Benefit Evaluation Model of Prefabricated Buildings in Seasonally Frozen Regions

In order to effectively develop the benefit evaluation model of prefabricated houses in seasonal frozen soil areas, and improve the comprehensive benefits of prefabricated buildings, this paper proposes a life cycle benefit evaluation model for prefabricated buildings in seasonally frozen regions. According to the climatic characteristics of the area, the impact of the seasonally frozen regions is listed as an evaluation index in the construction stage for comprehensive analysis. The 16 indicators that affect the comprehensive benefits of prefabricated buildings are grouped by the nearest neighbor element analysis method. Fuzzy cluster analysis and analytic hierarchy process are used to filter out the most influential index group to calculate the index weight. Then the model proposed in this paper is compared with the existing model to test the validity of the model. The research results show that research and development costs weight is 0.23, design cost weight is 0.10, construction cost weight is 0.22, resource consumption weight is 0.25, building demolition cost weight is 0.04, and seasonal freezing effect weight is 0.16. The calculation result passed the consistency test and the expert scoring result conformed to the normal distribution, which proved the accuracy of the conclusion. It is proposed that the calculation result of the comprehensive benefit score of the model is 1.8% lower than the previous results, which proves the validity of the model. The model can speed up the efficiency of comprehensive benefit evaluation of prefabricated buildings thereby improving the development level of prefabricated buildings.

An improved process-oriented hydro-biogeochemical model for simulating dynamic fluxes of methane and nitrous oxide in alpine ecosystems with seasonally frozen soils

The hydro-biogeochemical model Catchment Nutrient Management Model – DeNitrification-DeComposition (CNMM-DNDC) was established to simultaneously quantify ecosystem productivity and losses of nitrogen and carbon at the site or catchment scale. As a process-oriented model, this model is expected to be universally applied to different climate zones, soils, land uses and field management practices. This study is one of many efforts to fulfill such an expectation, which was performed to improve the CNMM-DNDC by incorporating a physically based soil thermal module to simulate the soil thermal regime in the presence of freeze–thaw cycles. The modified model was validated with simultaneous field observations in three typical alpine ecosystems (wetlands, meadows and forests) within a catchment located in seasonally frozen regions of the eastern Tibetan Plateau, including observations of soil profile temperature, topsoil moisture, and fluxes of methane (CH4) and nitrous oxide (N2O). The validation showed that the modified CNMM-DNDC was able to simulate the observed seasonal dynamics and magnitudes of the variables in the three typical alpine ecosystems, with index-of-agreement values of 0.91–1.00, 0.49–0.83, 0.57–0.88 and 0.26–0.47, respectively. Consistent with the emissions determined from the field observations, the simulated aggregate emissions of CH4 and N2O were highest for the wetland among three alpine ecosystems, which were dominated by the CH4 emissions. This study indicates the possibility for utilizing the process-oriented model CNMM-DNDC to predict hydro-biogeochemical processes, as well as related gas emissions, in seasonally frozen regions. As the original CNMM-DNDC was previously validated in some unfrozen regions, the modified CNMM-DNDC could be potentially applied to estimate the emissions of CH4 and N2O from various ecosystems under different climate zones at the site or catchment scale.

Calculation of Subgrade Moisture Index in Seasonally Frozen Regions considering Evapotranspiration at Subzero Temperatures and the Pavement Coverage Effect

The moisture index of subgrade material directly below a paved highway is typically represented by that of an uncovered slope. However, existing studies have demonstrated the existence of a significant moisture content difference between an uncovered slope and covered subgrade owing to evapotranspiration. Moreover, under the influence of solar radiation, wind, and other factors, soil evapotranspiration persists even at subzero temperatures. This paper presents an improved method for subgrade moisture index calculation for regions that freeze seasonally. Instead of the conventional Thornthwaite method, the Food and Agriculture Organization Penman–Monteith (FAO-56 PM) method was employed to estimate the potential evapotranspiration (PE) of slope soil at subzero temperatures. Based on the moisture balance principle, the PE and water runoff and deficit were used as input parameters to calculate the moisture index of an uncovered slope. After the effect of pavement cover on subgrade humidity was defined through a correction coefficient determined via the matric suction dependence of soil water content, an optimized calculation formula was developed to estimate the moisture index of the subgrade material according to that of the corresponding slope. The results calculated on a typical seasonally frozen region in Northeast China demonstrated the applicability and accuracy of the proposed method for predicting the subgrade moisture. The potential evapotranspiration of an uncovered highway slope soil at subzero temperatures could reach 9.8%–15.7% of the total annual evapotranspiration. The moisture index range for seasonally frozen regions was −14.2–57.3. These findings will have important implications for effective improvements in the design and construction of subgrade in regions that freeze seasonally or face similar climatic conditions.

Landslide Failure Mechanisms of Dispersive Soil Slopes in Seasonally Frozen Regions

Hydraulic projects with dispersive soil in seasonally frozen regions are susceptible to landslide failures. The mechanism of such landslide failures has not been fully understood thus far; therefore, it was investigated in this study by using on-site surveys, laboratory tests, and theoretical calculations. The results showed that the landslides of dispersive soil in seasonally frozen regions could be categorized as shallow-seated landslides and deep-seated landslides. The preconditions for landslide occurrence were soil mass looseness and cracks, caused by freeze-thawing. The degradation of dispersive soil led to a rapid influx of water into the soil. The reason for shallow-seated landslides was that the numerous sodium ions present in the soil mass dissolved in water and damaged the soil structure, resulting in a substantial reduction in shear strength. The reason for deep-seated landslides, however, was the erosion due to rainfall infiltration after the shallow-seated landslides caused tensile cracks at the top of the slope, leading to soil instability. Landslide failures occurred when the dispersing soil slope underwent freeze-thawing and saturated soaking. The sliding surface was initiated at the top of the slope and gradually progressed to the bottom along the interface between the soil layers.