and Commentaries are intended for guidance in planning, designing, executing, and inspecting construction. This document is intended for the use of individuals who are competent to evaluate the significance and limitations of its content and recommendations and who will accept responsibility for the application of the material it contains. The American Concrete Institute disclaims any and all responsibility for the stated principles. The Institute shall not be liable for any loss or damage arising therefrom. Reference to this document shall not be made in contract documents. If items found in this document are desired by the Architect/Engineer to be a part of the contract documents, they shall be restated in mandatory language for incorporation by the Architect/Engineer.

This is the first part of an investigation on improved assessment of mass concrete dams using Acoustic Travel Time Tomography (ATTT). It presents the concept and basic science for ATTT. ATTT combines aspects of ultrasonic measurements previously used for material characterization, ultrasonic methods applied to test concrete and features of methods used in shallow seismic surveys. This science/technology is integrated into a system that records travel time data and applies tomography software. The resulting tomographs have the potential to provide cross-sectional images of the structure that can be used to locate cracks, identify regions of structural damage, and other anomalies deep inside a massive concrete structure. Results from initial laboratory and field studies obtained with a system that embodies the approach presented in this paper and which provides proof-of-concept data, are presented in a companion paper (Kepler WF, Bond LJ, Frangopol DM. Improved assessment of mass concrete dams using acoustic travel time tomography. Part II — applications. Constr Build Mater, 2000; vol. 14, No. 3, pp. 147–156).

In a project to determine the feasibility of lining a canal with concrete without dewatering the canal, a 1.5 mile long test section is being constructed in the Imperial Valley of southeastern California. The canal will be lined with polyvinyl chloride (PVC) covered by a protective layer of concrete. The concrete contains an anti-washout admixture that prevents the washout of fines in the flowing water and facilitates placement. A water depth of 9 ft is being maintained in the canal during construction. The importance of cohesiveness in placing concrete under water, and the use of anti-washout admixture is emphasized. A water velocity of 3 ft/s or greater will, however, scour fresh concrete, and it is important to keep water velocity below 2.5 ft and protect the concrete from wave action. Other observations are also discussed.