A fully coupled thermo-hydro-mechanical model including the determination

 

of coupling parameters for freezing rock

 

冻结岩石全耦合流–固–热模型及其耦合参数计算

International Journal of Rock Mechanics and Mining Sciences, Volume 103,

March 2018, Pages 205-214

Shibing Huang, Quansheng Liu, Aiping Cheng, Yanzhang Liu, Guofeng Liu

摘要：The freeze-thaw damage of rock is mainly induced by cycling loading

of pore ice pressure and thermal stress under coupled thermo-hydro-mechanical

(THM) condition at low temperature. The accuracy and correctness of coupled

T-H-M model for freezing rock are controlled by critical parameters including

unfrozen water content, ice pressure, permeability, and the equivalent thermal

conductivity. The difference of THM coupling process between freezing rock and

freezing soil is the evolution rule of those critical parameters, which change

drastically with freezing temperature. The permeability is related to the

unfrozen water content and high enough to be considered at the temperature

above−5 °C. Combining numerical experiment with mixture theory, the equivalent

thermal conductivity of freezing rock is also studied which is proved to be well

expressed by exponential weighted mean model. Then the governing equations for

THM coupling of freezing rock under low temperature are deduced based on energy

conservation law, mass conservation law and the principle of static equilibrium

considering water/ice phase transition. Those equations include the effects of

seepage velocity and latent heat of phase transition on heat transfer, the

influences of segragation potential and volume strain on water flow, and the

impacts of temperature and pore water/ice pressure on frost heaving strain.

Compared with a famous coupled THM laboratory test conducted by Neaupane and

Yamabe, the proposed THM model has a good prediction of heat conductivity and

frost heaving strain for freezing rock.

 

 

Pore characteristics (>0.1 mm) of non-air entrained concrete destroyed

 

by freeze-thaw cycles based on CT scanning and 3D printing

 

基于CT扫描及3D打印的冻融循环损伤非含气混凝土的孔隙特征(>0.1 mm)

Cold Regions Science and Technology, Volume 151, July 2018, Pages 314-322

Wei Tian, Nv Han

摘要：In this study, the deterioration mechanism of concrete subjected to

freezing-thawing (F-T) actions was analyzed. The evolution and spatial

distribution of internal pore structure were key factors in the damage mechanism

and mechanical properties of concrete in the F-T environment. X-ray computed

tomography (CT) was used to examine the evolution of concrete internal damage

under F-T cycles. CT-identified pore structures were reconstructed as digital

virtual-models and the porosity and pore distribution of these pore structures

were characterized by image analysis. Three-dimensional printing (3DP) specimens

containing CT-identified pore structures were prepared and replicated based on

these digital virtual-models. Uniaxial compression tests were conducted on both

concrete specimens and 3DP specimens, which have a similar loss percentage of

uniaxial compressive strength (UCS). These results show that 3DP technology can

provide a new strategy for experimental study of concrete material.

 

 

Damage constitutive models of concrete under the coupling action of

 

freeze–thaw cycles and load based on Lemaitre assumption

 

基于Lemaitre假设的冻融循环荷载偶合作用下的混凝土损伤本构模型

Construction and Building Materials, Volume 173, 10 June 2018, Pages

332-341

Boxin Wang, Fei Wang, Qing Wang

摘要：In cold environments, concrete structures are subjected to a

combined action of load, freeze–thaw cycles, and salt attack. The performance

degradation of some concrete structures in such areas is serious, thus

shortening their service life. In this study, a macro-mesoscopic coupling damage

model was established to determine the durability of concrete under the coupling

action of freeze–thaw cycles and load based on the Lemaitre strain equivalent

assumption. Meanwhile, the an indoor accelerated test was conducted to verify

the rationality of the model. Results indicated that the damage in different

kinds of concrete under freeze–thaw cycles and load can be predicted by the

theoretical model. The structural coupling damage was determined by the

meso-damage caused by the freeze–thaw cycles and the macro-damage caused by the

applied load, which showed a nonlinear superposition relationship. The evolution

laws of coupling damage were entirely different because of the freeze–thaw

cycles and strain. The coupling damage and peak strain increased with the

increase in number of freeze–thaw cycles but the variation range of damage and

peak stress decreased. The peak strain can be the critical point of the coupling

damage when the number of freeze–thaw cycles was constant. The growth of

coupling damage was not significant before the peak strain. When the deformation

approached the peak strain, the coupling damage increased considerably, and the

concrete was destroyed rapidly.

 

 

Experimental study on gravitational erosion process of vegetation slope

 

under freeze–thaw

 

冻融条件下植被边坡重力侵蚀过程实验研究

Cold Regions Science and Technology, Volume 151, July 2018, Pages 168-178

Dahu Rui, Mingchang Ji, Dai Nakamur, Teruyuki Suzuki

摘要：Freeze–thaw is the major factor in gravitational erosion creep of

slopes in cold regions, but gravitational erosion is influenced remarkably by

vegetation cover. In order to investigate the phenomenon of the gravitational

erosion process of vegetation slopes under freeze–thaw in seasonally frozen soil

regions, on-site freeze–thaw tests of different vegetation slopes were conducted

in the frozen soil testing ground of Kitami Institute of Technology (KIT,

Hokkaido, Japan). Slope vegetation is divided into an external-soil spray

seeding section and a turfed section according to its method of formation.

Through field tests of four cycles, the slope temperature, frost depth, amount

of frost-heave, and amount of movement were observed dynamically in real-time,

initially revealing the regularity of the gravitational erosion process of the

vegetation slope, which provided a scientific basis for slope stability control

in cold regions. The experimental results show that the gravitational erosion of

the slope is a process of irreversible gradual evolution, that the extent of

erosion has a periodical fluctuation in time, that the target point of the slope

surface moves in a jagged trajectory down the slope year after year, and that

the maximum values of the amount of movement of the external-soil spray seeding

section and the turfed section are −13.1 and –6.1 cm, respectively, after four

freeze–thaw cycles. The space distribution of the slope surface has

inhomogeneity. The difference in temperature and water content of each part of

the slope surface is the main reason why the freezing front of the slope is not

parallel to the slope surface. The amount of frost-heave of the slope toe was

greater than that of the slope crest, which caused upward displacement along the

slope during early freezing. The movement of the slope is closely related to the

development of vegetation, and the heat insulation and reinforcement of

vegetation cover effectively restrain the displacement of the slope's shallow

soil. The results of this study have a certain significance in the prevention

and treatment of shallow slope sliding in cold regions.

 

 

Vertical variation of a black soil's properties in response to freeze-thaw

 

cycles and its links to shift of microbial community structure

 

冻融循环条件下黑土特性的纵向变化及其与微生物群落结构演变的联系

Science of The Total Environment, Volume 625, 1 June 2018, Pages 106-113

Ziming Han, Mingwen Deng, Anqi Yuan, Jiahui Wang, Jincai Ma

摘要：Soil freeze-thaw cycles (FTCs) change soil physical, chemical, and

biological properties, however information regarding their vertical variations

in response to FTCs is limited. In this work, black soil (silty loam) packed

soil columns were exposed to 8 FTCs, and soil properties were determined for

each of vertical layer of soil columns. The results revealed that after FTCs

treatment, moisture and electrical conductivity (EC) salinity tended to increase

in upper soil layers. Increments of ammonium nitrogen (NH4+-N) and nitrate

nitrogen (NO3−-N) in top layers (0–10 cm) were greater than those in other

layers, and increments of water soluble organic carbon (WSOC) and decrease of

microbial biomass carbon (MBC) in middle layers (10–20 cm) were greater than

those in both ends. Overall, microbial community structure was mainly influenced

by soil physical properties (moisture and EC) and chemical properties (pH and

WSOC). For bacterial (archaeal) and fungal communities, soil physical

properties, chemical properties and their interaction explained 79.73% and

82.66% of total variation, respectively. Our results provided insights into the

vertical variation of soil properties caused by FTCs, and such variation had a

major impact on the change of structure and composition of soil bacterial and

fungal communities.