Laboratory Resistivity Measurements for Soil Characterization

Field based electrical resistivity measurements, such as electrical resistivity tomography (ERT) and capacitively coupled resistivity (CCR), are geophysical methods that offer a non-destructive and rapid means to collect continuous data. As such, ERT and CCR are becoming increasingly popular tools for geotechnical engineers; however, it is challenging to derive geotechnical information such as soil type, density, and water content from the data. A laboratory geophysical investigation was carried out to gain a better understanding of the parameters that affect the electrical resistivity of soils and devise a relationship between resistivity and soil type or classification. In this study, a soil box attached to a resistance meter in a 4-electrode Wenner array was used for the resistivity measurements. Nine different benchmark soils were tested, representing most of the major soil groups according to the unified soil classification system. The effects of water quality, water content, degree of saturation, bulk density, dry density, Atterberg limits and temperature on the measured electrical resistivity of the soils were investigated. Although there is an apparent correlation between all of these parameters and the electrical resistivity of soils, the parameters that are most effective in the identification of soil type are bulk density and degree of saturation. The laboratory results indicate that if the soil is saturated, a reasonable estimate of the soil group classification can likely be made from resistivity alone. For unsaturated samples, the range of possible resistivity values is much larger; however, the estimate of soil group can be significantly narrowed down if an approximation of saturation or density can be made. To assess the feasibility of the developed approach, a series of verification studies using samples acquired from the field and other processed soils were also conducted

Non-invasive imaging and assessment of pavements

Eight electrical resistivity tomography (ERT) and multi-channel analysis of surface wave (MASW) case studies are presented. The objective is to assess the condition of pavement, base, native soil, and rock all the way down to the top of the bedrock. Each segment of road way is approximately 1000 ft. long. The cases include US 63 north of Rolla, US 54 in Camden County, Rte. 179 in Jefferson City, HWY AT in Franklin County, I-55 in Pemiscot County, I-55 in Perry County, HWY U in Dent County, I-35 in Daviess County. In addition, there are only three types of pavement in these sites portland cement concrete (PCC), asphalt concrete overlaying portland cement concrete (AC/PCC), and full-depth asphalt concrete (AC) pavements. Accordingly, the geophysical tools examined different types of pavements with different distress conditions. Based on the analyses of the acquired ERT and MASW data, the data of both tools correlate reasonably well and generate reliable and comprehensive information about variations in soil and rock rigidity, variations in rock lithology, pattern, placement and density of solution-widened joints and offset of faults, locations of air-filled voids, distribution of dry and moist soil, distribution of clayey soil, and mapping variable depth to top of bedrock. Therefore these technologies can be routinely used by not only the Missouri Department of Transportation but also worldwide agencies in support of its pavement management process. The research demonstrated that the ERT and MASW methods were effective tools for assessing the condition of pavement. This is the first comprehensive assessment of paved sections of roadway to the best of the author knowledge --Abstract, page iii

Integrated Geophysical Methods for Shallow Aquifers Characterization and Modelling

The book collects nine original contributions in the field of integrated geophysical methods for the characterization and modeling of shallow aquifers. The first contribution introduces the following eight contributions into the overall framework of the topic. The second contribution integrates seismic and electrical techniques to define geometry and identify the transient groundwater features in a coastal alluvial aquifer. The third contribution assesses the effectiveness of electrical and electromagnetic techniques to study the geometry of a thick carbonate aquifer. The fourth contribution couples electrical techniques with implicit modeling tools to characterize the geometry and saltwater intrusion in a coastal alluvial aquifers. The fifth contribution combines electrical techniques and datasets from borehole logs to analyze the inner geometry of a gravel-bed ephemeral stream. The sixth contribution uses electromagnetic and seismic techniques to evaluate the groundwater resource in a coastal town hydrologically influenced by peri-urban irrigation agriculture. The seventh contribution uses geophysical and hydrochemical data to assess groundwater contamination in an industrial chemical complex. The eighth contribution compiles and examines different geophysical prospecting surveys of interest in groundwater research in a large urban area. The ninth contribution uses electrical and electromagnetic techniques to assess surface water and shallow groundwater salinity in a coastal groundwater-dependent ecosystem

Integrated Geophysical Methods for Shallow Aquifers Characterization and Modelling

info:eu-repo/semantics/publishedVersio

Recent technological and methodological advances for the investigation of landslide dams

River-damming by landslides is a widespread phenomenon around the world. Recent advances in remote sensing technology and the rising commercial availability of their products enable the assemblage of increasingly more complete inventories and improve monitoring efforts. On the ground, multi-method dating campaigns enhance our understanding of the timelines of dam formation and failure. In comparison to single-dating methods, they reduce uncertainty by using different materials from the landslide deposit, facilitate the advantages of each method, and consider the deposit and the source area. They can pin dates on the time of lake drainage where backwater sediments are included in the dating campaign and thus inform about dam longevity. Geophysical methods provide non-invasive and rapid methods to investigate the properties and interior conditions of landslide dams. By identifying, e.g. evolving zones of weakness and saturation they can aid in the monitoring of a dam in addition to providing information on interior stratification for scientific research. To verify results from geophysical campaigns, and to add details of dam interior structures and geotechnical properties, knowledge of their sedimentology is essential. This information is gathered at sections from breached dams, other (partially) eroded landslide deposits, and through laboratory testing of sampled material. Combining the knowledge gained from all these methods with insights from blast-fill and embankment dam construction, physical and numerical modelling in multi-disciplinary research projects is the way forward in landslide dam research, assessment and monitoring. This review offers a broad, yet concise overview of the state-of-the-art in the aforementioned research fields. It completes the review of Fan et al. (2020) on the formation and impact on landslide dams

Applications of MASW and MHVSR Techniques for Infrastructure Evaluation with a Focus on the Effects of Different Transformation Techniques and Near-field Effects on Derived Dispersion Data

This dissertation is aimed at understanding two aspects of active surface wave methods to improve the accuracy and reliability of this method. These include (1) the performance of four common wavefield transformation methods for the multichannel analysis of surface wave (MASW) data processing and (2) near-field effects. Toward this end, extensive field measurements were conducted considering different factors affecting these two topics. The MASW and microtremor horizontal to vertical spectral ratio (MHVSR) were then employed to examine their efficiency for infrastructure health monitoring. Regarding the performance of the four common transformation techniques, it was observed that for sites with a very shallow and highly variable bedrock topography with a high-frequency point of curvature (\u3e20 Hz), the Phase Shift (PS) method leads to a very poor-resolution dispersion image compared to other transformation methods. For sites with a velocity reversal, the Slant Stack (p) method fails to resolve the dispersion image for frequencies associated with layers located below the velocity reversal layer. Overall, the cylindrical frequency domain beamformer (FDBF-cylindrical) method was determined to be the best method under most site conditions. This method allows for a stable, high-resolution dispersion image for different sites and noise conditions over a wide range of frequencies, and it mitigates the near-field effects by modeling a cylindrical wavefield. However, the FDBF-cylindrical was observed to be dominated by higher modes at complex sites. Therefore, the best practice is to use more than one transformation method (FDBF-cylindrical and FK methods) to enhance the data quality. Regarding the near-field effects for active surface wave methods, it was observed that near-field effects are independent of surface wave type (Rayleigh and Love) and depth to impedance contrast. For sites with a very shallow impedance contrast, the FDBF-cylindrical transformation technique outperforms others in terms of dispersion resolution by significantly mitigating near-field effects. It is also revealed that source type is an important parameter, influencing the normalized array center distance criteria required to mitigate near-field effects. The best practical criteria for near-field mitigation include a normalized array center distance of 1.0 or greater for low-output impulsive sources such as a sledgehammer and a normalized array center distance of 0.5 for high-output harmonic sources such as a vibroseis. These criteria should not be violated when using a limited number of source offsets (≤2). But, if the multiple source offset approach (≥3 source offsets) is used where some of the source offsets meet the criteria, the near-field criteria can be violated for other source offsets. Additionally, it is recommended to use the multiple source offset approach along with the FDBF-cylindrical for data processing to mitigate near-field effects. For health monitoring of earthen hydraulic infrastructures, MASW was determined to be effective for detecting weak zones of such structures. In this regard, it is very important to use the reference shear wave velocity profiles to avoid misinterpretation of the results. Additionally, the grid pattern MHVSR method was determined to very effective for landslide evaluations for sites with shallow and complex bedrock topography, where bedrock is a key feature in the slope stability model

Multiple geophysical techniques for investigation and monitoring of sobradinho landslide, Brazil

Geophysical methods have a varying degree of potential for detailed characterization of landslides and their dynamics. In this study, the application of four well-established seismic-based geophysical techniques, namely Ambient Noise Interferometry (ANI), Horizontal to Vertical Spectral Ratio (HVSR), Multi-Channel Analysis of Surface Waves (MASW) and Nanoseismic Monitoring (NM), were considered to examine their suitability for landslide characterization and monitoring the effect of seasonal variation on slope mass. Furthermore, other methods such as Ground Penetrating Radar (GPR) and DC Resistivity through Electrical Resistivity Tomography (ERT) were also used for comparison purpose. The advantages and limitations of these multiple techniques were exemplified by a case study conducted on Sobradinho landslide in Brazil. The study revealed that the geophysical characterization of the landslide using traditional techniques (i.e., GPR, ERT and MASW) were successful in (i) the differentiation between landslide debris and other Quaternary deposits, and (ii) the delineation of the landslide sliding surface. However, the innovative seismic based techniques, particularly ambient noise based (HVSR and ANI) and emitted seismic based (NM), were not very effective for the dynamic monitoring of landslide, which might be attributed to the short-time duration of the data acquisition campaigns. The HVSR was also unsuccessful in landslide site characterization i.e., identification of geometry and sliding surface. In particular, there was no clear evidence of the light seasonal variations, which could have been potentially detected from the physical parameters during the (short-time) ambient noise and microseismic acquisition campaigns. Nevertheless, the experienced integration of these geophysical techniques may provide a promising tool for future applicationsThis research was funded by Research of the Federal District Foundation (FAPDF), and The APC was funded by the Department of Geography, University of Brasilia

Aged embankment imaging and assessment using surface waves

Rapid, non-intrusive surface wave surveys provide depth profiles from which ground models can be generated for use in earthwork condition assessment. Stiffness throughout earthworks controls the behaviour under static and dynamic loads, and characterising heterogeneity is of interest in relation to the stability of engineered backfill and life-cycle deterioration in aged utility and transportation infrastructure. Continuous surface wave methods were used to identify interfaces between fine- and coarse-grained fill in an end-tipped embankment along the Great Central Railway in Nottinghamshire, UK. Multichannel analysis of surface wave (MASW) methods were used to characterise subsurface voiding in a canal embankment along the Knottingley and Goole canal near Eggborough, Yorkshire. MASW methods are currently being used to study extreme weather impacts on the stability of a high-plasticity clay embankment along the Gloucestershire–Warwickshire railway near Laverton. Optimal results were obtained using equipment capable of generating and detecting over wide frequency ranges

Moisture monitoring in clay embankments using electrical resistivity tomography

Systems and methods are described for monitoring temporal and spatial moisture content changes in clay embankments using electrical resistivity tomography (ERT) imaging. The methodology is based upon development of a robust relationship between fill resistivity and moisture content and its use in the transformation of resistivity image differences in terms of relative moisture content changes. Moisture level and moisture content movement applications are exemplified using two case histories from the UK. The first is the BIONICS embankment, near Newcastle (NE England), which was constructed in 2005 using varying degrees of compaction of a medium plasticity sandy, silty clay derived from the Durham Till. The second is a Victorian embankment south of Nottingham (Central England), constructed in 1897 using end tipping of Late Triassic siltstone and mudstone taken from local cuttings. Climate change forecasts for the UK suggest that transportation earthworks will be subjected to more sustained, higher temperatures and increased intensity of rainfall. Within the context of preventative geotechnical asset maintenance, ERT imaging can provide a monitoring framework to manage moisture movement and identify failure trigger conditions within embankments, thus supporting on demand inspection scheduling and low cost early interventions

Pavement testing by integrated geophysical methods: Feasibility, resolution and diagnostic potential

This work is focused on the assessment of the diagnostic potential of several geophysical methods when applied to the investigation of a rigid airport pavement. The potential and limit of each technique are evaluated as well as the added value deriving from their integration. Firstly, we reconstruct a high-resolution image of the pavement by a large electromagnetic and georadar screening. An advanced processing of georadar data, implemented through the picking of the arrival times of reflections for each profile, provides a quantitative estimation of the deviation between the design and the as-built thickness of layers. Additionally, electrical tomography has been applied to unequivocally identify the anomalous zones, where higher values of resistivity would be associated to porous zones that are prone to degradation and failure. The seismic tomographic survey had the additional purpose to recover the mechanical properties of the pavement in terms of both P- and S-waves and consequently of elastic constants (Poisson's ratio), whose values were consistent with those recovered in literature. The anomalies detected by each technique are consistent in their indications and they can be correlated to failure phenomena occurring at layer interfaces within the pavement structure or to unexpected variations of the layer thicknesses. The cost-effective geophysical campaign has validated the four-layered system deduced from the original design and has been used to reconstruct a high-resolution map of the pavement in order to discriminate fractures, crack-prone areas or areas where the as-built differs from the original design