Genetic Algorithm in Stability of Non-Homogeneous Slopes
In recent years, genetic algorithm search procedure has been used to locate the critical slip surface of homogeneous slopes. It has been found that genetic algorithm is a robust search technique which often gives global solution. In the present study, genetic algorithm has been used to locate the critical slip surface of non-homogeneous slope in conjunction with slope stability analysis method developed by Janbu (1973) for generalized slip surface. The results obtained from the present study have been compared with those available in the literature [Greco (1996) and Zolfaghari et al. (2005)]. The effect of various genetic algorithm parameters (population size, number of generations, crossover probability and mutation probability) on the solution has been studied. It has been found from the results that Janbu's method (1973) of stability analysis along with genetic algorithm as search procedure gives a better solution in terms of getting minimum factor of safety, compared to other methods.
Genetic Algorithms in Searching the Critical Slip Surface
Evaluation of stability is essential prior to any construction involving natural or man-made slopes. Various methods are available to evaluate the stability of slopes. However, the limits equilibrium method has been used over the years because of its simplicity and reasonable accuracy. The limit equilibrium method consists of following two steps : (1) the formulation of objective function (expression for factor of safety which is a measure of stability of a particular trial slip surface), and (2) a search technique which finds the critical slip surface corresponding to the minimum factor of safety. 
A considerable research was carried out in the past to develop the expression for factor of safety for different shapes of slip surface. They are surveyed and described in several text books of Soil Mechanics and Foundation Engineering (e.g. Huang, 1983; Fang, 1997). Several traditional search techniques, such as calculus of variation (Baker and Garber, 1977; Castillo and Revilla, 1977, Ramamurthy et al. 1977) , linear programming (Martin, 1982), dynamic programming (Baker, 1980), simplex method (Nguyen, 1985) and sequential unconstrained minimization techniques (Bhowmik and Basudhar, 1989) are used by various investigators to locate the critical slip surface. The above search techniques are applied to locate the critical slip surface of both circular and noncircular shapes. Even though , some of the above methods are successfully applied to locate the critical slip surface, they do not guarantee the global minimum, often, the solution is starting point dependent, converging to local minimum and requires large number of function evaluations.
The Inca Occupation of the South Coast of Peru
like the others, however; it forks into several nearly parallel ravines of which the largest are Huayuri, Rio Grande-Palpa, Ingenio (called Collao in ancient times), Nasca proper (the ancient Caxamarca), Taruga, and Poroma. Due to peculiarities of the local topography, the irrigated areas in Ica and the ravines of Nasca are located inland, at the foot of the mountains, rather than at the mouths of the rivers as is more usual in Peruvian coastal valleys. No sharp natural or cultural boundary separates the valley of Chincha from the valleys of Cafiete (ancient Huarco and Runahuana), Asia, and Mala, the next valleys going up the coast to the northwest. At the other end of the area we are considering, however, there is a sharp break; beyond Yauca the Andean foothills reach out to the sea, natural conditions are quite different, and there are important differences in the archaeological picture as well. The historical sources which mention the south coast are not particularly helpful, except in so far as they provide us with a few dates. To begin with, no chronicler gives an explicit account of the political organization of the south coast at the time it came into contact with the Incas. It can, perhaps, be inferred from Cabello Balboa's statements about common policy toward the Inca invaders that there was some sort of political connection between the valleys of Mala, Cafiete, and Chincha, but the connection need have been no more than a temporary military alliance. Cabello makes no mention at all of Pisco. The valleys of Ica, Nasca, and 125