American Journal of Environmental Sciences 1 (2): 119-125, 2005 ISSN 1553-345X © Science Publications, 2005 Corresponding Author: Dr. Thamer Ahmed Mohammed, Department of Civil Engineering, Faculty of Engineering, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia Tel: 603-89466352 E-mail: thamer@eng.upm.edu.my 119 Validation of Some Bridge Pier Scour Formulae Using Field and Laboratory Data Thamer Ahmed Mohamed, Megat Johari M. M. Noor, Abdul Halim Ghazali and Bujang B. K. Huat Department of Civil Engineering, Faculty of Engineering, Universiti Putra Malaysia 43400 UPM Serdang, Selangor, Malaysia Abstract: Estimation of maximum local scour depth at the bride pier site is necessary for the safety and economy of the designed bridge. Numerous formulae are available and almost all of these formulae were developed based on laboratory data. Validation of these formulae is necessary in order to ascertain which of the formulae will give a reasonable estimate of the local scour depth. In this study, four commonly cited formulae were selected for the validation process using both the laboratory and field data. They were the Colorado State University (CSU), Melville and Sutherland, Jain and Fisher, and Laursen and Toch formula. The experimental data was obtained from the laboratory model study done at University Putra Malaysia, whilst the field data were obtained from 14 bridges sites. Three statistical tests were carried out to determine the formula that gives minimum prediction errors. Comparison between the predicted and measured depth of scour from the experimental and field data showed that the Laursen and Toch and the CSU formulae appeared to give a reasonable estimate. Whilst the Melville and Sutherland and Jain and Fisher formulae appeared to over-predict the depth of the scour. This observation was supported by the statistical tests. Key words: Scour Formulae, Physical Model, Field Data, Validation, Testing INTRODUCTION Many bridges failed around the world because of extreme scour around pier and abutment. For example during the spring floods of 1987, 17 bridges in New York and New England USA were damaged or destroyed by scour. In 1985, floods in Pennsylvania, Virginia, USA, destroyed 73 bridges. According to the US Department of Transportation [1], a total number of 383 bridges failed in the USA alone in year 1973. The failure of bridges due to scour will result in economical loss and may also result in losses of human life. In an extensive study of bridge failures in United States, it reported that damage to bridges and highways from major regional floods in 1964 and 1972 amounted about $100,000,000 per event [2]. An accurate prediction of scour depth at piers is essential for the safe design of the bridge foundation because underestimation may lead to bridge failure and over estimation will lead to unnecessary construction cost. As a result, an intensive research has been conducted over the past three decades in order to develop reliable relationships for estimating maximum scour depth and also to reduce the impact of local scour on the bridge substructure. Numerous formulae for estimating maximum local scour at pier site have been developed by many researchers and the development of these formulae were based on limited data collected from physical models with conditions different from that existed in the prototype. So, the use of these formulae in design is uncertain because of the difference between site and laboratory conditions. For example, studies employed laboratory flumes, which were rectangular in cross section and had smooth fixed wall were different from natural channels that are non- rectangular with rough and mobile banks. Validation of the various formulae using both the laboratory as well as the field data is very necessary in order to improve the prediction of maximum local scour depth at bridge piers. This may decrease unnecessary expenses for scour counter measures, making the bridge design process more efficient. This will also lead to a greater accuracy of bridge scour prediction and increased confidence in bridge design, thus increasing public safety of the users. Coleman and Melville [3] presented evaluation on failure of three bridges in New Zealand. Johnson [4] made a comparison of pier scour formulae using field data. Koopaei and Valentine [5] compared the difference between the local scour data collected from self formed laboratory channels with predicted local scour depth computed using some formulae for estimating local scour depth at pier site. They concluded that most of the formulae over-predicted the