Numerical Analysis and Spot-Survey Study of Horizontal Artificial Ground Freezing in Tunnel Connecting Passage Construction
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In this paper, a comprehensive method combined spot-survey and numerical simulation tests has been used to make an approach to systematically study of the technology of level artificial ground freezing in tunnel connecting passage construction. By simulating the freezing process of artificially frozen soils of Dalian Road tunnel connecting passage with finite element analysis method, the varying laws of temperature fields, displacement fields and stress fields had been worked out. According to the results of actual field survey, the changing laws of frost heave pressure and tunnel deformation with freezing temperature, elapsed freezing time during the artificial ground freezing period are obtained. The laws from finite element analysis are consistent with that from field survey, which has proved that finite element analysis is correct. The conclusions of the research prove the advantages of horizontal artificial ground freezing in such similar construction and set up a successful model for related freezing projects in the future, which, will guide the coming practice and safeguard the success.Keywords:
Ground freezing
Frost heaving
Frost (temperature)
Safeguard
The developing characteristics of rate of frost heave of silty clay(undisturbed and disturbed) by artificial freezing are revealed,and different experimental results are compared.The influence of diverse experimental parameters on the rate of frost heave is analyzed and concluded.12 artificial freezing tests are performed on silty clay samples for this investigation,and the experimental parameters consist of two kinds of cooling temperature models for artificial freezing(sine-varying and constant),three kinds of freezing directions(vertical freezing,lateral freezing and vertical-lateral freezing),and different water contents(23.5%,28% and 32%),with or without water supply.It is significantly concluded that the existence of seasonal frozen layer will reduce or suppress the second frost heave caused by artificial ground freezing in the engineering projects.This study will provide significant instruction for the construction of artificial ground freezing,especially in seasonally frozen ground.
Frost heaving
Ground freezing
Frost (temperature)
Congelation
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A major experiment simulating ground freezing around a buried chilled pipeline in a controlled-environment facility provided an opportunity to examine the form and orientation of ice lenses associated with a vertical interface between silt and sand. The heave of the silt decreased towards the interface and ice lenses in the silt were found to dip at an increasing angle in the same direction. Consideration of the thermal regime suggests that the direction of heat flow influences the orientation of the lenses. The interface was irregular and ice lenses at the lower part of the interface were closely aligned to it, indicating that changes in soil texture also influence ice lens orientation. Deformation of ice lenses appears to have occurred in the silt near to the interface. The arrangement of the lenses can be explained by the different thermal properties and thermodynamic behaviour of the two materials and by the mechanical "anchorage" of the sand in which there is no ice lens formation. Cycles of freezing and thawing modify soil structure and produce cumulative residual deformations which are modified by a soil interface. Key words : frost heave, ice lenses, frozen soil, vertical silt–sand interface, chilled pipeline, differential heave.
Frost heaving
Ground freezing
Silt
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The Tianhe Station horizontal frozen construction in Guangzhou metro No.3 line is the longest and biggest artificial ground freezing(AGF) project of the national metro construction currently.In the different phases of the construction;several parameters such as brine temperature,ground temperature,surface settlement/heave,swelling pressure,tunnel liner convergence and so on,are monitored dynamically.According to the data obtained from about 400 days in-situ monitoring,the features of propagation speed of the frozen soil wall and the brine temperature variation are discussed.The characteristics of ground temperature and the swelling pressure of soil are analyzed.The relationship between the ground pressure and the soil temperature is also achieved.Results show that the temperature gradient variation and soil temperature variance ratio decrease with the increasing of freezing time in the active freezing phase.The safety of frozen earth wall is also evaluated by different monitored data.Moreover,the environmental influence of the project is evaluated based on the surface frost heave and settlement data monitored in the process of construction.It is found that the pre-freezing time is too long which induces large surface frost heave and increases the project capital cost.The analytical results show that the pre-freezing time should be reduced.
Frost heaving
Ground freezing
Brine
Settlement (finance)
Temperature Gradient
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Quasi coupling numeric analysis of frost heave effect of horizontal freezing in artificial ground is suggested.Regularity of frost heave of horizontal freezing is analysed for a subway;theoretical basis is provided for wide application of the method.
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Ground freezing
Frost (temperature)
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The key points of the freezing in the construction of the connection gallery of the running tunnel from Nanpu Station to Luoxi Station on the extended section of No.2 and No.8 line of Guangzhou Metro,such as pre-freezing preparation,excavation and settlement control,are presented.The brine water temperatures,the frozen soil temperatures,the pressures in the pressure-releasing boreholes and the frost-heaving pressures are monitored.The variation rules of the brine water temperatures,the frozen soil temperatures,the pressures in the pressure-releasing boreholes and the frost-heaving pressures are obtained by means of analysis on the monitoring results and advices are made on the construction of the connection gallery.Comparison and contrast are made between this project and other conventional freezing projects and the differences in terms of the pressures in the pressure-releasing boreholes,the frost-heaving pressure and the deformation induced by the frost-heaving and thaw settlement are described.The successful experience achieved in the project can provide reference for similar projects in the future.
Frost heaving
Ground freezing
Settlement (finance)
Brine
Frost (temperature)
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Frost heaving
Ground freezing
Frost (temperature)
Congelation
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With the development of undergroud structures in Shanghai,the ground freezing method has been more and more widely used in the construction of appurtenant parts of tunnels(such as the soil reinforcement of passways and pump house of tunnels).Exploring frost-heaving behaviors of artificial freezing soil is a key technology and an important research about artificial freezing method for municipal underground space.After the frost-heaving tests,the relationship between frost-heaving and freeezing end temperature is studied.The frost-heaving ratio and the frost-heaving stress are in linear relation with the freeezing end temperature.The freezing temperature of soil is measured by freezing temperature tests,and the freezing temperature distribution field of the soil samples is established.The relationship between freezing front and time is further revealed.
Frost heaving
Ground freezing
Frost (temperature)
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It was recognized that the tunnels deformed by ground freezing had common features in mode and progress of deformation, and these deformations were caused by frost heaving of rocks behind the lining. On the frost heaving, the geological factors had the greatest influence. And some of the physical qualities of rocks had each critical value for frost heaving. These results were checked by investigations of tunnels in cold areas and freezing tests of rocks.
Frost heaving
Ground freezing
Frost (temperature)
Frost weathering
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Abstract Artificial ground freezing (AGF) is used for constructing subway cross passages in coastal areas. The continuous construction of complex projects (cross-sea or cross-river tunnels) has resulted in freezing environments with high groundwater seepage velocities. Seepage cannot provide an open system in soil freezing for moisture migration, resulting in large amount of frost heave owing to segregated ice compared to close freezing system. The influence of frost heave under seepage on the compressive strength of frozen silt during artificial ground freezing must be studied to ensure AGF construction safety. Thus, a unidirectional freezing device that can control seepage and confining pressure conditions during freezing was designed to prepare frozen silt samples under different seepage velocities with confining pressures and to measure the relevant segregation frost heave. Subsequently, uniaxial compression tests were performed. The compressive strength of frozen silt under the influence of frost heave and seepage conditions was analyzed. The frost heave rate, uniaxial compressive strength, and elastic modulus of frozen silt in an open freezing system were measured. The seepage velocity during freezing increased the frost heave rate of the silt; the uniaxial compressive strength and elastic modulus of the frozen silt increased subsequently. The effective confining pressure suppressed frost heave of silt and reduced the uniaxial compressive strength and elastic modulus of the frozen silt. The test results were analyzed considering the segregation frost heave formation mechanism, and a theoretical improvement model of the uniaxial compressive strength and elastic modulus of frozen silt related to the content of segregated ice was proposed. This research is significant for ensuring the AGF construction safety in cross-river or ocean tunnel engineering under seepage conditions.
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Ground freezing
Silt
Frost (temperature)
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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.
Frost heaving
Ground freezing
Frost (temperature)
Brine
Vertical displacement
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