A Gauge For Measurements Of Soil-structureInterface Force Due To Explosive Loading

Abstract

The paper presents some work regarding construction of a soil-structure interface gauge measuring the interface force distribution over much larger areas than possible with conventional pressure gauges. Different backfill/backpack materials surrounding buried protective structures may have different effects regarding the interface forces between the soil and structure when exposed to explosive loading. The motivation of this work is to study these effects. The gauge concept consists of a grid of uncoupled plane areas using PVDF-film sensors between two mating surfaces to measure the pressure. The gauge is described in detail. This concept is attractive because all parts are commercially available and the concept is easy to extend to large scale gauges for use in full scale explosive tests. The interface gauge is designed to measure both uniform pressure and point loads from backfill/-backpack materials. Design, necessary equipment and some experimental evaluations of the demonstration gauge are presented. INTRODUCTION It has been known for many decades that certain crystals, like quartz, generates an electrical charge across the crystal when stressed. This is called a piezoelectrical effect. The amplitude of the signal are directly proportional to the deformation of the piezoelectric material [1 ]. Today appropriately treated polyvinylidene fluoride (PVDF) exhibits piezoelectric properties suitable for a variety of applications. Piezoelectric film is a flexible, lightweight, tough plastic film commercially available in a large variety of thicknesses and areas, and its properties as a transducer includes wide frequencies and vast dynamic range. This properties make the PVDF-film appropriate as impact and shock wave sensors. The Norwegian Defence Construction Service is running a research program regarding backfill/backpack materials surrounding buried protective structures. The Transactions on the Built Environment vol 8, © 1994 WIT Press, www.witpress.com, ISSN 1743-3509 358 Structures under Shock and Impact objective of this project is to study the interaction between soil and structure subjected to explosive loading, since different backfill/backpack materials are known to impose quite different loads on a buried structure. The following requirements were essential for development of the interface gauge To measure high pressures up to 50 MPa To measure point loads and their distribution Large scale, gauge size 1 nr Be flexible, give correct results also under structural deformation To be insensitive to tough surface conditions To our knowledge, no commercial gauge is available for this purpose, and hence it was decided to develop a small scale demonstrative gauge to come up with a possible construction.