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:: Volume 14, Issue 3 (11-2020) ::
2020, 14(3): 523-556 Back to browse issues page
Effects of Geotextile Applications on Bearing Capacity Clay-Gravel Mixtures in Pavement Layers
Semaneh Ghasemvash, Rouzbeh Dabir *1
1- , rouzbeh_dabiri@iaut.ac.ir
Abstract:   (2621 Views)
Pavement layers as a part of road structure play an important role and provide a flat and secure surface. Subgrade layer could act as a compacted embankment, natural or stabilized ground. Subgrade is a foundation of pavement layers, and it withstands all of loads due to vehicles that are transferred from upper layers (i.e., subbase, base and asphalt layers).Therefore, constructing pavements with bearing capability, high durability, quality, and maintenance in proper operating conditions is very important. However, suitable materials for constructing pavement layers are not available, and improvement techniques should be employed for them. Generally, different methods such as mechanical or chemical are available for improvement. Nowadays, geosynthetic materials such as geotextile and geogrid are used to optimize and enhance the bearing capacity of pavement layers. The present study is aimed to investigate the effects of geotextile applications on bearing capacity of clay-gravel mixtures in pavement layers.
Material and Methods
In this research, materials were prepared from Barandouz area. Clayey soil was mixed with gravel in 25, 50 and 75 percentages (by weight). Geotextile was woven and made of polypropylene (with commercial name Fibertex-F-32). Geotextile effects in mixture were evaluated in two conditions. Position number one indicates the arrangement of geotextile.  This means, at first, one geotextile layer was embedded in the middle of materials. Then, two and three geotextile layers in equal depths from each other were used in soil mixtures. Position number two shows the mixing pieces randomly. This means that geotextile pieces in 1×1 and 5×5 cm2 were prepared and were randomly mixed with materials in 1, 2 and 3 percentages (by weight). For evaluating geotechnical behavior of improved clay-gravel mixtures, compaction and California bearing ratio test (CBR) (in dry and saturate conditions) based on ASTM were performed.        
It should be noted CBR test in dry and saturate conditions were carried out in three different compaction energies (i.e. 10, 25 and 56 blow count for per layer). Moreover, CBR was evaluated for piston penetration at 2.5 and 5 cm in the specimen.
Results and discussion
The findings of this study could be summarized as:
1. Results of compaction test showed that, in the unimproved position, with increasing gravel content in clay, maximum dry unit weight (γdmax) has been increased, while simultaneous optimum water content (wopt) decreased.
In the improved position, in the first mode, when a geotextile layer was embedded in the middle of the specimens, γdmax reached to its upper value, whereas wopt reached to its minimum value. On the other hand, with an increase in the number of geotextile layers in clay-gravel mixtures, dry density has been decreased, but optimum water content increased. Furthermore, in the second mode, when geotextile pieces with 1×1 and 5×5 cm2 were randomly mixed in the specimens, the findings revealed that geotextile pieces with 1 cm2 areas and 1% by weight in clay-gravel mixtures increases γdmax and reduces wopt.
2. In dry and saturate conditions, California bearing ratio (CBR) test result displayed that in the unimproved condition, with an increase in gravel content in the clay, CBR value has been increased. In the improved situation, in the first mode, when a geotextile layer was embedded in the samples, CBR had a maximum value in all of the compaction energies even though it is reduced as the number of layers increased. In the second mode, when geotextile pieces in 1×1 cm dimensions with 1% (by weight) were randomly mixed with the specimens, CBR value reached at high.  In contrast, with increasing dimensions of pieces and percentages in the presence of geotextile in clay-gravel mixtures, CBR values declined.  Therefore, it can be concluded that, according to Code 234 (Iran Highway Asphalt Paving Code), the application of one geotextile sheet in the middle of materials or geotextile pieces in 1×1 cm dimensions with 1% (by weight) random mixing  is suitable for subbase and base layers in pavement design.
3. CBR test results in the saturate condition in clay-gravel mixtures illustrated that, in the non-reinforced condition, with an increase in clay content in specimens, swelling value keeps rising sharply. On the contrary, in the reinforced position with embedding a geotextile layer in the middle sector of samples or through adding geotextile pieces (1 cm2) with 1 % content  (by weight) to the specimens, the rate of swelling significantly decreased.   
To sum up, the main objective of the present study was to investigate the impact of geotextile applications on bearing capacity of clay-gravel mixtures in pavement layers. The findings demonstrated that when geotextile as a layer was embedded in the middle part of specimens or as pieces with 1×1 cm dimensions and 1% content (by weight) was randomly mixed with the mid materials, the bearing capacity of the reinforced specimens was enhanced.  In contrast, in the saturate condition, swelling potential significantly was reduced. It is noteworthy to mention that 1 cm2 pieces of geotextile is more effective than the layers. This is due to the fact these pieces make aggregates closer to each other. Thereby, minimum void ratio (emin) reaches its least value, the structure of grading improves, and the contacts between particles and geotextile pieces rise. As a suggestion for further research, it looks promising to evaluate the dynamic properties and the behavior of the improved materials with other geosyntheticses.
Keywords: Geotextile, clay-gravel mixture, Improvement bearing capacity, California bearing ratio (CBR), Pavement layers.      
Full-Text [PDF 1157 kb]   (283 Downloads)    
Type of Study: Research Paper | Subject: Geotecnic
Received: 2017/10/22 | Accepted: 2018/08/4 | Published: 2018/08/20
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Ghasemvash S, Dabir R. Effects of Geotextile Applications on Bearing Capacity Clay-Gravel Mixtures in Pavement Layers. Journal of Engineering Geology. 2020; 14 (3) :523-556
URL: http://jeg.khu.ac.ir/article-1-2711-en.html

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Volume 14, Issue 3 (11-2020) Back to browse issues page
نشریه زمین شناسی مهندسی Journal of Engineering Geology
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