Geophysical Tests Research Articles

Geologic and thermal conductivity analysis based on geophysical test and combined modeling

Strata thermal conductivity (λe) influences efficiency of medium-depth ground heat exchangers. However, a systematic approach to the acquisition of λe is still lacking. Hence, stratigraphic heat conduction was analyzed using geophysical test in Shenyang, combined with composite modeling. Cenozoic strata (0–730m) exhibited an average λe of 1.32 W·m−1·K−1 due to higher porosity and mud content; Archaean (730–2500m) strata displayed a higher λe of 2.80 W·m−1·K−1, due to dense quartz sandstone with lower porosity and mud content. The CBHE in Shenyang can achieve excellent heat extraction relying on good thermal conduction. Spearman correlation revealed strong negative correlations between λe and acoustic time difference, permeability, and porosity, while positive correlations were observed with depth, resistivity, wave speed, and rock skeleton. Higher rock skeleton thermal conductivity intensified the decrement effect of mud content on λe, while higher mud content diminished the enhancement effect of rock skeleton thermal conductivity. As porosity increased, the decline in λe slowed, particularly pronounced at higher saturation levels. λe exhibited a gradual decrease with temperature, with a more notable change rate observed at lower porosity levels. Principles for enhancing thermal conduction were elucidated through a three-phase analysis. These findings provide foundation for the study and design of medium-depth boreholes.

Construction of multi-purpose geophysical test site on a lateritic clay soil

Construction of multi-purpose geophysical test site on a lateritic clay soil

A Comparative Study of Subsurface Profile Using Bore Log Data and Geophysical Method at Mandideep Region, India

Before beginning construction on any civil structure, it is imperative to conduct a soil investigation to determine the soil’s parameters and to learn about the subsoil’s behavior. A thorough analysis must be performed, taking into account the foundation’s cost-effectiveness and any potential overdesign. In the early stages of a soil investigation, geophysical testing is used to find out about the subsurface. This is because geophysical tests are fast, easy to do, do not cause damage, and are cost-effective. In this study, subsurface profiling is performed using the inverse slope approach after resistivity tests are performed at numerous sites on varying terrain types. We generate a subsurface profile using inverse slope electrical resistivity testing and compare it with bore log data to identify any discrepancies. The results of the inverse slope method and the bore log data are comparable at different depths; further, the range of agreement of both results is determined by Bland–Altman analysis.

Characteristics of Deformation and Stability of Ultra-Deep Pit in Plateau Alluvial–Lacustrine Gravel Strata

Deformation of ultra-deep pit walls and surrounding geotechnical bodies due to engineering disturbances typically shows intricate spatiotemporal patterns. In this study, deformations at critical steps of the construction process were first numerically simulated by Midas GTS NX, and this was followed by lab-scale geophysical model tests of the entire process of the pit construction. Data on deformation obtained from numerical simulations and lab-scale geophysical model tests were compared with those obtained from a dynamic monitoring scheme in the field to analyze the characteristics of the deformation and evolution of the pit wall. This was used to derive a generally applicable theoretical expression to predict variations in the horizontal displacements.

A rapid detection method for diesel content in diesel-contaminated soil based on dielectric measurement and oven-drying tests

Geophysical testing techniques have been successfully applied to identify light non-aqueous phase liquids in soils, but challenges remain in rapidly detecting contaminant content. Detection of contaminants in soil using geophysical testing techniques relies on sensors sensitive to electrical and electromagnetic parameter changes. In this study, the complex permittivity of silty clay contaminated with 0# diesel was measured using an open-ended coaxial probe at frequencies from 200–3000 MHz, and the four-phase dielectric mixing models were evaluated. The measurement results showed that the complex refractive index method (CRIM) model provided a better match with the real permittivity of the four-phase system between 500–3000 MHz with relative errors within an acceptable range of 4%. To eliminate the unknown variable in the CRIM model, an improved equation for the relationship between water content and diesel content of the watery diesel-contaminated silty clay was established by the oven-drying method. Thus, a method for the rapid quantitative detection of the diesel content in contaminated soil has been developed based on dielectric measurement and oven-drying tests. The relative error between the calculated and actual set diesel content for ten manually configured diesel-contaminated soil samples was within 10%, with a maximum error of 15.75%.

A comparative study of empirical and machine learning approaches for soil thickness mapping in the Joshimath region (India)

Precisely determining the thickness of soil, which is an essential parameter in environmental modelling, presents difficulties when applied to heterogenic large-scale areas. Current prediction models primarily concentrate on shallow soil depths and lack comprehensive spatial coverage. This study addresses this limitation by presenting the results of soil thickness assessment along three important roads in the Joshimath region (Indian Himalaya). Three different methods were examined incorporating geological and geomorphological data as input to obtain soil thickness maps: (1) a customized version of the conventional geomorphologically indexed soil thickness (GIST) model, modified specifically for the peculiarities of the research area, (2) the GIST model enhanced by Monte Carlo simulations (GIST-MCS), and (3) the random forest (RF) algorithm integrated with the GIST model (GIST-RF). By quantifying their errors and conducting validation using geophysical tests, the effectiveness of the models was assessed. Moreover, a critical comparison of the results provided useful insights to understand the peculiarities of the test site and how to adapt the site-specific customization of the models to the local features. The results indicate that the GIST model inadequately accounted for the substantial spatial variations in soil thickness observed across the study area. This is evident from the root-mean-square error (RMSE) of 5.28 m and the mean absolute error of 3.94 m. In contrast, the GIST-MCS model showed improvements, achieving an RMSE of 4.48 m and a mean absolute error of 2.86 m. However, the GIST-RF model demonstrated superior performance, yielding an RMSE of 2.40 m and a mean absolute error of 1.64 m. From a practical perspective, the generated soil thickness maps are particularly significant because they may serve as a crucial input parameter for further studies, including geotechnical assessments, environmental modelling, and decision-making processes.

Depth estimation of buried targets using integrated geophysical methods: comparative studies at Ahmadu bello university geophysics test site

Accurate prediction of depth and position of underground structures is a critical step in structural foundation surveys such as civil engineering excavations to adequately maintain the existing underground utilities. The study presents the results of comparative studies conducted to evaluate the performance of electrical resistivity tomography (ERT) alongside the VLF-EM method regarding depth estimation and location of buried targets of known materials, properties and dimensions. A laboratory test was carried out on the buried targets to determine the electrical properties of the buried targets before burial. The pre-burial geophysical investigation indicates no major anomaly within the site that could influence the geophysical response of the buried objects significantly. The results of the post-burial geophysical investigation indicate high variations in electrical resistivity values varying from 47 Ωm – 1081 Ωm (before) and 0.113 Ωm – 19,879 Ωm (after) the buried targets, while the VLF-EM data indicates that the current density values within the site were significantly influenced due to the presence of buried materials, confirming major influence or distortion of geophysical signature of the site. In post-burial ERT investigation, the Wenner and dipole-dipole (DD) arrays registered 67 % and 80 % degrees of alignment with the actual depth of the buried targets, respectively. Both Wenner and DD arrays show strength in depth estimation. However, the DD array indicates higher strength in terms of depth estimation and it is potentially suitable for near-surface utilities investigation due to its high precision in depth estimation. In comparison, VLF-EM captured six (6) out of eight (8) buried targets with a 47 % degree of alignment with the actual depth of the buried targets, which is far lower than the ER method, and may not be considered the most preferable method for geophysical prospecting where depth estimation of targets is of prime interest. However, the depth of targets varies from one method to another and one array to another.

The Studying of Magnetic Anomalies Due to Shallow Underground Targets and the Environmental Applications.

The magnetic method of investigation is a well-known and dependable technique for detecting underground ferro-materials. However, the application of the magnetic method to identify the exact position of underground targets such as buried explosive devices (BED), illegally buried waste (IBW), metallic storage tanks, utility pipes, and communication cables is quite challenging in both civil and environmental engineering. This article presents the results of the investigation performed at a 55m by 55m area within the Ahmadu Bello University Geophysical Test Site (ABUGTS) to study the signals generated by similar buried targets to simulate situations encountered in environmental engineering. The total magnetic intensity (TMI) of the site without buried targets was obtained to identify the possible existing underground materials or faults that could generate false geophysical data. The magnetic susceptibility of the buried targets was determined in the laboratory before the burial to validate the field results. The influence of the buried materials over the magnetic signature of the site was examined, showing the TMI values vary between 34966 nT and 44510 nT before burial and 351607 nT to 49795 nT after burial. The Euler deconvolution (ED) and residual maps alongside the signal enhancement maps like analytical signal and first vertical derivative (FVD) were employed to study the magnetic anomalies due to buried targets. The results of the data interpretation confirmed the existence of cluster anomaly source bodies due to buried targets. The ED delineates the depth of the buried targets varying between 0.7m – 3.3m corresponding with the actual depth of burial. The analytical signal map produced a perfect behaviour of the magnetic anomalies to buried targets, capturing all the buried targets buried at the site. However, the shape of the anomaly signal is almost independent of the buried target orientation with a spherical pattern of anomalies. However, the exact size and shape of the buried targets were not achieved. Nevertheless, the FVD and analytical signal maps perform better than the residual and TMI maps due to the substantially smaller magnetic anomalies of the buried targets similar to expected. In addition, stronger magnetic anomaly signals occur maximally around buried larger ferro-materials with precise prediction of the buried target position. The magnetic method is a very powerful, convenient, cheap, and time-saving geophysical tool for investigating underground targets, which is highly applicable in engineering and environmental contexts.

Using blast energy as an effective technology to provide subgrade stability in road construction

Drilling and blasting technology is considered to be one of the most efficient and cost-effective ways to increase the bearing capacity of soft soils which form the subgrade of road embankments. This study investigates blast energy as a means of creating vertical sand drains in a section of Moscow-Saint-Petersburg Motorway M-11 (construction 2018) which crosses the Kolomenka River and is located in a swampy area. Geophysical and geological engineering tests were conducted, they included monitoring of pore pressure modification in soft soils as well as geodetic monitoring of settlement levels. The findings showed that the applied technology quickly allowed a large bulk of sandy soils (more than 500 thousand cubic meters) to compact in the subgrade of the road as a result of generation of excessive pore pressure. No other technology could have been used due to the presence of an embedded bulk of soft soils and swampiness of the site. Decreasing deformations of the subgrade and CPTU data revealed that the subgrade of the road embankment was compacted. This fact was also confirmed by geophysical tests. Drilling and blasting technology is very effective from an ecological and economic perspective in comparison with other technologies. In addition, this study highlights the importance of preserving swamp systems in order to protect river sources.

Small-strain stiffness of liquefiable sands: A comparison between bender elements and resonant-column tests

Soil stiffness can be estimated by geophysical and dynamic testing methods. In the laboratory, the most common methods to measure the small-strain stiffness are the bender elements (BE) and resonant-column (RC) tests. This paper focuses on the comparison between the results of the small-strain stiffness of sands by BE and RC tests. For this purpose, an experimental program involving three liquefiable sandy soils (i.e., NB, TP-Lisbon and Toyoura sands) was carried out. Such program covered the measurement of the small-strain stiffness of these soils by BE in triaxial and RC apparatuses for different mean effective stress conditions. All tests were carried out on saturated soil specimens, which were remoulded using the air pluviation method for various relative densities. The experimental results were interpreted in terms of shear-wave velocity (Vs) and maximum shear modulus (Gmax) to derive the stress-dependency laws of these parameters. The experimental results revealed differences between Vs obtained from BE and RC tests, evidencing a clear effect of relative density on the shear-wave propagation. However, such a variation may be significantly reduced when a normalisation of Gmax in terms of a void ratio function F(e) is applied. As a result, this study demonstrated and validated the importance of accounting for the soil state conditions, for adequate compatibility of BE and RC tests in the estimate of the small-strain stiffness of liquefiable sands.

The monotonic behaviour of a low- to medium-density chalk through in-situ and laboratory characterisation

Chalk is a highly variable cemented biomicrite limestone that can show widely different rock strengths and patterns of micro to macro fissuring and jointing, due to variations in depositional environments and local geological histories. This paper describes the characterisation of a very weak to weak, low- to medium-density chalk through in situ profiling and laboratory testing, which provided new insights into the geomaterial’s mechanical behaviour. The chalk de-structures when taken to large strains, leading to remarkably high pore pressures beneath penetrating cones and degraded responses in full-displacement pressuremeter tests. Laboratory tests on carefully formed specimens explored the chalk’s unstable structure and marked time-, rate- and pressure dependency. A clear hierarchy was found between profiles of peak strength with depth from Brazilian tension, drained and undrained triaxial and direct simple shear tests conducted from in-situ stress conditions. Highly instrumented triaxial tests sheared from low confining stresses indicated stiffness anisotropy and showed very brittle failure behaviour from small strains. Progressively more ductile behaviour was seen as confining pressures were raised, with failures being delayed until increasingly large strains and finally stable critical states were attained. The chalk’s mainly sub-vertical jointing and micro-fissuring led to properties depending on specimen scale, with high-quality laboratory stiffness measurements significantly exceeding those obtained from in-situ geophysical testing, which far exceed the operational stiffnesses of the chalk mass. While compressive strength and stiffness appear relatively insensitive to effective stress levels, consolidation to higher pressures closes micro-fissures and reduces anisotropy. The results provided the basis for numerical analysis with advanced constitutive models that inform the interpretation of axial and lateral tests on driven piles and inform the development of new practical design methods.

Features of localization of remaining oil in terrigenous reservoirs and potential for their recovery at the final stage of field development

The paper considers one of the unique fields in terms of geological reserves. The paper also analyzes the development of the D3ps formation sections of the Devonian terrigenous layer of the studied field. A detailed geological and hydrodynamic model was constructed based on the consolidation of all available information. An integrated analysis of actual well performance data, field geophysical tests, geological and technical measures, results of infill drilling, as well as geological and hydrodynamic modeling confirmed the localization of reserves primarily in the upper bed of D3ps.1. The analysis of all performed studies revealed higher values of current oil saturation in the upper bed – up to 0.8 unit fractions and lower values in the lower bed – up to 0.68 unit fractions. Similar results were obtained from 87 sidetracks. Drilling of wells and sidetracks is proposed in areas with no well stock. Despite the final stage and high degree of field development, the proposed strategy will support oil production levels, increase remaining recoverable reserves, increase the efficiency of reserve recovery and improve the economic performance of field development. The introduction of modern development technologies, approaches to the analysis and monitoring of development will increase the target value of the final recovery factor from 0.608 to 0.613 unit fractions, which, with a significant amount of in-place reserves, made it possible to increase the remaining recoverable reserves by 35%. The strategy will make it possible to achieve higher oil recovery rates. The approaches used to solve the tasks set in the study can be applied to the fields of the Volga region.

Numerical assessments of observed seismic performances of Lexington Dam during the 1989 Loma Prieta earthquake

Seismic performances of Lexington Dam during the 1989 Loma Prieta earthquake are assessed. Linear and nonlinear analyses are used to identify locations of tension zones where cracks are likely to occur. Numerical analyses are for longitudinal and transverse sections of the dam. Assessments of natural vibration characteristics of the dam are based on numerical simulation of geophysical and forced vibration testing procedures. Nonlinear analyses are based on equivalent linear and elastoplastic solution procedures. The acronyms of computer programs used are SHAKE, SHAKEM and FLAC. Analyses procedures and computer programs used are commonly used in dam engineering practice. Relative movements of observers representing onsite accelerometers are included. The information presented is expected to be of interest to engineers and seismologists in dam engineering practice.

DC Resistivity and Electromagnetic Induction Techniques for Soil Characterization in the Agriculture Land (Case Study in Cidadap, West Bandung, West Java)

ABSTRACTS Precision farming or precision agriculture is generally defined as information- and technology-based methods used for agricultural optimization. This concept can be applied to increase crop production and minimize the effect of the massive fertilizer use on the environment. The implementation of precision farming develops specific rules based on soil and hydrogeological properties that allow farmers to obtain more information for their crop management. This study used direct Current (DC) geoelectrical and electromagnetic (EM) methods to get the land’s water distribution data by measuring the soil’s resistivity and conductivity. Both methods are best used on preliminary surveys of precision farming because this method could measure the resistivity and conductivity of subsurface properties in the field and green environmental techniques. Measurements were made on agricultural land located in Parompong, Lembang, West Java. ARES II was used to measure the resistivity value, while EM38-MK2 was used to measure the conductivity value. From the processing results and its correlation with the pit test, the resistivity values were obtained in the 15-170 Ω.m range, while the conductivity values were 2-115 mS/m. There are good correlations between geophysical data and test pit data, which correspond to the resistive layers at a depth of 0.75 m and the conductive part at a depth of 1.5 m. DC Geoelectrical and EM methods are used to see the fertility distribution on agricultural land.

ISTRAŽIVANJE I SANACIJA KLIZIŠTA "RATAC", BAR, CRNA GORA

The "Ratac" landslide occurs on the section of Belgrade-Bar international railway from railway station Sutomore to railway station Bar. The paper deals with the rehabilitation of the "Ratac" landslide, which extends from km 449+309.00 to km 449+473.00, with a total length of 164m, and which was created in the last unfavorable geological structure (paleo - gully filled with a thick deluvium over 15 m), changing climatic conditions, inflow of groundwater and load from trains. Geodetic surveys and monitoring of landslide activity (2018), geotechnical and geological research, monitoring of measuring devices (2018-2020), monitoring of installed piezometers and geophysical tests of the geological environment were carried out for the purposes of the development of the Main Landslide Rehabilitation Project "Ratac". A geotechnical analysis of two variant solutions for the stabilization of an embankment affected by an active landslide was performed. Variant 1 includes the strengthening of the existing railway embankment with a curtain of piles (jet injected) Φ60 cm/1.5m, and Variant 2 includes the construction of three rows of bored piles diameter of 100 cm interconnected by a reinforced concrete cap at the toe of the railway embankment. Based on the data from the geological study, the geotechnical analyzes included: (i) stability calculations using the limit equilibrium method at critical sections and (ii) back-analysis for obtaining failure zone. Variant 2 was adopted for the rehabilitation of the "Ratac" landslide.

SIGNIFICANCE OF HYDRODYNAMIC MEASUREMENTS IN OIL FIELD DEVELOPMENT

The "Sopron - X" oil field is part of the "Z-1" oil field, located on the territory of Hungary. Several wildcat wells have been drilled within it so far, and their construction was preceded by numerous geological, geophysical, geochemical and hydrodynamic tests. They are used to define the stratigraphic characteristics of the deposit, tectonic relations, petrophysical characteristics of the rocks, and physical-chemical and PVT characteristics of the deposit fluids. Hydrocarbon reserves in the reservoir are also defined. The paper presents the production characteristics of the deposit and the characteristics of the fluid inflow into the considered wells were processed. To predict the possible production of wells, an analysis system was made in the software package "PIPESIM". Data obtained by hydrodynamic measurements, as well as data on fluid characteristics, were used for the analysis. At the ''Z-1'' deposit, after the hydrodynamic measurements were carried out, the production characteristics were determined, which are of great importance when making decisions about the way and methods of deposit exploitation, production intensity, economic profitability, as well as the length of commercial profitability of the "Sopron-X" oil field and Z-1 oil deposit in general. Key words: oil, gas, oil field, hydrodynamic measurements, stocks, oil recovery factor

Application of non-destructive geophysical methods for testing concrete structures

Non-destructive testing of reinforced concrete structures is of utmost importance in construction and civil engineering, where many factors can cause internal and external deterioration of reinforced concrete structures: the environment, nuclear radiation, and structural defects, among others. Geophysical non-destructive testing methods such as ultrasonic and radar have been increasingly used in civil engineering in recent years. Improvements in the ultrasonic testing of concrete have produced detailed images of the interiors of even the most complex structures and allowed for the earliest possible detection of deterioration. In this study, three geophysical methods were applied to inspect concrete structures: parallel seismic, sonic echo, and ultra-seismic. These three testing methods are applied to concrete foundations of two depths, namely 5, and 7 m; the deep foundation has a fracture at a depth of 4.5 m. The collected data are processed using a low-pass filter to remove the higher frequencies. These results of parallel seismic tests accurately predict foundation depths of 5.0 and 6.6 m and P-wave velocities of 2551 and 1097 m/s, respectively. Sonic echo tests yield depth predictions of 5.07 and 7.01 m for the tested foundations and 4.44 m for the depth of the crack. Meanwhile, ultra-seismic tests give depth predictions of 7.1 and 4.6 m for the foundation and fracture, respectively, while clarifying the P-wave velocities of the corresponding reflections: 3447 m/s exiting the 7-m foundation and 2668 m/s exiting the embedded fracture. Depth estimates based on each method show strong agreement with true depths. In conclusion, these three geophysical methods have great potential to provide quantitative data to drive quality assurance and remediation for concrete structures.

Stress state estimation – new data and variability assessment of model results

Abstract. The upper crust of the Earth is used more and more to transport and extract raw materials and energy. It is also used for the final disposal of radioactive waste in deep geological repositories with a particularly crucial requirement for long-term safety over 1×106 years. An accurate knowledge of the hosting rock and surrounding formation coupled with comprehensive modelling is fundamental to demonstrate the geological site has the required properties for safe and long-term underground storage. Besides other criteria, geomechanics play an important role. Even if the determination of rock properties is already a challenge, the estimation of the contemporary stress state in the upper crust is even more challenging. To predict the stress state 3-D geomechanical–numerical models are used, but high-quality underground structure, rock properties and in situ stress data for model calibration are needed. In particular, data of maximum and minimum horizontal stress magnitudes (SHmax and Shmin) are required to find suitable lateral displacement boundary conditions to produce a best-fit model. During the recent exploration phase for a deep geological repository for radioactive waste in Switzerland, a unique dataset of stress magnitude data has been acquired from eight cored boreholes. Rock mechanical properties were constrained from geophysical logging and laboratory testing. The empirically correlated rock properties were not simply averaged, but a probability distribution was provided. The stress field was explored by conducting more than 120 micro-hydraulic fracturing (MHF) and dry sleeve re-opening (SR) tests in different stratigraphic units, to estimate the magnitudes of Shmin and SHmax. We present the results of a 3-D geomechanical–numerical model that shows the best fit with respect to the measured stress magnitudes. Considering the uncertainties of the MHF/SR tests and the ones resulting from rock property variability, the model can reproduce most of the measurements. However, we do show not only the best-fit result but also a bandwidth of individual stress components within a P05–P95 probability range. We also show that there are still outliers for this bandwidth, but we will show that these can be explained by scaling effects.

Geophysical surveys in the Kashmir valley (J&K Himalayas) part I: Estimation of dynamic parameters for soils and investigation of the deep basin structure

A combined set of multichannel analysis of surface waves (MASW) and single-station microtremor horizontal-to-vertical spectral ratio (MHVSR) testing was performed at over 190 sites within the complete Kashmir Basin, mainly concentrated within the Greater Srinagar region. The aim was to establish the dynamic parameters of the main geomorphological units, especially the sedimentary deposits (Alluvial and Karewa) in the valley through widespread geophysical testing. Shear wave velocity (VS) and frequency parameters were estimated for each of the sites. Multiple impedance contrasts in the HVSR curves were found within the sedimentary deposits indicating a number of stratigraphic layers which were then correlated with the geology of the region. Further, forward modelling routine was utilised to extend the VS profile to deeper depths, to determine the first-order estimate bedrock depth and establish the basin structure which remains largely unexplored till now. Lastly, geological cross-sections were constructed using these results from the geophysical tests.

Mapping near-surface structures in a geophysical test site using magnetic and electromagnetic induction gradients

We applied Magnetic Gradiometry (MG) and Electromagnetic Induction (EMI) techniques to map and differentiate the geophysical response of 17 buried structures at <2.50 m deep in the Teoloyucan Geophysical Test Site (TGTS). To enhance the response of near-surface structures, we include the Electromagnetic Induction Gradient (EMIG) and complement MG and EMI acquisition and processing methodologies. This includes, acquiring and adding together orthogonal-transect surveys, computing the EMIG and sectioning area maps into close-up maps. The orthogonal-transect surveys clearly show distinct distributions of the physical properties resulting from the acquisition direction, the orientation of the transects and from the orientation and heading of the sensors. Compared with EMI, EMIG provides remarkable results for apparent conductivity although limited for in-phase data. For MG and EMIG, close-up maps yield better results than area maps. Also, adding the orthogonal-transect survey grids gives better results, followed by the E−W transect surveys and then by the S−N transect surveys. Most of the mapped structures present low-medium MG values and medium-high EMIG values. The proposed methodology is consistent for concrete and air-cavity structures, and for structures made with various materials and complex geometries. In some cases, the structures do not have enough contrast with their surrounding terrain and in others, the anomalies are shifted in <1.50 m. In this study, we demonstrate the convenience of computing the EMIG and the benefits of applying the used methodology to retrieve near-surface features that would be overlook with common-practice methodologies.