Stress Transmission Of Paddy Soil With Soil Stress Sensors

Development of agricultural mechanization resulted into severe soil compaction, which is related to dense soil state, reduced porosity, increased soil bulk density, degraded aeration and infiltration, higher mechanical strength and impedance to root penetration. Thus there is a need to illustrate stress transmitting mechanism and to assess soil compacting effect for the reduction and avoidance of soil compaction and protection of soil resources.A major methodology of the research was to use soil stress sensors as a tool to investigate paddy soil stress transmission properties, which was also combined with laboratory uni-axial compression test and in-situ plate sinkage test. The implementation of all these works was aimed to explain soil compaction mechanisms and compacting processes. The result of this work can be applied to better interpret soil compacting mechanisms and thus is significant for the solution of soil compacting problems.Calibration on the soil stress sensors with liquid bag, sand and soil led to contrasting results between soil calibrating and the other two. Differences were also found when the calibration was done on different soil moisture contents and different soil densities. This difference was a result of the changed soil structural states. Consequently there is the need to precisely quantify soil basic physical states before soil stress measurements.Paddy soil was sampled and tested in lab with uni-axial compression test to illustrate the stress transmitting properties of undisturbed soil. Load-stress-sinkage relation was measured and the influence of soil depth, density and water content was investigated. The result provided a quantified relation among soil porosity, load, soil depth, soil density and water content, and the load of plate changed exponentially with plate sinkage.A new system was designed to resolve the problems existed in the traditional soil stress sensing works, which were not only time consuming, but also disturbed soil severely and damaged soil structures. The system was composed of power supply system, stress sensor burial system, hydraulic loading system and data collection system. It was able to bury soil stress sensors to the test soil in a 30° downward direction. Synchronous with plate sinkage, plate displacement, load on the plate and stress in soil were measured. Trial test on paddy soil revealed that the system functions well and avoided soil disturbance to the maximum extent. Soil stress sensors were properly buried into soil, satisfying the need to measure multiple points in short durations.The designed system was used in paddy soil to illustrate stress transmission properties in-situ. Results showed that soil bearing strength to the plate changed and revealed sectioned appearances. The two sections were interpreted as soil strength increase and soil rheological failure stages. This finding confirmed that the south China paddy soil was unique in its structural properties and behaved differently from the continuum mechanics.