Dominique Ngan-Tillard

ISRM Suggested Method for the Needle Penetration Test

Estimation of mechanical properties of intact rock is usually required for assessment of the stability of rock structures. They are also important elements of the rock classifications used in empirical assessment of rock masses. Measurement of these properties requires laboratory testing, which must be performed on samples of certain dimensions to fulfill testing standards and/or suggested methods. Laboratory tests are also time-consuming due to sample preparation, as well as experimental procedures often require high-capacity loading devices. High-quality core samples recommended by standards and/or suggested methods for the laboratory tests cannot always be obtained, particularly from weak and clay-bearing rocks. For these reasons, some simple and inexpensive index test methods have been developed to indirectly estimate the mechanical properties of intact rock (ISRM 2007). However, even preparation of smaller samples from weak and clay-bearing rocks for some index tests is still troublesome. In addition, geo-engineering and/or restoration studies on natural and man-made historical rock structures and monuments or buildings built with masonry construction techniques may require the determination of mechanical properties of intact rock. Sampling from such ancient sites is not allowed due to preservation, and environmental and other concerns resulting in the lack of mechanical data for those studies. To overcome the above-mentioned difficulties, a portable, lightweight and non-destructive testing device, called needle penetrometer, was developed in Japan and released as a suggested method by the Rock Mechanics Committee of the Japan Society of Civil Engineers (JSCE-RMC 1980). Similarly, Public Works Research Institute (PWRI 1987) published a draft manual of the test for weak rock mass Please send any written comments on this ISRM Suggested Method to Prof. Resat Ulusay, President of the ISRM Commission on Testing Methods, Hacettepe University, Department of Geological Engineering, 06800 Beytepe, Ankara, Turkey.

Tools for Predicting Damage to Archaeological Sites Caused by One-Dimensional Loading

Tools are developed to predict damage to archaeological remains caused by the construction of line infrastructure on soft soil. They are based on numerical modelling and laboratory testing supported by X-ray microcomputed tomographic observations, and micromorphological analyses of thin sections. They have been validated for one-dimensional (1D) loading at two sites in the Netherlands where soil has been placed on top of organic layers rich in ecofacts and overlaying Pleistocene sands. Numerical prediction of the deformation of soft layers underneath an embankment remains a challenge for geo-technical engineers. Errors on surface settlement prediction reach ±15% of the measured total settlement. Laboratory observations show that vulnerable artefacts can get crushed when packed loosely in pure assemblies under 1D loading equivalent to less than 5 m of sand. Fragmentation is assimilated to loss of archaeological value as it compromises recovery during sieving. Embedment in a sandy or a very compressible organic matrix has a beneficial effect on the resistance of ecofacts. Embedded ecofacts can resist a load of more than 12 m of sand. Flattening and re-orientation of soft plant remains occur during 1D loading without microscopic damage of tissues.

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.

Determination of Elastic Parameters in the Lateral Stress Oedometer

Measurement of elastic parameters is a fundamental problem in soil mechanics. In cross-anisotropic soils, five independent elastic parameters are required to fully describe soil behaviour. It is possible to determine all of these parameters in oedometr ic testing conditions if lateral stresses are measured during vertical loading. The calculation requires that three tests be conducted on samples trimmed at different orientations. This article examines a new lateral stress oedometer and it s practical application for the measurement of cross-anisotropic elasticity parameters for a laboratory prepared kaolinite. Results of a series of tests on one -dimensionally consolidated kaolin yielded values of modulus and Poisson’s ratio that are consistent with publ ished literature. The lateral stress oedometer is a robust and relatively inexpensive test for determination of elastic parameters over a wide range of loading conditions.

Potential of Using Remote Sensing Data for Dike Inspection

Dikes are increasingly becoming structures of major importance in view of sea level changes. Dike inspectors monitor dikes visually whilst walking the dike. It has been proposed that remote sensing could be used to make dike inspection faster and cheaper. This paper presents the results of a study which investigates remote sensing for evaluating the soil moisture and dike grass cover quality. Correlations were found between soil moisture and thermal and multispectral remote sensing data, and between dike grass cover quality and multispectral remote sensing data. Remote sensing provides useful information for soil moisture and grass cover quality evaluation for dike inspection and may be useful for dike quality inspection.

Influence of Pore Fluid Conductivity and Water Content on the Complex Conductivity of Peat

This paper presents a new prototype cell that can perform simultaneous electrical and compression tests on peaty soils. Two different set-ups for measurements at high and low frequency are used. Results on the complex conductivity response of peat samples for different pore fluid salinities and degrees of compression are presented. This work presents reproducible results that can be utilized to improve interpretation of field measurements on peat.

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.

Assisting data interpretation: the cone penetration test

The construction of a subsurface model requires considerable expert knowledge, tends to be labour intensive, and may have a significant degree of data redundancy, especially for very large projects.