This paper presents the summary of experimental program to evaluate the soil stabilized with perlite and the geogrid-reinforcement. Due to its pozzolanic properties, perlite, a glassy volcanic rock, may be utilised as a stabilising agent. The standard California bearing ratio (CBR) laboratory tests were performed on the soil samples with various combinations of perlite and single layer of geogrid reinforcement placed at various height. The laboratory experiments were undertaken to investigate the impact of using perlite (0%, 10%, 20%, 30%) and geogrid (single layer of geogrid reinforcement placed at H/2, 3H/4 and H/4). The effect of geogrid reinforcement with respect to the position and varying contents of perlite on the strength behaviour of subgrade soil has been examined. Furthermore, the test was carried out by optimum percentage of perlite with geogrid placed at optimum height. Results of the current study indicate that there is a significant increase in CBR values for subgrade soil stabilized with perlite and reinforced with geogrid. Maximum CBR value was observed in the soil sample reinforced with single geogrid layer placed at H/4 (where H is height of CBR mould) with 20% perlite.
The presence of soft/loose soil at ground level is one of the main challenges faced by the engineers during the construction of highways. The need for greater granular material thickness when building roads over this loose soil drives up construction costs. Alternately, attempts to produce a construction that is more cost-effective by reducing the thickness of the pavement layer may result in early pavement deterioration, which will render the road impassable soon after construction.
Some states in India that are located in areas with high rainfall suffer from inadequate drainage and weak subgrade conditions. When exposed to moisture instability, expansive soil's volume variations are more harmful. Due to their behaviour during swelling and shrinking, expansive soils can cause structural failure. Low engineering qualities and bearing capacity are found in expanding clayey soils. On the other side, high settlement of expansive soil is bad for geotechnical projects and building structures. In order to lessen their harmful impact, expansive soils must be amended.
For the stabilisation of soft, expanding clayey soils, lime can be utilised as an additional ingredient. Studies on lime stabilisation are regularly conducted, according to the literature. Other than lime, pozzolanic additives have started to be used in recent studies. In the presence of water and especially when combined with lime, pozzolans are substances that, at normal temperature levels, may exhibit binding capabilities. Lime-induced chemical reactions result in the formation of compounds that are insoluble in water. In this stabilization study, perlite was used as a pozzolanic additive and geogrid is used as a reinforcement.
For the present study, soil for laboratory testing was collected from the GCT campus, Coimbatore which is of Latitude N 11° 0' 50.0004“and longitude E 76° 56' 49.9992“. The natural water content of soil is 17.05% and is classified as a medium compressible clay (CI). The detailed engineering properties of soil sample are listed in table 1.
Table 1 : Engineering Characteristics Of Subgrade Soil
% of Gravel
% of Sand
% of Clay and Silt
Liquid limit (%)
Plastic limit (%)
Optimum Moisture Content (%)
Maximum Dry Density (g/cc)
Geogrid is a geosynthetic material, made of polymers, that is used to reinforce soil. Geogrids are made from high molecular weight, high tenacity polyester multifilament yarns. The yarns are woven on tension in machine direction and finished with a polymeric coating, geogrids are polymeric in nature with tensile strength varying from 100 to 220KN. Engineering properties of geogrid material used in this study are mentioned in table 2. The interlocking of the base aggregate and geogrid is a function of the gradation and angularity of the aggregate and the geometry of the geo-grid. It has been noted that for geogrids, the interlocking of soil particles through the geogrid apertures creates an efficient interlocking effect.
Table 2 : Engineering Features Of Geogrid Material
Ultimate tensile strength
Strain at Ultimate strength
200 g/ m³
Perlite is an amorphousvolcanic glass that has a relatively high water content, typically formed by the hydration of obsidian. Perlite is a non-renewable resource. The world reserves of perlite are estimated at 6700 million tonnes. Although perlite possesses pozzolanic properties. Because of its low density and relatively low price, many commercial applications for perlite have developed. Properties of perlite used in this study are mentioned in table 3.
Table.4 shows the variation of the maximum dry density and optimum moisture content for soil mixed with different percentage of perlite. The Standard Proctor Test Result shows that there is no marginal improvement in the dry density of soil, whereas, little increase in the optimum moisture content is observed due to water absorption capacity of perlite.
Addition of perlite increase the CBR value due to its water absorption capacity. Table 5 demonstrates the variation in efficiency of the soil for varying contents of perlite. Based on CBR values, it can be concluded that 20% perlite yields best results in unreinforced case. Table 6 illustrates the variation in reinforcement efficiency by varying the position of geogrid. Based on CBR values, it can be concluded that geogrid placed at the height of H/4 yields best results in reinforced case. Maximum CBR value was observed at 20% perlite and geogrid placed at H/4 distance which was already found as an optimum. The improvement of the CBR value is probably due to water absorption capacity of perlite and the interlocking capacity of geogrid. The vertical stress transferred to the geogrid layer causes a stress reduction. The geogrid, which acts as a thin slab, redistributes stress over a larger area. As a result, the load-deformation response increased, with less vertical deformation observed. The vertical deformation rate decreases with the presence of a geogrid layer in the stabilized laterite soil.
In the current study, CBR values have been used to evaluate the strength behaviour of different combinations of perlite and effort has been made to enhance the strength of subgrade soil using geogrid reinforcement by varying the position. In addition, reinforcement efficiency has been used to evaluate the performance of subgrade soil with the inclusion of geogrid reinforcement. It is to be noted that the strength of the subgrade is significantly altered positively by the positioning of the geo-grid at varying depth. It was observed that the highest subgrade strength is achieved when it is placed at H/4 for a single layer although has a satisfactory result at H/2 and 3H/4 respectively. On the other hand, in the unreinforced case CBR values increase with increase in perlite content. The test result shows that there is no marginal improvement in the dry density of soil, whereas, little increase in the optimum moisture content is observed due to addition of perlite as an admixture. Maximum CBR value was observed at 20% perlite and geogrid which is placed at H/4 distance which was already found as an optimum. Overall, it can be summarized that there is a significant amount of improvement in the strength of subgrade soil stabilized with perlite and reinforced with geogrid material.
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