Shallow Ground Research Articles

An analytical solution for heat extraction from shallow ground using a single-phase closed thermosyphon: A model for artificial ground freezing

Artificial ground freezing can be costly. Except for drilling and installation costs, they may also include maintenance and electricity consumption. What if there is a possibility to build an apparatus that naturally works without a need for external energy? Closed thermosyphons filled with a working fluid (antifreeze) that has a proper thermal conductivity can be the solution whether there is a need for heat extraction for a greenhouse area or an intention to freeze the ground artificially. A portion of a vertical closed pipe is installed in the soil while the other is in contact with the ambient air. The heat transfers from the high-temperature zone, soil, to the low-temperature zone, wellbore, and is released into the air. The results show that increasing the target depth underground from 1.5 m to 3.5 m increases the freezing time from 5 days to 24 days. Expanding the length outside of the ground (cooling) from 1.5 m to 3.5 m improves the heat transfer by 10 W, decreasing the freezing time by 2.5 days. A slight growth in diameter allows for a larger soil-water mixture to be involved in freezing, and thus the freezing time increase; however, since it enhances the heat transfer rate, a larger amount of freezing storage is obtained (e.g., an increase from 3.9 in. to 5.5 in. shows a 150-kJ growth at the end of 60 days). A decrease of 10 °C in air temperature also shows a staggering growth in freezing storage by >1500 kJ.

Field Investigation on Thermal Regime of Permafrost and Talik in a River Terrace, the Interior of Qinghai-Tibet Plateau

To carry out engineering construction in a permafrost area, it is of great importance to grasp the spatial distribution of permafrost and its hydrothermal characteristics within the scope of engineering activities. Compared with the continuous permafrost area, the permafrost distribution in discontinuous permafrost area is complicated due to existence of island talik, which causes highly poor continuity and uniformity of ground hydrothermal conditions and brings great difficulty and uncertainty to the engineering geological investigation. In the present study, the spatial distribution of permafrost and the freeze-thaw process of shallow ground at the I-stage terrace of a river on the Qinghai-Tibet Plateau were studied based on field investigation including drilling, electrical resistivity tomography, and borehole temperature measurement. The results show that the relict permafrost, patchy permafrost, and island talik are distributed in the limited range of the study area. Among them, the buried depth of relict permafrost layer is in the range of 7 ~ 14 m, while the patchy permafrost layer is in the range of 3.0 ~ 17.0 m depth, and the mean annual ground temperature of both is close to -0.1°C, which belongs to extremely high-temperature permafrost. The seasonal freezing/thawing depths of shallow ground within the relict permafrost, patchy permafrost, and island talik range from 2.5 to 3.0 m. The freezing period of the seasonal freezing layer is 5.5 months, while the thawing period of the seasonal thawing layer is 6 months. The complex plane and spatial distribution of permafrost in the field are closely related to local factors such as topography, geomorphology, groundwater, and lithology of shallow ground. It is believed that the formation of the island talik in the study area is controlled by solar radiation and precipitation infiltration.

Estimation and prediction of shallow ground source heat resources subjected to complex soil and atmospheric boundary conditions

5th generation district heating and cooling networks operating at near ground temperature offer a low-cost, zero-carbon energy solution. Detailed understanding and accurate estimation of ground behaviour for its heat storage and recharge potential are of paramount importance for the success of such networks. In this paper, an advanced modelling tool, based on a coupled Thermal-Hydraulic (TH) modelling framework, is presented to calculate and predict temperature and soil-moisture behaviour of a shallow ground under complex atmospheric, temperature and hydraulic boundary conditions. Atmospheric data e.g., solar radiation, rainfall, humidity, air temperature, wind velocity is considered together with subsurface soil data to investigate thermal and hydraulic responses of the ground, and its individual soil layers. Furthermore, a transient method for estimating shallow ground source heat (SGSH) resources is proposed based on the simulated temperature and saturation distributions of the ground. The model is applied to predict the long-term ground temperature and saturation level of a test site located in Warwickshire County, UK. The total heat content per unit area and the annual/seasonal/monthly net heat content per unit area of the site are predicted for a five-year period. The total heat content of the sandy clay layer varied between 2.32 and 11.6 MJ/m2, silty clay from 34.0 to 50.5 MJ/m2, and mudstone from 50.7 to 55.0 MJ/m2. A parametric sensitivity study is also conducted to investigate the effects of soil types and hydraulic drainage conditions on the ground heat supply potential, and it revealed that the spatial and temporal distributions of ground heat is significantly affected by the underlying soils. This study highlights the influences of atmospheric conditions and coupled ground processes, and the parameters that should be considered for designing a 5th generation low-temperature heat network.

Comparative study on the thermal performance and economic efficiency of vertical and horizontal ground heat exchangers

The ground-coupled heat pump is a shallow geothermal exploitation method taking soil as the thermal energy source. The ground heat exchanger is an important component of this system, which includes vertical or horizontal configurations. However, to the best of our knowledge, few studies exist involving the comparison of thermal performances and installation costs of two heat exchanger types considering the influence of ground climate, which makes the selection of heat exchanger configuration challenging for a specific field application. Hence, a 3-dimensional numerical model considering the variations of atmospheric conditions and soil water content is constructed in this paper. Based on this model, the thermal performances and economical efficiencies of vertical and horizontal ground heat exchangers are compared. The results indicate that the thermal performance difference between the two heat exchangers is greater in winter than in summer. The thermal performance is hardly influenced by the injection mass flow rate, while it is considerably affected by the length of heat exchanger. The thermal power rises linearly with the increase in heat exchanger length, and the increment of the vertical ground heat exchanger is higher. In addition, when the heat exchanger length is shorter than 40 m, the installation cost and thereby the total cost of the horizontal ground heat exchanger is considerably higher. With regard to both the thermal performance and economic efficiency, a vertical ground heat exchanger is only recommended when installing a single shallow ground heat exchanger. Cited as: Cui, Q., Shi, Y., Zhang, Y., Wu, R., Jiao, Y. Comparative study on the thermal performance and economic efficiency of vertical and horizontal ground heat exchangers. Advances in Geo-Energy Research, 2023, 7(1): 7-19. https://doi.org/10.46690/ager.2023.01.02

Seasonal variations of geofluids from mud volcano systems in the Southern Junggar Basin, NW China

Variations in the chemical composition of geofluids and of gas fluxes are significant parameters for understanding mud volcanism and correctly estimate their emissions in carbon species, particularly greenhouse gas, methane. In this study, muddy water and gas samples were collected from the Anjihai, Dushanzi, Aiqigou, and Baiyanggou mud volcanoes in the southern Junggar Basin during the four seasons, around a year. This region hosts the most active mud volcanism throughout China. Gas and water were analyzed for major molecular compositions, carbon and hydrogen isotopes of the gas phase, as well as cations and anions, hydrogen and oxygen isotopes of water. The emitted gases are dominated by CH4 with some C2H6, CO2, and N2. The seasonal changes in the chemical composition and carbon isotopes of emitted gases are not significant, whereas clear variations in the amounts of cations and anions dissolved in the water are reported. These are higher in spring and summer than autumn and winter. The CH4, CO2, and C2H6 fluxes are 157.3–1108 kg/a, 1.8–390.1 kg/a, and 10.2–118.7 kg/a, respectively, and a clear seasonal trend of the gas seepage flux has been observed. In January, the macro-seepage flux of open vents is ≥65 % higher than in April, whereas the micro-seepage flux significantly decreased, probably due to the frozen shallow ground and blockage of soil fractures around the vents by heavy snow and ice during January. This probably causes an extra gas pressure transferred to the major vents, resulting in higher flux of the macro-seepage in the cold season. However, the total flux of the whole mud volcano system is generally consistent around a year.

Framework for the identification of shallow ground movement in modified slopes (an expert opinion)

This paper has discussed and analyzed some significant ways to quickly find the root course of landslides on slopes, especially on shallow artificial slopes. Many mechanisms that trigger ground movement leading to landslides in slopes are discussed here. The general idea was to study the occurrence of slips on a modified slope under certain environmental conditions for a specific duration and develop a simple framework that can help to identify landslides’ causative factors subjectively. This whole idea was to help locals and other experts easily identify the triggering mechanisms of landslides to reveal the possible time when the slides will occur and control their impact. Furthermore, a framework was developed to help us understand the critical factors leading to shallow landslides on modified slopes. Establishing the mechanism that triggers landslides in an area helps greatly identify the landslides-prone locations, especially for the locals living in high-risk areas. The research also presented significant forms of landslides with their presumed causes. Although the general causes of landslides are not limited to what was presented in this text, the environment is the main factor deciding the nature and extent of landslides in an area.

Control of Short‐Stature Vegetation Type on Shallow Ground Temperatures in Permafrost Across the Eastern Canadian Arctic

AbstractThe Arctic has warmed three times the rate of the global average, resulting in extensive thaw of perennially frozen ground known as permafrost. While it is well understood that permafrost thaw will continue and likely accelerate, thaw rates are nonuniform due, in part, to the expansion of Arctic trees and tall shrubs that may increase ground temperatures. However, in permafrost regions with short‐stature vegetation (height < 40 cm), our understanding of how ground temperature regimes vary by vegetation type is limited as these sites are generally found in remote high‐latitude regions that lack in situ ground temperature measurements. This study aims to overcome this limitation by leveraging in situ shallow ground temperatures, remote sensing observations, and topographic parameters across 22 sites with varying types of short‐stature vegetation on Baffin Island, Canada, a remote region underlain by rapidly warming continuous permafrost. Results suggest that the type of short‐stature vegetation does not necessarily correspond to a distinct shallow ground temperature regime. Instead, in permafrost regions with short‐stature vegetation, factors that control snow duration, such as microtopography, may have a larger effect on evolving ground temperature regimes and thus permafrost vulnerability. These findings suggest that anticipating permafrost thaw in regions of short‐stature vegetation may be more nuanced than previously suggested.

A Case Study of Energy-Saving and Frost Heave Control Scheme in Artificial Ground Freezing Project

In large-scale shallow buried artificial ground freezing (AGF) engineering, frost heave control and energy-saving have always been the most critical problems. By the research and analysis, this manuscript points out the applicability and superiority of intermittent freezing in large-scale shallow buried freezing projects and conducts in situ tests for the freezing project of a metro entrance. The test results show that intermittent freezing can effectively control the surface frost heave, but it has a certain hysteresis. The freezing wall thickness, average temperature, and optimization scheme during the freezing process are discussed. The results show the following: (1) Intermittent freezing would degrade the thickness of the freezing wall and the average temperature together. (2) The stop freezing scheme in intermittent freezing is not fit to frost heave control during the excavation stage. Therefore, it is necessary to establish a freezing cycle scheme with precise temperature control to control the frost heave to ensure the bearing capacity. Based on the above conclusions, a dual-circuit liquid supply scheme, the specific brine temperature control scheme, and its application method were proposed. Through this method, the development process of the freezing front can be effectively controlled, and the goal of being precise and controllable can be achieved. This research can provide practical technical guidance for frost heave control of similar AGF projects.

The Thermal Imbalances Recorded at the NE Rift during the 2012 Explosive Activity at the South East Cone (Mt. Etna, Italy)

Mild thermal anomalies are sensitive to change in the advection processes in a volcanic system. A mild thermal anomaly, near the top of the North-East Rift of Mt. Etna (Italy), has been monitored from January 2010 to September 2012 by means of four temperature sensors buried in the shallow ground. The pulses of the convective circulation have been tracked and the diffuse heat flux has been evaluated. The positive pulses of the convective front reflected the local increases of volcanic degassing; conversely, the negative pulses showed the contraction of the convective front emerging through the North-East Rift. The steam condensation depth fluctuated below the monitoring site, from depths of a couple of meters to more than 30 meters, while the New South-East crater was erupting. The data hourly recorded, relative to the 2012 eruptive period, were compared to the radiant energy released by the paroxysms. We registered a dramatic decrease in the diffuse heat flux several hours before the onset of the two most energetic paroxysms (12 and 23 April). Thereafter, the convective front (the steam condensation depth) showed many negative pulses, reaching the deepest recorded levels. Thermal transients could be one of the early signals, possibly heralding transitions in the dynamic equilibrium conditions.

Energy Performance Evaluation of Shallow Ground Source Heat Pumps for Residential Buildings

This paper evaluates the energy performance of shallow ground source heat pumps using the state-of-art whole building energy simulation tool. In particular, the paper presents a systematic and easy to implement approach to model the energy performance of shallow and helical ground heat exchangers and assess their energy efficiency benefits to heat and cool buildings. The modeling approach is based on the implementation of G-functions, generated using a validated numerical model, in a state-of-art whole building energy simulation tool. Both the numerical model and the simulation tool are applied to assess the energy performance of various shallow geothermal systems designed to meet heating and cooling needs for detached single-family homes in California. Specifically, a series of sensitivity analyses is conducted to determine the energy performance of the shallow geothermal systems in 16 locations representing all California climate zones. It is found that the suitability and the efficiency of the shallow geothermal systems vary widely and depend on several factors including their design specifications as well as the climate conditions. Compared with conventional air-to-air heat pumps, the shallow ground source heat pumps can be more energy efficient in most climate zones in California except those locations with extreme weather conditions resulting in either heating or cooling only operation. Moreover, configurations of shallow ground source heat pumps with 16 boreholes with 6.7 m (22 ft) depth are found to be cost-effective in several California climate zones.

Influence of subgrade filling types on covering effect in seasonally frozen soil area

The existence of a large area of expressway pavement in seasonally frozen soil region causes the moisture in roadbed filler to migrate upward and accumulate under the action of external temperature gradient and road barrier which aggravates the frost heave and thaw settlement of the subgrade. The formation process of subgrade covering effect in seasonally frozen soil area is reproduced by laboratory experiment. The water-vapor-heat model of unsaturated soil is established to simulate the formation process and difference of different subgrade filling cover effect in a certain area of Lanzhou. The results show that under the effect of seasonal temperature changes， soil water accumulates to the bottom of the impervious layer， and the accumulation phenomenon intensifies with freezing-thawing cycles. When the subgrade fillings are sandy soil， silty soil and silty clay， the maximum frozen depths are 1.21， 0.97 and 0.89 m， respectively， due to the difference in thermal conductivity and soil moisture diffusivity of the fillings. Water vapor migration dominates the water transport in shallow ground， which is most significant in silty soil. Water accumulations of sandy soil， silty clay and silty soil subgrade are 0.68%， 2.86% and 12.56%， respectively. The accumulation depth becomes shallower in turn. It is important to prevent and control the subgrade hazards caused by water vapor migration in the existing subgrade engineering. <fig fig-type="abstract-image" id="F1" orientation="portrait" position="float"><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="SP.J.1249-2022-39-1-59/733994E6-A745-493b-B2C8-B61D2BDE06B2-F001.jpg"/></fig>

Heat Extraction from Shallow Ground Using Multiple Closed Single-Phase Thermosyphons

Heat Extraction from Shallow Ground Using Multiple Closed Single-Phase Thermosyphons

An analytical solution for heat extraction from shallow ground using a single phase closed thermosyphon: a model for artificial ground freezing

An analytical solution for heat extraction from shallow ground using a single phase closed thermosyphon: a model for artificial ground freezing

Shaking table model test on liquefaction countermeasure of shallow ground by log piling method

Shaking table model test on liquefaction countermeasure of shallow ground by log piling method

Application status and development trend of geothermal energy heating technology

With the rapid development of economy, people have higher and higher requirements for the quality of life. The traditional heating mode has serious pollution, uneven temperature, inconvenient installation, poor comfort, large energy consumption and low social benefits. It has been unable to meet people's pursuit of modern quality of life and the construction needs of environment-friendly and resource-saving society. The northern part of China is cold in winter, so it needs indoor heating. As the traditional heating mode has the problems of high energy consumption and environmental pollution, it needs to be updated and optimized. Based on the classification of geothermal energy heating technology, this paper expounds in detail the basic concepts, development and application status of shallow ground source heat pump technology, hydrothermal heating technology and middle-deep buried pipe heating technology. The emergence of geothermal energy heating technology has effectively solved a series of problems existing in traditional heating and has been widely used. In order to explore the heating potential of geothermal resources and its value in the "dual carbon" goal, the endowment and distribution characteristics of geothermal resources in China are briefly described, and the applicable geothermal energy supply models in different regions are given. By summarizing the existing reported research directions and related achievements of geothermal energy heating technology, from the perspective of operation mechanism and application practice, the technology development in this field is prospected.

Pixel-based vs. object-based anthropogenic impervious surface detection: driver for urban-rural thermal disparity in Faridabad, Haryana, India

Anthropogenic impervious surface area (AISA) expansion with its impact on temperature is current research trend. Majority of earlier research focused on land surface temperature (LST) versus AISA relationship in specific year independently. Therefore, present research is a novel attempt to study ΔLST–ΔAISA correlation during 2012–2017 in core urban, semi urban, and rural region of Faridabad. Results demonstrate applicability of object-based image classification (OBIC) over pixel-based image classification (PBIC) to detect AISA with higher accuracy (OBIC: 2012—94%, 2017—93%, PBIC: 2012—79%, 2017—84%). Degree of non-linearity of LST-AISA relationship increases from urban to rural region, evident from the coefficient of AISA% (0.03-core urban, 0.07-semi-urban, 0.08-rural). Absolute temperature is low in land with shallow ground water depth up to 10 m. Higher percentage of land with shallow water depth causes significant increase in (ΔLST/ΔAISA) in rural region. Consequently, authors suggest avoiding acquisition of land with water table depth 3–10 m for future impervious surface development.

Field performances of energy pile based on the secondary utilization of sonic logging pipes

An energy pile has dual functions of bearing the upper structure load and transferring shallow ground temperature energy. Cross-hole sonic logging (CSL) is used to evaluate the integrity of large-diameter bored piles. CSL test tubes are usually abandoned after integrity tests. A secondary utilization of tubes can be advocated to save resources. In this paper, a new scheme is proposed to connect the bottom end of the access tube in a CSL test to form a new type of loop in the energy pile. A CSL tube is made of galvanized steel pipe (GSP). The thermal and thermomechanical performance of the energy pile with GSP loops and conventional polyethylene (PE) loops is measured by a thermal performance test at the cooling phase. The influence of the modified GSP tubes on the pile integrity can be neglected in the integrity test (CSL test). The heat exchange performance indicates that secondary utilization technology has good prospects. Owing to the discrepancies of different tube materials (thermal conductivity, heat capacity, and thermal coefficient), the heat exchange rate of the energy pile with GSP loops is approximately 26% higher than that of the energy pile with PE loops. The displacements at the pile top with GSP and PE loops after 120 h cooling are 0.15% and 0.083% times the pile diameter, respectively.

Quality Assessment of Dry Soil Mixing Columns in Soft Soil Areas of Eastern China

To investigate the quality of dry soil mixing (DSM) columns in different soft soil areas of east China, a large number of laboratory test results and field test results of DSM columns were collected and analyzed statistically. Furthermore, a quality assessment method for DSM columns is proposed in this paper. The hardness description (HD), standard penetration test (SPT), unconfined compressive strength (UCS), and soil-cement column quality designation (SCQD) are used as assessment indexes. The statistical analysis showed that the test results of SPT, UCS, and SCQD were scattered, particularly in shallow ground. The mean values of the SPT blow count, UCS, and SCQD of the DSM columns decreased with depth: the greater the depth, the worse the quality of DSM columns. The quality assessment results showed that the proportion of the great quality columns was 64.84%, and the proportion of the unqualified columns was 1.4%. The proportion of DSM columns with great quality in the lagoon soft soil area was greater than in other areas. The proportion of unqualified columns in the lacustrine soft soil area was the largest. For all soft soil areas, the proportions of great quality, good quality, general quality, and unqualified soil decreased in that order. The quality assessment of 8627 DSM columns showed the proportions of great quality and unqualified were 64.84% and 1.4%, respectively. It was found that the greater the depth of the DSM column, the more unqualified DSM columns, and the more difficult it was to control the quality of DSM columns.

Water isotope variation in an ecohydrologic context at a seasonally dry tropical forest in northwest Mexico

We conducted an isotopic characterization of precipitation, streamflow, groundwater and bulk soil moisture (<60 cm depth) to assess ecohydrologic separation and its seasonal variation in a tropical dry forest in northwestern Mexico using four representative tree species. We present a data set that allows analyzing the connection of vegetation to soil or movable water in a highly seasonal ecosystem throughout one year (2015) but relies on baseline data set of local precipitation. A local meteoric water line was created using 5 years (2012–2017) of isotopic data (δ2H = 7.64*δ18O + 7.34, r2= 0.97) at the study site. Ecohydrologic separation was clear throughout the dry season but during the wet monsoon season the upland trees L. divaricatum, A. cochliacanta and L. watsonii showed the opposite pattern since the isotopic composition of xylem water was similar to the meteoric water and shallow soil, stream and ground water. The riparian tree T. huegelii resulted in an isolated dynamic showing a similar isotopic composition to stream water. Results of this work suggest that ecohydrologic separation is not a universal pattern because it does not occur in all vegetation types and it may vary seasonally.

Commercial catches and discards composition in the central Tyrrhenian Sea: a multispecies quantitative and qualitative analysis from shallow and deep bottom trawling

In the Mediterranean Sea, the catch of bottom trawl fisheries is composed of a complex mix of fish and invertebrates with a considerable amount of discards. Seasonal composition of catches and discards of bottom trawls operating at different depths in the central Tyrrhenian Sea were investigated from October 2014 to October 2015. The mean total catch per unit effort (CPUE) ranged between 30.93±8.43 and 27.52±9.88 kg/h in shallow and deep fishing grounds, respectively. The discarded fraction of the catch was 39.9 % in shallow and 43.3% in deep fishing grounds. The mean CPUE of commercial target species were similar in shallow and deep trawling (10.81+5.82 vs 8.92±3.16 kg/h). The commercial bycatch was lower in shallow (6.66±1.25 kg/h) than in deep grounds (8.24±2.91 kg/h), whilst the discards were lower in deep (10.43±5.14 kg/h) than shallow grounds (13.43±5.29 kg/h). Overall, 246 species were caught during fishing operations, out of which 209 were included in discards. The number of species recorded in shallow grounds (199 caught species with 166 discarded) was higher than that recorded in deep grounds (116 caught species with 102 discarded). Fish were the most represented taxa in the shallow discards, followed by echinoderms; crustaceans, and were the main discarded taxa in deep water. Depth was the main factor affecting both commercial catches and discards composition, whereas the season affected the CPUE of main target species only. The results confirmed that discards were higher in shallow than in deep trawling, suggesting that the latter is more efficient than the former in catching fishery resources for human consumption. Understanding the factors that affect discarding is the starting point for adopting management measures to mitigate negative impacts of trawl fisheries on marine resources and benthic communities.