Vedrana Krstić

Ground Improvement Utilizing Vibro-Concrete Columns

The use of Vibro-Concrete Columns (VCC) to improve soft ground is growing in popularity in various parts of the world due to its cost effectiveness and proven performance. A case history involving the first use of VCC by a US Department of Transportation to support an approach embankment is presented. The project involves the installation of VCC supporting 10 m high back-to-back mechanically stabilized earth walls underlain by a geotextile-reinforced sand platform. The design concept of the embankment supporting system is outlined. Static load tests results performed on two VCC are also presented and the acceptance criteria are discussed. The performance of the embankment supporting system is assessed based on monitoring data obtained from various instruments installed during construction including settlement platforms, probe extensometers, inclinometers, piezometers and strain gages attached to the sand platform geotextile reinforcing elements. Finally, recommendations are presented regarding the design aspects of the VCC and the geotextile-reinforced sand platform.

C-D-c-t diagrams for practical design of concrete durability parameters

Abstract Structures (especially bridges), in Croatian coastal marine environment, are exposed to influence of different aggressive factors. Since many old structures have to be repaired and since many new have to be constructed in that area, there is a special interest of both, experts and the public to perform works with high quality standards. In this paper we propose a method for durability design of structures built in marine environment based on space and time distribution of chloride ions in reinforced concrete structures. This method, which is developed as the computer program CHLODIF, is applied during the construction of new Maslenica bridge.

Willis Avenue Swing Bridge: Design and Construction of Drilled Shaft Foundations

Drilled shaft foundations are currently being constructed to support selected piers of the new, four lane, 106 meter long Willis Avenue Swing Bridge and approach structures. The Willis Avenue Swing Bridge over the Harlem River is being replaced under a

Backcalculation of Pavement Profiles from the SASW Test by Neural Networks

612 million project which is the largest ever undertaken by the Movable Bridge Group of the New York City Department of Transportation. Drilled shafts vary in diameter from 1220 mm to 1524 mm and extend into bedrock which is composed of Inwood Marble or Fordham Gneiss. The design capacity of the drilled shafts was estimated from the side resistance within the rock socket, discounting any side resistance above the rock socket in accordance to empirically derived methods outlined in the AASHTO Bridge Design Specifications. The design capacity of the drilled shafts is in the process of being verified by means of an Osterberg Cell static load test conducted on four instrumented test shafts representing each drilled shaft size and each type of bedrock on the Bronx side of the project. The load test results suggest that empirical design methods combined with field rock properties data underpredicted the drilled shaft capacity in reported bedrock.