A. Mulder

Estimating rock strength with the equotip hardness tester

This technical note reports the preliminary results of the investigation of the Equotip Hardness Tester by the Section of Engineering Geology of Delft University of Technology. The tester is a relatively new product in the field of hardness testing, and was developed to measure the hardness of nonmetallic materials. It is a small battery-operated electronic spring-loaded device, in which a 3mm diameter spherical tungsten carbide test tip is mounted in an impact body, which bounces under spring force against a test surface from which it rebounds. A digital display shows the measured values of the impact and rebound velocities. The device was used in experiments on a series of rock samples, mostly limestone, prepared for the unconfined compressive strength test. During testing, rock samples were placed on a table with a 10cm thick rock top. For example, tests were performed on three types of limestone, each with four different surface treatments giving different grades of roughness. No major difference was found between the measurements taken on the different surface treatments. The authors conclude that the Equotip seems to be a convenient portable tool for estimating the unconfined compressive strength of rock material. The Equotips ability to make diametral measurements on rock cores makes it very useful for core logging.

Under Pressure: A Laboratory Investigation into the Effects of Mechanical Loading on Charred Organic Matter in Archaeological Sites

The present publication investigates what happens to archaeological sites when they are built over. Focus is put on the degradation of charred organic materials by static loading. It is assumed that materials lose archaeological value if their fragments become too small to be recovered, or too distorted to be classified at species level. Several charred ecofacts of a few millimetres in size (wood fragments, hazelnut shells, and seeds) have been selected and subjected to individual particle strength tests. Assemblages of these particles have also been compressed one-dimensionally and scanned at several stages of testing using laboratory based X-ray microtomography. Microscopic damage by splitting or crushing is found to be limited at the macroscopic yield stress. It initiated at stresses less than 80 kPa for the weakest assemblages, and in all cases at stresses below 320 kPa. (80 kPa represents the load of a 6 m high sand embankment on soft soil that has half-settled underneath the groundwater table, while 320 kPa corresponds to stresses applied beneath the pile foundation level of high-rise buildings.) Sand seeded with charred particles has also been tested to illustrate the beneficial effect of embedment of charred particles in sand during static one dimensional loading.

Resistance of Buried Archeological Site to One-dimensional Mechanical Loading

Our article focuses on wetland archeological sites that are subjected to one dimensional compression by the placement of a soil body for the construction of a line infrastructure or a landfill. We study the resistance to mechanical loading of ecofacts that are often investigated in archeological prospection works: charred and non charred plant remains and shells. We conducted one dimensional compression tests on assemblies of ecofacts, sand samples seeded manually with ecofacts and natural soils rich in ecofacts and used X-ray micro-tomography to evaluate the integrity of the ecofacts as function of loading. We assumed that fragmentation of ecofacts results in a loss of archeological value if particles become too small to be recovered. The ecofacts tested so far are unlikely to get crushed when included in an archeological soil above which a sand embankment of 1 to 10 m height is constructed. Some might however be deformed, flattened and re-aligned.

Investigating the susceptibility of iron ore to liquefaction

Liquefaction of cargo in a bulk carrier can cause the cargo to shift, which in turn can cause a ship to list and eventually can cause the ship to capsize. When liquefaction occurs, a material undergoes a transition from a solid to a liquid state and, in general, it is caused by the pore water pressure increasing above the total stress and overcoming the effects of cohesion, i.e. shear strength becomes negligible. In this paper, a number of iron ore samples, representing loosely the range of iron ore cargos from around the world, are characterised and tested. The grain size distribution and particle density were determined along with the tests which are prescribed by the International Maritime Solid Bulk Cargoes (IMSBC) code to assess the liquefaction potential: the Proctor/Fagerberg test, the penetration test and the flow table test. It is found that the results from these test methods correspond reasonably well, however they are not applicable for all ore types and the conditions at which the tests are performed do not correspond with the conditions encountered in the ship. Therefore one cannot quantify the risk of liquefaction based on the results of these tests alone, and further investigations on the liquefaction mechanism and the factors which influence this process are required. Part of these investigations have shown that the liquefaction behaviour is strongly linked to the grain size distribution, both in terms of particle size and grading. It is anticipated that the permeability, compaction and water retention behaviour are also of influence in determining liquefaction potential and are governed, in part, by the grain size distribution. Examples of these properties are presented, although the experimental programme is still ongoing.

Instrumenting uniaxial compressive strength tests to assess the anisotropic deformability of a one-dimensionally consolidated kaolinite

The concept of the axial shear was developed to catch severa l aspects of the anisotropic behaviour of soils. It was inspired by the end shear forces and moments which develop when specimens are cut at an angle to the material axes of symmetry and subjected to triaxial testing between rough platens. In routine triaxial and uniaxial compressive strength tests, these horizontal forces are unknown. In the laboratory work presented in this paper, they were measured. Tests were performed on specimens of one-dimensionally consolidated kaolinite. The testing program highlighted the difficulty of producing in the laboratory a material exhibiting a strong stiffness anisotropy. Despite this, the horizontal forces which developed along the base of inclined specimens and are at the base of the concept of the axial shear apparatus could be picked up. They were found to be low (less than 10N) but higher than those measured in vertical and horizontal specimens.