The relationship among the pre-compaction stress, volumetric water content and initial dry bulk density of soil

摘要

Pre-compaction can occur as a result of a combination of soil settlement and the effect of fieldmachinery operations and, therefore, provides some insight into the loading history of a soil. Bylimiting stress to below that which determined the pre-compaction, the risk of further damage to thesoil through additional compaction can be minimised. Pre-compaction stress can be determinedaccurately using plate sinkage test results; however, these tests are time-consuming and requirespecialist equipment. An indication of pre-compaction stress, predicted from readily determined soilproperties, could provide a useful measure of the mechanical state of soils for use by advisory andextension staff in the planning and management of agricultural mechanisation systems. Therelationship among pre-compaction stress, volumetric water content and initial dry bulk density wasinvestigated in trials conducted initially under laboratory conditions on a sandy loam, and in the fieldon a sandy loam and a clay soil. Pre-compaction stress for sandy loam soil was found to increase with increasing dry bulkdensity and decreasing volumetric water content which is characteristic of the dominance offrictional resistance within this soil. For clay soil, however, increases in pre-compaction stress werefound to be largely independent of dry bulk density but closely correlated with decreases involumetric water content which influences the cohesive nature of this soil type. Relationships amongthese parameters were statistically significant for clay soil in the field and sandy loam soil undercontrolled conditions in a soil bin. Similar relationships, for a range of different soils and conditionscould complement existing soil survey databases to provide indications of the susceptibility of aparticular soil series, in a given condition, to further compaction. These data provide a usefulmanagement tool to aid selection of the number, size and specification of equipment required tocomplete necessary land work in the time available.