Artificial Ground Research Articles

Investigation of creep characteristics and microscopic mechanism in cemented-soil subjected to freeze–thaw during artificial ground freezing

Investigation of creep characteristics and microscopic mechanism in cemented-soil subjected to freeze–thaw during artificial ground freezing

Thermal and mechanical impact of artificial ground-freezing on deep excavation stability in Nakdong River Deltaic deposits

This paper presents a case study of deep excavation using the artificial ground freezing (AGF) method for tunnel restoration work in the Nakdong River deltaic deposits. The study involved detailed construction monitoring and data analysis to assess the thermal and mechanical impacts on surrounding ground and underground structures. Factors influencing heat transfer were identified and evaluated for their effect on ground temperature distribution. The excavation and frost expansion of the ground led to unique lateral deformation of the diaphragm wall. However, the frozen soil effectively resisted earth pressure and suppressed deformation of the wall. The axial stress applied to the braced strut was closely related to the deformation of the diaphragm wall and was influenced by both excavation-induced and frost-expansion pressures. Boreholes near the frozen soil functioned as stress-relief holes, enhancing excavation stability. These comprehensive findings enhance the understanding of AGF techniques and their impact on complex deltaic geological conditions and adjacent structures.

Metasurface loaded twin-port microstrip antenna with circular polarization features for UHF RFID applications

Abstract This communication designs and investigates a twin-port microstrip antenna loaded with a metasurface (MS). The proposed MS works in two ways: (i) artificial ground plane for radiator and (ii) as an ideal absorber of normal incoming waves at the same time. A stair shaped slot is loaded on rectangular patch for creating circularly polarized wave in between 835–894 MHz. Antenna port slots oriented in a mirror manner increase isolation by 25 dB. To act as a validation tool, the suggested antenna was built and its executions in individually operating modes evaluated by statistical and experimental analysis. It is shown that combining the patch and absorber results in a well-matched antenna in between 710–980 MHz with improved gain (more than 3.0 dBi). The proposed antenna design effectively used for UHF (Ultra High Frequency)radio-frequency identification (RFID) applications, which is due to its ability to mitigate multipath reflection issues and incorrectRFID reading.

Bidirectional seismic response of assembled monolithic subway station-aboveground structure system under artificial bedrock ground motions

Assembled monolithic subway station partly synthesizes the advantages of cast-in-place and precast subway stations. However, the related seismic response analysis considering the influences of vertical ground motion and aboveground structure is still scant. In this study, we firstly performed the statistical analysis on bidirectional bedrock ground motion parameters (response spectrum, duration and envelope function) using KiK-net data, and obtained some suggested values of the above parameters. Then, four sets of artificial bedrock ground motions with statistical meanings were generated and a three-dimensional finite element analysis of the seismic response of an existing two-story three-span subway station was conducted. The main results are summarized below. (1) The significant damage to assembled monolithic station under far-field strong motion firstly occurred at side middle slab; middle slab, upper column and related grouting sleeve joints were more damage-prone. (2) When horizontal peak ground acceleration stayed constant, overall the damage of far-field motion was stronger than that of near-fault motion. (3) Vertical ground motion obviously accelerated the damage progresses of various structural members at various positions, then aboveground structure further enhanced the damages and vertical displacement responses of parts of top slab. (4) For the axial force time-history of upper column during far-field strong motion, aboveground structure uplifted the baseline, and vertical ground motion increased the amplitude and advanced the obvious drop of the baseline, among which the latter effect of vertical ground motion on assembled monolithic station was stronger than that on cast-in-place station. (5) Vertical ground motion enhanced inter-story displacement during far-field strong motion, among which the influence on the upper story of assembled monolithic station could be obviously amplified by aboveground structure, and the amplification effect lagged behind the influence of vertical ground motion. Based on the results of this study, some suggestions for the seismic design of subway station are also provided.

Nonlinear seismic response analysis of long-span railway cable-stayed bridges crossing strike-slip faults

Active faults along railways in the mountainous regions of western China pose significant challenges to bridge safety. To ensure the safe operation of long-span railway bridges under complex geological conditions, this study investigates the synthesis of artificial ground motions for bridges crossing strike-slip faults and analyzes their nonlinear seismic response. First, we develop a theoretical method for simulating high- and low-frequency seismic motions using a finite fault and an equivalent velocity pulse model. Next, using a specific long-span railway cable-stayed bridge as a case study, we construct a nonlinear finite element model with OpenSees software. Finally, we assess the seismic response of key bridge components considering various crossing angles, seismic amplitudes, fault rupture directivity, and fling-step effects. The results show that the crossing angle significantly influences the seismic response, with longitudinal and transverse responses exhibiting opposite patterns. Additionally, the scaling factor of seismic motion significantly affects bridge response. For bridges crossing strike-slip faults, the longitudinal response exhibits a sudden increase in displacement due to instantaneous velocity pulses, while the transverse response shows notable residual displacement influenced by the fling-step effect. However, the critical section curvatures of bridge towers and piers remain within the elastic range across all crossing angles, indicating that controlling large displacement deformations is crucial for the seismic design of bridges crossing strike-slip faults.

Artificial ground freezing for underground construction – a brief review of the theory, practice and challenge

Since Artificial ground Freezing (AGF) appeared in the 1880s in the mining sector in Europe, it has been used for various construction applications worldwide. In recent years, it has been increasingly popular in urban projects due to its versatility and applicability to complicated site conditions. So far, it has been used to stabilize substrata to nearly 1,000 m below the ground surface, which is considered not possible for many other ground improvement technologies. Due to the growth in field applications, the practice and theories related to AGF have become more mature in the most recent two decades. The improvement in understanding of this topic is a result of lessons that have been learned through numerous projects, as well as a variety of comprehensive studies that have been completed. This paper reviews the existing practice, the recent development on AGF and the challenges of AGF.

Assessing the reuse of liquid nitrogen in artificial ground freezing through field experiments

Assessing the reuse of liquid nitrogen in artificial ground freezing through field experiments

A novel large-scale direct shear apparatus considering size effects on strength of frozen coarse-grained soils

As engineering activities in cold regions expand and the application of artificial ground freezing technology in constructions grows, understanding the strength of frozen coarse-grained soils has become imminently crucial. While existing research and testing methods have provided valuable opinions into the behavior of coarse-grained materials in frozen states, there is a recognized need to enhance and expand these methods to gain a more comprehensive understanding of how size effects influence the strength of these materials. To further investigate this issue, a novel large-scale direct shear apparatus was employed to determine the shear strength of frozen coarse-grained soil materials. The apparatus features a unique design capable of accommodating square specimens with five different section lengths: 100 mm, 150 mm, 200 mm, 250 mm, and 300 mm. Depending on the maximum load requirements and budget constraints of the experiment, the equipment can provide a maximum normal stress of 5.5–50 MPa and a maximum shear stress of 3.5–30 MPa for different sample sizes, along with precise temperature control down to −30 °C. The efficacy of the device is validated through experiments conducted on frozen coarse-grained soil samples with specific particle size distributions. This study presents the technological details involved in the development of the apparatus and offers preliminary insights into the strength characteristics of frozen coarse-grained soils, highlighting the influence of size effects. The innovative features of the apparatus help the geotechnical community to comprehensively understand the strength characteristics of this complex material, thereby improving the reliability of engineering practices that involve it.

Studying the Freezing Law of Reinforcement by Using the Artificial Ground Freezing Method in Shallow Buried Tunnels

Studying the Freezing Law of Reinforcement by Using the Artificial Ground Freezing Method in Shallow Buried Tunnels

Research on Bursapherenchus Xylophophilus Disease Recognition Based on HSV Space

Abstract This study aims at the shortcomings of traditional artificial ground detection methods for Bursapherenchus xylophophilus disease and applies HSV(Hue-Saturation-Value) color model to realize automatic identification of Bursapherenchus xylophophilus disease and determine its degree of disaster.The entire process is divided into forest data collection, image processing, nematode disease identification and grade determination.The study conducted repeated comparisons and adjusted HSV threshold tests to obtain the HSV threshold with optimal recognition results, and then identify Bursaphelenchus xylophophilus disease and calculate its disease severity. This method is simple to operate and has good identification effects. It can also effectively improve the accuracy and efficiency of pine wood nematode diagnosis. It can be widely used in the field of agriculture and forestry to help better complete disease detection and carry out prevention and control measures more accurately, thereby effectively Protect forest natural resources and improve forestry production efficiency.

Seismic testing and fragility analysis considering material strength uncertainty of 1100 kV GFRP composite power transformer bushing

Nowadays glass-fibre reinforced polymer (GFRP) composite insulators are widely employed in electrical equipment in substations. However, there is a scarcity of reports on seismic qualification of transformer bushings that adopt GFRP insulators. Thereby, this case implements shaking table tests on a 1100 kV GFRP composite power transformer bushing. The study analyses the acceleration responses and dynamic amplification effects, as well as the strain responses. The combined stresses at the vulnerable positions are computed to authenticate the seismic performance. Using a simulation model, the seismic fragility of the transformer bushing considering the material strength uncertainty is assessed and discussed. The results indicate that the GFRP composite bushing meets the requirements of the relevant code and its seismic performance is qualified under an artificial ground motion with PGAs of 0.6 g and 0.8 g. For a given factor of safety of 1.67, the bushing can sustain 0.4 g earthquakes with a failure probability near 0 and 0.8 g earthquakes with a failure probability<50 %. Controlling coefficient of variation of the GFRP material strengths is beneficial to decreasing seismic fragility of the transformer bushing within a specific PGA range. Weibull and Normal distributions for fitting the strength distributions of the GFRP materials have different impacts on the seismic fragility of the bushing, which should be given more attention in seismic design.

Study of Slope Stability of the Mining Wall in an Open-Pit Coal Mine by the Paste Cut-and-Backfill Method

According to this study’s findings, slope stability problems in open-pit coal mines can be avoided, and mine wall collapse can be effectively mitigated by the use of cut-and-backfill mining techniques. The main research results are as follows: (1) The stope and waste rock’s geotechnical, physical, and mechanical characteristics were gathered and examined; the geotechnical and mechanical characteristics found in this study largely satisfy the criteria for slope stability analysis. (2) Cemented paste backfill (CPB) materials were made of mine waste rock and fly ash at a desired ratio, mixed with cement as a bond material, and were tested in the laboratory, using a combination of cement percentages of 6%, 8%, and 10% for the cement content and 25%, 30%, 35%, and 40% for the fly ash content, to determine the ideal mix for artificial ground support in underground mines, taking into account both economic and performance factors. (3) By using this model, the changes in CPB strength were investigated under various factors influencing the cement ratio, and limit equilibrium modeling was used with the FLAC-Slope 8.1 program with different cement paste backfill ratio to calculate the factor of safety for each cement percentage after 1 day, 3 days, 7 days, and 28 days of curing time (CT) to obtain the optimum compressive strength and shear straight of cemented paste backfill with high paste fill shear strength on the slope. (4) The research results are of great significance for the safety of important facilities in open-pit mines and provide a basis for the design and safety implementation of open-pit slope engineering.

Artificial Ground Freezing—On the Soil Deformations during Freeze–Thaw Cycles

Artificial ground freezing (AGF) has emerged as a prominent treatment method due to its ability to mechanically strengthen the soil while reducing its permeability. However, its implementation has raised concerns about its impact, particularly with respect to frost heave and subsequent thaw-induced displacements. These soil movements can cause subsidence and pose a significant threat to the integrity of surface structures. Overburden pressure plays a crucial role in AGF and determines the amount of heave generated. This paper presents an analysis of the existing literature about soil freezing and thawing. The aim is to offer an understanding of these processes, specifically with regard to their application in AGF. This paper explains the behavior of soil during freezing, with particular emphasis on the influence of overburden pressure. It also investigates frozen soils’ thawing and freeze–thaw (FT) cycles’ long-term effects on soil properties. AGF offers improved soil strength and reduced water permeability, enhancing construction project stability. However, the interplay between the temperature, soil composition, and initial ground conditions during freezing is complex. This thermo-hydro-chemo-mechanical process strengthens the soil and reduces its permeability, but it can also induce frost heave due to water expansion and ice lens formation. Overburden pressure from the overlying soil limits ice lens growth. FT cycles significantly impact soil properties. In fine-grained soils, FT cycles can lead to over-consolidation, while rapid thawing can generate high pore pressures and compromise stability. Importantly, FT acts as a weathering mechanism, influencing soil properties at both the microscopic and macroscopic scales. These cycles can loosen over-consolidated soil, densify normally consolidated soil, and increase overall hydraulic conductivity due to structural changes. They can also weaken the soil’s structure and deteriorate its mechanical performance.

Aerobic Training on the Physical Fitness and Technical Variables of Male Ice Hockey Players

Hockey attained greater level of popularity all over the World and played on sand, natural grass and artificial turf ground. The modem game of hockey demands that each member of the team be able to play in all positions. The purpose of the study was to find out the effect of aerobic training on physical fitness and skill variables of men hockey players. The selected physical fitness and skill variables were hitting and dribbling, To achieve this purpose total (N=30) subjects selected from Faculty of General Adapted Physical Education and Yoga, Ramakrishna Mission Vivekananda Educational and Research Institute, Coimbatore. The subjects are selected by purposive sampling method. The subjects are equally divided into two groups namely group - I (n - 15) Aerobic training with Skill Training group and group –II (n - 15) acted as control group. Their age ranged between 18 to 25 years. The physical fitness variable cardio respiratory endurance was measured with 12 minutes run/walk test and skill variables namely dribbling was tested with SAI Hockey Skill Test. The training periods consists a total of eight weeks, which includes training for 5 days a week from evening 5 to 6 pm. The collected data were treated with paired ‘t’ test. The results of the study shows that aerobic training play a significant role in improving physical fitness variables namely cardio respiratory endurance and skill performance variables namely hitting and dribbling of college men hockey players.

Investigation on evolution law of frozen wall thickness in artificial ground freezing under seepage conditions

Frozen wall thickness (E) is an important index that reflects the freezing performance of artificial ground freezing (AGF). In previous design and numerical studies, the inherent spatial variability of soil properties is often neglected. Moreover, groundwater seepage can remarkably affect the freezing performance in the AGF system, while the specific relations between seepage and E remain unclear. Accordingly, this study aims to explore the evolution of frozen wall thickness under seepage conditions via a numerical model that considers the coupled thermo-hydraulic process and variations in hydrothermal properties. As two vital soil properties, spatial variability of thermal conductivity and intrinsic permeability is simulated by random field combined with Monte Carlo simulations (MCs). Based on the coupled model, the effects of seepage velocity, direction, and pipe spacing are examined by sensitivity analysis. Two indicators are introduced to quantify the influences of uncertainty in hydrothermal properties and seepage. The unfavourable scenarios (i.e., lower bound) of E from random models are tabulated and formulated via evolutionary polynomial regression for practical references. These findings contribute to an enhanced understanding of the freezing behaviours of AGF and provide a rule of thumb for predicting frozen wall thickness under complex seepage conditions and design parameters.

Numerical investigation of artificial ground freezing–thawing processes in tunnel construction

Artificial ground freezing is a frequently used method for temporary support of the soil in geotechnical interventions, such as tunneling. Besides the time required to form a supporting frozen soil structure during freezing, the prediction of temperature evolution during the thawing process and the final thawing time are also relevant, since settlements induced by thawing of the frozen soil can pose a risk to sensitive structures in urban tunneling. The freezing and thawing process of soils depends strongly on the unfrozen liquid content. The unfrozen liquid content during the freezing and thawing cycles is known to have a pronounced hysteresis response, whose effect on the temperature distribution and groundwater flow, especially at the structural level has not been extensively studied. In this work, we present a thermo-hydraulic finite element model for freezing soils and incorporate the hysteresis behavior of soil. We aim to investigate the suitability of the presented numerical model for tunnel construction on the one hand, and quantify the extent of the influence of the hysteresis response of the unfrozen liquid content at the structural level on the other. To this end, the model is first validated with the help of experimental data from a soil test subjected to a freezing–thawing cycle and subsequently used to analyze three problems of artificial ground freezing in tunnel construction during the freezing phase or freezing–thawing phases. The results show a good agreement with the experimental measurements. We show that the computational model is capable of providing accurate prognosis of the temperature profile as well as broader metrics such as the thickness and shape of the frozen body for tunneling applications under hydrostatic and seepage flow conditions. The hysteresis response is shown to have a significant influence on the coupled thermo-hydraulic process, with thawing times differing depending on whether hysteresis is considered. It is concluded, that the inclusion of the hysteresis response is crucial for obtaining an accurate representation of the freezing process.

Effects of Salt Content and Freeze-Thaw Conditions on Dynamic characteristics and its microscopic mechanism of Chloride Silty Clay

Generally, artificial ground freezing (AGF) technology is utilized to guarantee tunnel safety during construction. However, the soil structure changes significantly after freeze-thaw, resulting in uneven deformation of the tunnel under traffic loading from subway vibration. To solve this problem effectively, it is necessary to consider the combined impact of freeze-thaw, salt, and traffic loading damage that marine soft soil must withstand simultaneously. For this reason, cyclic triaxial test and NMR test were performed on the silty clay saturated with NaCl solution in this study. The influence of three main factors on dynamic properties has been thoroughly investigated, namely freeze-thaw, salt content, and confining pressure. According to cyclic triaxial test, the shape of the hysteresis loop of the specimens after freeze-thaw changed more significantly with increasing loading cycles. The dynamic elastic modulus was weakened by freeze-thaw, while improved by the addition of NaCl. Damping ratio was consistent with the dynamic elastic modulus law. It was worth noting that the different freezing temperatures (−10 °C, −20 °C and − 30 °C) had only a slight impact on dynamic elastic modulus, as well as damping ratio. Mathematical models were proposed to forecast the dynamic elastic modulus and damping ratio regarding marine soft clay. NMR test indicated that the addition of salt made the internal pore environment of the specimens tend to be consistent and enhanced the water-solid interaction. The increase in porosity resulted in the decrease in dynamic elastic modulus. The results have provided valuable insights into the mechanical characteristics of marine soft clay when AGF technology is applied.

Numerical Analyses of the Effect of the Freezing Wall on Ground Movement in the Artificial Ground Freezing Method

The advancement of massive construction in urban subway projects contributes to the increased use of the artificial ground freezing (AGF) method in the construction of cross passages due to its reliability and environmental friendliness. However, the uplift or subsidence of the ground surface induced by the frost heave and thawing settlement of the soil can be a problem for existing buildings, and the current design method places way too much emphasis on the strength requirement of the freezing wall. In this study, FLAC3D was employed to develop a series of state-of-the-art numerical models of the construction of a typical subway cross passage by the AGF method, utilizing freezing walls with different thicknesses. The results of this study can be used to examine the ground deformation arising from the AGF method and the influence of the thickness of the freezing wall on the AGF method.

Artificial ground reflector size and position effects on energy yield and economics of single‐axis‐tracked bifacial photovoltaics

AbstractArtificial ground reflectors improve bifacial energy yield by increasing both front and rear‐incident irradiance. Studies have demonstrated an increase in energy yield due to the addition of artificial reflectors; however, they have not addressed the effect of varying reflector dimensions and placement on system performance and the impact of these parameters on the reflectors' financial viability. We studied the effect of high albedo (70% reflective) artificial reflectors on single‐axis‐tracked bifacial photovoltaic systems through ray‐trace modeling and field measurements. In the field, we tested a range of reflector configurations by varying reflector size and placement and demonstrated that reflectors increased daily energy yield up to 6.2% relative to natural albedo for PERC modules. To confirm the accuracy of our model, we compared modeled and measured power and found a root mean square error (RMSE) of 5.4% on an hourly basis. We modeled a typical meteorological year in Golden, Colorado, to demonstrate the effects of artificial reflectors under a wide range of operating conditions. Seventy percent reflective material can increase total incident irradiance by 1.9%–8.6% and total energy yield by 0.9%–4.5% annually after clipping is considered with a DC–AC ratio of 1.2. Clipping has a significant effect on reflector impact and must be included when assessing reflector viability because it reduces reflector energy gain. We calculated a maximum viable cost for these improvements of up to $2.50–4.60/m2, including both material and installation, in Golden. We expanded our analysis to cover a latitude range of 32–48°N and demonstrated that higher‐latitude installations with lower energy yield and higher diffuse irradiance content can support higher reflector costs. In both modeling and field tests, and for all locations, the ideal placement of the reflectors was found to be directly underneath the module due to the optimized rear irradiance increase.

A prolegomenon to Design Input Energy Spectra for the Himalayan region

Energy-based design is becoming progressively significant as a new age of earthquake-resistant design unfolds. Thitherto, very little is known about energy-based design in India despite the fact that the Himalayan region is one of the most seismically active regions in the world. Therefore, the current work provides a preliminary analysis of the elastic input energy and equivalent velocity (Vea) spectra for the active regions in the Himalayas. In this regard, the ground motions of Himalayan databases are blended with NGA WEST2 to estimate the Vea spectra, an inertia-independent representation of the input energy spectra. Incipiently, an Artificial Neural Network-based ground motion model (GMM) is developed for Vea spectra based on the predictor variables as magnitude, distance, hypocentral depth and site conditions. Consequently, a Probabilistic Seismic Hazard analysis is performed to obtain the uniform hazard energy spectra for a 2475-year return period. In addition, a Design Input Energy Spectra is proposed for the active regions in the Indian Himalayas. In addition, the relationship between the Vea and pseudo-spectral velocity (PSV) is analyzed to develop a Vea-informed GMM for PSV. Furthermore, the PSA estimated from the Vea-PSV model is compared with the design spectra recommended by the Indian Standard Code of Practice (IS1893-1:2016).