Prediction of the volume of concrete backfill materials excavated using a pick

Abstract

Pick excavatability of controlled low-strength materials was experimentally studied to circumvent the fact that current classification systems or empirical excavatability criteria lack relevance (they do not refer to digging facilities and depend on the mix design and the granular skeleton of the material). Manual excavation is separated into two steps: the impact of the pick and decompaction. This was analysed by a mechanical approach. Energy is mainly consumed during the first step. A laboratory punching test was therefore proposed to evaluate excavatability (a confined cylindrical specimen was loaded by a cylindrical punch). Results were compared between the mechanised and the manual pick excavation tests on field trenches backfilled with air-entrained mortars or very lean concretes. These comparisons confirmed that a limited compressive strength was an indicator of excavatability. A model was proposed to evaluate the excavated volume by punching penetration for a given level of energy and a maximum size of aggregates in the material.

Keywords:

• concrete
• excavatability
• impact energy
• punching test
• trench
• compressive strength

Acknowledgements

The authors would like to acknowledge the assistance provided by ENPC (Ecole Nationale des Ponts et Chaussées) to determine the impact velocity of the pick and that provided by the Research Institute in Civil and Mechanical Engineering of the Ecole Centrale located in Nantes and by LCPC-Nantes (now Ifsttar). Financial support received from GDF SUEZ is also gratefully acknowledged.