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The scale effect on bearing capacity of shallow footings supported by unreinforced granular soils has been evaluated extensively. However, the subject has not been addressed for shallow footings on geocell-reinforced granular soils. In this study, load-settlement characteristic of large square footings is investigated by performing large-scale loading tests on unreinforced and geocell-reinforced granular soils. The effects of footing width (B), soil relative density of soil (Dr), and reinforcement depth (u) have been investigated. The test results show that the scale effects exist in geocell-reinforced soils, like unreinforced soils, and the behavior of small-scale models of footings cannot be directly related to the behavior of full-scale footings due to the difference between initial conditions of tests and the initial state of mean stresses in the soil beneath the footings having different dimensions. Large footings create higher mean stresses in the soil, resulting in low soil friction angle and initial conditions of the test approach to the critical state lines. The results of tests indicate that model experiments should be conducted on low-density soil for better prediction of the behavior of full-scale footings, otherwise, the predicted behavior of full-scale footings does not seem conservative.

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Biocementation is a microbially induced technology that increases the shear strength of soil through the production of soil particle-binding materials known as calcite (calcium carbonate). This process makes use of urease-positive microorganisms, urea and calcium ions. The main aim of this study was to introduce an indigenous soil bacterium belonging to the genus Staphylococcus that was capable of hydrolyzing urea and precipitating calcium carbonate (CaCO 3 ). Molecular identification of this isolate by 16S rDNA sequencing showed 98% homology to Staphylococcus sp. Several culture media were employed to investigate the growth, urease production and CaCO 3 precipitation of this strain (designated Staphylococcus sp. IR-103, accession number LT853888). When Staphylococcus sp. IR-103 was grown in YN medium containing 20 g L −1 of yeast extract and 10 g L −1 of NH 4 Cl, maximal growth yield (OD 600 ), urease activity and carbonate precipitation values of 2.8 ± 0.1, 3.33 ± 0.12 IU and 47.6 ± 0.9 mg mL −1 were obtained, respectively. The precipitated CaCO 3 was characterized by FTIR, AAS, XRD and SEM analyses. In order to study the effects of the bacterium's biocementation activities on soil strength, bacterial suspension and cementation solution was injected into a column packed with uniform sandy soil under defined condition. In conclusion, Staphylococcus sp. IR-103 is a high urease producer, which can grow on a simple and cost-effective medium without staying viable for long following the biocementation process. Hence this newly isolated strain has the potential to be employed in soil improvement for large-scale field applications.