ABSTRACT:

A penetrometric test under taken in a well-known granular medium (particle size distribution and water content) is directly linked with the dry density of the material. Hence it is possible to establish a relationship between dry density and cone resistance for a material at given water content. Due to extreme sensitivity of cone resistance, the penetrogram is a signature of dry density variation and nature of the soil. This method gives an efficient method of quality control in trenches up to 8 meters deep. It is proposed to use cone resistance qd to verify the in situ dry density and the whole penetrogram (qd in function of depth) to detect layers and their thickness in a compacted trench or backfill.

INTRODUCTION

The mechanical behaviour of a granular medium can be approached by two different ways. Either the granular medium is considered as a continuous medium with its constitutive laws, or the granular medium is described as a discontinuous medium. In the first approach, the mechanical behaviour is characterised with a set of mechanical parameters. In the second approach, the soil behaviour is well predicted by using grain parameters (mineralogy, shape texture) and assembly parameters (distribution of contacts, density and water content). Soil classification and a dynamic penetrometer test are used for quality control of compaction. The French GTR soil classification is used in this paper, but the method could be applied with any other accurate classification. A database is build, which contains physical and mechanical parameters and the penetrogram for all backfill material, at varying density and water contents. The quality control of compaction consists also of detecting verifying the layer thickness of a compacted soil structure. This paper proposes an algorithm based on the statistical properties of the penetrogram to detect layer thickness.

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