Ground Depth Research Articles

The influence and calculation method of ground settlement induced by tunnel construction in sand

ABSTRACT In order to study the influence of tunnel construction on ground settlement in sand, the distribution and variation characteristics of ground settlement during tunnel construction were explored through model tests. The results showed that during tunnel construction in sand, the variations of surface settlement and ground settlement at different ground depths were basically the same at the same monitoring section. The distribution and variation characteristics of the ground settlements along the width and length directions of the tunnel were basically the same. The ground loss increased in power function from the surface to the underground. The maximum ground settlement and the width coefficient of the settlement trough were strongly positively correlated with the ground loss. Based on the experimental study and statistical analyses, the relation between ground loss and ground surface loss at different burial depths was established. The calculation of an equation of ground loss at different depths was put forward, and the calculation of an equation of the width coefficient of ground settlement trough was modified, both of which enable the calculation for ground settlement in an arbitrary position above the tunnel during tunneling.

Finite Difference Method for the One-Dimensional Non-linear Consolidation of Soft Ground Under Uniform Load

Initial stress and additional effective stress distributions in soil greatly influence the degree of ground consolidation when calculating one-dimensional soft clay ground consolidation in deep soil. The one-dimensional nonlinear consolidation governing equations of soft ground under uniform loads are derived and solved with the finite difference method. This method is based on the assumptions that the initial stress in soil varies with the ground depth and the additional effective stress caused by external loads changes with both the ground depth and consolidation time, and the hyperbolic model of the soil stress-strain relationship. Formulas for the degree of consolidation and the settlement of the ground are presented. A case study shows that the degree of consolidation of the ground calculated with the finite difference method agrees with the traditional analytical solution, and the computational efficiency of the finite difference method can be effectively improved when the segmental calculation method is used throughout the consolidation process. The results of another example show that the settlement of the ground calculated with the finite difference method agrees with the in situ data. The suggested method can greatly simplify the consolidation calculation and has a high application value in engineering.

EXPERIMENTAL STUDY OF SEISMIC RESPONSE OF THE SQUARE TUNNEL IN GRANULAR SOIL

In this study a series of shaking table tests were carried out to investigate the effect of tunnel model depth and direction of ground acceleration on the horizontal acceleration of tunnel model and soil beside it, ground surface settlement, and the dynamic earth pressure on the tunnel wall. Square tunnel model embedded in both dry and saturated soil (Karbala Sand). It subjected to three input sinusoidal motions 0.05g, 0.1g, and 0.2g. Two relative densities used, 30% for the upper layer and 70% for the lower layer. The results obtained indicate that the direction of seismic loading has significant effect on the horizontal acceleration of tunnel model. The increase of tunnel model depth lead to decrease the horizontal acceleration of tunnel model. While, the settlement of soil surface increases with an increase of tunnel model depth and ground acceleration especially at 0.2g earthquake loading. The change of direction of seismic loading leads to a small change in the settlement for dry soil. The results appear that dynamic earth pressure (DEP) was positive in dry soil and negative in saturated soil in all test. In saturated soil, the effect of direction of ground acceleration and depth of tunnel model on DEP in 0.2g is quite little.

Similar Bird Communities Across Grazing Systems in the Nebraska Sandhills

ABSTRACTMuch of the remaining native rangeland in the Great Plains in the United States is privately owned and managed for beef production, and this single priority for land use may be contributing to declining avian biodiversity through a loss of structural heterogeneity. One proposed solution is to use multiple grazing systems across ranches, under the assumption that this approach will increase heterogeneity of vegetation structure and avian diversity across the landscape. We tested the relationship between grazing systems and avian diversity in the Nebraska Sandhills during 2014 and 2015 on a landscape that included 11 management units containing 5 different grazing systems. We used multivariate models to examine the relationship of bird diversity and communities to grazing systems at the management unit scale, and we used simulations to combine empirical data from ≥1 grazing system into virtual landscapes to test the hypothesis that multiple grazing systems would result in greater heterogeneity. The 5 most common avian species made up 84% of observations (28 species), and songbird richness was 5–6 species/7.06 ha at 53% of our plots. Variation in each of the diversity measures (Shannon diversity range = 0.41–2.2, Simpson's diversity range = 0.24–0.88) was best explained by the previous dormant season's stocking rate, and richness declined by about 1 species/plot with an increase in 1 animal unit month (AUM)/ha. Songbird community structure showed the most variance between management unit, but grazing system explained little community variation. None of the simulated landscapes consistently had greater structural heterogeneity of visual obstruction reading, litter depth, and cover of bare ground than others, and there was a limited level of heterogeneity overall in the simulated landscapes. In contrast to our predictions, a variety of grazing systems did not increase heterogeneity of vegetation structure across the landscape. Thus, conservation practitioners should encourage the use of other strategies to create structural heterogeneity, such as prescribed fires and extreme stocking rates, which will support a diverse grassland songbird community (i.e., a greater variety of bird species) across the landscape. © 2020 The Wildlife Society.

Model Test Study on the Influence of Tunnel Construction on Existing Pipeline Under the Condition of Pipeline Leakage

An indoor model test was carried out to study the influence of tunnel construction on the existing pipelines in the case of water leakage. The results showed that when the tunnel depth was deep, the pipeline was simultaneously deformed with the soil. However, when the tunnel depth was shallow, the separation of the pipeline and soil become more obvious with the increase in leakage scale. As the ground depth increased, the ground settlement above the pipeline increased first and then decreased. As the leakage scale enlarged, the position of the maximum ground settlement gradually moved downward, and the range was within 1.5–2.5 times of the pipeline diameter from the top of the pipeline. Under the condition of the no water leakage, the pipeline displacement was less than the surface settlement; therefore, it is safe to replace the pipeline displacement with surface settlement for analysis, while under the condition of the water leakage, the situation was opposite, and it is dangerous to replace the pipeline displacement with surface settlement. Based on the test results, the relation between pipeline displacement and surface settlement was established.

Evaluation of Applicability of Deep Cement Mixing Method as Soft-Ground Improvement for Reinforced Subgrade for Railways

The deep cement mixing method, as a means for soft-ground improvement, was applied to achieve a short construction period for reinforced subgrade for railways (RSR). The RSR was modeled using the finite-element method for the parametric study of three kinds of its height. The parameters for the numerical analysis were the improvement ratio, and the width and depth of the soft ground. On the basis of the analysis results, in the case of 10-m-high RSR, we assured residual and differential settlements. Furthermore, the horizontal displacements were under the control limits by satisfying both the condition of the total improvement of soft layers by the range of RSR wall foundation and the improvement ratio of 54%. Keywords: DCM, RSR, Numerical Analysis, Applicability Evaluation

Heat transfer in the ground with a horizontal heat exchanger installed – Long-term thermal effects

Heating and cooling of buildings using heat pumps coupled with ground heat exchangers (GHE) causes changes in the ground temperature. Long-term temperature changes, regardless of cyclical changes, can occur in the ground depending on the relation between the extracted and supplied heat from/to the ground when a horizontal GHE coupled with a heat pump is installed in the ground. Determining the size and direction of these changes is the main objective of this work. A mathematical model of the heat transfer process was developed and temporal changes of the ground temperature, temperature profiles in the ground and heat fluxes in various conditions of heat extraction and supplying were determined. It was found, that changes in annually averaged temperature of the ground in the initial period of exchanger operation concern only the subsurface layer. In the following years, these temperatures in this layer do not change further. The longer the operation time of the exchanger, the annually averaged temperature changes expand their range to larger ground depths. The concept of sol-air-evaporation temperature is used in the model. This allowed the description of heat transfer between the ground and the environment with a simple equation analogous to the heat transfer equation.

Distribution characteristics of circular grounding ground potential in HVDC transmission system

This paper presents a model of double-ring type grounding pole unequal depth embedding for high-voltage direct current (HVDC) transmission system; and introduces calculation formula of DC ground potential distribution when double-ring type grounding pole is unequal buried. Furthermore the ground potential distribution and stride voltage level around the grounding pole and influence of grounding depth and soil parameters on the current field are discussed in this paper. The electric field zoning model of the ring current source is established by using the power system grounding pole analysis software CDEGS to verify the feasibility of this method. As the model is able to make the grounding current overflow density and potential distribution as uniform as possible, there is no serious local current concentration.

Lateral thermal influences of roadway and railway embankments in permafrost zones along the Qinghai-Tibet Engineering Corridor

Abstract In permafrost zones, the ground thermal regime beneath and around foundations is of great importance to long-term stability and integrity of engineering infrastructures. In this study, ground temperatures beneath and around embankments of the Qinghai-Tibet Highway (QTH) and the Qinghai-Tibet Railway (QTR) were observed at two profiles in continuous permafrost zones on the Qinghai-Tibet Plateau. The lateral thermal influences of the embankments on natural ground in the vicinity were analyzed based on the field observed data. The results indicated that the lateral thermal influence of the QTH and QTR embankments on shallow ground in the vicinity was very slight. The permafrost table depth or freeze-thaw process in the shallow ground near the embankments was mainly determined by the ground surface conditions. Different from the case of shallow ground, the lateral thermal influence of the QTH embankment on the permafrost in the vicinity was significant. Based on the permafrost temperature distribution at −10 m depth, the scopes of the lateral thermal influence of the QTH embankment calculated from the embankment shoulder were as much as 30–40 m at the two observation profiles. Whereas, the lateral thermal influence of the QTR embankment on the permafrost in the vicinity was slight. Because the QTR was constructed using cooling method of crushed rock embankment at the two profiles, the underlying permafrost either maintained well in thermal regime or experienced a slight cooling. The factors affecting the scope of the lateral thermal influences of embankments on permafrost in the vicinity were discussed at the end of the paper, as well as the related mitigation method. This study provides information that could aid engineering design of linear transportation projects and the assessment of environmental impacts in permafrost zones.

Numerical determination of temperature distribution in heating network

This paper presents the determination of the heat losses of the pre-insulated pipe and twin pipe in the heating network. The paper compares the heat losses calculated by using the analytical solution (1D model) and numerical model (2D model) based on the Finite Element Method. The developed numerical model considered undisturbed ground temperature at various depths. Therefore, it allowed to study the effect of temperature distribution at various ground depths on heat losses in heating network. Various variants of insulation are considered including standard, plus and plus-plus types for pre-insulated tubes. The remaining heat loss calculation is based merely on temperature levels and thermal resistance factors (in the ground), determined by the pipe dimensions and materials. The differences in calculated heat losses by analytical and numerical model do not exceed 10%.

Understanding the Permafrost–Hydrate System and Associated Methane Releases in the East Siberian Arctic Shelf

This paper summarizes current understanding of the processes that determine the dynamics of the subsea permafrost–hydrate system existing in the largest, shallowest shelf in the Arctic Ocean; the East Siberian Arctic Shelf (ESAS). We review key environmental factors and mechanisms that determine formation, current dynamics, and thermal state of subsea permafrost, mechanisms of its destabilization, and rates of its thawing; a full section of this paper is devoted to this topic. Another important question regards the possible existence of permafrost-related hydrates at shallow ground depth and in the shallow shelf environment. We review the history of and earlier insights about the topic followed by an extensive review of experimental work to establish the physics of shallow Arctic hydrates. We also provide a principal (simplified) scheme explaining the normal and altered dynamics of the permafrost–hydrate system as glacial–interglacial climate epochs alternate. We also review specific features of methane releases determined by the current state of the subsea-permafrost system and possible future dynamics. This review presents methane results obtained in the ESAS during two periods: 1994–2000 and 2003–2017. A final section is devoted to discussing future work that is required to achieve an improved understanding of the subject.

Experimental validation of horizontal air-ground heat exchangers (HAGHE) for ventilation systems

A large part of primary energy is used for heating and cooling the buildings. The exploitation of renewable resources in the building sector is still critical to ensure a high level of energy and environmental sustainability.Nowadays, a great attention is focused on geothermal energy, which reduces heating and cooling in buildings, allowing natural pre-heating and pre-cooling of the inlet air.The effect of different burial depth and thermal conductivity of ground on thermal performance of HAGHE under transient conditions has been analyzed. The results show that the transient thermal performance of HAGHE is independent from the thermal conductivity of the ground but is dependent on burial depth.In this work, it is presented the experimental validation of a mathematical model implemented by the CFD Fluent for the simulation of heat exchange that takes place within a HAGHE for geothermal heat pumps. The validation of the model is based on a comparison between the experimental data, obtained from the software, and real data, for a HAGHE located in the town of Rubiana (Turin-Italy).

Relationship between subsurface damage depth and breaking strength for brittle materials

Subsurface damages (SSD) induced by lapping strongly influence performances of optical components. However, to date, a wide variety of destructive and non-destructive techniques for measuring the SSD depth have been explored. In the present study, a novel destructive technique was proposed based on breaking strength of the lapped materials. The proposed technique relates the length of median cracks, formed through the Vickers indentation test, and the breaking strength of the indented samples. With this technique, subsurface damage depth can be practically evaluated via measuring breaking strength of lapped samples. The subsurface damage depth and surface roughness of ground and lapped BK7 glass were measured by the bonded interface sectioning technique and contacting profilometer, respectively. In order to validate the feasibility of the proposed technique, the values of SSD depth obtained by the calibration curve were compared with the values of SSD depth measured by the bonded interface sectioning technique. The obtained results are in concordance in the both used methods, which prove the efficiency of our technique to estimate the SSD depth of brittle materials.

Thermodynamic analysis of cryogenic vacuum cooling of superconducting cables

This paper presents a thermodynamic analysis of cryogenic vacuum cooling of superconducting cables in a specific practical application to achieve the characteristic critical temperature where the electrical resistance of the superconducting cables becomes theoretically zero, which results in no heat generation. The characteristic critical temperature (where the electrical resistance of the superconductor becomes zero) of the superconducting cable used in the project is around −200 °C and it is operating with only 6% losses. To reach the necessary temperature liquid nitrogen is used in the system, the refrigerant is cooled with the use of a vacuum chamber pumped by a vacuum pump to decrease the boiling point of the liquid nitrogen (−196 °C at 1 atm). The vacuum chamber is kept at −209 °C, which is one degree less than the freezing point of liquid nitrogen (−210 °C at 1 atm). The refrigeration system is analyzed in terms of energy and exergy methodologies to evaluate the performance of the vacuum chamber. Also, the effects of various system parameters, such as ground depth, ambient temperature, wire diameter and ground type are examined. The energy and exergy efficiencies of the overall system are calculated as 79.37% and 66.14%, respectively.

Field study on swelling-shrinkage response of an expansive soil foundation under high-speed railway embankment loads

This paper presents a comprehensive field investigation of the swelling-shrinkage behavior of an expansive soil ground under high-speed railway embankment loads. In this study, a test site close to the Kunming-Nanning high-speed railway (KNHR) was chosen for the construction of four full-scale field test facilities for artificially soaking the expansive soil ground. Three of the facilities consist of embankments of three different heights, while the fourth facility is for a series of plate load swelling tests. All the test embankments were fully instrumented to monitor the ground deformation and the changes in volumetric water content profiles of the foundations. The full-scale field tests were complemented by a detailed site investigation comprised of cone penetration tests (CPTs), standard penetration tests (SPTs) and a comprehensive laboratory characterization of intact expansive soil samples retrieved from the test site. The results obtained from the laboratory and field tests show that the swelling behavior of the expansive soil ground mainly depends on the embankment load. By properly designing the embankment height and considering the maximum swelling pressure the expansive ground could induce, the heave of the embankment could be controlled efficiently. The measured displacements at the ground surface are well correlated with the evolution of measured volumetric water contents within a ground depth of around 4.5 m. The majority of these displacements occurred when the ground was approaching saturation along both wetting and drying paths. Finally, a simple method based on one-dimensional test results was proposed, and a good performance was shown in predicting the heave or settlement of embankments over an expansive soil ground upon wetting and drying.

DIFFERENT BEHAVIOUR OF CIRCULAR AND RECTANGULAR TUNNELS UNDER THE IMPACT OF EARTHQUAKES: A CASE STUDY FROM THE TUNNEL OF HANOI METRO SYSTEM

Currently, the metro system is built in Hanoi, the capital of Vietnam. Hanoi's metro system wasdesigned to be shallow that of near-surface (with an average depth of ground is H = 20 m). Hanoi is located inthe Northern part of Vietnam, where it can be influenced by the highest magnitude of earthquakes is up to Mw= 6.5 Richter, so the study of the effects of earthquakes to the tunnel's stability in the Hanoi metro system isnecessary. The paper studied and calculated for two cases of the tunnel’s cross-section of the Hanoi metrosystem is circular and rectangular under effects of the earthquake, this has been the strongest earthquake mayhave the impact to Hanoi. Based on the results obtained, the paper has given comments on the effects ofearthquakes to tunnel’s stability in studies of two case and given suggests about the cross-section shape of thetunnel in Hanoi metro system that may be used to under the effect of the earthquakes.

Development of a Simplified Regression Equation for Predicting Underground Temperature Distributions in Korea

The Korea Meteorological Administration (KMA) measures outdoor temperature and ground surface temperature at 95 observation points, but monthly ground temperatures by depth, which are important for using geothermal heat, are only provided for nine points. Since the ground temperature is known in the vicinity of only nine observation points, it is very difficult to predict underground temperature in the field. This study develops a simplified regression equation for predicting underground temperature distributions, compares the prediction results with the experimental data of Korea’s representative areas and the data measured in this study, and examines the validity of the developed regression equation. The regression equation for predicting temperature amplitudes at ground depths of 1.0, 3.0, and 5.0 m was derived using the amplitude ratio of outdoor temperature and surface temperature provided by KMA at nine points in Korea from 2006 to 2015. The coefficient of determination was as high as 0.93 (95% confidence level). In addition, the field-measured ground temperature distribution at a depth of 3 m was in good agreement with the predicted ground temperature distribution in Changwon districts for the whole of 2017.

Occurrence of Anisakis and Hysterothylacium larvae in commercial fish from Balearic Sea (Western Mediterranean Sea).

This study investigates the occurrence of anisakids and raphidascarids in commercial fish from Balearic Sea (Western Mediterranean). A total of 335 fish including 19 black anglerfish (Lophius budegassa), 33 white anglerfish (L. piscatorius), 129 European hake (Merluccius merluccius), 30 red mullet (Mullus barbatus), and 124 striped mullet (M. surmuletus) were examined using enzymatic digestion. A total of 948 nematode larvae were isolated (prevalence 52.53%) being the highest prevalence observed in striped mullet. Forty-six larvae were identified using molecular analyses which included PCR and sequencing of the 629-bp fragment of mitochondrial cox2 gene region. Anisakis pegreffii (80.43%), A. physeteris (8.69%), Hysterothylacium fabri (6.52%), and A. simplex (4.35%) were detected based on molecular analyses of larvae. Total nematode prevalence was positively correlated with weight, length, condition factor, and maturity stage of the host and also with fishing ground depth. Statistical differences between total nematode prevalence and geographical sector of capture were observed when fishing hauls were grouped according to the abundance of sperm whales or common bottlenose dolphins. The results also corroborate that fishing water depth may play an important role in anisakid and raphidascarid parasitization.

Estimating Seasonally Frozen Ground Depth From Historical Climate Data and Site Measurements Using a Bayesian Model

AbstractWe develop a Bayesian model to predict the maximum thickness of seasonally frozen ground (MTSFG) using historical air temperature and precipitation observations. We use the Stefan solution and meteorological data from 11 stations to estimate the MTSFG changes from 1961 to 2016 in the Yellow River source region of northwestern China. We employ an antecedent precipitation index model to estimate changes in the liquid soil water content. The marginal posterior probability distributions of the antecedent precipitation index parameters are estimated using Markov chain Monte Carlo sampling methods. We compare the results of our stochastic method with those obtained from the traditional deterministic method and find that they are consistent in general. The stochastic approach is effective for estimating the historical changes in the frozen ground depth (root‐mean‐square errors = 0.13–0.35 m), and it provides more information on model uncertainty regarding soil moisture variations. Additionally, simulation shows that the MTSFG has decreased by 0.31 cm per year over the last 56 years on the northeastern Qinghai‐Tibet Plateau. This decrease in frost depth accelerated in the 1990s and 2000s. Considering the lack of data on seasonally frozen soil monitoring, the Bayesian method provides a pragmatic approach to statistically model frozen ground changes using available meteorological data.

A simple temperature-based method to estimate heterogeneous frozen ground within a distributed watershed model

Abstract. Frozen ground can be important to flood production and is often heterogeneous within a watershed due to spatial variations in the available energy, insulation by snowpack and ground cover, and the thermal and moisture properties of the soil. The widely used continuous frozen ground index (CFGI) model is a degree-day approach and identifies frozen ground using a simple frost index, which varies mainly with elevation through an elevation–temperature relationship. Similarly, snow depth and its insulating effect are also estimated based on elevation. The objective of this paper is to develop a model for frozen ground that (1) captures the spatial variations of frozen ground within a watershed, (2) allows the frozen ground model to be incorporated into a variety of watershed models, and (3) allows application in data sparse environments. To do this, we modify the existing CFGI method within the gridded surface subsurface hydrologic analysis watershed model. Among the modifications, the snowpack and frost indices are simulated by replacing air temperature (a surrogate for the available energy) with a radiation-derived temperature that aims to better represent spatial variations in available energy. Ground cover is also included as an additional insulator of the soil. Furthermore, the modified Berggren equation, which accounts for soil thermal conductivity and soil moisture, is used to convert the frost index into frost depth. The modified CFGI model is tested by application at six test sites within the Sleepers River experimental watershed in Vermont. Compared to the CFGI model, the modified CFGI model more accurately captures the variations in frozen ground between the sites, inter-annual variations in frozen ground depths at a given site, and the occurrence of frozen ground.