# Review of the Research on Soil Disturbance by Tools
## 1 Introduction  
Tillage tools usually cut, turn, pulverize and disturb the soil [1]. The simulation methods to study the interaction between soil and tools mainly include FEM and DEM. The discrete element method overcomes the shortcomings of continuous numerical methods and can intuitively display microscopic particles. Discrete element simulation software includes YADA, PFC3D, EDEM, etc. They are widely used in particle parameter calibration and soil disturbance analysis by tools [2]. The effect of tools on soil can be predicted by analyzing the disturbance between tillage tools and soil with the discrete element method. Based on it, the structure and parameters of tillage tools can be optimized.  
Soil disturbance can be defined as soil loosening (decrease in bulk density), movement (change of position in three dimensions) and mixing (relative exchange of positions, especially in the vertical direction) caused by tools. The quantitative parameters of the profile shape after disturbance are shown in Figure 1, namely, the cross-sectional area of the loose ditch (A1, A2), the maximum lateral soil throwing amount, the ridge height of the ditch, the inclined area of the ditch (A2), the width of the ditch and the backfill of the ditch. Lateral soil throwing was assessed in DEM simulations using the distance from the center of the ditch to the farthest throwing particle and soil coverage [3; 4]. After the soil is thrown, the surrounding of the ditch will form soil accumulation, which are lateral accumulation and forward accumulation, respectively. The resistance of soil will increase with high soil accumulation.  
The connection between soil particles is simulated by the forces bonds. When the tools enter the soil, the forces bonds between the particles will be destroyed. The forces bonds failure state and particle velocity field characterize the soil failure state. The optimization goal of the tools is often to reduce energy consumption and improve the tillage effect. During the simulation, DEM software is used to supervise the change of kinetic energy of soil particles, which can effectively simulate the energy conversion of the tools in the soil.  
It can be used as a design index for low energy consumption. Soil loosening efficiency is the ratio of soil disturbance area to traction force [5]. The soil disturbance characteristics can be evaluated by the soil expansion rate and the soil disturbance coefficient. The soil disturbance coefficient is equal to the ratio of the disturbed soil area to the soil area before tillage [6]. The animal paw has strong adaptability to the environment and has good digging performance. Selecting suitable animals for the development of bionic tools can reduce viscosity, drag and soil disturbance [7]. Some animals/animal parts good at digging soils, such as bear claws, dung beetles, earthworms and pangolins, shark scales, mole cricket claws and boar bow nose structures, etc., can move freely in cohesive soils due to their special non-smooth surface structure. This structure does not adhere to the soil, and is often used for bionic tools.  
The structure of the article is mainly divided into three parts: theory, simulation method and experimental method. In each chapter, the parameters involved in the soil disturbance, such as disturbance area, are classified. After classification, the respective parameter simulation and experimental methods are described in detail. This paper analyzes and summarizes the current research status of soil disturbance caused by tools. The theory includes contact model, the forces bonds and energy consumption mechanism, energy dissipation analysis, disturbance shape, soil layer mixing, etc. The test involves soil pile disturbance shape, mixing of different soil layers, soil and residue mixing, tillage resistance, etc. This study provides readers with disturbance research forms, research methods, etc., and provides references for further research on soil disturbance and tool optimization [8; 9].