Geosynthetics are widely used in Geotechnical Engineering to reinforce soil/gravel in pavements, retaining wall backfills, and embankments. It is important to measure strains in geogrids in the determination of their strength parameters such as tensile strength and secant stiffness, and in evaluating their performances in geogrid-reinforced structures. Strain gauges are commonly used in measuring strains in geogrids. However, it is important to verify the strains measured by strain gauges as these strains are affected by the data logging device, gauge factors, quality of bonding between grain gauge and geogrid, and temperature. Therefore, this study was conducted to verify the performance of strain gauges attached to Geogrids and also to investigate the possibility of using PIV technique and GeoPIV-RG software to measure the local strains developed in a geogrid specimen under tensile testing in the laboratory. In the experimental program of this study, six composite geogrid specimens were tested for tensile strength (wide-width tensile tests) while measuring/calculating its tensile strain by using strain gauges attached to the specimens, Geo-PIV-RG analysis and crosshead movements of Instron apparatus. Good agreement between the strains obtained from strain gauges and geoPIV-RG analysis was observed for all the tests conducted. These results suggest that the PIV technique along with geoPIV-RG program can effectively be used to measure the local strain of geogrids in the laboratory tests. It was also able to verify that properly installed strain gauges are able to measure strain in the geogrids which are used in the field applications.
Expansive soils are common in arid and semi-arid climate regions of the world and cause severe problems on civil engineering structures. The Swelling potential of the expansive soil mainly depends upon the properties of soil and environmental factors, and stress conditions. Swelling pressure is a key parameter used in designing structures in and on expansive soil. The swelling pressure of soil is measured in the laboratory using a representative soil samples. The size and the surface friction of the sample ring used in the swelling pressure test have effects on the measured swelling pressure and they have not properly been investigated. In this study, a series of constant volume swelling tests were conducted using an automated consolidation-swell apparatus to evaluate the effect of sample ring size, ring friction, initial dry density, and initial moisture content (IMC). Test results indicate an exponential growing trend of swelling pressure when the dry density is increased. Similarly, high swell pressures are achieved when the IMC is increased for the same dry density. A higher swelling pressure was measured when the friction of the specimen ring was reduced. The measured swelling pressure increases with increasing the height of the sampling ring and it decreases when the ring diameter is increased. Therefore, it is recommended to use a standard sample ring reducing inside wall friction using lubricants when measuring the swelling pressure in the laboratory. Further, the sample ring size, initial density and initial moisture content of soil should be given when reporting swelling pressure of soil.
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