An X-ray tomographic investigation into the effects of compressive shear on analogues to charred seeds embedded in archaeological sand

Abstract

By signing the Valletta Treaty, several countries have obliged themselves to save archaeological heritage sites and fund relevant research. UNDERSTRESS is a proposal for funding which does research and provides data to predict damage done to such archaeological site by construction of linear infrastructure. As a preliminary study this BSc thesis is carried out in the framework of UNDERSTRESS. Although research has been done on archaeological artefacts embedded in sand, charred organic seeds have not been investigated thoroughly yet. The sand, which comes from a depot near Dronten in the Netherlands, has been used because multiple archaeological artefacts have been found in that sand layer. As analogue for the charred organic seeds coco pops, the cereal, have been used. The characteristics of the sand as well as of the coco pops have been investigated. A falling height of fifty centimetres has proven to create a reproducible density. To test the damage to the coco pops samples have been triaxial tested with a vacuum pressure applied of 80 kPA. This vacuum pressure create an effective confining pressure of 80 kPA as well. With the falling height and the confining pressure, a sample configuration in which two layers of coco pops are placed, the damage to those coco pops is zero when applied to a strain of five millimetres. The damage is made visible by using 3D visualising software called Avizo. The grain have not been damage during that test and they have not reallocated as well. For another configuration the coco pops did not react the same. The entire sample was filled with coco pops and sand as supporting material and this time the strain was 15 millimetres. Three scans made at three different times during the loading show that the coco pops are not damaged until after the sample has reached its maximum stress. All the damage to the coco pops as well as the reallocation of the coco pops happens between the peak stress and the unloading. At the slice where the radial deformation of the sample is the largest are all coco pops are damaged with most of them crushed. Two centimetres above and below this slice, the coco pops are partially damage and further away from this slice, the coco pops are not damaged. In total, 10 percent is damaged during the loading. The coco pops are damaged so severely, not much information they have stored would be available if it were charred organic seeds. The charred organic seeds do have twice the strength of a coco pop according to earlier research.