水稻土的机械承载力和机械失效力学模型及其应用

The poor tilled-layer soil structure largely restricts annual grain yield of the rice-wheat system. Transition of paddy soil structure from compact and sealed state to the pulverized and aerated state has to be implemented to coordinate the contradicted requirements of soil physical states by the rice and wheat seasons. The governing mechanism of this transitional process is the structural change of soil under mechanical stressing. This project thus focuses on the two mechanical models, i.e. soil bearing capacity and soil failure mechanics models, which will be acquired from extensive field experiments. Soil bearing capacity model is derived from the result from two measurements: plate sinkage test and cone penetration test, and soil failure model is based mainly on in situ tillage experiment, which is complimented with indoor soil fragmentation test and soil cutting test. Soil stress sensors will be applied to measure bulk soil stress processes under externally applied load and the respective soil structural change undergone will be quantified. Thereby the relation between paddy soil structural stability and workability and their influential factors can be illustrated. Wheat will be planted to reveal its response to the mediated tilled-layer soil structure and the respective soil stressing processes. The ultimate goal of this work is to quantify the mechanical interactions among the soil-machine-cropping system by encompassing the 3 staged research targets, i.e. from paddy soil mechanical models to its influence on tiller-layer structure, and finally to the response of wheat production to the managed soil structure.

不良的耕层构造严重影响稻麦系统的粮食产出，水稻土应在稻麦换季环节实现由紧实粘闭到松碎透气状态的转变以协调稻麦2种作物完全不同的土壤物理要求，该转变的实质是耕层构造在外加机械应力作用下的结构变化行为。项目围绕水稻土的机械承载力和机械失效2个力学模型，进行稻茬田的耕作实验，分别进行平板下陷和圆锥贯入测试，获取水稻土的机械承载力特征并建立机械承载力模型；以机械耕作为主，辅以破碎和切削机理实验，获得水稻土的机械失效力学模型。使用力传感器测试水稻土在外加机械力过程的土体内应力动态及耕层构造的物理变化，建立影响水稻土的力稳性和耕性的各因子之间的定量关系。进行小麦种植试验并用小麦的生长响应评价耕层构造及不同机械力学过程的影响，从而实现水稻土的机械力学模型、力学模型对耕层构造的影响、以及耕层构造对稻茬麦生长的影响3个层次研究内容的统一，描述水旱转换环节的土壤-机器-作物系统内部确定性的力学联系。

针对水稻土的2个力学模型：机械承载力模型和机械失效模型，项目在1年期内分别进行多种土壤力学实验研究，包括原位平板下陷、圆锥贯入、原位犁耕、原位旋耕等多项测试，对所得数据分析后表明水稻土机械失效模型具有特殊性。研究发现水稻土的应力传递过程表现为阶梯型变化特征，土壤应力过程的同步分析进一步表明水稻土具有应力屏蔽的能力，且水稻土的机械承载力模型表现为一个分段函数。原位犁耕测试进一步表明土壤结构受尺度控制的影响规律，水稻土不仅在深度方向的结构性及可耕性发生显著的分层，而且切土尺度同样影响着土壤结构的尺度分布特征，除此之外，模型切削及FEM仿真的结果也进一步表明土壤水稻土的机械失效力学模型受多重因子的影响，包括结持度、尺度与边界条件、切土楔角等，因此不再是一个可有简单自变量构成的单一函数。项目初步探讨了双层深旋耕对土壤物理的正面效应以及正旋与反旋耕的埋草性能对比，同时系统探讨了小麦根构型测试与构型分析方法。.项目在水稻土机械承载力方面的研究成果其意义在于论证了原位非扰动土壤状态在屏蔽应力传递方面的能力，以及土壤失效的阶梯型特征，这一发现为进一步系统探究非扰动水稻土不同于均质材质的力学机制奠定了基础。在水稻土的机械失效模型方面的成果表明同时存在多重优化策略实现土壤结构的优化，为今后进一步探讨强化土壤结构的机制和技术策略奠定了基础。项目在稻茬麦根构型测试与分析方法的成果不仅在3D空间拓扑的角度表达了水稻土不良物理状态对根构型的影响，而且该方法也为今后系统研究土壤结构与根构型的关系提供了条件。