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Author: *Raghad Mohammed Kudadad
Journal: Journal of Engineering and Sustainable Development مجلة الهندسة والتنمية المستدامة ISSN: 25200917 Year: 2018 Volume: 22 Issue: 4 Pages: 39-56
Publisher: Al-Mustansyriah University الجامعة المستنصرية


The geotechnical engineering considers the gypseous soils as collapsible soils. The existence of these soils causes problems for the structures, because of the dissolution and filtration of the gypsum from soil texture by the flow of water through the soil mass, this problem was the focus of attention of many researchers over the years to improve the properties of these soils. This research aims to study the effect of using geogrid reinforcement to reduce the collapse of gypseous soils upon soaking. A series of laboratory models tests in addition to routine laboratory tests carried out on three soils with different gypsum contents. The soils were brought from AL-Najaf district, the first soil S1 was taken from 0.5 meter below the ground surface with high gypsum content (26%). The second soil S2 was taken from 4 meter below the ground surface, with Slight gypsum content (6.9%), the third soil S3 was artificially prepared, by mixing the first soil S1 with the second soil S2 to get the required moderate gypsum content. A new technique manufactured locally for this work and a series of tests including dry and soak tests carried out using steel container (280×280×250) mm. The soils were placed in steel container at their field densities. The single layer geogrid reinforcement test was conducted by placing the geogrid layer at three different depths for all soils [(Depth of the reinforcement layer, D = 0.25 width of foundation, B), (D = 0.5B) and (D = 0.75B)]. The study includes also the effect of number of reinforcing layers (N) on the collapse behavior of gypseous soils. The models were reinforced with N=1, N=2 and N=3 (the vertical distance between geogrid layers, Z=0.25B). The study includes the observation of collapsibility of soaked gypseous soils at stress level of 100 kPa. A strip footing of (270×40×30) mm dimensions was taken as a testing model. This footing was placed at the center of the top surface of the bed soil. For all testing models, the footing was loaded gradually up to 100 kPa, after 24 hours, the corresponding settlement was recorded. Then, the soil is soaked for 24 hours and the generated settlement recorded under the same stress level 100 kPa. The results showed that the most effective depth for single layer reinforcement is at (D=0.25B) for the three soils, which gives a collapse reduction factor (CRF) of about (28.5%, 29.41%, 30.43%) for soils (S1, S2, S3) respectively. The effective number of reinforcement layers was (N=3: D=0.25B: Z=0.25B), which gives (CRF) of about (54.08%, 82.35%, 69.56%) for (S1, S2, S3) respectively compared with unreinforced model.

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