Effect of Grading and Water Content on Thermal Conductivity of Natural Peat Aggregated Soils
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摘要: 地表泥炭土是天然保温材料，对多年冻土保护具有重要意义.自然状态下，泥炭土通常含有粗团粒，且级配具有空间变异性.然而，级配对其导热特性的影响鲜有报道.采用非稳态探针法，对泥炭土开展了66组导热系数试验，以探究粗粒含量Cc、粒径比R和含水率w等因素对导热特性的影响.研究表明：在同一相对密度下，泥炭土的导热系数K随Cc的增加先增大后减小，在Cc=50%时取到最大值；粗粒主导时，随R的增大而增大，细粒主导时，R变化对其影响不显著.在相同孔隙比下，由于颗粒间接触热阻和配位数随Cc和R的变化，导热系数随着Cc的增加而增大；细粒主导时随R的增大而增大；粗粒主导时，则随R增大而降低.此外，泥炭土的导热系数随w增加而显著增大，其增长率随试样中团粒内部和团粒间孔隙中的水分分布而变化.Abstract: Peat soil is a natural insulation material, which has a significant effect on the underlying frozen soil layer. Natural peat soil usually exists in the form of aggregates, and its particle size distribution has a spatial variability. However, the effect of gradings on the thermal conductivity is rarely reported. In this work, 66 laboratory tests were conducted on the peat soil to investigate the effects of coarse content, particle size ratio and water content on its thermal conductivity by a non-steady-state probe method.The results show that under the same relative density, the thermal conductivity of peat soil first increases and then decreases with the increase of coarse content, and reaches the peak value when the coarse content reaches 50%. For the peat soil with coarse dominated structure, the thermal conductivity increases distinctly with the increase of particle size ratio. However, the effect of particle size ratio reduces in the fine dominated structure. For a given void ratio, the thermal conductivity increases with the rising coarse content due to the thermal resistance and the particle contacts which are affected by particle size distribution; it increases with increasing particle size ratio in fine grain dominated structure but decreases in coarse grain dominated structure. In addition, the thermal conductivity of peat soil increases significantly with increasing water content, and the growth rate varies with the internal pores and the water distribution in the pores.
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图 1 天然泥炭土筛分后不同粒径范围的泥炭土颗粒
Fig. 1. Aggregates of natural peat soil with different grain sizes after being sieved
图 3 热导率实验装置
a.导热系数测定装置图；b.试样测试图
Fig. 3. Experimental apparatus for thermal conductivity
图 4 温度-时间关系的典型结果
Fig. 4. Typical record of the temperature in the measurement of thermal conductivity
图 5 不同粗粒及粒径比试样的粒径分布曲线
a.不同粗粒含量试样粒径分布曲线；b.不同粒径比（Cc=40%）试样粒径分布曲线；c.不同粒径比（Cc=75%）土样粒径分布曲线
Fig. 5. Particle size distribution curves of soil samples with different coarse grain and particle size ratio
图 6 泥炭土最大和最小孔隙比与粗粒含量的关系
Fig. 6. Relationship between maximum and minimum void ratios and coarse content of peat
图 7 不同粗粒含量变化下土体微观结构示意图
a.细粒主导结构；b.过渡粗粒含量；c.粗粒主导结构
Fig. 7. Soil structure at various coarse contents
图 8 泥炭土最大和最小孔隙比与粒径比的关系
a.细粒主导结构；b.粗粒主导结构
Fig. 8. Relationship between maximum and minimum void ratios and particle size ratio of peat
图 9 不同粒径比下土体微观结构示意图（细粒主导结构）
a.粒径比=3.8；b.粒径比=10.2
Fig. 9. Soil structure with various particle size ratio(fine-grained dominant structure)
图 10 不同粒径比下土体微观结构示意图（粗粒主导结构）
a.粒径比=3.8；b.粒径比=10.2
Fig. 10. Soil structure with various particle size ratio (coarse-grained dominant structure)
图 11 泥炭土导热系数与粗粒含量和相对密度的变化
Fig. 11. Change of thermal conductivity of peat with coarse grain content and relative density
图 12 泥炭土导热系数和孔隙比与粗粒含量的变化（Dr=50%）
Fig. 12. Change of thermal conductivity and void ratios of peat with coarse particle content (Dr=50%)
图 13 泥炭土导热系数与孔隙比和粗粒含量的变化
Fig. 13. Change of thermal conductivity of peat with coarse grain content and void ratios
图 14 粒径大小对传热路径的影响
a.细粒结构中的传热路径；b.粗粒结构中的传热路径
Fig. 14. Effect of particle size on heat transfer path
图 15 导热系数与粒径比和相对密度的变化（细粒主导结构）
Fig. 15. Change of thermal conductivity of peat with particle size ratio and relative density (fine-grained dominant structure)
图 16 导热系数与粒径比和孔隙比的变化（细粒主导结构）
Fig. 16. Change of thermal conductivity of peat with particle size ratio and void ratios (fine-grained dominant structure)
图 17 导热系数与粒径比和相对密度的变化（粗粒主导结构）
Fig. 17. Change of thermal conductivity of peat with particle size ratio and relative density (coarse-grained dominant structure)
图 18 导热系数与粒径比和孔隙比的变化（粗粒主导结构）
Fig. 18. Change of thermal conductivity of peat with particle size ratio and void ratios (fine-grained dominant structure)
图 19 泥炭土导热系数与含水率的变化
Fig. 19. Change of thermal conductivity of peat soil with moisture content
图 20 随含水率变化的泥炭土颗粒结构微观示意图
Fig. 20. Microstructure diagram of peat soil particle structure with moisture content change
表 1 泥炭土基本物理参数
Table 1. Basic physical parameters of natural peat soil
物理参数 参数值 最优含水率wop（%） 40.10 最大干密度ρdmax（g/cm3） 1.098 比重Gs 2.33 塑限wp（%） 47.53 液限wL（%） 62.82 塑性指数IP 15.29 有机质含量（%） 17.42 
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表 2 粗粒和细粒的基本物理参数表
Table 2. Basic physical parameters of coarse and fine particles
物理参数 粗粒 细粒 粒径范围(mm) 0.2~2 < 0.2 平均粒径d50(mm) 0.625 0.064 不均匀系数Cu 2.907 1.794 最大干密度ρmax（g/cm3） 1.162 1.094 最小干密度ρmin（g/cm3） 0.693 0.744 最大孔隙比emax 2.354 2.128 最小孔隙比emin 1.002 1.126
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表 4 不同粗粒含量及粒径比干土试样的物理特性参数
Table 4. Physical characteristic parameters of dry soil sam- ples with different coarse particle content and particle size ratio
试样编号 粗粒含量Cc（%） 粒径比R 相对密度Dr（%） emin emax 1~3 0 - 30, 50, 75 1.126 2.128 4~6 25 10.2 30, 50, 75 1.088 1.963 7~9 40 3.8 30, 50, 75 0.980 1.847 10~12 40 4.9 30, 50, 75 0.975 1.822 13~15 40 5.7 30, 50, 75 0.958 1.825 16~18 40 6.9 30, 50, 75 0.973 1.809 19~21 40 8.0 30, 50, 75 0.964 1.788 22~24 40 10.2 30, 50, 75 0.995 1.829 25~27 50 10.2 30, 50, 75 0.932 1.780 28~30 65 10.2 30, 50, 75 0.941 1.771 31~33 75 3.8 30, 50, 75 1.051 2.184 34~36 75 4.4 30, 50, 75 1.058 2.145 37~39 75 5.2 30, 50, 75 1.052 2.115 40~42 75 10.2 30, 50, 75 0.945 1.840 43~45 85 10.2 30, 50, 75 0.964 1.956 46~48 100 - 30, 50, 75 1.002 2.354
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表 5 不同含水率试验方案
Table 5. Different water content test scheme
试样编号 干密度ρd（g/cm3） 含水率w（%） 49~54 1.098 0, 10, 20, 30, 40, 48 55~60 0.988 0, 10, 20, 30, 40, 48 61~66 0.879 0, 10, 20, 30, 40, 48
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