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Emerging Characterization of Geomaterials Using Advanced Geo-Sensors

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A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Remote Sensors".

Deadline for manuscript submissions: closed (30 June 2021) | Viewed by 37079

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Prof. Dr. Jong-Sub Lee

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School of Civil, Environmental and Architectural Engineering, Korea University, Seoul 02841, Republic of Korea
Interests: wave and ICT based characterization; pile foundation
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Understanding the behaviors of geomaterials is critical to design and maintain the subsurface infrastructure so as to build a resilient society. For decades, we have implemented the conventional sensors to characterize soils and rocks in geotechnical engineering whereas a wdie variety of innovative sensors have been recently developed and used to measure the spatio-temporal responses of geomaterials subjected to various boundary conditions. The thermal, electrical, chemical and geomechanical sensors have been successfully deployed in nondestructive and invasive manners not only to elucidate the underlying mechanism but also to evaluate geotechnical parameters and properties and compare the performance of sensors in geometrials. The examples of geo-sensors include bender element, piezo disk element, electrode, manufactured electrical resistivity meter, (shock) accelerometer, geophone, piezo electric ring actuator, time domain reflectometry probe, and X-ray computed tomography.

The special issue aims to provide the recent advances in characterizing geomaterials with the aid of a wide range of sensors and their application and the innovative applications of sensor technologies in the fields of subsurface characterization, nondestructive monitoring, offshore and onshore geotechnology, geo-energy recovery, geoenvironmental engineering, road and pavement, and engineered soils. To minimize the uncertainty in the results of subsurface characterization using the nondestructive methods, geophysical properties have been also evaluated by using the invasive testing apparatus instrumented with the geomechanical sensors. This special issue also welcomes discussions on the latest advances in sensoring technologies and methods for the characterization of geomaterials.

Prof. Dr. Jong-Sub Lee
Guest Editor

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Keywords

Elastic wave
Electromagentic wave
Geophysical surveys
Geotechnical property
Long-term performance
Non-destructive testing
Numerical analysis
Performance comparison
Heterogeneity and anisotropy
Geotechnical Imaging

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Published Papers (12 papers)

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16 pages, 3595 KiB

Open AccessArticle

Evolution of Small Strain Soil Stiffness during Freeze-Thaw Cycle: Transition from Capillarity to Cementation Examined Using Magnetic and Piezo Crystal Sensors

by Junghee Park, Jong-Sub Lee, Jongmuk Won and Jongchan Kim

Sensors 2021, 21(9), 2992; https://doi.org/10.3390/s21092992 - 24 Apr 2021

Cited by 5 | Viewed by 2380

Abstract

Freeze-thaw cycles caused by seasonal temperature fluctuations significantly affect the geotechnical engineering properties. This study investigated the crucial role of water distribution patterns in the characterization of elastic wave properties for the fine F-110 sand during a freeze-thaw cycle. Sand specimens with four different water distribution patterns were prepared, namely homogeneously-mixed, evaporation-driven, vertically-, and horizontally-layered specimens. The P- and S-wave signatures of the specimens were monitored using piezo crystal sensors. Results indicated the criticality of water distribution patterns in the determination of small-strain soil properties even though the specimens had identical global water saturation. The nuclear magnetic resonance-based water volume depth profiles indicated that the evaporation-driven specimens had more heterogeneous pore-invasive ice-bonding layers at a high water saturation region; by contrast, the drying process facilitated uniform meniscuses around the particle contacts near the air percolation threshold. Elastic wave measurements for laboratory-prepared specimens might over/underestimate the small-strain soil stiffness of sediments in nature, wherein the drying processes prevailed to control the water saturation. This study highlighted a clear transition from capillary-controlled to cementation-controlled elastic wave properties during temperature oscillations. Full article

(This article belongs to the Special Issue Emerging Characterization of Geomaterials Using Advanced Geo-Sensors)

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19 pages, 4656 KiB

Open AccessArticle

Estimation of Cavities beneath Plate Structures Using a Microphone: Laboratory Model Tests

by Seonghun Kang, Jung-Doung Yu, Won-Taek Hong and Jong-Sub Lee

Sensors 2021, 21(9), 2941; https://doi.org/10.3390/s21092941 - 22 Apr 2021

Cited by 7 | Viewed by 2576

Abstract

The objective of this study is to detect a cavity and estimate its size using sound waves in a laboratory model chamber filled with dry sand. One side of the chamber is covered with an acrylic plate, and a cavity is placed between the plate and sand. Sound waves are generated by impacting the plate with an instrumented hammer, and are measured using a microphone. The measured sound waves are analyzed with four comprehensive analyses including the measured area under the rectified signal envelope (MARSE) energy, flexibility, peak magnitude of wavelet transform, and frequency corresponding to the peak magnitude. The test results show that the accuracy of cavity detection using the MARSE energy is higher for thicker plates, whereas that using flexibility is higher for thinner plates. The accuracies of cavity detection using the peak magnitude of wavelet transform, and frequency corresponding to the peak magnitude are consistently high regardless of the plate thickness. Moreover, the cavity size may be under- or overestimated depending on the plate thickness and the selected analysis method. The average of the cavity sizes estimated by these methods, however, is slightly larger than the actual cavity size regardless of the plate thickness. This study demonstrates that microphones may be effectively used for the identification of a cavity and the estimation of its size. Full article

(This article belongs to the Special Issue Emerging Characterization of Geomaterials Using Advanced Geo-Sensors)

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15 pages, 20227 KiB

Open AccessArticle

Response of Transitional Mixtures Retaining Memory of In-Situ Overburden Pressure Monitored Using Electromagnetic and Piezo Crystal Sensors

by Sang Yeob Kim, Jong-Sub Lee and Junghee Park

Sensors 2021, 21(7), 2570; https://doi.org/10.3390/s21072570 - 6 Apr 2021

Cited by 1 | Viewed by 2815

Abstract

The major and minor components in granular soil materials determine their properties and behavior. This study explores the transitional behavior within threshold fines fraction of soil mixtures based on the data from the literature and experiments. From the literature survey, the void ratio, shear wave velocity, compression index, and friction angle capture the transitional turning point between the low and data-adjusted high threshold fines fractions. In particular, there is a dramatic change in hydraulic conductivity below the low threshold fines fraction that highlights the critical role of small amounts of fines in the fluid flow (e.g., clogging). From an experimental study, the engineering properties of natural soil samples identified using deformation and elastic wave sensors show transitional trends within the Revised Soil Classification System framework. The evolution of compressibility and shear wave velocity indicate that either coarse, fine, or both particles are likely to contribute to large and small strain stiffnesses when the effective stress is below 400 kPa. Thereafter, both engineering properties indicate that the soil sample retains a memory of in-situ overburden pressure when the effective stress is around 400 kPa. There is a critical role of fines that are slightly higher than low threshold fines fraction on engineering properties that promote the application of Revised Soil Classification System RSCS to natural soils. Full article

(This article belongs to the Special Issue Emerging Characterization of Geomaterials Using Advanced Geo-Sensors)

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17 pages, 2545 KiB

Open AccessArticle

Evaluation of Thawing and Stress Restoration Method for Artificial Frozen Sandy Soils Using Sensors

by Jongchan Kim, Jong-Sub Lee, Cody Arnold and Sang Yeob Kim

Sensors 2021, 21(5), 1916; https://doi.org/10.3390/s21051916 - 9 Mar 2021

Cited by 3 | Viewed by 2386

Abstract

Undisturbed frozen samples can be efficiently obtained using the artificial ground freezing method. Thereafter, the restoration of in situ conditions, such as stress and density after thawing, is critical for laboratory testing. This study aims to experimentally explore the effects of thawing and the in situ stress restoration process on the geomechanical properties of sandy soils. Specimens were prepared at a relative density of 60% and frozen at −20 °C under the vertical stress of 100 kPa. After freezing, the specimens placed in the triaxial cell underwent thawing and consolidation phases with various drainage and confining stress conditions, followed by the shear phase. The elastic wave signals and axial deformation were measured during the entire protocol; the shear strength was evaluated from the triaxial compression test. Monotonic and cyclic simple shear tests were conducted to determine the packing density effect on liquefaction resistance. The results show that axial deformation, stiffness, and strength are minimized for a specimen undergoing drained thawing, restoring the initial stress during the consolidation phase, and that denser specimens are less susceptible to liquefaction. Results highlight that the thawing and stress restoration process should be considered to prevent the overestimation of stiffness, strength, and liquefaction resistance of sandy soils. Full article

(This article belongs to the Special Issue Emerging Characterization of Geomaterials Using Advanced Geo-Sensors)

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15 pages, 3992 KiB

Open AccessArticle

Piezoelectric Ring Bender for Characterization of Shear Waves in Compacted Sandy Soils

by Dong-Ju Kim, Jung-Doung Yu and Yong-Hoon Byun

Sensors 2021, 21(4), 1226; https://doi.org/10.3390/s21041226 - 9 Feb 2021

Cited by 7 | Viewed by 4309

Abstract

Shear wave velocity and small-strain shear modulus are widely used as the mechanical properties of soil. The objective of this study is to develop a new shear wave monitoring system using a pair of piezoelectric ring benders (RBs) and to evaluate the suitability of RB in compacted soils compared with the bender element and ultrasonic transducer. The RB is a multilayered piezoelectric actuator, which can generate shear waves without disturbing soils. For five compacted soil specimens, the shear waves are monitored by using three different piezoelectric transducers. Results of time-domain response show that the output signals measured from the RB vary according to the water content of the specimen and the frequency of the input signal. Except at the water content of 9.3%, the difference in the resonant frequencies between the three transducers is not significant. The shear wave velocities for the RB are slightly greater than those for the other transducers. For the RB, the exponential relationship between the shear wave velocity and dry unit weight is better established compared with that of the other transducers. The newly proposed piezoelectric transducer RB may be useful for the evaluation of the shear wave velocity and small-strain shear modulus of compacted soils. Full article

(This article belongs to the Special Issue Emerging Characterization of Geomaterials Using Advanced Geo-Sensors)

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17 pages, 5431 KiB

Open AccessArticle

Horizontally Elongated Time Domain Reflectometry System for Evaluation of Soil Moisture Distribution

by Dong-Ju Kim, Jung-Doung Yu and Yong-Hoon Byun

Sensors 2020, 20(23), 6834; https://doi.org/10.3390/s20236834 - 29 Nov 2020

Cited by 12 | Viewed by 2462

Abstract

The objective of this study was to develop a horizontally elongated time domain reflectometry (HETDR) system to evaluate the water content in nonuniformly wetted soils. The HETDR probe consists of three rods of stainless steel and a cuboid head: A center electrode and two outer electrodes are connected to the inner and outer conductors of a coaxial cable, respectively. An acrylic container divided into several segments was used to prepare nonuniformly wetted soils with different water contents for a series of model tests. The HETDR probe was placed horizontally at the middle height of each soil specimen, while a conventional time domain reflectometry (TDR) probe was applied vertically on the surface of the specimen. The experimental results show that as the soil water content (SWC) at a segment increases, the average amplitude decreases and the duration increases. The estimated SWC increases with the measured SWC, and especially, the difference between actual segment length and the segment length estimated from the HETDR probes is significant under dry conditions. This study demonstrates that HETDR may be a promising field-testing method for evaluating the average water content in nonuniformly wetted soils. Full article

(This article belongs to the Special Issue Emerging Characterization of Geomaterials Using Advanced Geo-Sensors)

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19 pages, 5991 KiB

Open AccessArticle

Instrumented Cone Penetrometer for Dense Layer Characterization

by Jong-Sub Lee and Yong-Hoon Byun

Sensors 2020, 20(20), 5782; https://doi.org/10.3390/s20205782 - 13 Oct 2020

Cited by 15 | Viewed by 5673

Abstract

Subsurface characterization is essential for a successful infrastructure design and construction. This paper demonstrates the use of an instrumented cone penetrometer (ICP) for a dense layer characterization at two sites. The ICP consists of a cone tip and rods equipped with an accelerometer and four strain gauges, which allow dynamic driving, in addition to quasi-static pushing of the cone. The force and velocity of the cone are measured using the ICP instrumentation and compared with the N value, dynamic cone penetration index, and static cone resistance. A strong correlation has been observed between the total cone resistance estimated from the ICP and the dynamic cone penetration index and static cone resistance. After the correction of the dynamic cone resistance effect, the static component of the total cone resistance can be used as an alternative to a static cone resistance. This novel approach of soil resistance estimation using the ICP may be useful for dense layer characterization. Full article

(This article belongs to the Special Issue Emerging Characterization of Geomaterials Using Advanced Geo-Sensors)

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17 pages, 7099 KiB

Open AccessArticle

Strength Characteristics of Sand–Silt Mixtures Subjected to Cyclic Freezing-Thawing-Repetitive Loading

by Jong-Sub Lee, Jung-Doung Yu, Kyungsoo Han and Sang Yeob Kim

Sensors 2020, 20(18), 5381; https://doi.org/10.3390/s20185381 - 20 Sep 2020

Cited by 10 | Viewed by 3065

Abstract

Daily freezing-thawing-repetitive loading is a critical factor affecting soil stability. This study assesses the strength of sand–silt mixtures with various silt fractions (SFs) subjected to cyclic freezing-thawing-repetitive loading. Specimens with SF of 0–100% were prepared with a fixed relative density of 60%. The number of repetitive loadings (N) was 1, 100, and 1000 for each specimen with different SFs. After three cycles of freezing-thawing-repetitive loading, the specimens were frozen at −5 °C for the uniaxial compression test. Test results show that the change in relative density (∆D_r) increases with the increase in SF up to 30% and decreases as SF increases beyond 30% owing to the change in the void ratio. The volumetric unfrozen water content (θ_u) increases with the increase in both SF and N owing to the effect of the physicochemical characteristics of soils on small voids. Unconfined compressive strength of sand-dominant mixtures (SF ≤ 30%) is reinforced by ∆D_r. By contrast, for silt-dominant mixtures (SF > 30%), the unconfined compressive strength decreases with the increase in θ_u and N due to lubricant role and sands dispersion. Thus, the effects of SF and N should be considered for sand–silt mixtures that have a probability to undergo cyclic freezing-thawing-repetitive loading. Full article

(This article belongs to the Special Issue Emerging Characterization of Geomaterials Using Advanced Geo-Sensors)

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12 pages, 4949 KiB

Open AccessTechnical Note

Comparative Study on Estimation Methods of Dynamic Resistance Using Dynamic Cone Penetrometer

by Sang Yeob Kim, Jong-Sub Lee, Dong-Ju Kim and Yong-Hoon Byun

Sensors 2021, 21(9), 3085; https://doi.org/10.3390/s21093085 - 28 Apr 2021

Cited by 17 | Viewed by 3028

Abstract

Dynamic resistance, which can be used to express strength in the unit of stress and improve the reliability of the dynamic cone penetration test (DCPT), has been estimated by numerous methods. This study aims to compare different dynamic resistance estimation methods by using an instrumented dynamic cone penetrometer (IDCP). DCPTs are conducted using a standard dynamic cone penetrometer (DCP) and IDCP in the laboratory and field. Dynamic responses are obtained from the strain gauges and an accelerometer installed at the cone tip of the IDCP. The test results show that dynamic resistance is more efficient in distinguishing profiles than the dynamic cone penetration index. Among the methods to estimate the dynamic resistance at the cone tip, the force-velocity integration method and force integration method are more related to the conventional dynamic resistance considering the potential energy of the hammer than the force squared integration method. Additionally, the dynamic resistance estimated for a longer time period is more reliable, particularly for small driving rod lengths. Regarding the limitation of the dynamic response from an accelerometer in a previous study, the force-based dynamic resistance estimated for a longer time period can be used as the most reliable approach for further soil strength characterization. Full article

(This article belongs to the Special Issue Emerging Characterization of Geomaterials Using Advanced Geo-Sensors)

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9 pages, 2695 KiB

Open AccessLetter

Modified Fixed Wall Oedometer When Considering Stress Dependence of Elastic Wave Velocities

by Jong-Sub Lee, Geunwoo Park, Yong-Hoon Byun and Changho Lee

Sensors 2020, 20(21), 6291; https://doi.org/10.3390/s20216291 - 5 Nov 2020

Cited by 6 | Viewed by 2208

Abstract

A modified oedometer cell for measuring the applied stresses and elastic waves at the top and bottom of the specimen is developed to evaluate the effect of the side friction on the stress dependence of the elastic wave velocities. In the modified cell, two load cells are installed at the top and bottom plates, respectively. To generate and detect the compressional and shear waves, a pair of piezo disk elements and a pair of bender elements are mounted at both the top and bottom plates. Experimental results show that the stresses measured at the bottom are smaller than those measured at the top during the loading and vice versa during unloading, regardless of the densities and heights of the specimens. Under nearly saturated conditions, the compressional wave velocities remain almost constant for the entire stress state. With plotting stresses measured at top, the shear wave velocities during unloading are greater than those during loading, whereas with plotting stresses measured at bottom, the shear wave velocities during unloading are smaller than those during loading owing to the side friction. The vertical effective stress may be simply determined from the average values of the stresses measured at the top and bottom of the specimens. Full article

(This article belongs to the Special Issue Emerging Characterization of Geomaterials Using Advanced Geo-Sensors)

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11 pages, 3680 KiB

Open AccessTechnical Note

Expansion-Induced Crack Propagation in Rocks Monitored by Using Piezoelectric Transducers

by Chi-Hyung Ahn, Dong-Ju Kim and Yong-Hoon Byun

Sensors 2020, 20(21), 6054; https://doi.org/10.3390/s20216054 - 24 Oct 2020

Cited by 4 | Viewed by 2292

Abstract

The objective of this study is to develop a new vibration-free excavation method based on vermiculite expansion for rock cracking and to evaluate the performance of the heating system via elastic wave monitoring. Natural vermiculites expand rapidly in volume when heated above 800 °C. MgO powder is used to evenly transmit the surface temperature of a heater rod, which can attain high temperatures rapidly, to the vermiculites. The insertion direction of the heater rod greatly affects the expansion pressure. Three cuboid rock specimens are prepared and equipped with the heating system at different hole-to-face distances. Crack propagation is monitored by a pair of disk-shaped piezoelectric transducers. For short hole-to-face distances, the wave velocity and maximum amplitude rapidly decrease after certain time. For the greatest hole-to-face distance, the shear wave velocity remains constant during the test, while the maximum amplitude decreases after a certain time. The time taken for the velocity and amplitude of the shear waves to decrease reasonably corresponded to that taken for detectable crack propagation to occur on the surface of the rock specimen. The proposed method and materials may be useful from the viewpoints of rapid expansion, economy, and crack control. Full article

(This article belongs to the Special Issue Emerging Characterization of Geomaterials Using Advanced Geo-Sensors)

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13 pages, 2957 KiB

Open AccessTechnical Note

Estimation of the Structural and Geomechanical Anisotropy in Fault Gouges Using 3D Micro-Computed Tomography (μ-CT)

by Eomzi Yang, Tae Sup Yun, Kwang Yeom Kim, Seong Woo Moon and Yong-Seok Seo

Sensors 2020, 20(17), 4706; https://doi.org/10.3390/s20174706 - 20 Aug 2020

Cited by 1 | Viewed by 2669

Abstract

Fault gouges play an important role in the shear deformation of fault zones, by causing weakness and frictional instability in structures. Previous studies have investigated the evolution of shear deformation of fault zones by observing experiments using remolded and synthetic gouge specimens at a micro-scale. However, how the spatial configuration of the rock constituents accounts for the 3D anisotropy of intact structures of fault gouges, particularly at the core-scale, is not well understood. We obtained 3D μ-CT images of directionally cored gouge specimens and performed statistical analysis to quantify the major orientation of the internal structures. Direct shear tests were conducted to investigate the relationship between the distribution of the internal structures and geomechanical behavior. The results show that the undisturbed fault gouge has a clear anisotropy parallel to the fault plane even at the core-scale. Moreover, the direct shear test results show that the frictional resistance of a fault gouge has anisotropy related to the fault plane. The simple, yet robust method proposed in this study confirms that the core-scale structural anisotropy is correlated to the anisotropic shear resistance. Full article

(This article belongs to the Special Issue Emerging Characterization of Geomaterials Using Advanced Geo-Sensors)

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