Freeze Pipes Research Articles

Application of BIM Technology in Freezing Design of Metro Section Lateral Pump House

With such characteristics as deep buried, complex geological conditions and sensitive surrounding environment, a metro section lateral pump house in Zhengzhou is conducted using horizontal ground freezing reinforcement method within metro tunnel, combined with mine excavation and lining. In order to ensure the expected effect of freezing reinforcement, BIM technology is applied in layout test of freezing holes. A 3D parameterized freezing pipe model adapted to stakeout data is build, and mathematical relationship of main model parameters is obtained. The rationality of freezing hole layout is verified through collision detection analysis and formation prediction analysis of frozen soil wall, providing reference for application of BIM technology in freezing design of complex cross passage.

Research on layout optimization of freezing pipes based on numerical calculation of hydro-thermal model

In order to study the influence of seepage flow on the development of frozen curtain in the artificial ground freezing project and optimize the distribution of freezing pipes. A coupled hydro-thermal model base on Darcy law and thermal balance equation has established and verified by the model test. The result shows that it can effectively improve the efficiency, reduce the completed freezing time and strength of frozen soil curtain. And the best distance which is all gratefully acknowledged between freeze pipe in upstream and section of original design freeze pipes is 75% of the distance of freeze pipes. In the end, the influence range of one pipe in upstream will be 3∼4 times the distance of freeze pipes.

Model Test of Liquid Nitrogen Freezing-Temperature Field of Improved Plastic Freezing Pipe

Liquid nitrogen freezing technology is widely applied to reinforce the water-bearing ground around launching and receiving shafts of shield machines in subway tunnel construction projects. An improved liquid nitrogen freezing pipe that can be cut by a shield machine is proposed in this paper. The improved pipe features a plastic outer pipe instead of a stainless steel outer pipe into which small-diameter holes are symmetrically drilled at equal distances along the wall of the inlet pipe to ensure the uniformity of the wall temperature. A model test was conducted to examine the liquid nitrogen freezing-temperature field of the improved plastic freezing pipe. Model test results showed that the wall temperature is unevenly distributed when the traditional freezing pipe (i.e., one that is open only at the bottom of the inlet pipe) is used for liquid nitrogen freezing. By contrast, a relatively uniform wall temperature distribution was obtained when the improved freezing pipe (i.e., with equidistant holes drilled on the wall of the inlet pipe) was used. Similarity ratios indicated that, if a 100-mm-diameter improved plastic freezing pipe is used for on-site liquid nitrogen freezing, the growth velocity of the frozen soil is approximately 75–150 mm/day.

Thermal and hydraulic analysis of selective artificial ground freezing using air insulation: Experiment and modeling

Abstract In some artificial ground freezing (AGF) applications of civil or mining projects, only particular parts of the ground need to be frozen. Selective artificial ground freezing (S-AGF) is an AGF technique where a specific portion of the freeze pipe is insulated, usually by an air gap, to prevent any undesirable ground freezing. In this study, a laboratory scale experimental setup that mimics actual S-AGF systems has been established. The experimental rig is built in a fully controlled environment and equipped with advanced instrumentation. Additionally, a mathematical model coupling the flow of the coolant, air, and porous ground is developed by solving the conservation equations of mass, momentum, and energy. The mathematical model is then validated against the experimental measurements of the ground and outlet coolant temperatures. Moreover, the natural convection inside the air gap is further validated at higher Rayleigh numbers with an experimental study from the literature. The results indicate that the energy consumption of AGF plants can be significantly reduced by applying the S-AGF concept, as compared to convectional AGF systems. Also, it is found that the optimum air gap thickness, L opt , relates to the cavity height, H, and Rayleigh number, Ra H , as L opt ~ 2 HRa H - 1 / 4 .

Research and Application of the Local Differential Freezing Technology in Deep Alluvium

Aiming at the complicated engineering conditions of the auxiliary shaft repair in the Banji coal mine, it was proposed to seal the water around the shaft lining by differential control freezing technology using double rows of holes. The outer row of holes is completely frozen, and the inner row of holes is local differential frozen according to the degree of destruction of the shaft lining. The local differential freezing pipe was successfully developed according to engineering requirements. Numeral simulations were used to predict the development of the freezing temperature field; the results showed that the inward expansion range of the frozen wall formed by the inner row freezing holes was effectively limited and the temperature drop rate of the shaft lining was significantly reduced after the local differential freezing technique was adopted. The on‐site monitoring data showed that the temperature of the limited freezing layer was about 5°C higher than that of the conventional freezing layer. During the drainage work and the construction of the new shaft lining, the thickness and average temperature of the frozen wall remained stable, indicating that the implementation of the local differential freezing technology achieved the expected results. Further analysis showed that when the temperature of the limited freezing part of freezing pipes in the inner row was controlled within the range of −15 to −10°C, not only could the frozen wall reach the design thickness and strength but the frost heaving pressure on the existing shaft lining could be effectively eliminated.

Analytical Solution of Steady‐State Temperature Field of Single Freezing Pipe under Action of Seepage Field

To accurately describe the distribution law of the temperature field formed by a single freezing pipe under the action of a seepage field, the shape of the freezing front was simplified using a segmentation‐equivalent method. The analytical solution of the steady‐state temperature field was derived, and the accuracy was verified using a physical model test. Combined with the results of the model test and the calculation results of the analytical solution, the distribution law of the freezing temperature field formed by a single pipe under different seepage velocities was analyzed. It was found that compared with the no flow rate, when the seepage velocity was 3, 6, and 9 m/day, the frozen area was reduced from 17.97 × 104 mm2 to 15.77 × 104, 3.84 × 104, and 3.05 × 104 mm2, respectively. The proportion of frozen area below −5°C increased from 39.43% to 40.19%, 49.84%, and 51.52%, respectively. The average freezing temperature field reduced from −5.78 to −5.86, −7.31, and −7.50°C, respectively. As the seepage velocity increased, the frozen area formed by a single pipe decreased while the proportion of the low‐temperature zone increased and the average temperature of the temperature field decreased.

Improved analytical prediction of ground frost heave during tunnel construction using artificial ground freezing technique

The reasonable prediction of ground frost heave provides guiding significance for tunnel construction that uses artificial ground freezing technique. Single-pipe freezing theory, which considers the freezing point of soil and assumes the constant surface temperature of a freezing pipe, is suggested for solving the radius of the freezing front before the closure of the frozen wall. By contrast, the radius of the freezing front after the closure of the frozen wall can be calculated using flat-panel freezing theory, which considers the freezing point of soil and determines the average temperature of the freezing pipe circle. On the basis of these suggestions and the analytical prediction proposed by Cai et al. (2014), an improved analytical prediction of ground frost heave was established by the stochastic medium theory according to the formation process of the frozen wall. The improved analytical prediction was applied to an actual tunnel freezing project. Then, the heaving and horizontal displacements of the ground surface are obtained, which agree well with the field-measured data. The effectiveness and practicality of the improved analytical prediction are verified in this study.

Ground temperature characteristics during artificial freezing around a subway cross passage

Abstract Artificial ground freezing (AGF) has been extensively used in the construction of subway cross passages in soft ground to ensure the safety of excavation. The temperature characteristics during freezing are of great interests, as it can be used to determine whether the frozen wall satisfies the design requirements in terms of dimension and strength. This paper presents a detailed case study of a cross passage including the temperature variations in brine and selected monitoring points around the passage based on the field testing results during freezing and frozen wall maintenance. In particular, temperature data was collected at various depths along settlement observation holes installed on top of the frozen wall. It was found that the frozen wall development rate toward the cross passage is 1.43 times faster than that away from the passage in the silt. A three-dimensional numerical model was used to analyse the temperature distribution and was able to accurately reflect the temperature distribution within the entire frozen zone with uneven distribution of the freezing pipes during freezing. This paper provides a valuable case study of the temperature characteristics of a cross passage with uneven freezing pipe distribution and a thermal model with complete thermal properties at both frozen and unfrozen status, which can be useful for thermal model calibration and/or temperature field prediction in artificial freezing engineering.

Heat transfer analysis in artificial ground freezing under high seepage: Validation and heatlines visualization

The primary goal of artificial ground freezing (AGF) system is to create a hydraulic barrier encircling working areas and stall groundwater seepage. This goal is achieved once a consolidated frozen wall is developed between the freeze pipes. Groundwater flow, however, has an undesirable effect on the formation and the growth rate of the frozen body - high water flow could hamper, totally, the establishment of a merged frozen wall between two freeze pipes. Therefore, it is of great interest to evolve a reliable prediction of the transient response of the ground structure toward the AGF process under high seepage flow conditions. This work interprets the multiphase heat transfer that accompanying the development of a frozen body between two freeze pipes with and without the presence of the groundwater seepage. A mathematical model has been derived, validated, and implemented to simulate the effect of the coolant's temperature, the spacing between two freeze pipes, and the seepage temperature on the closure time and the shape of the frozen body. The results are presented in terms of temperature fields, phase-change interface, velocity-streamlines, and heatlines. The results indicate that spacing between two pipes and seepage velocity have the highest impact on the closure time and the frozen body width.

Advanced ground freezing method and its applications in underground construction

During underground construction works in complex geological environment, special ground improvement techniques have to be used. One of them is artificial ground freezing (AGF). It can be applied in diverse projects in dense populated urban areas that place constraints on an application of other ground improvement methods. In Russia in the late 1980th was developed one new method of ground freezing. It uses solid carbon dioxide (SCD) that is loaded directly into freeze pipes, where it sublimates. As the result, the quite low temperature of freezing can be achieved easily. In this article are discussed several first application cases of this method. The results of these projects allow SCD freezing became widely used ground improvement method in Russia.

Conjugate heat transfer in artificial ground freezing using enthalpy-porosity method: Experiments and model validation

Artificial ground freezing (AGF) system is a temporary excavation-support method that is used in underground mines and tunneling projects to improve and stabilize ground structure, and to control groundwater seepage. The conjugate heat transfer between the bayonet freeze pipes and the ground plays a vital role in determining ice wall formation, heat extraction rate and closure time. In this study, a controlled laboratory scale AGF experimental rig is conceived and developed at Mine Multiphysics laboratory, McGill University. It is equipped with more than 80 temperature readings, thorough properties characterization, and an advanced instrumentation system to quantify the conjugate heat transfer process. We also developed a three-dimensional conjugate mathematical and numerical model of the bayonet freeze pipes and porous ground structure using enthalpy-porosity method. The model is further validated against global heat balance and local temperature distributions from our experiments at various operating conditions. Good agreement between model predictions and experimental data was achieved with R2=0.972. The results indicate that higher coolant Reynolds number gives rise to a higher Nusselt number and, thus, higher heat extraction rate which is mirrored by a shorter closure time. Coolant Reynolds number is found to have a higher effect on the heat transfer performance as compared to coolant temperature and grounds initial temperature. Finally, the model is a reliable tool that can be extended and employed for design and optimization of industrial AGF system.

Study on the influence of water flow on temperature around freeze pipes and its distribution optimization during artificial ground freezing

Artificial ground freezing is usually used to improve ground and provide temporary support. However, the freezing process is dramatically influenced by water flow. Evidently, water flow with high velocity brings large heat energy that prevents the freezing of porous media around freeze pipes. In this paper, for safety and energy-saving, the influence of water flow on freezing process is simulated by a developed coupled hydro-thermal model considering water/ice phase transition and the positions of freeze pipes around circular tunnel are optimized through combining this model with Nelder–Mead simplex method based on COMSOL multiphysics platform. According to the evolution law of freezing band under well-distribution of freeze pipes, three kinds of potential frequently-used probability distribution functions are adopted to reduce control parameters and improve the efficiency of optimization program including normal distribution, Poisson distribution and chi-square distribution. The results show that the proposed combining simulation method is suitable for optimization of freeze pipes arrangement. The freezing time is significantly reduced no matter which one of the above distribution functions is employed through careful design.

Optimization of the freeze pipe arrangement for artificial ground freezing

Optimization of the freeze pipe arrangement for artificial ground freezing

Effects of material and drilling uncertainties on artificial ground freezing of cement-admixed soils

The artificial ground freezing method can be used jointly with the deep cement mixing method during break-in and break-out processes of shield machines in a tunnel shaft. The frozen ground can fully cut off groundwater seepage, thus ensuring a watertight working platform. Cement-admixed soils can restrict frost heave and thaw-induced settlement because of the decreased permeability. Both methods can also enhance mechanical strength of the soil to enable construction to proceed. Two main sources of heterogeneity are likely to influence the freezing effect: spatial variability in in situ water content in natural soil and spatial variability in binder concentration in cement-admixed soils. Furthermore, positioning error when installing freeze pipes can also affect freezing efficiency. This study simulates in situ water content and binder concentration as Gaussian random fields, whereby variations in the thermophysical properties are estimated. Positioning error is also assessed by prescribing an incline angle in freeze pipes. The influences of those two sources of spatial variability as well as positioning error are examined with random finite-element analyses and statistical characteristics are estimated based on the results. Results are tabulated to offer practitioners a rule of thumb for estimating additional efforts needed in artificial ground freezing, accounting for variations in the thermophysical properties and positioning errors in installing freeze pipes.

Investigation of Frost-Heaving Characteristics of Horizontal- Cup-Shape Frozen Ground Surface for Reinforced End Soil Mass in Shield Tunnel Construction

Artificial freezing method is commonly adopted for reinforcingend soil mass of shield tunnel in the weak and rich aqueousformation, which is expected to prevent the construction riskin the originating and arriving of shield machine, whereas thearrangement of freezing pipes is sometimes varied due to variouscomplex limitations, and the corresponding frost-heavingcharacteristics of ground surface also differs from others. Inthis paper, a case of artificial freezing end soil mass with cupshape arrangement of horizontal freezing pipes is studied byfield investigation and numerical analysis, in which a numericalmodel coupled with water-heat-force interactions is proposedfor appropriately evaluating the frost-heaving characteristicsof ground surface in artificial freezing method. Theresults demonstrate that all the considered factors on brinetemperature, buried depth and cup bottom thickness have significantlyinfluences of frost-heaving characteristics of groundsurface in the artificial ground freezing (AGF) with cup shapearrangement of horizontal freezing pipes, in which the frostheave displacement of horizontal-cup-shape frozen groundsurface is increased with the increasing brine temperature andburied depth, whereas that is decreased with the increasing cupbottom thickness.

Improving the Efficiency of Artificial Ground Freezing in Urban Underground Construction by Using Solid Carbon Dioxide

At the present time there are several basic methods of soils characteristics increase during the underground structures construction. Though, frequently the ground freezing method is the most efficient way. Modern Russian investigations show, that in case of small values of frozen grounds (less than 1000 m3) the cost of construction works significantly increase. In such conditions the relevant construction technology is a ground freezing method with the use of solid carbon dioxide, which nowadays is under development in the Mining College in National University of Science and Technology MIS&S.The present article shows the brief review of the main manufacturing schemes of the ground freezing, results of the new theories and experimental investigations, also the analysis of a commercial introduction experience of the ground freezing technology with the using of carbon dioxide.So far, the main difficulties during freezing process design were with the determination of a heat flow to the freezing pipe`s direction. It was not possible to predict the dynamic of ice wall formation and the discharge of carbon dioxide. According to the last investigations, we were succeed in determinating the change dependence of the heat dissipation, depending on the rock massive characteristics, granulometric composition of solid carbon dioxide and also its changing along the freezing pipe. That is why, now we may say that, the developing technology became not just a laboratory workout, but can already has a widespread adoption in praxis

Optimization of artificial ground freezing in tunneling in the presence of seepage flow

Artificial ground freezing is an environmentally friendly technique to provide temporary excavation support and groundwater control during tunnel construction under difficult geological and hydrological ground conditions. Evidently, groundwater flow has a considerable influence on the freezing process. Large seepage flow may lead to large freezing times or even may prevent the formation of a closed frozen soil body. For safe and economic design of freezing operations, this paper presents a coupled thermo-hydraulic finite element model for freezing soils integrated within an optimization algorithm using the Ant Colony Optimization (ACO) technique to optimize ground freezing in tunneling by finding the optimal positions of the freeze pipe, considering seepage flow. The simulation model considers solid particles, liquid water and crystal ice as separate phases, and the mixture temperature and liquid pressure as primary field variables. Through two fundamental physical laws and corresponding state equations, the model captures the most relevant couplings between the phase transition associated with latent heat effect, and the liquid transport within the pores. The numerical model is validated by means of laboratory results considering different scenarios for seepage flow. As demonstrated in numerical simulations of ground freezing in tunneling in the presence of seepage flow connected with the ACO optimization algorithm, the optimized arrangement of the freeze pipes may lead to a substantial reduction of the freezing time and of energy costs.

Thermo-hydraulic modeling of artificial ground freezing: Application to an underground mine in fractured sandstone

The difficult geological conditions of underground mines in permeable and fractured rocks require the use of ground support and inflow management methods. Artificial ground freezing offers the opportunity to reduce the permeability of the ground and to consolidate it. However, the establishment of this technique can be made complicated by two phenomenas: the strong ground heterogeneity, which renders delicate an overall freezing prediction, and the potential presence of high seepage-flow velocities, which may have a negative impact on freezing progress. The present article presents a coupled use of the thermo-hydraulic model and the freeze-pipe ground model presented in Vitel et al. (2016, 2015) with an application to the Cigar Lake underground mine in Northern Saskatchewan, Canada. The first model allows the estimation of the temperature and pressure distribution in the ground during freezing while the second model simulates the heat transfer between a freeze pipe and the surrounding ground, which is useful to determine the boundary conditions of the thermo-hydraulic model. First, the article restates the governing equations of both models. Then, after the validation of the numerical results with respect to field measurements, a joint use of the models is proposed, in particular to (i) predict the ground temperature evolution, (ii) study the impacts of the geological conditions on the freezing progress and (iii) optimize the freezing system design.

Finite Element Analysis on 3D Freezing Temperature Field in Metro Cross Passage Construction

Artificial ground freezing has been widely practiced in construction of metro cross passage in soft ground. The ground freezing process creats a frozen mass of improved compressive strength and impermeability, which will make the ground safely stand by itself at the point of excavation and prevent cave-ins from happening. With this technique, freeze pipes are arranged like stretchers of a half opened umbrella from two ends of the cross passage. Usually finite element analysis on transient temperature field of frozen soil can simulate propagation process of frozen wall (frozen barrier) before construction and evaluate rationality of freeze pipes arrangement. Usually finite element analysis on temperature field has been mostly simplified to the plane problem, which is difficult to simulate the actual situation because freeze pipes are not horizontal parallel along the cross passage. In this article, for one cross passage in Shanghai Metro Line No. 13, taking into account the initial conditions and boundary conditions, such as such as ground temperature, ground surface convection and latent heat of phase change, a 3D finite element numerical model is presented for the temperature field evolution. The modeling yields a detailed distribution pattern for freezing temperature field. The results are compared with the in-situ monitoring soil temperature changes, which verify the reliability of finite element numerical analysis.

Modeling heat transfer between a freeze pipe and the surrounding ground during artificial ground freezing activities

The artificial ground freezing method (AGF) is widely used in civil and mining engineering. In AGF numerical models, the thermal boundary conditions at the freeze pipe wall, whether they be expressed in temperature or in flux, are generally determined based on in situ measurements, which are not readily available. The purpose of this paper is to study the complete heat transfer problem in order to develop a thermal model that can be easily used in field applications. In this numerical model, the freeze pipe and the surrounding ground are considered in a coupled way. External data of temperature or flux at the pipe wall is therefore not needed to predict the temperature evolution in the ground. Moreover, the developed model can be used to conduct parametric studies on operating conditions, refrigerant type, system geometry or ground properties. Indeed, the reduction of the heat transfer problems in the ground and in the pipe into highly time-saving 1D problems allows the rapid resolution of many calculations. Then, the developed model can also find its use in the optimization and the design of AGF systems.