Search Results (26)

In order to investigate the impact of freeze–thaw damage on sandstone under the coupling of ground stress and pore water pressure, three types of porous sandstone were subjected to freezing at different negative temperatures (−5 °C, −10 °C, −15 °C, and −20 °C). Subsequently, hydraulic coupling triaxial compression tests were conducted on the frozen and thawed sandstone. We analyzed the effects of porosity and freezing temperature on the mechanical properties of sandstone under hydraulic coupling and performed nuclear magnetic resonance tests on sandstone samples before and after freezing and thawing. The evolution of the pore structure in sandstone at various freezing and thawing stages was studied, and a statistical damage constitutive model was established to validate the test results. The results indicate that the stress–strain curves of sandstone samples under triaxial compression after a freeze–thaw cycle exhibit minimal changes compared to those without freezing at normal temperature. The peak deviator stress shows a decreasing trend with decreasing freezing temperature, particularly between −5 °C and −10 °C, and then gradually stabilizes. The elastic modulus of sandstone with different porosity decreases with the decrease in freezing temperature, and the decrease is more obvious in the range of −5 °C~−10 °C, decreasing by 2.33%, 6.11%, and 10.5%, respectively. Below −10 °C, the elastic modulus becomes similar to that at −10 °C, and the change tends to stabilize. The nuclear magnetic porosity of sandstone samples significantly increases after freezing and thawing. The smaller the initial porosity, the greater the rate of change in nuclear magnetic porosity after a freeze–thaw cycle. The effects of freeze–thaw damage on the T2 distribution of sandstone with different porosity levels vary. We established a statistical damage constitutive model considering the combined effects of freeze–thaw damage, ground stress, and pore water pressure. The compaction coefficient K was introduced into the constitutive model for optimization. The change trend of the theoretical curve closely aligns with that of the test curve, better characterizing the stress–strain relationship of sandstone under complex pressure environments. The research findings can provide a scientific basis for wellbore wall design and subsequent maintenance in complex environments. Full article

In the context of a main road area with significant traffic flow, posing challenges to constructing the freezing station on the ground, an innovative proposal suggests situating the freezing station at the station. This approach aims to facilitate construction at the same time for the connection aisle, tunneling, and track laying, thereby reducing the construction period; however, this will lead to a corresponding increase in the freezing pipeline distance. The theoretical analysis, numerical analysis, and integration with engineering practices were employed to examine the essential aspects and key technologies in the long-distance freezing design and construction, including the freezing hole construction, thermal insulation method of brine pipelines and tunnel segments, and technique program to retain the brine pressure and flow discharge, as well as the method to reduce the interplay of cross-construction. The validity of the construction program for the long-distance frozen excavation was finally evaluated based on onsite monitoring and theoretical analysis. The results show that the temperature of the brine in both the delivery and return pipelines first decreases linearly and then stabilizes gradually with freezing time, and the temperature difference is between 1 °C and 1.5 °C at the later freezing period. The temperature variation of the frozen wall is similar to that of brine in the delivery and return pipelines, and there is a good correlation between them. After the frozen wall encloses, the internal pressure of the frozen wall increases quickly, which can be effectively reduced to prevent wall cracking and breakage by regulating the pressure relief holes. The above theoretical analysis result shows that the average temperature of the frozen wall should be less than −9.7 °C when the designed thickness of the frozen wall is 2.2 m. The monitoring data indicates that the average temperature of the frozen wall reaches −13.9 °C, which satisfies the design requirement. The design and construction technology of long-distance freezing enhance the construction of the subway connection aisle. The novel method deviates from the conventional practice of establishing freezing stations within tunnels and offers valuable insight and guidance for comparable projects. Full article

The technology for freezing shaft sinking is widely used for shafts to pass through deep, unstable alluvia with the continuous exploitation of mineral resources. Due to the technique using the sectional excavation and shaft lining construction adopted in deep alluvia, the radial stress at the inner edge of a frozen wall is incompletely unloaded. In this paper, a mechanical model was established for a frozen wall with its inner edge radially incompletely unloaded. A parameter, α, expressing the degree of being unloaded was introduced, and then a new method of designing and calculating the thickness of the frozen wall was proposed. The range of parameter α was estimated based on the frozen wall–shaft lining interaction forces from field data from a given project. The results indicate that the range of α can be chosen to be from 0.05 to 0.15 in deep alluvia. The design thickness of the frozen wall can be reduced by at least 5% for the frozen wall with the inner edge radially incompletely unloaded. The design thickness is significantly influenced by the strength and elastic modulus of the frozen soil and the elastic modulus of the surrounding unfrozen alluvium. The design and calculation method of frozen wall thickness can provide new ideas for guiding the design of frozen walls in deep alluvia. Full article

It is generally accepted that the human abdominal wall comprises skin, subcutaneous tissues, muscles and their aponeuroses, and the parietal peritoneum. Understanding these layers and their mechanical properties provides valuable information to those designing procedural skills trainers, supporting surgical procedures (hernia repair), and engineering-based work (in silico simulation). However, there is little literature available on the mechanical properties of the abdominal wall in layers or as a composite in the context of designing a procedural skills trainer. This work characterizes the tensile properties of the human abdominal wall by layer and as a partial composite. Tissues were collected from fresh-never-frozen and fresh-frozen cadavers and tested in uniaxial tension at a rate of 5 mm/min until failure. Stress–strain curves were created for each sample, and the values for elastic moduli, ultimate tensile strength, and strain at failure were obtained. The experimental outcomes from this study demonstrated variations in tensile properties within and between tissues. The data also suggest that the tensile properties of composite abdominal walls are not additive. Ultimately, this body of work contributes to a deeper comprehension of these mechanical properties and will serve to enhance patient care, refine surgical interventions, and assist with more sophisticated engineering solutions. Full article

Using the temperature and seepage field-coupling module within COMSOL Multiphysics software, we examined freezing behavior and its evolving patterns in curved underground freezing pipes. This study employed transient states, with the Darcy’s law and porous-media heat-transfer options activated in the Physical Field Interface of the Physical Field and Variable Selection column. The models were created to establish numerical models of freezing reinforcement for both single and multiple pipes with various curvatures. These models were designed to simulate the evolving temperature and seepage fields of soil under diverse freezing conditions. Subsequently, this research utilized the models to simulate the freezing and consolidation conditions of a shallowly buried tunnel within the context of shallow tunnel conditions. The study reveals that after freezing a single pipe using water flow, the change in thickness of the frozen wall in curved pipes is notably smaller than that in straight pipes. This difference is particularly pronounced in the upstream section. Specifically, at a distance of −2000 mm from the main surface, the change in thickness of the frozen wall in straight pipes exceeds that in s = 7 curved pipes by approximately 350 mm. The smaller the long arc ratio s, the greater the arc of the freezing tube and the better the water-blocking effect. In the multi-pipe freezing model, the s = 7 curved pipes exhibit a frozen-wall thickness approximately 120 mm greater than that of straight pipes at a distance of −2000 mm from the main surface. Under the condition of a shallow buried concealed excavation with surging water, a pipe with a long arc ratio s = 7 arc freezing at 46 d attains a permafrost curtain thickness that is equivalent to that achieved by the straight pipe freezing at 58 d. This reduction in thickness shortens the working period by 12 days, resulting in a more efficient process. The successful application of the freezing method in the water-rich aquifer is expected to be a valuable reference for similar projects in the future. Full article

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 $\lambda$ on the contour line of plastic zone and tensile stress zone are analyzed by combining the project case, the calculation results show that: the $\lambda =0.485$ is the critical point where the inner edge of the frozen wall just happens to have tensile stress. When $\lambda <0.485$, the tensile stress zone is inevitable in the inner edge of the frozen wall vertical direction, and its range is only related to $\lambda$ and increases with the decrease of $\lambda$. 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 $0.485<\lambda <0.61$, 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 $\lambda >0.61$, 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 study investigated the distribution and evolution characteristics of the temperature field during the freezing and excavation of inclined shafts, with the freezing open-excavation section of Shengfu Mine’s main inclined shaft (located in Shaanxi Province) as the project background. Utilizing field-measured data and the finite element software COMSOL Multiphysics, a 3D freezing temperature-field numerical calculation model was constructed to examine the temporal and spatial evolutions of the temperature field during the construction of the inclined shaft. The findings showed that after 88 days of freezing, the average temperature of the frozen wall in the open-excavation section was below −12 °C. The frozen wall thickness in the sidewalls of different layers exceeded 4 m, and the thickness at the bottom plate exceeded 5 m, meeting the excavation design requirements. For the same freezing time, the average temperature of the frozen wall in the fine sand layer was 0.28 to 2.39 °C lower than that of the frozen wall in the medium sand layer, and its effective thickness was 0.36 to 0.59 m greater than that in the medium sand layer. When the soil was excavated, and the well side was exposed, a phenomenon known as “heat flow erosion” occurred in the soil at the well-side position, causing the well-side temperature to rise. Nevertheless, this increase was generally limited, and when continuous cooling was applied, the well side could maintain a very low negative temperature level. Consequently, there was no spalling phenomenon. The effective thickness of the frozen wall during excavation did not decrease, with the average temperature remaining below −10 °C. Consequently, there was no large-scale “softening” of the frozen wall during excavation, thus ensuring construction safety. The numerical calculation model in this paper can be used to predict the development law of the freezing temperature field of the water–rich sandy layers in Shengfu Mine and adjust the on–site cooling plan in real time according to the construction progress. This research provides valuable theoretical insights for the optimal design and safe construction of freezing inclined-shaft sinking projects. Full article

The issue of freezing often occurs when using all-glass vacuum tube solar water heaters during cold winter seasons, leading to problems such as pipe ruptures and tank leakage. In order to further study the nocturnal heat dissipation and freezing characteristics of these heaters, a three-dimensional transient numerical model of their nocturnal heat dissipation was established. The model simulated the nocturnal heat dissipation process, and experimental validations were conducted through nocturnal temperature drops of the collector and temperature drops of individual tubes without a storage tank. Experimental and simulation results revealed that in clear weather conditions during cold winters in Luoyang, the all-glass vacuum tube solar water heaters experienced freezing issues during the night, with freezing predominantly starting from the bottom surface of the vacuum tubes. The frozen length along the tube wall and the thickness of ice at the bottom section reached up to 1180 mm and 5 mm, respectively. In the absence of a storage tank, the freezing situation was severe, with approximately 4/5 of the individual tubes completely frozen. Under specified operating conditions, different storage tank volumes exhibited varying degrees of freezing in the all-glass vacuum tube solar water heaters. When the volume was increased to 15 L, the temperature drop in the storage tank and the vacuum tubes decreased by 12.1% and 7.6%, respectively. Larger storage tank volumes resulted in reduced freezing risks in all-glass vacuum tube solar collectors. This study provides valuable guidance for the design and application of solar collectors and serves as a reference for the development and application of solar energy utilization technologies. Full article

The mechanism of pipe–soil interaction under frost heaving is complicated due to many factors affecting the pipe–soil system. In order to analyze the sensitivity of various pipe–soil interaction influencing factors and highlight the relationship between the factors and the pipe’s mechanical characteristics during frost heaving, a pipe–soil interaction model based on a semi-infinite elastic frozen soil foundation is developed. Besides, the mechanical indices characterizing the influence factors and their change law are emphatically explored. The results show that the pipe stress changes most obviously at the transition region between the frost-heaving and non-frost-heaving regions. The equivalent stress increases nonlinearly with the increase of foundation coefficient, linearly with the increase of frost heave and elastic modulus of pipe, and decreases nonlinearly with the increase of transition length and pipe wall thickness. The peak stress of the pipe increases linearly with the increase of temperature difference. Moreover, the maximum allowable frost heave deformation decreases nonlinearly with the increase of oil pressure. This study helps provide theoretical reference for the adjustment, control, and prediction of stress and deformation in the design of buried pipelines under frost heaving. Full article

In order to visualize the evolution and distribution law of the ground temperature field during artificial freezing construction, an indoor model test study was carried out based on the independently constructed hygrothermal coupling artificial ground freezing test platform. The test results show that the soil temperature in the freezing process went through the three stages of a steep drop, a slow drop, and stabilization, the earliest closure position of the frozen wall was the intermediate point between two freezing pipes, and the thickness of the frozen wall on different sections showed Section 1 > Section 2 > Section 3 after 61 min of positive freezing. The soil temperature in the natural thawing process went through the four stages of a rapid rise, short hysteresis, a second rapid rise, and a linear slow rise. By fitting the test data, the distribution function of the pipe wall temperature along the pipe length under natural thawing conditions was obtained. The research results can provide a valid basis for the numerical calculation model of a three-dimensional non-uniform natural thawing temperature field and can also provide a reference for the design of settlement grouting under natural thawing conditions. Full article

Cryo-induced hydrogel from cellulose is a new class of biomaterials for drug delivery, cell delivery, bone and skin tissue engineering for cell proliferation and regeneration applications. This research aimed to synthesize cryo-induced hydrogel from cellulose and carboxymethyl cellulose (CMC) produced from empty bunch’s cell wall of Elaeis guineensis. First, the experiment was to produce cellulose-rich material using hot-compressed water extraction followed by alkaline delignification and bleaching with H₂O₂. The obtained bleached EFB cellulose was used as the substrate for CMC, and the optimal condition with the highest degree of carboxyl substitution (DS) of 0.75 was achieved when varying NaOH and monochloroacetic acid concentration as well as etherification temperature using fractional factorial design. For cryogelation study, hydrogels were synthesized from cellulose, CMC and beta-cyclodextrin (β-CD) by dissolving cellulose-based matrix in a NaOH/urea system, and the cellulose (CEL) solution was frozen spontaneously at −40 °C followed by high speed mixing to loosen cellulose fibrils. Epichlorohydrin (ECH) and Polyethylene glycol diglycidyl ether (PEGDE) were used as a cross-linker. First, the ratio of cellulose and CMC with different amounts of ECH was investigated, and subsequently the proper ratio was further studied by adding different crosslinkers and matrices, i.e., CMC and β-CD. From the result, the ECH crosslinked CMC-CEL (E-CMC-CEL) gel had the highest swelling properties of 5105% with the average pore size of lyophilized hydrogel of 300 µm. In addition, E-CMC-CEL gel had the highest loading and release capability of tetracycline in buffer solution at pH 7.4 and 3.2. At pH 7.4, tetracycline loading and release properties of E-CMC-CEL gel were 65.85 mg g⁻¹ dry hydrogel and 46.48 mg g⁻¹ dry hydrogel (70.6% cumulative release), respectively. However, at pH 3.2, the loading and release capabilities of Tetracycline were moderately lower at 16.25 mg g⁻¹ dry hydrogel and 5.06 mg g⁻¹ dry hydrogel, respectively. The findings presented that E-CMC-CEL hydrogel was a suitable material for antibiotic tetracycline drug carrying platform providing successful inhibitory effect on Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa, respectively. Full article

In order to study the elastic–plastic stress field distribution of a double-row-pipe frozen wall, the temperature field of the double-row-pipe frozen wall is equivalent to a trapezoidal distribution, and the frozen wall is regarded as an elastic–plastic thick-walled cylinder with functionally gradient material (FGM) characteristics in the radial direction. Considering that the elastic modulus and cohesion of the frozen wall material change linearly with the radius, the elastic–plastic analysis of the frozen wall is carried out based on unified strength theory. The analytical solutions of the elastic–plastic stress field distribution, the elastic ultimate bearing capacity, the plastic ultimate bearing capacity, and the relative radius of the plastic zone of the frozen wall are derived. The analytical solution is calculated based on the engineering case and compared with the numerical solution obtained based on COMSOL. At the same time, the influence of strength theory parameters on the mechanical properties of heterogeneous and homogeneous frozen walls is analyzed. The results show that the analytical solution and the numerical solution are in good agreement, and their accuracy is mutually verified. The external load on the frozen wall of the selected layer is greater than its elastic ultimate bearing capacity and less than its plastic ultimate bearing capacity, which indicates that the frozen wall is in a safe state of stress. The radial stress increases with the increase in the strength theoretical parameter b and the relative radius r, the tangential stress increases with the increase in the strength theoretical parameter b, and first increases and then decreases with the increase in the relative radius r. The larger the strength theoretical parameter b, the smaller the relative radius of the plastic zone of the frozen wall. The strength theoretical parameter b increases from 0 to 1, the elastic ultimate bearing capacity and plastic ultimate bearing capacity of the heterogeneous frozen wall increase by 33.3% and 40.8%, respectively, and the elastic ultimate bearing capacity and plastic ultimate bearing capacity of the homogeneous frozen wall increase by 33.3% and 41.0%, respectively. Therefore, considering the influence of intermediate principal stress, the potential of materials can be fully exerted and the ultimate bearing capacity of frozen walls can be improved. This study can provide theoretical reference for the design and construction of frozen wall. Full article

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

We aimed to assess the temporal and spatial evolution law of the freezing temperature field of water-rich sandy soil in underground freezing engineering, taking the newly built west ventilating shaft freezing engineering in the Yuandian No. 2 Mine of Huaibei Coalfield as the engineering background. The influence of groundwater seepage on the freezing temperature field was qualitatively analyzed using field measured data. Based on the mixture medium theory, a hydrothermal coupling numerical calculation model of the freezing temperature field was established. The temporal and spatial evolution law of the freezing temperature field of water-rich sandy soil was obtained via the analysis of field measured data and numerical calculation results. It was found that the proportion of water that froze into ice in the soil mass within the freezing pipe circle is more than that outside of the freezing pipe circle; thus, the phase change in the soil mass within the freezing pipe circle is highly obvious. Groundwater seepage has an “erosion” effect on the upstream and side frozen walls and a “cooling superposition” effect on the downstream frozen wall. Under the effect of groundwater seepage of 2.81 m/d, the average temperature of the effective frozen wall during excavation is below −15 °C, while the thickness is above 5 m for the selected sandy layer at the site, meeting the construction and design requirements. When the groundwater flow rate increases from 0 to 10 m/d, the closure time of the frozen wall increases from 27 to 49 days, an 81.48% increase; the upstream thickness of the effective frozen wall decreases from 5.635 to 4.65 m, which represents a 17.48% decrease, while the downstream thickness increases from 5.664 to 7.393 m, an increase of 30.60%. The numerical calculation model in this paper can be used to predict the development law of the freezing temperature field of the water-rich sandy layers in the Yuandian No. 2 mine and to adjust the on-site cooling plan in real time according to the construction progress. This study provides some theoretical basis and reference for the construction and designs of the freezing temperature fields of water-rich sandy soil layers. Full article

Taking the Qingdong Mine as the research object, combined with field measurement data, numerical simulation and theoretical analysis are used to examine the temperature field and stability of the frozen wall in the mine, respectively. The results show that during the active freezing period, under the same freezing time, the average temperature of the effective frozen wall of the fine sand layer is 0.2–1.0 and 0.5–2.5 °C lower than that of the sandy clay layer and clay layer, respectively. The effective frozen wall thickness of the fine sand layer is 0.04–0.17 and 0.17–0.33 m larger than that of the sandy clay layer and clay layer, respectively. The soil cooling between the two circles of freezing holes is the fastest. Due to the deflection of the freezing holes, the interface temperature field is asymmetrical. For deep clay with a depth of 200–250 m, it is most economical and reasonable for the brine temperature in the active freezing period to be −25 and −30 °C. At the designed brine temperature for cooling, during the excavation of the control layer of the topsoil layer (−216 m sandy clay), the side-wall temperature, average temperature, and thickness of the frozen wall meet the design requirements. The ultimate bearing capacity of the frozen wall is 3.20 MPa. When the well is empty for 30 h after excavation, the maximum radial displacement is 26.85 mm, so the frozen wall strength and stability are in a safe state. Overall, the findings of this study can serve as a useful reference for similar freezing projects. Full article