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Title: A method of predicting changes of soil dry bulk density beneath agricultural wheels
Author: Blackwell, Paul Stuart
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1979
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A prediction model of soil compaction beneath agricultural wheels is constructed from estimations of soil stresses and information on soil stress/strain relationships. The soil stress estimations are based on prediction equations developed by Sohne and tested against stress measurements made in situ beneath tractor wheels of three different loadings. The soil stress measurements were made by deformable spherical stress transducers; a water-filled rubber ball and a mastic ball. The stress/strain relationships of the soil are examined using the Critical State theory of soil mechanics. Interpretations of this theory are made to derive soil mechanical functions from the dry bulk density before and after the application of certain levels of stress. These functions are the apparent virgin compression line ('VCL') and the primary function. One or both of these stress/strain functions could be derived from field or laboratory measurements. Field measurements of dry bulk density were made by gamma-ray transmission equipment. A computer program was developed to apply the compaction prediction model. Soil stresses were derived from tyre-soil contact area and wheel load as well as soil cone resistance. Stress/strain relationships were derived from soil texture and gravimetric soil moisture content. Data from separate field experiments was used to test the model. A good correspondence was found between observed and predicted dry bulk density changes for sandy loam and loam soils of dry bulk density greater than 1.1 g/cm3 and cone resistance greater than 5 bar. The research suggests that maximising tyre contact area and minimising wheel load will minimise compaction in the topsoil and subsoil.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available