Journal of Cold Regions Engineering

Cemented paste backfill (CPB) is a novel cementitious construction material that is used extensively for underground mine support and/or mine waste management worldwide. CPB consists of a mix of tailings (mine waste), water, and binder. In other words, tailings are transformed into construction materials. Key engineering properties required for the geotechnical design of CPB structures include strength and deformation behavior. However, there is a paucity of technical data and information about the effect of sub-zero temperatures on these properties. This paper presents an experimental study that focuses on the investigation of the influence of sub-zero curing temperatures on the strength, deformation behavior, and microstructure (e.g., pore structure, porosity, and binder hydration products) of CPB. Several CPB samples with various combinations of compositions (e.g., binder type, cement amount, and water content) cured at different temperatures (sub-zero and room temperatures) and times (7–90 days) are tested with regard to strength, stress–strain behavior, and microstructural characteristics. It is found that frozen CPB (FCPB) exhibits remarkable strength compared with unfrozen CPB and has a great resemblance to frozen soil. No obvious peak stress is observed from FCPB samples during compression, and strain hardening phenomena are commonly seen after the initial yield point. Factors that may affect the behavior of FCPB are thoroughly examined. Binder contents and types are found to be irrelevant; in contrast, water content plays a dominant role. This negligible effect of binder on the properties of FCPB is due to the inhibition of the binder hydration by sub-zero curing temperatures. FCPBs show coarser pore structure than unfrozen CPBs. The results obtained in this study have significant practical engineering applications for mines located in permafrost or cold regions.

Freeze–thaw (F–T) cycles exert a significant effect on engineering activities in cold regions, thus attracting increasing attention around the world. In this study, a set of triaxial compression tests, scanning electron microscopy (SEM), and X-ray computerized tomography (X-ray CT) tests were conducted on silty clay samples with various moisture contents after different number of F–T cycles. The mechanical parameters of silty clay, such as peak shear strength and resilient modulus, and the microstructure evolution before and after F–T cycles were obtained. The results show that all the stress–strain curves of silty clay samples exhibit a strain-hardening behavior, and the higher the confining pressure is, the higher the hardening degree will be. The peak shear strength, resilient modulus, and cohesion of the silty clay samples are reduced after being exposed to F–T cycles. These parameters reach a minimum around the fifth cycle and gradually stabilize after 10 cycles. However, the change in internal friction angle induced by F–T cycles is trivial. With increased water content, the resilient modulus and cohesion decrease linearly. SEM and CT results show that the inner microstructure of silty clay sample becomes looser, and the pores and connections between soil particles deteriorate as the number of F–T cycles increase. The porosity of sample after five F–T cycles is higher than that before exposure to F–T cycles. The microstructural results agree well with the deterioration in the strength of silty clay.

As part of an ongoing effort to update the ground snow load maps in the US, this paper presents an investigation into snow densities for the purpose of predicting ground snow loads for structural engineering design with ASCE 7. Despite their importance, direct measurements of snow load are sparse, compared with measurements of snow depth. As a result, it is often necessary to estimate snow load using snow depth and other readily accessible climate variables. Existing depth-to-load conversion methods, each of varying complexity, are well suited for snow load estimation for a particular region or station network, but none is consistently effective across regions and station networks. In this paper, a random forest regression model is proposed for estimating annual maximum snow loads in the conterminous US that makes use of climate reanalysis data and overcomes the limitations of existing methods. The effectiveness of the random forest model is demonstrated through accuracy comparisons of existing depth-to-load conversion techniques using a compilation of national and state-level data sources. The accuracy comparisons show that the random forest model is competitive for all regions and station networks, whereas other methods are competitive only for certain regions or station networks. These results highlight the feasibility of developing a single depth-to-load conversion method that appropriately characterizes region and climate specific differences in the snow depth–load relationship across the conterminous US. Such universal models are an essential component for creating a unified set of national snow load requirements that eliminate the case study regions currently defined in current national standards.

This study focuses on the investigation of the predictive capability of the Clausius–Clapeyron (C–C) equation in conjunction with soil–water retention characteristics to estimate soil-freezing curves (SFC). The Clausius–Clapeyron equation together with soil–water retention (SWR) models can provide a quick estimation of SFCs. However, the validity of the equilibrium assumption may not be applicable in all scenarios of freezing and thawing. The overall goal of this study is to provide a comprehensive assessment of SWRC-derived soil-freezing curves for different types of soils under varying environmental conditions. An extensive set of data obtained from studies reported in the literature pertaining to thermally induced hydraulic properties of sand, silt, and clay soils from multiscale experiments was analyzed. In addition, in-house laboratory freeze–thaw experiments were performed using silty soil. The SFCs derived from the SWRC were in good agreement with the measured SFCs for sands, whereas significant discrepancies were noted for silt and clay soils. Intensified discrepancies were noted when the results from different experimental methods and changing boundary conditions were compared. A significant hydraulic hysteresis was observed and possible controlling mechanisms were explained. A reliable method to predict SFC from SWRC will enable accurate modeling of coupled heat transfer and water flow processes in the Arctic subsurface for sustainable built and natural environments.

To study the energy characteristics and damage laws of frozen rock during mine freezing, a triaxial compression test and synchronous acoustic emission test of frozen sandstone are conducted. The results show that (1) the peak stress of frozen sandstone is more than as thrice as that of sandstone at 20°C. According to the elastic energy conversion rate, two stress thresholds are determined, and the peak stress is combined to divide the frozen sandstone damage section. When the stress is in the range of 0–σ_eb, the increase rates of the dissipation energy (U_d) and acoustic emission cumulative energy (AECE) of the frozen sandstone are significantly less than those of the sandstone at 20°C. The total input energy (U), elastic energy (U_e), and U_d at the peak stress of frozen sandstone are more than as twice as those of sandstone at 20°C. As the negative temperature of the sandstone decreases, U, U_e, and the elastic energy conversion rate at the peak stress slightly increase. (2) The AECE of the 20°C sandstone at the peak stress is approximately 1/2 the AECE_max. The AECE of the frozen sandstone at the peak stress accounts for approximately 1/5 the AECE_max. As the negative temperature decreases, the AECE_max of the sandstone increases. (3) As the confining pressure of frozen sandstone increases, U, U_e, and U_d at the peak stress increase, the elastic energy conversion rate decreases, and AECE_max significantly increases. For frozen sandstone under different confining pressures, AECE at the peak stress accounts for 11%–25% of AECE_max, and the proportion increases with increasing confining pressure. (4) AECE is used to define the damage variables, and a constitutive model of frozen sandstone is obtained. Before the peak stress, the results of the constitutive model are in agreement with the test results. The two damage evolution curves of frozen sandstone based on U_d and AECE can describe the damage evolution process.