Geotechnical Conditions Research Articles

Sustainable construction and quality of improved columns with three types of water-cement ratios on deep mixing method in Saga Lowland, Kyushu, Japan

In this study, we investigated the application of the deep mixing method (DMM) to cohesive soil in the Saga Lowland of Kyushu, Japan. The study focused on examining three types of water-cement ratio (W/C) conditions, with a constant addition of cement-based binder (C). Due to the soft clay nature of the Saga Lowland, frequent ground settlement and deformation occur, necessitating measures to prevent adverse effects on the surrounding environment. The objective of this research is to provide a valuable approach to optimizing the quality of the improved columns while minimizing ground displacement in an environmentally considerate manner. In Saga Lowland, it is common to fix the W/C ratio at 1.0 and vary the cement content. Through experimental construction for improved columns on the field, the study confirmed that W/C values of 0.5, 1.0, and 1.5 influence the quality of the improved structure. A higher W/C value of 1.5 resulted in a more fluid cement slurry due to a higher injection rate (IR = 23.9%), as evidenced by statistical analysis revealing higher average unconfined compressive strength ( qu¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\overline{{q }_{u}}$$\\end{document}), and a lower coefficient of variation (CV). The defective rate of 10% (qudr) from the design standard strength shows that values are lowest for Case 2, followed by Case 3 and then Case 1. Comparing the values of Case 2 and Case 3, it is observed that in Case 3, with a higher W/C, the CV is lower.. Regarding horizontal ground displacement (Sh), Case 3 exhibited a Sh value of 2.0 to 6.5 mm, significantly lower than Saga prefecture standards (20 mm). This outcome is attributed to reduced viscosity during mixing, leading to improved fluidity and minimal lateral displacement of the soil–cement columns (which often results in lateral ground uplift). Even though with a higher W/C = 1.5, the implementation cost remains the same, but the constructed structure would be of higher quality and smaller displacement, with the overall structure corresponding to the standard quality. The study includes the specific geotechnical conditions of the Saga Lowland and the scope of experimentation. Nonetheless, in terms of the applicability and optimization of DMM in Saga Lowland, the findings provide practical guidance for engineers in selecting W/C ratio and IR during construction for future DMM implementations, thereby contributing to the development of long-lasting infrastructure and sustainable societal development.

Liquefaction potential hazard assessment and its effect on toll road construction in Seyegan Subdistrict, Yogyakarta

Toll road construction is a vital infrastructure connecting the two economic centers on Java Island. However, given the potential disaster risks in the region, it is essential to assess the geological and geotechnical conditions to determine the potential for liquefaction in the area. The special region of Yogyakarta is susceptible to earthquakes and associated disasters. One of the most significant earthquakes occurred on May 27, 2006 with a magnitude of 6.3 Mw resulting from the Opak Fault. Furthermore, the toll road is constructed above the Mataram Irrigation Canal, characterized by a shallow groundwater level and young volcanic deposits that are vulnerable to liquified. The study aimed to determine the potential for liquefaction in the area and predicted the vertical settlement caused by liquified soil. The analysis of liquefaction potential utilized the simplified procedure to obtain factor of safety and Liquefaction Severity Index (LSI) to assess the vulnerability index of liquefaction. Results indicated the research area had a very low to medium liquefaction susceptibility index. In addition, the calculation of vertical settlement using Idriss and Boulanger (2008) equation showed a predicted vertical settlement range of 0.4 cm – 44.64 cm. The predicted vertical settlement range underscores the importance of considering the potential for liquefaction to mitigate any adverse effects on the toll road’s construction and operation.

Dynamic response of existing embankment dams in specific geotechnical and seismological conditions: contemporary framework for Serbian national guidelines

We suggest a new approach for evaluating the dynamic response of existing embankment dams as a guideline for national engineering regulations in Serbia. This novel concept is applied to the case study of the existing embankment dam “Zavoj” (Serbia), built at the place of the previously formed natural dam (due to large landslide activity), and exposed to Mw7.4 Vrančea earthquake and under double impact of Kresna earthquake (Mw6.8 and Mw7.1). Results of transient FEM and direct dynamical analysis of the three-dimensional FEM model of the “Zavoj” dam indicate that the existing dam is stable in dynamic conditions, while the surrounding terrain is either on the verge of stability or becomes unstable, depending on the assumed geotechnical conditions and a relevant earthquake analyzed. As a result, we construct a landslide hazard map in dynamic conditions and the dam damage map, which enables the identification of unstable, damaged, or weak parts of the dam, its immediate surroundings, and the accumulation zone in general. The results indicate that direct dynamical analysis is obligatory when two succeeding earthquakes occur and temporal evolution of displacements in the model is required. Additionally, the application of the remaining bearing capacity criterion indicates a much larger zone of potential instability compared to the extent of equivalent plastic strain and the location of the old sliding surface. By following the proposed guidelines, one secures the inclusion of all the relevant influential factors in the comprehensive dynamic analysis of existing embankment dams, leading eventually to reliable decisions on further design, (re)construction, and/or monitoring activities.

Rock mass classification in slope engineering with special emphasis on Slope mass rating: Current status and future projections

Rock mass classification (RMC) systems in the realm of rock slope engineering have gathered a lot of attention. The present review article delves into the major RMC systems, elucidating their fundamental principles, key parameters and practical applications. Among the various RMC systems for rock slope designing, Romana's Slope mass rating (SMR) was found to be the most comprehensive; therefore, the focus of the discussion centres around the SMR method. The article provides a crisp overview of the major advancements, evolution and potential challenges of SMR. The radical concept of wedge failure in SMR and the use of continuous functions are discussed in detail. A thorough discussion is provided on the efforts made by different researchers, encompassing the inclusion of novel factors such as slope height, heterogeneity in rock mass or lithology, weighted consideration of existing discontinuities, fuzzy sets and overburden thickness. Various automated calculation techniques and empirical correlations of SMR with other classification systems and rock engineering parameters are also outlined. Moreover, a critical examination of the variations among major extensions of SMR and their geotechnical relevance have also been discussed. Based on a meticulous assessment of the susceptibility to toppling failure in SMR, two sub‐factors to include block shape and interlayer slip between discontinuities have been suggested. These sub‐factors were validated by Goodman's tests for toppling failure. The scope of future projections or possible aspects for revisiting and refinement of the SMR method are suggested to enhance the applicability of the method under a diverse initial set of geotechnical conditions.

Back analysis of cohesion and friction angle of failed slopes using probabilistic approach: two case studies

In general, geotechnical investigations deal with the back analysis of the geotechnical parameters on the basis of the field observation. According to the back analysis method introduced in the present study, geometry of a number of failed slopes have been carefully mapped and then statistical features of the groundwater level, the bulk unit weight and other measurable parameters have been determined. After that, a series of two-dimensional models for back analysis of the failures have been established. Moreover, statistical analyses based on probabilistic approaches have been utilized to estimate the variation ranges of the shear strength variables. The study provided the probabilistic back analysis of the slope failure with the two case studies in the copper mines of Anjerd and Daraloo. Results indicated that the approach to the probabilistic back analysis has been effective in the analysis of the slope failures wherein considerable uncertainty has been observed in the shear strength and other influential variables. Furthermore, the probabilistic back analysis presented a lot of information in comparison to the approach to the deterministic back analysis and thus had more reasonable matching with the practice of geotechnical engineering in the real world. Therefore, this method would be beneficial and practical for stability analysis, redesigning the slopes, designing the new slopes under the same geotechnical conditions and promote the construction safety. The probabilistic back analysis could be also used to estimate the shear parameters and analyze the stability of slopes as a cost-effective and high reliability method.

Development of Rock Classification Systems: A Comprehensive Review with Emphasis on Artificial Intelligence Techniques

At the initial phases of tunnel design, information on rock properties is often limited. In such instances, the engineering classification of the rock is recommended as a primary assessment of its geotechnical condition. This paper reviews different rock mass classification methods in the tunnel industry. First, some important considerations for the classification of rock are discussed, such as rock quality designation (RQD), uniaxial compressive strength (UCS) and groundwater condition. Traditional rock classification methods are then assessed, including the rock structure rating (RSR), rock mass rating (RMR), rock mass index (RMI), geological strength index (GSI) and tunnelling quality index (Q system). As RMR and the Q system are two commonly used methods, the relationships between them are summarized and explored. Subsequently, we introduce the detailed application of artificial intelligence (AI) method on rock classification. The advantages and limitations of traditional methods and artificial intelligence (AI) methods are indicated, and their application scopes are clarified. Finally, we provide suggestions for the selection of rock classification methods and prospect the possible future research trends.

Deep learning–based inverse analysis of GPR data for landslide hazards

In mountainous landscapes, the diverse geotechnical conditions amplify landslide susceptibility. Factors such as precipitation and seismic activity can trigger landslides, while inherent hazards such as voids, fissures, and compaction deficits jeopardize long-term slope stability. Detecting and forecasting these susceptibilities accurately is crucial. In this paper, the time-domain finite-difference approach and the gprMax software are used to conduct forward modeling of landslide susceptibility. An electrical model of subsurface aqueous structures is created, including water-filled and air-filled cavities, fracture zones, and fault lines. The distinctive radar signal responses within these environments are examined, and a dataset of B-scan images associated with their electrical models is constructed. By employing deep learning algorithms and the robust nonlinear mapping ability of convolutional neural networks in the Pix2Pix generative adversarial network, we accelerate the intelligent inversion of the geological radar data on landslide susceptibility. This innovative approach effectively reconstructs hazard models, offering a reliable basis for interpretation of radar signals.

Small-strain site response of soft soils in the Sacramento-San Joaquin Delta region of California conditioned on VS30 and mHVSR

Sites located in the Sacramento-San Joaquin Delta region of California typically have peaty-organic soils near the ground surface, which are characteristically soft, with shear wave velocities as low as 30 m/s. These unusually soft geotechnical conditions, which are outside the range of applicability of existing ergodic site amplification models, can be anticipated to produce significant site effects during earthquake shaking. We evaluate site response for 36 seismic stations in the Delta region using non-ergodic methods with low-amplitude ground motion data. We model first-order site effects using a period-dependent relation conditioned on the 30 m time-averaged shear wave velocity ( VS30). Relative to extrapolations of global ergodic models, this Delta-specific model provides lower and higher levels of amplification for short and long periods, respectively. While the local model provides unbiased predictions for Delta sites as a whole, it smooths over site-specific effects such as resonant peaks. Microtremor-based horizontal-to-vertical spectral ratios (mHVSRs) were measured for 34 sites, from which additional site parameters such as peak frequency ( fp), peak amplitude ( ap), and average mHVSR amplitude over some frequency bandwidth ([Formula: see text]) are derived. Sites with prominent mHVSR peaks are found to often exhibit site resonance effects, while sites without prominent peak features generally do not. A modified Ricker wavelet pulse function conditioned on fp is used to model resonance effects, while a logistic function whose amplitude is correlated with [Formula: see text] is used to model general broadband amplification that transitions to zero at long periods. These mHVSR-informed models are implemented as additive components to the VS30-scaling model. Relative to a global ergodic model, the VS30-scaling model does not appreciably change the site-to-site aleatory variability ([Formula: see text]) for periods shorter than about 1.5 s but reduces [Formula: see text] by ~0.1 (natural log units) at long periods. When the mHVSR-informed model components are used, [Formula: see text] is reduced by ~0.05 to 0.1 for short-to-intermediate periods (up to ~2 s). A model for nonlinear effects, derived from nonlinear ground response analyses, will be presented in a separate paper.

CD-A twin niches in the Mont Terri Rock Laboratory: Characterization and interpretation of hydraulic parameters with regard to safety aspects

In the Mont Terri Rock Laboratory (Switzerland), a comprehensive interdisciplinary exploration program is carried out to increase knowledge about long-term coupled hydraulic–mechanical effects in Opalinus Clay. As these effects are of significant interest regarding the stability and integrity of a potential storage facility for high radioactive waste, the “Influence of humidity on cyclic and longterm deformations” (CD-A) experiment aims to characterize the Opalinus Clay, especially its heterogeneous sandy facies, and to investigate the evolution of the water content, pressure and deformation in the formation. This article provides an overview of measurement examinations and geologic investigations carried out in the context of the CD-A experiment. The twin niches of the CD-A experiment are located in the upper sandy facies of the Opalinus Clay which is characterized by the existence of different subfacies types and fault zones. This contribution focuses on the detailed characterization of the claystone, while the evolution of the water content. Combined geophysical and geological investigations during the first two years after the excavation of the niches have been carried out. They indicate that the subfacies type and pre-existing fault zones do not affect the distribution of water content severely, which could be an essential finding in the context of detection procedures for potential high level waste (HLW) repositories. Furthermore, miniseismic as well as pulse tests indicate clearly, that the extent of the excavation damaged zone (EDZ) strongly depends on the climatic conditions in the underground galleries: After 1.5years the EDZ and the increase of permeability is much more pronounced in the open than in the closed twin. Future work aims on an increased process understanding based on a verified constitutive model for Opalinus Clay and a comprehensive system understanding considering long-term effects due to climatic conditions as well as the impact of geotechnical boundary conditions and heteregeneities.

Inertial and kinematic demands of isolated pile-supported wharves in liquefiable soils: Centrifuge tests

Pile-supported wharves in liquefiable soils are prone to severe damage during earthquakes. This study employs seismic isolation techniques to adapt for wharf construction, evaluating their seismic performance under lateral ground deformation due to liquefaction. Experimental and numerical analyses are necessary for confirming the efficiency of the isolation in decreasing the requirements for pile-supported wharves. The study initially tests two pile-supported wharves under geotechnical centrifuge conditions, one reinforced by isolation bearings and the other without. The objective is to simulate the force characteristics of isolated pile-supported wharves in liquefiable soils and to analyze the impact of isolation on reducing the seismic response of these wharves. Subsequent analysis delves into the interaction between inertia and kinematics for two types of pile-supported wharves, providing crucial insights. The development of plastic hinges for two kinds of pile-supported wharves under inertia and kinematics is also analyzed. Quantifiable thresholds are established to study the influence of isolation on the resistance of wharves to seismic disruptions, thus preventing pile-supported wharves damage.

Development of a probabilistic seismic microzonation software considering geological and geotechnical uncertainties

ABSTRACT Modern seismic risk assessment software includes seismic hazard analysis algorithms or relies on precomputed hazard maps. In both cases, a major step is incorporating the impacts of the local geological and geotechnical conditions. The common practice to address this phenomenon, often referred to as site effect, is to use shear wave velocity (Vs)–depth correlations and a deterministic geological model as a proxy for Vs mapping. The Vs of the top 30 m (Vs30) and often the fundamental site period (T0) are then used as predictors of the potential amplification of seismic shaking. Recognising that uncertainty in local soil properties inevitably affects the seismic site response, a stochastic approach for evaluating Vs30 and T0 is proposed herein, considering a combination of probabilistic Vs–depth correlations and a probabilistic 3D geological model. Monte Carlo simulations are then applied to study the impact of the uncertainties on the seismic site characterisation model. The generated stochastic maps consist of Vs30 and T0 realisations accompanied with spatial distribution of uncertainty as an indication of areas where further fieldwork is needed to improve predictions. The developed methodology is currently being used in a homemade risk assessment software.

Impacts on Embankments, Rigid and Flexible Barriers Against Rockslides: Model Experiments vs. DEM Simulations

AbstractAs a result of climate change, rockfalls and rock avalanches as well as landslides lead to an increasing hazard for settlement areas and infrastructures. The hazards of such mass movements mean that numerous protective structures must be planned and built. In addition to building such constructions, the refurbishment of existing protective structures is also playing an increasingly important role. Some of these protective structures are rigid structures consisting of concrete and/or steel elements. Due to the difficult accessibility, flexible net constructions are often considered. Embankment constructions are normally erected to protect against large mass movements. The choice of the right type of construction is based not only on geotechnical and geographical conditions, but also on the occurring energies and the impact of rockslides on the protective structure. In this study, small-scale laboratory experiments with different protective structures are presented. Rigid and flexible structures as well as reinforced embankments are investigated. Based on the results of the experiments, the impacts and deformations are recalculated numerically using the discrete element method (DEM). From the small-scale laboratory experiments and numerical simulations, the differences regarding the construction type of the protective structure can be investigated. An essential main point concerns the relationship between the flexibility of the barrier and the total impact load. The presented work is limited to the investigation of strongly fragmented gravitational mass movements such as rock avalanches.

Geospatial liquefaction probability models based on sand boils occurred during the 2017 M5.5 Pohang, South Korea, earthquake

The 2017 Pohang earthquake, triggered by an enhanced geothermal system, had a moment magnitude (M) of 5.5 and caused liquefaction in Pohang City, South Korea. Notably, approximately 600 sand boils were observed only in the soft Quaternary alluvial sediments. This contrasts with most historic liquefaction cases that occurred in earthquakes with M ≥ 6.0. In addition, ground and building settlements were reported in Pohang City. To assess the liquefaction hazard for the Pohang earthquake within the city, we define a 14.4 km2 area where the majority of liquefaction was observed. Using the liquefaction data, we develop eight geospatial liquefaction probability models using logistic regression (LR) and random forest (RF) algorithms (five LR- and three RF-based models). These models consider geospatial data (peak ground acceleration, peak ground velocity, slope-derived average shear wave velocity of the upper 30 m, compound topographic index, distance to the nearest water, and roughness) and geotechnical data (averaged standard penetration test N values up to 20 m depth, depth to rock). We evaluate the performances of our eight models and existing global and regional geospatial models using four indicators: accuracy, balanced accuracy, F1 score, and area under the receiver operating characteristic curve. The three RF-based models outperform the other models, followed by the best LR-based model and the global geospatial model from Zhu et al. (2015). Finally, we apply the best RF-based model to the entire Pohang City and evaluate its applicability to other regions and earthquakes. The estimated liquefaction probabilities agree well with the observed distributions of the sand boils and settlements. These geospatial liquefaction models provide a valuable tool for continuously mapping liquefaction hazards in areas with similar geological and geotechnical conditions to Pohang.

Investigation of a large-scale waste dump failure at the Mae Moh mine in Thailand

This research investigates the potential mechanisms and possible causes of a large-scale waste dump failure in the Mae Moh Lignite Mine, which is Thailand's largest open-pit coal mine. The large-scale failure of the waste dumpsite covered an area of approximately 1.56 km2 when the dump materials reached a height of 135 m from the original ground. The failure event involved the mobilization of a 70-Mm3 mass of the dump material with 1.2 km in length and 1.3 km in width. The causes of this failure were investigated in this research based on a scientific investigation approach for the remedial action. The geophysical and geotechnical investigation was first performed to characterize the waste dump materials and the perched water condition. The electrical resistivity tomography analysis was also performed within the failure zone and its results were calibrated with the boreholes and interpreted to depict the overview of the geotechnical conditions of waste dump materials. Finally, the stability of the waste dumpsite was investigated using the finite element method (Plaxis 2D program). Based on the critical analysis of the studied data, the causes of waste dump slope failure could be attributed to two main factors, which are the presence of a perched water table associated with the high porewater pressure and the presence of a weak basal layer at the interface between the hard foundation and the waste dump materials. This weak basal layer was the claystone deposited in the swamp area above the hard foundation and deteriorated over time with the increasing amount of waste dumped. The dumping of waste materials over the natural river and pond and the rainwater infiltration over time caused the presence of a perched zone in the waste dumpsite. Failure of the dump slope can be classified as due to a wedge mode of failure, which causes the kinematics with the horizontal translation of a passive wedge and vertical subsidence of an active wedge.

Sheet pile walls as a part of the substructure of bridges. Practical application in Denmark

The usage of “sheet pile wall” is very common solution in Denmark due to the geographic situation of the country – low sea level, a significant part of the state border is sea, high groundwater level, poor geotechnical conditions. The “sheet pile wall” is used for strengthening of embankments, reclaim marine territories and as a supporting walls of railway lines and roads. As a consequence of this, a very common solution is to use the sheet pile walls as a part of the substructure of bridges – overpasses of railway lines and roads when the alignment is in excavation. From one side, the “sheet pile wall” are used as wing walls of the bridge and they support the road embankment. From another side, it is used as an abutment walls of the bridge. The part of the wall acting as a bridge support is design with some concrete “hammer beam”. The “hammer” in some cases is connected to the bridge deck by means of concrete hinges. Very often, “sheet pile wall” in the zone of the wing walls is combined with anchors in order to take increased section forces. Common variants in Denmark practice for connection of the bridge superstructure and sheet pile substructure are presented and analysed in the paper.

Analyzing stability of protective structures as the elements of geotechnical tailing pond safety

Purpose is the assessment of soil retaining wall stability to ensure geotechnical safety during the radioactive waste tailing pond closure and further recultivation (or rehabilitation) in Kamianske town (Ukraine). Methods. Geomechanical stability of the protective structure has been assessed relying upon the analysis of geological-hydrogeological, engineering-geological, and geotechnical conditions of the certain tailing pond area using a deformation elastic-plastic model of a medium implemented on the basis of finite-element method. For the purpose, the dam slopes have been detalized taking into consideration their geometry as well as changes in vertical section of rock material characteristics in accordance with the earlier geophysical studies; exploration drilling; and engineering-geological surveys. Findings. Stability coefficients of protective tailing pond dam have been identified within the typical areas of a hydraulic structure; it provides high reliability and representativeness of the whole structure health in time as well as under various conditions of the industrial waste water saturation. It has been defined that the stability coefficients varies from ks = 1.372 to 4.758. Comparison of the indicators between 2022 and 2016 demonstrates a tendency of the slope stability coefficient decrease due to water saturation and groundwater level rise. Nevertheless, design characteristics of the structure make it possible to ensure satisfactory a stability coefficient along the whole dam length being 1.13 times higher than the standard one (i.e. ks = 1.250). Originality. The dependence of the tailing pond protective dam stability upon a water supply degree at the forecasted groundwater level rise at the expense of atmospheric and melt water ingress to the tailing pond has been defined. The danger of complete radioactive waste water saturation is a significant reduction in the stability coefficient of the protective structure, which can be supported by predictive modelling data. If strength parameters of a dam material decline for the most critical area then the strength coefficient decreases starting from 1.532 in terms of the current groundwater level down to 1.372 as for the forecasted dam water supply. The figure is more than 10% of its initial stability. Practical implications. The obtained results substantiate the necessity; moreover, they are of practical value while improving hydrological, hydrogeological, and geotechnical monitoring of the analyzed tailing pond to ensure its radiation safety under different conditions of further behaviour during closure, recultivation, or rehabilitation.

Geotechnical conditions of in-field road design in northern territories of Yamalo-Nenets Autonomous Okrug (Tomsk)

The Yamal-Nenets Autonomous District is the largest hydrocarbon resource base, supplying up to 300–330 billion m3/year of gas and up to 10–15 million t/year of liquid hydrocarbons. Mineral extraction is accompanied by the development of engineering infrastructure, namely: cluster pads, oil storage tanks, pumping stations and automobile roads that link both within and between sites. The area is unique in terms of complexity of geotechnical conditions due to permafrost soils in particular in the upper open-cast. The assessment of geotechnical conditions of the field development as well as adverse processes, hazards, risks and impacts on designed, constructed and operating roads to the cluster pads is undoubtedly relevant.Purpose: The evaluation of geotechnical conditions of design, construction and operation of in-field roads in the Severo-Komsomolsk field.Methodology/approach: The analysis and generalisation of materials of geotechnical surveys for design and construction documentation of the cluster pad 11 in the Severo-Komsomolsk oilfield, performed by AO "TomskNIPIneft". Determination of composition and physical properties of undisturbed soils taken when equipping observation posts, performed in the Laboratory of Ground Science and Soil Engineering, TSUAB.Research findings: Natural and geotechnical conditions of the Yamal-Nenets Autonomous District includes areas with hard frozen soil and areas with complete or partial absence of permafrost soils. In the first case, the subgrade design envisages that the upper permafrost horizon is not lower than the embankment bottom and remains at this level during the entire period of the road operation. In the second case, the design implies preliminary thawing of frozen soil lenses and road drainage prior to the subgrade construction. In the first case, the position of perennially frozen soils is evaluated by the appropriate embankment height, when non-cemented road-building materials are used, and by arranging heat-insulating layers (peat, polystyrene foam, hard frozen soil) with their thermotechnical calculation. The first principle implies the subgrade construction only in winter. To prevent deformation of embankment slopes, it is recommended to build peat benches fixed with a geosynthetic material. Land reclamation in the road construction zone should be avoided to prevent erosion of the soil cover.

Optimization of Injection Methods in the Microbially Induced Calcite Precipitation Process by Using a Field Scale Numerical Model

Microbially induced calcite precipitation (MICP) is a promising, more eco-friendly alternative method for landslide prevention and foundation reinforcement. In this study, we investigated the optimization of injection methods within the MICP process in porous media to enhance calcite mass and consolidation effect. The results demonstrated that staged injections with considerable advantages significantly improved precipitated calcite mass by 23.55% compared with continuous injection methods. However, extended retention times in staged injections reduced reinforcement effects. Moreover, setting the additional time in all injection methods can improve the consolidation area and effect without added injections. Apart from the injection methods, the changes in porosity and substance concentration also directly affected calcite masses and the reinforcement effect. Both the total calcite mass and the reinforcement effect should be taken into account when selecting appropriate injection methods. In terms of influencing factors on the total calcite mass, substance concentration ≫ average porosity ≫ additional time > retention time in staged injection. For the consolidation effect, substance concentration ≫ retention time in staged injection > average porosity ≫ additional time. The 5 h retention time in staged injections was recommended as the optimum injection method in the geotechnical conditions for average porosity from 0.25 to 0.45, with the changes in different reactant concentrations.

A Feasibility Study of Thermal Infrared Imaging for Monitoring Natural Terrain—A Case Study in Hong Kong

The use of infrared thermography (IRT) technique combining other remoting sensing techniques such as photogrammetry and unmanned aerial vehicle (UAV) platforms to perform geotechnical studies has been attempted by several previous researchers and encouraging results were obtained. However, studies using time-lapse IRT survey via a UAV equipped with a thermal camera are limited. Given the unique setting of Hong Kong, which has a high population living in largely hilly terrain with little natural flat land, steep man-made slopes and natural hillsides have caused significant geotechnical problems which pose hazards to life and facilities. This paper presents the adoption of a time-lapse IRT survey using a UAV in such challenging geotechnical conditions. Snapshot and time-lapse IRT studies of a selected site in Hong Kong, where landslides had occurred were carried out, and visual inspection, photogrammetry, and IRT techniques were also conducted. 3D terrain models of the selected sites were created by using data collected from the photogrammetry and single (snapshot) and continuous monitoring (time-lapse) infrared imaging methods applied in this study. The results have successfully identified various thermal infrared signatures attributed to the existence of moisture patches, seepage, cracks/discontinuities, vegetation, and man-made structures. Open cracks/discontinuities, moisture, vegetation, and rock surfaces with staining can be identified in snapshot thermal image, while the gradient of temperature decay plotted in ln(T) vs. ln(t) enables quantifiable identifications of the above materials via time-lapse thermography and analysis.

Monitoring of aerological risks of accidents in coal mines

The assessment and management of aerological risks in coal mine accidents are based on the development of a data analytics system that hosts design values for various parameters and subsystems related to coal mines, as well as the real-time monitoring of operational parameters through various sensors and devices. This study presents the methodology for monitoring aerological risks. It utilizes mining, geological, and geotechnical conditions for seam extraction, along with statistical data concerning elements of coal mine ventilation and gas drainage systems, to assess aerological risks at individual coal mine functionality levels and individual risk factors. Eight coal mines have been ranked according to their aerological risk level. For rank I, the minimum aerological risk is 0.0769, while the maximum is 0.5698. Rank II is associated with category II mines. Aerological risk for this rank is the lowest and ranges from 0,1135 to 0,3873. In the case of rank III, the minimum aerological risk is 0.057, with a maximum of 0.595. This ranking of coal mines by aerological risk level allows to identify potentially unsafe mines in terms of aerology, and enables us to determine aerological risk mitigation measures (technical, technological, and organizational) for each mine to enhance aerological safety.