基于压实分析模型的土壤应力传递系数研究

Soil Stress Transmission Coefficient Based on Compaction Analytical Model

机械压实是造成土壤退化的重要原因之一,研究并预测土壤应力有助于科学规划田间机械使用,缓解压实问题。基于分析模型预测土壤应力的关键在于选择合适的集中系数。然而在已有的研究中集中系数取值混乱,导致该模型使用时存在很大争议,其原因在于对该参数随土壤环境的变化缺乏规律性认识。本文通过对集中系数表达式的进一步推导,在理论上提出了能够代表土壤环境对集中系数影响的无量纲参数σ_z/σ_0,定义为应力传递系数(STC)。基于水稻土和黄棕壤两种土壤,通过控制含水率和湿密度于室内重塑30种状态的土壤,在单轴压缩实验中运用土压力传感器测量计算应力传递系数,建立应力传递系数与土壤环境参数,如含水率、干密度和先期固结压力等之间的相关性分析。结果表明应力传递系数随土壤含水率的增大而增大,土壤初始干密度和先期固结压力与应力传递系数之间负相关性明显。根据所得应力传递系数计算相应土壤状态下的集中系数,其取值在1.20~12.39之间,与以往的研究结果相差不大,但包含了关于集中系数随土壤环境变化的具体信息。这意味着作为一个稳定可测的无量纲参数,应力传递系数为集中系数的计算提供了一个相对科学的方法,在定量描述土壤环境对集中系数影响的同时,完善了分析模型。

Predicting soil stress with analytical models requires proper selection of the models ＇concentration factor.But due to the insufficient knowledge about the effects of soil conditions on stress transmission,little is known about how the concentration factor varies with soil states and loading conditions.The function of the concentration factor was transformed and a dimensionless factor σz/σ0 standing for soil-induced attenuation on the stress transmission was defined as the soil stress transmission coefficient and is denoted as STC.Since soil stress transmission property is affected by soil states and loading conditions,a modified oedometer testing setup with a soil stress sensor was used to evaluate controlled soil properties on STCs.Totally 30 soil states were tested by controlling soil water contents and bulk densities based on different soil styles.Correlation analysis was performed between measured STCs and soil state parameters, i.e.water content, bulk density and soil strength.The highly linear correlation between soil stress and applied surface stress indicated a stable STC for each particular soil state.STC was also found both linearly decreased with dry bulk density and precompression stress.The back-calculation of concentration factor from measured STCs illustrated that the proposed solution for soil stress transmission provided a means to define concentration factor for each soil state with measured result.Concentration factor varied from 1.20 to 12.39,being in agreement with the past reports.And the detail of how the concentration factor was affected by the changed states of soils was provided.