Estimating production and cost for clamshell mechanical dredges

Abstract

Clamshell dredges are used around the United States for both navigational and environmental dredging projects. Clamshell dredges are extremely mobile and can excavate sediment over a wide range of depths. The object of this thesis is to develop a methodology for production and cost estimation for clamshell dredge projects. There are current methods of predicting clamshell dredge production which rely on production curves and constant cycle times. This thesis calculates production estimation by predicting cycle time which is the time required to complete one dredge cycle. By varying the cycle time according to site characteristics production can be predicted. A second important component to predicting clamshell dredge production is bucket fill factor. This is the percent of the bucket that will fill with sediment depending on the type of soil being excavated. Using cycle time as the basis for production calculation a spreadsheet has been created to simplify the calculation of production and project cost. The production calculation also factors in soil type and region of the United States. The spreadsheet is capable of operating with basic site characteristics, or with details about the dredge, bucket size, and region. Once the production is calculated the project cost can be determined. First the project length is found by dividing the total amount of sediment that is to be excavated by the production rate. Once the project length is calculated the remainder of the project cost can be found. The methods discussed in this thesis were used to calculate project cost for 5 different projects. The results were then compared to estimates by the government and the actual cost of the project. The government estimates were an average of 39% higher than the actual project cost. The method discussed in this thesis was only 6% higher than the actual cost.