Economic comparison of options

In the course of designing engineering structures, especially transport and hydraulic engineering, naturally, there are several possible solutions to the design problem, to a greater or lesser extent, satisfying the set requirements. Each of these solutions is called a variant. Quite often, a survey arises from two to five options, and sometimes more. Comparison of such competing options allows you to find the best solution to the problem. To attract a large number of options is impractical, since in this case, the advantage of one option over another is often insignificant, and calculations for a large number of options lengthen the deadlines for making the final decision.

Economic indicators option reflected in the estimates. Calculation of cost for each option is based on the cost of construction and the subsequent period of operation of the structure. When calculating the cost of construction should be considered two main types of costs:

a) directly for the construction of a structure or direct costs;

b) for other works due to the construction of the structure, or additional costs.

Direct costs consist of the cost of labor, building materials, finished structures, the cost of transport, electricity, operation of construction machines, etc. They characterize, for example, the cost of 1 m3 earth dam, 1 running. km of road, pipeline, tunnel.

The appearance of additional costs due to the fact that the erected structure comes in contact with the surrounding area and in one way or another affects it. For example, the construction of a dam on a river leads to the formation of a reservoir, into the flooded area of ​​which many objects may be required that require their transfer, reorganization or protection, fig. 5.1. Some of the objects, such as roads, communication lines, power lines, agricultural land, while completely lost. All this is detrimental to the economy, requires significant additional cash costs.

Fig. 5.1. The nature of the change in flooded area with changes in the level of the upstream

The size of the additional cost depends on the type of construction. From the above example, fig. 5.1, it is obvious that in the construction of hydropower plants additional costs can be very significant. The role of additional costs in hydraulic engineering construction is also significant because their magnitude to a certain extent affects the basic parameters of the structure. Indeed, it is higher than the level of the headwater head H and, as a result, the power of the hydroelectric station. At the same time, with an increase in the height of the dam, the area of ​​flooding increases, sometimes very dramatically, and, consequently, additional costs. In this case, only materials from economic surveys allow choosing the optimal variant of hydroelectric power plants, i.e. one of the main parameters of hydraulic structures.

Additional costs for other types of structures are usually less and their influence on the technical parameters of the structures is not so great.