Improving fine-grained gypsiferous soil by increased compaction

2019

Geo-Engineering

IntroductionSoil compaction is the process whereby soil is mechanically compressed through a reduction in the air voids [22]. It is one of the basic construction procedures used in building subgrades and bases for roads and airport pavements, embankments, earth-fill dams, and other similar structures [13,15,20]. Since, compaction helps to decrease the susceptibility of the unbound materials to environmental changes [7], a proper compaction of unbound materials is considered as one of the most important components in the construction of pavements, and embankments to ensure their adequate performance over time.The impact compaction laboratory methods are the ones most commonly used to establish the compaction characteristics of unbound materials. These methods involve compacting a sample of the material to be used in the field in a standard mold using a drop hammer [11]. AbstractConstruction of earth structures involves the use of compacted soils. In roads construction quality controls like the bearing capacity of the subgrade, base and subbase layers, CBR values and compaction characteristics are primarily important. In Sweden, it has become interesting to correlate new testing parameters collected by simple tests to the conventional compaction parameters collected from modified Proctor tests. This action will help in assessing the bearing capacity of the selected material simply and quickly using the recent developed techniques instead of the conventional techniques which have been considered as time consuming methods. The aim of this study is to demonstrate that the laboratory dynamic California bearing ratio (CBR LD ) test can be used as a method of compaction assessment of selected subgrade soil. Moreover, it has been demonstrated in this study that the CBR LD can strongly be correlated to the compaction densities and molding water contents using polynomial correlation and a best-fit multiple regression model for a wide range of molding water contents. In addition, the repeatability of the dynamic laboratory CBR test was examined as discussed in the current article.

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mentioning

confidence: 99%

Strong correlation between the laboratory dynamic CBR and the compaction characteristics of sandy soil

2019

Geo-Engineering

“…The improvement of gypsum-rich soil strength by increased compaction has been investigated by Razouki and Ibrahim [15] and Razouki et al [16]. For gypsum sand having a gypsum content of 28%, Razouki and Ibrahim [15] reported a significant increase in CBR value for both soaked and unsoaked conditions due to increase in compaction effort (10-70 blows/ layer) for soil samples compacted at the optimum moisture content of the modified AASHTO compaction.…”

Section: Introductionmentioning

confidence: 98%

“…For gypsum sand having a gypsum content of 28%, Razouki and Ibrahim [15] reported a significant increase in CBR value for both soaked and unsoaked conditions due to increase in compaction effort (10-70 blows/ layer) for soil samples compacted at the optimum moisture content of the modified AASHTO compaction. For finegrained gypsiferous soil having a gypsum content of 33% and compacted at optimum moisture content of the modified AASHTO compaction, Razouki et al [16] used four different compaction efforts of 12, 25, 56 and 70 blows/layer. The CBR tests indicated a nonlinear increase in CBR with increasing compaction effort showing improvement in soil strength with increased compaction.…”

Section: Introductionmentioning

confidence: 99%

Challenging choice of safety factor for design of strip footings on gypsum-rich soils

Razouki

Innov. Infrastruct. Solut.

2020

Self Cite

A fine-grained gypsum-rich clayey soil having a gypsum content of 33% is subjected, in CBR moulds, to modified American association of state highway and transportation officials compaction at optimum moisture content. Two sets of samples were prepared. The first set remained unsoaked, while the second was soaked in fresh water for 120 days. From each CBR sample, three specimens were extracted for unconsolidated undrained triaxial test and the Mohr–Coloumb failure envelopes were obtained for soaked and unsoaked conditions. Soaked samples suffered a significant drop in both cohesion and angle of internal friction. The ultimate bearing capacity of a strip footing was calculated for each of soaked and unsoaked conditions revealing the critical region. For important structures on gypsum-rich soil, the paper shows that the allowable bearing capacity should be based on soaked condition. Based on unsoaked conditions, a safety factor of 8 is required to assure a safety factor of 3 based on soaked condition. For less important structures in regions of hot dry climate with low probability of soaking, safety factors of 4 and 3, based on unsoaked conditions, are required to give safety factors of 1.5 and 1.1 based on soaked conditions, respectively.

“…However, in regions of hot dry climate where water for compaction is very expensive, the use of gypsiferous soil for embankments in hot desert areas becomes logical and economical as discussed by Razouki et al (2008). The problem of improving gypsum-rich soils by increasing the compaction effort has received attention by Kuttah (2004), Ibrahim (2007 and, Razouki et al (2012b), and Najah et al (2013b).…”

Section: Introductionmentioning

confidence: 99%

Effect of Relative Compaction on Water Absorption and Gypsum Dissolution in Gypsum-Rich Clayey CBR Samples

Razouki

Transp. Infrastruct. Geotech.

2020

A clayey gypsiferous soil of CL group according to the Unified Soil Classification System was studied for the effect of relative compaction on water absorption and gypsum dissolution during long-term soaking. The soil has a gypsum content of about 33%. Two sets of soil samples were prepared at optimum moisture content of 11.75% of the modified Proctor compaction test. The first set received 100%, while the second received about 93.5% relative compaction with respect to modified Proctor. These samples were soaked for 4, 7, 15, 30, and 120 days under 40 lbs (178 N) surcharge load. The moisture content was determined at top, quarter points, midpoint, and bottom of each soil sample. The test results revealed that for each compaction effort, the moisture content along each soaked soil sample is not uniform and increased with increasing soaking period. This increase in moisture content is greater for soil samples compacted at the lower compaction effort. The moisture content at top of each soil sample is greater than at the bottom, and the least moisture content took place at the middle of the sample. The dissolution of gypsum, at the top of soil samples, was greater than that at the middle. A multiple regression equation was developed relating strongly the decrease in gypsum content along the clayey CBR samples, with compaction effort and increase in average moisture content along the samples due to soaking. Similarly, strong correlation was obtained from the multiple regression developed between absorbed water, soaking period, and compaction effort. The paper shows that the water absorption and gypsum dissolution decrease with increasing relative compaction as the soil becomes denser.