Since the last three decades, several studies have been conducted related to improvement in bearing capacity of pavements, embankments, and shallow foundations resting on geosynthetic reinforced soil. Most of the work has been carried out on single layer soil e.g., sand or clay layer only. Very few studies are available on a double layer soil system; but no study is available on the local soil of Carbondale, Illinois. The present study investigates the physical and engineering properties of a local soil and commonly available sand and improvement in the bearing capacity of a local soil for a rectangular footing by replacing top of the local soil with sand layer and placing geogrids at different depths. Seven tests on the model footing were performed to establish the load versus settlement curves of unreinforced and reinforced soil supporting a rectangular foundation. The improvement in bearing capacity is compared with the bearing capacity of the local soil and double layer unreinforced soil system. The test results focus on the improvement in bearing capacity of local soil and double layer unreinforced soil system in non-dimensional form i.e., BCR (Bearing Capacity Ratio). The results obtained from the present study show that bearing capacity increases significantly with the increasing number of geogrid layers. The bearing capacity for double layer soil increases, by placing three inch sand layer at the top of local soil, was not significant. The bearing capacity of the local soil increased at an average of 7% with three inches sand layer. The bearing capacity for the double layer soil increases with an average of 16.67% using one geogrid layer at interface of soils (i.e., local soil and sand) with u/B equal to 0.67. The bearing capacity for the double layer soil increases with an average of 33.33% while using one geogrid in middle of sand layer having u/B equal to 0.33. The improvement in bearing capacity for double layer soil maintaining u/B equal to 0.33 and h/B equal to 0.33; for two, three and four number geogrid layer were 44.44%, 61.11%, 72.22%, respectively. The results obtained from this research work may be useful for the specific condition or similar type of soil available anywhere to improve the bearing capacity of soil for foundation and pavement design.

The objective of this research was to apply a previously recommended laboratory testing protocol to specific aggregate base materials that are also the subject of ongoing full-scale field testing. The scope of this research involved three aggregate base materials selected from three sites where full-scale field testing programs have been established. The first and second field sites included five different geogrid types, categorized as either biaxial or triaxial, in a singlelayer configuration, while the third site included only the triaxial geogrid type in either a singleor double-layer configuration. Geogrid-stabilized and unstabilized control specimens were evaluated using the American Association of State Highway and Transportation Officials T 307 quick shear testing protocol. Measurements of load and axial displacement were recorded and used to develop a stress-strain plot for each specimen tested. The peak axial stress, the modulus to the peak axial stress, the modulus of the elastic portion of the curve, and the modulus at 2 percent strain were then calculated. Statistical analyses were performed to investigate differences between geogridstabilized specimens and unstabilized control specimens and to investigate differences between individual geogrid products or geogrid configurations. Depending on the method of data analysis, the quick shear test results indicate that geogrid stabilization, with the effect of geogrid stabilization averaged across all of the geogrid products evaluated in this study, may or may not improve the structural quality of the aggregate base materials evaluated in this study. The results also indicate that, regardless of the method of analysis, one geogrid product or configuration may be more effective than another at improving the structural quality of a given aggregate base material as measured using the quick shear test. All results from this research are limited in their application to the aggregate base material types, geogrid products, and geogrid configurations associated with this study. Additional research is needed to compare the results of the laboratory quick shear testing obtained for this study with the structural capacity of the geogrid-stabilized and unstabilized control sections that have been constructed at corresponding full-scale field testing sites. Specifically, further research is needed to determine which method of laboratory data analysis yields the best comparisons with field test results. Finally, correlations between the results of quick shear testing and resilient modulus need to be investigated in order to incorporate the findings of the quick shear test on geogrid-stabilized base materials into mechanistic-empirical pavement design.

The modulus of aggregate base layers in pavement structures can potentially be increased through the use of geogrid. However, methods for determining how much structural benefit can be expected from a given geogrid product have not been standardized. A laboratory testing protocol is therefore needed to enable evaluation, in terms of modulus or California bearing ratio (CBR), for example, of the degree of improvement that may be achieved by a given geogrid. Consequently, the objective of this research was to identify a laboratory test method that can be used to quantify improvements in structural capacity of aggregate base materials reinforced with geogrid. For this research, National Cooperative Highway Research Program Report 598 repeated load triaxial, American Association of State Highway and Transportation Officials (AASHTO) T 307 quick shear, and CBR testing protocols were used to test unreinforced and geogrid-reinforced aggregate base materials from northern Utah. Biaxial and triaxial geogrid were investigated in multiple reinforcement configurations. Several statistical analyses were performed on the results of each test method to identify the test that is most likely to consistently show an improvement in the structural capacity of aggregate base materials reinforced with geogrid. The results of this research indicate that, for the methods and materials evaluated in this study, calculation of the modulus at 2 percent strain from the AASHTO T 307 quick shear data is the test method most likely to consistently show an improvement in structural capacity associated with geogrid reinforcement. Of the three configurations investigated as part of this research, placing the geogrid at an upper position within a specimen is preferred. Given that the end goal of the use of geogrid reinforcement is to improve pavement performance, additional research is needed to compare the results of the AASHTO T 307 quick shear test obtained in the laboratory with the structural capacity of geogrid-reinforced aggregate base materials measured in the field. In addition, correlations between the results of the AASHTO T 307 quick shear test and resilient modulus need to be investigated in order to incorporate the findings of the AASHTO T 307 quick shear test on reinforced base materials into mechanistic-empirical pavement design.

La presente investigación tiene como objetivo el análisis del comportamiento de la geomalla biaxial extruida incorporada en un suelo granular a nivel de la sub-base para el pavimento que está ubicado en la av. Defensores de Morro en el distrito de Chorrillos, en el Departamento de Lima. Por ello, el procedimiento de esta investigación es realizar un programa experimental para el suelo en estudio e incluyendo la geomalla biaxial a nivel de la sub-base en dos diferentes posiciones una colocada en el medio y las dos capas en los extremos de la misma para encontrar la mejor alternativa que aumentara el valor del CBR del suelo para este tipo de suelo granular. La avenida en estudio presenta un tipo de suelo según clasificación SUCS de arena pobremente gradada con limo y grava. De acuerdo a los resultados obtenidos se observa que la geomalla incorporada en el medio mejora el CBR del suelo en un 6,5% y las colocadas en los extremos mejora el CBR del suelo en un 3,2%. La metodología utilizada para la investigación es del tipo de diseño experimental ya que se realizó un ensayo completo del suelo para determinar las características físicas y mecánicas necesarias, y conocer el valor del CBR de este suelo, cuyo valor fue muy importante para esta investigación, ya que con este se pudo saber si valor aumentaba favorablemente para una suelo granular. Teniendo como resultado que el valor de CBR ubicado en el medio de la capa sub-base mejora el valor del CBR en mayor porcentaje. / The present research aims to analyze the behavior of the extruded biaxial geogrid incorporated in a granular soil at the sub-base level for the pavement located in av. Defensores de Morro in the district of Chorrillos, in the Department of Lima. Therefore, the procedure of this research is to carry out an experimental program for the soil under study and including the biaxial geogrid at the sub-base level in two different positions, one placed in the middle and the two layers at the ends of it to find the best alternative that will increase the value of the soil CBR for this type of granular soil. The avenue under study presents a type of soil according to the SUCS classification of poorly graded sand with silt and gravel. According to the results obtained, it is observed that the geogrid incorporated in the middle improves the CBR of the soil by 6.5% and those placed at the ends improve the CBR of the soil by 3.2%. The methodology used for the research is of the type of experimental design since a complete test of the soil was carried out to determine the necessary physical and mechanical characteristics, and to know the value of the CBR of this soil, whose value was very important for this investigation, since that with this it was possible to know if the value increased favorably for a granular soil. As a result, the CBR value located in the middle of the sub-base layer improves the CBR value by a greater percentage. / Trabajo de investigación