Journal of Engineering Geology

The Engineering Characteristics of Silty Loess Contaminated with Natural Salts

Emad Namavar

A considerable part of Golestan Province is covered by loess soils, most of which are of the silty loess type, which is one of the most problematic soils. The proximity of the Caspian Sea leads to salinity of the groundwater in some areas of the province. Due to high evaporation, salts reach the surface and cause salinization of the silty loess soils at the surface. The presence of soluble salts can lead to changes in the engineering properties of silty loess soils at the site of construction projects. It is therefore necessary to investigate the influence of salts on the geotechnical properties of silty loess soils. The aim of this study was to investigate the effect of sodium chloride or halite (NaCl) and calcium sulphate or gypsum (CaSO₄.2H₂O) salts, as the two most abundant natural salts, on the engineering properties of silty loess soils. For this purpose, silty loess soil samples were collected from Maraveh Tappeh city, Golestan province, Iran. Geotechnical tests including uniaxial compressive strength, shear strength and standard compaction tests were then carried out on soil samples in the natural state and with 3, 5, 7, and 9% NaCl and CaSO₄.2H₂O. Based on these tests, the variation in optimum water content (ω_opt), maximum dry density (ρ_dmax), uniaxial compressive strength (UCS), cohesion (C), internal friction angle (φ) were evaluated. The results showed that these parameters increased with increasing both natural salts concentration. Finally, the reason for the changes in the engineering properties of the soil samples due to the presence of these two natural salts was discussed.

Rupture Status of the Southeastern Fault Segment of the June 20, 1990 (Mw 7.4) Rudbar Earthquake

Ali Misaghi

In this study, we investigate the spatial distribution of landslides, strong motion data, and seismic intensity patterns associated with the June 20, 1990, earthquake, with a moment magnitude (Mw) of 7.4. Our primary objective is to elucidate the rupture status of the southeastern segment, Zard Geli, of the coseismic rupture by integrating geological and seismological data, Our findings indicate that the southeastern segment experienced only a partial rupture during the 1990 earthquake. This partial rupture is evidenced by the disproportionate distribution and density of landslides along the surface rupture. The incomplete rupture of this segment suggests that it retains a considerable amount of accumulated strain energy that was not fully released during the 1990 event. Consequently, this segment remains a potential source for future seismic activity. These findings have implications for seismic hazard assessment and risk mitigation in the region. This study highlights the need for continued monitoring and detailed geological and seismological investigations to better anticipate and mitigate the effects of future earthquakes.

Experimental study on the performance of strip footings on geocell-reinforced granular slopes

Ali Ghanbari

A series of reduced scale plate load tests was conducted to evaluate the bearing capacity of a strip footing resting on granular slopes. The effect of three factors including geocell burial depth, geocell length and spacing of geocell layers were discussed and evaluated. In this regard, 18 tests were performed to investigate the behavior of one and two layered geocell-reinforced slopes as well as the unreinforced slope and plain conditions. The results suggest that in single-layered geocell-reinforced slope, the optimum burial depth of the first layer of geocell reinforcement is 0.1 times of the strip footing width, whereas at greater depth beneficial effect of the geocell will reduce. In addition, expanding the reinforcement length up to approximately three times the foundation width could effectively increase the bearing capacity, whereas extending the length beyond that does not lead to any significant improvement. Furthermore, it was observed that use of two geocell layers by considering an optimum geocell space of 0.2 times of the foundation width could enhance the bearing capacity up to 226% in comparison with the unreinforced slope, and up to 79% of the plane condition for settlement ratio of 15%. Finally, the results indicate that the efficiency of the geocell reinforcements in lessening the gap between slope and plane conditions increases as the settlement of the footing rises due to better mobilization of dilation characteristics of granular backfill material and better lateral confinement of coarse aggregates in greater strains.

Review of geotechnical characteristics of soil contaminated with hydrocarbon substances and residues from a burnt oil refinery

Mahdi Khodaparast

Soil contamination by petroleum contaminants and their derivatives has harmful effects on ‎the soil environment. ‎The structure and geotechnical parameters of the soil will change as a result of the interaction between the contaminant and the soil. The double layer thickness of the clay will change, and the structure of the clay soil will become similar to that of the granular soil. In the present study the effect of contamination by burnt-oil waste from refineries on the compaction and resistance behavior of clayey sand soils was investigated. The geotechnical characteristics of soil types contaminated with different percentages of hydrocarbons from previous research were also reviewed and analyzed. The primary effects were decreases in the internal friction angle, California bearing ratio and permeability of the soil and increases in the cohesion and Atterberg limits of the soil. The shear strength of the contaminated soil did not show a definite or constant trend of change. When contaminated with acidic sludge, despite an increase in the cohesion of the soil, a decrease in the internal friction angle caused a decrease in the shear strength. When contaminated with dirt filter residue, the shear strength of the soil increased with the substantial increase in cohesion, despite a decrease in the internal friction angle.