Cost Forecasting Analysis on Bored and Cast-In-situ Piles in Sri Lanka: Case Study at Selected Pile Construction Sites in Colombo Metropolis Area

Installation of bored and cast-in-situ (CIB) piles is a complicated process and relates to a large number of factors connected with subsurface uncertainties, contractor experience and site-specific factors. Such factors make it difficult for the estimator to predict the cost of a CIB pile in the tendering stage. This study was carried out to identify most influential factors on cost of CIB pile construction with relevance to local conditions and to develop a cost prediction criterion for CIB construction in Sri Lanka. It was initiated with a study on cost influential factors and estimation models developed in the international context. Then the study proceeded to identify additional specific factors relevant to the local conditions using a questionnaire survey and analysis. Cost prediction models were then developed for local context using regression analysis based on the identified most influential factors, and finally, developed models were validated using actual cost data. It was revealed that the most critical cost affecting factors are pile size, pile drilling time, depth of pile, concrete pouring time, rock socket length, drilling type and weather conditions. Linear cost models developed for each of these factors were amalgamated to one overall cost prediction model. This was found to be successful during the validation with actual costs of executed piling projects. Moreover, it is recommended to be used along with the intuitive judgment of the decision maker and the model should be timely readjusted with updated market rates at least in three-month periods.