaluate the feasibility of the proposed procedure, it has been applied to the Tuscany Region in Central Italy. Unbiasedness of outcomes has been tested by considering detailed microzonation studies available for the considered area. Results of the proposed approach could be easily implemented in extensive seismic risk analyses where detailed seismic microzonation studies are lacking.

Flow sliding instability of saturated loess slopes is a common geological hazard in loess areas of China. Previous studies have found that the occurrence of flow-slip loess landslides is closely related to static liquefaction and is controlled by physical characteristics and load conditions. In this work, we comprehensively study these influences of physical properties (i.e. initial pore structure, gradation, dry density) and shear rate on the static liquefaction of saturated loess through a series of consolidated undrained triaxial tests, and the effect mechanism of these related factors on the static liquefaction of saturated loess are also discussed. The results present that: (1) The peak deviator stress and the maximum pore pressure of the undisturbed loess are much greater than these of the remodeled one under each level of confining pressure (except 450 kPa). Further, the calculated liquefaction potential index (LPI) of undisturbed loess is much greater, indicating that undisturbed loess is more prone to static liquefaction due to the initial pore structure. (2) The lower the relative clay/silt content ratio of the saturated remodeled loess, the stronger the potential liquefaction ability. With the increase of the relative content of clay from 0.125 to 0.698, the stress-strain curve gradually transitions from strain softening to hardening. (3) The remodeled loess show the steady-state strength tends to continuously increase with the increase of dry density from 1.38 g/cm³ to 1.56 g/cm³, while the LPI increases first and then decreases, and the largest value appears when the dry density reaches to 1.44 g/cm³. The reason is that the value of 1.44 g/cm³ is the normal consolidated condition, which essentially reflects the potential liquefaction change during the transformation from under consolidated to over consolidated state.(4) The effect of shear rate on the stress-strain curve of remolded loess is not significant, but the peak strength and ultimate pore pressure show a trend of increasing and then decreasing with the increase of shear rate. There exists a “critical shear rate “of 0.1 mm/min reflecting the liquefaction of loess is more likely to occur when reaches to this critical value. (5) Based on the comparison of static liquefaction tests, the influencing factors of static liquefaction of saturated loess are: initial pore structure> gradation > dry density > shear rate. This study can provide a systematic evaluation for understanding the influencing factors of static liquefaction capacity of saturated loess (especially remolded one), and also has a reference for explaining the loess flow-sliding failure mechanism under disturbance conditions.

Natural fractures directly affect the permeability and mechanical strength of reservoirs, and their development degree has an important impact on the design and implementation of engineering and development projects. Although there is some correlation between logging data and fracture development, studies using algorithms to optimize logging predictions are still scarce. Meanwhile, there is a scarcity of calculations and analyses concerning the distribution of geostress at the block scale, and the pivotal role that geostress plays as a tectonic factor in the development of fractures. In this study, machine learning methods are used to predict reservoir fracture development, and regional geostress distribution patterns derived from well test data and finite element methods are combined for verification. The support vector machine (SVM), random forest (RF), extreme gradient boosting (XGBoost) and back propagation neural network (BPNN) algorithms are used to predict the fracture development of No.15 coal reservoir in the block. The results showed that the accuracy of SVM is 83.3 %, RF is 91.6 %, XGBoost is 93.7 % and BPNN is 95.8 %. The BPNN can effectively predict the reservoir fracture development of the block. Combined with the regional finite element stress-strain analysis and geostress measurement, the prediction of No.15 coal geostress distribution and fracture development model is established. Under comprehensive verification, the established distribution of the degree of regional fracture development under the control of geostress is consistent with the results of the BPNN prediction of fracture development. These results show that the regional geostress calculated in association with finite element analysis (FEA) can reflect the development of fracture in coalbed methane (CBM) reservoirs, and the neural network has good performance in predicting regional fracture development. This work provides a new approach to the application of machine learning in the field of geological engineering, and the comprehensively validated model provides geologists and geological engineers with ideas in algorithmic practice.

The shear strength behavior associated with a large shear deformation of both the fine- and coarse-grained unsaturated soils is important in interpreting and forecasting the initiation and movement of landslides. For this reason, a suction-controlled ring shear apparatus was designed by introducing modifications to the conventional Bromhead ring apparatus extending the axis translation technique. A series of suction-controlled ring shear tests were performed on fine- and coarse-grained unsaturated soil specimens subjecting to large shear deformation. The experimental results are presented and interpreted for highlighting: (i) the shear stress/void ratio-shear displacement relationships; (ii) the envelopes of the residual shear strength; (iii) the void ratio, water ratio and degree of saturation of the fine-grained soil specimens sheared to the residual state under different net normal stresses and matric suctions. These results provide valuable information toward understanding and interpreting the behaviors of landslides in unsaturated soils that experience the first failure and the reactivation along a pre-sheared slip surface.

The Corumbataí Geopark Project, located in São Paulo state, southeast Brazil, features valuable geosites that represent Earth's heritage and attract visitors with geoturism activities such as climbing. Rock anchors are crucial for ensuring climbers' safety in case of falls. This study reveals that the load capacity performance of expansion rock anchors is influenced by the applied torque, the physical-mechanical properties of the rock, and the weathering-induced strength degradation over time. The sandstone of Botucatu Formation, the predominant lithotype at these geosites, was assessed through petrographic analysis, non-destructive testing, physical and mechanical assessments, and pull-out tests of the anchors. Our findings indicate that the sandstone generally meets the geotechnical properties requirements for load capacities outlined in international climbing guidelines, a threshold of 80 MPa is recommended for effective rock anchor performance. However, prolonged exposure leads to rock degradation, compromising safety. Consequently, anchors should not be used in weathered rock and regular maintenance is strong recommended for climbing safety, approximately every 6 six years. This study provides a novel approach to characterizing rock-anchor interactions, supporting the development of effective management plans for outdoor activities.

Robust site characterization and ground response analysis require a thorough understanding of subsurface features, including geophysical properties and geometries of sediment bodies. Late Quaternary paleovalley systems, often overlooked in seismic hazard assessments, represent a potential threat due to their unconsolidated infill (with shear wave velocities <200 m/s) and sharp contrast with the adjacent substrate. Through an integrated approach that combined geophysical and stratigraphic data, we characterized the subsurface of the Pescara paleovalley system. Geostatistical interpolation of microtremor measurements enabled mapping resonance frequencies, highlighting abrupt changes and delineating the paleovalley boundaries. High-resolution core descriptions were then correlated with resonance frequencies, enabling the reconstruction of a 3D geophysical depth model of the buried paleovalley morphology. Furthermore, analyzing velocity profiles from down-hole tests led to the identification of five main seismic/stratigraphic layers within the valley fill. The geometry and facies architecture were reconstructed through a cross-section transversal to the paleovalley axis and then implemented into a 2D finite element model. Seismic response was computed, revealing significant amplification factors at frequencies closely matching the direct observations. Amplification factors peaked at frequencies between 0.9 and 1.1 Hz in the paleovalley center and up to 5.5 Hz towards the flanks, reaching a factor of 4.6. These findings suggest a notable increase in amplification amplitude compared to simpler geological contexts and emphasize the potential impact on common building types. Response spectra show strong amplifications in the paleovalley system, potentially leading to an underestimation of spectral accelerations compared to NTC18 guidelines. The comparisons of 1D and 2D modeling approaches revealed minimal differences, indicating that the generally flat geometry of the valley may not exhibit clear 2D effects. However, local subsurface stratigraphy strongly influences lateral changes in seismic response, emphasizing the importance of detailed subsurface knowledge for realistic seismic response estimates.

The behavior of water and salt inside porous sandstone is crucial for determining the durability of stone heritage. This involves multiphase coupled processes, yet previous analyses have paid insufficient attention to the spatial and temporal characterization of solution-crystal phase change. Based on the salt crystallization experiments, theoretical models and numerical computational frameworks are synthesized to simulate multiphase processes. Subsequently, equations are established for coupled water-salt-heat-mechanical interactions in the multiphase media. Then, the critical state of solution-crystal phase change is analyzed through the evolution of saturation, crystallization pressure, and porosity. The findings indicate rapid solution saturation growth at positions with minimal wetting front fluctuations, leading to initial crystallization. Further tracing reveals that crystallization evolves through discrete crystallization, annular crystallization, and crystallization expansion stages. By investigating the crystallization pressure and the crystal morphology, it is possible to quantify the dynamics of crystal pressure on constraint surfaces and solution pressure. In addition, the change in porosity can be observed by simulation of dry and wet cycles to obtain crystallization initiation. The numerical calculations agree well with the experimental results, providing valuable insights into the deterioration mechanism induced by salt crystallization in the porous sandstone of Dazu Rock Carvings.

Preferential infiltration is prevalent in loess and is pivotal in disasters such as landslides. However, the inherent multi-scale heterogeneity of loess makes traditional in-situ monitoring techniques challenging for characterizing the preferential infiltration process. This study employed the Geostatistical Electrical Resistivity Tomography (GERT) to examine the spatial distribution of mass water content (ω_s) in loess strata to understand the preferential infiltration processes in loess. This study improved stimulus-response data quality and used GERT to characterize the spatial-temporal distribution of electrical conductivity (σ) and estimate ω_s through the σ-ω_s relationship. This study indicates that the surface loess layer has higher ω_s than deeper layers, rapidly declining as depth increases. Under preferential infiltration, early-stage water forms a spherical saturated zone, transforming into an ellipsoid as it descends. Using equivalent homogeneous parameters as prior information effectively improved σ estimation. This study found a 15.9% error in the total change in water content based on the GERT survey compared to the known amount of injected water. It explores the possible impacts of the uncertainty of the unknown relationship between σ and ω_s, its spatial variability, and the accuracy of the survey on the error. The formation of an electric double-layer structure within the loess as the saturation increases, which reduces the sensitivity of GERT to changes in water content, is likely another cause. Finally, these areas are essential for advancing future studies on applying geophysical tools to accurately estimate water distributions in loess formations.

Surface moisture has recently been reported to be used in regional-scale landslide early warning. Nevertheless, near-surface multi-depth hydrothermal measurements as a hillslope scale are often less concerned and rarely linked to landslide kinematics. In this paper, we selected two neighboring landslides with different deformation mechanisms as case studies. Using in-situ multi-source sensors, we monitored real-time soil temperature and moisture at specific depths within approximately 1.5 m. The measurements span two complete monsoon seasons, representing concurrent dry and wet hydrological extremes. Statistical Pearson correlation analysis was employed to quantify the relationships between landslide activity and environmental variables such as soil temperature and moisture content. The results indicate that the near-surface soil temperatures and moisture contents contribute to a better understanding of the factors controlling landslide activity, in which variations synergistically reflect hydrothermal interaction and potential deformation mechanisms. These soil temperatures and moisture contents at certain depths (specifically at 20, 50, and even 100 cm) show moderate to strong correlations (with Pearson correlation coefficient values ranging from 0.4 to 0.8) with landslide deformation. In cases where discrete daily rainfall data exhibited unsatisfactory correlations due to their data attributes, soil temperature and moisture effectively served as alternative indicators for rainfall inputs, aiding in the analysis. Overall, this work emphasizes the critical influence of soil moisture and temperature on landslide dynamics. This study also highlights the need for comprehensive monitoring and forecasting strategies that consider a wide range of environmental factors to mitigate landslide risks associated with climate change, particularly in the context of intensified extreme weather events.