Wim Haegeman

SOME MECHANICAL PROPERTIES OF RECONSTITUTED BOOM CLAY

SummaryThe mechanical behaviour of reconstituted normally consolidated Boom clay was examined in a series of laboratory triaxial stress path tests. The aim was to establish some basic characteristics of this soil. The compressibility of the reconstituted Boom clay was found to be moderate, corresponding to the soils of the same plasticity. The results indicated also that the destructured Boom clay exhibited a brittle behaviour. The undrained secant stiffness was found to vary with strain level and also to be dependent on the consolidation pressure.

Characterization of Disposal Sites from Surface Wave Measurements

Nonintrusive Rayleigh wave investigation using the Spectral‐Analysis‐of‐Surface‐Waves (SASW) technique is a powerful tool for characterization of waste disposal sites in a broad range of waste materials. Applications of SASW surveys for site characterization at waste fills include determination of stiffness parameter profiles for the waste mass, evaluation of cover thickness, location of native ground interface and quantitative monitoring of improvement techniques. SASW surveys at five waste fills in Belgium composed of municipal waste, (dredged) sludge, cinders or slags demonstrate the potential applications of SASW and provide insight into typical shear wave velocity profiles for treated and untreated waste materials. Shear waves and SASW estimation of shear waves are proving to be valuable geotechnical assessment data and this paper highlights some important areas wherein the technique can be used successfully.

3D printing of an instrumented DMT: design, development and initial testing

This paper describes the design, fabrication and initial testing of an instrumented Flat Dilatometer Test (iDMT) device. Compared to the DMT test involving pressure readings at two-fixed displacements, this device is designed to have a direct displacement-measuring system and a larger-displacement range to evaluate the continuous pressure-displacement relation of a soil, which may afford an opportunity to improve the interpretation to take non-linear soil behaviors into account rather than using linear elasticity in the DMT analysis. However, technical constraints are encountered in the iDMT blade machining using traditional technologies, alternatively, a 3D printing technology is successfully applied to fabricate the iDMT blade. Then, the calibrations of the iDMT device are performed, followed by an iDMT test in conjunction with a DMT test in a calibration chamber, demonstrating that the new iDMT device can be used to investigate non-linear soil behaviors, and the 3D printing technology is proved not only to be an expedient solution but also to be used as a routine tool in improving geotechnical testing apparatus.

Dynamic behavior of silica sand under repeated cyclic loading

The nature-inspired concept of self-healing materials in construction is relatively new and has recently attracted significant attention as this could bring about substantial savings in maintenance costs as well as enhance the durability and serviceability and improve the safety of our structures and infrastructure. Much of the research and applications to date has focused on concrete, for structural applications, and on asphalt, with significant advances being made. However, to date no attention has been given to the incorporation of self-healing concepts in geotechnical and geo-environmental applications. This includes the use of concrete and other stabilising agents in foundations and other geotechnical structures, grouts, grouted soil systems, soil-cement systems and slurry walls for ground improvement and land remediation applications. The recently established Materials for Life (M4L) project funded by EPSRC has initiated research activities in the UK focussing on those applications. The project involves the development and integration of the use of microcapsules, biological agents, shape memory polymers and vascular networks as healing systems. The authors are exploring development of self-healing systems using mineral admixtures, microencapsulation and bio-cementation applications. The paper presents an overview of those initiatives to date and potential applications and presents some relevant preliminary results.By contrast to studies in petroleum geology and, despite their world-wide occurrence, geotechnical studies of ancient fluvial sediments are rare. This paper introduces the main characteristics of these sediments by reference to a classic UK example. Attention is then drawn to a number of major overseas examples where, although the principal features can be recognised, large differences arise as a result of factors such as the tectonic setting, the volume and mineralogy of the source material and the climate at the time the sediments were deposited. The first, over-riding problem for their engineering evaluation comes during the site investigation phase with the difficulty of deducing the geological structure and distribution of the widely varying lithologies.Strain accumulation in granular soils due to dynamic loading is investigated through long term cyclic triaxial tests and cyclic triaxial tests according to ASTM D 3999-91. Soil parameters, test equipment and loading conditions have a significant influence on strain accumulation, therefore a parameterization of the silica sand and a description of the cyclic triaxial test device are explained. Cyclic triaxial tests are performed and test results are presented illustrating the evolution of Young’s modulus during long term cyclic loading. The influence of the width of the stress-strain loop and the initial void ratio on strain accumulation is investigated and validated with existing accumulation models. The usefulness of Miner’s rule on sand subjected to cyclic loading is demonstrated by two tests with different packages of loading cycles.

Shear wave energy from seismic sources subjected to varying soil-coupling stresses

ABSTRACT: Modern downhole seismic cone penetration tests (SCPTs) are used in geotechnical studies to determine shear wave velocity and dynamic modulus profiles in soils. Although recommended test procedures exist for the SCPT, no standard specification is available for the sources size, type, impact energy and coupling stresses. Results of tests performed on three steel beams subjected to varying coupling stresses, as part of an ongoing research program on seismic response of SCPT sources, are presented. The test results confirm an increase in signal energy with increasing coupling stress as previously known. However, the results show that this increase occurs relatively fast and reaches a maximum at low coupling stresses between 15 kN/m2 and 28 kN/m2, irrespective of size and type of the source, for similar impact energies. One of the beams with metal blades, which were added to improve coupling, performed better than the others with smooth coupling surfaces.