# The S-Curve as a Tool for Planning and Controlling of Construction Process--Case Study
## 1 Introduction
An effective tool for measuring the utilization of the financial outlays of a construction project is the presentation of the planned financial flows on a timeline using a cumulative cost chart, the representation of which is the S-curve. The S-curve shows the progress of the investment project from the beginning of the construction works through to their completion. The cumulative cost chart for construction projects takes the shape of the letter \"S\", hence the name of the curve. The variable slope of the cost curve indicates the changing progress of works per unit of time [14]. The S-curve is flatter at the beginning and end of the execution of a construction project, and steeper in the middle. This is due to the fact that a traditional construction project starts quite slowly. At the beginning of the construction process, human resources are organized, construction site development is prepared and simple preparatory works are carried out. After some time, the implementation of work begins to accelerate. Works are carried out on several working fronts using various working teams. Contractors start to undertake more and more tasks simultaneously. The mutual implementation of parallel tasks generates a much greater increase in costs when compared to the initial stage of implementation [15]. As a result of the continuing research, the classic S-curve method is being expanded and constantly modified in the following ways: through the use of the least square method and fuzzy S-curve regression model [16; 17], the use of a polynomial function to generalize the S-curve [18], the use of methods of artificial intelligence [19], the use of an S-curve Bayesian model [20] or by dividing the entire duration of a construction project into three periods for the improved accuracy of cost forecasting [21]). The second large group of methods that are used for controlling and monitoring the progress of the construction project implementation is earned value management. Earned value management involves the control of the investment task through the cyclical comparison of the actually executed scope of work with the planned time and cost of implementation [22]. Project management that uses earned value management is a well-known management system that integrates schedule, costs and technical performance [23; 24]. Earned value management allows cost and schedule deviations as well as performance indicators, project cost forecasts and schedule durations to be calculated [25; 26]. In literature, there are many studies that present the effective application of earned value management in real-life construction projects [27; 28; 29; 30]. Classic earned value management is being expanded and modified by way of, among others, the introduction of a hybrid methodology based on work packages and logical time analysis [31], the introduction of new parameters (e.g., the Schedule Forecast Indicator (SFI) [32]) or by taking into account of the impact of unplanned time and cost deviations on the financial liquidity of a construction project [33]. The purpose of this article is to analyze the course of an sample construction project by comparing the planned costs of the scheduled work with the actual costs of the performed work, and to identify reasons leading to failures to meet planned deadlines and the budget of the project's implementation. The goals of the paper are to demonstrate the reasons for construction project cost overruns and time delays using a representative case study. Both factors are strongly based on the Earned Value Method (EVM) approach, using an indicated project budget breakdown and timeline deviations. In this particular case study the poorly managed project was carried out and the cost spent exceeded the expected and planned figures by over 50%, which is not uncommon in the Polish investment process nowadays.