CBR Improvement of Clayey Soil with Geo-grid
The quality and life of pavement is greatly affected by the type of sub-grade, sub base and base course materials. The most important of these are the type and quality of sub-grade soil. But in India most of the flexible pavements are need to be constructed over weak and problematic sub-grade. The California bearing ratio (CBR) of these sub-grade have very low, it needs to more thickness of pavement. Decrease in the availability of suitable sub base and base materials for pavement construction have leads to a search for economic method of converting locally available problematic soil to suitable construction materials. The present research have to study the effect of geo-grid reinforcement on maximum dry density (MDD), Optimum Moisture Content (OMC), California Bearing Ratio (CBR) and E-Value of sub-grade soil. The clayey type of soil and one type of geo--grid were selected for this study. From the study it is clear that there is considerable improvement in California Bearing Ratio (CBR) of sub-grade due to geo-grid reinforcement. In case of without reinforcement (Geo-grid) the soaked CBR value was 2.9% and when geo-grid was placed at 0.2H from the top of the specimen the CBR increases to 9.4%.
CBR of Soaked Clay Drained by Sandy Layer
The quality of pavement is affected mostly by the type of subgrade soil, and in many countries, the subgrade soil is clay. The California Bearing Ratio CBR of clay is generally very low which leads to a thicker layer of pavement and sub base materials. This increase in quantities leads to a significant increase in cost. Since the use of the clay as subgrade is inevitable, many private and public institutions searched on a way to increase its CBR, but most of the conducted studies focused on increasing clay CBR by reinforcing the clay either by geogrids or by fibers which are very expensive. One common finding in all the studies was that the CBR of unsoaked clay is higher than CBR of soaked one which means that CBR of clay is affected by its moisture content. In our work, the objective is to increase the CBR of clay by draining it instead of reinforcing it. Drainage can be obtained by adding a layer of granular soil between clay layers. Sand was used as granular soil for the sake of its workability in the CBR mold and for its relatively small particles size. Our aim is to verify if sandy layer can play a drainage role for the clayey soil and to also find the most efficient position of the sandy layer. We collected six soils from different regions to cover as much as possible the different clay types in Lebanon. For each soil, we found CBR values for clay alone and clay with layer of sand and compares them. Identification tests were necessary in order to build our analysis. At the end, from the results and analysis, we found the position of the sandy layer which increases most the clay CBR and we proved that the existence of sandy layer is beneficial for CBR of clay.
Geomagnetic Polarity Epochs: Sierra Nevada Data, 3
Available paleomagnetic and radiometric results for about 60 igneous rocks 3.6 m.y. old or less are consistent with the following geomagnetic polarity epoch time scale: Brunhes normal polarity epoch, 0.0 to 0.85±0.15 million years; Matuyama reversed polarity epoch, 0.85±0.15 to 2.4±0.1 million years; Gauss normal polarity epoch, 2.4±0.1 to 3.35±0.1 million years; Gilbert reversed polarity epoch, 3.35±0.1 million years to (?). A brief interval of normal polarity (the Olduvai event) occurs within the Matuyama reversed epoch at about 1.9 m.y., and a brief interval of reversed polarity (the Mammoth event) occurs within the Gauss normal epoch at about 3.06 m.y. Data for twelve units from eastern California and Nevada, reported here for the first time, are particularly useful in defining the Gauss-Gilbert boundary and for recognizing the Mammoth event.