Research

26 pages, 5355 KiB

Open AccessArticle

Experimental and Theoretical Study of the Influence of Saline Soils on Frozen Wall Formation

by Sergey Bublik, Mikhail Semin, Lev Levin, Andrey Brovka and Ivan Dedyulya

Appl. Sci. 2023, 13(18), 10016; https://doi.org/10.3390/app131810016 - 05 Sep 2023

Viewed by 663

This paper examines the impact of salinity on the thermophysical properties of soils during artificial freezing. It focuses on analyzing heat and mass transfer in saline soils for constructing a frozen wall around a mineshaft at a potash salt deposit. The presence of [...] Read more.

This paper examines the impact of salinity on the thermophysical properties of soils during artificial freezing. It focuses on analyzing heat and mass transfer in saline soils for constructing a frozen wall around a mineshaft at a potash salt deposit. The presence of salts in the groundwater near the contact point with water-protective strata is common in these deposits. Experimental studies were conducted on clay, chalk, and sand to understand the effect of salinity on the freezing temperature, unfrozen water content, specific heat capacity, and thermal conductivity of wet soil. These findings were used to simulate heat and mass transfer in saline soils using a one-dimensional model. The technique of circumferential averaging was introduced to account for the thermal impact of freeze pipes. The results indicate that higher soil salinity leads to a faster decrease in soil temperature under freezing conditions, although this dependence is weak for clay. This study also revealed that an increase in initial salinity results in a reduction in the thickness of the frozen wall. It was found that, for chalk and sand, there exists a range of initial salinity during which the frozen wall’s thickness is almost independent of the initial salinity. Full article

(This article belongs to the Special Issue Artificial Ground Freezing Technology)

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19 pages, 6161 KiB

Open AccessArticle

Research on the Elastoplastic Theory and Evolution Law of Plastic Zone Contours of Horizontal Frozen Walls under Nonuniform Loads

by Shilong Peng, Yuhao Xu, Guangyong Cao and Lei Pei

Appl. Sci. 2023, 13(16), 9398; https://doi.org/10.3390/app13169398 - 18 Aug 2023

Cited by 1 | Viewed by 669

Abstract

The study of the changes in stress and deformation of frozen walls during excavation has always been a hot topic in underground freezing engineering, and the size of the plastic zone is an important basis for evaluating the stability of frozen walls. In [...] Read more.

The study of the changes in stress and deformation of frozen walls during excavation has always been a hot topic in underground freezing engineering, and the size of the plastic zone is an important basis for evaluating the stability of frozen walls. In response to the shortcomings in the current design of horizontal frozen walls, based on the internal excavation unloading conditions of the frozen wall in artificial ground freezing, an elastoplastic mechanical model for the interaction between a circular horizontal freezing wall and unfrozen soil mass is established under nonuniform loads to obtain the corresponding solutions for stress and displacement in the system. In this study, considering the shear stress of the plastic zone, the method for solving the traditional plastic zone contour equation is modified; consequently, the modified solution of the contour equation of the plastic zone for the frozen wall is obtained. Using this theoretical solution, the influence of the external load

p_{0}

and the lateral pressure coefficient

λ

on the contour line of plastic zone and tensile stress zone are analyzed by combining the project case, the calculation results show that: the

λ = 0.485

is the critical point where the inner edge of the frozen wall just happens to have tensile stress. When

λ < 0.485

, the tensile stress zone is inevitable in the inner edge of the frozen wall vertical direction, and its range is only related to

λ

and increases with the decrease of

λ

. The

p_{0}

only affects the magnitude of tensile stress in the region, but does not affect its range. At this time, the frozen wall compression plastic zone contour evolves from crescent shaped to ear shaped with the increase of

p_{0}

. When

0 . 485 < λ < 0.61

, there will be no tensile stress zone, the frozen wall compression plastic zone contour also evolves from crescent shaped to ear shaped with the increase of

p_{0}

. When

λ > 0.61

, there will be also no tensile stress zone, with the increase of

p_{0}

, the compression plastic zone contour evolves from the crescent shaped in the horizontal direction to the elliptical shaped, and there is no ear-shaped plastic zone in the whole evolution process. Based on our results, we show that our method can be used to provide a theoretical basis for the stability evaluation and parameter (thickness) design calculation of horizontal frozen walls under nonuniform loads. Full article

(This article belongs to the Special Issue Artificial Ground Freezing Technology)

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17 pages, 2360 KiB

Open AccessArticle

Partitioning of Dissolved Organic Carbon, Major Elements, and Trace Metals during Laboratory Freezing of Organic Leachates from Permafrost Peatlands

by Irina S. Ivanova, Liudmila S. Shirokova, Jean-Luc Rols and Oleg S. Pokrovsky

Appl. Sci. 2023, 13(8), 4856; https://doi.org/10.3390/app13084856 - 12 Apr 2023

Cited by 1 | Viewed by 1238

Abstract

Climate change is likely to modify the freezing–thawing cycles in soils and surface waters of permafrost-affected and subarctic regions. However, the change of solution chemical composition during ice formation and the evolution of the remaining fluids remain very poorly known. Towards a better [...] Read more.

Climate change is likely to modify the freezing–thawing cycles in soils and surface waters of permafrost-affected and subarctic regions. However, the change of solution chemical composition during ice formation and the evolution of the remaining fluids remain very poorly known. Towards a better understanding of dissolved (<0.45 µm) organic carbon, as well as major and trace element behavior in permafrost peatland environments, here we performed laboratory freezing of peat leachates, from complete freezing to complete thawing, in order to quantify the partitioning of solutes between the aqueous solution and the remaining ice. Freezing experiments were conducted, with and without polyurethane insulation. Two main types of experiments involved (i) progressive freezing, when we started from liquid leachates (filtered <0.45 µm) and allowed them to freeze at −18 °C, and (ii) progressive thawing, where first, we froze solid a series of <0.45 µm filtered leachates and then monitored their thawing at room temperature, 20 °C. We hypothesized the existence of two main groups of solutes, behaving conservatively or non-conservatively during freezing, depending on their incorporation into the ice or their ability to coagulate in the form of insoluble minerals or amorphous materials in the fluid phase. An unexpected result of this work was that, despite a sizable degree of element concentration in the remaining fluid and possible coagulation of organic, organo-mineral, and inorganic compounds, the freezing and subsequent thawing produced final concentrations of most solutes which were not drastically different from the initial concentrations in the original leachates prior to freezing. This demonstrates the high stability of dissolved (<0.45 µm) organic carbon, iron, aluminum, and some trace metals to the repetitive freezing and thawing of surface waters in permafrost peatlands. Full article

(This article belongs to the Special Issue Artificial Ground Freezing Technology)

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19 pages, 9250 KiB

Open AccessArticle

Mechanical Properties and Constitutive Relationship of Cretaceous Frozen Sandstone under Low Temperature

by Siyuan Shu, Zhishu Yao, Yongjie Xu, Chen Wang and Kun Hu

Appl. Sci. 2023, 13(7), 4504; https://doi.org/10.3390/app13074504 - 02 Apr 2023

Cited by 3 | Viewed by 1109

Abstract

During the construction of coal mine shafts through Cretaceous water-rich stratum using the freezing method, the frozen shaft lining can break and lose stability. Hence, it is necessary to examine the mechanical properties and constitutive relationship of Cretaceous water-rich sandstone under the effect [...] Read more.

During the construction of coal mine shafts through Cretaceous water-rich stratum using the freezing method, the frozen shaft lining can break and lose stability. Hence, it is necessary to examine the mechanical properties and constitutive relationship of Cretaceous water-rich sandstone under the effect of surrounding rocks. To this end, in this work, the mechanical properties of red sandstone at different confining pressures and freezing temperatures were examined by using a ZTCR-2000 low-temperature triaxial testing system, wherein the 415–418 m deep red sandstone in the Lijiagou air-return shaft of Wenjiapo Mine was taken as the research object. The test results indicated that the stress–strain curves of rock under triaxial compression and uniaxial compression presented four stages: pore compaction, elastic compression, plastic yield, and post-peak deformation. The difference between the two cases was that the post-peak curve of the former was abrupt, while the latter exhibited a post-peak strain softening section. As the freezing temperature was constant, with the raise in the confining pressure, the elastic modulus and peak strength of the rock rose linearly, while the Poisson’s ratio decreased quadratically. As the control confining pressure was constant, the elastic modulus and rock’s peak strength increased with the decrease in the temperature, and under the condition of negative temperature, the two parameters were linearly correlated with the temperature, while the Poisson’s ratio showed the opposite trend. The two-part Hooke’s model and the statistical damage model based on Drucker–Prager (D-P) yield criterion were used to establish the stress–strain relationship models before and after the rock yield point, optimize the model parameters, and optimize the junction of the two models. The results revealed that the optimized model curve was in good agreement with the experimental curve, which suggests that the proposed model can accurately describe the stress–strain characteristics of rock under three-dimensional stress. This verified the feasibility and rationality of the proposed model for examining the constitutive relationship of rocks. Full article

(This article belongs to the Special Issue Artificial Ground Freezing Technology)

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14 pages, 3888 KiB

Open AccessArticle

Facies and Origin of Tufa Deposits from the Gostilje River Basin and the Sopotnica River Basin (SW Serbia)

by Natalija Batoćanin, Wojciech Wróblewski, Ivana Carević, Uroš Durlević, Violeta Gajić and Aleksandar Valjarević

Appl. Sci. 2023, 13(5), 3190; https://doi.org/10.3390/app13053190 - 02 Mar 2023

Viewed by 1299

Abstract

Tufa accumulations from the Gostilje River Basin and the Sopotnica River Basin in SW Serbia are represented by both active and fossil tufa precipitates. The aim of this study is to distinguish and describe different tufa facies and to determine the environmental conditions, [...] Read more.

Tufa accumulations from the Gostilje River Basin and the Sopotnica River Basin in SW Serbia are represented by both active and fossil tufa precipitates. The aim of this study is to distinguish and describe different tufa facies and to determine the environmental conditions, based on stable isotope data. We also compare our analysis with other tufa deposits in Europe. Four facies are distinguished: moss tufa, algal tufa, stromatolitic laminated tufa, and phytoclastic tufa. The dominant constituent of all tufa samples is low Mg-calcite, whereas the presence of sylvite is noted in two samples from the Gostilje River Basin. The δ¹⁸O values range from −9.07‰ to −10.79‰ (mean value: −9.81‰), while the δ¹³C values range from −6.50‰ to −10.34‰ (mean values −9.01‰). The stable isotope values (δ¹³C and δ¹⁸O) indicate that these tufa deposits were precipitated from cold, ambient water supported by CO₂ of an atmospheric origin. We emphasize that this is the first data about stable isotope analyses of tufa deposits from Serbia. Full article

(This article belongs to the Special Issue Artificial Ground Freezing Technology)

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18 pages, 4167 KiB

Open AccessArticle

Analysis of Elastoplastic Mechanical Properties of Non-Uniform Frozen Wall Considering Frost Heave

by Bin Wang, Shenwei Liang, Yi Cao, Chuanxin Rong and Shengmin Yu

Appl. Sci. 2023, 13(2), 1038; https://doi.org/10.3390/app13021038 - 12 Jan 2023

Viewed by 1071

Abstract

The aim of this study was to analyze the force and deformation law of an artificial frozen wall. Thus, the frost heave coefficient was introduced to describe the frost heave characteristics, and the frozen wall was regarded as a heterogeneous material whose material [...] Read more.

The aim of this study was to analyze the force and deformation law of an artificial frozen wall. Thus, the frost heave coefficient was introduced to describe the frost heave characteristics, and the frozen wall was regarded as a heterogeneous material whose material properties changed in a parabolic pattern with the radius. The elastoplastic stress and displacement formulas of a non-uniform frozen wall considering frost heave characteristics were derived according to different strength criteria. Consequently, the derived formulas were used to calculate and analyze the mechanical characteristics of the artificial frozen wall. The results showed that the radial stress of the frozen wall changed linearly, whereas the circumferential stress change followed a parabolic pattern after considering the non-uniform characteristics. Moreover, the displacement of the outer edge of the frozen wall was always greater than that of the inner edge, and the displacement of the inner edge changed with the increasing temperature, significantly greater than that of the outer edge. When the frozen wall was in the elastic state, its displacement caused by frost heave was constant. When the frozen wall entered the elastic–plastic state, the displacement of its inner edge caused by frost heave increased with the increase in the radius of the plastic zone, whereas the displacement of the outer edge caused by frost heave decreased with the increase in the radius of the plastic zone. Full article

(This article belongs to the Special Issue Artificial Ground Freezing Technology)

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19 pages, 6955 KiB

Open AccessArticle

Research on Frost Heaving Distribution of Seepage Stratum in Tunnel Construction Using Horizontal Freezing Technique

by Mengkai Li, Haibing Cai, Zheng Liu, Changqiang Pang and Rongbao Hong

Appl. Sci. 2022, 12(22), 11696; https://doi.org/10.3390/app122211696 - 17 Nov 2022

Cited by 1 | Viewed by 1180

Abstract

During the horizontal freezing construction of a subway tunnel, the delay of the closure of the frozen wall occurs frequently due to the existence of groundwater seepage, which can be directly reflected by a freezing temperature field. Accordingly, the distribution of ground surface [...] Read more.

During the horizontal freezing construction of a subway tunnel, the delay of the closure of the frozen wall occurs frequently due to the existence of groundwater seepage, which can be directly reflected by a freezing temperature field. Accordingly, the distribution of ground surface frost heaving displacement under seepage conditions will be different from that under hydrostatic conditions. In view of this, this paper uses COMSOL to realize the hydro–thermal coupling in frozen stratum under seepage conditions, then, the frost heaving distribution of seepage stratum in tunnel construction using horizontal freezing technique is researched considering the ice–water phase transition and orthotropic deformation characteristics of frozen–thawed soil by ABAQUS. The results show that the expansion speed of upstream frozen wall is obviously slower than that of the downstream frozen wall, and the freezing temperature field is symmetrical along the seepage direction. In addition, the ground frost heaving displacement field is asymmetrically distributed along the tunnel center line, which is manifested in that the vertical frost heaving displacement of the upstream stratum is less than that of the downstream stratum. The vertical frost heaving displacement of the ground surface decreases with the increase in tunnel buried depth, but the position of the maximum value remains unchanged as the tunnel buried depth increases. The numerical simulation method established in this paper can provide a theoretical basis and design reference for the construction of a subway tunnel in a water-rich stratum under different seepage using the artificial freezing technique. Full article

(This article belongs to the Special Issue Artificial Ground Freezing Technology)

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15 pages, 6223 KiB

Open AccessArticle

An Analytical Solution to Steady-State Temperature Field in the FSPR Method Considering Different Soil Freezing Points

by Yin Duan, Chuanxin Rong, Xianwen Huang and Wei Long

Appl. Sci. 2022, 12(22), 11576; https://doi.org/10.3390/app122211576 - 15 Nov 2022

Cited by 1 | Viewed by 917

Abstract

Taking the freeze-sealing pipe roof method (FSPR) adopted in the Gongbei Tunnel project as the background, this study develops a simplified calculation model by considering different soil freezing points, tube layout, and site conditions. The analytical solution of the linear single row tubes [...] Read more.

Taking the freeze-sealing pipe roof method (FSPR) adopted in the Gongbei Tunnel project as the background, this study develops a simplified calculation model by considering different soil freezing points, tube layout, and site conditions. The analytical solution of the linear single row tubes is then used to formulate the analytical solution of the freezing temperature field of two kinds of linear single row tubes, with equal spacing in the image plane. This is achieved through conformal mapping and the variable separation method. Finally, the analytical solution to the steady-state temperature field of FSPR in the object plane is obtained. The numerical solutions of common freezing parameters in freezing engineering are analyzed to evaluate the accuracy of the analytical solution, and the influence of parameter differences on the freezing temperature field are also discussed, to provide a theoretical reference for popularization and application of similar construction methods. Full article

(This article belongs to the Special Issue Artificial Ground Freezing Technology)

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18 pages, 9337 KiB

Open AccessArticle

The Quantification and Evolution of Particle Characteristics of Saturated Silt under Freeze–Thaw Cycles

by Jie Zhou, Zeyao Li and Wansheng Pei

Appl. Sci. 2022, 12(21), 10703; https://doi.org/10.3390/app122110703 - 22 Oct 2022

Cited by 1 | Viewed by 1180

Abstract

Freeze–thaw action is a complicated process. How it affects particle characteristics of saturated silt may provide a much clearer understanding of its internal mechanism. A series of specific apparatus were developed for sample reconstitution, including sand pluviation device, freeze–thaw device, and special sampling [...] Read more.

Freeze–thaw action is a complicated process. How it affects particle characteristics of saturated silt may provide a much clearer understanding of its internal mechanism. A series of specific apparatus were developed for sample reconstitution, including sand pluviation device, freeze–thaw device, and special sampling device. After reconstituting samples by sand pluviation method and a specific parameter-controlled freeze–thaw testing, scanning electron microscope (SEM) and laser scattering and transmissometry (LST) tests were conducted to explore the particle characteristics of silt under freeze–thaw cycles. The test results show that freeze–thaw action could probably induce the particles’ (60–200 μm) breakage, also affecting the clay particles’ (less than 5 μm) aggregation. With the increase of freeze–thaw times, freeze–thaw action on the particle impact decreases. The larger the effective confining pressure, the lower the freezing temperature, greater the compaction degree, and higher the fine content, which can all aggravate the effects of freeze–thaw action on silt particles. Finally, two characteristic evolution modes of particle structure under freeze–thaw cycles have been inferred based on particle interaction during the freeze–thaw process, which could provide a reference for long-term durability evaluation of pavements in cold regions. Full article

(This article belongs to the Special Issue Artificial Ground Freezing Technology)

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14 pages, 7946 KiB

Open AccessArticle

Analysis of Freeze–Thaw Response and Pore Characteristics of Artificially Frozen Soft Soil under Combined Formation Seepage

by Jie Zhou, Zhongqiu Guo, Chuanhe Wang, Zeyao Li, Huade Zhou and Wansheng Pei

Appl. Sci. 2022, 12(20), 10687; https://doi.org/10.3390/app122010687 - 21 Oct 2022

Cited by 2 | Viewed by 1272

Abstract

Artificial ground freezing (AGF) is a widely used method in coastal tunnel construction and reinforcement. With more and more underground construction in coastal areas, clay–sand combined formation, which is common in coastal areas, brings more challenges to AGF. In this paper, the frost–thaw [...] Read more.

Artificial ground freezing (AGF) is a widely used method in coastal tunnel construction and reinforcement. With more and more underground construction in coastal areas, clay–sand combined formation, which is common in coastal areas, brings more challenges to AGF. In this paper, the frost–thaw characteristics of soft clay during AFG under the construction of combined formation seepage were studied by model test. It was found that the shape of the freezing curtain changed under the condition of seepage, and the water content of the upper soft soil layer decreased markedly after settlement. Subsequently the micro characteristics of melted soil by CT were also conducted for further mechanism analysis, and it was indicated that the distribution of CT number had obvious segmentation characteristics along the height. Finally, the 3D structure of melted clay was reconstructed, and a method was proposed to calculate freeze–thaw settlement through CT numbers. Full article

(This article belongs to the Special Issue Artificial Ground Freezing Technology)

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15 pages, 5986 KiB

Open AccessArticle

Orthogonal Test on the True Triaxial Mechanical Properties of Frozen Calcareous Clay and Analysis of Influencing Factors

by Chuan-Xin Rong, Zhi Wang, Yi Cao, Qing Yang and Wei Long

Appl. Sci. 2022, 12(17), 8712; https://doi.org/10.3390/app12178712 - 30 Aug 2022

Cited by 1 | Viewed by 1144

Abstract

In the Huainan and Huaibei mining areas, a layer of calcareous clay is buried deep in the surface soil layer (at approximately 400 m). This layer is in a high-stress state and is prone to freezing pipe fractures in the freezing method. To [...] Read more.

In the Huainan and Huaibei mining areas, a layer of calcareous clay is buried deep in the surface soil layer (at approximately 400 m). This layer is in a high-stress state and is prone to freezing pipe fractures in the freezing method. To obtain the true triaxial mechanical properties of this clay in its frozen state, this study conducted a cross test (L₁₆(4⁵)) to explore the change law of the strength of frozen calcareous clay under the influence of multiple factors. The results showed that the true triaxial stress–strain curve of frozen calcareous clay was divided into three stages: the strain within 0.5% showed linear elasticity. Under compressive stress, ice crystals and their cements were damaged or melted and shrank. At approximately 5%, they showed plastic hardening. The soil particles and ice crystals in the frozen soil recombined and became denser, resulting in irreversible deformation. As the compression progressed, cracks bred and swelled. The failure stage was manifested as strain hardening due to the test loading conditions. As the deformation increased, the stress also slightly increased. The consistent strength-influencing factors could be obtained through range and hierarchy analyses. The primary and secondary order of influence of σ₁ was the confining pressure σ₃, water content ω, temperature T, Bishop parameter b, and salt content ψ. The influence weight of each factor was quantitatively calculated. In the significance analysis, when the interaction was not considered, the effects of the pressure and moisture content on the strength were always significant. The effect of temperature was significant only when the significance level Ω > 0.05. The salt content and b value had no significant influence on the strength, and the significance of each factor followed the order of the results of the range analysis method and analytic hierarchy process; when considering the interaction, the interaction factors had different effects on the strength. When Ω > 0.01, the influence of factor A (temperature T) × B (water content ω) on the strength showed significance, even exceeding that of temperature. This demonstrated that when studying the strength characteristics of frozen soil, it is necessary to comprehensively consider the various factors and their interaction to more accurately characterize the mechanical behavior of frozen solids. Full article

(This article belongs to the Special Issue Artificial Ground Freezing Technology)

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18 pages, 5692 KiB

Open AccessArticle

Optimization of the Cooling Scheme of Artificial Ground Freezing Based on Finite Element Analysis: A Case Study

by Jun Hu, Ke Li, Yuwei Wu, Dongling Zeng and Zhixin Wang

Appl. Sci. 2022, 12(17), 8618; https://doi.org/10.3390/app12178618 - 28 Aug 2022

Cited by 3 | Viewed by 1248

Abstract

The present study was envisaged to evaluate the influence of different brine cooling schemes on the freezing process in the formation of sand-cobble strata in an underground connection aisle in Hohhot, China. The brine cooling schemes were set up by modifying the starting [...] Read more.

The present study was envisaged to evaluate the influence of different brine cooling schemes on the freezing process in the formation of sand-cobble strata in an underground connection aisle in Hohhot, China. The brine cooling schemes were set up by modifying the starting and ending brine temperatures in the construction of an underground connection aisle. Using ADINA finite element software, the simulation of the temperature field during the freezing process of the sand and pebble strata under three different schemes was performed. It was found that the freezing process was accelerated by lowering the freezing start temperature during the cooling process when the starting and ending brine temperatures remained unchanged. Furthermore, if the initial freezing temperature was changed, keeping the same freezing time at constant soil thermophysical parameters, the final effective thickness of the frozen wall was almost identical. Considering the same location of the temperature measurement points, the measured temperature of the inner and outer holes of the freezing curtain was found to be consistent with the numerical simulation, demonstrating the rationality of the numerical model. On the basis of this study, a brine cooling plan is proposed, which could serve as a reference for future construction. Full article

(This article belongs to the Special Issue Artificial Ground Freezing Technology)

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13 pages, 7491 KiB

Open AccessArticle

Experimental and Modeling of Residual Deformation of Soil–Rock Mixture under Freeze–Thaw Cycles

by Chao Wang, Jing Chen, Lilei Chen, Yue Sun, Zelei Xie, Guoan Yin, Minghao Liu and Anyuan Li

Appl. Sci. 2022, 12(16), 8224; https://doi.org/10.3390/app12168224 - 17 Aug 2022

Cited by 2 | Viewed by 1258

Abstract

Projects in seasonal frozen soil areas are often faced with frost heaving and thawing subsidence failure, and the foundation fill of most projects is a mixture of soil and rock. Therefore, taking soil–rock mixture with different rock contents as research objects, the residual [...] Read more.

Projects in seasonal frozen soil areas are often faced with frost heaving and thawing subsidence failure, and the foundation fill of most projects is a mixture of soil and rock. Therefore, taking soil–rock mixture with different rock contents as research objects, the residual deformation of soil–rock mixture under multiple freezing–thawing cycles is studied. In addition, the deep learning method based on the artificial neural network was pioneered combined with the freezing–thawing test of the soil–rock mixture, and the Long short-term memory (LSTM) model was established to predict the results of the freezing–thawing test. The LSTM model has been verified to be feasible in the exploration of the freeze–thaw cycle law of a soil–rock mixture, which can not only greatly reduce the period of the freeze–thaw test, but also maintain a high prediction accuracy to a certain extent. The study found that the soil–rock mixture will repeatedly produce frost heave and thaw subsidence under the action of freeze–thaw cycles, and the initial frost heave and thaw subsidence changes hugely. With the increase of the number of freeze–thaw cycles, the residual deformation decreases and then becomes steady. Under the condition that the content of block rock in the soil–rock mixture is not more than 80%, with the increase of block rock content, the residual deformation caused by the freeze–thaw cycle will gradually decrease due to the skeleton function of block rock, while the block rock content’s further increase will increase the residual deformation. Furthermore, the LSTM model based on an artificial neural network can effectively predict the freezing and thawing changes of soil–rock mixture in the short term, which can greatly shorten the time required for the freezing and thawing test and improve the efficiency of the freezing and thawing test to a certain extent. Full article

(This article belongs to the Special Issue Artificial Ground Freezing Technology)

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19 pages, 19095 KiB

Open AccessFeature PaperArticle

Evolution Law of Three-Dimensional Non-Uniform Temperature Field of Tunnel Construction Using Local Horizontal Freezing Technique

by Changqiang Pang, Haibing Cai, Rongbao Hong, Mengkai Li and Zhe Yang

Appl. Sci. 2022, 12(16), 8093; https://doi.org/10.3390/app12168093 - 12 Aug 2022

Cited by 3 | Viewed by 1081

Abstract

The formation quality of a frozen wall is one of the prerequisites for tunnel excavation using artificial ground freezing techniques. However, the non-uniformity of temperature distribution along the length direction of the freezing pipe is often ignored in the actual freezing engineering, which [...] Read more.

The formation quality of a frozen wall is one of the prerequisites for tunnel excavation using artificial ground freezing techniques. However, the non-uniformity of temperature distribution along the length direction of the freezing pipe is often ignored in the actual freezing engineering, which leads to a thin frozen wall at a local position that does not meet the design requirements. Therefore, exploring the evolution law of three-dimensional non-uniform freezing temperature fields is necessary. In this paper, a tunnel horizontal freezing model test system was established based on the similarity criterion of hydro–heat coupling, and the temperatures at three sections were tested using thermocouple temperature sensors. The results show that the temperature drop curves of measurement points suffer from three periods: steep drop, slow drop and tending to be stable. The temperature curves on the main and vice planes of the frozen wall all present a “V” type; specifically, the temperature on the axis plane is the lowest, while the temperature away from the axis plane is higher, and the temperature gradient outside the axis plane is greater than that inside. The frozen wall develops from frozen soil columns to a sector ring, and the average thickness of the frozen wall at three sections is 50.6, 40.7 and 75.1 mm after freezing for 60 min, respectively, which shows an obvious non-uniformity. The temperature distribution along the length of the freezing pipe is T = −0.000045z² + 0.0205z − 13.5125. The freezing temperature contours calculated by ABAQUS are basically consistent with those calculated by the model test after calling the temperature function of the freezing pipe wall. Full article

(This article belongs to the Special Issue Artificial Ground Freezing Technology)

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