Roohollah Kalatehjari

The effects of method of generating circular slip surfaces on determining the critical slip surface by particle swarm optimization

The main objectives of slope stability analysis are evaluating factor of safety for a given slip surface and determining the critical slip surface for a given slope. Factor of safety is usually calculated by limit equilibrium method. The main steps to determine the critical slip surface are generating trial slip surfaces as probable solutions and searching among them to determine the one with the lowest factor of safety. Although the process of searching the critical slip surface received much attention between researchers, the significance of method of generating slip surfaces is seldom addressed in the literature. The authors believe that this ignorance can affect the accuracy of the results of slope stability analysis even in the simplest problems with circular slip surfaces. Consequently, this paper focused on the method of generating circular trial slip surfaces as the simplest mechanism of sliding and considered its effect on determining the critical slip surface. A new method of generating circular slip surface was presented, which is more efficient and less restricted than the conventional method. A computer program was also developed to determine the critical slip surface of slopes by using particle swarm optimization. The performances of the proposed method and developed computer program were verified during comparative studies and sensitivity analysis. Based on the results, the effect of method of generating circular slip surfaces on determining the critical slip surface was confirmed successfully. In all considered problems, the proposed method of generating circular slip surfaces led to the lower values of factor of safety compare with the conventional method.

A typical weathering profile of granitic rock in Johor, Malaysia based on joint characterization

One of the most important challenges in the study of slope stability, foundation, and excavation in rocks is understanding the weathering states. This issue is more important in tropical climates, where severe weathering produces thick weathering profiles. Thick weathering profiles are normally classified or graded differently based on some field observations, geological studies, and material properties of rock. This paper considers the relationship between joint characterization and the state of weathering of granitic rock as an important factor to describe the mass weathering. A total of 24 panels of rock exposures was studied in two active granite quarries located in Johor, Malaysia. This region has a tropical climate condition. A typical profile was proposed for granitic rock, mainly based on joint characterization, topography, and geological condition. This profile includes a common weathering ranging from fresh rock to residual soil. Based on the presence of corestones, two additional subgrades were introduced in completely and highly weathered zones. It is believed that the proposed weathering profile may contribute to engineering design and classification of weathered granitic rock in tropical region.

The contribution of particle swarm optimization to three-dimensional slope stability analysis.

Over the last few years, particle swarm optimization (PSO) has been extensively applied in various geotechnical engineering including slope stability analysis. However, this contribution was limited to two-dimensional (2D) slope stability analysis. This paper applied PSO in three-dimensional (3D) slope stability problem to determine the critical slip surface (CSS) of soil slopes. A detailed description of adopted PSO was presented to provide a good basis for more contribution of this technique to the field of 3D slope stability problems. A general rotating ellipsoid shape was introduced as the specific particle for 3D slope stability analysis. A detailed sensitivity analysis was designed and performed to find the optimum values of parameters of PSO. Example problems were used to evaluate the applicability of PSO in determining the CSS of 3D slopes. The first example presented a comparison between the results of PSO and PLAXI-3D finite element software and the second example compared the ability of PSO to determine the CSS of 3D slopes with other optimization methods from the literature. The results demonstrated the efficiency and effectiveness of PSO in determining the CSS of 3D soil slopes.

Utjecaj temperature na stišljivost i potencijal kolapsibilnosti rezidualnog granitnog tla

U ovom se radu istražuje utjecaj temperaturnih promjena na indeks stišljivosti i potencijal kolapsibilnosti rezidualnog granitnog tla na koje se često nailazi u Maleziji. Zbijeno tlo analizirano je pomoću modificiranog edometra s kontrolom temperature. Dvije serije uzoraka tla s raznim vrijednostima suhe gustoće ispitane su pri temperaturama od 27, 40 i 60°C. Rezultati ispitivanja pokazuju da vrijednost indeksa stišljivosti ne ovisi o temperaturi. S druge strane, grijanje dovodi do smanjenja potencijala kolapsibilnosti, a ta je pojava izraženija pri niskim vrijednostima suhe gustoće.

Optimization of Abrasive Wear Behavior of High Chromium Cast Iron and Hadfield Steel

Abstract: Wear properties of two different crushers used for grinding raw materials of cement industry are compared us-ing pin on disk wear test. The wear test was carried out with different loads on a pin. Abrasive wear behavior of two crushers made of Hadfield steel and high chromium cast iron was evaluated by comparing weight loss, wear resistance, microhardness and friction coefficient. The results showed that abrasive wear of high chromium cast iron was lower than Hadfield steel because of the larger amount of carbides and higher work hardening in the steel at the higher applied loads. Increase in surface hardness of Hadfield steel was more noticeable compare to high chromium cast iron due to the work hardening and formation of the twining sites during the wear test. Owing to the presence of M 7 C 3 carbides in high chro-mium cast iron matrix, impact crushers exhibited higher friction coefficient. In addition, a wear loss equation was derived based on a real crushing condition. However, a new approach in optimization of the wear parameters was developed and wear behavior of the materials was predicted based on the maximum number of the effective factors. The optimization of the parameters by genetic algorithm showed that optimum wear loss for hammer and impact crushers under real condition is 5.2958 mg and 3.8449 mg, respectively. Results of the numerical simulation show that the genetic algorithm optimiza-tion is effective and very useful in designing the hammer and impact crushers. In addition, some recent patents on abra-sive wear behavior of the high chromium cast iron and Hadfield steel are discussed in details.