The Preliminary Researches of Pull-Out of GFRP Rods From Mineral Coarse-Grained Soils

Introduction

The rapidly developing road and bridge infrastructure places more and more demands on designers and contractors. Very often, the biggest problem to overcome is the weak quality of the subsoil, which requires replacement or strengthening. Therefore, despite the wide range of solutions used, new, more effective and economical solutions are still being sought. The results presented in the chapter are part of the preliminary research and analyzes under the project “System for strengthening the soil with GFRP composite bars with fiber optic monitoring”, performed at the Rzeszów University of Technology in Poland, aimed at introducing an innovative method for soil reinforcement. The project concerns the innovative use of GFRP (Glass Fiber Reinforced Polymer) composite rods to strengthen the subsoil, instead of using geosynthetics or steel rods. Nowadays, GFRP rods are effectively used to reinforce concrete in engineering structures, therefore attempts have been made to protect the selected subsoil with them in order to improve its geotechnical parameters. The GFRP rods are lightweight, high strength and durability, connected in girds and placed in the soils creates an effective reinforcement of the substrate, minimizing settling. As part of the main research project selected rods will be equipped with optical fibers, which will allow continuous monitoring of the ground, providing information on the behavior of the structure. This is important for high-rise buildings, embankments, landslides. The project includes the perform of works to identify system components (GFRP rods, various soils), check their cooperation in the strengthening system (friction resistance, wedging effect) and assess efficiency fiber optic monitoring of the subsoil.

The research project in question is aimed at determining mainly the pull-out strength of bars and geogrid made of GFRP bars from coarse (non-cohesive) soil in laboratory conditions using a large-size model, which requires very careful preparation of both the necessary equipment and the research program itself. The described target tests were to be carried out in a box generating a prepared soil sample with dimensions (B) 1000 mm x (L) 1500 mm x (H) 700 mm. A very important issue is the very process of preparing the soil material, which should be homogeneous (humidity) and equally compacted in every place of the prepared sample. The problem that should not be underestimated is also the method of applying the loads, because in the case of a crate designed for real model tests, the expected stress in the soil sample is achieved by loading with an appropriate number of road slabs of known weight, which requires the use of heavy equipment and precise application. The presented possibility of using GFRP rods can be an alternative to geosynthetic materials commonly used in geotechnics, which, despite their obvious advantages, also have weaknesses: relatively high price, low stiffness and resistance to damage, which is of particular importance at the stage of installation in the ground and requires a high technological regime. GFRP rods, due to their stiffness, strength, durability and favorable price, can eliminate these problems, primarily in situations where strength and stiffness of the reinforced substrate are important, although the scope of their application will not be identical to that of alternative geosynthetic materials. This solution is also economically advantageous.

Due to the considerable advantages of GFRP bars compared to steel and other composites, their share in the application in the construction industry increases, which generates the need to conduct specialized research dedicated to specific market needs. The GFRP materials, including reinforcing bars, are characterized by properties that are very desirable in the construction industry, and the most important of them are (according to https://mrg-composites.com): resistance to various types of corrosion, incomparable to other materials, makes it possible to use them indoors and outdoors, they are very durable and do not degrade in the presence of chemicals, reinforcing bars are almost twice as strong as steel ones, weigh much less and are cheaper, they are also easy to install due to the ease of cut and bent as specific requirements. In addition, the relatively low weight of the GFRP rods facilitates transport, storage and installation at the construction site, often does not require heavy equipment, it makes the construction process faster and more efficient which has its significant economic dimension. Therefore, a wide range of research and development works are carried out, the aim of which is to determine the parameters of the bars themselves, optimize their composition and structure, as well as the conditions of cooperation with the substrate, which may be concrete, soil or even wood.