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采用Gompertz函数的水稻土压缩特性研究

Compression characteristics of paddy soil based on Gompertz function

  • 摘要: 土壤压实模型是预测压实破坏的常用方法,但土壤压实模型的应用常因输入参数(土壤压缩特性及其与不同土壤物理性质之间的关系)的缺乏而受到限制。为定量地评价土壤水力学性质和土壤结构对土壤压缩特性的影响,该文利用土壤固结仪对25种不同含水率和容重的重塑土样进行单轴压缩试验,并采用Gompertz函数对试验数据进行拟合以获取土样的回弹指数、压缩指数和先期固结压力。试验结果表明,Gompertz函数对水稻土试验数据的拟合效果较优,决定系数为0.991~0.999。水稻土回弹指数为0.003~0.138,与容重呈负相关,与含水率呈正相关。水稻土压缩指数为0.115~0.839,与容重呈负相关,与含水率呈二次多项式关系。水稻土先期固结压力为33~127 kPa,与容重呈正相关,与含水率呈负相关。该研究建立的土壤压缩特性与含水率和容重之间的传递函数,可用于大尺度范围内水稻土压缩特性的预测;同时这些传递函数可作为土壤压实模型的输入参数,用于农业机械作业引起的压实破坏的量化和土壤压实风险的评估。

     

    Abstract: Soil compaction caused by agricultural field vehicles can significantly affect soil physical properties and soil structure, and thus have an enormous impact on crop yield and agroecological environment, which has become one of the obstacles for sustainable agriculture. Quantification and prediction of soil compaction is helpful for the rational use of agricultural machinery in the field and soil structure protection, and can reduce or avoid the risk of soil damage. In order to quantitatively evaluate the effects of soil structure and hydraulic state on soil compaction, twenty-five remolded soil samples with different moisture content of 15%, 20%, 25%, 30%, 35% and bulk density of 1.1, 1.2, 1.3, 1.4, 1.5 g/cm3 were made. The effects of moisture content (w) and bulk density (ρ) were investigated in this study on the characteristics of the soil compression curves and soil compression properties. Soil compression curves were got using the Gompertz function to fit uniaxial compression test results and three important soil compression properties, such as the swelling index, the compression index, and the pre-compression stress were obtained from the curves. The fitting results showed that all the compression curves had the similar shape and Gompertz function fit the experimental data of paddy soil well. The root-mean-square error of paddy soil was in the range of 0.001-0.019, with an average value of 0.008. The values of the parameters of Gompertz function were as follows: a =0.289-0.643, b=0.980-2.883, c=0.128-1.087, m=2.157-2.598. The swelling index values of paddy soil ranged from 0.003 to 0.138. The swelling index for paddy soil was maximum when w=35% and ρ=1.1 g/cm3, and at was minimum when w=15% and ρ=1.5 g/cm3.The swelling index showed a significant positive dependence on moisture content, while bulk density was negative. The compression index was in the ranges of 0.115-0.839. The compression index for paddy soil was maximum when w=25% and ρ=1.1 g/cm3, and was minimum when w=15% and ρ=1.5 g/cm3.A quadratic polynomial function was established between moisture content and compression index; the compression index showed a significant negative correlation with bulk density. The pre-compression stresses of paddy soil were in the ranges of 33-127 kPa. The pre-compression stresses for paddy soil was maximum at w=15% and ρ=1.5 g/cm3 and minimum at w=35% and ρ=1.1 g/cm3. The pre-compression stresses showed a prominent negative correlation with moisture content and a significant positive correlation with bulk density. Consequently, it was concluded that agricultural field operations should be avoided when the soil has a higher moisture content and a lower bulk density, in order to protect the soil structure. Moreover, it was established that a set of pedo-transfer functions based on moisture content and dry bulk density can be used to predict the swelling index, compression index, and pre-compression stress of paddy soil, therefore laborious and time-consuming compression tests can be avoided. These soil compression properties as input parameters also can be used in the soil compaction models which can supply references for establish strategies and recommendations to prevent of soil compaction.

     

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